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Cletus
25-Jul-2012, 07:11
Ever have something that you just accepted and took for granted suddenly become crystal clear to you? I know that most of you will groan and flip to the next page on this - I should have too, I've been a photographer for over 20 years, but large format only for the last three or four.

I'm getting ready to get my first 8x10 soon and I was thinking about a 4x5, or other smaller format reducing back to go with the camera. I got to wondering, what if I have a 300mm lens mounted and set up for an 8x10 photo, then change the back to 4x5. What else will need to change if I don't want to change the lens? And also, how will all my 4x5 lenses, which mostly won't cover 8x10, work with the reducing back? Exactly the same?

Suddenly, the "Big Light" came on about the relationship between focal length and format, or image area. I never intuitively understood why "effective" focal length always increases as the format gets smaller (or vice-versa) as in, "why does my Nikkor 50mm become an 75mm on an APS size camera?" I just accepted that it did and carried on.

So it just occurred to me why this is:

Let's say, just for fun, I have a house that happens to have a window smack in the center, and I have an 8x10 all set up to have the whole house completely fill the frame. The FL of the lens is 300mm. Then, I leave everything else the same and change to a 4x5 reducing back. Now, with the smaller format and the same FL I've lost most of the house and "zoomed in" on the window in the center, just as though I had increased the FL of the lens!

The actual projected image, or image circle, of the 300mm FL is still all there and never changed, but now only the center part of the image area is being "used" by the little 4x5 frame and the effective FL of the lens has now became longer! And it's become longer by exactly the same as the difference, or the ratio between the two format sizes! Ha ha!

I know this is relatively simple if not obvious, but I never really understood it. Maybe, by chance, there is someone else reading this who gets it now, too.

E. von Hoegh
25-Jul-2012, 07:20
The effective focal length never changes, ever. The perspective doesn't change, either, unless you move the camera. The part of the image you record on film is what changes.

Cletus
25-Jul-2012, 07:23
Well, my terminology may have been wrong then. Maybe I should have said the "Apparent" Focal Length. Anyway, the point is the same...

E. von Hoegh
25-Jul-2012, 07:24
Angle of view, which is not the same as image circle. Compare 300mm lenses on 35mm, 4x5, and 8x10.

Saying a 50mm "becomes" a 75mm will take you down the wrong road.

Cletus
25-Jul-2012, 07:55
I guess I'm still stuck on the whole "equivalent to 35mm" in the way that I understand the meaning, or better, the application, of focal length. Do you think my example is way off though?

I know that nothing actually changes with the 300mm lens in my example, but when I change camera backs from 8x10 to 4x5, with all else being the same, it's as though I've installed a lens with a longer focal length.

Angle of view, such as "a lens with a 105deg angle of view", I still don't really understand. Two lenses of different focal lengths can have the same angle of view can't they? Or am I thinking of something else?

BrianShaw
25-Jul-2012, 07:55
Cropping does the same thing.

Cletus
25-Jul-2012, 08:01
Sure it does, but that's not what I'm getting at. All I was trying to say was that I never really understood why the...I have to choose my words carefully now...why "evident", "apparent", "seems to be" focal length of any lens, on any format on any camera, seems become a "longer lens" as format gets smaller.

I have a pretty good feeling I'm just being messed with here, but that was my only observation. Like I said, most of you already know this, I just didn't really understand why that was.

BrianShaw
25-Jul-2012, 08:23
Yes, I assumed you knew that cropping gives the same effect but thought that saying it may help. How, IDK... but it had been unsaid.

Since you are talking mostly about how to express that effect in words... yuup, it is hard to express. I often say "xmm lens when used on 6x7 gives the same appearance as a yymm lens used on 4x5." That is probably wrong too but people seem to understand.

Yes, you will get "messed with" here... whether you like it or not, and whether you deserve it or not. Smile, nod, and then get even!

Oren Grad
25-Jul-2012, 08:31
You've basically got it right. Think of lenses as projecting an image circle of a given size. In that projected image you can place a sheet of film of any size you want, to capture as much or as little of the projected image as you want (or even beyond it, if you want or don't mind vignetting). That's what you're doing, of course, when you swap backs for different formats on your camera.

EDIT: As you gain more experience working with view cameras in different formats, it's easier to get away from the "equivalent focal length" thinking, which can sometimes lead to fallacies. You eventually develop your intuition for how large a piece of film you need to stick behind a lens of a given focal length to capture how wide a view of the scene in front of you.

Oren Grad
25-Jul-2012, 08:39
Angle of view, such as "a lens with a 105deg angle of view", I still don't really understand. Two lenses of different focal lengths can have the same angle of view can't they? Or am I thinking of something else?

The angle of view tells you how wide a cone of light the lens projects toward the film. The size of the sheet of film that you place within that cone determines how broad a view you actually capture of the scene before you.

sully75
25-Jul-2012, 09:07
Also DOF is the same of lenses of equivalent focal length. So a 90mm lens on 35mm, which is a slightly long lens, has the equivalent DOF at a given aperture as a 90mm lens on 4x5 (which is a wide angle). On 4x5, the 90mm will have a lot more DOF at a given aperture than a longer lens, however it will have a lot less than the equivalent field of view lens on a 35mm camera (a 28mm lens on 35mm will have a lot more in focus at a given aperture than a 90mm lens will have on 4x5).

E. von Hoegh
25-Jul-2012, 09:08
The angle of view tells you how wide a cone of light the lens projects toward the film. The size of the sheet of film that you place within that cone determines how broad a view you actually capture of the scene before you.

Image circle is the size of the useful image the lens will project and is independent of focal length. Angle of view is a function of image circle and focal length.

The "looks like 50mm on 35" is a sometimes useful comparison to use with non-photograper types, but saying a 50mm becomes a 75mm when used on a smaller sensor is just plain wrong. It's a 50mm, always and for ever. The format size it what changes, similar, as Brian pointed out, to cropping.

E. von Hoegh
25-Jul-2012, 09:11
I have a pretty good feeling I'm just being messed with here, but that was my only observation. Like I said, most of you already know this, I just didn't really understand why that was.

Your observation is incorrect. The focal length does not and can not change. This is very important to know, if you wish to be a competent photographer.

Steve Smith
25-Jul-2012, 09:18
Although it's common practice, I think it's a mistake to think of things in terms of 35mm camera lenses. Better to understand what a normal lens is for each format you use and work it out from there.


Steve.

Oren Grad
25-Jul-2012, 09:24
Image circle is the size of the useful image the lens will project and is independent of focal length.

Not sure what you mean by that. Within a given design type, image circle indeed scales with focal length. OTOH, starting from a blank piece of paper, for a given focal length a lens designer can choose from a variety of optical formulas to achieve a very wide range of possible image circles.

Anyway, I'm not inclined to haul out the wet noodle over the "equivalent focal length" usage unless the person using it stretches the analogy too far and starts to draw incorrect inferences from it. There's a glimmer of useful insight there; starting as beginners we find our way to a more complete understanding through many different paths.

E. von Hoegh
25-Jul-2012, 09:36
Not sure what you mean by that. Within a given design type, image circle indeed scales with focal length. OTOH, starting from a blank piece of paper, for a given focal length a lens designer can choose from a variety of optical formulas to achieve a very wide range of possible image circles.


A 6 1/4" WA Velostigmat has about the same image circle as a 9 1/2" Dagor and a 16 1/2" Artar. Independent of focal length. A 350mm image circle will give slight movements on 8x10 regardless of the focal length or design of the lens wich projects it, be it 160mm wide angle or a 19" process lens. Angle of view expressed in degrees is a function of lens design, image circle expressed as diameter of a circle is independent of lens design and focal length.

And, if you read the thread, you will see that the OP is indeed drawing incorrect inferences from "equivalent focal length".

Cletus
25-Jul-2012, 09:45
Okay, let me just restate my point, since I seems to have offended the sensibilities of some here with my crude and uneducated vocabulary in reference to the focal length of a lens.

I noticed that the smaller the piece of film I use, the smaller the picture I get.

E. von Hoegh
25-Jul-2012, 09:52
Okay, let me just restate my point, since I seems to have offended the sensibilities of some here with my crude and uneducated vocabulary in reference to the focal length of a lens.

I noticed that the smaller the piece of film I use, the smaller the picture I get.

Cletus, we are trying to steer you in the correct direction. This is how things go here. We argue amongst ourselves all the time here. There are many incredibly highly skilled folks - in more than photography- here, and this focal length issue has been dealt with more than once.

BrianShaw
25-Jul-2012, 10:09
I noticed that the smaller the piece of film I use, the smaller the picture I get.

By jove... now you've got it! :D ;) :o

E. von Hoegh
25-Jul-2012, 10:10
By jove... now you've got it! :D ;) :o

I restrained myself.......

Leigh
25-Jul-2012, 14:25
The "equivalent focal length" concept is just a new and improved way to confuse people.

Ignore it. Pretend the phrase was never invented. It's nonsense.

- Leigh

Steve Smith
25-Jul-2012, 15:21
I noticed that the smaller the piece of film I use, the smaller the picture I get.

Then you need a bigger enlargerificator.


Steve.

RichardSperry
25-Jul-2012, 19:06
The effective focal length never changes, ever. The perspective doesn't change, either, unless you move the camera. The part of the image you record on film is what changes.

The images will look different.

E., What is the acceptable word for that difference?

Or do you say that only a wordy paragraph works, for explaining something obvious that one word will do?

RichardSperry
25-Jul-2012, 19:08
The "equivalent focal length" concept is just a new and improved way to confuse people.

Ignore it. Pretend the phrase was never invented. It's nonsense.

- Leigh

Likewise to you, Leigh. What is your acceptable word for the difference?

You know that the two images will look different, everyone does. What is your word to describe the difference?

sully75
25-Jul-2012, 19:21
The "equivalent focal length" concept is just a new and improved way to confuse people.

Ignore it. Pretend the phrase was never invented. It's nonsense.

- Leigh

confusing? Really? Seems totally simple to me.

RichardSperry
25-Jul-2012, 19:36
Your observation is incorrect. The focal length does not and can not change. This is very important to know, if you wish to be a competent photographer.

I think a competent photographer should know that an image made with a 300mm lens will look different on an 8x10 camera back versus a 4x5 back. It's something a beginner photographer would notice off the bat, a layperson would notice the difference.

This whole discussion is merely a terminology debate. Some like to include all the details of image circle or DOF or whatever, unnecessary. If all you did was agree on what word works to describe the obvious difference, then the debate would be settled. And then it would be clear to everyone, instead of debating something that no one is arguing(it is beyond obvious that the focal length does not change, why argue that point). There is a difference, and you certainly don't have to jump down Cletus' throat for noticing it, He doesn't know the word or term, and is politely asking what that word or term is.

So am I. What is your word to describe the difference, E.?

Leigh
25-Jul-2012, 19:45
confusing? Really? Seems totally simple to me.
The concept of "equivalent focal length" is based on an invalid premise, specifically,
the idea that a photographer will know intuitively the angle of view of a specific focal length on a 35mm camera.

Back in "the day", when digital first came out, it was assumed that everyone was familiar with 35mm lenses and what image they would produce.
Therefore it made sense to convert the true focal length into an "equivalent" FL that would yield the same image on 35mm as you got on digital.

That assumption is no longer valid.

Couple that with the fact that the aspect ratios are different for 35mm and LF, and any suggestion of "equivalence" becomes invalid.

- Leigh

Leigh
25-Jul-2012, 19:53
...an image made with a 300mm lens will look different on an 8x10 camera back versus a 4x5 back.
Disregarding the actual image circle diameter, every 300mm lens will produce exactly one image of a given subject,
and that image will be identical for every 300mm lens regardless of what, if any, film or sensor is behind the lens.

This is absolutely obvious since the lens has no knowledge of what's behind it, so there's no way to adjust the image for the medium.

The medium will determine what portion of that image is captured for future use.

If you shoot a picture on a piece of 8x10 film, you get an image containing some portion of the subject.
If you then take a pair of scissors and cut out a 4"x5" section of that negative, that's what a 4x5 camera would capture.
Then take the scissors and cut a 6x6 section out of that negative, and that's what an MF camera would capture.
Then cut out a 24mmx36mm section of that negative and you have the image from a 35mm camera.

The image thrown by the 300mm lens has not changed in any manner whatsoever.
The only change is what portion of that image you choose to retain.

- Leigh

RichardSperry
25-Jul-2012, 19:56
Leigh,

How about sticking with Cletus' first example.

Take an 8x10 camera with a 300mm lens. The camera has an 8x10 back and a 4x5 back. The image produced will be different for each back, obviously. What term do you use for this difference, Leigh?

It's the same camera, same aspect ratio, same lens, same distance, same DoF, same image circle, same field of view, same angle of view. But the image is different, what is this called?

RichardSperry
25-Jul-2012, 20:02
Disregarding the actual image circle diameter, every 300mm lens will produce exactly one image of a given subject,
and that image will be identical for every 300mm lens regardless of what, if any, film or sensor is behind the lens.

This is absolutely obvious since the lens has no knowledge of what's behind it, so there's no way to adjust the image for the medium.

The medium will determine what portion of that image is captured for future use.

If you shoot a picture on a piece of 8x10 film, you get an image containing some portion of the subject.
If you then take a pair of scissors and cut out a 4"x5" section of that negative, that's what a 4x5 camera would capture.
Then take the scissors and cut a 6x6 section out of that negative, and that's what an MF camera would capture.
Then cut out a 24mmx36mm section of that negative and you have the image from a 35mm camera.

The image thrown by the 300mm lens has not changed in any manner whatsoever.
The only change is what portion of that image you choose to retain.

- Leigh

You have just described something that has a name, a term; cropping.

I am not debating that. I am asking you for the word to describe two different images taken with two different sizes of film, with all other things remaining non variable.

What is that word, or term, or phrase that describes that difference.

If you don't know it, just say so.

Leigh
25-Jul-2012, 20:08
You have just described something that has a name, a term; cropping.
No, I'm not talking about cropping. I'm talking about how one lens works with different film formats.


What term do you use for this difference, Leigh?
It's the same camera, ..., same field of view, same angle of view. But the image is different, what is this called?
You're asking for something that does not exist, because your analysis is wrong.

The field of view and angle of view are different for the two formats.
Those are determined by the size of the medium (8x10, 4x5, or whatever).

This is basic optical design and trigonometry.
The distance from the film to the rear node of the lens = the lens focal length when focused at infinity.
The angle of view is between that line and a line drawn from the rear node to one corner of the film, times two.
Obviously that angle changes with the size of the film.

- Leigh

RichardSperry
25-Jul-2012, 20:23
There is a noticeable difference, IT exists. It is a thing.

Your word or terminology may not exist.

A system of science would have a system for naming things, describing things within it. Why doesn't photography, Leigh? You called photography a science; where's the word?

Any noob or layperson can see the difference between these two images, why isn't there a word for it? There is no analysis required, it is observational. The images obviously look different.

RichardSperry
25-Jul-2012, 20:38
The field of view and angle of view are different for the two formats.

How can it? It's the same camera and lens. That's no different than saying the focal length changes.

On the 4x5 back, the same image is projected. Half of it hits the back adapter and not the film. The field of view or angle of view does not change within
the camera(behind the same lens).

RichardSperry
25-Jul-2012, 21:02
What's the word or term then, Leigh?

You're getting close with "angle of view", I suppose. You're probably using the 8x10 ground glass to compose even for the the 4x5 sheet. Are you saying the angle of view of the camera and lens changes as soon as you slide the 4x5 holder in?

Is that the term you use?

Do your caretakers let you surf the Internet without supervision, I hope they have some kind of Alzheimer's LoJack on you in case you leave the house in the middle of the night. Safety suggestion, tattoo your name and address on your arm, that way when you wander off people will be able to get you back home. I've seen people like you do that.

RichardSperry
25-Jul-2012, 21:18
Obviously that angle changes with the size of the film.

It's not obvious to me.

I can't see how the angle changes, it's the same lens. How does it know what film or sensor is behind it?

Is there a switch, or does it use telepathy to make this miraculous change of physics?

http://en.m.wikipedia.org/wiki/Angle_of_view

This makes no mention of this change that you say happens with the lens. Can you post a link to a source that states how it occurs?

Leigh
26-Jul-2012, 03:07
OK. Let me try this with a diagram.

http://www.mayadate.org/pix/AoV.png

The rectangle on the right represents the subject (a building or whatever).

There are two dimensions on the left, 8" representing an image on 8x10 and 4" representing an image on 4x5.

The red lines delimit the angle of view obtained with 8x10 film.
The blue lines delimit the angle of view obtained with 4x5 film.

As you can seel, the only parameter that changes is the Angle of View, being the angle between lines of the same color.

The camera position and lens position have not changed.

- Leigh

rince
26-Jul-2012, 03:33
To me it is still cropping. If all stays the same but the size of film, I am just cropping the image circle more with a 4x5 the image the lens produces is still the same, I only decide to record less of it. If you lay the 4x5 neg on top of the 8x10 , the information on the 4x5 and the corresponding section of the 8x10 are the same. So to me a 300mm stays a 300mm regardless of the format.

Leigh
26-Jul-2012, 03:41
If you lay the 4x5 neg on top of the 8x10 , the information on the 4x5 and the corresponding section of the 8x10 are the same.
So to me a 300mm stays a 300mm regardless of the format.
Exactly. That's what I said in post #28.

I think of cropping as an operation that's done on the negative image when printing,
but perhaps the term can be applied in-camera.

- Leigh

Mark Barendt
26-Jul-2012, 04:11
It's the same camera, same aspect ratio, same lens, same distance, same DoF, same image circle, same field of view, same angle of view. But the image is different, what is this called?

I don't know there is another proper term but for all intents and purposes I can think of, it's cropping.

In an enlarger the scene is the negative, from the scene the light passes through the lens and an image circle is projected on the baseboard or floor, many times both. Changing the size of the film or paper you might use is simply cropping.

The conceptual difference for most non or new large formaters is that they come from a world where the size of the film is fixed for the camera in their hand.

Effective focal length is non-sense as far as I'm concerned, it's only use was to sell cameras. It isn't a principle of optical science. Half frame and APS size cameras are simply cropping more than full frame 35mm film cameras.

It is a fresh thought for most people to think that the limit to the camera system's angle of view may be the lens and that the film size in play is just one possible arbitrary crop.

RichardSperry
26-Jul-2012, 04:52
Saying a 50mm "becomes" a 75mm will take you down the wrong road.

Isn't what Leigh is NOW saying is that the 50mm has the same 'angle of view' as the 75mm?

Now what is so hard about that?

Instead of resorting to intentional obfuscation, 5th grade insults, and condescension, why don't you just acknowledge the difference and just explain the terminology?

Leigh
26-Jul-2012, 04:56
Isn't what Leigh is NOW saying is that the 50mm has the same 'angle of view' as the 75mm?
I absolutely DID NOT say that.

The distance from the rear node to the film is different for a 50mm lens versus a 75mm lens.

Therefore the angle of view is different.

The illustration I gave above is for a lens of one focal length on two different formats, which yields two different angles of view.

- Leigh

RichardSperry
26-Jul-2012, 06:45
If I am taking a photo of, say, a yard stick with an 8x10 with a 300mm lens. Such that the ends of the yard stick are just included on the 8x10 sheet of film.

And I take a photo of the same yard stick with a 4x5 camera with a 150mm lens; again the ends of the yardstick just included on the 4x5 film sheet.

The angle of view is different for the two formats, using these (what a stupid person might call equivalent) lenses, is that what you are saying now?

Help me out here, Leigh. I am stupid and don't understand geometry, the angle is different?

E. von Hoegh
26-Jul-2012, 06:53
Wow. There must be some bizarre conjunction of stars, or something.

rdenney
26-Jul-2012, 07:33
It's about magnification. A given focal length provides a given magnification no matter what size film sits behind it.

A full-face portrait with an 8x10 camera using a 300mm lens will magnify the sitter's nose the same amount as when using a 300mm lens on a 35mm camera from the same position. The difference will be that the 35mm photo will only include that nose. The key to understanding is that the nose is the same size in both photos.

Angles bring clarity when they refer to subject elements, but confusion when they refer to the edges of the picture. The angle subtended by any subject element is controlled only by the focal length and camera position.

Sinar calls their multiformat rollfilm holder the Zoom. Once a camera is set up, one might tighten the view by selecting a smaller format, which is the same reason one might zoom in using a zoom lens. But each uses a different strategy to tighten the view. Changing formats trims the format to accommodate the magnification, and changing focal lengths (as with a zoom lens) alters the the magnification to accommodate the format.

Rick "noting that angles can describe magnification, but angles can describe other things, too; hence the confusion" Denney

Mark Barendt
26-Jul-2012, 07:37
If I am taking a photo of, say, a yard stick with an 8x10 with a 300mm lens. Such that the ends of the yard stick are just included on the 8x10 sheet of film.

And I take a photo of the same yard stick with a 4x5 camera with a 150mm lens; again the ends of the yardstick just included on the 4x5 film sheet.

The angle of view is different for the two formats, using these (what a stupid person might call equivalent) lenses, is that what you are saying now?

Help me out here, Leigh. I am stupid and don't understand geometry, the angle is different?

The angle of view is the same in the cases you describe here but: the the subject to camera distance will also be cut in half for the 4x5 shot as will the film to lens distance (300 to 150).

E. von Hoegh
26-Jul-2012, 07:37
I think "obtuse" is a word referring to an angle... and something else, as well.

Leigh
26-Jul-2012, 08:33
The angle of view is different for the two formats, using these ... lenses, is that what you are saying now?
That's correct, as I've said all along.

The reason is that the distance from the film to the lens is different for the two different focal lengths.

- Leigh

Ben Syverson
26-Jul-2012, 10:40
Wow, I think some folks are overthinking this.

• There's absolutely nothing wrong with stating a focal length in "35mm equivalent." It's not in any way inaccurate, and can often be helpful. To get it, take the dimension you're interested in (I use "longest side"), divide focal length by that dimension, then multiply by 36. So 300mm on 8x10 would be: 300mm / 254mm * 36mm = 42.5mm equivalent. If you contact print the 8x10 and blow up the 35mm to 8x10, they will have the same horizontal field of view, and elements in the scene will be reproduced at the same size.

• A 300mm lens on 8x10 and a 150mm on 4x5 have exactly the same horizontal and vertical field of view (HFOV and VFOV). Those are the "angles" of the lens, and they are 100% equivalent.

• DOF obviously changes with format. If you want to compare DOF between lenses with the same FOV in two different formats, divide the focal length by the aperture. For example, a 300mm ƒ/9 lens ("bokeh value" 33.333) on 8x10 has similar DOF characteristics to a hypothetical 40mm ƒ/1.2 on 35mm.

Leigh
26-Jul-2012, 10:56
A 300mm lens on 8x10 and a 150mm on 4x5 have exactly the same horizontal and vertical field of view (HFOV and VFOV). Those are the "angles" of the lens, and they are 100% equivalent.
Field of view and angle of view are absolutely NOT the same thing.

- Leigh

Ben Syverson
26-Jul-2012, 11:13
Field of view and angle of view are absolutely NOT the same thing.
They are synonyms...

Leigh
26-Jul-2012, 11:14
They're not even related, except that the angle of view of a particular lens design limits its field of view.

Field of view is a linear parameter having a pair of values, those being the x and y dimensions of the subject rendered on the film,
like 8' x 10' or 80' x 100' or whatever.

Angle of view is an angular measurement, given in degrees.
It is determined by film format and is invariant with subject distance.


- Leigh

Mark Barendt
26-Jul-2012, 11:15
Wow, I think some folks are overthinking this.

There's absolutely nothing wrong with stating a focal length in "35mm equivalent." It's not in any way inaccurate, and can often be helpful. To get it, take the dimension you're interested in (I use "longest side"), divide focal length by that dimension, then multiply by 36. So 300mm on 8x10 would be: 300mm / 254mm * 36mm = 42.5mm equivalent. If you contact print the 8x10 and blow up the 35mm to 8x10, they will have the same horizontal field of view, and elements in the scene will be reproduced at the same size.

A 300mm lens on 8x10 and a 150mm on 4x5 have exactly the same horizontal and vertical field of view (HFOV and VFOV). Those are the "angles" of the lens, and they are 100% equivalent.

DOF obviously changes with format. If you want to compare DOF between lenses with the same FOV in two different formats, divide the focal length by the aperture. For example, a 300mm /9 lens ("bokeh value" 33.333) on 8x10 has similar DOF characteristics to a hypothetical 40mm /1.2 on 35mm.

To your first point each time the format aspect ratio changes your math needs to adapt and it becomes silly trying to figure out which way to measure to compare. Different aspect ratios create different compositions.

Your second point is correct but it also illustrates the problem if you compare 35mm film with its 2x3 ratio. The short edge measurement is the on to compare if you want to crop/shorten the 35mm composition to fit 8x10 paper. Conversely for 8x12 paper you would compare long edges because the short edge of the 4x5 or 8x10 composition will get shortened.

On the third point, it is simply wrong. DOF changes with focal length and aperture and distance to subject. For a given fixed focal length lens at a given aperture with a given subject distance; the DOF remains the same regardless of the format or size of film behind it.

Ben Syverson
26-Jul-2012, 11:16
Many normal humans express "Field of View" in degrees, as in: "50 horizontal field of view." That's perfectly valid.

Ben Syverson
26-Jul-2012, 11:20
To your first point each time the format aspect ratio changes your math needs to adapt and it becomes silly trying to figure out which way to measure to compare. Different aspect ratios create different compositions.
Yes, different aspect ratios create different compositions, but that does NOT mean that you can't compare two lenses for formats with different aspect ratios. You just need to figure out what you're interested in comparing. Saying something is a 50mm equivalent is perfectly fine. We all know what that means.


On the third point, it is simply wrong. DOF is a changes with focal length and aperture and distance to subject. For a given fixed focal length lens at a given aperture with a given subject distance; the DOF remains the same regardless of the format or size of film behind it.
This "DOF remains the same" thing is such a frustratingly stubborn misread of the intention of a photographer. A photographer does not compare a 35mm frame with a 35mm crop from an 8x10. You look at the WHOLE picture. My DOF comparison assumes that you'll look at the whole picture at one time, like most people do with photographs. If you put an 8x10 contact shot with a 300mm ƒ/9 next to an 8x10 enlargement from a 35mm frame shot with a 40mm ƒ/1.2, the degree of defocusing and overall level of DOF will be very similar. That's all that metric is designed to compare.

Mark Barendt
26-Jul-2012, 17:06
Yes, different aspect ratios create different compositions, but that does NOT mean that you can't compare two lenses for formats with different aspect ratios. You just need to figure out what you're interested in comparing. Saying something is a 50mm equivalent is perfectly fine. We all know what that means.


This "DOF remains the same" thing is such a frustratingly stubborn misread of the intention of a photographer. A photographer does not compare a 35mm frame with a 35mm crop from an 8x10. You look at the WHOLE picture. My DOF comparison assumes that you'll look at the whole picture at one time, like most people do with photographs. If you put an 8x10 contact shot with a 300mm ƒ/9 next to an 8x10 enlargement from a 35mm frame shot with a 40mm ƒ/1.2, the degree of defocusing and overall level of DOF will be very similar. That's all that metric is designed to compare.

But one does compare 8x10 crops and 4x5 crops from a 300 mm lens image circle, as was the example that started this thread.

We are also on a large format site where switching film size and format is normal, we are not on Nikonians pandering to 35mm shooters.

Cletus
26-Jul-2012, 23:18
Good grief.

Cletus
26-Jul-2012, 23:53
So what makes a 300mm lens designed for 35mm different then a 300mm large format lens? Certainly the image circle of the lens designed for 35mm is much smaller, but the magnification is also much greater than the same "focal length" of the LF lens.

I'm only asking this question to add to the 'circle of confusion' (that's an optical term too, unrelated to angle..I mean FIELD of view). And also because I enjoy fireworks....:eek:

Steve Smith
27-Jul-2012, 00:19
If you put an 8x10 contact shot with a 300mm ƒ/9 next to an 8x10 enlargement from a 35mm frame shot with a 40mm ƒ/1.2, the degree of defocusing and overall level of DOF will be very similar. That's all that metric is designed to compare.

But if they were both taken at f8, the enlarged 35mm frame will show more depth of field.


Steve.

Mark Barendt
27-Jul-2012, 03:23
So what makes a 300mm lens designed for 35mm different then a 300mm large format lens? Certainly the image circle of the lens designed for 35mm is much smaller, but the magnification is also much greater than the same "focal length" of the LF lens.

I'm only asking this question to add to the 'circle of confusion' (that's an optical term too, unrelated to angle..I mean FIELD of view). And also because I enjoy fireworks....:eek:

Yes the image circle is smaller, long lenses for 35mm cameras are also regularly telephoto designs so the lens can sit closer to the film when focused instead of roughly 12" (300mm) away.

But, given the same subject to film distance, if you put a standard 300mm large format lens in front of a 35mm camera and attach it with a bellows the size of the subjects projected on the film should be essentially the same size as the image from the 35mm telephoto lens; no difference in magnification. The photos should be essentially identical with either lens.

rdenney
27-Jul-2012, 03:27
So what makes a 300mm lens designed for 35mm different then a 300mm large format lens? Certainly the image circle of the lens designed for 35mm is much smaller, but the magnification is also much greater than the same "focal length" of the LF lens.

I'm only asking this question to add to the 'circle of confusion' (that's an optical term too, unrelated to angle..I mean FIELD of view). And also because I enjoy fireworks....:eek:

No, the magnification provided by the lens onto the film is exactly the same. The only difference is that the small-format 300mm lens is only required to make an illuminated circle about two inches in diameter, while a 300mm lens for 8x10 must make a circle at least 12 inches in diameter (and they usually provide more).

What is different with respect to the circle of confusion, which is a standard you set based on your intended display size, is that the small piece of film must enlarged by a much greater amount to make a given size print.

Rick "don't play with fireworks" Denney

E. von Hoegh
27-Jul-2012, 06:50
So what makes a 300mm lens designed for 35mm different then a 300mm large format lens? Certainly the image circle of the lens designed for 35mm is much smaller, but the magnification is also much greater than the same "focal length" of the LF lens.

I'm only asking this question to add to the 'circle of confusion' (that's an optical term too, unrelated to angle..I mean FIELD of view). And also because I enjoy fireworks....:eek:

No. Absolutely wrong. This is the whole crux of your misperception. A 300mm lens is a 300mm lens, always and forever regardless of the film format used behind the lens. This is why I pointed out in one of my first posts that saying something like "a 50mm lens becomes a 75mm lens on a smaller sensor" would lead you down the wrong path. The only difference between a 300mm lens for 35mm and a 300mm lens for 8x10 is the size of the image circle.

Remember to play very carefully with fireworks. They can blow up in your face, leaving no one here willing to answer your questions.

Leigh
27-Jul-2012, 06:59
A 300mm lens is a 300mm lens, always and forever regardless of the film format used behind the lens.
Absolutely true under all conditions and in all circumstances. Period.

- Leigh

E. von Hoegh
27-Jul-2012, 07:13
Absolutely true under all conditions and in all circumstances. Period.

- Leigh

It seems that this is too complex a point for some to grasp. Why? It's basic physics; any average 5th grader is capable of understanding it.

Leigh
27-Jul-2012, 07:23
...any average 5th grader is capable of understanding it.
Ability and desire are two very different and unrelated things. :eek:

- Leigh

E. von Hoegh
27-Jul-2012, 07:24
Ability and desire are two very different and unrelated things. :eek:

- Leigh

I know, my question was at least semi rhetorical.

Cletus
27-Jul-2012, 13:10
Okay so I guess I better retract the fireworks remark, it wasn't meant to raise any further ire, or get myself blackballed fom the forum. I was just a little surprised about how heated the discussion became over such a seemingly harmless notion. FWIW, I've been reading through everyone's commentary and now I truly see the error in my thinking with regard to my initial comment.

I'll be much more deferential in the future.

Regards - Phil aka "Cletus"

E. von Hoegh
27-Jul-2012, 13:24
It isn't a harmless notion. It's wrong. Period. Engineer types do not like or tolerate wrong.

Ben Syverson
27-Jul-2012, 14:17
But if they were both taken at f8, the enlarged 35mm frame will show more depth of field.
Exactly, because the number is relative to the focal length. Thus, you cannot compare them apples-to-apples between formats.

Cletus
27-Jul-2012, 15:24
E., lighten up. This isn't life or death here. I admitted my folly ( although it seems strange I should have to ) and that should be an end of it. I am interested and will continue to read this discussion, if it continues, but I see no reason I should continue to be chastised over something as inoffensive as this.

It's beginning to look like you don't have enough to do. Why don't you go take a picture?

cowanw
27-Jul-2012, 16:02
Cletus, I too take joy in having a sudden Eureka moment.
Alot of people understand exactly what you are saying.
Posts 61-65 were starting to sound like Statler and Waldorf on the Muppets.
It's not about you or what you said.

Cletus
27-Jul-2012, 18:13
cowanw -

No kidding! And a minor Eureka moment was all it was too. The only intention of my little post was only ever to illustrate a concept (one that I KNOW most of us can directly relate to) and the fact that I had gained a little insight into something that I just hadn't previously given much thought to.

I thought there just might be someone else out there in the ether who just might have been wondering that same thing and thus, gain a little deeper understanding of an everyday concept that photographer's deal with from time to time. Excuse me for trying to contribute!

In the future I'll need to be a little more careful about what "insights" I try to "illustrate" around here. It appears some of those more established members are frightfully quick to take offense and pounce if an idea is presented in the more abstract and un-technical way I chose to do it. And I can deal with the proper explanation of a principle, it's the vitriol and condescension that I have trouble with...

Note to self: Next time I must do my research and thoroughly brush up on theory and conventional terminology prior to posting.

Vaughn
27-Jul-2012, 21:54
Long time ago it was made clear to me that even if no one calls fixer 'hypo' anymore, one should not shorten HCA to 'hypo'.

Mark Barendt
28-Jul-2012, 05:23
FWIW, I've been reading through everyone's commentary and now I truly see the error in my thinking with regard to my initial comment.


It's worth a bunch Phil.

To me your original post shows that your motive for sharing was great and that the pieces were really falling into place for you.

Many simplifications though, like "effective focal length", are crutches used to be able to talk with people who don't yet get it.

Simplifications can totally confuse a situation though and lead people to ask the wrong questions and make the wrong decisions in the field and in the darkroom. Simplifications require context that doesn't always exist.


Long time ago it was made clear to me that even if no one calls fixer 'hypo' anymore, one should not shorten HCA to 'hypo'.

Vaughn's comment is a great illustration of how lost context and our drive to simplify can totally and wrongly change the usage of a word and it is just one of many.

John Koehrer
28-Jul-2012, 11:10
For the OP, without going into the arguments and overkill math, As a rule of thumb it'll work out.
If your work needs to be technically precise, use the math. Then try to find that 86.02 lens you need to match your figures.

If you want APPROXIMATELY the same picture as a 28mm lens(35mm) you're going to need APPROXIMATELY a 90mm on 4X5.
It's an APPROXIMATION, A EDUCATED GUESS.
And no, the aspect ratio won't be the same.

Leigh
28-Jul-2012, 11:27
If you want APPROXIMATELY the same picture as a 28mm lens(35mm) you're going to need APPROXIMATELY a 90mm on 4X5.
The fallacy with this "equivalence" lies in the assumption that a newbie will know what
field of view a particular focal length produces on a 35mm negative.

That's seldom the case.

The whole idea was conceived when digital imaging was first introduced, as a way of advising people
what field of view to expect when using their existing 35mm lenses on a digital body.

- Leigh

E. von Hoegh
28-Jul-2012, 11:58
Long time ago it was made clear to me that even if no one calls fixer 'hypo' anymore, one should not shorten HCA to 'hypo'.

My name is Nemo.
I still call 'fixer' 'hypo'.... (winking smiley)

It's important to avoid oversimplifying, especially when the subject is basic to an understanding of something. You don't build a stone house on a styrofoam foundation.

Leigh
28-Jul-2012, 12:12
My name is not Nemo.
I still call 'fixer' 'hypo'....

- Leigh (Who the heck is Nemo?)

John Koehrer
28-Jul-2012, 12:14
"I've been a photographer for over twenty years" suggests enough familiarity with cameras to use a "Rule of Thumb"
Or........perhaps it's experience with a Brownie Hawkeye?

In any case, it's close enough to get an idea. Oh, that's right, I forgot. Do it your way or it won't work.

E. von Hoegh
28-Jul-2012, 12:18
My name is not Nemo.
I still call 'fixer' 'hypo'....

- Leigh (Who the heck is Nemo?)

"Nemo" is Latin, meaning 'no one' or 'nobody'. Captain Nemo was literally Captain Nobody.

Leigh
28-Jul-2012, 12:21
Yes, I'm familiar with the Latin, and with Captain Nemo.

I didn't realize he was a photographer. :D

If you mix your fixer with salt water rather than distilled or tap water, does it still work OK?

- Leigh

E. von Hoegh
28-Jul-2012, 12:23
Yes, I'm familiar with the Latin, and with Captain Nemo.

I didn't realize he was a photographer. :D

If you mix your fixer with salt water, does it still work OK?

- Leigh

*bangs head on desk*

Leigh
28-Jul-2012, 12:24
Poor desk! :D

- Leigh

rdenney
28-Jul-2012, 21:49
The fallacy with this "equivalence" lies in the assumption that a newbie will know what
field of view a particular focal length produces on a 35mm negative.

That's probably the one thing most photographers actually did know, say 10 years ago with digital cameras first started to make real inroads. They had spent so much time gaining intuition about 35mm that they didn't learn how to translate that to other formats. So, the fallacy wasn't that they lacked intuition about what focal lengths meant for 35mm, it was that equivalency would give them instant intuition about other formats, without already knowing how to perform the translations for themselves. Those who already understood different formats didn't need equivalence factors and therefore find them annoying. And there were those who gave primary importance to the equivalence factor, thinking it dictated focal length rather than merely describing what focal length meant in one format in terms of another. But there were lots of people who used the equivalence factor appropriately until they gained intuition in the new format, and then no longer needed it.

I've heard many times that one should just multiply focal lengths used in 35mm by three to get the equivalent focal length for 4x5. That's the same potential mistake as someone stating that their Canon 10D (APS-C format) made their lenses longer than they were on their 35mm Elan II.

I tell people to judge the meaning of focal length by comparing it to the diameter of the film, with the caveat that it is an approximation that ignores important effects, such as 1.) the difference in aspect ratio and 2.) the different way they will see the scene when using a ground glass versus a viewfinder. They will gain intuition soon enough, and they won't be tempted to believe that changing formats somehow changes the actual focal length of the lens.

Rick "who wrote fingerings in the music when learning F tuba, 20 years after learning Bb tuba, as a temporary crutch" Denney

RichardSperry
29-Jul-2012, 00:52
Those who already understood different formats didn't need equivalence factors and therefore find them annoying.

Understand and use.

Imagine if these rabid twits objected, argued, and insulted when someone discussed using a 150 lens for enlarging(or making) 4x5 negatives compared to using a 300mm for 8x10.

One of the Rollei lenses I've bought even had a little lens equivalence chart in it. Made long before digital cameras became prevalent enough to discuss equivalence. Equivelence charts are myriad on the web from many respectable sources.

This irrational objection to lens equivalence is about as absurd as the analogy of a stone house being built on styrofoam. What houses are built of stone, even?

Castles?

rdenney
29-Jul-2012, 07:40
Imagine if these rabid twits objected, argued, and insulted when someone discussed using a 150 lens for enlarging(or making) 4x5 negatives compared to using a 300mm for 8x10.

Be careful. Some swords cut both ways.

Rick "seeing people talk past each other--on purpose" Denney

Mark Barendt
29-Jul-2012, 07:42
Be careful. Some swords cut both ways.

Rick "seeing people talk past each other--on purpose" Denney

Yep.

RichardSperry
29-Jul-2012, 08:02
Yes, they do.

The problem with the site ignore feature is that it drops when the site logs the user out.

Anyway, my mother taught me that people treat other people how they wish to be treated. It's an obligation.

Mark Stahlke
29-Jul-2012, 08:17
I think a lot of the confusion arises when people compare focal lengths when they really want to compare angles of view (NOT angles of coverage). I'm sure most folks here know angle of view depends upon the format size. That's why a 150mm lens on 8x10 has a much wider angle of view than it does on 4x5 or 35mm.

Leigh
29-Jul-2012, 08:37
I'm sure most folks here know angle of view depends upon the format size.
Angle of View* is a function of the lens design, and is invariant.
It has nothing to do with the imaging system behind the lens.

AoV is the value that's engraved on the lens barrel, on lenses that bear such notation.
Obviously such designation would be impossible if it varied with the format in use.


- Leigh

*Ref: Schneider-Kreuznach Large Format Lenses catalog, where the term is used unambiguously in many places.

Note: Other manufacturers avoid the term entirely. Nikon uses "covering power", Rodenstock "image angle", and Fujinon "angle of coverage".

Mark Stahlke
29-Jul-2012, 08:47
Angle of View* is a function of the lens design, and is invariant.
It has nothing to do with the imaging system behind the lens.

AoV is the value that's engraved on the lens barrel, on lenses that bear such notation.
Obviously such designation would be impossible if it varied with the format in use.


- Leigh

*Ref: Schneider-Kreuznach Large Format Lenses catalog, where the term is used unambiguously in many places.

Note: Other manufacturers avoid the term entirely. Nikon uses "covering power", Rodenstock "image angle", and Fujinon "angle of coverage".
And therein lies another source of much confusion. If we must be pedantic then let's call one of them "angle of view" and the other "field of view". I prefer the terms "angle of coverage" and "angle of view".

Leigh
29-Jul-2012, 09:03
If we must be pedantic then let's call one of them "angle of view" and the other "field of view".
Yes, I agree with that. In fact I've posted such a distinction previously.

Schneider uses Angle of View as the design-dependent parameter.

I think Field of View is a reasonable designation for the portion of the subject being recorded on the film [personal opinion].

- Leigh

rdenney
29-Jul-2012, 10:08
We should remember that definitions are descriptive. When a term is generally confusing, doing battle over our preferred definition means we'll be doing a lot of battle. Let me show you my scars. But it does get tiresome, and that approach does little to advance real understanding.

Angle of view in lieu of coverage is senseless to me, Schneider's use of it notwithstanding. If it's not in the picture, there is nothing to view. I know what all these principles mean, of course. But there is the matter of using plain English.

Rick "nomenclature battles are the bloodiest and the least worth the pain" Denney

Leigh
29-Jul-2012, 10:19
It's really an academic exercise, at best. I see no particular relevance to the terms.

I've never seen a photographer pull out a protractor, measure the desired optical angle, then consult a lens catalog to select the proper optic.

The only practical application relates to light fall-off approaching the IC perimeter, which gets worse as the angle increases.

- Leigh

Mark Stahlke
29-Jul-2012, 10:52
It's really an academic exercise, at best. I see no particular relevance to the terms.What's relevant to this thread is using the terminology consistently to avoid confusion.


I've never seen a photographer pull out a protractor, measure the desired optical angle, then consult a lens catalog to select the proper optic.I've used a protractor on a map to measure angles of view (or fields of view, if you insist) as an aid to selecting a lens kit for a given trip.

Leigh
29-Jul-2012, 10:55
I've used a protractor on a map to measure angles of view (or fields of view, if you insist) as an aid to selecting a lens kit for a given trip.
That makes sense. I've never had occasion to do that type of planning.

I always carry all 16 lenses with me, but then I'm never far from the van. I don't do hiking or backpacking.

- Leigh

BrianShaw
30-Jul-2012, 06:25
That makes sense. I've never had occasion to do that type of planning.


Me either, but I've sometimes been disappointed when I forgot to bring the "right" lens. Great idea... I'll be adding a protractor to my LF accessory bag (or learning how to "fake" a protractor using a compass, which is essential LF gear to me). Or, I can just buy 10 more lenses to keep up with Leigh! :)

E. von Hoegh
30-Jul-2012, 07:00
Understand and use.

Imagine if these rabid twits objected, argued, and insulted when someone discussed using a 150 lens for enlarging(or making) 4x5 negatives compared to using a 300mm for 8x10.

One of the Rollei lenses I've bought even had a little lens equivalence chart in it. Made long before digital cameras became prevalent enough to discuss equivalence. Equivelence charts are myriad on the web from many respectable sources.

This irrational objection to lens equivalence is about as absurd as the analogy of a stone house being built on styrofoam. What houses are built of stone, even?

Castles?

You know, I've yet to see you add anything other than contention to a thread. Your posts in this and the reciprocity thread are deliberately obtuse, misinformed, argumentative, and unproductive. Why don't you just stick to the image threads, enjoy the pretty pictures, and stop bothering the rest of us with your shenanigans? I'm sure I'm not the only one who is uninterested in being a bit player in your little psychodrama.....

E. von Hoegh
30-Jul-2012, 07:16
... When a term is generally confusing, ...

When a term is generally confusing, it's best not to use it - or the concept which gave rise to the term, in this case.