Formats & lenses

[Chip]

Hi Folks,

Before joining this forum I had planed on buying a 6x9 view camera to supplement my MF SLR system. After reading a lot of the archives I've decided that a 4x5 with roll film backs is a better decision; especially since 4x5s are more numerous and less expensive than 6x9s. Roll film convenience, cost and speed for color and sheet film for B&W.

Lens selection is where I'm having some difficulty. I know what focal lengths I want but what I don't understand is image circle to film format to focal length variables. Let me use a 150 mm lens as an example-standard lens for 4x5 and slightly long for 6x9 but with the image circles ranging from 150 mm to 400mm how do I determine what I'll actually see? Has anyone worked out a "crop factor" or able to explain this to a geometry drop-out?

Thanks for any help,

Chip

[Nick_3536]

Image circle isn't cropping. It's usefull image circle.

let me put it this way. If you take a portrait and never use the movements then an image circle little bigger then the film format is fine. If OTOH you're doing something that requires extreme movements then you'll want all the image circle your camera and lens can provide.

You'll want more then 150mm if you're shooting 4x5. OTOH 400mm sounds more like a 8x10 wide angle lense.

[Ron Marshall]

To use a lens on a given format the lens must have an image circle that is at least equal to the diagonal of the film format, which is 153mm for 4x5. But in practice, the image circle should be at least 20% greater to allow for movements, tilts or shifts.

Usually, the larger the image circle the heavier the lens. Almost all of the current 150mm lenses sold have image circles larger than 210mm, ample for 4x5 in most situations.

[David Rees]

Chip,

I mostly do the same as you are planning to do -- I picked up a Wista DX wooden field camera, designed for 5x4, and then mostly use it with Cambo/Calumet C2 medium format film backs (6x9 in my case, though you can find them for 6x4.5, 6x6, 6x7 , 6x9 and 6x12 I believe). I have a dedicated MF film scanner (Nikon 8000) so 6x9 is normally plenty big enough for my needs -- and as you say, cheaper too.

To get the best optical quality, I went with modern 5x4 lenses, largely from Schneider, though I do have one Nikkor (64mm f4), and one Rodenstock (90mm f6.8). All such lenses cover 5x4, often with an image circle which allows movement on 5x4, so there is ample movement for 6x9. Only lenses to be careful about are lenses with a focal length below 65mm -- some can have image circles too small for 5x4, though likely to be fine for 6x9. If you make sure that any lens you buy has an image circle of 166mm (or larger) at f22, you will be fine, at least for landscape work.

If you intend to stick to 6x9 exclusively, then an image circle beyond 200mm is unlikely to be of much use to you, and result only in an increase in cost, weight and bulk in your kit bag. Only caveat to that is if you are planning to do work which requires extensive movements (architecture, say) and are getting a camera with extensive movement potential (typically a monorail, as opposed to a field camera).

One other point -- the shorter focal lengths have smaller image circles, in general -- no need to worry about it for modern lenses beyond 150mm.

[Gordon Moat]

A really, really, really rough rule of thumb would be to take half the focal length, then add it to that for the similar 4x5 lens. An example is that a 105mm on 6x9 has close to the same view as a 150mm on 4x5. However, the aspect ratios are different, so there is not a direct relationship. As others mentioned, the image circle more relates to movements, though if you are using a 4x5 lens with a 6x9 back, then you can safely use more extreme movements. Buying used, a dedicated 4x5 lens should not be too much different in price than a dedicated 6x9 lens, until you get to really wide lenses.

I had a 4x5 system in the past, then sold it. After that I went with a custom made 6x9, though found I missed having the movements. Now I am back into 4x5 again, and the 6x9 doesn't get used much. However, like you, I am now considering getting a roll film back, though I am undecided on 6x7 or 6x9. There can sometimes be an advantage to showing clients a pre-cropped 6x9 image intead of a 4x5 on a light table; since unfortunately not everyone has enough imagination to understand cropping.

Ciao!

Gordon Moat

[Chip]

Thanks for the answers so far.

Let me try to clarify my question: Is there an easy way to visualize what field of view will be seen on the ground glass when the image circle is much larger than the format diagonal?

I'll use a 150 mm lens again and say it has an image circle of 220 mm. If I use a 6x9 roll film back I'll only be using approx. half of the available image circle which will change the field of view to that of a longer lens. What would that be?

Geometry gives me a headache:>)

Thanks again,

Chip

[Sheldon N]

The image circle is independent of field of view. That is to say, a 150mm lens with a 160mm image circle will look the same on a 4x5 or 6x9 as a 150mm lens with a 400mm image circle. All the image circle means is that you have greater capability to use rise/fall/swing/tilt movements without hitting the edge of the image circle, or to use a larger film format.

If you are looking for 35mm equivalents of lens focal lengths, try using a multiplier of 2.5 for 6x9 and 3.75 for 4x5. That means a 150mm lens is like a 60mm lens when shooting 6x9 and like a 40mm lens when shooting 4x5 (in 35mm terms).

The reason lenses with larger image circles are sometimes referred to as wide angle designs (i.e. a 150mm lens with a 400mm image circle) is because they were principally designed to be used with larger film formats, where they act as a wide angle lens. A 150mm lens on 8x10 is like a 20mm lens in 35mm terms. However, if you put that same lens on a 4x5 or 6x9, it will behave like any other 150mm lens. It will however cost much more and be a larger/heavier lens.

[Emmanuel BIGLER]

Thanks for the answers so far....Is there an easy way to visualize what field of view will be seen on the ground glass....
Geometry gives me a headache:>)


There are various approaches to visualize the field covered by the final image recorded on film.
The simplest and easiest is to build a simple frame finder. Another approch is to convert in equivalent focal length what is seen in a 35mm reflex camera fitted with a zoom.

An old discussion about viewfinders, including home-made cardboard cutout viewfinders
http://www.largeformatphotography.info/forum/archive/index.php/t-1443.html

If you are using a 6x9 rollfilm back, effective image size will be 56x82 mm. (varies from 80 to 84 actually according to the actual back you are using).
Cut a 56x82 mm rectangle inside a piece of cardboard and hold the frame at 150mm from your eye, you'll approximately see what will be recorded on film on 6x9 with a 150 f.l.
In 4"x5" format = 94x120mm make another frame of 94x120mm and from 150mm you'll get what will be recorded with a 4x5" cut fiml holder with the 150mm lens.
The frame viewfinder works fine for standard and long focal lengths, but it is a bit difficult to see the whole angular field if you put the 56x82 frame closer than, say, about 50-80 mm from your eye to simulate a 50-80mm wide angle lens ... 50 to 80mm are wide-angle focal lengths for 6x9.

[Leonard Evens]

If you are using a 4 x 5 camera only with a 6 x 9 roll film back, it might make sense to cut out a 6 x 9 mask (actual dimensions as Emmanuel recommended) and place that over the ground glass. It should be positioned to lie just where the roll film holder would place the film.

As to equivalent focal lengths, it has already been pointed out that the aspect ratios are different, and that confuses matters. If you compare 56 to 96 (approximate short distances), you get a multiplier of about 1.7. If you compare 84 to 120 (approximate long distances), you get a multiplier of about 1.4. Comparing diagonals, you would get something in between.

Is there some reason why you have fixed on 6 x 9? If you chose 6 x 7 instead, you would find the aspect ratios to be very close and a multiplier of 1.7 would work. 90 mm in 6 x 7 would be roughly equivalent to 150 mm in 4 x 5. Also, you would get 10 shots per roll. If you are going to print on paper with a 4:5 aspect ratio, which is a fairly common choice, you would have to crop a 6 x 9 frame, and with a view camera, there is little reason to crop since you can set the frame where you want it with camera movements.

[Chip]

Once again I want to thank everyone for their answers!

I understand lens and format equivalencies: a 100mm lens on my 67 system is equal to a 150mm lens on 4x5 or a 50mm lens in a 35mm system. Got it! I also know that the focal length stays what ever the manufacturer made it. But if I put my 300mm 6x7 lens on my 35mm camera it has a much different field of view than if I put my 300mm 35mm system lens on and in this case it's roughly equal to a 400mm lens. This is what I'm trying to figure out.

Most of the wide angle lens (for 6x9) have small enough image circles that most of it can be used, except for the 72mm Schneider Super-Angulon XL, and have a wide angle feel but at the longer focal lengths and the bigger image circles most of it is lost to the 6x9 format.

Why 6x9? I already have 6x7 and wanted to try a format that was more rectangular. Why roll film for color? At print sizes up to 16x20 it matches anything I've seen from
4x5.

I can't wait to play with a 4x5 FP-4 Plus neg.!

Again thanks for the answers,

Chip

[Nick_3536]

Most of the wide angle lens (for 6x9) have small enough image circles that most of it can be used, except for the 72mm Schneider Super-Angulon XL, and have a wide angle feel but at the longer focal lengths and the bigger image circles most of it is lost to the 6x9 format.


You're too tied up with image circle. Plus it seems you're still confused by what it means.

A 75mm lens with a small image circle provides the same view that one with a bigger one does. The problem with the smaller one is if the image circle is too small you'll get lousy corners. In the extreme you'll have a circular image.

Yes the greater image circle of a 4x5 or bigger lens won't be used on a 6x9 usually. But it still won't change the view. I use the same lenses on 4x5/5x7 and 8x10. The view changes because of the format not because of the change in the image circle. My 300mm is kind of tight for 8x10. A lens with a bigger image circle would let me use greater movements but then I can live with the limited image of my older Fuji 300mm.

What are you going to photograph? How much excess image circle you'll need will depend alot on what you intend to photograph. To a certain extent with wider lenses the camera matters to. You might find your camera doesn't allow much movements with very wide lenses.

Image circle is a trade off. I think we'd mostly like lenses with massive image circles that cost almost nothing and weighed less. But it's usually the other way. Lens with big image circles cost more and weigh more.

[Nick_3536]

But if I put my 300mm 6x7 lens on my 35mm camera it has a much different field of view than if I put my 300mm 35mm system lens on and in this case it's roughly equal to a 400mm lens. This is what I'm trying to figure out.


Something is wrong with this to. A 300mm lens on 35mm is always a 300mm lens. It's a longer view then a 300mm lens on a bigger camera but two 300mm lenses on a 35mm should be the same.

[Sheldon N]

Something is wrong with this to. A 300mm lens on 35mm is always a 300mm lens. It's a longer view then a 300mm lens on a bigger camera but two 300mm lenses on a 35mm should be the same.

I agree. Likely, differences in lens designs have resulted in slightly different actual focal lengths. They may both be marketed as 300mm lenses, when in actuality one is a 285mm and the other is a 310mm. If they were both truly 300mm lenses, then they would both show the same field of view.

[Dan Fromm]

Once again I want to thank everyone for their answers! <snip>

I understand lens and format equivalencies: a 100mm lens on my 67 system is equal to a 150mm lens on 4x5 or a 50mm lens in a 35mm system. Got it! I also know that the focal length stays what ever the manufacturer made it. But if I put my 300mm 6x7 lens on my 35mm camera it has a much different field of view than if I put my 300mm 35mm system lens on and in this case it's roughly equal to a 400mm lens. This is what I'm trying to figure out. <snip>


Chip Huh? I shoot 2x3 and 35 mm, use 35 mm for testing lenses longer than 100 mm or so that I intend to shoot on 2x3. Just hung several ~ 200 mm lenses made for 5x7 in front of a Nikon, took some shots with each to evaluate central sharpness. They give me the same image on 35 mm as my 200 MicroNikkor does. AFAIK I'm not hallucinating, and the images on film agree with this. Are you hallucinating?

In no way is a 100 mm lens anything but a 100 mm lens. Changing the size of the bit of film held behind the lens does nothing to the lens. It may change the size of the image captured, that's all. If you'll stop looking for focal length equivalences and start thinking in terms of angles of view given the format's diagonal, I think you'll be less confused.

Good luck, have fun,

[Oren Grad]

I think Dan's nailed the key issue. To summarize:

(1) The image circle determines how large a piece of film you can stick behind the lens and still have it be entirely covered by the projected image - or, conversely, how much room you have for perspective- or focus-correcting movement on a given film format. The larger the image circle compared to the diagonal of the film format, the more room you have for movement of the lens relative to the film while still covering the entire piece of film with a projected image.

(2) For a given focal length, the size of the film determines how wide a view you'll get in your picture. The larger the piece of film, the larger the chunk you'll capture of the image projected by the lens, and the wider the subject you'll be able to fit into the picture. So for example, if you had a 300mm lens with a very large image circle, putting an 11x14 piece of film behind it would give you a wide view, putting an 8x10 piece of film behind it would give you a normal view, putting a 4x5 piece of film behind it would give you a narrow view, and putting a 6x9cm piece of film behind it would give you a very narrow view.