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Sheldon N
20-Mar-2014, 12:43
So I've just started shooting 8x10 and am discovering that portraits are now more like macro work with the amount of bellows extension involved!

One thing I've noticed is that my lens seems to "feel" a bit longer in focal length than I would have expected. I set up a shot a couple days ago and focused and the resulting field of view was narrower than I'd anticipated based on my experience with 35mm lenses. I'm shooting with a 12" (305mm) lens, which the field of view calculators say should be roughly like a 35mm lens on 35mm film (with the edges cropped off the 35mm frame to match aspect ratios). But when I set up the 8x10 shot, it felt more like I was shooting with a 50-60mm lens equivalent.

Does significantly extending the bellows into a macro territory alter the effective field of view of the lens? Or is this all in my head?

Bob Salomon
20-Mar-2014, 12:55
A 305mm on 810 is the same as a 45mm on 35mm. 45mm is a true normal on 35mm. A 360mm is equal to a 53mm on 35mm. If you are doing tight portraits with a 305 or 360 on 810 then that is really too short a lens. To get away from the foreshortening from a normal lens on 810 you would need a 500mm or so. That would have the look of an 88mm lens on 35mm.

But you also have the film's proportion involved here. 810 is a short squat format like 4x5. 35mm is a long, narrow proportion like 5x7 or 11 x 14. So that could also be part of the feeling that you are getting.

And you are not in macro territory if you are just doing a portrait. Unless you are shooting body parts like an eye, a nose or an ear only.

Sheldon N
20-Mar-2014, 13:04
A 305mm on 810 is the same as a 45mm on 35mm.

No, my original comments are correct. If you crop the edges of an image from a 35mm lens on 35mm film to share the same aspect ratio as 8x10, it's the same as a 300-305mm lens. Both have a roughly 37 degree vertical angle of view.


And you are not in macro territory if you are just doing a portrait. Unless you are shooting body parts like an eye, a nose or an ear only.

This is 8x10 film I'm shooting with. Just an eye would be ridiculous. A subject size of 8x10 inches (ie a medium tight headshot) is a 1:1 macro and would require 600mm of bellows from a 300mm lens. For my slightly looser portrait shot I had about 400-450mm of bellows extension with the 300mm lens. I had to put on the rear rail extension on my Kodak 2D to focus the shot. That's approaching macro territory for 8x10.

Sheldon N
20-Mar-2014, 13:20
As a side note, I just realized I can observe the phenomenon on the ground glass. If I point the camera out the window and look at the field of view on the ground glass while I add extension I can see the background get more magnified with a narrower field of view as it defocuses.

ic-racer
20-Mar-2014, 18:28
S
Does significantly extending the bellows into a macro territory alter the effective field of view of the lens? Or is this all in my head?

For certain. For example when you get to 1:1 your field of view is cut in half. For exampe the 300mm lens at 1:1 has the same angle of view on the film plane as a 600mm lens at infinity.

Ari
20-Mar-2014, 18:39
One thing I've noticed is that my lens seems to "feel" a bit longer in focal length than I would have expected.


If you crop the edges of an image from a 35mm lens on 35mm film to share the same aspect ratio as 8x10, it's the same as a 300-305mm lens.


These seem to be contradictory statements. The second statement leads me to think you no longer feel that the lens is too long, despite its normal-ish FL.
Mr Salomon was offering a reason why you might feel the lens to be longer than expected, and his math is bang-on.
8x10 has a diagonal of 312mm, so a 305mm lens would correspond very closely to a 45mm lens in tiny format.

Sheldon N
20-Mar-2014, 19:07
For certain. For example when you get to 1:1 your field of view is cut in half. For exampe the 300mm lens at 1:1 has the same angle of view on the film plane as a 600mm lens at infinity.

Awesome, that makes perfect sense! Thanks for the reply. That would mean that basically the lens has an effective angle of view based on the amount of bellows extension.


These seem to be contradictory statements. The second statement leads me to think you no longer feel that the lens is too long, despite its normal-ish FL.
Mr Salomon was offering a reason why you might feel the lens to be longer than expected, and his math is bang-on.
8x10 has a diagonal of 312mm, so a 305mm lens would correspond very closely to a 45mm lens in tiny format.

I guess I should have been more specific... it felt "long" when I'd set up a fairly close portrait with a decent amount of bellows extension. Out at infinity it behaves exactly as expected.

I have a really good natural sense of what that focal length would look like when shooting with an SLR, I can frame the shot in my mind's eye before pulling out the camera. So when I set up the shot with the 8x10 camera and focused, I was surprised to see how much narrower the field of view was than I was expecting.

Now I understand this was due to the bellows extension. With 8x10 the bellows extension comes into play much sooner than with smaller formats. I'd never really experienced this with 4x5 or smaller formats, and hadn't had it explained to me before.

ic-racer
20-Mar-2014, 19:10
Awesome, that makes perfect sense! Thanks for the reply. That would mean that basically the lens has an effective angle of view based on the amount of bellows extension.

The other neat optical property is that at 1:1 just about any 150mm lens made for a 4x5 camera not only covers 8x10 but also has the same angle of view on the film plane as a 300mm lens at infinity.

Sheldon N
20-Mar-2014, 19:31
That is very cool indeed.

Now does this principle apply to the finished image perspective as well? It seems like lots of people shoot 8x10 portraits with a near normal focal length and the images don't look nearly as distorted as one would expect.

ic-racer
22-Mar-2014, 09:20
finished image perspective as well?

That is only altered by change in subject to lens distance. Film format, aperture, focal length, etc have no direct effect (though they may cause you to alter your subject distance).

Dan Fromm
22-Mar-2014, 10:07
Folks, you have puzzled me considerably. I can't for the life of me see how changing extension changes the lens' angle of view. Surely it is set by (take your choice) mechanical vignetting if the coverage concept used is angle illuminated or off-axis aberrations if the coverage concept used is angle covered with acceptable image quality.

I understand very well how the circle covered with acceptable image quality changes with extension, but that has nothing to do with the angle covered, so please don't tell me about that.

Sheldon N
22-Mar-2014, 10:16
That is only altered by change in subject to lens distance. Film format, aperture, focal length, etc have no direct effect (though they may cause you to alter your subject distance).

Yes, that what I was expecting after thinking this through. Focusing for magnification/desired framing will narrow the effective field of view, which will alter where you need to place the camera to get your desired framing, which will in turn alter perspective.

Very different than what I'm used to from smaller formats. It's essentially like having a variable focal length lens which is dependent on how tight you frame the shot. With 8x10 I'm finding that there's a noticeable effect even at distances of 4 feet from lens to subject. At that distance I need to add ~100mm of additional extension, so my 300mm lens is acting more like a 400mm lens. I imagine the issue is even more significant with 11x14 portraiture.

Sheldon N
22-Mar-2014, 10:29
Folks, you have puzzled me considerably. I can't for the life of me see how changing extension changes the lens' angle of view. Surely it is set by (take your choice) mechanical vignetting if the coverage concept used is angle illuminated or off-axis aberrations if the coverage concept used is angle covered with acceptable image quality.

I understand very well how the circle covered with acceptable image quality changes with extension, but that has nothing to do with the angle covered, so please don't tell me about that.

Here's what I've been doing to wrap my head around it. I've got the camera set up looking out a window where I can see the distant horizon and trees, but I can also see reference points on the window itself (frame, trim, etc).

If I hold the lens in a fixed position and just add rear extension to focus closer, I can see field of view narrow on both the near window and the far horizon, though obviously the horizon is defocusing as this is happening. Lens and camera position haven't changed, but the angle of view that the film is seeing off the lens has.

If you imagine the lens projecting that infinity image all the way to the back wall of the room, covering the entire wall with the scene (ie camera obscura room), it would be a very large projection. Cutting out an 8x10 slice of that projection off the back wall would be a very narrow field of view (and additionally VERY defocused). So it makes sense that as you move the film away from the lens, you are capturing a smaller and smaller angular view of the scene while at the same time moving the plane of focus closer to the lens.

Normally in macro photography there isn't foreground and background to consider, but with 8x10 you start to enter the realm of macro photography for normal portraits, and you can still shoot a shot that shows the scene/background.

ic-racer indicated that by the time you have doubled extension to get to 1:1, you've halved the field of view. That seems right to me based on what I'm experiencing with my little window tests, and also makes logical sense. So assuming you're using a normal/300mm lens, 600mm of extension gives you the field of view of a 600mm lens and 300mm of extension gives you the "correct" field of view of the 300mm lens shooting at infinity. I'm inferring that the relationship is linear, so roughly whatever your amount of bellows extension is, that's roughly the field of view you're getting (as though you had that focal length at infinity).

I'd never expected this issue when I got an 8x10 camera, but it's certainly an interesting phenomenon.

ic-racer
22-Mar-2014, 11:22
Folks, you have puzzled me considerably.

OP wants to discuss "effective angle of view" which is the angle of view on film; the portion of the image circle cropped by the film holder edges.

This is a screenshot from a spreadsheet I made a while back. The spreadsheet calculates the angle of view for focused images on film, taking into account the three factors that affect the angle of view on the film: subject distance, film holder opening size and lens focal length.
112594

Dan Fromm
22-Mar-2014, 11:23
Sheldon, I still don't get it. A cone of light enters the lens at the front, exits it at the rear. The positions of the film plane and plane of best focus don't change the cone's shape.

When you focus closer you increase the magnification. The amount of distant and now out-of-focus distant horizon that fits on the GG or film decreases. What the lens sees doesn't change.

ic-racer
22-Mar-2014, 11:46
When you focus closer you increase the magnification.

Exactly, and as you cut off the edges of your view, the angle of view decreases. Think of it this way, "extra" image circle and room for movements one gets at close magnification has to come from somewhere. Either the angle of view of the lens increases (of course not) or the angle of view on the film plane decreases (yes).

John Koehrer
22-Mar-2014, 20:03
It seems that a "moderately tight" head shot isn't going to be done at 1:1. That's very tight, pretty much the same as your ~50mm lens with 50mm extension. 1:1, that's one eye.
As Mr Solomon says a longer lens/greater camera/subject distance is needed.

Following on with Dan Fromm's comment. The angle of view of the LENS does not change it cannot unless you physically change the lens formula, it's constant But the APPARENT angle of view changes as magnification changes.

ic-racer
23-Mar-2014, 09:51
For clarification to anyone finding this thread, these three terms have been used to represent the same thing:

Original Post: "Effective Field of View"
ic-racer: " Angle of View on Film Plane"
JK: "APPARENT angle of view"

Also, note below:

"ANGLE OF FIELD OR OF VIEW"
"The angle subtended by two lines drawn from the node of emergence of any lens to the corners of the film in use. As a general rule, when the angle of field of a lens is referred to, the extreme angle which the lens is capable of covering is meant, and it should be clearly stated in all cases whether this angle is measured along the longest side of the pate or diagonally from the opposite corners. "
Encyclopedia of Photography

Dan Fromm
23-Mar-2014, 10:00
Right, ic, and defined that way it is invariant with respect to magnification.

Sheldon N
23-Mar-2014, 12:26
"ANGLE OF FIELD OR OF VIEW"
"The angle subtended by two lines drawn from the node of emergence of any lens to the corners of the film in use. As a general rule, when the angle of field of a lens is referred to, the extreme angle which the lens is capable of covering is meant, and it should be clearly stated in all cases whether this angle is measured along the longest side of the pate or diagonally from the opposite corners. "
Encyclopedia of Photography

Right, ic, and defined that way it is invariant with respect to magnification.

No, the definition above speaks to the angle to the corners of the film in use. That would not be invariant with respect to magnification. The angle of field/angle of coverage of the lens would remain invariant, but the angle of view is dependent on both the film size in use and the magnification.

Definitions aside, the main point of the thread is that lenses behave like "longer" focal lengths as you focus more closely. Which is why you see many people making pleasing portraits with 300mm or 360mm lenses on 8x10, despite the fact that these would seem to be close to the normal focal length for the format.

Dan Fromm
23-Mar-2014, 12:56
Sheldon, in the plane of best focus it is invariant. What's behind the plane of best focus doesn't count. Well, of course it does, but the angle subtended by rays going from the corners of the film in use to the corners of the subject in the plane of best focus is the same for all magnifications.

At this point we're quibbling about semantics. You've been very clear about what you see and what you mean. Thanks very much for that.

mdarnton
23-Mar-2014, 13:14
Dan, you're insisting on thinking of this as a lens issue, not a film thing. The farther a lens is from the film, the smaller the angle of what the film sees, that's all. As you move the lens away, the film sees a narrower angle of the outside world. You're thinking too hard here.

Dan Fromm
23-Mar-2014, 14:32
I'm thinking in terms of subject plane and image plane.

Sheldon N
23-Mar-2014, 15:41
Sheldon, in the plane of best focus it is invariant. What's behind the plane of best focus doesn't count. Well, of course it does, but the angle subtended by rays going from the corners of the film in use to the corners of the subject in the plane of best focus is the same for all magnifications.


Ah, but that's not the case. There can only be one angle of view of the world that the ground glass sees, whether that's near or far or in focus or out of focus, the angle is the angle. Ignore optics and just imagine straight lines coming from the corners of the ground glass, through the center of your aperture, out to your subject. Move the ground glass away from the lens, and the angle of those imaginary lines toward the corners of your subject is going to tighten up.

The implication is that as you increase magnification/bellows extension you are going to have to reposition the camera farther away from your subject than you would expect in order to properly frame the image. It's just as if your lens becomes a longer focal lens as your focus closer.

Dan Fromm
23-Mar-2014, 18:15
Sheldon, when you focus closer than infinity both conjugates move.

Sheldon N
23-Mar-2014, 19:41
Sheldon, when you focus closer than infinity both conjugates move.

I'm not particularly good at math, so excuse me if I'm not following... Can you clarify?


I guess my whole premise of this thread was me beginning to understand a couple things...

1) With 8x10, I can't just shoot like I did with 35mm and assume that my lens is going to give me a constant field of view. I took this portrait of my daughter (http://tinyurl.com/n7pkvg2) positioning her and the camera picturing a "normal" focal length field of view. However when I focused the field of view was a lot narrower than I previsualized. That interaction of focus distance and effective focal length was entirely new to me.

2) The whole idea that you need to use a longer lens to shoot a tighter portrait to get a pleasing perspective isn't necessarily true with big formats. I've seen this common wisdom espoused many, many times (ie Bob Salomon's off the cuff response early in this thread). But with bigger formats by the time you've focused close enough to shoot a tight portrait your short focal length lens is now giving you the angle of view and resulting subject distance of a much longer lens. That's not to say that longer lenses won't give a greater subject distance and improved perspective, but it explains why not many people are shooting 8x10 portraits with the theoretical equivalent of an 85mm lens (600mm).

jb7
24-Mar-2014, 07:37
... It's essentially like having a variable focal length lens which is dependent on how tight you frame the shot. ...

That's it. I call it Focus Zoom. A distinctly large format phenomenon which might be difficult to get a grip on if you're only used to smaller formats...