Portrait perspective: Quiz and two questions

[Jerry Fusselman]

The old timers with their big Century Bi Centennial camera stands and their Century 9A cameras knew exactly what they were doing.

Jim, would you be willing to please expound on this a little as to format, focal length, and magnification?

[Jerry Fusselman]

Frank,

Thanks for responding! (And that goes for everyone, even those, unlike Frank, who insist that my questions are stupid and could not possibly benefit anyone.)

I bet if you could calculate the focal length of many famous paintings, they'd be wide enough to surprise you.

Hmm..., how would you go about calculating the focal length of a painting?

I also narrow most faced 5% or so in Photoshop because I am a fashion victim and don't want my faces looking fat.

I wonder what focal length we would calculate your images with the 5% Photoshop narrowing. The entire program you describe for calculating focal lengths for unreal images sounds almost hopelessly impossible to me, but I am willing to learn otherwise.

[Bob Younger]

For your math questions, go download a copy of VadeMecum. http://www.bobwheeler.com/photo/ .
It runs on a variety of small devices (handhelds) and has calculations for virtually every photographic requirement. Most of which you'll never use because few landscape or other photographs are actually made of flat planes; there always seems to be a tree or rock that intrudes and messes up the calculations.
But they are helpful in mentally envisioning what you're trying to do, and in defining the limits of what you can do. It's saved me from exposing film that would have been just wasted.

[Henry Ambrose]

Jerry,

Your original post began:

"I hope someone's answer to questions #1 and #2 in boldface below will help me to choose great perspective for portraits in 4x5 and 8x10. I want a careful answer that I can understand, so I introduce some math. The quiz is supposed to be a fun way to introduce my questions , and I think it can help us avoid the pointless arguments and inadequate rules of thumb that usually dominate this kind of subject."

Its the difference in magnification between the tip of the nose and the ears. (for instance) Get too close and the person looks strange - we're outside of our "normal view of the world". The nose being closer to the camera it is magnified more than things farther away. As we move away from the subject the difference between magnification of the parts of the subject (nose and ears in this example) lessens, as we move closer the "magnification ratio difference"(?) increases.

So if we get too close to a portrait subject we may get a "big nose" look because the nose is magnified more than the other parts of the object. Setting up the camera farther away "flattens" the look - decreases the difference in magnification between the parts of the subject.

Now if we want to "avoid pointless arguments" then its very simple that perspective is determined by:
1) where you stand
2) how far you set up the camera from the subject
3) the distance from the object being photographed to the film plane
4) object distance to the rear principal point of the lens

All being esentially the same location stated differently and in increasing levels of precision. Number 4 becomes difficult because the values change for different lens types and anyway are way beyond the precision needed for a portrait.

For that matter, precision higher than number 1 is probably not needed. If it were we'd all be using exactly the same focal length for portraits. We don't because we all know that effective portraits can be made lots of different ways, from varying distances. But still the one rule that stands is distance to the subject. Perspecitive is contolled only by how far we are from the subject. I think dressing it up past that point is needless. Unless it makes the 'light bulb" of realization come on over someone's head (but I can't see that labored complication does that - but it might for some).

[Henry Ambrose]

How about a formula that goes like this:

1) I want to be X inches from my subject
2) My film is X inches tall
3) I want the chin to top of head to be X inches tall on my film.
4) What focal length gives that result?

[Jim Galli]

Jim, would you be willing to please expound on this a little as to format, focal length, and magnification?

The big century stands and cameras are designed for 2 things that are extremely needful in LF 8X10 and larger portraiture. First, they are a sturdy platform for giant heavy lenses. When you get into 16" f3.8 lenses you get into very large very heavy glass. The Century (and others like Ansco) portrait cameras were simply a giant billboard size front standard with 9X9 lensboards. They facilitated lenses like 19" f4 Sigmar's (street car headlamps) with ease. The big front also made it easy to have BIG packard shutters inside with apertures large enough to facilitate a 19" f4. Then with bellows draws like 36" (necessary to get a bust with a 19" lens) the camera had the capacity for that, and by design it simply sits flat on a table platform. No tripods when you get into the big stuff.

9a Set up for a macro of indian rice grass with a 16" Beach Multifocal lens.


This is an 11X14 Bausch & Lomb Tessar Ic mounted in a universal aperture holder.

I've divided my portrait lens collection into groups. Portable and NON. The portable lenses like the 13" P&S can travel in the field and work well on a Kodak 2D. The giants like an 18" Hyperion f4 are confined to the 9a / Studio. The big 9a with it's stand makes using the giants easy though.

The big Universal Aerture lens holder with a packard behind becomes a versatile test stand for a host of lenses that find their way to Tonopah Nevada.

[Henry Ambrose]

Jerry wrote:
"Thanks for responding! (And that goes for everyone, even those, unlike Frank, who insist that my questions are stupid and could not possibly benefit anyone.)"

Just to be sure you know --- I don't think your questions are stupid.

I don't exactly understand "where you're coming from" but I sure don't think bad of you and I'm not here for an argument. I am trying to help.

[vijayn]

Finally a math problem on this otherwise dull and mundane forum (sarcasm alert) ... but no Jerry, your math is surely wrong - a 280 on 8x10 cannot equal 180 on 4x5 - for you see, 8x10 is exactly 2x of 4x5 in dimensions.

And coming from an engineer, your problem has simpler solutions if you solve for angles instead of linear dimensions. So ask yourself this: what angle of view gives you a portrait that you find most flattering; and what lens focal length will yield this angle of view on the format that you want to use. Simple trigonometry will work instead of lens equations.

And having done this exercise I can tell you that as you go up in format size, you have to live with larger angles of view for the same task. Obviously you cannot use an 1800mm lens (300/50 * 300; 300mm on 35mm is 300/50 = 6x the standard focal length which would be 6x of 300mm on 8x10, since 300mm is the standard focal length on 8x10), so the next question becomes what focal length is acceptable.

As for the math, we can take it offline if you want.

[Maris Rusis]

If there is no time for calculations an alternative approach is to put the camera lens at the distance you would be if you were relating to your portrait subject in a respectful, interested, and engaged way. Too close is no good. It invades personal space. Too far seems aloof and cool. When the distance feels right it is pretty sure to look right.

Different cultures have different personal spacings. For average "western" subjects 1.5 metres is a typical friendly (but not too friendly) distance for all cameras, lenses, and formats. If you want more coverage use a shorter lens: want tighter framing, go for a longer focal length but leave the distance the same.

[Jerry Fusselman]

Sorry, vijayn, I believe yours is a common mistake, and since you expressed yourself so clearly, it is easiest to address it here. You were right in all respects except one. Let me first try to summarize what I think you are saying with an example.

In brief, I think you are forgetting that back focus increases more than you expect when focusing closer than infinity and shifting to a larger format. This is just intuition, and my upcoming example is more careful.

Suppose we are shooting 4x5 with a 300 mm lens and we focus on a 15-inch tall subject in portrait orientation. This is a head-and-shoulders portrait, if you like. The magnification is 1/3 (5 inches of film/15 inches of subject), the subject-to-front-nodal-point distance is 1.2 meters, and the distance to the film plane is 400 mm (meaning we focus 100 mm out). All of these numbers make sense. You can either use the lens equation or set it up and measure it. Do whichever is easier for you.

I think you say two things now about shifting to a 600mm lens:

1. When you change to a 600mm lens, you get the same perspective as before provided the subject-to-front-nodal-point distance stays at 1.2 meters. I hope we agree that this is true!

2. You say that when you change to a 600mm lens and use 8x10 film at that distance, you get the same percentage of the face on the film as before. Or stated another way, if you switch to 600mm and keep the same perspective as before, the correct film for capturing the entire image is 8x10.

But I say it ain't so---#2 is wrong. To keep that 1.2 meter distance in focus with a 600mm lens, you know that you must move the distance from the lens (rear nodal point) to the film from 400 mm to 1200 mm, and the magnification becomes exactly 1. Because of that magnification, what you need to get the face framed as before is not 10 inches, but 15 inches of film.

Not convinced? OK, instead of going from 300 mm to 600 mm, go from 300 mm to 3000 mm. I.e., let us be more extreme. Imagine using 40x50 inch film to focus this image, but everyone knows that one cannot focus 1.2 meters away with a 3 meter lens. Now I hope you are convinced!

Of course, I have to agree with your logic in all respects when focusing at infinity.

This was all described without math. You can measure it. My key point is that doubling the focal length to match the perspective when moving from 4x5 to 8x10 makes sense only when focusing near infinity (with m near zero).

By the way, the correct answer for 8x10 with matching perspective is a 480 mm lens for a magnification of 2/3 and a back focus distance of 800 mm. Again, use either the lens equation or measure it, whichever is easier for you.

For those who did my problem 1 in the original post for this thread, a more-general answer is easy: If we like the perspective with a 300 mm lens with 4x5 film at magnification m, then the proper lens to match that perspective with 8x10 film is 300 x (2m+2)/(2m+1). In the case I gave, m = 1/3, which is why we get that a 480 mm lens matches the perspective.

Vijayn, you are right about doubling the focal length only when m = 0.

This analysis assumes that my answer to my question #1 is correct. It is so odd to me that nobody has yet answered my bold-faced question #1! However, I am becoming more and more confident in my guess, and here is why. Ignoring gravity and diffraction, light moves in straight lines in air. Because light moves in straight lines, moving the rear standard back has no effect on perspective at all, so it must be the front nodal point that determines perspective. Or if you do not like to think of nodal points, imagine a thin lens and say the the lens location relative to the subject determines the perspective. Imagine a standard ray diagram, which seems to bolster my position. Anyone disagree with this? Does anyone agree or disagree with my answer to original bold-faced question #1?