Lens/Optics Question for 8x10

bvy · Dec 15, 2015

I have a 12 inch lens on an 8x10 camera. Now I extend the bellows to 18 inches, to focus on an object closer to the camera. The background is now out of focus, but is the angle of view of the (out of focus) background (at infinity) the same as I would see on an 18 inch lens focused at infinity? I think it is.

Here's where I'm a bit confused. I'm using my 12" lens to make a portrait of a person right in front of my camera. To focus, I have to extend the bellows to 18" as described. Looking at 35mm equivalents, a 12" lens on 8x10 is roughly equivalent to 45mm; 18" to 65mm. Is the resulting portrait going to have the look ("compression") of a 45mm lens or 65mm lens equivalent?

I think it's the latter. But intuition tells me that the closer I put my lens to the subject, the more unnatural it's going to look with widened features. I can bring the person closer and focus longer... Clearly I'm missing something.

Dan Fromm · Dec 15, 2015

I must be missing something. You have the lens. You have the camera. You have a sitter. You can look at the camera's ground glass, in fact you have to do that to focus. What you see on the GG is that you'll get. Why don't you have the answers to your questions?

bvy · Dec 15, 2015

You're not missing anything. I have questions and I asked them. The goal is to better understand the science behind all of this in order to make more informed decisions when evaluating lenses or cameras.

RobC · Dec 15, 2015

I think you need to stop trying to equate an 8x10 to a 35mm format. They are completely different aspect ratios so there is no direct equivalent.

I suspect what you are getting at is what lens do you need to give a similar head shot at the same distance. Well the ball park answer to that is that a standard lens on 8x10 is 300mm (12 inches approx). For a head and shoulders shot on 135 format you would use maybe an 85mm lens which is 35mm longer than the standard 50mm lens on 135 format. And that is 70% longer than standard. So on your 8x10 camera with 300mm lens, 70% longer would be a 510mm lens as a ballpark head and shoulders shot lens. But it ain't really that good a way of estimating which lens is a good lens for head and shoulders shot because the aspect ratio is different. So it wil be somewhere between about 400 and 550 depending on how you like it. The 300mm lens should be good for full length portrait (head to toes). Again all ballpark becasue it depends how far from subject you want to be.

gzinsel · Dec 15, 2015

LF, . . . . . strike that!, LF photography is NOT 35mm photography, nor can they BE COMPARED !. I don't even know where to begin. Your last sentence is the OP. suggests your lens distorts at close range???? you claim "the more unnatural it's going to look with widened features" THEN USE AN APO LENS. OR A PROCESS LENS!!!!! if you are going to photograph something close to 1:1 then use an APO lens that has been optimized for 1:1

John Koehrer · Dec 15, 2015

At 18"/~450mm you should be about 1/2 life size and will get some foreshortening/exaggeration of your subjects features.

Also you're not going to get the same coverage of the background because the extension is like a telephoto and gives only the center part of the image formed at 300mm. IE: you lose the edges, they're outside the film area being exposed..

Formats don't equate exactly because of the ratios of negative format.
Technically these not exact, but close enough.

Measuring ONLY horizontal coverage, the 300/12" @ infinity covers ~73 degrees for 8X10
" " " " " ~ 65 @ " " ~65 covers just less than 31 degrees.

Lou Baleur · Dec 15, 2015

Good lord. Why all the fuss about asking valid questions that I have asked myself in the past.

You are correct. Any lens at 18" bellows draw has the angle of view as an 18" lens focused at infinity. This is proven by geometric projection.

You are also correct that foreshortening will increase as the lens gets closer to the subject. If you want the subject to look natural, you must think of how far the print will be viewed from. If you will be viewing the final print from 5 feet away, then the lens should be positioned 5 feet from the subject.

If you intend to view very close, say 12", and viewed with one eye, then the lens should be 12" from the subject and it will look natural. Note that nobody really ever views a person's face from 12". Usually faces are viewed from at least three feet away. Since you view a person mostly at farther distances, you will need a shooting distance equal to these farther distances, at least three feet and usually five to ten feet for people you are not intimately aquainted with. Strangers are always remembered when viewed from the distance you see them at--strangers keep their distance.

There are other things going on, however. Sometimes you want to have intentional foreshortening in someone's face which is very flat--shoot that face up closer and it will round it out. Similarly, a pointy face will be flattened out when shot from farther away. The correct distance depends on the person's face and the photographer's taste as to what he or she thinks is attractive. Each person has an angle and a distance where they look best.

Dan Fromm · Dec 15, 2015

Lou Baleur said:
You are correct. Any lens at 18" bellows draw has the angle of view as an 18" lens focused at infinity. This is proven by geometric projection.

Are you sure? I ask for two reasons. Not all 18" lenses have the same coverage, so there's no such thing as the angle of view of an 18" lens focused at infinity. Secondly, if I understand what I've taken advantage of in closeup work, it is the circle covered. not angular coverage, that grows as magnification increases. I could be confused.

OP, testing will get you better answers more quickly than applying half-baked or poorly understood models. FWIW, I'm an obsessive calculator but I don't use calculations to assess lenses or cameras. When I want to assess equipment I test it. I calculate what a lens can and can't give -- coverage, resolution where it matters -- and what I have to do to use a lens -- generally extension given desired magnification -- when deciding which gear won't do.

Cheers,

Dan

ic-racer · Dec 15, 2015

Yes, in terms of simple lenses, as you focus closer, the angle of view on the film decreases. There are certain cine lenses that are designed to minimize these effects. For example, not all lenses focus by moving the center of the lens with respect to the film plane and it is possible to make a lens that zooms as it focuses to keep the angle of view constant.

Dan Fromm · Dec 15, 2015

ic-racer said:
Yes, in terms of simple lenses, as you focus closer, the angle of view on the film decreases. There are certain cine lenses that are designed to minimize these effects. For example, not all lenses focus by moving the center of the lens with respect to the film plane and it is possible to make a lens that zooms as it focuses to keep the angle of view constant.

Absolutely, because magnification increases on focusing closer.

But this is not equivalent to "Any lens at 18" bellows draw has the angle of view as an 18" lens focused at infinity" because not all lenses have the same angular coverage. Consider a 500 mm lens that covers 24x36 and another that covers, at least 8x10. At infinity, the lens that covers 24x36 will put a small (not much larger than 43 mm) circle of good image on 8x10 film. The lens that covers at least 8x10 will fill 8x10. Now do you see the difference?

Oh, yeah, I switched the example focal length from 18" to 20" because I couldn't think of an 18" lens for 24x36 but can think of many 20 inchers for that format.

Ian Grant · Dec 15, 2015

Lou Baleur said:
Good lord. Why all the fuss about asking valid questions that I have asked myself in the past.

You are correct. Any lens at 18" bellows draw has the angle of view as an 18" lens focused at infinity. This is proven by geometric projection.

You are also correct that foreshortening will increase as the lens gets closer to the subject. If you want the subject to look natural, you must think of how far the print will be viewed from. If you will be viewing the final print from 5 feet away, then the lens should be positioned 5 feet from the subject.

If you intend to view very close, say 12", and viewed with one eye, then the lens should be 12" from the subject and it will look natural. Note that nobody really ever views a person's face from 12". Usually faces are viewed from at least three feet away. Since you view a person mostly at farther distances, you will need a shooting distance equal to these farther distances, at least three feet and usually five to ten feet for people you are not intimately aquainted with. Strangers are always remembered when viewed from the distance you see them at--strangers keep their distance.

There are other things going on, however. Sometimes you want to have intentional foreshortening in someone's face which is very flat--shoot that face up closer and it will round it out. Similarly, a pointy face will be flattened out when shot from farther away. The correct distance depends on the person's face and the photographer's taste as to what he or she thinks is attractive. Each person has an angle and a distance where they look best.

That's what it's lke here these days.

The OP is right that the field of coverage improves at close distances so a lens that doesn't remotely cover 10x8 at infinity may cover well ay 1:2 or 1:1

Personally I'd put one poster in this thread on ignore as he constantly posts absolute rubbish.

Ian

MattKing · Dec 15, 2015

In a perfect world, you would have a variety of lenses available to you. That would permit you to first choose a working distance that results in a flattering perspective, and then a lens that fills the film with your desired field of view when working at that distance.

If you are trying to determine what change in focal length you need, bellows draw calculations won't always help you with the calculation. Things like lens designs, including telephoto designs, will get in the way.

bvy · Dec 15, 2015

Thanks everyone. In spite of some of the lively responses, I'm not sorry I asked! My using 35mm equivalents was just to quantify the idea of perspective in what I thought were mutually understandable terms. For example, a tight head and shoulder shot taken with a 40mm lens on a 35mm camera, will (typically) look less flattering than one taken with an 80mm lens. Focus doesn't upset the equation like it does with 8x10.

Yes, I can use my eyes and decide what looks good for a particular person or model. I do that.

My 8x10 camera has a maximum bellows draw of about 24 to 26". Given that, I'm trying to decide if I can improve on my 12" lens for portraits. I want a tight head and shoulder shot, but I also don't want the rail of my camera poking my subject in the neck. If the answer is that 24" isn't long enough, then I'm looking for that "sweet spot." I just need to work it out on paper now.

Dr Croubie · Dec 15, 2015

bvy said:
My using 35mm equivalents was just to quantify the idea of perspective in what I thought were mutually understandable terms.

It's perfectly understandable to try to equate it with what you know, and it works at infinity very well. But as pointed out above, things get weird when you get closer to macro distances.
A head+shoulders frame is what, almost 8x10, maybe 10x16"? That's a 1:1 or 1:2 macro range on 8x10".
Cover that with a 1x1.5" 35mm frame instead and you're around 1:10 or worse, that's not even going to be called "macro" by Sigma's marketing department. At those ratios, things behave a lot more like they do at infinity and you probably won't even notice the difference in a regular portrait.

Dan Fromm said:
But this is not equivalent to "Any lens at 18" bellows draw has the angle of view as an 18" lens focused at infinity" because not all lenses have the same angular coverage.

I think the original point that was trying to get across missed the disclaimer of "as long as it covers the format".
My 90mm Angulon will cover 4x5" (just), so will my 90mm Super Angulon, so will my 90mm Fujinon SWD. Take a picture with all 3 of them on 4x5" and they'll have the same angle of view on the film.
The SWD will be a buttload sharper, get more coverage, shift, tilt, etc, but with all 3 perfectly centered they'll all look near enough the same (within tolerances and focal-length rounding, of course).
On 5x7" they'll look different, of course, because the Angulon won't cover it, but on 4x5" they're the same as each other, and 6x9 they're the same as each other, etc...

RobC · Dec 15, 2015

bvy said:
Thanks everyone. In spite of some of the lively responses, I'm not sorry I asked! My using 35mm equivalents was just to quantify the idea of perspective in what I thought were mutually understandable terms. For example, a tight head and shoulder shot taken with a 40mm lens on a 35mm camera, will (typically) look less flattering than one taken with an 80mm lens. Focus doesn't upset the equation like it does with 8x10.

Yes, I can use my eyes and decide what looks good for a particular person or model. I do that.

My 8x10 camera has a maximum bellows draw of about 24 to 26". Given that, I'm trying to decide if I can improve on my 12" lens for portraits. I want a tight head and shoulder shot, but I also don't want the rail of my camera poking my subject in the neck. If the answer is that 24" isn't long enough, then I'm looking for that "sweet spot." I just need to work it out on paper now.

get this predesigner software which is free and it will save you a lot of calculating

http://www.winlens.de/index.php?id=70

note: there is a bug in the software. When you start it, maximise the window and keep it that way which avoids the bug.

Dan Fromm · Dec 15, 2015

Hmm. OP, there's a magic formula that will make things a little easier for you. Extension needed, given magification and lens' focal length, is focal length * (magnification + 1). A half live-size head and shoulders shot has magnification = .5, and so on.

bvy · Dec 15, 2015

Dan Fromm said:
Hmm. OP, there's a magic formula that will make things a little easier for you. Extension needed, given magification and lens' focal length, is focal length * (magnification + 1). A half live-size head and shoulders shot has magnification = .5, and so on.

Your timing is perfect. I was just in the process of deriving this myself. Thanks.

bvy · Dec 15, 2015

From this, I've derived the following relationship:

d = F(m+1) / m

where d is the subject distance (from the lens), m is the magnification, and F is the focal length of the lens. The numerator, F(m + 1), gives the bellows extension.

Maybe there's a more succinct or intuitive way to state it.

Dan Fromm · Dec 16, 2015

bvy said:
From this, I've derived the following relationship:

d = F(m+1) / m

where d is the subject distance (from the lens), m is the magnification, and F is the focal length of the lens. The numerator, F(m + 1), gives the bellows extension.

Maybe there's a more succinct or intuitive way to state it.

Correct.

RobC · Dec 16, 2015

You should realise that witha 300mm lens you will get 0.5X manginfication with the bellows at 450mm extension. Subject will be at 900mm from lens board.

Now you need to start thinking what that means in terms of being able to light the face without the camera casting a shadow at that distance and how the subject will feel about having a 300mm lens stuffed up their nostrils.

Now start paying attention to using a lens 70% longer than standard 300mm.

Dr Croubie · Dec 16, 2015

RobC said:
You should realise that witha 300mm lens you will get 0.5X manginfication with the bellows at 450mm extension. Subject will be at 900mm from lens board.

Now you need to start thinking what that means in terms of being able to light the face without the camera casting a shadow at that distance and how the subject will feel about having a 300mm lens stuffed up their nostrils.

Now start paying attention to using a lens 70% longer than standard 300mm.

Probably depends on where your light is coming from, but yeah, 90cm ain't much.

I've also read of LF portrait photographers going for shorter rather than longer lenses on purpose, so that they're a) closer to their subject and can get more of a conversation going to make them feel more comfortable (nothing worse than a portrait of someone looking bored and/or tense), and b) if it's too long a lens it just won't fit in the studio.
There's a happy medium in there somewhere usually.

I don't shoot many portraits, and haven't done one on my 8x10 (yet). But I'm covered if/when I want to, I've got a 300/500mm convertible Symmar, and a 12"/24"/28" convertible Gundlach.
I'd suggest to the OP to also consider playing around with focal lengths to find the happy medium between "not up their nostrils" and "still fits in the studio".
Older convertible lenses are great for determining the focal length you want, plus they're generally a lot cheaper than newer fixed lenses (and rare specialist portrait lenses that cost more than a used car).

ic-racer · Dec 17, 2015

Well if one wants to distance themselves from "the taking of pictures" and remove "film frame" from the discussion, one can describe behavior of projected circular images by indicating the image and the circle get bigger as one focuses closer.

RobC · Dec 17, 2015

A tight head and shoulders shot of approx 500cm in subject height gives that 0.5X magnification at with subject 900cm from lensboard and a 300mm lens.

With a 510mm lens the distance becomes 1530mm from lensboard which is more workable. i.e. the 70% increase in focal length from standard 300mm is about right providing a more comfortable working distance of 4 to 5 ft. Lens extension would be 765mm.

But its down to the photographer to decide what they want and what the limitations of therir lens and camera rail are.

The software I pointed you at provides all this information very quickly without having to do reams of calculations.

[edit]
I just saw you posted max extension as 26in.

If you want frame a little looser then I think the 510 lens will be fine but no longer. Maybe a 450mm lens would let you frame a little tighter given your limited extension.

bvy · Dec 17, 2015

As far as my limitation, I have the rail, but not the bellows. The bellows is maxed out at 24 to 26 inches. The rail is 36 inches.

I should add that I'm already doing head and shoulder portraits (not tight) with a 300mm lens. Looking around, a lot of people are. I don't think it's hopeless, as long as one accepts the close perspective (possibly more unflattering on some subjects than others) and that there will be limitations -- like keeping all features in the plane of focus so they won't appear disproportionally small or large -- or, of course, out of focus. The image below was taken with the subject somewhere between three and four feet in front of the camera (probably on the near side).

Given my parameters, a 16" lens will put my subject about a foot further back without any loss of magnification. It's not the six feet that I want, but it's closer. Finding a 16" lens is another story.

jimgalli · Jan 12, 2016

Some seat of the pants from someone already down this road. My extension is 30". Once you pass 15" (lens fl) or so, you're in the land of diminishing returns. With an 18" lens you'll never get a full head with 26" extension, and so on. There's more to the seat of the pants thing. Most of us want a fast lens wide_ish open for portraits. At least f4.5. Once you've passed 15", the glass is getting so big the field cameras can't hold it up.

It's fun to get a copy of Professional Portrait Lightings by Charles Abel and turn the clock back to 1947 when all of this stuff was common as dirt, and read what those old boys were doing. 15 - 16" lenses were king. Most of them had the big Century Studio cameras though, which had a good 36" bellow draw.

It's fun to re-invent the wheel, but . . . probably smarter to see what the really smart guys were doing when they had to depend on this stuff to make a living.

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