Wide angle and film format

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nickthetasmaniac

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I was reading an article on the B&H blog talking about the Hassy SWC cameras, and stumbled across this comment re. the 38mm Biogon:

The beauty of the Superwide is its ability to capture wide-angle pictures that simply don’t look wide-angle. They’re wide-angle, but the Zeiss 38mm Biogon renders the spatial relationships between visual elements within the frame with less perceptual distortion than a comparable wide lens on a full-frame 35mm camera.

The article doesn’t elaborate...

So, what are they on about? Does film format affect how lenses with comparable field of view render ‘spatial relationships’ - and if so how/why? - or is B&H talking out their proverbial..?

I don’t have a great technical understanding of optics, but this doesn’t quite make sense to me...
 
I think that the obvious visual cues to “wide-angle-ness” are generally missing from the Biogon’s signature. I have seen plenty, and shot a few pics myself, from that camera that do not look “wide angle” at all.
It may have something to do with the square format.
 
Yep, just a low radial distortion lens. In the past it was harder to correct this distortion for wide lenses. But there are plenty modern 35mm examples with the same FoV (~20mm) that have minimal distortion nowadays.
 
I use the SWC for street and if I hold it perfectly level the results look like it came from a longer lens. While this is not a street shot where I would be 6 feet from the subject this is the only example I have on Flickr while my negs are out getting scanned. Does it look like it came out of a standard lens?
Varanasi by ray tai, on Flickr
 
The 38mm Biogon is a symmetrical type lens, which has lower distortion than retrofocus type lenses found on reflex cameras. Symmetrical-type wides are used on 35mm rangefinders or large format view cameras.
 
It's because the 38mm lens does not "pull" or exaggerate features as a rectilinear wide angle with the same angle of view does on 35mm. The "equivalent" is about 18mm on a 35mm camera, if I recall correctly. That is to say, you'll get the same composition with a 35mm camera using an 18mm lens and cropping the center 24x24mm section, as you would on the SWC. But the SWC has a lens which is twice the focal length of the 18mm and is getting close to a "normal".

You could do this same thing with a 135mm lens with the same angle of coverage, for example, projecting onto a 16.5 x 16.5 inch film plane. The 135mm will not distort at all and will actually compress the near/far relationship as long focus lenses do. But you still have the same relationship with regard to angle of view. If you took all three photos taken with their respective formats and printed them the same size, the one shot with the 18mm would have a lot of the pulling distortion towards the edges, the 38mm would look as it does with minimal distortion, and the 135 would have a wide field of view but would not distort at all.

EDIT: It is not just the fact that the 38mm Biogon is a symmetrical non-retrofocal lens. So is the 21mm Super Angulon, but it has more of the edge distortion (the "pulling" that can give us "banana heads") than the Biogon simply because the focal length is shorter.

Phil Forrest
 
Phil_F_NM said:
EDIT: It is not just the fact that the 38mm Biogon is a symmetrical non-retrofocal lens. So is the 21mm Super Angulon, but it has more of the edge distortion (the "pulling" that can give us "banana heads") than the Biogon simply because the focal length is shorter.

Phil Forrest
Click to expand...


I thought perspective distortion was only a function of angle of view + subject distance, not absolute focal length?
 
OlivierAOP said:
I thought perspective distortion was only a function of angle of view + subject distance, not absolute focal length?
Click to expand...

If this were so, we would see distortion when using long focal length lenses up close, but this is the opposite. A "normal" on a cell phone camera is about 7mm but those distort incredibly, giving people "noodle arms". Focal length is key and there is no way to get around it. If you view images printed the same size, across numerous focal lengths from 6 to whatever, you will see perspective distortion in the wider focal lengths starting below 35mm.

Phil Forrest
 
Phil_F_NM said:
If this were so, we would see distortion when using long focal length lenses up close, but this is the opposite. A "normal" on a cell phone camera is about 7mm but those distort incredibly, giving people "noodle arms". Focal length is key and there is no way to get around it. If you view images printed the same size, across numerous focal lengths from 6 to whatever, you will see perspective distortion in the wider focal lengths starting below 35mm.

Phil Forrest
Click to expand...


Here's a thought experiment. Hopefully I'm correct. Take an optical design, say a generic 50mm for 35mm format. Now scale the design by 1/2, you now have a 25mm lens sitting half the distance to a m43-sized sensor, but with the exact same optical properties, FOV, etc... Scale it by 2 and you have a 100mm lens for ~6x9. Sames images, no dependence on focal length.


Edit: I guess this only works for the focus plane image: the depth of field depends on the absolute entrance pupil size. But the perspective should be the same.
 
Yep perspective distortion depends only on the distance of the subject from the lens.

The radial distortion of this lens (-.5%) is about the same as newer type 35mm (FF) lenses of similar FoV .
 
Phil_F_NM said:
If this were so, we would see distortion when using long focal length lenses up close, but this is the opposite. A "normal" on a cell phone camera is about 7mm but those distort incredibly, giving people "noodle arms". Focal length is key and there is no way to get around it. If you view images printed the same size, across numerous focal lengths from 6 to whatever, you will see perspective distortion in the wider focal lengths starting below 35mm.

Phil Forrest
Click to expand...

You do see that same distortion exactly in spatial relationships if you get close enough. The thing is that by the time you get close enough, the greater magnification of a long lens will be concentrated on smaller details, so the overall effect may be less obvious. Heck, you can observe this with the naked eye: people’s faces get rounder and more dimensional when you’re close enough to hug or kiss them than when in handshake distance.

If you can get close enough with a 24, 25 or 28mm lens, the perspective distortion of a 135 format film or digital camera will be exactly the same as an equivalent cell phone. However, people frame pictures with cell phones differently because the lenses focus closer than equivalent 135 format lenses and composition is not restricted by having to look through a viewfinder.
 
My understanding of this is that the distortion is there, we just don’t see it because of the square format. When I use my 20mm lens on 35mm the distortion is at the margins of the frame, not in the center. If I cropped the frame to square - presto, no edge distortion as the edges are gone.
 
KenR said:
My understanding of this is that the distortion is there, we just don’t see it because of the square format. When I use my 20mm lens on 35mm the distortion is at the margins of the frame, not in the center. If I cropped the frame to square - presto, no edge distortion as the edges are gone.
Click to expand...

Hmmm, interesting perspective.
 
KenR said:
My understanding of this is that the distortion is there, we just don’t see it because of the square format. When I use my 20mm lens on 35mm the distortion is at the margins of the frame, not in the center. If I cropped the frame to square - presto, no edge distortion as the edges are gone.
Click to expand...

All lenses we use project a circle of light. Of all rectangular ratios, given the same area of picture, 1:1 takes most advantage of the area of a circle and wider ratios take the least advantage (require more cropping). A native square format will show a lens’s qualities more completely than a system with a native 3:2 ratio given the same area of image, if the lens designs are equal.

It also makes no sense to go out of your way engineer a wide angle lens and crop to the center, still wanting a wide angle result, at least for still photography purposes.*

*Lenses for reflex cinema camera systems on the other hand often project more area than their intended final picture to aid in framing. Even with SLRs, the expense and logistics of filmmaking makes it useful to be able to see outside the frame both to track the movement of actors and to make sure things such as boom microphones are out of view.
 
Thanks for the responses everyone, some very interesting thoughts (although I am no less baffled).

I understand that the 38mm Biogon is a very good wide angle, and may render differently to other less good wide angles. My question was specific to the implication that film size/format plays a role, not the quality of the individual lens.

So a hypothetical to remove some uncertainties...

- A 'perfect' 38mm rectalinear lens* on a 120 camera shooting 9x6 frames.
- A 'perfect' 20mm rectalinear lens* on a 135 camera shooting 3x2 frames.

*or whatever fl would give the exact same fov.

Disregarding depth of field, would these two lenses render spatial relationships between elements in an identical composition the same way?
 
Phil_F_NM said:
It's because the 38mm lens does not "pull" or exaggerate features as a rectilinear wide angle with the same angle of view does on 35mm. The "equivalent" is about 18mm on a 35mm camera, if I recall correctly. That is to say, you'll get the same composition with a 35mm camera using an 18mm lens and cropping the center 24x24mm section, as you would on the SWC. But the SWC has a lens which is twice the focal length of the 18mm and is getting close to a "normal".
Click to expand...

I'm afraid you've lost me here. Isn't the whole concept of a 'normal' lens format dependant? Ie. on M43 normal is ~25mm, on 135 it's ~50mm, on 120 it's ~80mm etc. etc.?

You could do this same thing with a 135mm lens with the same angle of coverage, for example, projecting onto a 16.5 x 16.5 inch film plane. The 135mm will not distort at all and will actually compress the near/far relationship as long focus lenses do. But you still have the same relationship with regard to angle of view. If you took all three photos taken with their respective formats and printed them the same size, the one shot with the 18mm would have a lot of the pulling distortion towards the edges, the 38mm would look as it does with minimal distortion, and the 135 would have a wide field of view but would not distort at all.

EDIT: It is not just the fact that the 38mm Biogon is a symmetrical non-retrofocal lens. So is the 21mm Super Angulon, but it has more of the edge distortion (the "pulling" that can give us "banana heads") than the Biogon simply because the focal length is shorter.

Phil Forrest
Click to expand...
 
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