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Four thirds, telephoto lenses and perspective compression. (question)

cjlacz

Member
This may be a silly question, I'm probably over thinking it.

I know a telephoto lens compresses the perspective. The longer the telephoto the more the effect. At least on the DPreview forums people keep saying 150mm is 150mm and it's just a crop to get a 300mm angle of view. Would that mean a picture taken with the 150mm on a Olympus would have a view then a 300mm lens on something like a D700? The full frame camera compressing the perspective more then the Olympus? Ignoring DoF field differences etc.

Thanks,
Charles
 

jlm

Workshop Member
i believe the telephoto compression effect is simply a function of distance to subject. as you get farther away, the image will get smaller, so one uses more magnification, either by a longer fl lens or cropping a smaller portion of the image and enlarging, or both
 

Robert Campbell

Well-known member
Perspective depends solely on camera position. A telephoto lens magnifies -- it doesn't actually compress the perspective, rather it brings far away things 'closer'.

Using a telephoto won't alter the perspective, only the angle of view -- how much of the scene is recorded on the sensor.

A smaller sensor records less image than a big sensor for the same focal length of lens.

From the same camera position, an Olympus 4/3 sensor and a 150mm lens will record the same scene as a 'full frame' camera with a 300 mm lens [of course the sensors are slightly different shapes].

Try taking a pic with a wide angle and a telephoto lens, and magnifying the centre of the wide angle pic; the perspective will be the same in both.

Theoretically, all you need is a wide angle but rectilinear lens -- you can get the effect of a telephoto lens by magnifying a small area -- but, of course, the quality of the resulting pic is poor.
 

cjlacz

Member
Thanks to both of you for your explanations. I was just over thinking the problem and what you said makes sense. Thanks!
 
I

indorock

Guest
Perspective depends solely on camera position. A telephoto lens magnifies -- it doesn't actually compress the perspective, rather it brings far away things 'closer'.

Using a telephoto won't alter the perspective, only the angle of view -- how much of the scene is recorded on the sensor.

A smaller sensor records less image than a big sensor for the same focal length of lens.

From the same camera position, an Olympus 4/3 sensor and a 150mm lens will record the same scene as a 'full frame' camera with a 300 mm lens [of course the sensors are slightly different shapes].

Try taking a pic with a wide angle and a telephoto lens, and magnifying the centre of the wide angle pic; the perspective will be the same in both.

Theoretically, all you need is a wide angle but rectilinear lens -- you can get the effect of a telephoto lens by magnifying a small area -- but, of course, the quality of the resulting pic is poor.
Patently and totally incorrect. It's funny how the internet is full of opinions without supporting evidence, haphazardly stated as "facts".

17mm (cropped): http://media.offcentric.com/17mm.jpg
200mm: http://media.offcentric.com/200mm.jpg

Setup: closest object placed at about 170cm from the camera, furthest object 4 meters.

The difference isn't huge, but it's there. And it's not huge because my apartment isn't big enough for a bigger setup. I'd say to anyone in doubt, take your 2 lenses (or one zoom lens) outside, and try it for yourself. Flower in the foreground, mountain in the background for instance.

Furthermore anyone in filmmaking will be quite aware of the "dolly in, zoom out" or conversely "dolly out, zoom in" techniques, used for example in many Alfred Hitchcock films. You can clearly and plainly see there what effect focal length has on perspective.
 
V

Vivek

Guest
Patently and totally incorrect. It's funny how the internet is full of opinions without supporting evidence, haphazardly stated as "facts".

17mm (cropped): http://media.offcentric.com/17mm.jpg
200mm: http://media.offcentric.com/200mm.jpg

Setup: closest object placed at about 170cm from the camera, furthest object 4 meters.

The difference isn't huge, but it's there. And it's not huge because my apartment isn't big enough for a bigger setup. I'd say to anyone in doubt, take your 2 lenses (or one zoom lens) outside, and try it for yourself. Flower in the foreground, mountain in the background for instance.

Furthermore anyone in filmmaking will be quite aware of the "dolly in, zoom out" or conversely "dolly out, zoom in" techniques, used for example in many Alfred Hitchcock films. You can clearly and plainly see there what effect focal length has on perspective.
Indorock, Strong words with fuzz supporting :)confused:) your statements?
 

ggibson

Well-known member
Furthermore anyone in filmmaking will be quite aware of the "dolly in, zoom out" or conversely "dolly out, zoom in" techniques, used for example in many Alfred Hitchcock films. You can clearly and plainly see there what effect focal length has on perspective.
I'm still wrapping my mind around the concept as well, but indorock is right. Take a look at this video:

http://www.youtube.com/watch?v=Y48R6-iIYHs

A crop of 300mm =/= 150mm non-cropped.
 

s.agar

Member
+1

Patently and totally incorrect. It's funny how the internet is full of opinions without supporting evidence, haphazardly stated as "facts".

17mm (cropped): http://media.offcentric.com/17mm.jpg
200mm: http://media.offcentric.com/200mm.jpg

Setup: closest object placed at about 170cm from the camera, furthest object 4 meters.

The difference isn't huge, but it's there. And it's not huge because my apartment isn't big enough for a bigger setup. I'd say to anyone in doubt, take your 2 lenses (or one zoom lens) outside, and try it for yourself. Flower in the foreground, mountain in the background for instance.

Furthermore anyone in filmmaking will be quite aware of the "dolly in, zoom out" or conversely "dolly out, zoom in" techniques, used for example in many Alfred Hitchcock films. You can clearly and plainly see there what effect focal length has on perspective.
 

laptoprob

New member
The key difference is object distance. That makes every comparison relative. So at the same distance, a telephoto lens does compress the perspective. But a crop factor is just that, a crop factor. Doesn't change perspective characteristics.
My 25mm lens will always give wideangle perspective, only cropped to 50mm equivalent.
 
V

Vivek

Guest
My 25mm lens will always give wideangle perspective, only cropped to 50mm equivalent.

Hmmm..that is incorrect.

The key is magnification and that is what Robert said and there are others supporting a wrong notion.
 

pellicle

New member
Hi Cj

[side steps arguments]

firstly I find that the DoF that I get on the telephoto is slightly deeper than if I was using the same "equivalent" on a 35mm. I mean that a 200mm more or less has the same angle of view as a 400mm on a 35mm camera. But when I use the 200 on the G1 I get better DoF at f4 than if I was using a 400 on a 35mm or full frame.

Some samples of a FD200 f4

sorto of close


mid distance



far distance



as to compression of field ... well ... that's a function of telephoto anyway :)
 

brianc1959

New member
Patently and totally incorrect. It's funny how the internet is full of opinions without supporting evidence, haphazardly stated as "facts".

17mm (cropped): http://media.offcentric.com/17mm.jpg
200mm: http://media.offcentric.com/200mm.jpg

Setup: closest object placed at about 170cm from the camera, furthest object 4 meters.

The difference isn't huge, but it's there. And it's not huge because my apartment isn't big enough for a bigger setup. I'd say to anyone in doubt, take your 2 lenses (or one zoom lens) outside, and try it for yourself. Flower in the foreground, mountain in the background for instance.

Furthermore anyone in filmmaking will be quite aware of the "dolly in, zoom out" or conversely "dolly out, zoom in" techniques, used for example in many Alfred Hitchcock films. You can clearly and plainly see there what effect focal length has on perspective.
Perspective is determined by the position of the center of perspective of the lens. This is also known as the entrance pupil. Unless you have taken care to make sure the location of the entrance pupil for your 17mm and 200mm lenses is exactly the same relative to your two objects then your experiment is invalid. Hint: If you simply kept the camera fixed and switched lenses then you've made a mistake!
 
V

Vivek

Guest
Brian, Very happy to see you here! :)

[For those who do not know: Dr.Brian Caldwell is a professional lens designer.]
 

pellicle

New member
Hello Brian

Unless you have taken care to make sure the location of the entrance pupil for your 17mm and 200mm lenses is exactly the same relative to your two objects then your experiment is invalid.
not knowing enough to know why (but keen to be pointed at readings) are we talking about being out by much or just a little?
 

sangio

New member
Hi all:

What Robert, Brian and others have said can be very easily verified by putting a zoom lens on a camera, attaching said camera to a tripod and zooming in and out. The magnification changes with focal length, but the perspective (i.e. the relationship between near and far objects) does not change.

I just took a couple of test shots with my old Sony R1 since it has a greater zoom range, 5X, than my Panasonic kit zoom.

The first image was taken at 120 mm equiv and simply downsized for posting.
The second image was taken at 24 mm equiv, cropped, then upsized so that the fire hydrant was the same size as in the tele shot. Take note of the bird bath and the church in the background in relation to the fire hydrant.

regards
Santo
 

ggibson

Well-known member
OK, I see... the dolly-zoom effect shows a changing perspective because the camera is moving towards or away from the focal plane. But two cameras with different crop factors at the same distance matched with equivalent lenses WILL show the same perspective.
 

JBurnett

Well-known member
As the angular field of view of a 50mm lens on an M-4/3 camera is roughly the same as that of a 100mm lens on a full-frame camera, I would expect that the "perspective" in shots from each would be about the same (DOF aside).

As for the discussion regarding "compression" etc., I think that the important part is to grasp -- visually -- the impact that using a wide angle or a telephoto may have on a subject and it's relationship to the background. It's why we may choose an 80-120mm lens for a more traditional head & shoulders portrait (full-frame), rather than a 17mm or 300mm (working distance aside).
 

kwalsh

New member
Patently and totally incorrect. It's funny how the internet is full of opinions without supporting evidence, haphazardly stated as "facts".
Just like yours!

Buy a tripod and learn how to use it! Notice how the relative position of the chair has changed - you clearly moved in between shots completely invalidating your results.

The difference isn't huge, but it's there. And it's not huge because my apartment isn't big enough for a bigger setup.
It is there because you screwed up, see the properly done examples in this thread. Also, in your tiny apartment you need to account for the entrance pupil location of the lens which you failed to do. In fact, in a bigger setup the errors you made would be less accentuated and your erroneous result diminished.

I'd say to anyone in doubt, take your 2 lenses (or one zoom lens) outside, and try it for yourself. Flower in the foreground, mountain in the background for instance.
Ta-da! Someone did, and they got the results than anyone who understands anything about optics would expect!

Furthermore anyone in filmmaking will be quite aware of the "dolly in, zoom out" or conversely "dolly out, zoom in" techniques, used for example in many Alfred Hitchcock films. You can clearly and plainly see there what effect focal length has on perspective.
Anyone who knew what they were talking about would understand that that dolly in/zoom out is changing perspective because the dolly moved. Duh! That's what everyone has been saying.

In the future when making flame-bait posts at least try to know what you are talking about first, it will go over a lot better.

Ken
 

Robert Campbell

Well-known member
Patently and totally incorrect.
I missed the fun here -- too busy trying to print. I had to search a little for the source of my contention that perspective depends solely on your position -- it came from John Hedgecoe's The Photographer's Handbook [1977]. He was Professor of Photography at the Royal College of Art [now emeritus].There is a description with pix on pp 104-105.

Magnification with lenses. Image magnification varies according to focal length. You might argue that everything could be shot with a wid-angle lens and the required picture area enlarged from the negative through the enlarger.To show just how different the result would be, the picture, below right, is from a whole negative taken with a 500mm lens. The one, below left, is enlarged from the center of the 40 mm lens negative. Immediately you can see that the depth of field is much shallower with the long-focus lens. The degree of enlargement given to the 40mm negative has also increased its graininess destroying fine detail. The result is an image which has been flattened in tone, even though perspective and scale remain in each picture.
[My italics]
 
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