M8: Extension (crop) factor vs Perspective

[sparkie]

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What is the consensus on this..

 

Does a 28mm lens on an M8 for instance produce a 37mm 'perspective' or is it still a 28mm perspective with the edges cropped?

 

would like to hear people's thoughts and conclusions..

[Morten Grathe]

The perspektive is only dependant of the distance to the subject. At a given distance the 28mm on a M8 records the same view as a 37mm lens does on a filmcamera.

[Shootist]

The comparison of lens focal lengths between film M's (or any full 35mm camera), 36x24, and digital M, Cropped at 27x18, is not totally correct. A 28mm lens on the M8 captures less on the horizontal side, when shooting in landscape orientation, and more on the verticle side then a 37mm lens would on a film M.

The horizontal length is 9mm narrower on the M8 compared to a standard 35mm camera and only 6mm shorter on the verticle side. Yes the ratio is the same, 3x2, but what it captures is different.

This has been the biggest stumbling block for me when I went from film to digital crop.

Even though a 35mm lens on the M8 seems to fairly equal a 50mm on film it's NOT the same view.

To keep the same perspective as a film 35mm the sensor should of been 30x18. That way it would of been 3mm shorter all around.

[lars_bergquist]

This has been discussed before in this forum. All photographic lenses that are orthoscopic, i.e. picture straight lines as straight lines, produce the same perspective, the classical Western central perspective. Perspective is exclusively a matter of the internal geometry of the image, that is, the geometrical relations between the subject points in the image. The only difference between lenses of different focal length is how they crop the subject, which is a different matter entirely. A change of camera-subject distance on the other hand does change perspective, because this is a geometrical change.

 

The superstition that wide angle lenses have a "steeper perspective" than standard or long lenses, is engendered by the fact that people approach the subject closer in order to have the main subject larger in the picture – which of course defeats the entire idea and purpose of a wide angle lens, which is to get more in the picture!

 

The old man from the Age of 50mm Lenses

[lars_bergquist]

Ed, the "50mm" lens of a Leica is actually 52mm, and has been so since 1925. A 35mm lens on a M8, with a 1.33 crop factor, becomes equivalent to 47mm. This is indeed different, and noticeably so.

 

The old man from the Age of Standard Lenses

[jaapv]

– which of course defeats the entire idea and purpose of a wide angle lens, which is to get more in the picture!

 

The old man from the Age of 50mm Lenses

 

 

I disagree. To use a wideangle to capture both Aunty Priscilla and her poodle instead of just the poodle is a trivial use of a wideangle. The main use is the ability to approach a given subject closer and thus change the perspective (dramatically)

[lars_bergquist]

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Ha ha Jaap, which part of your argument is the chicken, and which is the egg? Agreed, if you actually want the poodle to be larger than Auntie, then a wide angle lens is the obvious choice. But I do never approach poodles this close, they tend to lick the front element which does degrade the image.

 

The old man from the Age of the Portrait Tele

[jaapv]

Ha ha Jaap, which part of your argument is the chicken, and which is the egg? Agreed, if you actually want the poodle to be larger than Auntie, then a wide angle lens is the obvious choice. But I do never approach poodles this close, they tend to lick the front element which does degrade the image.

 

The old man from the Age of the Portrait Tele

 

For the Auntie Priscilla I had in mind you'll need a 12 mm to get the poodle larger...

[Shootist]

Ed, the "50mm" lens of a Leica is actually 52mm, and has been so since 1925. A 35mm lens on a M8, with a 1.33 crop factor, becomes equivalent to 47mm. This is indeed different, and noticeably so.

 

The old man from the Age of Standard Lenses

 

I think you missed my point. A 35mm lens on a M8 would capture less horizontally and more vertically then a equivalent 47mm lens would on a film 35mm camera. Your reference that the Leica 50mm really being 52mm has no real baring on this. It is the size of the sensor, see my above post.

This is one reason the wide lenses, or any focal length lens, just don't seem the same on a M8, or any cropped digital camera, compared to a film 35mm camera when taking the crop factor into account.

[Guest tummydoc]

A 28mm lens on the M8 captures less on the horizontal side, when shooting in landscape orientation, and more on the verticle side then a 37mm lens would on a film M...Yes the ratio is the same, 3x2, but what it captures is different.

 

I'd love to see the math on that

 

 

To respond to the original question, the difference is most strikingly seen w.r.t. the respective expansion/compression of foreground and background. Standing at the correct distance so that the compositions are identical, a shot with a 28mm on full-frame will make the background appear closer than the same shot taken with a 21mm on the M8.

[sparkie]

My understanding is similiar to the following posts from photo.net: Note: the disc. was regarding a 1.5X crop

 

 

Vivek Iyerphoto.net patron prolific poster, Jul 24, 2006; 05:51 p.m.

 

Fredrick, Crop factor or whatever factor, does not change the focal length of a lens. It just captures a cropped image.

 

50mm does not "become" a 75mm lens. Never.

 

Andy Aitkenphoto.net patron, Jul 24, 2006; 05:51 p.m.

 

The crop factor is irrelevant. The depth of field of a lens of a given focal length and aperture remains unchanged whatever the crop factor/format is. So 18mm would remain adequate.

[Skippy Sanchez]

I'd love to see the math on that.

 

Since I'm not a mathematician, I tried something easier. I made two blank images in photoshop: a white one at 36x24mm (to replicate film size), and a black one at 27x18 (to replicate the M8 sensor).

 

i multiplied the black 27x18mm frame by the 1.33 crop factor and pasted it on the white 35mm 'film' template. it was the exact same proportion but just a hair smaller. the shape was identical. or, perhaps, there was something i didn't take into account.

[blakley]

I think you missed my point. A 35mm lens on a M8 would capture less horizontally and more vertically then a equivalent 47mm lens would on a film 35mm camera. Your reference that the Leica 50mm really being 52mm has no real baring on this. It is the size of the sensor, see my above post.

This is one reason the wide lenses, or any focal length lens, just don't seem the same on a M8, or any cropped digital camera, compared to a film 35mm camera when taking the crop factor into account.

 

Here you're discussing not perspective, but rather aspect ratio. Aspect ratio is a property of the capture medium (film or sensor), not of the lens. Perspective, as noted above, depends only on the distance from the subject to the lens' nodal point; aspect ratio simply crops the image circle to some other shape (usually a rectangle).

[jaapv]

My understanding is similiar to the following posts from photo.net: Note: the disc. was regarding a 1.5X crop

 

 

Vivek Iyerphoto.net patron prolific poster, Jul 24, 2006; 05:51 p.m.

 

Fredrick, Crop factor or whatever factor, does not change the focal length of a lens. It just captures a cropped image.

 

50mm does not "become" a 75mm lens. Never.

 

Andy Aitkenphoto.net patron, Jul 24, 2006; 05:51 p.m.

 

The crop factor is irrelevant. The depth of field of a lens of a given focal length and aperture remains unchanged whatever the crop factor/format is. So 18mm would remain adequate.

 

You missed the obvious answer: to get the same end image a smaller sensor, given the same coverage of the subject, will have to be enlarged more, producing shallower DOF. DOF is not a property of any given lens, DOF is a result of many factors throughout the whole optical process from subject to final print, the major one being enlargement. As such Andy is right, and the crop factor gets irrelevant when it is the only parameter to be variable. But it will produce a different image as it is changed.

Say Hi to Vivek from me

[charlesphoto99]

I think that depth of field does play into it, and the way the lens draws. For example, it's bandied about a lot that the M8 (or 1ds MkII) has the same resolution as a MF camera. Maybe, but a normal lens on a 6x7 MF camera is going to give you a very different look than a normal on a 35 (cropped or not).

 

Same can be said for a cropped 28 vs a true 35mm lens. Or a cropped 35 vs a true 50mm. One can't get close to the subject and include a wide field and shallow depth with a 28 Cron with a M8 like one can with an M7. So in order to include the same wide field one must step to a 21mm which won't give you the shallow depth and therefore will have the apperance of a much wider lens, regardless of the crop factor.

[blakley]

I think that depth of field does play into it, and the way the lens draws. For example, it's bandied about a lot that the M8 (or 1ds MkII) has the same resolution as a MF camera. Maybe, but a normal lens on a 6x7 MF camera is going to give you a very different look than a normal on a 35 (cropped or not).

 

Same can be said for a cropped 28 vs a true 35mm lens. Or a cropped 35 vs a true 50mm. One can't get close to the subject and include a wide field and shallow depth with a 28 Cron with a M8 like one can with an M7. So in order to include the same wide field one must step to a 21mm which won't give you the shallow depth and therefore will have the apperance of a much wider lens, regardless of the crop factor.

 

Here you're confusing two issues - perspective (or perhaps DOF) effects, and subject distance effects. If you stand with the M8 and an M7 at the same distance from the subject with the same lens, you'll get the same DOF and the same perspective - but the M8 image will appear to be cropped.

 

If you stand CLOSER with the M7, in order to get the same amount of stuff into the frame as you would with the M8 at the original distance, you will get shallower depth of field. But this is entirely an effect of how far you are standing from the subject, and has nothing to do with the sensor or the lens.

[sparkie]

Look folks I'm just trying to figure out if the M8's 1.33x sensor is really just producing a crop to the edges while leaving the lens Perspective intact. That's all I want to know

 

If this isn't the case. ie. that somehow the 1.33 sensor 'alters' the perspective - then this is a new one on me.

 

The fact that everyone is buying a 'wider' lens to accommodate for the M8's crops sensor is a compromised solution. Yes you'll capture more in your photos with a wider lens but the problem is you are swapping for a wider lens perspective ie. exagerating expansion/compression of foreground and background elements

 

SO, wouldn't it be better to just take three or four steps back? assuming you dont have a wall or cliff in the way

[blakley]

Look folks I'm just trying to figure out if the M8's 1.33x sensor is really just producing a crop to the edges while leaving the lens Perspective intact. That's all I want to know

 

If this isn't the case. ie. that somehow the 1.33 sensor 'alters' the perspective - then this is a new one on me.

 

Not to worry, sparkie. You really are just cropping the edges. Your lens does not bend light any differently when you put it on an M8.

[sparkie]

Here you're confusing two issues - perspective (or perhaps DOF) effects, and subject distance effects. If you stand with the M8 and an M7 at the same distance from the subject with the same lens, you'll get the same DOF and the same perspective - but the M8 image will appear to be cropped.

 

If you stand CLOSER with the M7, in order to get the same amount of stuff into the frame as you would with the M8 at the original distance, you will get shallower depth of field. But this is entirely an effect of how far you are standing from the subject, and has nothing to do with the sensor or the lens.

 

 

At last, someone who can 1. agree with my thinking and 2. explain in simple plain english!

 

Thanks Blakley. I can sleep now:D

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Hallo,

Look here: Leica M

[Guest tummydoc]

Since I'm not a mathematician, I tried something easier. I made two blank images in photoshop: a white one at 36x24mm (to replicate film size), and a black one at 27x18 (to replicate the M8 sensor).

 

No need to be a mathemetician, just ask any middle-schooler. 27=0.75x36 and 18=0.75x24. Each dimension is reduced by 25%. There is no way, unless a)the sensor dimensions are incorrect, or b)Mr. Shootist lives in a different dimension, that there is more vertically and less horizontally on an M8 shot than a simple crop from full-frame.