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75mm Summilux Bokeh


hlansing

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The cropped sensor size certainly has its negative impact on bokeh ... these are 35mm FF lenses.

 

I can't figure out what you're talking about here. The cropping has no effect whatsoever on bokeh that I can see in my own shots, nor can I imagine any reason why cropping should affect bokeh.

 

Certainly leaving off the outer image zones may simply omit some out-of-focus details; this of course does not change the rendition of the OOF areas which remain in the picture at all.

 

Can you offer any rationale at all for why you think the same lens should display different bokeh on a cropped sensor vs. a full-frame sensor?

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I can't figure out what you're talking about here. The cropping has no effect whatsoever on bokeh that I can see in my own shots, nor can I imagine any reason why cropping should affect bokeh.

 

Certainly leaving off the outer image zones may simply omit some out-of-focus details; this of course does not change the rendition of the OOF areas which remain in the picture at all.

 

Can you offer any rationale at all for why you think the same lens should display different bokeh on a cropped sensor vs. a full-frame sensor?

 

 

I agree with your comments! Misleading concept is very dangerous to knowledge. In addition to your comment I would like to add that while it is true that the crop sensor size should not affect the bokeh of the lens. However, crop factor affects how far we stand from the subject and therefore affects the depth of field. Thus, in physics there should be no changes in bokeh but in application it does affect the bokeh.

 

-Son

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Thus, in physics there should be no changes in bokeh but in application it does affect the bokeh.

 

It seems that you've answered your own questions ... because there's no such a thing called bokeh in physics. It's just the rendition of OOF areas which could be affected by many factors with the effective DoF being one of them.

 

Just take a look at those 4/3 lenses, now that's something.

 

Dangerous enough? sounds you're just repeating what I've said but perhaps I should be more specific. The conclusions are the same ... cropped sensor does make bokeh look different.

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It seems that you've answered your own questions ... because there's no such a thing called bokeh in physics. It's just the rendition of OOF areas which could be affected by many factors with the effective DoF being one of them.

 

Just take a look at those 4/3 lenses, now that's something.

 

Dangerous enough? sounds you're just repeating what I've said but perhaps I should be more specific. The conclusions are the same ... cropped sensor does make bokeh looks different.

 

Repeated assertion does not make a statement true.

 

If cropping the sensor makes bokeh look different, then, because the same lens and the same light are involved:

 

1. Cropping a negative should also make bokeh look different

2. Cropping a print made from the full negative should make bokeh look different too

3. Using high-speed crop mode on the Nikon D2X, which uses only the center of the sensor and produces a 2x crop factor, should produce (with the same lens) a photo with bokeh which differs from the same photo taken with the full 1.5x crop factor sensor.

 

None of these things happen, of course, because cropping does not affect bokeh.

 

If what you're trying to say is "out-of-focus areas look different if you move farther away from the subject", this is of course true. It has nothing to do with the sensor, though, and it also has nothing to do with the lens, and it also has nothing to do with bokeh.

 

What it does have to do with is perspective. If you stand farther away, less stuff is out of focus, because the zone of acceptably sharp focus is deeper. Since stuff which is IN focus doesn't exhibit bokeh AT ALL, the bokeh is in to different parts of the picture when you stand far away from the point of focus than when you stand close to it. But the bokeh isn't qualitatively any different - it's just in a different place.

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1. Cropping a negative should also make bokeh look different

2. Cropping a print made from the full negative should make bokeh look different too

 

Bob, if you're going crop or cut a negative or the print, the bokeh is already frozen in your image ... that's very different from the one in the making with your digital camera.

 

Put it this way, cropping a picture after the shot and cropping the "view" before a picture is taken are different.

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I can't figure out what you're talking about here. The cropping has no effect whatsoever on bokeh that I can see in my own shots, nor can I imagine any reason why cropping should affect bokeh.

 

Well, in order to get the same frame you must to get closer with a full frame camera (film or digital), and distance to the subject affects bokeh.

 

Bokeh is negatively affected by 1 Aperture, 2 Closer distances to the subject, 3 Farther distances to the background (out of focus), 4 Contrasty character of that background.

 

I have a Summilux 75mm and a M8 (1,33 crop). I am taking pictures farther than I would do using the same lens on a M7 (35mm full frame).

 

I am not saying the bokeh is deteriorated due to this reason. In fact, I don't know how much impact the crop has on the lens rendering, but I think crop affects positively the bokeh rendition, due to farther distances to the subject for the same frame.

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Bob, if you're going crop or cut a negative or the print, the bokeh is already frozen in your image ... that's very different from the one in the making with your digital camera.

 

Put it this way, cropping a picture after the shot and cropping the "view" before a picture is taken are different.

 

Really? Fascinating! Let's analyze this using the Nikon D2X example.

 

We start with a Nikon D2X, which has a 12MP 16x24mm sensor. We place the camera on a tripod in front of a still life - let's say a tulip - with the subject in centered in the frame in controllled artificial lighting which does not vary with time. We meter the light, set the manual exposure controls, and take a correctly exposed photo. The light comes through the lens and illuminates the whole sensor.

 

Now we switch the camera into High-Speed Crop mode. Using the same exposure settings, we take another photo. In High-Speed Crop mode on the D2X, the SAME light strikes the SAME locations on the SAME sensor, but the camera only sends the 7MPs of data from the 12x18mm region in the center of the sensor to the memory card, thus cropping the image.

 

We now have two images, a 12MP image and a 7MP image.

 

The subject didn't change. The distance to the subject didn't change. The light didn't change. The lens didn't change. The sensor didn't change. Only the cropping changed.

 

Keeping in mind that anyone with a D2X can actually perform this experiment and examine the results, please explain exactly what about the bokeh of the 7MP image looks different from the bokeh of the 12MP image, and why.

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If you frame a shot the same with a crop camera, the aperture is affected in the same way as the effective focal length. The depth of field is proportional to the square of the distance, IIRC, and you will stand further away with a given lens on the M8.

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The subject didn't change. The distance to the subject didn't change. The light didn't change. The lens didn't change. The sensor didn't change. Only the cropping changed.

 

Now you're talking to the right person because I know a lot about Nikon and the D2X, Bob ... remember, in full DX mode and cropped DX mode the captures are the same, it's just the output from the peripheral channels are trashed in cropped mode, only the data at the center is preserved to construct the image file.

 

Same theory as the cropping and cut with a "Print" ... so it's no surprise that you won't see any different in effective DoF and bokeh.

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Now you're talking to the right person because I know a lot about Nikon and the D2X, Bob ... remember, in full DX mode and cropped DX mode the captures are the same, it's just the output from the peripheral channels are trashed in cropped mode, only the data at the center is preserved to construct the image file.

 

Same theory as the cropping and cut with a "Print" ... so it's no surprise that you won't see any different in effective DoF and bokeh.

 

Precisely. Because cropping doesn't affect bokeh.

 

If you move the camera, the picture looks different. Not because bokeh changes, but because perspective changes. Framing a picture the same way with a cropped sensor as you would with a full-frame sensor requires you to change perspective by moving further away. This changes the way the picture looks. But it has nothing whatsoever to do with bokeh, which is a property of the way the lens design and abberations "paint" the light onto the sensor, and not a property of the way the sensor "processes" that light.

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Bokeh can be largely related to the amount of under-corrected spherical aberrations in the lens design. Since these aberrations usually also increase as you move from the center of the image circle to the outer edge of the image circle, it is possible for a crop to eliminate some of the outer edge effects. So I suspect in theory, the bokeh in a crop could appear different enough than the full frame shot to be noticed by some folks.

 

To be sure though, when "The subject didn't change. The distance to the subject didn't change. The light didn't change. The lens didn't change. The sensor didn't change. Only the cropping changed." the only thing possible to be missing is the outer edges, or what got lopped out in the crop. The stuff in the remaining part of the image will look identical.

 

Now if we want to keep the subject size relatively the same with any given lens, we will be required to move in a bit closer with the full-frame camera. This will generate a similar framing but not an identical image, because the perspective changed as soon as we moved the camera position. Since the closer image includes more of the lens' edge effects, I guess this could impart a different look to the image when similar framing is compared -- at least in theory. However, I remain doubtful the edge effect is different enough between a 1.3 crop and full-frame to show a significant difference in the bokeh in an actual image. I'll need to see an example to be convinced...

 

Jack

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So you're Nikon shooter, Bob ... it seems the only way you could be convinced is to find a SLR/n and shoot side by side against the D2X with a 85/1.4 (?). The high speed crop mode in the D2X won't show you any difference.

 

Cropping the print doesn't change the look of bokeh - I agree, cropping the sensor will.

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I'm not sure I can make that leap without seeing an actual example that illustrated it...

 

I believe there're a lot of forum members here who have both a 5D and a 20D ... or a 350D/400D, so it's easy to prove this with a 85/1.2, or a 85/1.8 ... anybody take this one? :)

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I believe there're a lot of forum members here who have both a 5D and a 20D ... or a 350D/400D, so it's easy to prove this with a 85/1.2, or a 85/1.8 ... anybody take this one? :)

 

YOU can show us with just one of YOUR cameras -- just take a shot with any lens, move back 25% and take another shot, then crop the second afterward to the same approximate subject size as the first and post them. But to be fair, you'll need to keep the subject relatively close and the background relatively distant so effects of the extended DoF from moving farther away for the subject are mitigated and don't skew the result...

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YOU can show us with YOUR camera -- just take a shot with any lens, move back 25% and take another shot, then crop the second afterward to the same approximate subject size as the first and post them.

 

Again, this will prove nothing ... an valid test would be with two cameras, one FF, one 1.5x, same lens, same object, same aperture, same speed, and same distance. The magic is inside the camera, not outside the camera.

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Again, this will prove nothing ... an valid test would be with two cameras, one FF, one 1.5x, same lens, same object, same aperture, same speed, and same distance. The magic is inside the camera, not outside the camera.

 

And right here is where your argument falls apart, so let me repeat... IF YOU SHOOT THEM BOTH AT THE SAME DISTANCE, IT IS THE SAME AS CROPPING AFTER THE FACT. And if you compare the 1.5x image to the same central part of the full frame image, THEY WILL BE IDENTICAL. To state that some kind of magic is going on inside the camera is a ridiculous assertion.

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