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Compression and Bokeh Qn

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ongsw

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Hi Guys,

A question that has bugged me for a while.

Is the compression and bokeh of telezoom lenses similar between a say 50mm (4/3) and a 100mm (35mm FF) similar or will I only get similar compression if it is 100mm for both formats given all else equal?

I understand the perspective of view between the 50mm (4/3) and the 100mm (35mm FF) is similar.

--
Francis
 
ongsw said:
Hi Guys,

A question that has bugged me for a while.

Is the compression and bokeh of telezoom lenses similar between a say 50mm (4/3) and a 100mm (35mm FF) similar or will I only get similar compression if it is 100mm for both formats given all else equal?

I understand the perspective of view between the 50mm (4/3) and the 100mm (35mm FF) is similar.
Click to expand...
The perspective depends only on the subject-camera distance, it does not depend on focal length or format.

As for "compression", I'm not exactly sure what you mean. The diagonal AOV (angle of view) is the same for 50mm on 4/3 and 100mm on FF.

The bokeh is the quality of the background blur, not the quantity of background blur. The bokeh varies from lens to lens, and the quantity of background blur depends on the perspective, framing, and aperture diameter.
 
Francis,

Compression is the same, depth of field depends on the aperture (f/2 on FT is equivalent to f/4 on 135 at the same distance), bokeh - aesthetic quality of the area that is out of focus - depends on the lens; there are lenses with 'fine' bokeh on both FT and 135.

HTH,

Regards,

Claus.

--

... when the photograph annihilates itself as medium to be no longer a sign but the thing itself...

 
No. DOF for a 100mm lens at f/2.8 is the same no matter what system it's on.
ongsw said:
Hi Guys,

A question that has bugged me for a while.

Is the compression and bokeh of telezoom lenses similar between a say 50mm (4/3) and a 100mm (35mm FF) similar or will I only get similar compression if it is 100mm for both formats given all else equal?

I understand the perspective of view between the 50mm (4/3) and the 100mm (35mm FF) is similar.

--
Francis
Click to expand...
 
DOF at F/2 or any aperture is the same on any system.
Claus A said:
Francis,

Compression is the same, depth of field depends on the aperture (f/2 on FT is equivalent to f/4 on 135), bokeh - aesthetic quality of the area that is out of focus - depends on the lens; there are lenses with 'fine' bokeh on both FT and 135.

HTH,

Regards,

Claus.

--

... when the photograph annihilates itself as medium to be no longer a sign but the thing itself...

Click to expand...
 
I'm not talking about equivalents or same perspectives like the articles you linked to. 100mm f/2.8 on full frame will yeild the same DOF as 100mm f/2.8 on 4/3ds. It's the angle of view that will be different.

DOF is a function of the lens. When you talk equivalents, you are talking different lenses.
Great Bustard said:
dgrogers said:
No. DOF for a 100mm lens at f/2.8 is the same no matter what system it's on.
Click to expand...
DOF is not a function of only the lens. It is a function of many variables:

http://www.josephjamesphotography.com/equivalence/#dof

Pay special attention to the different situations in the box in the above link. This DOF calculator:

http://www.dofmaster.com/dofjs.html

presumes that the photo is displayed with a 12.8 inch diagonal and viewed from 10 inches with 20-20 vision.
Click to expand...
 
Go and check with an E3 and the f/2 50mm and a Canon 5D and the f/2.8 100mm at f/4 at the same distance. -C.
--

... when the photograph annihilates itself as medium to be no longer a sign but the thing itself...

 
dgrogers said:
I'm not talking about equivalents or same perspectives like the articles you linked to. 100mm f/2.8 on full frame will yeild the same DOF as 100mm f/2.8 on 4/3ds. It's the angle of view that will be different.

DOF is a function of the lens. When you talk equivalents, you are talking different lenses.
Click to expand...
If the link I gave you did not make it clear that it is not just the lens:

http://www.josephjamesphotography.com/equivalence/#dof

then perhaps this one will:

http://en.wikipedia.org/wiki/Depth_of_field

If neither of those links show you the light, then perhaps this question will: since the DOF is decided by the lens, what is the DOF of a 100 / 2.8 lens?

If you can't give me a number as an answer to my question, then perhaps it might occur to you that the reason you can't tell me the DOF of a 100 / 2.8 lens is because it depends on factors other than the focal length and f-ratio.

Now, let me answer my question: the DOF of a 100 / 2.8 lens on FF at f/4 with a camera subject distance of 10 ft displayed at 8x10 inches and viewed from 10 inches away with 20-20 vision is 0.71 ft. The DOF of a 50 / 2 lens on 4/3 at f/2 with a subject-camera distance of 10 ft displayed at 8x10 inches and viewed from 10 inches away with 20-20 vision is 0.72 ft.

I can get different DOFs by varying the subject-camera distance, the focal length, the f-ratio, the display size, the viewing distance, and the visual acuity. In other words, DOF is not merely a function of the lens alone.

As it turns out, for the same perspective, AOV, display diagonal, viewing distance, and visual acuity, all formats will have the same DOF. Regardless, the DOF is a function of many variables besides the focal length and f-ratio.
 
So you're saying if you take a shot on a full frame DSLR with a 100mm f/2.8 lens at f/2.8 and crop it to 4/3 size, DOF will be different if you take a shot of the same subject from the same distance on a 4/3 DSLR using a 100mm f/2.8 lens at f/2.8?

Here's a quote from your wiki link:

Cropping an image and enlarging to the same size final image as an uncropped image taken under the same conditions is equivalent to using a smaller format under the same conditions, so the cropped image has less DOF.

A 100mm f/2.8 lens has the same DOF on any system. It's the "crop" that's different.
Great Bustard said:
dgrogers said:
I'm not talking about equivalents or same perspectives like the articles you linked to. 100mm f/2.8 on full frame will yeild the same DOF as 100mm f/2.8 on 4/3ds. It's the angle of view that will be different.

DOF is a function of the lens. When you talk equivalents, you are talking different lenses.
Click to expand...
If the link I gave you did not make it clear that it is not just the lens:

http://www.josephjamesphotography.com/equivalence/#dof

then perhaps this one will:

http://en.wikipedia.org/wiki/Depth_of_field

If neither of those links show you the light, then perhaps this question will: since the DOF is decided by the lens, what is the DOF of a 100 / 2.8 lens?

If you can't give me a number as an answer to my question, then perhaps it might occur to you that the reason you can't tell me the DOF of a 100 / 2.8 lens is because it depends on factors other than the focal length and f-ratio.

Now, let me answer my question: the DOF of a 100 / 2.8 lens on FF at f/4 with a camera subject distance of 10 ft displayed at 8x10 inches and viewed from 10 inches away with 20-20 vision is 0.71 ft. The DOF of a 50 / 2 lens on 4/3 at f/2 with a subject-camera distance of 10 ft displayed at 8x10 inches and viewed from 10 inches away with 20-20 vision is 0.72 ft.

I can get different DOFs by varying the subject-camera distance, the focal length, the f-ratio, the display size, the viewing distance, and the visual acuity. In other words, DOF is not merely a function of the lens alone.

As it turns out, for the same perspective, AOV, display diagonal, viewing distance, and visual acuity, all formats will have the same DOF. Regardless, the DOF is a function of many variables besides the focal length and f-ratio.
Click to expand...
 
That's not what I'm talking about. Check the E3 with a 100mm f/2.8 lens and a 5D with a 100mm f/2.8 lens cropped to 4/3 dimensions. They are the same.
Claus A said:
Go and check with an E3 and the f/2 50mm and a Canon 5D and the f/2.8 100mm at f/4 at the same distance. -C.
--

... when the photograph annihilates itself as medium to be no longer a sign but the thing itself...

Click to expand...
 
dgrogers said:
So you're saying if you take a shot on a full frame DSLR with a 100mm f/2.8 lens at f/2.8 and crop it to 4/3 size, DOF will be different if you take a shot of the same subject from the same distance on a 4/3 DSLR using a 100mm f/2.8 lens at f/2.8?
Click to expand...
I neither said nor implied any such thing. Here's the link I gave you:

http://www.josephjamesphotography.com/equivalence/#dof

And here's a quote from the box down that link that addresses that particular scenario (last bullet in the box):

For the same perspective and focal length, larger sensor systems will have a wider framing. If the same f-ratio is used, then both systems will also have the same aperture diameter. As a result, if the image from the larger sensor system is displayed at a larger size in proportion to ratio of the sensor sizes, or the image from the larger sensor system is cropped to the same framing as the image from the smaller sensor system and displayed at the same size, then the two images will have the same DOF.

So, for the specific case of a photo with the same camera-subject distance taken at 100mm f/2.8, all systems cropped to the same framing, all photos displayed at the same size, viewed from the same distance and with the same visual acuity, then the DOFs will be the same.

But notice that I had to specify the conditions, and the box in the link above discusses other conditions. The most natural condition is the same perspective and framing. People don't go around taking pics at 100mm and cropping them to a 200mm AOV unless they are either incompetent, or focal length or magnification limited.

So, saying 100mm f/2.8 gives the same DOF regardless of the system when you crop them to the same framing is not a particularly useful comment to make for most all photography, and is hugely misleading if the specific, and unusual, conditions when it does work out are not spelled out.
dgrogers said:
Here's a quote from your wiki link:

Cropping an image and enlarging to the same size final image as an uncropped image taken under the same conditions is equivalent to using a smaller format under the same conditions, so the cropped image has less DOF.
Click to expand...
Yes.
dgrogers said:
A 100mm f/2.8 lens has the same DOF on any system. It's the "crop" that's different.
Click to expand...
The lens does not have a DOF -- the photograph has a DOF, and that DOF has to do with more than just the focal length and f-ratio, and to say that the DOF is the same for the same focal length and f-ratio because it works out that way for one specific and unusual circumstance is counterproductive, to say the least.
 
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