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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Red Vs Viper

Anders Holck said:
Note that pixel binning is not oversampling. It equals a larger photosite, but won't help reduce aliasing between adjacent bins.
Click to expand...

You're right. Used the wrong wording here. Oversampling is temporal while pixel binning is spatial. Sorry about that. :blush:
 
I don't believe that is true Brook.
-A
 
Brook Willard said:
DOF discussions rapidly become semantic. Simply put, DOF is determined by your stop, focal length and subject distance. Format has no effect on DOF. A 100mm lens on a 35mm camera has the same DOF as a 100mm lens on a 1/3" camera. Only the FOV changes in that equation.
Click to expand...

Hi Brook,

If the 1/3 inch had enough resoloution that would be true.

I maintain DOF is determined by stop & image size only.

Stephen
 
a 100 mm lens at any f stop will have more dof on a 1/3' sensor than on a 35mm sensor at the same f stop.
-A
 
Chris Kenny said:
Um... focal length is what determines image magnification.
Click to expand...

Hi Chris,

Focal length and distance equal image magnification.

If image magnification remains constant DOF remains constant regardless of lens focal length.

Stephen
 
Chris beat me to it...

So uh, what he said.
 
Poi Boy said:
a 100 mm lens at any f stop will have more dof on a 1/3' sensor than on a 35mm sensor at the same f stop.
-A
Click to expand...

Not true. A 100mm lens on a 1/3" sensor will have a dramatically narrower FOV than it would on a 35mm sensor. It will appear that the focal length is longer [the apparent focal length will be longer], but the actual focal length will be the same. Accordingly, as the focal lengths are identical, the DOF is identical.

Look on a 1/3" camera [think HVX]. The focal lengths available are something like 4.2mm to 15mm. A 4.2mm lens on the HVX is a wide/normal lens. A 4.2mm lens on 35 would be ungodly wide... I'm not even sure if it's optically possible. That's just an aside to consider the available focal lengths on a 1/3" camera vs. a 35mm camera.

If you matched FOV instead of focal length, the 1/3" camera would have something like a 15mm lens and the 35mm camera would have something like an 85mm lens. Then, with the FOV matched, the DOF would be different... because you would be comparing a 15mm lens to an 85mm lens.

Poorly explained, I know. Did it make any more sense?
 
Regarding DOF, read this:

http://www.bluesky-web.com/dofmyth.htm

Focal length IS NOT a factor. It's determined f-stop and subject distance or focus distance (which is where the image size issue comes into play).

The stretching of wide angle lenses and compression of long lenses will give the images different characteristics which can also lend to the impression of more or less DOF.

Format size has to do with FOV ONLY.

So, Stephen is correct on this issue.
 
Brook Willard said:
Unless I'm misunderstanding you, mathematically speaking you are incorrect.
Click to expand...

Hi Brook,

100mm @ 40'
50mm @ 20'
25mm @ 10'

The image will be the same size on the sensor and at the same F stop so will the DOF.

Stephen
 
The dof is defined by the following variables: Focallenght, F stop, Subject distance (focal point) and COC.
If you change any of these your variables DOF will change.
 
Stephen Williams said:
Hi Brook,

100mm @ 40'
50mm @ 20'
25mm @ 10'

The image will be the same size on the sensor and at the same F stop so will the DOF.

Stephen
Click to expand...

Completely agreed. But in this scenario, you are changing two factors: the focal length and the subject distance. If the subject distance was maintained [which is what I was thinking of], then the different focal lengths would have an effect on the DOF.
 
Stephen Williams said:
100mm @ 40'
50mm @ 20'
25mm @ 10'

The image will be the same size on the sensor and at the same F stop so will the DOF.
Click to expand...

That's right. But now you're changing two variables at the same time: subject distance and focal length. In the field you don't know about any magnification factor (subject distance divided by focal length) but you know exactly what subject distance and focal length you have.

So we're both right. But calculating the DOF using focal length, f-stop and subject distance is far more practical.
 
I think the focal length vs. magnification argument is getting a little pedantic. While the magnification level combined with f-stop does account for the DOF, focal length is what determines the FOV at the desired magnification level.

Point being, in the real world, we use longer lenses or different focal lengths to alter DOF properties as that's often the most practical solution.
 
I think we're all agreeing... we just don't know how to say it.

Stop, subject distance and focal length. Change any single factor and DOF will change. Change multiple factors in a complimentary fashion and DOF will not change.
 
OK, I learned something after reading that link. The dof doesn't technically change. However the illusion of dof most certainly does therefore I'll change my statement . A 100 mm lens at any f stop will have the ILLUSION of more dof on a 1/3' sensor than on a 35mm sensor at the same f stop.
-A
 
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