DEPSSI cards

markta

markta

Suspended / Banned
Messages
3,036
Name
Mark
Edit My Images
Yes
Hi all,

I've decided to use my Sigma 10-20mm lens a lot more and mix wide angles with my usual wildlife 'tography.

Question is...I have a DEPSSI card for hyperfocal focusing ranges but was wondering whether the focal length indicator is after the 1.6x crop is taken into account, or before.

Cheers :thumbs:
 
The crop doesn't affect the depth of field, that's purely a function of the focal length of the lens versus the aperture.
 
Steep said:
The crop doesn't affect the depth of field, that's purely a function of the focal length of the lens versus the aperture.
Click to expand...

I'm sorry Steep but that's not correct. The hyperfocal distance with a crop (1.6x) sensor will be 1.6x the distance for a FF sensor.

Bob
 
Bob, I have an A4 sheet of paper onto which I've 'projected' the image from a lens. I do nothing to the lens but shrink the paper down to A5. Explain to me how the depth of field from the lens changes?
 
That ^ sounded a bit sharp, it wasn't my intention but I can't get my head around a sensor affecting the dof (or the focal length)
 
I read something on here a while back which showed that DOF is affected by a crop sensor.
Wait until the person who said it comes along to explain it, it made brilliant sense once you got your head around it.
 
Steep said:
That ^ sounded a bit sharp, it wasn't my intention but I can't get my head around a sensor affecting the dof (or the focal length)
Click to expand...
A sheet of white paper is not a good example to use....:lol:

DOF isn't a physical property of a lens or, indeed, a sensor. DOF is perceived by individuals as whether a point (plane) is in acceptably sharp focus or not.

A standard way to measure this is to detemine a value that the average human eye can resolve as being sharp or not....the "circle of confusion" When making this evaluation, a print is used and viewed from a certain distance (the size of print and distance are arbitary but usually have defined dimensions).

To obtain the print, the image (or portion thereof) is magnified. The crop sensor derived image requires 1.6x less magnification than a FF derived image (talking Canon APS-C here) and hence the OOF detail remains smaller than the human eye can resolve/distinguish.

I know what I mean but find it difficult to explain....someone else have a bash please :help:

Bob

Edit....if you have a lens with a DOF scale then this is based on FF usage (unless the lens is exclusively designed for a crop sensor)
 
Hmm... swings and roundabouts.

If you take a shot from the same position and lens with a crop and full frame then print both at 12x8 then crop frame will have less apparent DoF. This is because the smaller details have been enlarged more than those on the FF. If you printed the FF to 12x8 and the crop to 7.5x5 then they'd have the same DoF and indeed the subject in both would be the same size when measured on the print.

So the answer is take the crop factor into account unless you always print 1.6x smaller than you would with FF.
 
You must log in or register to reply here.
Back
Top