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Steven M. Anthony
9th of April 2005 (Sat), 21:27
Note: This post is not intended to start a multi-page thread. I just thought it was interesting given the discussions over the last couple of days and wanted to share.

Check out the May issue of Popular Photography… (okay, I know… But I have a kid whose school does mag subscriptions for fund raising…) Interesting article on sensor size.

They accurately report that the APS-C-sized sensors do not magnify the focal length of 35mm-format lenses, and that the focal length of a lens is determined without regard to the size of film/sensor in the camera. Oddly enough, they also refer to “how your telephoto lenses become superteles.”

But they say that the smaller sensor will capture the same DoF that a full-frame image would have. The DoF calculator Slin100 (I think) directed me to earlier this week shows otherwise. Which source is correct?

It also better articulates the point I was trying to make on perspective: That to get the same general composition across sensor sizes (full vs APS-C), there will be both perspective and DoF differences (because you have to move to get the same composition).

Bodog
10th of April 2005 (Sun), 00:15
Steve, there are already many multi-page threads on this subject. Check this from the EOS sticky page: http://photography-on-the.net/forum/showthread.php?t=45388

Steven M. Anthony
10th of April 2005 (Sun), 09:04
Steve, there are already many multi-page threads on this subject. Check this from the EOS sticky page: http://photography-on-the.net/forum/showthread.php?t=45388

Sorry Jim. I looked through that sticky and didn't see anything that referenced the May issue of Popular Photography. I must have missed it.

Bodog
10th of April 2005 (Sun), 11:10
I guess I thought you were bringing up the old "magnification vs. crop factor" debte. Sorry if I misunderstood.

Steven M. Anthony
10th of April 2005 (Sun), 11:26
I guess I thought you were bringing up the old "magnification vs. crop factor" debte. Sorry if I misunderstood.

No problem. I wasn't so much bringing up the debate as I was trying to get clarification on something I learned through the debate--namely my question on DoF. The Pop Photo article is at odds with the DoF calculator site on the web.

cyclone
10th of April 2005 (Sun), 13:33
Steve-

I'm a closet Popular Photography subscriber (shhh, don't tell anyone). I gave that article a passing glance earlier, but re-read it in light of your post. You're right about what they claim. They correctly say that depth of field (DOF) will change if you use different lenses to adjust for the crop factor, but imply that the sensor size itself will not change the DOF. This is wrong in that the sensor size should change the circle of confusion (CoC) parameter in the depth of field calculation. The equation for the CoC (from JohnHendry.com) is 1 / (r x (D/d) ) , where d=diagonal of the negative (or sensor in this case) in mm, D=diagonal of the print size in mm, and r= your desired resolution in lines/mm. So according to this, DOF should change.

Good catch.

Cyclone