Do lens focal length and sensor size influence depth of field

[Solarflare]

I heard rumors that the Fuji X 56mm 1.2 APD was not a success; sales are much less than Fuji expected.

I wasnt too surprised about this information:

1. The normal 56mm f1.2 already has great Bokeh
2. The 56mm f1.2 was just released before; many who wanted a 85mm equivalent already got it and now probably dont want to switch; the APD version should have been released at the same time or a lot of time later
3. Anyone who needs best Bokeh probably wants a full frame or larger sensor with an extreme aperture; with bokeh every little bit makes a huge difference.



About the OP: Obviously the depth of field is a function of the optics, NOT the sensor.

Thus depth of field depends upon aperture, distance to focus plane, and focal length, but NOT the sensor size.

HOWEVER the sensor size decides what the focal length actually means in respect to actual viewing angle.

This means for example an APS-C/half format/crop factor 1.5/24x16mm sensor will have the exact same depth of field on any focal length lens, lets say its a 50mm, than a small format/full frame/35mm film sized/crop factor 1.0/36x24mm sensor, but the small format sensor will see a 50mm normal lens, while for the APS-C sensor, only recording the middle of the frame, will see a 75mm equivalent and thus a short telephoto lens.

 

[Ysarex]

About the OP: Obviously the depth of field is a function of the optics, NOT the sensor.

Thus depth of field depends upon aperture, distance to focus plane, and focal length, but NOT the sensor size.

This is incorrect. All DOF determinations require a value for circle of confusion. Without CoC DOF is not calculable. CoC changes with sensor size. This is one of the most fundamental DOF equations:

H = f^2/Nc

H is hyperfocal distance
f is focal length
N is distance
and c is circle of confusion which is determined by sensor size.

Change c in that equation and you change H.

In doing DOF comparisons between different format cameras the most logical and useful comparison to make is to use the different format cameras to take the same photo. When you make that comparison you get different DOF results. If however you want to make the comparison by using the same lens focal length from the same distance on both cameras you also get different DOF results because CoC, which changes with sensor size, is a required factor.

The CoC value does not cancel out of any of the equations against another variable. It is an essential factor, it is the sensor/film size, and it is a determinant of DOF.

The math is clear.

Joe

HOWEVER the sensor size decides what the focal length actually means in respect to actual viewing angle.

This means for example an APS-C/half format/crop factor 1.5/24x16mm sensor will have the exact same depth of field on any focal length lens, lets say its a 50mm, than a small format/full frame/35mm film sized/crop factor 1.0/36x24mm sensor, but the small format sensor will see a 50mm normal lens, while for the APS-C sensor, only recording the middle of the frame, will see a 75mm equivalent and thus a short telephoto lens.

 

[fjrabon]

I heard rumors that the Fuji X 56mm 1.2 APD was not a success; sales are much less than Fuji expected.

I wasnt too surprised about this information:

1. The normal 56mm f1.2 already has great Bokeh
2. The 56mm f1.2 was just released before; many who wanted a 85mm equivalent already got it and now probably dont want to switch; the APD version should have been released at the same time or a lot of time later
3. Anyone who needs best Bokeh probably wants a full frame or larger sensor with an extreme aperture; with bokeh every little bit makes a huge difference.

LOL, it came out like a 60 days ago and was always supposed to be an extreme specialist lens. How in the world would it "not be a success" when it hasn't been out three months yet?

 

[daved31415]

Thank you all for the responses. I'm happy to find what looks I think may be the best photography forum on the net.

also im sure at this point the op is sufficiently confused by this when im pretty sure we are more or less ultimately in agreement since im sure we both ultimately understand how DoF works in all its gory detail.

Sufficiently confused, yes — but — I have a few 17" x 22" sheets of paper filled with notes and a desire to better understand all of this. I am sure it will take some time. I've probably watched Tony Northrup's YouTube video a few too many times. I'll be referring back to Bob Atkin's page I'm sure. I would like to get beyond the point of deriving the DOF equation but I am still far from simply deriving it.

P.S. Did you notice that the OP was brand new and this was 1st post? You know it's possible we just got trolled.

I'm glad that didn't deter you from responding!

More like; he'll not return.

I've never particularly enjoyed proving someone I just met wrong but something tells me you'll be okay with this one.

Indeed.

Haha, or a lot post and simply forget they ever asked the question.

You too. Or maybe I just made a bunch of enemies.

Uhm I hate it when someone just post a question to test us.

Glad to help turn that frown upside down.

We must chalk this thread up as being yet another successful trolling pass made.

Nah, I'm just slow.

Seriously though, thanks again. There's a wealth of information on the first page (when I realized there was a page 2 and a page 3 I figured I'd be stuck just giving the thread a first-time read for another hour or more).