On a crop body there is a FF field of view equivalent. Is there also a DOF equivalent

[TMR Design]

Im sure this has been asked and answered before but I think it's worthy of its own thread.

The field of view equivalent of a crop body is 1.6x that of a full frame body but I'd like to know if depth of field works the same way.

In other words, if you're using a very shallow depth of field on a full frame body, is there an euqivalent when using the same depth of field on a 1.6x crop body?

Will f/2 appear the same on a full frame as it does a 1.6x crop? If you were to crop the full frame to the same view as the 1.6x crop body would the depth of field look the same or would it have slightly greater depth of field?

If not then is there a method of determining that equivalent?

[Ronald S. Jr.]

Originally Posted by TMR Design

Will f/2 appear the same on a full frame as it does a 1.6x crop?

Nope. It'll have much more shallow depth of field.

If you were to crop the full frame to the same view as the 1.6x crop body would the depth of field look the same or would it have slightly greater depth of field?

then it would look the same. The difference of depth of field between FF and a crop is only perceptive. As you know, to get the "same" shot on FF, you have to either use a longer lens, or move in closer. Both will give you less depth of field. Taking the same shot from the same place with the same lens and settings, you can indeed crop the shot to match, and should have relatively equal depth of field.

[Wilt]

Robert, get a DOF calculator program for yourself, free on the web. It will show you some interesting things...
For example 50mm f/2 on APS-C focused at 100' has a field in focus of 89' deep, but same lens and settings on 135 format has field in focus of 193' deep!
Remembering that the field of view is not the same in the previous pairings, moving the APS-C camera back to 160' distance to get same FOV (as 50mm on 135 format at 100') results in field in focus of 310' deep (99'-409')
Or put a 30mm f/2 lens on APS-C focus at 100' and you have an infinite field in focus of (49-Infinity)

[Curtis N]

These questions always result in argument, because you can't change camera formats and produce an identical image unless you also change the focal length. So let's lay down the proper parameters here.

1) If you compare the DOF of two camera formats without changing anything else (focal length, distance or aperture), the larger format will create an image with greater DOF. The hyperfocal distance from a 1.6x camera will be 1.6 times greater than the hyperfocal distance from a full frame camera. This is because the larger format camera will require less magnification to produce a print of the same size. But since the two images will have different fields of view, this is a pointless comparison.

2) If you compare the DOF from two different camera formats using lenses that generate equivalent fields of view (i.e. 160mm lens on a FF camera vs. 100mm lens on a 1.6x camera), The DOF from the larger format camera will be shallower than the DOF from the smaller format camera. The HFD of a FF camera will be 1.6 times greater than the HFD from a 1.6x camera. In this scenario, in order to create images with identical DOF, you need to use an aperture proportionally greater in the larger format camera. The following two scenarios will generate identical fields of view and identical depth of field:

36mm x 24mm camera format (full frame)
160mm lens
f/16

22.5mm x 15mm camera format (1.6x crop factor)
100mm lens
f/10

[TeeJay]

^^^

[timnosenzo]

Hmm, this is interesting. So with a lens like the 17-55 f/2.8 EF-S as compared to the 24-70 f/2.8 (which has a similar field of view), you will likely get a DOF equivalent more like an f/4 lens with the EF-S as opposed to the EF? Hope that makes sense (and not trying to start any arguments )

[Curtis N]

Originally Posted by timnosenzo

Hmm, this is interesting. So with a lens like the 17-55 f/2.8 EF-S as compared to the 24-70 f/2.8 (which has a similar field of view), you will likely get a DOF equivalent more like an f/4 lens with the EF-S as opposed to the EF? Hope that makes sense (and not trying to start any arguments )

There is no difference in the DOF from an EF-S lens vs. an EF lens at the same focal length when mounted on the same camera.

[timnosenzo]

Originally Posted by Curtis N

There is no difference in the DOF from an EF-S lens vs. an EF lens at the same focal length when mounted on the same camera.

I guess what I'm asking is, will a 17mm lens (on a crop body) @ f/2.8 have the same DOF at a 27mm lens (on a FF body) @ F/2.8?

[Curtis N]

Originally Posted by timnosenzo

will a 17mm lens (on a crop body) @ f/2.8 have the same DOF at a 27mm lens (on a FF body) @ F/2.8?

Nope. You'll get more DOF with the crop body and shorter lens. But if you stop down the 27mm lens on the FF body to about f/4.5 the DOF will be the same (2.8 * 1.6 = 4.5).

[djeuch]

Originally Posted by timnosenzo

I guess what I'm asking is, will a 17mm lens (on a crop body) @ f/2.8 have the same DOF at a 27mm lens (on a FF body) @ F/2.8?

If the post above is accurate, the 1.6x multiplier applies to both... so

17mm f/2.8 crop is
27mm f/4(.5) full frame.

So a 27mm FF at f/2.8 will have shallower DOF than you can achieve with a cropped sensor. (27mm f/2.8 would be a 17mm f/1.75!)

Mathematically speaking, of course.

[timnosenzo]

Pretty interesting, thanks guys!

[rkkwan]

Curtis is absolutely right.

Another example is the compact digital P&S. Most have f/2.8, but because the sensors are even smaller than APS-C (crop factor of ~6x), you can never get that shallow DOF shots with them.

[TMR Design]

It's very easy to get confused but I think I'm getting it.

This was all prompted by the recent thread with an 85mm f/1.2 L where it was said that the incredibly shallow depth of field created by that lens on a 5D could not be replicated on a 30D/40D.

[Ronald S. Jr.]

and they're correct, no?

[TMR Design]

Hi Ronald,

Now that I understand the concept and the mathematics... yes, they are correct.
This is something else I never considered in my "I don't need full frame" mind set.

I still don't need full frame but the more I understand the format and how lenses perform I do see some clear advantages to using full frame for certain types of work.