The way I understand it FF gives you a smaller DOF at the same focal length. So if I zoom to 17mm on my crop body and to 28mm on my FF camera, giving them effectively the same field of view, the FF will have a shallower DOF?
kdw75 said:The way I understand it FF gives you a smaller DOF at the same focal length. So if I zoom to 17mm on my crop body and to 28mm on my FF camera, giving them effectively the same field of view, the FF will have a shallower DOF?
kdw75 said:The way I understand it FF gives you a smaller DOF at the same focal length. So if I zoom to 17mm on my crop body and to 28mm on my FF camera, giving them effectively the same field of view, the FF will have a shallower DOF?
Sorry, that's not correct. Effective focal length doesn't matter - real focal length matters. In the situation you describe, the FF sensor would give shallower DoF.Tijn said:17mm f/2.8 on your crop body vs. 28mm f/2.8 on a full frame camera means the same aperture, same subject distance and the same effective focal length. Real focal lengths are different. Blur is the same for both in this situation - as I understand it.
Basically, there are four factors that determine DoF:kdw75 said:The way I understand it FF gives you a smaller DOF at the same focal length. So if I zoom to 17mm on my crop body and to 28mm on my FF camera, giving them effectively the same field of view, the FF will have a shallower DOF?
PaperTiger said:Just an aside as well that I think is interesting (something I spent some time investigating empirically and mathematically) is that depth of field is identical (for the same sensor) between lenses if the framing and aperture is identical.
The main reason that a larger sensor means shallower DoF is that for the same framing with a smaller sensor, you need to either be further from the subject, or use a longer focal length, either of which means deeper DoF.
Thanks for the explanation. I did put in the "as I understand it" because I wasn't totally sure.neuroanatomist said:Sorry, that's not correct. Effective focal length doesn't matter - real focal length matters. In the situation you describe, the FF sensor would give shallower DoF.Tijn said:17mm f/2.8 on your crop body vs. 28mm f/2.8 on a full frame camera means the same aperture, same subject distance and the same effective focal length. Real focal lengths are different. Blur is the same for both in this situation - as I understand it.
kdw75 said:Say I have two camera bodies that are 18 megapixel and both are using a 50mm lens. The only difference between the two is that one is FF and the other APS-C. I realize the borders would be cropped on the C but would the zoom be the same, or would things appear larger on the FF when viewed at 1:1 pixel size?
neuroanatomist said:Sorry, that's not correct. Effective focal length doesn't matter - real focal length matters. In the situation you describe, the FF sensor would give shallower DoF.Tijn said:17mm f/2.8 on your crop body vs. 28mm f/2.8 on a full frame camera means the same aperture, same subject distance and the same effective focal length. Real focal lengths are different. Blur is the same for both in this situation - as I understand it.
Basically, there are four factors that determine DoF:kdw75 said:The way I understand it FF gives you a smaller DOF at the same focal length. So if I zoom to 17mm on my crop body and to 28mm on my FF camera, giving them effectively the same field of view, the FF will have a shallower DOF?
- Aperture - wider means shallower DoF
- Subject distance - closer means shallower DoF
- Focal length - longer means shallower DoF
- Circle of confusion - smaller means shallower DoF
The main reason that a larger sensor means shallower DoF is that for the same framing with a smaller sensor, you need to either be further from the subject, or use alongershorter focal length, either of which means deeper DoF.
For example, say you put a 70-200/2.8 lens on an APS-C camera, set it to 125mm, and take a picture at f/2.8 of a model's head. Now you put that lens on a FF camera, and if you don't change anything else, you'd be taking a shot of the torso and head. To re-create the framing of the head shot, you have two options - stay in the same place and zoom the lens to 200mm, or leave the lens at 125mm and walk closer to the subject. Either way, you get a shallower DoF, based on points 2 and 3 above. To get the same DoF as you had with the APS-C shot, you'd have to stop down to f/4.5 on the FF camera (in addition to moving or zooming).
PaperTiger said:Just an aside as well that I think is interesting (something I spent some time investigating empirically and mathematically) is that depth of field is identical (for the same sensor) between lenses if the framing and aperture is identical.
Exactly, for the same reasons as above. Focal length and subject distance have equal and opposite effects, so if you're talking about same framing and same sensor, DoF is determined only by the aperture.
Read on if you have some tolerance for a detailed technical point that's not usually relevant in practical terms.
- Circle of confusion - smaller means shallower DoF
You may have noticed that I left this one out of the disucssion - the reason is that, as the term implies, it's confusing. In reality, if you hold the other three factors constant - same aperture, same distance, same focal length - and change only the sensor size, the APS-C sensor will actually produce a shallower DoF than FF (CoC is smaller for APS-C). Obviously, this is contrary to the conventional wisdom that FF means shallower DoF, but nevertheless, it's true (spend a little time with DoFMaster to convince yourself). The reason it's practically irrelevant is that you'd have a completely different framing, i.e. to expand the example above, if you frame the headshot on FF, then switched to APS-C and didn't move or zoom or change aperture, your DoF would be shallower - but the crop factor would give you an eyes-and-nose portrait instead of a head shot, and as soon as you zoomed out or backed up, your DoF would get deeper. The only place you really notice this is when testing a lens, e.g. for AF microadjustment. In that scenario, you shoot with the lens at a given distance independent of sensor size, and when you do that, you notice that DoF really is thinner with APS-C.
bainsybike said:The main reason that a larger sensor means shallower DoF is that for the same framing with a smaller sensor, you need to either be further from the subject, or use a longer focal length, either of which means deeper DoF.
shorter
Kernuak said:Maybe I'm just reading it wrong after a long day, but if you're referring to a full frame sensor, shouldn't it be closer to the subject or longer focal length?
neuroanatomist said:For the same framing using a smaller (APS-C) sensor, you need to be further from the subject, or use a shorter lens.
JonJT said:I'm going to try posting this again. Canon Rumors seems to be deleting my posts.
Anyway, FF sensors will have a shallower DOF for a given perspective and aperture. But, considering how small the DOF is with my crop camera and the fast lenses I have, I have no need for the even smaller DOF a FF sensor would provide me. I don't really see FF as having an advantage in this regard.