Which one produces shallower depth of field.....

[bartjeej]

My head hurts reading the replies, but here's what I know from experience, and I'm avoiding the DOF Calc.

If you use the same exact lens, and you shoot the subject at the same exact distance, DOF should be the same, but the APS-C will give a tighter crop. It's the same as if you shot it with the FF camera, and then just cropped in LR. DOF does not change just because you cropped the picture.

This is theoretically correct, but practically wrong. Only one point (or plane) is ever in focus; everything in front of it or behind it is technically OOF, however slight the difference. But, human vision and camera sensors can only resolve so much detail, which makes the zone in front of and behind the plane of focus seem focused too - simply because the OOF blur is so small that it seems sharp. Technically, "apparent DOF" would be a better term than "DOF". If you blow up the image - be it by cropping the image, or by using a longer equivalent focal length - the same amount of blur is going to be enlarged more. That means the area where the OOF blur is smaller than we can see (aka smaller than the circle of confusion) decreases, giving a shallower apparent DOF.

If you move positions (i.e. getting closer with the FF or moving further away with the crop) to get similar framing, then the DOF should be less on the FF, because you are now closer to the subject. The focal length and the physical aperture size has not changed. If, however, you grabbed a 75mm lens to shoot with the FF and a 50mm lens on the crop (assuming a 1.5 crop), and you kept distance to subject the same, then DOF will be driven by the physical aperture size, so if f/stops were the same (e.g. both 1.4), then the FF should have shallower DOF because 50/1.4=35.7mm vs. 75/1.4=53mm.

I think you're mixing up lenses and bodies here; the FF camera needs the 75mm lens to give the equivalent field of view to the APSC with 50mm. But yes, the longer absolute focal length coupled with the same f-number means a larger physical aperture opening, and since subject distance and equivalent focal lengths are the same, the FF body/lens combo will have shallower DOF.

That's the way I understand it, but actually don't really care, lol. I have the lenses I have (50/1.4 and 85/1.8 on FF and 22/2 on my EOS-M) and I like the look of these lenses a lot, so if I'm wrong, I'm wrong

Also, if "viewing distance" to the picture comes into play here, well then I'll just keep quiet. My viewing distance is just about always 2 feet (distnance from my chair to my monitor)

yup, the look is more important than being right or wrong
viewing distance... well that's a whole different matter, more related to output size (monitor or print size). So long as you're close enough to the image to see the maximum detail resolved by the monitor or print, it doesn't have any influence on DOF. If you get further, apparent DOF will become deeper, but that's true regardless of which camera/lens combo you used.

[edit]
for what it's worth flash, I also limited myself to the simple formula that Focal length / Physical aperture size = f-number, throughout this discussion. Bokeh... indeed let's not go there

 

[flash]

I'm just thinking aloud now.

Generally speaking, a larger sensor will give you shallower depth of field.

But if you only have one lens, and you want to do some street photography at night where you have to stay wide open, and you don't want to be constantly dealing with razor thin depth of field ... you're better off with a full frame sensor rather than a crop sensor because the crop sensor is going to have shallower depth of field than a full frame sensor.

nope

If the FRAMING OF THESHOT IS THE SAME (ie; you're standing furter back with the cropped sensor), then the smaller sensor will have more DOF.

IF YOU'RE STANDING IN THE SAME SPOT (ie: you're ignoring the differences in framing) the smaller sensor will have less DOF.

Could be worse. It could be confusing......

Gordon

 

[TraamisVOS]

So it's all moot because if you're street shooting at night, you'll never know where you're going to be standing in relation to the subject matter if we're talking about spontaneous opportunistic street photography?

 

[bartjeej]

So you scenario is this:
-you have a 50/1.4 lens on your body.
-you run into a subject, you aim, you shoot; no time to change your position relative to the subject or to change lenses.
-you really want to use the maximum 1.4 aperture in order to maximize shutter speed or minimize ISO.
-you want the deepest DOF possible to increase the chances of getting your subject in focus.

Then yes, go for the largest sensor possible. It'll have the deepest DOF (as well as the widest field of view).

 

[TraamisVOS]

That's quite counter-intuitive and that is why it screwed with my brain for months.

 

[Luckypenguin]

This topic is like the average University subject: plenty of theory but minimal real world application. I dare you to try using the same lens on different formats and NOT be influenced by the different fields of view.

 

[wt21]

This topic is like the average University subject: plenty of theory but minimal real world application. I dare you to try using the same lens on different formats and NOT be influenced by the different fields of view.

I've done the DOF calcs, but a few years back when I was moving from a Canon 400D (APS-C 1.6 crop) to a 5D classic (FF), I ran them side by side in the same way you are mentioning, and with the same lenses as well as equivalent lenses. The FF always came ahead in obtaining more background blur, which looking back I suppose I attributed to shallower DOF, though someone might now tell me I'm wrong, lol.

Another thing about FF, for some reason, it always seems easier to get that "3D" look. There's a topic! Talk amongst yourselves

 

[TraamisVOS]

Hah yeah that's why I wanted to conceptualise it in my mind rather than plugging the figures into the calc and getting a number back.

 

[TraamisVOS]

Another thing about FF, for some reason, it always seems easier to get that "3D" look. There's a topic! Talk amongst yourselves

But that comes down to depth of field and that would bring us back to where we started.

 

[TraamisVOS]

 

[wt21]

OK, I peeked at the DOF calc, and there it is in B&W. same FL, same aperture ratio, same distance, narrower DOF on crop. But, in reality, you step back with the crop, because nearly all the time, you are working to the framing you want. When you increase the distance to the ratio of the crop (i.e. 1.5 crop, increase the distance 50%), then you DOF for the APS-C gets bigger than that of FF for the same lens and same f/stop. I guess I always modulated distance to subject, as it's framing I'm after.

Interesting, but maybe not field relevant most of the time.

 

[TraamisVOS]

But, in reality, you step back with the crop, because nearly all the time, you are working to the framing you want.

In practice I don't really do that though. I just snap a photo when and where I can. I take a lot of photos of my cats and dog for example, there is no time or space to reframe a shot when you're dealing with animals.

 

[wt21]

In practice I don't really do that though. I just snap a photo when and where I can. I take a lot of photos of my cats and dog for example, there is no time or space to reframe a shot when you're dealing with animals.

You do frame, though. If you had a FF, you would get closer. If you were shooting APS-C you would move back. You just do it naturally, unless you are really looking for a picture of just the nose and left eye. But if you were looking for that with FF, you'd use a longer lens or get closer. Or if you are shooting crop, would ask around and buy a shorter lens. We see that all the time on DSLR boards. People asking about what 35mm to get for their crop once they realize the 50mm nifty fifty is too long for indoor shooting. We all shoot to framing.

You have to, otherwise you end up with pictures you don't like.

 

[TraamisVOS]

A lot of the times I don't frame. It's opportunistic photography.

Take this photo for example, taken at the park a couple of hours ago. I wouldn't have had enough time to get closer and I didn't want to disturb little exchange between my dog and the other dog.

 

[flash]

A lot of the times I don't frame. It's opportunistic photography.

Now this is a far more interseting topic than DOF. Does James frame? Or doesn't he?

I think you do, but on an instinctive level. It may not be concious but you're aware of the focal lengths you have available and you "see" the world that way.

Oh, and I love that shot. The tree, the perspective of the people. Very interesting.

Gordon

 

[TraamisVOS]

(I cropped it)

 

[TraamisVOS]

Here's the original uncropped unprocessed photo in all its glory from where my stationary lazy ass took the photo.

 

[wt21]

James, I just think you are over-thinking it. (and btw, love the shot)

This shot was taken with a wide angle at a great distance, so DOF is, speaking practically, irrelevant. You would need some examples that are closer to your issue. Having said that, what if you had a big telephoto, and you could only get one dog? The answer is, you wouldn't have this shot. Period. Instead, you shoot wide and crop. That's fine, but DOF doesn't come into play.

If you don't have the right lens for the right moment, and if the moment is fleeting, then you simply don't get the picture. Period. Comparing a 50mm lens on APS-C vs. FF is not the right comparison. You need to compare the same Angle of view, if distance must be held constant. So, the proper compare is 35mm on APS-C vs 50mm on FF. If you walked around with a 50mm or 85mm on your crop, you might eventually conclude "I need something wider" wheras maybe the 50mm would work fine on a FF rig.

I think for what you shoot, the more proper decision points are DR, ergos, ability to shoot from waist level (or other than eye level), and size. Maybe AF speed or easy MF, too. And then get the lens that gets you the all-purpose FOV that you need. But someone like Ray would know better than I, as I'm not much of a street shooter.

Just my 2 cents.

 

[Luke]

Now this is a far more interseting topic than DOF. Does James frame? Or doesn't he?

I think you do, but on an instinctive level. It may not be concious but you're aware of the focal lengths you have available and you "see" the world that way.

I agree 100% with Gordon here. I've seen enough of James shots to know that he "sees" the shot. If you started using a different sized sensor, you would need a short period of adjustment, but suddenly you either start getting further (I think it's further.......I haven't had my morning coffee yet) from your subjects to get the kinds of shots you naturally take or you'd get shots you didn't like.

 

[Armanius]

Who would win a fight between a shark and a crocodile?

How funny!! I just watched this whole episode on TV about Crab Island that showed encounters between crocs and sharks! On shallow water, the crocs win. On deeper waters, the sharks wins.

Feeling like Cliff Clavin now.