F stop & DOF on aps-c

Merlin5

Merlin5

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Hi guys. I'm not a beginner though this probably might be seen as a bit of a beginner's question. I've been going out shooting photos, often at f5, or 6.3 or 7.1 thinking that's what my DOF will be. And often I sacrifice light because of these f stops and end up with a higher ISO. But I guess that's a mistake.

Since each f stop is multiplied x1.5 because of it being aps-c, then if I want a DOF of say f7.1, should I set my aperture to f4.5 which x1.5 is 6.75, or f5 which x1.5 is 7.5? Then I'd get more light onto the sensor with a faster f stop while still getting the equivalent DOF of a smaller f stop?
 
The whole point of f/stops is that they are independent of both lens and sensor. F/8 on a large format camera is f/8 on a medium format camera is f/8 on a "full frame" camera is f/8 on an APS-C camera.

As far as depth of field is concerned, to produce a print that is the same size, an APS-C image needs to be enlarged 1.5 times as much as a "full frame" image does and this increased enlargement decreases the depth of field in the print. To keep the depth of field the same, you need to multiply the f/number by 1.5 so to produce the DOF of f/8 on "full frame" camera you need an f/number of f/12 on an APS-C camera. To compensate for the reduced light, you need to decrease the shutter speed or increase the ISO setting.
 
john.margetts said:
The whole point of f/stops is that they are independent of both lens and sensor. F/8 on a large format camera is f/8 on a medium format camera is f/8 on a "full frame" camera is f/8 on an APS-C camera.

As far as depth of field is concerned, to produce a print that is the same size, an APS-C image needs to be enlarged 1.5 times as much as a "full frame" image does and this increased enlargement decreases the depth of field in the print. To keep the depth of field the same, you need to multiply the f/number by 1.5 so to produce the DOF of f/8 on "full frame" camera you need an f/number of f/12 on an APS-C camera. To compensate for the reduced light, you need to decrease the shutter speed or increase the ISO setting
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Oh, that's different from what I hoped to hear. So f12 to get f8 depth of field. And f6 to get f4 depth of field, is that right? Except I don't have f6, I have f6.3. What about my fastest lens aperture of f1.4, does using that give me about f0.95?
 
Best bet is to shoot a series of images at assorted aperture settings and see what gives you the DoF etc. that you're after.
 
john.margetts said:
The whole point of f/stops is that they are independent of both lens and sensor. F/8 on a large format camera is f/8 on a medium format camera is f/8 on a "full frame" camera is f/8 on an APS-C camera.

As far as depth of field is concerned, to produce a print that is the same size, an APS-C image needs to be enlarged 1.5 times as much as a "full frame" image does and this increased enlargement decreases the depth of field in the print. To keep the depth of field the same, you need to multiply the f/number by 1.5 so to produce the DOF of f/8 on "full frame" camera you need an f/number of f/12 on an APS-C camera. To compensate for the reduced light, you need to decrease the shutter speed or increase the ISO setting.
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Merlin5 said:
Oh, that's different from what I hoped to hear. So f12 to get f8 depth of field. And f6 to get f4 depth of field, is that right? Except I don't have f6, I have f6.3. What about my fastest lens aperture of f1.4, does using that give me about f0.95?
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Brain melting madness. IMO.

Best keep it simple.

If you use equivalent lenses on FF and APS-C for example 50mm on FF and 35mm on APS-C you can indeed use wider apertures on APS-C and get the same DoF for the same framing.

For example FF f8 and 50mm will be about the same DoF as APS-C 35mm and f5.6. You'll be shooting from about the same distance (lets not nit pick the differences in APS-C chip sizes, lets stick to x1.5, and lets not nit pick the differences between f5 and f5.6...) but using a wider lens with wider aperture. And as a bonus you get to use a faster shutter speed or a lower ISO with APS-C because you're using a wider aperture but getting decent DoF as you're using a wider lens.

Here's another way of looking at it.

FF 50mm f8 how big is your aperture? Answer = 50mm/f8 = 6.25mm.
APS-C 35mm f5.6 how big is your aperture? Answer = 35mm/f5.6 = 6.25mm.

Making sense?

Image quality equivalence makes sense if you look at focal length and aperture and ISO and adapt and change the settings you use. FF will give better image quality than APS-C but you can claw back some of the difference by using a wider aperture with possibly a lower ISO.

MTF, even easier as it's x2. FF 50mm f8 = MFT 25mm f4.

The only time you get less DoF from a smaller system and would need to stop down the smaller system to get more DoF would be when using the same lens as on FF at the same distance, and you'd get different framing. ie. FF 50mm and APS-C 50mm from the same distance and with different framing.
 
@Merlin5

This DoF calculator https://www.dofmaster.com/dofjs.html

Will show you in measurement terms the DoF when using FF, crop, mFT etc sensor bodies with whatever lens and chosen aperture. As for the bokeh IMO that is where you may likely need to take some example images...... bearing in mind that bokeh is not just about the DoF but also "how far back" the background objects are beyond the outer limits of DoF to be OOF nicely in the bokeh!
 
Box Brownie said:
@Merlin5

This DoF calculator https://www.dofmaster.com/dofjs.html

Will show you in measurement terms the DoF when using FF, crop, mFT etc sensor bodies with whatever lens and chosen aperture. As for the bokeh IMO that is where you may likely need to take some example images...... bearing in mind that bokeh is not just about the DoF but also "how far back" the background objects are beyond the outer limits of DoF to be OOF nicely in the bokeh!
Click to expand...

Thanks Box! Actually, my Sony a6600 isn't in the list on that calculator site.

woof woof said:
Brain melting madness. IMO.

Best keep it simple.

If you use equivalent lenses on FF and APS-C for example 50mm on FF and 35mm on APS-C you can indeed use wider apertures on APS-C and get the same DoF for the same framing.

For example FF f8 and 50mm will be about the same DoF as APS-C 35mm and f5.6. You'll be shooting from about the same distance (lets not nit pick the differences in APS-C chip sizes, lets stick to x1.5, and lets not nit pick the differences between f5 and f5.6...) but using a wider lens with wider aperture. And as a bonus you get to use a faster shutter speed or a lower ISO with APS-C because you're using a wider aperture but getting decent DoF as you're using a wider lens.

Here's another way of looking at it.

FF 50mm f8 how big is your aperture? Answer = 50mm/f8 = 6.25mm.
APS-C 35mm f5.6 how big is your aperture? Answer = 35mm/f5.6 = 6.25mm.

Making sense?

Image quality equivalence makes sense if you look at focal length and aperture and ISO and adapt and change the settings you use. FF will give better image quality than APS-C but you can claw back some of the difference by using a wider aperture with possibly a lower ISO.

MTF, even easier as it's x2. FF 50mm f8 = MFT 25mm f4.

The only time you get less DoF from a smaller system and would need to stop down the smaller system to get more DoF would be when using the same lens as on FF at the same distance, and you'd get different framing. ie. FF 50mm and APS-C 50mm from the same distance and with different framing.
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Thanks Alan. Yep, makes perfect sense. And what you detailed was what I had thought. That whatever f/stop I use, I multiply it by 1.5 to get the FF equivalent or near enough. Meaning, just as you said, I can use faster aperture, faster shutter and lower ISO.
 
Merlin5 said:
Thanks Box! Actually, my Sony a6600 isn't in the list on that calculator site.
Click to expand...

Hmmm! all APS-C sensors are the same size...........perhaps just pick the nearest Sony model to the A6600 with the same sensor!
 
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Box Brownie said:
Hmmm! all APS-C sensors are the same size...........perhaps just pick the nearest Sony model to the A6600 with the same sensor!
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All APSC sensors aren’t the same size!
But the OP can pick a different Sony or Nikon APSC camera because they are the same size.
 
All the APS-C bodies but the canon ones are same size because they all buy sensors from Sony anyway :p
Not entirely true because Samsung for example made their own sensor but it was the same size as Sony sensors.

Sony sensors have a 1.52x crop and canon ones have 1.6x crop. Makes a tiny bit of difference to your DoF calculations but IMO not enough to lose sleep over it especially when you are trying to maximize your DoF.
So pick any APS-C body and it'll be fine IMO.
 
john.margetts said:
The whole point of f/stops is that they are independent of both lens and sensor. F/8 on a large format camera is f/8 on a medium format camera is f/8 on a "full frame" camera is f/8 on an APS-C camera.

As far as depth of field is concerned, to produce a print that is the same size, an APS-C image needs to be enlarged 1.5 times as much as a "full frame" image does and this increased enlargement decreases the depth of field in the print. To keep the depth of field the same, you need to multiply the f/number by 1.5 so to produce the DOF of f/8 on "full frame" camera you need an f/number of f/12 on an APS-C camera. To compensate for the reduced light, you need to decrease the shutter speed or increase the ISO setting.
Click to expand...

This confuses even me. I don’t understand how Depth of Field ie the focus plane can change in printing. Surely what’s in focus when the photo was taken stays in focus. You can’t make blurred areas sharp later.....can you?

I’ve always thought depth of field is dependent on both the aperture and focal length. This is where it gets confusing comparing the two as focal length are multiplied by the crop factor (1.5 or 1.6).

I’ve always thought the benefit of full frame was the shallower depth of field. Therefore crop sensors should have a longer focal plane but it gets confusing when equivalent field of view comes in.
A few years back when I had both a full frame and crop camera I tried to test it briefly myself. 300mm full frame and 200mm crop. Both at f5.6.

D71_8462 by -Rob - Nikon-

DSC_9172 by -Rob - Nikon-

This was my only workable test as I didnt have a stuffed squirrel!
 
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rob-nikon said:
This confuses even me. I don’t understand how Depth of Field ie the focus plane can change in printing. Surely what’s in focus when the photo was taken stays in focus. You can’t make blurred areas sharp later.....can you?
Click to expand...

Depth of field and equivalence are difficult things to talk about as people usually introduce different things and go on at cross purposes and it usually all ends up in a complete mess but if I can say for a moment.. it doesn't really all change with printing or how closely we look... it's all always there but sometimes we perceive it differently.... The depth of field is set when you pick up the equipment, set the focal length and aperture and position yourself at point A to take a picture of something at point B with something else at point C, D and E and so on. It's all there and it's all set and all you can do is reveal it by printing BIGGER or smaller or looking more closely or not.

Think of a portrait at wide aperture. One eye is sharp and the other isn't. If we print the picture the size of a postage stamp and look at it at arms length both eyes may look sharp but if we print the exact same picture at A3 and look at it at arms length we can easily see that one eye is soft. If we then put down the A3 and pick up the postage stamp and look at it through a magnifying glass we'll see that the eye that we thought was sharp isn't and that both the stamp and the A3 pictures are exactly the same and it's not that we've actually changed things by altering the print size but we have made the fact that one is is soft easier to see.

I hope that makes sense :D
 
rob-nikon said:
This confuses even me. I don’t understand how Depth of Field ie the focus plane can change in printing. Surely what’s in focus when the photo was taken stays in focus. You can’t make blurred areas sharp later.....can you?
!
Click to expand...
Depth of field and focal plane are two entirely separate things.

If your image is well focused, all on the focal plane will be in focus. The rest will not be. The depth of field is the range of out of focus that our eyes cannot detect so it looks the same as being in focus. If you enlarge the image more, our eyes can detect more of the out of focus parts as being out of focus - so, the more you enlarge an image the shorter the depth of field.
 
A big influence on dof is distance from the subject. Which is why a dof calculator can be useful. Maybe more so when doing close up work such as macro or flowers etc.
 
Phil V said:
All APSC sensors aren’t the same size!
But the OP can pick a different Sony or Nikon APSC camera because they are the same size.
Click to expand...
Doh! In my haste....... it was kind of late ;) I forgot about the 'differences' in crop sensor sizes!

Though I did say he should choose another similar Sony.........not a Canon or Nikon.......;)
 
And also but not really on point... but just out of interest... :D For most of photography's history haven't people usually been fighting for more DoF not less? :D
 
The DOF at a given f-stop at a given focal length is the same, regardless of sensor size. However DoF changes with lens focal length so for the same field of view you use a shorter focal length lens on a crop sensor than on a "full-frame" sensor. E.g. 35mm on APS might be equivalent field of view to 50mm on full-frame. So on APS you get 35mm DoF and on FF you get 50mm DoF but if you put a 35mm lens on an FF camera you get the same DoF
 
Just a point of clarification - the aperture ("f-stop") is not a measure of the depth of field, but it is an indication of what the depth of field will be.

I agree that for a (relative) beginner a DoF calculator would be a good idea. In days gone by and with fixed focal length lenses there was a depth of field scale marked on the lens barrel which gave you a measure of what the DoF would be at any particular aperture. Not sure if modern lenses have this?
 
Depth of field is a nightmare because it depends on the aperture, focal length and distance from subject etc....

With a zoom its even more of a nightmare, with a prime lens you have a chance to have a ball park idea of DOF with experience or study charts for that focal length.

Even with a DOF calculator you need to know the distance and that is not an easy thing to know unless you carry a laser range finder in your pocket.

Many photographers dont actually know what DOF they will get, especially if using full auto modes and DOF previews are not great in my experience.

The best thing i seen was expensive Sony lenses that had a digital readout telling you DOF in front and behind subject.
 
jerry12953 said:
Just a point of clarification - the aperture ("f-stop") is not a measure of the depth of field, but it is an indication of what the depth of field will be.

I agree that for a (relative) beginner a DoF calculator would be a good idea. In days gone by and with fixed focal length lenses there was a depth of field scale marked on the lens barrel which gave you a measure of what the DoF would be at any particular aperture. Not sure if modern lenses have this?
Click to expand...

Some do but a lot and probably even most new AF lenses will be fly by wire and lack all markings.

There are modern manual focus Voigtlanders and you can buy a new one today :D

wIZIoC4.jpg
 
sirch said:
The DOF at a given f-stop at a given focal length is the same, regardless of sensor size.
Click to expand...

The DOF on the sensor will be the same but not the DOF on a print (or computer screen) as that depends on the degree of enlargement as well.
 
Should we talk about Circles of Confusion, or would that just confuse everybody - or even circle them?
 
Boots said:
Should we talk about Circles of Confusion, or would that just confuse everybody - or even circle them?
Click to expand...
The circle of confusion is a group of photographers sitting in a circle, talking about depth of field . . .
 
All this talk of DoF just reminds of my old EOS650 35mm film camera and its A-Dep setting.................focus on the nearest you wished to be in focus, then of the farthest away point, finally focus on the subject and fire the shutter. At the time I thought what an innovation, even though I had a good understanding of "f" number/aperture choice and the DoF I wanted so never really used the A-Dep mode.
 
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