Difference in aperture and sensor size - anyone willing to help

photoguy99 · Feb 8, 2015

I don't think you're thinking this through. Or we're taking past each other.

I do know that smaller sensors yield more dof when you use them to take the same pictures. But your example, as I read it, isn't that.

I'm taking about the same distance, same lens, same apertures scenario you mentioned, in which the fov changes but the bokeh 'remain the same'

Trever1t · Feb 8, 2015

Yeah, perhaps we're both saying the same thing....that if taken from a mount and the only change is FX to DX the ONLY difference at that point is the FOV

Sorry, I'm tired

photoguy99 · Feb 8, 2015

I'm totally agreeing with you!

I'm just adding on the caveat that you have to consider final output size.

Dave442 · Feb 8, 2015

Full Frame will help as already noted if you can move to keep the image filling the same percent of the sensor as it was filling on the DX sensor. The best gain that I see is if you go to FF and move the subject closer to fill the same amount of the frame, that gives the added bonus of decreasing the distance to the subject while at the same time increasing the distance to the background.

Now with the equine photography I expect you could be stuck with the camera to subject distance, but to fill the same amount of the sensor on the FX body then go to the 200mm f/2 lens and no more distracting background.

Also, in the original post the question was to compare a 135mm lens at f/2 on full frame and f/2.8 on crop sensor, I think the better comparison is to use f/2.8 on full frame and f/2 on the crop sensor, at least according to the article that Brian posted (but not according to my DOF calculator on my phone). Does this subject always have too many answers?

TCampbell · Feb 9, 2015

Photoguy is right. Try not to think of a lens so much as having a focal length... instead try to think of it as having an "angle of view".

If you shoot with a 135mm lens on a full frame body, then you've got a diagonal angle of view of about 15.2º.

If you shoot with a 90mm lens on a 1.5x crop factor DX body, then you've ALSO got a diagonal angle of view of the 15.2º.

Since the angle of view is the same, and if using the same f-stop, then the DOF will be the same.

ALSO... if you put the 135mm lens on the DX body (so now it's the same lens on both cameras), the DX camera will capture an angle of view of just 10.2º. But if you take the center section of the FX camera's image and crop that, then enlarge it to the same physical print size that you produced for the DX camera, then both cameras will be showing you a 10.2º angle of view and therefore the DOF will be the same.

If the "angle of view" is the same and the f-stop is the same... then no matter how you managed to achieve that result... the DOF will also be the same.

Overread · Feb 9, 2015

One day I'll get that fullframe camera and see all this for myself - my thanks for the input all! Guess there really is no solution (f2.8 to f2 might have some difference, but on its own I suspect not enough and I'd hate to go any smaller in aperture as depth of field on the horse would be far too think to work with in a showjumping scene.

Braineack · Feb 9, 2015

ignore most of his talk, it's complete bs, but this video does a good job showing what you want, i think.

Ysarex · Feb 9, 2015

TCampbell said:
Photoguy is right. Try not to think of a lens so much as having a focal length... instead try to think of it as having an "angle of view".

If you shoot with a 135mm lens on a full frame body, then you've got a diagonal angle of view of about 15.2º.

If you shoot with a 90mm lens on a 1.5x crop factor DX body, then you've ALSO got a diagonal angle of view of the 15.2º.

Since the angle of view is the same, and if using the same f-stop, then the DOF will be the same.

ALSO... if you put the 135mm lens on the DX body (so now it's the same lens on both cameras), the DX camera will capture an angle of view of just 10.2º. But if you take the center section of the FX camera's image and crop that, then enlarge it to the same physical print size that you produced for the DX camera, then both cameras will be showing you a 10.2º angle of view and therefore the DOF will be the same.

If the "angle of view" is the same and the f-stop is the same... then no matter how you managed to achieve that result... the DOF will also be the same.

Not quite right. If the angle of view is the same and the f/stop is the same then a smaller sensor camera will produce more DOF -- the circle of confusion for the smaller sensor is smaller. Between DX and FX sensors we're not talking a big difference.

Joe

TCampbell · Feb 9, 2015

Ysarex said:
Not quite right. If the angle of view is the same and the f/stop is the same then a smaller sensor camera will produce more DOF -- the circle of confusion for the smaller sensor is smaller. Between DX and FX sensors we're not talking a big difference.

Joe

Yep - good point. In the Tony Northrup video that Braineack linked above, he points out that it would become the same if you also multiply the f-stop by the camera crop factor when comparing it to a full frame (no crop factor) camera.

If you had a 1.4x crop-factor camera (nobody makes such a thing to my knowledge... Canon used to make a 1.3x and Nikon makes a 1.5x -- so those are both close) then by the math it would be a 1 stop difference in terms of how much blur you'd get. An APS-C camera is basically getting "about" 1 stop less worth of blur (or one stop more worth of DOF -- depending on how you'd prefer to think about it.)

Trever1t · Feb 9, 2015

That's what I've been saying this whole time

astroNikon · Feb 9, 2015

What subject distance are you looking for ?
but I don't have a fixed 135, but can get there with a 80-200/2.8 but then can't do f/2 @ 135.

Overread said:
One day I'll get that fullframe camera and see all this for myself - my thanks for the input all! Guess there really is no solution (f2.8 to f2 might have some difference, but on its own I suspect not enough and I'd hate to go any smaller in aperture as depth of field on the horse would be far too think to work with in a showjumping scene.

After all I read I was still amazed when I got my FF and compared it to the Crop. Especially for LowLight.
If I had a 135/2 I'd help. But other than f/2.8 80-200 @135
I only have a 50 or 85/1.8s to test the f/2 to f/2.8 on FF vs crop

The DOF calculators make more and more sense since I understand it more over time.

Trever1t · Feb 9, 2015

Final answer, FX is going to give softer, more blurred backgrounds if you crop in or get closer.

Dave442 · Feb 9, 2015

So the only thing that is confusing me is that when I use my DOF calculator on my laptop, if I select my D200 camera with the 135mm f/2.8 lens and 8 feet distance it gives me a far distance of 8.06 feet. With my sisters D700 and same settings it shows 8.09 feet. So the Full Frame gives more DOF while I thought it would be less.

photoguy99 · Feb 9, 2015

Identical lens and identical aperture, the FF gives more DOF because the assumption is that you'll be enlarging it less (larger "Circle of Confusion")

If you use an appropriately different lens and/or distance, to get the same picture out of the crop sensor, you'll find that you get more DoF from the small sensor at the same aperture. But that's a different situation. You're either using a different lens, at 8 feet, OR you're using the same lens and backing away from 8 feet.

DoF conversations are hard. Just shoot. And look. And internalize it.

Ysarex · Feb 9, 2015

Dave442 said:
So the only thing that is confusing me is that when I use my DOF calculator on my laptop, if I select my D200 camera with the 135mm f/2.8 lens and 8 feet distance it gives me a far distance of 8.06 feet. With my sisters D700 and same settings it shows 8.09 feet. So the Full Frame gives more DOF while I thought it would be less.

It's not a comparison if you don't take the same photo with both cameras. That means the same perspective and the same field of view at the same f/stop. In the comparison you have here the field of view changes due to the sensor size change -- those are two different photos. When you compare taking the same photo with both cameras you'll find more DOF from the smaller sensor. Put a 90mm on your D200 and run it again for a "same photo" comparison.

Joe