DOF FX vs. DX?

fishguy

All,

I have a question about depth-of-field. I've noticed that my new Nikon D800 has a much shallower DOF than my old DX D300. I knew this would be the case...however, I did NOT relaize that setting the apeture to gain more DOF causes the D800 to produce severe diffraction due to the high resolution.

DOF is pretty important for aquarium shots, what with moving fish, etc. Does anyone know - if I shoot the D800 in DX crop mode, will I regain that lost DOF? I tried some test shots, but it was inconclusive to my untrained eye.

If not, does in-camera downsampling improve DOF at all?


Thanks,

~Fishguy

Msmoto

@ fishguy

Yes, if you shoot in DX crop mode and use a shorter focal length lens, it will be the same as using that lens on the D300.

As to aquarium shots...I used a 16-35mm f/4 VR on a D4 for these:

http://www.flickr.com/photos/fantinesfotos/sets/72157630874292652/

Admittedly, ISO 10,000, but the results were not too bad. At f/4, I had a reasonable DOF, and this was in lighting conditions which were horrid. My thoughts on this, if I wre to do it again, would be to use an LED source (no heat) above and to one side of the camera. All the above shots were done holding the lens right up to the aquarium "plastic". I think it was about one inch thick.

sevencrossing

">...however, I did NOT realize that setting the aperture to gain more DOF causes the D800 to produce severe diffraction due to the high resolution.
~Fish Guy

Have you actually experience any severe refraction or just read about it
Which lens and f number are you using ?
downsampling should not have any significant effect on DOF

TaoTeJared

I think you have a misunderstanding of what diffraction is - the D800 is not "severe" at all and the D300 will shot it in the same f-stops as the D800. I really notice diffraction at f22+. (I have both camera's as well.) If you are shooting at any angle to the tank, the diffraction of the aquarium glass and water will introduce diffraction. None of it though is what you are describing. Can you post a few example images (full size) so we can see what it is?

ChromiumPrime

Short answer: Yes, switching to DX mode should give you the same DOF effect that you used to get with the D300.

Long answer: DOF depends only on three main variables which are FL, f/stop and subject distance. Sensor size by itself has no bearing on an image's DOF. Yet the reason we see a difference between FX and DX DOF is because we usually compare shots that have the same framing. In other words, if we take the same shot with two cameras, one DX and one FX, from the same spot and of the same subject using the same FL and f/stop then we end up with the same DOF in both shots. However, the framing of the two shots will be different with the FX obviously being a wider shot. So the moment we try to match the framing of the two shots, we also end up changing at least one of the variables that affect DOF and therefore end up with more/less DOF.

I won't try to get into diffraction as there are many split opinions on this but ask yourself this, for the purposes that you're going to use the shots for, is diffraction going to be really that noticeable in the final shot and the way it will be used/displayed?

Off topic:

@sevencrossing

If there are no spelling or grammar mistakes in the above,
it's a forgery.
FX forever!

Here, fixed it for ya :-B )

Paperman

@fishguy

The D800 technical user manual suggests not stopping down beyond f8 to stay below diffraction limits.

You must decide what is more important to you - the DOF or IQ . I don't think the effects of diffraction would be that visible to the eye as lack of DOF would be.

By the way, where do you find the light to take shots at f11 and above + decent speed to freeze action in aquarium shots ? .

spraynpray

@ChromiumPrime: Wassup bro, British humour too dry for you (sevens footnote)? :P

fishguy

Thanks all.

@paperman - DOF is of primary importance for me. The shots I need are "specimen IDs" and need to show the whole animal, side view, center framed, all in focus. No art to it - just a technical product photo. I use a SB-600 flash on an off camera sync cord and hold it off to one side to reduce glare off of the tank glass. Also - I need to take macro shots of insects, and run into the same issue there.

Benji2505

Little OT: For shots in any water glass container it usually helps to point the flash straight into the basin (90 degree angle) From the side. For me two flashes from right and left or two flashes, one from front and one from right worked well. Depending how much power your flash has you can go very low with the f-stop.

TaoTeJared

Fishguy - what setting are you normally shooting at that you are seeing issues with?

ChromiumPrime

@spraynpray Nah, just donning my grammar police hat just to be a pain )

And while I'm at it... it's "What's up brother? Is British humour too dry for you (seven's footnote)?"

:P

Gareth

dx mode is just cropping. you may as well just use a wide lens and crop to your needs.

roombarobot

Here is a great video from That Nikon Guy demonstrating depth of field vs. sensor size:
Sensor size and depth of field

And another one from him on the same topic:
Bokeh, depth of field and sensor size

They are very clear and helped me understand what is really going on.

spraynpray

Good God that bloke is such a Canon Fanboy! Anyway; his depth of field video is just going to confuse newcomers. To say that the dof is the same because if you change bodies onto a lens in the same location at the same focal length then compare the shots is ridiculous - if you are taking a shot, the composition of that shot - be it a portrait or a landscape or any other genre - is going to mean that you change focal length or physical location to regain the desired composition. When you regain the composition, what happens? the depth of field changes. That blokes brain is wired bass-ackwards.

Msmoto

This is so simple...DOF is dependent on focal length, aperture, and subject distance. When we change the area on the sensor, there is no difference in DOF, just like cropping in post processing does not change DOF.

Now, apparent DOF, when we take a 4"x6" print and enlarge to 20"x30" what we see is a degradation in the image, and the apparent DOF may change.

But, all of this is obvious only to folks who ave been hanging around behind a camera for some time. Beginners may get confused as spraynpray has suggested.

And, after the canon cameras were pulled out, I lost interest... )

spraynpray

Exactly - it is like shooting in manual mode - beginners think it is hard but in reality, hard is trying to understand the complexity of a DSLR without that basic fundamental understanding.

ChromiumPrime

Thanks for the vids roomba! I found them to the point and easy to follow myself.

roombarobot

I think one important thing to remember is that while a lens on a crop sensor appears 1.5x longer, it is just a cropped image. The DOF does not decrease, it is the same DOF as the native focal length of the lens. The only thing that changes is the FOV.

Interesting thing, I tried this online depth of field calculator and it changes the DOF with sensor size. That's not right.

spraynpray

@Roombarobot & ChromiumPrime: Read this for a proper understanding:

http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

TaoTeJared

I think one important thing to remember is that while a lens on a crop sensor appears 1.5x longer, it is just a cropped image. The DOF does not decrease, it is the same DOF as the native focal length of the lens. The only thing that changes is the FOV.

Interesting thing, I tried this online depth of field calculator and it changes the DOF with sensor size. That's not right.

That is the same DOF calc I use and it is correct and DOF (the distance of focused area) does change with the sensor.

Some idiots out there use "DOF" instead of "bokeh effect" or "circle of confusion" and screw people up on this. They are usually trying to describe something that is not the distance of focus, and back into it so badly that it comes across that way. Their are even books that do this. It drives me batty.

If you want to test it for your self, pull a tape measure out and set up marks, and compare FX with DX sensors. You will see the difference and it will match that online calculator.
http://www.dofmaster.com/dofjs.html

@spraynpray - Nice link!

spraynpray

+1 Tao. What also drives me mad is people sticking to the correct technical explanation at the expense of clarity for those who have not yet fully grasped the concept. In my post (7 posts up) I try to get that point across. To an inexperienced reader, the correct answer causes confusion because nobody ever goes on to explain REALITY. 8-|

sevencrossing

I think a lot people get confused by the term "equivalent"
Equivalent means, equivalent fov, to a full frame lens, on a full frame camera
equivalent is always fov
equivalent never means dof

The focal length of a "standard lens" is approx the diagonal of the image
with Fx this is about 50mm 43.2666mm
with Dx this is about 35mm 28.3185mm

At the same f number,

A 35mm lens on a dx camera with give aprox the same filed of view as the 50mm lens on a FX camera but a greater depth of focus

put the 35mm lens on an Fx camera and you get a wider wider field of view ,than you would get with the 50mm and a greater depth of focus

put the 50mm on a Dx camera and you will get a narrower filed of view than with the 35mm and smaller dof

dof is not a step function, the image does not suddenly go out of focus, it gradually becomes blurd,

hope this helps

Msmoto

@ sevencrossing

Actually, when calculated as you have said, the diagonal, full frame "normal" lens is 43mm focal length, and on crop sensor, about 28mm is "normal".

If we go back to the 4"x5" format from the old days, we calculate even wider "normal" lenses based upon the 135mm as a normal in those days, the numbers are 36mm for full frame and 23mm for crop sensor.

This is a large part of the problem you are discussing, when folks use "equivalent" what does it actually mean?

Now...what is a "file of view"? LOL ) ) )

roombarobot

Are you all sure about that? As Msmoto says "DOF is dependent on focal length, aperture, and subject distance". if you just change sensor size and nothing else at all, you won't change DOF. DOF is set by the optics. The focal length of the lens doesn't really change when you put it on a DX camera. One can think of a crop sensor as just cropping out the center of an full-frame sensor. The DOF would stay the same, but the FOV shrinks.

Here is a good explanation of why many get this mixed up:
As sensor size increases, the depth of field will decrease for a given aperture (when filling the frame with a subject of the same size and distance). This is because larger sensors require one to get closer to their subject, or to use a longer focal length in order to fill the frame with that subject. This means that one has to use progressively smaller aperture sizes in order to maintain the same depth of field on larger sensors.
http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm

sevencrossing

Are you all sure about that? As Msmoto says "DOF is dependent on focal length, aperture, and subject distance". if you just change sensor size and nothing else at all, you won't change DOF.

correct
If you do not change the lens, then DOF does not change
but in order to get the same FOV you have got to change the lens
when going from fx to dx to get the same FOV you will need a shorter focal length, which will give you a greater dof

roombarobot

Exactly, if the only thing you change is the sensor, then the DOF does not change.

Then why in this DOF calculator if you change just the sensor size does it change the DOF amounts?
http://www.dofmaster.com/dofjs.html

On the other hand, if you change your lens or your distance from the subject to maintain the same FOV, then of course your DOF changes.