A  month or so ago I stumbled onto a internet thread over the introduction of the then new Nikon D2X.  Yeah I know, the article was a bit out of date, but . . .  How I got to this thread is a bit of a mystery to me (riding an internet wave too far I guess).  In the thread one of the main contributors (a very self convinced person) and what he had to say is the reason that I chose to write this blog entry.  So here I go, let’s just hope this doesn’t turn into my rant.

Throughout the thread there were the usual pros and cons being discussed about the D2X and it’s merits or lack of.  As I said above, one of the lines in the thread, really got my interest.  This line involved the thoughts of a person who worked for a company (undisclosed) doing some kind of photographic work for them (again undisclosed).  The company had recently (most likely within the previous two years) invested twenty three thousand dollars in photographic equipment (Nikon and digital).  The person to whom I am referring to, convinced the company to sell off this fairly new equipment at a loss of sixteen thousand dollars and buy the Canon EOS 1Ds Mk II and associated lenses and accessories.  This new investment (and the substantial loss) was predicated on the fact that the “full 35mm frame” of the Canon would yield better control over the DOF (depth of field) from the APS size sensor in the NIkon.  This person really came across as being very self convinced and had put up some pretty good sounding arguments when questioned by the others.  The main argument that he was trying to get across, was that sensor size of the D2X (and all other APS size sensors or smaller) dictate that there is too much DOF and consequently, nearly uncontrollable.

Since I teach my basic photography class that the two most important things to remember about controlling the DOF is in the aperture opening and more importantly in subject magnification, I had to look into this.  Also I happen to be someone who mostly shoots at wide apertures and had by this time shot with the D2X for enough time to know the camera and assess this problem.  The same D2X (DX/APS) is still in my possession as is a D3 (FX or full 35mm frame), thus I could put the two cameras to the test and find out for myself.  Despite having a pretty good idea what the results would be, I still tried to enter into the test with an open mind.  Again I feel that it is subject magnification that limited DOF most comes into play.  Whether it be by being close to the subject or using longer focal lengths to achieve “closeness” to the subject.  And of course the aperture opening.

Before I go any further, let me I say that I am not trying to champion the cause for Nikon here.  Quite the contrary I love the idea of competition between manufactures, regardless of what they make.  In the case of Canon vs. Nikon (and now Sony) they keep improving upon their products and we as end users and consumers benefit form it.  What I am trying to do, is to say that the question of  the DOF difference between sensors sizes is not that black and white.

Admittedly my testing has it’s flaws from a technical testing standpoint.  You will not see MTF charts or focusing charts, etc.  That sort of testing I leave to others who are better qualified.  However I feel that a few flaws and an absence of charts in the testing is more like “real life” and gives us a better idea how different equipment functions in the “field”.   One evident fault in my testing that could be pointed out, is that the focusing was done fairly close up to the subjects.  This was due on account of the limitations of this blog and to make viewing easier.  Also for the most part (with the exception of the 300mm test) the cropping would be similar to a tight head shot.  Though being this close, shortens the DOF considerably, it still shows the comparative depths of field of both sensor sizes.

With the exception of the last series of tests, the cameras were both mounted on a tripod and left in the exact same position.  Mirror lock-up and a cable release were utilized for accuracy.  Both cameras were shot at their native ISO’s (100 iso on the D2X and 200 iso on the D3).  Some cropping was done in post (where noted) for better viewing, again as my blog site is not set-up for larger images to be shown.  Anyway have a look at these tests with an open mind and see for yourself.

For the first  part of the test, I chose a 80-200mm AF-D f/2.8 Nikkor lens.  With the aspect ratio difference of 1.5 between the D2X and the D3, I decided to make life easier for myself, by using an easy number to start the test.  First thing was to shoot both cameras at 150mm and then change the lens to 100mm and shoot the test scene again with only the D2X.  This was done so as to give the same angle of view for both cameras (sensor sizes).  To me the angle of view is not the same as subject magnification.  The APS size sensor will be referred to as DX in the test shots and FX will be used to denote the “full 35mm frame” test shots.

In the second round of tests I employed the use of the 80-200mm, set at 200mm, on the D2X and on the D3, a 300mm f/4.0 AF-S (simple arithmetic again).  Just another attempt at getting the same angle of view.  The second round also includes both cameras with the 300mm lens from the same camera position.  With a cropped FX version for easier viewing and an uncropped FX version.

For the last test I decided to go with two different lenses that both have a maximum aperture of  f/1.4. The 85mm and 50mm Nikkor lenses.  On this test I did move the D2X with the 50mm on it to within a distance to replicate the same angle of view as the 85mm on the full frame D3.  With this set-up I went form f/4, to f/1.4 in increments of one stop.  The last shot on this series is the 85mm now mounted on the D2x (DX camera).  Which was moved to attain the same angle of view as it appears on the D3 (FX camera).

CONCLUSION

Does the larger sensor size offer less DOF / more back ground blur?  What we have found here, is that the issue is not really all that clear cut.  Using a shorter lens on the APS / DX  size sensor (giving the same angle of view), will indeed produce “more in focus” or deeper DOF (around 1 to 1 1/2 stops worth).  This is of course attributable to the shorter focal length required to overcome the aspect ratio difference and achieve the same angle of view.  The same could be said, if a shorter focal length lens is used on the same camera (whatever the sensor or image plane size is).  Of course this applies equally to the reverse situation, needing a longer focal length.   Using the exact same focal length on both sensor formats, results in either the same DOF or possibly a little less or more, but certainly not enough to warrant selling off a camera system.

The quality of the lens and how it renders the out-of-focus areas also plays a big part in the perceived DOF.   I think this can be seen and compared best, in the case of the 300mm vs. the 200mm and again with the 85mm vs. the 50mm.  Some lenses render the out-of-focus area with an edge around high contrast areas, making it appear that they are less out-of -focus.  The better lenses will provide good contrast in the “focused area” and lowering of contrast in the “out-of-focus areas” making for a smoother transition and a “creamy” look, which creates good “bokeh”.  Stronger contrast always appears “sharper” then lower contrast.

So either using a longer focal length or moving closer to the subject or employing wider apertures can be used with a great deal of effectiveness in both formats.  Even in regards to the very small sensor formats found in the point and shoot cameras (though the problem of overcoming the aspect  ratio differences there is somewhat harder).  On the other hand and something the “thread contributor” did not mention, was when there is a need for more depth of field.  Knowing how to achieve both limited and deeper DOF are both important disciplines to learn in photography, as different situations require.

The last thing that can be learned is simply to know your equipment and how to use it for the effect you want.  Though I guess that can be said about most things in life.

Coming up next:  After performing the above test, I was once again impressed with the Nikkor 300mm f/4.0.  So I will be writing up my impressions with a number of examples, from both formats.