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02/01/2009 06:49:30 AM · #51 |
Originally posted by Chinarosepetal:
Using a DOF calculator with those figures the values are different :) |
By very, very little. Other variables are in play that we have only touched on. The difference is not substantial enough to make the case for the 100mm as having "more DOF" at 1:1... The key is that the analysis that counts is the one performed by the human eye/brain, not the one that's calculated. Also, I have seen different results from different DOF calculators. In no case have I seen a difference of more than a few hundredths of an inch.
R.
Message edited by author 2009-02-01 06:56:46.
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02/01/2009 06:53:27 AM · #52 |
Originally posted by Artifacts:
Correct me if I am wrong... but here is what I am testing:
Hypothesis:
At 1X magnification (1:1 life size) at the same f/stop, DOF for the 100mm macro and 180mm macro lenses are identical
The Test:
Both lenses will shoot the same scene with the same camera. Their primary subject will be at the 1:1 (life sized) distance - i.e. the distance from focal plane to subject; approximately 12" for the 100mm and 19.5" for the 180mm. Pictures will be shot at the same f/stop setting and lighting conditions. This process will be monitored by an unbiased and knowledgeable 3rd party observer to be sure the testing requirements are properly met.
DOF is subjective so the actual results will be posted and viewers can decide for themselves. |
Add to your criteria that the point of focus has to be the same. and you have to be shooting from the same angle. That is to say, if you're testing on a ruler at a 45-degree angle, you should be focusing on the same inch marking and you need to move the camera closer/further (to attain 1:1) by moving it along the lens axis. Easier said than done :-)
R.
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02/01/2009 07:20:06 AM · #53 |
Originally posted by Bear_Music:
Originally posted by Artifacts:
Correct me if I am wrong... but here is what I am testing:
Hypothesis:
At 1X magnification (1:1 life size) at the same f/stop, DOF for the 100mm macro and 180mm macro lenses are identical
The Test:
Both lenses will shoot the same scene with the same camera. Their primary subject will be at the 1:1 (life sized) distance - i.e. the distance from focal plane to subject; approximately 12" for the 100mm and 19.5" for the 180mm. Pictures will be shot at the same f/stop setting and lighting conditions. This process will be monitored by an unbiased and knowledgeable 3rd party observer to be sure the testing requirements are properly met.
DOF is subjective so the actual results will be posted and viewers can decide for themselves. |
Add to your criteria that the point of focus has to be the same. and you have to be shooting from the same angle. That is to say, if you're testing on a ruler at a 45-degree angle, you should be focusing on the same inch marking and you need to move the camera closer/further (to attain 1:1) by moving it along the lens axis. Easier said than done :-) |
You read my mind. The point of focus should be the same in order to make the results obvious one way or the other and sliding the subject along the X-axis after switching lenses is my plan. I like your suggestion to use a ruler, preferably with mm markings. I had a slightly different idea. I might try for an angle less than 45 degrees to make the DOF differences even more pronounced. Just depends how things look through the lens.
In addition to that, no image post processing whatsoever will be applied and only 100% crops will be posted.
I expect the results to be definitive.
Message edited by author 2009-02-01 07:26:32. |
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02/01/2009 07:28:50 AM · #54 |
Originally posted by Artifacts:
I might try for an angle less than 45 degrees to make the DOF differences even more pronounced. Just depends how things look through the lens.
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The 45 degrees was just arbitrary. It might be easier to align to than a shallower angle, however...?
R.
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02/02/2009 07:10:07 AM · #55 |
Found out the camera store does NOT have a Canon 180mm macro in stock so I will not be conducting the 100mm vs. 180mm DOF test on Tuesday. :(
However, it is an empirical test I intend to conduct at the earliest convenient time because DOF is of such crucial importance in macro photography that any consideration for increasing it should be taken into serious consideration when buying a macro lens.
DOF is an issue of physics so a definitive answer to the question whether DOF is independent of lens focal length when in macro mode will be useful information to anyone considering a macro lens purchase regardless of make, model or manufacturer.
I will start a new forum discussion devoted entirely to that topic alone when I am able to present accurate results.
Note:
It is not that I disbelieve those who say DOF is independent of focal length in 1:1 macro imagining; it is because it goes against the grain of my fundamental beliefs regarding DOF and lens focal length that I have held near and dear since I first took up photography. I just GOTTA see it for myself.
Validated truth settles all misunderstanding. |
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