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Category: New Answers

Photography Question 

Piper Lehman 		 

DOF When Shooting With Extension Tubes


 
 
Hey anyone and everyone. I have a question about determining sharp focus while using extension tubes on a macro lens. Why I chose to use both macro and ext. tubes is beyond me, but that's beside the point really. I took some closeups of this orchid I'm about to upload using my 28-105mm lens in macro mode. This lens has a maximum aperture of f/3.5-4.5, which means that when using any other focal length besides 28mm, the max aperture becomes 3.5. The macro mode encompasses only the 50-105mm focal lengths, so, of course, when set at 105mm, I had a maximum ap of 3.5.

Now, here's my question. When focusing on a certain point on my flower, I wanted just a tad to be in sharp focus. I meant to throw the rest out of focus. The problem is that the point of sharp focus I saw when taking the picture did not come out sharp when viewing the prints. I did not check DOF with the preview button, but now I'm thinking I should have and then set my focus according to this. Is my problem the maximum aperture thing, or is it the extension tube? (I was using a 12mm tube.) Also, I only know my aperture was 4.5 because I was shooting at 105mm. (The ap info does not show up in the viewfinder when using my extension tubes.)

Anyway, I wanted to know if this was my problem, or if it was just a bad print. Though I seem to be seeing this a lot in my macro shots, especially when focusing manually.

Here are two shots that show my problem. The flower is the shot I've described above. The angel is a 300mm macro shot WITHOUT ext tubes. I could've SWORN I had a sharp view of the angel's face--or at least part of it--when shooting this last week.

Thanks in advance.


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May 22, 2002

 

Jon Close 		  Hi Piper.
The angel pic looks to me to be suffering from camera shake rather than being out of focus. Maybe your tripod wasn't quite steady or wind or other vibration source (do you have/use mirror lock-up or a remote shutter release?).


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May 23, 2002

 

Hermann Graf 		  When shooting with telephoto lenses with focal lengths >200mm, and using exposure times between 1/15 sec and 2 sec or so, MLU (mirror lock up) is inevitable to get sharp pics. If you don't have one, change aperture and/or film speed to avoid this exposure time range (also a tripod does not help in this case).
Also note that 1) zooms do often not work very well with extension tubes; close-up lenses, especially achromates, work better, and 2) the DOF range becomes very small when using extension rings.


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May 24, 2002

 
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