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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 14 Jun 2009 (Sunday) 13:35
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Focus Issues???

 
Mac
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Jun 14, 2009 13:35 |  #1

Hello,

I am having an interesting issue with a couple of my lenses of late, primarily my 100-400 and 70-200 f/4. I am shooting with a 40D. I have just started to see these issues, and I have been extremely happy with both lenses and body for the past year and a half, this just seems to have started showing up.

Over the last couple of weeks, I just haven't been happy with the sharpness of the 100-400. I went ahead and did some tests today with all of my lenses, and the 100-400 and 70-200 have resulted in some questions.

All of my tests were done with the camera/grip on my Bogen 3021PRO tripod using a remote control to release the shutter. I decided to shoot at text, since I figured that would help me see the focus best. The shots were done indoors, to avoid any wind. What is interesting is that I get better sharpness when I crank the ISO. I attached 2 100 % crops from the test shots. The first shot is ISO 100, 400mm, f/7.1 @ 1/6 seconds. The second is ISO 1600, 400mm, f/7.1 @ 1/100. The IS was OFF for both shots.

The ISO1600 is obviously sharper. I saw the same results when I tested with the 70-200, although not as severe. On my 28-75 and 12-24 the ISO 100 was equally, if not sharper then the ISO 1600.

Any ideas on what could be the issue? Should I try a different test? And is it normal for issues like this to show up after prolonged use? I normally wouldn't worry so much, but I am seeing focus issues in my real world shots.

At first I thought it may be the focus system in the body, but my shorter lenses are not showing this, so I am not sure where to problem is even occurring...

Thanks for any help!

Sean


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Perry ­ Ge
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Jun 14, 2009 13:39 |  #2

As you said, 1/6s in the first, 1/100s in the second. Therein lies the problem, even if you're on a tripod. The first shot's blurriness is motion blur.


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Saint728
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Jun 14, 2009 13:50 |  #3

Try the same test again with more light and a faster shutter speed and see what happens?

Take Care,
Cheers, Patrick


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Lowner
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Jun 14, 2009 13:58 as a reply to  @ Saint728's post |  #4

I have read a number of articles that suggest that shutter speeds around 1/10s are the worst. Even using Mirror LockUp, the shutter introduces vibrations that can affect things.

Slower shutter speeds, around 1 second or more on a tripod seem to be OK, as do faster speeds, around 1/100s and above.


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Mac
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Jun 14, 2009 17:59 |  #5

Thanks for the quick replies. I went out and tried this outside as well, behind the garage, so the small wind would be blocked. I was getting 1/100 shutters at ISO 100 @ f/6.3 and the sharpness did improve.

I also noticed while I was looking through the viewfinder that if the wind caught, or I bumped the neck strap, there was a bit of movement in the viewfinder...so it may be time for me to lose the neck strap, as that may be causing some of my softness when out shooting.

Thanks again, I feel better now that it is me and my technique, rather than a hardware problem.

Sean


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vadim_c
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Jun 14, 2009 19:41 |  #6
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The only conclusion i can make from this is that you have an excellent lens but Bogen 3021PRO tripod is a piece of junk,


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Lowner
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Jun 15, 2009 09:51 |  #7

The best camera support is probably a 30 ton granite block, but thats a little difficult to transport so we have to compromise. To say the 3021 is junk is probably unfair, as all tripods will have problems to a varying degree.


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Focus Issues???
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