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Focussing

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Old Tuesday 30th April 2019, 23:19   #1
shrek48
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Focussing

I currently use a Nikon D7200 with a Tamron 150-600 G1..... I am having issues with focussing. I am using AFS with back-button focussing but my issue is the set up seems to "hunt" when focusing a few times before settling to a set focus, often it is slightly out of focus too. I use a tripod so do not understand why this happens.
When I press the back-button the camera seems to focus in and out a few times then sets, but when I get home and look at the picture on my computer the image is not perfectly sharp! My eyes not being able to see if the focus is perfect or not using the camera viewfinder or screen (old eyes)

I have watched many you tube videos but not seen anything on the D7200 specifically talking about my issue...
Any advice please?
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Old Wednesday 1st May 2019, 04:18   #2
nikonmike
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Have you checked for front or back focus?
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Old Wednesday 1st May 2019, 07:09   #3
shrek48
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Yes Mike , I am using back button focus not the shutter button, is that what you mean?
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Old Wednesday 1st May 2019, 09:31   #4
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I have now set my Focus to continuous and 9 points not 1 also set fine tune AF at +3 after taking shots at min and max focal length.. Seems to have improved, will test it with some bids when I get a chance.
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Old Wednesday 1st May 2019, 15:03   #5
marcsantacurz
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Those f/6.3 lenses need a fair bit of light to focus well. Does the problem happen if the subject is brightly illuminated?
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Old Wednesday 1st May 2019, 16:40   #6
coopershawk
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It may be an AF fine tune issue like Mike said. In case you don't know of a good accurate way of fine tuning, here's a link to a video I found helpful: https://www.youtube.com/watch?v=7zE50jCUPhM. There is a link to a focusing target in the text below the video.
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Old Sunday 5th May 2019, 03:08   #7
shrek48
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Thanks, it happens anytime but especially when the area is busy, like a tree etc. Fine tuning done so we shall see if it improves when next out in the field. Light should not be an issue as I live in the Philippines now and it is summer time, 35 degrees and blue skies from 6 am ;-)
thanks everyone.
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Old Sunday 5th May 2019, 12:10   #8
ericbowles
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There are a lot of sources of error - and fine tuning and equipment issues are near the bottom of the list.

The D7200 will only reliably focus with the center AF point on lens combinations that are at f/6.3 and above wide open. Are you using the center AF point?

Are you referring to focus accuracy or image sharpness? Focus should be accurate, but there are a range of small AF errors. No lens and camera combination is perfect. Fine tuning is possible, but may not be necessary. Image sharpness is different. The Tamron lens you are using is known to be softer at 500-600mm than 400mm. Technique is more demanding at long focal lengths. And that lens may be a little better stopped down to f/8 at the long end.

Is your shutter speed fast enough? I'm looking for 1/2000 of a second for moving subjects and 1/1000 sec on a tripod for other wildlife. Slower speeds can be used, but motion is part of the equation.

Are you using long lens technique? I've found the light long lenses tend to suffer from both mirror slap and shutter shock even at 1/1000 sec. or faster. A cable release does not help unless you have a suitable time to settle, and even then, shutter shock is possible. If you have your hand over the lens barrel using long lens technique, you can reduce a lot of vibration.

You also need to have a reasonable AF target. Typically this is a high contrast target in the same focal plane as your desired subject. If you can find something close to that plane, your camera will usually be able to refine focus further on your subject.

AF does not help much when your subject is small relative to the AF sensor. Tiny distant subjects may fool the camera. Sometimes you just need to be closer. :)
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Old Monday 6th May 2019, 23:29   #9
shrek48
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Thanks Eric, I have found a few issues, such as the back plate loose on the lens(don't know how the hell it came loose never remove the lens) causing the focus not to work properly then not to work at all, then the settings had changed from afc to afa (must of been me) and fine tune was off so I have sorted all that and taken a few shots and am happier now.
My main issue was/is the amount of "out of focus" shots I had when using AF and the time it took for the set up to actually focus on the subject.
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Old Tuesday 7th May 2019, 17:55   #10
Sbiriguda
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Informative thread I’m following
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Old Wednesday 8th May 2019, 06:53   #11
nikonmike
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Have you got focus priority set on the shutter button, if so BBF overrides this setting on the D7200 and uses release.
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Old Wednesday 8th May 2019, 09:35   #12
shrek48
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I will look into that as I do not understand what it is. Thanks Mike
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Old Wednesday 8th May 2019, 12:38   #13
nikonmike
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Quote:
Originally Posted by shrek48 View Post
I will look into that as I do not understand what it is. Thanks Mike
You have two settings on the shutter, one will let you take a picture even if its not in focus, the other in theory needs the subject to be in focus before the shutter will fire, if you have the second one set and then use BBF it will ignore this setting and allow the shutter to fire even if the subject is not in focus.
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Old Wednesday 8th May 2019, 23:33   #14
shrek48
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Thanks Mike got it ;-)
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