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Author Topic: Microfocus adjusting my 17-40?  (Read 2655 times)

Rob

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Microfocus adjusting my 17-40?
« on: December 16, 2011, 11:14:43 AM »
Hi Everyone, was hoping to get some advice about Microfocus adjusting my 17-40 on my 5Dmk2. It is tack sharp on my 5D mark 1 but on both my 5dmk2 bodies it isnt. I have read that microadjustment works well on a prime lens, but havnt herd if anyone has sucsesfuly adjusted a zoom?
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Microfocus adjusting my 17-40?
« on: December 16, 2011, 11:14:43 AM »

Viggo

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Re: Microfocus adjusting my 17-40?
« Reply #1 on: December 16, 2011, 12:33:12 PM »
No problem adjusting a zoom, do it at 17mm, then at 40mm, then at some thing in between, often the miss by the same through the range, and if it doesn't, you just have to go middleway.

Only the 1d X can correct for different focusing errors at wide and "tele" end of a lens.
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Mt Spokane Photography

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Re: Microfocus adjusting my 17-40?
« Reply #2 on: December 16, 2011, 01:12:31 PM »
Zooms adjust just fine with MA. 

I'd recommend adjusting it at your normal shooting distance, and then checking other zoom focal lengths.  It its grossly off at some zoom focal lengths and good at others, then Canon will have to adjust it.  However, you would have seen this with your 5D.

I adjust all my lenses, zooms and primes alike with no issues.  I did send my 35mm L into Canon for warranty adjustment and it came back perfect.  It needed +2 on my 5D MK II, but plus 17 on my 1D MK III.  Now its zero on both.

Kent

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Re: Microfocus adjusting my 17-40?
« Reply #3 on: December 16, 2011, 01:19:40 PM »
Check this. I have tested it and it seems to work pretty good.

http://www.reikan.co.uk/focal/index.html

neuroanatomist

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Re: Microfocus adjusting my 17-40?
« Reply #4 on: December 16, 2011, 01:52:31 PM »
It's often best to adjust the zoom at the long end.  The rationale for that is the DoF is usually thinner with a longer focal length, and thin DoF is where AF problems are more evident.
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thepancakeman

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Re: Microfocus adjusting my 17-40?
« Reply #5 on: December 16, 2011, 02:00:49 PM »
It's often best to adjust the zoom at the long end.  The rationale for that is the DoF is usually thinner with a longer focal length, and thin DoF is where AF problems are more evident.

Okay, definitely not going to challenge neuro on a technical concept, BUT...isn't the depth of field greater the further you are away from a subject?  So if you have a longer focal length, for the same framing you will have to be further away--is that a wash on DoF then, or exactly what happens?

Still thinking...(that's a big taks sometimes!   :-\)...you're saying keeping the subject and camera at the same distance, as you increase focal length the DoF will decrease, hence that's where you set your microfocus?  That still feels backwards to me.  I want to understand this so I can start setting my (wife's) lenses on my new 7D!   ;D

neuroanatomist

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Re: Microfocus adjusting my 17-40?
« Reply #6 on: December 16, 2011, 04:47:07 PM »
Okay, definitely not going to challenge neuro on a technical concept, BUT...isn't the depth of field greater the further you are away from a subject?  So if you have a longer focal length, for the same framing you will have to be further away--is that a wash on DoF then, or exactly what happens?

Exactly - for the same framing, it's a wash that reduces to aperture, i.e. the shallower DoF from the longer focal length exactly cancels out the deeper DoF from the greater distance, so for the same framing, only aperture determines DoF. 

But, most people don't frame the same shot at 17mm vs. 40mm.  If you're shooting at 17mm, you usually want that wide angle view.

Quote
Still thinking...(that's a big taks sometimes!   :-\)...you're saying keeping the subject and camera at the same distance, as you increase focal length the DoF will decrease, hence that's where you set your microfocus?  That still feels backwards to me.  I want to understand this so I can start setting my (wife's) lenses on my new 7D!   ;D

In a nutshell, for a given sensor size, DoF is determined by three factors:

  • Aperture - wider means shallower DoF
  • Subject distance - closer means shallower DoF
  • Focal length - longer means shallower DoF

If you change more than one at once, the effects will add or subtract.  You're statement, "...keeping the subject and camera at the same distance, as you increase focal length the DoF will decrease," is absolutely correct (assuming same aperture). 

Setting the AFMA at the long end of the zoom lens does two things - it sets the adjustment at the place it's most likely to be needed, and it makes the calibration easier. 
« Last Edit: December 16, 2011, 09:09:12 PM by neuroanatomist »
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Re: Microfocus adjusting my 17-40?
« Reply #6 on: December 16, 2011, 04:47:07 PM »

Rob

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Re: Microfocus adjusting my 17-40?
« Reply #7 on: December 16, 2011, 05:06:45 PM »
Thanks Guys for all your advice, will give it a bash this weekend.  :D
Better to live in denial, that way you wont be disappointed!

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Richard8971

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Re: Microfocus adjusting my 17-40?
« Reply #8 on: December 19, 2011, 09:33:18 PM »
Check this. I have tested it and it seems to work pretty good.

http://www.reikan.co.uk/focal/index.html

I checked out their website and there doesn't seem to be a download available. They said something about the beta program being available for testing for the first 50 posters (to a specific thread at their website). I regestered and just received an email saying that I had been "selected" as one of the bata testers. I am learly of course but hopeful this will work as planned. Wish me luck!

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Re: Microfocus adjusting my 17-40?
« Reply #8 on: December 19, 2011, 09:33:18 PM »