why micro focus adjustment ?

Started Feb 25, 2013 | Questions thread
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Dave Oddie Veteran Member • Posts: 4,029
Re: why micro focus adjustment ?

I think the compromise of using MA at the long end of a zoom is fair enough.  The adjustments tend to be small anyway and as you zoom to wider focal lengths I think the increased depth of field is going to take care of any "errors" you introduce by using MA at the long end.

So if you have a 70-300 F4.5 to F5.6 zoom at 70mm @ F4.5 the total d.o.f is 1.09ft if you are 10 feet away from the subject.  At 300mm and @ F5.6 there is virtually no depth of field at all at that distance.

I would suggest therefore any front of back focus would show up when sent to 300mm but would not when set to 70mm.   So even if the lens didn't need correcting when set at 70mm the fact you made an adjustment at 300mm won't affect things detrimentally at 70mm.

It is even less of a problem with lenses like a 16-80 as the depth of field soon gets very large as you move away from 80mm.

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