why micro focus adjustment ?

Started Feb 25, 2013 | Questions thread
Marco Cinnirella
Marco Cinnirella Veteran Member • Posts: 6,380
Re: why micro focus adjustment ?

Dave Oddie wrote:

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.

What if you have a fast tele zoom like a 70-200 2.8 Dave ? Would it still be OK to MA for the 200mm end even if you still want to regularly use the 70mm end do you think ?

Or the Sony 16-50 2.8 if you shoot at 2.8 a lot ?

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