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Geoff Pain

Rural Member
Am I right in thinking that if I want to test my 300mm lens I need to set the target at 50 feet,70 feet with a 1.4 tc and 100feet with a 2x tc?

Cheers Geoff
 

GYRob

Well-known member
Normally you go 50 times the focal length ,just make sure your target is big enough to clearly see what is happening .

first I take a spot on manual focus shot so I have something to compare too then

I take 3 shots and pick the best turning the lens back to minimum focus between each shot .

I tend to do this around every 3 months as imho the value can change as it gets warmer or colder and it doesn't take long to do.

Rob.
 

jimthomson

Well-known member
That would be correct if those were the distances that you expect to shoot at. 25 to 50 times the focal length is the number that is usually given for the distance for afma. You adjust based on where you think you are going to take the bulk of your shots.
 

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