DSLR noob
TPF Noob!
- Joined
- Feb 7, 2007
- Messages
- 1,527
- Reaction score
- 9
- Location
- Atlanta, GA
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- Photos OK to edit
No the lens can't open up to 3.5 at 300mm so the aperture value of a fully opened up lens at that time is 6.3 and AF won't work. I know I contradicted myself, I thought you meant at any given aperture focal length doesn't change AF performance, which I agree with. But the aperture DOES NOT equal 3.5 at 300mm and physically can not equal 3.5, even if the same lens is able to do that at 28mm. The lens is fully open at 300mm, it doesn't stop down to 6.3 when you take a picture, therefore fully open it is at 6.3, so the camera sees 6.3 and does not autofocus. It might work in REALLY bright light but the lens, under normal conditions, won't be able to AF.