Back focus issue

L

long_woods

Carbonite Member
I've got a 28mm, 50mm, and a 105mm lenses all nikon primes.

I set my back focus by taking my 1.8 50mm & set it to f16 then I point the lense to something that was bright, keep the adapter off and focus to the ground glass grain. Once the grain looks like sand-paper I lock it off with gaffers tape.

For what-ever reason it is, when I switch from the 50mm to the 28mm it always looks a bit softer for some reason, anyone know what I should do?
 
I always noticed that wider lens appeared much softer with adapters. Does it look sharper with the 105 on compared to the 50?

I'm sure you backfocus is fine...When you put the 28 on, do you check the backfocus again and notice that it's fine? Sometimes some lenses are just softer than others.
 
Well the 50mm is sharp, the 28mm doesn't seem sharp, yesterday we were shooting a POV bed shot & the talent was right in front of the lens and it looked sharp.

The 105mm is also sharp too!

However how do I check backfocus?
 
Your not adjusting back focus there but focusing the video camera on the adapter screen. The word is often used incorrectly.

I have a long note I've been meaning to post as a sticky that addresses that but in the meantime just look up backfocus on this board.

Softness of the 28 could be the lens itself or poor real backfocus. What are the fstops of your lenses. I used to have a terrible 28 that was an f 3.5.

If your lenses get best infinity focus near or at the infinity mark on the lens barrel back focus is probably close to correct. Likewise if the focus distances on the lens barrel are correct its probably OK.
 
so not really the greatest lenses. You might also take a good look at the lens itself to see if it has any haze
 
The explanation can be deceptively simple: a wider lens is harder to focus correctly. With a telephoto it's much easier to focus on finer details in the shots because you can see the subject in close up, with a wide angle not so much. A good HD monitor and eyes will be critical to proper focusing.
 
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