Focusing to infinity?

[Polyphony]

Well I know that in both my 18-55 and 50 prime, going past infinity on the focus throws the image completely OOF. I think my Sigma 2.8 does it too. *shrugs* Just what I know from experience.

I am not doubting that occurrence. (It could be due to a number of things) I am simply questioning the ability to do anything past infinity.

Also, the camera may be marked "infinity" but there actually is a distance that the lens is focusing on.

I think there are a number of reasons they do it.

The main ones I can think of is tolerances built in to allow for expansion/contraction due to temperature.

The other is so that AF can pass it, then come back to it. So there isn't some kind of mechanical stop that the motor would be slamming against every time you tried to AF on a distant object.

Another is for non-visible light. IR and UV focus differently than visible light, so you might need to go a little past infinity for that.

Yes but you must understand, you are not actually focusing past infinity. That's like saying: I am going to walk past infinity and meet you on the other side.

You are focusing passed whatever distance happens to be marked "infinity" on your lens.

 

[Petraio Prime]

Most lenses will go a little past infinity

Can you explain what you mean by this?

Some lenses (mostly big teles) allow you to turn the focussing ring past the infinity mark to allow you to have free motion through the infinity point. My 350mm Telyt-R does this.

"The350 mm TELYT-R f4.8 can be focused beyond infinity. This facilitates focusing in the region of the infinity setting."

See:

http://www.fonooni.com/Leica_350_mm_f_4_8_lens_Telyt-R.html​