Red 18-50 and Infinity Focus

[Brian Broz]

Hi,
My primary background is the video world, and standard 1/2" or 2/3" Canon or Fuji Lenses.
Loving the optical quality and minimal breathing of the 18-50 but focus at infinity is soft (I have to back it off where the lens "stops" to get a sharp infinity focus). It would be nice to have the barrel hard stop sharp at infinity when pulling focus myself from background to foreground.
I haven't messed with the backfocus yet, as I'm not sure if this is a backfocus issue or simply inherent in the 18-50 lens design.
If someone could chime in that would be great!
Cheers,


BB

 

[Adrian T.]

That's not a bug, it's a feature. If the backfocus is off or extreme temperatures change the focal plane of the lens you will still be able to focus for infinity.

 

[Paul Leeming]

Actually I'm curious how the Viewfactor electronic follow focus is going to auto-calibrate with this in mind?

Methinks it may have to be a manual adjustment for the 18-50....

Paul

 

[Justin McAleece]

my 18-50 doesn't work that way. seems like either your system or mine is off. mine is sharp at infinity. :cold:

 

[M_Sanderson]

Thats interesting that its not consistent.
I had a similar situation when doing timelapses on the canon 5d with the 24mm f1.4 and the 15mm f2.8, the latter hitting infinity at the end of the barrel and the 24mm going past (into space). Very annoying, that first star timelapse was all soft (was a nice shot too) it made focussing on the stars very hard because the 24mm was off and the lcd screen is too small to focus with.
It would be good the find out the theory behind why some lenses have it and some dont. or whether is a fault.

 

[Brandon Fraley]

I have to back it off where the lens "stops" to get a sharp infinity focus)

aren't most lenses like this? My dvx100 is.

 

[Adrian T.]

You don't need to go up to infinity to get sharp infinity focus. It's enough to go to hyperfocal distance.

 

[Stephen Williams]

You don't need to go up to infinity to get sharp infinity focus. It's enough to go to hyperfocal distance.

Hi,

Then your focus will be well in front of infinity as well, that may not be what you want. If the lens is not collimated (the 18-50 does not even have witness marks) how could you be sure that you were setting focus to the hyperfocal distance.

Stephen