collimative question

R

ruben

Guest
Within my ignorancy on optics, I believed upon reading RFF pages that collimating a lens was some kind of adaption (either of the glass or the metal) to accurately focus on the film plane.

Now I have found a serious camera seller and refurbisher, who advertizes an SLR medium format lens, saying he has collimated it to infinity.

Is it good, what it means ?

Cheers,
Ruben
 
As I understand it - that when the lens indicates that it is focused on infinity the actual focus plane (by which I mean the surface of the negative) will also be focused on infinity and not focused either just before or just after infinity.

I assume that medium format SLR means a Kiev or Arax modified Kiev. I note that the Arax website advertises that when they prepare a Kiev for sale that they make sure the cameras have a correct infinity focus.

Cheers,

Tyrone
 
Thanks Tyrone,

Then my question is if this type of adjustment, as you described it, is the only optical one that can improve the optics of the lens.

Thanks,
Ruben
 
Apart from cleaning obviously problematic defects, I would assume so. I would think that provided a lens is correctly manufactured according to its specifications and not damaged from misuse or mis-handling, collimating for infinity couldn't 'improve' a lenses optics beyond what they are. Rather collimating (if done correctly) would simply serve as a check that the lens was actually up to spec / working as it should.

Potentially there could be pitfalls to collimating. The one that comes to mind is that someone collimates a lens to their camera (which is 'out of spec' somehow) and thus renders the lens mis-collimated for all other versions of that model camera. I think this is how it is done with movie making cameras.

Here's a good example of how collimating could be done at home.

And here's a reasonable discussion of the liklihood of a lens needing to be collimated in the first place.

I've always assumed that given depth of field when focused at infinity that there wouldn't be a problem unless a lens was really defective in some really gross way.

Sorry for the longish answer, but collimating a lens to work on a camera that it was designed for sounds a bit unnecessary to me. I mean either the lens works or it doesn't - you know what I mean?

Perhaps other RFF'ers would have more of an idea about this / or illustrate where I'm wrong.

Cheers,

Tyrone
 
tyrone.s said:
The one that comes to mind is that someone collimates a lens to their camera (which is 'out of spec' somehow) and thus renders the lens mis-collimated for all other versions of that model camera.

Cheers,

Tyrone
Click to expand...

the most obvious problem would be the mis-alignment of the rangefinder mechanism in your camera as it is more delicate that the construction of a lens. Most serious shooters would send both their body and lens(es) in to have them culminated (matched) to each other. I remember a few years ago when I was using 2 different M bodies (different film speeds/focal lengths) but would swap the lens' on either body, where images from one body would not be as sharp as the other. it is best to have all your equipment matched to each other to eliminate problems

culminating a specific lens to specification without servicing the body would serve no useful purpose, IMHO

bob
 
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