Jump to content

out of focus at infiity


David Dominguez

Recommended Posts

hello,

 

I have a kern switar 10mm that seems to slightly out of focus when looking through the diopter at infinity.

 

It looks in focus on the closer focal lengths of that lens. The kern switar 25mm i have is in focus at infinity as well.

 

I think the diopter isn't perfectly focused to my eye It has some issues and was recently serviced but i don't think was fully fixed.

 

Could that be the issue? I'm nervous the wider landscape stuff i'm shooting is going to be out of focus.

 

thanks!

Link to comment
Share on other sites

  • Premium Member

Kern lenses have a mechanical stop at infinity, but worth checking that it is stopping at the infinity mark.

 

What is the issue with the eyepiece diopter? To adjust for your eye, defocus the lens completely, point the camera at a bright diffuse subject like the sky, and focus the diopter until you can see the texture of the ground glass. Then lock it off and you're good to go.

 

It can be hard to judge exact focus with a 10mm lens, especially distant objects, through a Bolex viewfinder. If you feel the 10mm is focussing correctly at close distances (ie a subject at say 2 feet away is sharp in the viewfinder when the lens focus ring reads 2 feet) then it should be ok at infinity too. If the focus scale is out, the lens needs adjusting (it will focus at infinity either before or after the mechanical end stop). If all the lenses are out, the camera probably needs adjusting.

 

If a lens is very worn in the focus threads it may focus at different points depending on whether you turn the focus ring towards infinity or towards close focus (so it may be ok focussed down to 2 ft, but not get sharp as you focus up to the infinity stop because of a lag in the focus threads).

 

If you can afford to send everything to a Bolex technician, they can measure things like camera flange depth, ground glass focus and lens collimation, and make adjustments if needed. They can also check if a lens has worn threads or needs relubrication, and identify other potential issues, clean the viewfinder optics, relubricate the camera mechanism, etc.

 

Otherwise, shooting a film test is the ultimate way to check if your camera and lenses are focussing properly.

  • Upvote 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...