[rollei_list] Re: Zeiss Ikoflex Lens Issue - Checking focus

Elias,

In one of my books on DIY repair, ;-) it recommends using a camera with known 
good focus (A) to check and adjust the camera with unknown focus (B). I have 
used this method.

Method: with camera A on a tripod, back open, aperture fully open and shutter 
open on 'B' and lens focussed at infinity, place a piece glass (I used a piece 
of perspex) with a very fine hairline cross scratched on it, on the film rails. 
Camera B is set up a short distance away (not important but up to a couple of 
metres although image size in camera B is dependant on distance and focal 
length of lenses used) similarily set-up but with a ground glass screen (again 
I used perspex having rubbed very fine (>600grit) 'wet & dry' paper over one 
surface) on the film rails. Position and orientation of Camera B is adjusted so 
as to see directly into the lens of camera A (i.e. both optical axies are 
aligned). The cross hair from camera A can now be seen on the ground glass of 
camera B. It should be in perfect focus if camera B is correctly adjusted.

The thoery behind this is that an object in camera A's focal plane will project 
light rays through the lens of camera A which will be them emerge from the lens 
as parallel rays (ie focused at infinity). Camera B, if correctly adjusted, 
will accept parallel rays (from infinity) and focus a sharp image at the focal 
plane.

I am not a camera repair man nor do I have optical training but I have used 
this to check a secondhand Rollei 35S which had been dropped by the previous 
owner. The image size on a piece of glass in the back of a 35mm camera is small 
and not easy to check. 6x6 is easier. Possibly by projecting light through the 
back of camera A would improve critical inspection. Failing that I am still 
looking for a collimeter for just a few £s. :-)

If camera B focus does 'not quite' turn to infinity then you will not be able 
to accurately check unless the focus stop is loosened so the lens can be turned 
past the infinity point and back again until the image is 'pin-sharp'.

I hope this is not too complicated.

Another method (if you definitely know it is out of focus) is to adjust the 
focus stop so that it could turn past infinity and put a sticky label on the 
focus ring with close numbered graduations on it. I then set the camera up on a 
tripod with film loaded and took a number of shots of a suitable land mark as 
far away as possible, adjusting the lens focus slightly to the next graduation 
between each shot. When inspecting the negatives, it becomes apparent which is 
the sharpest image(s)and the lens can be turned to that graduation(s) and 
locked off.

However neither of these will tell you if the lens elements have not been 
accurately adjusted in assembly (Friday afternoon) or damaged through impact, 
so it may never give a really sharp image as it is. In which case it will have 
to be sent off to a competant repairman for overhaul. ;-)

Good luck.......

Happy New Year

John

-----Original Message-----
From: rollei_list-bounce@xxxxxxxxxxxxx 
[mailto:rollei_list-bounce@xxxxxxxxxxxxx] On Behalf Of eroustom@xxxxxxxxxxx
Sent: 29 December 2006 18:31
To: rollei_list@xxxxxxxxxxxxx
Subject: [rollei_list] Re: Zeiss Ikoflex Lens Issue

Richard, that's the generous spirit that defines the best of email user groups!

To check focus on a camera I was playing with, I took a clean thin sheet of 
tracing paper and afixed in the place the film would be, with the back open - 
with a towel over the back of the camera and my head, and the shutter locked 
open (B and cable), I could see pretty much what the film would "see". Is there 
a better, less silly way to do it?

Elias

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