[rollei_list] Re: Zeiss Ikoflex Lens Issue - Checking focus
- From: "John Wild" <JWild@xxxxxxxxxxxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Sat, 30 Dec 2006 11:11:06 -0000
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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