[rollei_list] Re: 3.5E and 2.8F questions

  • From: `Richard Knoppow <dickburk@xxxxxxxxxxxxx>
  • To: rollei_list@xxxxxxxxxxxxx
  • Date: Sat, 18 Jul 2015 09:45:53 -0700

Jan, I never heard of a short break wire cutter and I have been in the electronics business for about fifty years. I couldn't find anything from a Google search. Perhaps he meant a hot-wire cutter. Most thin plastic sheet can be cut using a carbide tipped scriber. Those can be found in most hardware stores or on the web.
Ground glass location: The reference surface for the ground glass in the older types of Rolleiflex finders was the inner frame of the hood. This is why the ground glass thickness is important. In many cameras the reference surface is the outer surface of the finder where the ground surface of the glass presses. This is not changed by the thickness of the glass. I do not know what the reference surface is for the later Rollei finder where the ground glass is interchangible.
If you change the ground glass in the earlier Rollei you must adjust the focus. While many resort to shims the correct way is to disassemble the front of the camera to get access to the focus adjustment for the finder lens and adjust that. Since the finder lens is the same focal length as the taking lens (or supposed to be) the adjsutment can be made at one object distance and will be right for all. This is not a simple job because it requires removing at least part of the leather covering on the front to get access to the screws that hold it to the body. The cover is removed. The finder lens focuses on a screw thread and is locked by a clamp or a set screw depending on the model. While the ideal location for a field lens is with its ridged surface against the ground surface of the ground glass and on the lens side it works fine as in the Rolleigrid. The main advantage of the ideal position is that it minimizer internal reflections in the glass and may have a very slight advantage in the angle of the light rays emitted by the system. I've experimented with this and don't see any definite difference. Most of the screen brighteners seem to be Fresnel field lenses. Fresnel discovered that it is possible to approximate a solid lens by having a series of concentric prisms on the surface of a flat surface. I think the first ones were used as lenses in light house lamps. Actually, the flat Fresnel can be slightly curved to correct some of the spherical aberration (it has the same problems as solid lenses).
There are other screen brighteners that use some sort of high diffusing surface in place of the ground glass surface. At least one is a coating of fine wax. I don't think these can work as well as a field lens and may diffuse the image too much for precision focusing.
BTW, there are cameras with solid field lenses, for instance the finder in the old Kine Exakta.

On 7/18/2015 1:39 AM, David Sadowski wrote:

What is a "test cool?"

On Jul 18, 2015 3:25 AM, "Jan Decher" <jdecher@xxxxxxx <mailto:jdecher@xxxxxxx>> wrote:

Hi Everyone,

Thanks for all your answers. I will probably just cut the
splentrings. Need to find strong enough "short-beak wire cutter"
though (you learn new words every day).

Maybe I will leave the gridded, split-center screen in the 2.8F. It snaps into focus quite nicely it's just a bit darker than the
Maxwell. The Maxwell has been a good bright replacement for the
original murky screen in the 3.5E but it is tricky to focus (I
always focus with the magnifier).

Will pick up the test cool at noon today. It will be interesting
if the meter gave me good readings. It looks like its weak at the
bright end of the light range.

SL66 came back with new crank, stop-down lever, new mirror lever
and used brighter screen installed and a bag of removed old parts
(nice touch). Will probably send Mr. Bruer the 2.8F later this year.


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Richard Knoppow

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