On 20/08/2011, at 12:07 AM, CarlosMFreaza wrote:
> I think your diagram works perfect for 220 film, there is a physical
> contact with 120 film between the film paper back and the "pressure
> plate" most of the times, I did a test some years ago putting a fine
> cream layer on the plate and the film paper back touched the cream
> along the film travel, it does not mean the plate "presses" the film
> BTW, but it is showing the paper could be a problem for the film
> flatness. In fact, there is a very perceptible difference when you
> advance the film with 120 film and with 220, the film advance
> mechanism can be pretty heavy with 120 film sometimes, it is caused by
> the film paper back resistance to advance brushing the pressure plate
> and the paper additional weight, in the other hand 220 film passes
> "clean" along the film channel and you tend to believe there is no
> film in the camera, the film advance mechanism becomes very light, I
> used 220 film with the 3.5F, 2.8C and Rolleicord IV and the difference
> is similar for the three cameras.
>
> Chris Perez lens resolution tests for the Rolleiflex TLR are not
> convincing to me, he did a good job but the numbers show differences
> too large amid some lenses and unbalanced performances too much for
> the same lens I never saw in my photographs, he used the regular
> viewfinder for focusing and I suspect some issues with the
> parallelism between the lens board and the focal plane for the cameras
> used, as he perceived for the Schneider Xenar test, my 'cord IV Xenar
> has an excellent sharpness at f4 as you can see in some of my
> portraits taken camera hand-held. For example, the Xenar test shows
> the best performance at f 22 with identical figures for the three
> measurements, this is impossible for a camera-lens combo with right
> adjustment, the Xenotar 2.8/80 shows some impressive numbers, however
> at f5.6 they are 120 68 17 showing an abnormal difference from the
> center to the edge for a standard lens, f5.6 is one ofmy preferred f
> stops with the Xenotar and I never saw a so big difference in my
> photographs for the center and the edges.-
>
> Carlos
>
> 2011/8/19 Emmanuel Bigler <
Emmanuel.Bigler@xxxxxxxx>:
>>
>> hello all !
>>
>> I take the liberty to change the subject to the film flatness issue
>> and the (in)famous Rollei TLR plane glass.
>>
>> I made some time ago a rough diagram to explain how I see the 120
>> film
>> positioning in the Rollei TLR, with and without the glass plane.
>>
>>
http://farm4.static.flickr.com/3411/4573709647_e2452f3150_z.jpg
>>
>> The specs say that in the standard, basic configuration, the film is
>> allowed 0.45 mm of "freedom" between the "(non-)pressure" plate and
>> the inner rails. Note how the glass plate should be positioned with
>> 2/3 inside and 1/3 outside the inner rails to compensate for
>> refraction effects.
>>
>> I think, in addition (or I should I say : addiction !! Isn't the
>> Rollei-TLR-mania an addiction ? ;-);-)) to what has been said, that
>> the F-number in use plays a major role in final image sharpness,
>> whatever any detrimental "film bulging" issues might be.
>>
>> My understanding is that the Zeiss study related film flatness for
>> the Contax 645 was triggered by the use of f/2 lenses for which the
>> depth of focus at f/2 is 4 times more critical than for a TLR stopped
>> down to f/8. If we take a conventional depth-of-focus model, with a
>> very stringent circle of least confusion of 30 microns like for 35 mm
>> photography, we end up at f/8 with a depth of focus of plus or minus
>> 8x30 = plus or minus 240 microns, by a strange coincidence 2x240 =
>> 480
>> very close to the 450 microns in the gap between the "pressure" plate
>> and the inner film rails.
>>
>> Chris Perez in his famous tests
>>
http://www.hevanet.com/cperez/MF_testing.html
>>
>> where he reaches over 90 cy/mm at f/5.6 and f/8 with a well-tuned
>> Rollei TLR
>> planar or xenotar, does not use the plane glass (I think I got this
>> information from him by private e-mail).
>>
>> But we do not know how he winds his film up during tests ... since it
>> was a series of shots, probably the film has no time to "relax"
>> between shots ....
>>
>> --
>> Emmanuel
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