Tele Rollei / The plane glass question

[Slowfauto]

Hi everyone,
I am shopping for a Tele Rollei and I wonder what model is the best. My concern is mostly about the plane glass system available on both the model 1 ans the so called Transition model. Is this system any good? Will it really insure a sharper image by flattening the film at is best? But is the dust on this glass a real problem then? And what about the pressure plate? I understand that the camera back that has a bump in the lower part indicates that there is a plane glass and a special pressure plate designed for it. Right? If so, will the camera model 1 work as fine as a model 2 (flat back and no plane glass) if we use it without it's plane glass? If any lucky Tele Rollei owner can help me out...
Thanks !

[DPurdy]

I don't own a Tele. I have however owned and used a plane glass. It might be that the film flatness issue is different for a tele lens than the 2.8 80mm lens I used. If anything I would guess that it is more useful for the Tele. There was a time when film base thickness was more and films had more curl than the modern films have. I did get slightly sharper results with mine at wide fstops. But once down to f8 there was no difference I could find in sharpness. There is definitely a dust problem with the glass, as well as a scratch problem. I did a lot of looking for a non Rollei piece of glass that was the right thickness and size. I was not successful really. I got close.
The hump back has different settings for using with glass and without glass. It works fine without glass.
My personal opinion is that the plane glass is not worth the trouble... but then I rarely use my Rolleis at a wide open fstop. Getting the glass clean and dust free was a major hassle for me.
Dennis

[Slowfauto]

Thank you Dennis for your science! This story about the film thickness that has changed makes sense. I personally shoot often with my 3.5F wide open, and rarely down to f8. So the flattest the film, the best it is. But having to fight with dust is a pain indeed. I already play this game in my darkroom and I don’t always will. Yes, I still print! So I guess I will rely on your film theory and assume that the film will be flat enough without glass. Anyway, I also have the feeling the Tele DOF is so small that I will have to close down to f5,6 or f8 to get someone sharp. I don’t have the camera yet but I do have both Rolleinar 0.35 and 0.7 designed for it. Can’t wait to try!
Pierre

[JanBoettcher]

The Tele has less issues with film flatness then the regular Rolleiflex or the Wide Angle Rolleiflex.

I would not go throught the dust trouble with a Tele.

[Slowfauto]

Why is that? It suprises me because a 135mm lens should have less DOF, no?

[JanBoettcher]

There is a difference between DOF and "DOF". "Regular" DOF is "way in front of the lens", but the "DOF" you're thinking of is "right behind the lens".

When taking pics with a TLR we are not talking about 1:1 macro work, but about distances from 1m (3ft) to "infinity". Typically from a little more than 1m, especially with the Tele-Rollei. In this configuration the lens to film distance is roundabout 13,5cm or 135mm to 143mm to be more precise with the Tele (80mm Rolleiflex 2,8, 75mm Rolleiflex 3,5 and 55mm wide angle Rolleiflex) (the curved disks will give 8mm of travel to the lens board).

So, just a little movement of the lens towards or from the film will change the subject-distance in focus damatically. When checking the theory of DOF (like here http://en.wikipedia.org/wiki/Depth_of_field or with online DOF calculators) you will usually find sketches / drawings that will not show proper scale. But with a "fancy" DOF calculator (sorry, I only have a German one at hand http://www.mhohner.de/formulas.php#calc ) you can calculate not only the DOF regarding the subject but the lens to film distance as well. You will see to get 1mm change in lens to film distance (play around a bit!) you will have vary the lens to subject distance les with shorter lenses (well in case you have 35mm equipment including tele- and wide-lenses you can observe this directly).

http://www.mhohner.de/formulas.php#calc
"neu berechnen" bottom left is the button to get the calculator calculate things over.
Brennweite (f) mm = focal length
Entfernung (d) m = subject distance (from film plane)
Blende = f-stop
Objektweite (g) 4.944 m = subject distance (from lens to subject)
Bildweite (b) 0.056 m = lens to film distance
Streuungskreis (c) mm = circle of confusion
Tiefenschärfe 3.913 m–6.922 m (3.009 m) = DOF from to
Hyperfokale Entfernung 18.01 m (9 m–∞) = hyperfocal distance
Format = format (I chose 6x6 from the drop down, but it doesn#t really matter
horizontal vertikal diagonal = (self explanatory)
Bildgröße (B) 56 mm 56 mm 79.2 mm = image size
Objektgröße (G) 4.978 m 4.978 m 7.04 m = covered subject size
Bildwinkel (α) 53.96° 53.96° 71.51° = angle of view
Abbildungsmaßstab (B/G) 1:88.9 (0.01×) = reproduction ratio

[Slowfauto]

Waouw ! Thank you for this great focal lesson! So I understand that the rule is inverted. The longer the focal, the shorter the DOF ahead, but the longer DOF on the film plane. Good to know. And this is a good news for me indeed because I didn’t feel safe using the glass neither. I am fixed! Thanks again.