Attention owners of 300mm lens in Prontor Pro 3 Shutter

[BennehBoy]

I have a 300/5.6 Schneider MC lens mounted in a Prontor Pro 3 shutter but am fairly sure the shutter aperture is not correctly calibrated.

The Prontor Pro is configured using a series of stops and slides on the rear face of the shutter (small screws).

If anyone else has one of these that is calibrated correctly could they please send me a photo of the shutter rear so I can attempt to clone the mechanical settings?

Thanks

Ben

[Steven Tribe]

I don't know it would help, but I could take some photos of the stop screws/linkages on my 360mm Schneider Prontor pro so you see approximately where they should be?
Need daylight tomorrow and don't expect super sharp photos

[BennehBoy]

Thanks.

[Steven Tribe]

Here are the relevant linkages for a 360mm schneider in a prontor prof.

[BennehBoy]

Thanks.

[Steven Tribe]

Is the issue with settings resolved?

[BennehBoy]

Nah, looks like a 360mm lens requires a completely different setup, but thanks all the same for taking the time to make a photo - it's much appreciated.

[Bob Salomon]

You are going about this the wrong way, apparently. It appears that this lens was put into the PP shutter by someone along the way. If you look at the aperture scales you will see that unlike the shutter speed scales, the aperture scales are screwed on to the shutter. When one buys a new shutter it comes with blank scales that are to be calibrated to your lens. You do not have to make any adjustment to the shutter itself. If you can not recalibrate the scales any camera repair shop can.
The Prontor Professional system shutters also accepted optional aperture and shutter speed controllers that mounted to the shutter. All 3 size PP shutters took the same shutter speed controller but every different lens that was mounted into the shutter required it's own aperture control stick. The aperture markings on the control stick were on a label and labels with various minimum and maximum apertures were available from the lens manufacturers and distributors (we carried all of the scales for the PP for Rodenstock lenses of the era of the PP since we were the USA Rodenstock distributor).

In short, don't adjust the controls on the rear face of the shutter. Get down to a repair shop and have them make a set of scales for your lens.

[Steven Tribe]

Thanks Bob! So it is like every other shutter/stop system. But it seems strange that there is so much adjustment for the open position and range of the iris movement provided at the back.

[Bob Salomon]

Thanks Bob! So it is like every other shutter/stop system. But it seems strange that there is so much adjustment for the open position and range of the iris movement provided at the back.

There is nothing behind the shutter that needs to be adjusted by the user.

[BennehBoy]

Schneider told me that the calibration is all done at the rear of the shutter, and that the scale is for indicated aperture only (so is interchangeable dependent on lens).

[Bob Salomon]

Schneider told me that the calibration is all done at the rear of the shutter, and that the scale is for indicated aperture only (so is interchangeable dependent on lens).

You talked to the wrong person at Schneider. Talk to a camera repair shop.
BTW, 300mm is not the actual focal length. It is the nominal focal length. Another 300mm 5.6 could be a different actual focal length. Since the aperture is a ratio of the usable diameter of the lens and the actual focal length different 300mm 5.6 can require different aperture scales. If you look closely at the scales on your shutter you will see that they have a small catalog number as there were several sets of scales for each PP shutter.

[BennehBoy]

OK Bob, nice to know - next problem is finding someone in the UK that knows how to calibrate this thing at a reasonable cost.

[mrossano]

Bob, with all your good intentions on this matter, you are mistaken.

The Prontor Professional shutters and late-production Compur shutters are similar in that the aperture linkage is adjustable. You and I have had this discussion over the telephone some years ago and you were and still are incorrect in saying that the aperture calibration is dependent on the use of a particular scale for a particular lens. That would be true for Copal shutters, but not for Prontor Professionals and later Compurs. These German shutters had (usually) one or two scales for each maximum aperture. When two scales were offered, one would be used for shorter focal lengths, the other for longer focal lengths, so that the minimum aperture marked was appropriate to the lens (some were f/45, some f/64, some f/90). The back of the shutter has two screws to lock the adjustment of the aperture linkage, with another screw that limits the travel. On the Prontor, the entire aperture setting mechanism that the user positions is simply a variable-position, ring-shaped cam that actuates the internal mechanism via a pin-type follower mounted on a teardrop shaped lever, whose shaft penetrates the shutter case to connect to the actual aperture mechanism.

I went through all of this with John Sioringas at Schneider not long after I spoke with you about trying to obtain aperture scales for these discontinued shutters. It is my understanding that he was a qualified Compur and Prontor technician in the times before he moved to his current customer service duties. In any case, I've had several of these shutters in all of the sizes made and have set them up for use with remounted lenses, so I'm speaking from first-hand experience as well.

You are almost always correct in the information you so generously provide on this forum, but in this case I must submit this correction.

The point I am making for the group is that these shutters can, for the most part, be adjusted to provide correct aperture setting for most any lens that fits, without the need for a unique set of scales for each of hundreds of lens models.

[Bob Salomon]

We sent all of our scales to Marflex and he would be more qualified to discuss this as I am not a repairman. I only know how many scales we had for the shutters. There were PP scales for each focal length available for that shutter and for the aperture range of that lens. So while you might have a 4.5 Grandagon 90 in PP 1 and a 210 Apo Sironar S and a 180 Apo Sironar S and a 150 Apo Sironar W and a 115 Grandagon N f8 they can all have different minimum apertures as well as varying maximum apertures. They didn't all have scales from 5.6 to 64.



Bob, with all your good intentions on this matter, you are mistaken.

The Prontor Professional shutters and late-production Compur shutters are similar in that the aperture linkage is adjustable. You and I have had this discussion over the telephone some years ago and you were and still are incorrect in saying that the aperture calibration is dependent on the use of a particular scale for a particular lens. That would be true for Copal shutters, but not for Prontor Professionals and later Compurs. These German shutters had (usually) one or two scales for each maximum aperture. When two scales were offered, one would be used for shorter focal lengths, the other for longer focal lengths, so that the minimum aperture marked was appropriate to the lens (some were f/45, some f/64, some f/90). The back of the shutter has two screws to lock the adjustment of the aperture linkage, with another screw that limits the travel. On the Prontor, the entire aperture setting mechanism that the user positions is simply a variable-position, ring-shaped cam that actuates the internal mechanism via a pin-type follower mounted on a teardrop shaped lever, whose shaft penetrates the shutter case to connect to the actual aperture mechanism.

I went through all of this with John Sioringas at Schneider not long after I spoke with you about trying to obtain aperture scales for these discontinued shutters. It is my understanding that he was a qualified Compur and Prontor technician in the times before he moved to his current customer service duties. In any case, I've had several of these shutters in all of the sizes made and have set them up for use with remounted lenses, so I'm speaking from first-hand experience as well.

You are almost always correct in the information you so generously provide on this forum, but in this case I must submit this correction.

The point I am making for the group is that these shutters can, for the most part, be adjusted to provide correct aperture setting for most any lens that fits, without the need for a unique set of scales for each of hundreds of lens models.

[mrossano]

You are certainly correct in what you just stated.

My point was that the scales offered an assortment of appropriate numerical ranges of maximum to minimum aperture. The actual pupil diameter was matched to the scale for a particular lens model by adjusting the linkage. In this way, one scale set served for several lens models of equal maximum aperture, within a range of focal lengths.