establish aperature settings

[octagon]

Sir:
I have a 1;4.5 F=75MM rodenstock-ysaron lenses. It is mounted in a Prontor shutter which is labled Polaroid on the bottom. I thought I would try for some macro shots. My problem is that the shutter has no aperature settings. I do have a shutter speed tester. Can I use it to establish my own aperature numbers?
Sincerely,
Jerry

[Ralph Barker]

The short answer is no. Your shutter speed tester will only measure the shutter speed, although you might see some fluctuations in the measured speed at different apertures (i.e. where the aperture blocks part of the shutter). However, the procedure for measuring the aperture to create your own scale has been discussed here a couple of times. The search function should turn up those threads.

[Ernest Purdum]

I am surprised that there are not aperture settings on the lens. Perhaps a solution for you might be to buy one of the Polaroid Mp-4 lenses made by Tominon. With a little patience I am quite sure you can find one on eBay for very little money.

[Mark Sawyer]

I've got one here in front of me; picked it up cause it was real cheap, but I've never put it on a camera. Mine has an aperture scale right on the same strip of metal as the shutter speed scale. The smallest aperture on mine is f/22, though youyours might be different. You might be able to open it up and adjust it to go smaller, too. Just measure the opening size in mm, divide into 75, and there's your f/stop number.

Don't know if this lens covers 4x5 or not...

[Bob Salomon]

"Just measure the opening size in mm, divide into 75, and there's your f/stop number."

There is the approximate aperture. The actual aperture requires that you know the actual focal length not the nominal one.

[David Van Gosen]

Bob - Would a lens manufacturer have different aperture scales printed for multiple possible focal lengths, or would they use the average (published) focal length? Just wondering.

Jerry - You can always verify your calculated aperture against a known lens by taking a light meter reading from the ground glass. It's covered in Blaker's Field Photography.

[Glenn Thoreson]

If I'm not mistaken, this item is for a Polaroid MP-3 copy camera. The original shutters for thes things usually do not have an aperture adjustment on the shutter for a very simple reason. They have no iris blades. The ones with no blades have the iris in the lens barrel. The Tominon lemses for the MP-4 are a good example. People buy the shutter for these on ePay thinking they a getting a bargain. Until they try to use it. S.K. Grimes can make an accurate f/stop scale scale for your shutter/lens, provided it actually has an iris.

[Mark Sawyer]

"The actual aperture requires that you know the actual focal length not the nominal one."

Well, yes Bob, but then, if we really wanted to be accurate, we'd have to take into account the speed of the Earth in relation to the stability of the Universal Constant, as that speed slows time for the matter which exists upon the Erth's moving surface, while the speed of light remains constant with relation to the Universal Constant. Thus, the light entering the lens, due to its increased duration in time in relation to the Earthbound Photographic System (EPS) shutter duration creates a paradox wherein the light enters the shutter for a longer time than the shutter is open, which, (when you factor in the reciprocity effect), can decrease the exposure by 0.00000000000000000000000000000000001% (I woulda put in more zeros, but I didn't want to waste the bandwidth...)

Jesus Christ, Bob, I've heard of splitting hairs, but you're splitting quarks...

[Mark Sawyer]

Oh, and I just remembered, Bob, the gravitational pull of the Earth bends the rays of light ever so slightly, and the advantage of the view camera is that it allows you to correct for this with the perspective controls. In fact, that's the only reason most of us gave up 35mm.

"Nominal focal length." Jeez...

[Bob Salomon]

:Bob - Would a lens manufacturer have different aperture scales printed for multiple possible focal lengths, or would they use the average (published) focal length? Just wondering.:

Yes see the little letter in the upper corner on some aperture scales. They showw which pair for the aperture range on the lens is used.

[Struan Gray]

Err Mark. When calculating the f-number you use the size of the aperture stop as seen through the front element. Take a Tessar, whose front element has little magnifying power, and compare it to a plasmat of the same focal length (where the front element has roughly half the power of the whole lens) and you'll see different hole sizes once you remove the front glass. It's easy to get up to a photographically relevant third of a stop, although it's hard to be off by a stop or more.

The inestimable Richard Knoppow posts regular reminders on this topic to the usenet group rec.photo.equipment.large-format. There's one version here (http://groups-beta.google.com/group/rec.photo.equipment.large-format/browse_frm/thread/1f44ec6328b93c4/6f34818d9133b095?q=measure+aperture+knoppow+group:rec.photo.equipment.large-format&rnum=2&hl=en#6f34818d9133b095)

[Mark Sawyer]

Struan- Quite true, and through years of trial-and-error, I've discovered it helps somewhat if you open the shutter before trying to measure the aperture...

And apologies to Bob. I should learn to never turn on the computer after the second beer...