12x16 Rapid Rectilinear

I have a 12x16 Rapid Rectilinear lens that I rescued from a junk bin and am cleaning up. I have a few questions:
1. If stopped down far enough, would it cover 16x20? I am guessing not.
2. Should I measure its focal length from the ground glass to the waterhouse stop slot? I am thinking yes.
3. I have to make waterhouse stops; how close to my calculated dimensions should my holes be? I don't want to have to buy drill bits in some odd in-between size if I can avoid it.

Some of the smaller RR lenses could be separated into two halves because they were in shutters. Thus you could use one essentially as a 'convertible' at very near double the f.l., if your bellows was long enough. In that configuration it would be a meniscus achromat lens.

The Waterhouse slot is likely exactly where you should measure from. If not, it's justifiably close enough.

When a stop is between lens elements it's effective aperture is modified by the lens magification. Sometimes it's VERY different...depends on the lens.

I have a Gundlach 5x7 Symmetrical which is essentially the same type of lens. The iris measurement with and without glass are very approximately 10% different . You cannot generalize to all lenses, but I would think that your longer lens has a lower effective diopter equivalence and thus lower magnification, so MAYBE the true hole diameter will be even closer to the effective aperture size.

When the aperture is in front of or behind a single lens cell, the true measurement is applicable.

You can make one before proceding with a full set, and see if it's close enough. I'll guess, assuming 12x16 neg, that the lens is ABOUT 20". Say for the sake of argument it's a 22" lens. A 1" hole would thus be f/22 there, a 1.4" hole f/16, a 2" hole f22, and a 1/2" hole for f/44.

If you're going for f/64 or even 128 drill bits may be relevant. Those big holes you might be able to do with an Xacto/razor knife.

Some would argue that you will have significant variables elsewhere in exposure metering , development etc that may equal any imprecision in determining an exact aperture size.

Let's see...

A 12x16" RR would be aroung 500mm focal length. That means that each cell is about 1000mm, very roughly.

Assuming the stop is 7cm from the front cell (in the middle of a 14cm long barrel, that should be close-ish), that puts the stop at 70/1000 or about 1/14 of the focal length. That again means that the entrance pupil diameter will be larger than the true size of the aperture by 1/14th, or 7%. That's about a third of a stop, you get about 14% more light on the film. So that should be just about enough to compensate for the loss to reflection from the uncoated surfaces...

Incidentally, this is approximately correct for ALL normal Rapid Rectilinears. WA Rectilinears are a little different, since the spacing is very different.

Ole said:

Let's see...

A 12x16" RR would be aroung 500mm focal length. That means that each cell is about 1000mm, very roughly.

Assuming the stop is 7cm from the front cell (in the middle of a 14cm long barrel, that should be close-ish), that puts the stop at 70/1000 or about 1/14 of the focal length. That again means that the entrance pupil diameter will be larger than the true size of the aperture by 1/14th, or 7%. That's about a third of a stop, you get about 14% more light on the film. So that should be just about enough to compensate for the loss to reflection from the uncoated surfaces...

Incidentally, this is approximately correct for ALL normal Rapid Rectilinears. WA Rectilinears are a little different, since the spacing is very different.

Click to expand...

Thanks Ole. But, ummm... I am not sure what this means and which question this is in reply to. Pardon my lack of knowledge here.

That means that if you make a hole which is 1/11th of the focal length of the whole lens, that will be close enough to f:11 that there is no need to worry about it.

Or that if you make a hole and measure it afterwards, the aperture given by that stop will be f/d where f is focal length and d is diameter of the hole. Still close enough that you don't have to worry about it.

And if your hole turns out to be something like 1/28th of the Fl, you have an f:28 stop.

Ole said:

That means that if you make a hole which is 1/11th of the focal length of the whole lens, that will be close enough to f:11 that there is no need to worry about it.

Or that if you make a hole and measure it afterwards, the aperture given by that stop will be f/d where f is focal length and d is diameter of the hole. Still close enough that you don't have to worry about it.

And if your hole turns out to be something like 1/28th of the Fl, you have an f:28 stop.

Click to expand...

I see what you mean. Instead of trying to match a standard, I can just make any hole and calculate its actual f/stop.

Do you think I can make it to 16x20 with a small aperture?

Frank R said:

Do you think I can make it to 16x20 with a small aperture?

Click to expand...

That depends on the actual lens, but the short answer is "probably not" - or better in English: "not bloody likely"!

Jim Galli's advice on making stops:

I make my stop's known whole numbers either in mm or inches whatever you like. I never use these lenses at infinity anyway. So if I have a stop with 1" hole and I measure from GG to center of the lens and it's 16", I'm at f16. 1/2" hole and 22 inch bellows, I'm at f44, and so on. No bellows factor to figure that way.

Click to expand...

Best way to save time I've heard in a long while. Rough and ready, but that doesn't seem to hurt his work at all.