question of aperture old lens in a new shutter

[fuegocito]

Dear all,

I have replaced the shutter on an old 305 Repro Claron with a newer Polaroid Copal 1 press shutter. My question, the old lens' maximum aperture is f/9 and the max aperture marking on the new shutter is f/4.5. Does that mean now the lens can be used with a max aperture of f/4.5? The aperture does showing greater opening beyond f/8.

thanks for all the help in advance

Rob

[Howard Petefish]

Rob, the lens construction, not the shutter, determines the maximum aperture that can be used. It would be great if replacing a shutter with one marked at a larger maximum aperture would increase the speed of a lens but optics do not work like that!

[fuegocito]

Hi Howard,

That is exactly what I am thinking as well, so essentially I gain some extra opening in viewing/focusing purpose but when in actual shooting, I still close down beyond f9. The rest of the aperture markings still apply the same way even though the shutter used to house a 75mm lens?

Thanks

Rob

[Ole Tjugen]

No, the aperture scale is only valid for the original lens. The point where you can just see the aperture blades corresponds to f:9, so you can't open up more and get more light. The difference in f-stop from the marked value will be constant from that point as you stop down.

Since 305mm is about 4x 75mm, you can assume that the difference is very close to two stops. That means that f:4.5 on the scale is f:9 in use, and f:11 on the scale is f:22, and so on.

[fuegocito]

That is very useful information before I go out there and happily, yet wrongly exposing all those emulsions:) Thanks Ole. It took me a while to wrap my head around that one.

While I am here, I have a question about another shutter; I have this old 330mm Wollensak Raptar in a Alphax shutter, the shutter stays in the open position while I can hear the shutter fires off inside. It seems to operate just like the Polaroid Self cocking Press shutter but at this point, the shutter just wouldn't close, any quick and simple fixes??? The reason I am reluctant in investing in fixing the shutter properly is that the rear element has a ring of haze inside and the coating on the front element, actually I don't knows if it's the coating but it looks like there is permanent water marks on it or something that can not be clean off. I tried.

[seawolf66]

Suggest you contact this web site and have you shutter CLA'd as for the lens take it apart and clean it that should do that for you:
http://home.earthlink.net/~flutotscamera/Website/index.htm

[Darko]

You have to measure diameter of an aperture at any stop, write down the values, now devide the focal lenghtof the new lens/diameter and you will get your new f stop value...

..darko

[fuegocito]

Thanks Seawolf and Darko

[Neil Purling]

Anyone used one of those tiny Wide-Angle Rectilinear lenses. With a 6" focus Wray there is an internal 'baffle' behind which the disc of f stops rotates. It looks like if I had that re-mounted I could gain another stop of light for focusing.

[Ole Tjugen]

I use "one of those tiny Wide-Angle Rectilinear lenses". In fact I use several of them...

The baffle is there for a very good reason. If you open up the aperture more, you get too much aberrations, leading to "focus shift" and other unpleasant problems. One of mine (a 3 1/4" f:16) opens up to about f:11 (no baffle), and the focus shift is visible. You do however get a rather funky effect if you forget to stop it down...

A good 6" WA Rectilinear should cover at least 8x10", so you won't get much "funk" on 4x5"!