Aperture markings: 150mm G-Claron and 90mm Super Angulon

[Jeremy]

I've got a 150mm G-Claron in barrel and a 90mm f/8 Super Angulon in a Copal 0 shutter. Since I don't have the funds to buy another shutter, but I want to use the 150 in the Copal 0 I already have (and the fact that I only have one Copal 0 lensboard) how far off will my apertures be in the switch from f/8 to f/9? Since I develop by inspection I can adjust a little as long as I'm in the ballpark so I figured I would ask and see if I could just use the SA's settings from f/11 onward. Thoughts?

 

[Nick Zentena]

No. They are all wrong. What I did was I wrote myself a little note. X marked equals Y. You need to measure or what I did was a little math.

F/8 with a 90mm lens is an opening of 90/8 or 11.25mm. With a 150mm lens this works out to be F /13.33. I don't think this is perfect either. My understanding is you're supposed to measure the apparent opening. But that's what I did.

OTOH my 150mm seems really dark. I don't understand that.

 

[jimgalli]

Roughly 1 1/2 stops different. When the 90's aperture indicates f8 1/2, the 150 will be at f16 f11 1/2 indicated would be f22 for the 150 etc.

 

[philldresser]

Jeremy

What you need to bear in mind is the apurture number is related to the focal length
focal length(mm) x 1/f-stop = size in mm

150mm @ F9 = 16.66mm
90mm @f8 = 11.25

So if you swapped the 150 onto the 90 shutter then the apurture which reads f8 would be actually f13 (1.5.stops)

Hope that helps

Phill

 

[philldresser]

You guys type faster than me

 

[Jeremy]

No. They are all wrong. What I did was I wrote myself a little note. X marked equals Y. You need to measure or what I did was a little math.

F/8 with a 90mm lens is an opening of 90/8 or 11.25mm. With a 150mm lens this works out to be F /13.33. I don't think this is perfect either. My understanding is you're supposed to measure the apparent opening. But that's what I did.

OTOH my 150mm seems really dark. I don't understand that.

I'm too dense at the moment (working on a paper about the effects of neurotransmitters on smooth muscle tissue) to follow the math. So 90mm/9 = 11.25mm and 150mm/x = 11.25mm where x is the f/stop of the 150mm lens at that opening size (or f/13.33)? So when the 90mm aperture scale is set to f/22 it has an opening of 4.09mm and on the 150mm lens this corresponds to an f-stop of 36.67?

Hmm, maybe I should just see if Jim Galli will email me a jpeg of his aperture scale for the 150mm that I can print out and tape onto my shutter. Jim...? :-D

 

[philldresser]

Jeremy
Quick method: Leave the scale as it is and over expose by 1.5 stops when using that lens!

Phill

 

[Jeremy]

Jeremy
Quick method: Leave the scale as it is and over expose by 1.5 stops when using that lens!

Phill

Good deal, I can do that easily and I'll even tape a BIG note on the shutter so that I check before hand.

While we are on the subject, what is the change from a 240mm f/5.6 to a 355mm f/9?

 

[philldresser]

Which lens is moving to the new home?

 

[Jeremy]

Which lens is moving to the new home?

Ahh, good point. A 240mm f/5.6 lens in a copal 3 shutter and I want to be able to swap out the elements and put in a 355mm f/9 G-Claron.

Too bad shutters aren't cheaper, but alas....

 

[jl]

Good deal, I can do that easily and I'll even tape a BIG note on the shutter so that I check before hand.

While we are on the subject, what is the change from a 240mm f/5.6 to a 355mm f/9?

That might work for exposure, but if you want to set a specific aperture for depth of field, I think a better way would be to do it visually by setting the aperture you want, then move the indicator to open up the shutter 1.5 stops...

 

[Ole]

Sometimes it's easy, sometimes it's unreasonably difficult:

I use a shutter from a 90 f:6.8 Angulon with the elements of a 121 f:6.8 Leitmeyr Weitwinkel-Anastigmat. The only difference is that I read the aperture directly over the "knob" instead of at the end of the angled pointer.

When I tried a 355 f:9 G-Claron in the shutter from a 360 f:5.5 Tele-Xenar, all the apertures were way off... I'll need to make a completely new scale for that one.