Wheel Stop Apertures on Dallmeyer Rapid Rectilinear 1A Lens

[bigdog]

I recently acquired a Dallmeyer Rapid Rectilinear 1A lens (serial #49098) with a wheel stop and apertures marked "30, 40, 75, 150 and 200".
I believe the lens specs claim it will cover whole plate and is 7" focal length?
Focusing at infinity is seems closer to a 5" lens.
I mounted it on my Speed Graphic 4x5 and intend to shoot some dry plates.
Can anyone tell me what the approximate corresponding f/stops match the five numbers marked for aperture openings?
It appears to be a slow lens starting at f/11 stopping down to f/32 just by my guesstimate dialing through the 5 aperture holes.

Any information on this lens would be appreciated.

 

[Ron (Netherlands)]

Indeed it is Dallmeyers own aperture numbering system which started by the number 1 and ended by the 500. The Dallmeyer system was based on exposure, proportional to square of the f-number.
The equivalent f/ numbers with respect to the Dallmeyer numerals on your wheel stop is as follows:
30 > f 17.32
40 > f 20
75 > f 27.36
150 > f 38.7
200 > f 44.72
..... derived from this table

 

[bigdog]

Thank you Ron, I will put a piece of tape on the lens board with the scale!

No wonder I could barely see any image on the ground glass with such small apertures. It almost eliminates the need for using the focal plane shutter if I buy 3 ISO dry plates.

I will have to shoot Tri-X 320 if I utilize the focal plane shutter or go the other direction and shoot slow film with good reciprocity performance and make a lens cap for exposure. I already mounted the lens on a Graflex board but I could alternatively mount it on a Linhof board to use with my Wista 45 which has brighter Fresnel glass and a reflex viewing hood.

It makes you wonder how these "rapid" lenses were used in practice back in the day.

 

[Ron (Netherlands)]

It makes you wonder how these "rapid" lenses were used in practice back in the day.

Welcome, and they were probably just used with a cap since they had only very slow glass plates in the day.
But an f/ stop slower than f8 is a bit odd for a rapid (i.e. fast) rectilinear. However since its widest opening is near f16 your lens most probably is meant to be a W.A.R. lens, i.e. a wide angle rectilinear - they were 'only' used for wider landscapes, therefore it has more resolution than the 'normal' RR lenses, but its tradeoff is two stops slower (or even a bit more). For landscapes they didn't feel the need for a fast lens (my older achromats - used in the day as landscape lenses - are as slow or even slower than you W.A.R. lens).

Any picture of your lens?

 

[bigdog]

I believe you are correct it being a "wide angle rectilinear" . What do you think the focal length is mounted on my 4x5, approximately 127mm?
It has more resolution due to the lens formula/glass/smaller aperture?
Photos attached!

 

[Ron (Netherlands)]

Thanks for showing the lens; have a comparable lens from Perken, Son & Rayment; indeed these are W.A.R. lenses. Don't know about the focal length. You can measure it by focussing the lens at infinite and measuring from the hart of the lens (about the same point where the diaphragm disc is situated) until the ground glass screen. My Perken, Son & Rayment is meant to be used for a half plate camera: 6,5x4,5 inch plates; no focal length is mentioned.

<edit> I just posted a picture of my vintage brass lenses; the Perken W.A.R. lens is on the far left, it has a max opening of f11:
https://www.flickr.com/photos/zorki_2007/50960743432/in/dateposted-public/