Dallmeyer wide angle landscape no.4

[David Hedley]

I have some questions on this lens which arrived with this morning's post, which I'm hoping the cognoscenti on this forum can answer.

First, what I do know is, by looking at the Dallmeyer catalogue that the lens is a wide angle landscape no.4, which covers up to 12x10 inches, and has a focal length of 12 inches (approx 300mm);

http://farm6.static.flickr.com/5287/5305775045_9d923d478d_b.jpg

Its serial number is 46546, which seems to date it to 1899/90.

The rotating stops have values of 30, 50, 75, 100 & 150. I have found a table which seems to provide the equivalent f/stop for these values;

http://farm6.static.flickr.com/5010/5306386114_47aa0123a4_z.jpg

Is this table correct? The Dallmeyer catalogue seems to suggest f/15 for the largest f/stop - ie a difference of about half a stop from the table.

[goamules]

I would trust the lens. I.E. just measure the iris diameter wide open, and divide by the 12 inch focal length (make sure that's what it is, I've have variation with these lenses). That is the true speed. Also, most lenses are not what the ads say, once they install an iris or wheelstops. Close, but not exactly.

[Steven Tribe]

I'll think about this- but my first guess is that the F15 applies to the Waterhouse stop version - or this version with the rotary plate removed. A rotary system may mean that the designers of the size and number of the holes choose the optical satisfactory (for photographic demands then!) for the diameter of the largest hole. I think it is quite common that the number of different holes required (in this case 5) makes the largest hole undersized in relation to what the lens can do.

And having seen the comment that came while I was writing this I would say "trust the rotary/wheel stop markings"!

[goamules]

These meniscus Dallemeyers can be really confusing. I've not seen any labeled "Long Focus" or "Rapid Landscape" or "Wide Angle" but they are all in a can-type barrel with an open iris. They all look the same, but can act differently.

For example, I have two that fit in a 2" flange. One is 7.5 inch, the other is 18 inch. Same size lenses. I "assume" the longer is a "Long Focus" but have never been sure.

[Emil Schildt]

hmm - mine has a strange numbering on the rotary plate:

15 - then 2 - then X - then 3 and finally another X....

(I dont really "care" as I never use the rotating wheel... I use the lens part alone. But I am curious....)

EDIT: I unscrewed the top part with the rorating wheel, and noticed another aperture further in the barrel... Is it possible that it is so, that one could use the lens with and without the much smaller apertures?...

[David Hedley]

I've measured the lens focal length and the diameter of each opening. It's definitely 12", or 305mm. For each opening, that then gives me these f/stops;

Wide open (top of lense removed) - f/11

30 - f/16.9
50 - f/21.8
75 - f/26.5
100 - f/32.1
150 - f/38.1

These are very close to the values in the comparative table above, which is encouraging. I can round these to the nearest 1/3 stop in practice. I have now got the lens onto a temporary board and will try it out tomorrow.