Busch Vademecum sets

[David A. Goldfarb]

I bought Jason's Busch Vademecum Satz II (minus the 15 cm objective and flange) and had the good fortune to have a flange and lens caps that fit it perfectly, so I've been experimenting a bit--no actual photographs yet.

Can anyone explain how the corrector lenses work? If I am reading the instructions correctly, I think I'm supposed to focus wide open with the corrector in place (corrector I for lenses from 4-10.5" and II for 11" and longer), stop down and remove the corrector for the exposure, and I'm guessing that the corrector is supposed to compensate for focus shift that may occur when stopping down, but in practice, at least with a loupe on the groundglass, it seems better just to refocus at the taking aperture.

In any case, these look like interesting, relatively soft lenses, but with nice coverage, and sharp enough stopped down for contact prints.

[Ole]

Again, Cameraeccentric has the answer: http://www.cameraeccentric.com/html/...sch/busch.html

The correction plate is intended to correct the focus shift between "optical and chemical focus" - when plates were only sensitive to blue and UV. It says it should not be used with orthochromatic plates, if my understanding of the French text is correct.

[David A. Goldfarb]

Ahhh...the French is clearer or perhaps later than the English instructions that I have.

[Ole]

Glad you think so - I feel English and German are enough "foreign languages", and I have no plans for learning French as well!

[David A. Goldfarb]

I think you've got the part about the "chemical and optical focus" right.

The next part says, "The corrector lenses are only used for focusing, the filters ("screens") for making exposures with orthochromatic plates. To make exposures with ordinary plates, remove the corrector lens after focusing."

So I guess in 1911 "ordinary plates" maybe were more orthochromatic (UV sensitive, I suppose) than "orthochromatic plates"? Following this procedure of focusing with the corrector lens, stopping down and removing the corrector lens definitely doesn't bring the image into the best focus in the visible spectrum.

[Ole]

"Ordinary plates" had no extended sensitisation dyes, and were only sensitive to blue and UV light. When orthochromatic plates were introduced, it was a great advance! Orthochromatic plates (and films) have sensitivity extending into green and yellowish green, which matches the visual or "optical focus". These relatively simple meniscus lenses pass a lot of the UV which is absorbed by thicker lenses, so you may find a heavy bias towards the blue end of the spectrum.

[David A. Goldfarb]

I've attached a quick test shot. This is the 15cm wide combination of 35+25 cm without the extension tubes, medium yellow filter (one of the three filters that comes with the set), f:25, about 3/4 sec, Polaroid 4x5" Type 55, on my Sinar 8x10" P with 4x5" reduction back. I used about a cm of rear fall. Scan at 1000 dpi from the neg (the detail is at full resolution). I processed the film about 50% extra (30 sec. total at room temp.) thinking I would need more contrast, but this was actually unnecessary.

[Ole]

There's a nice little trick that photographers knew all about when these lenses were new, which just about everybody has forgotten about....

You'll sometimes see old pictures of street scenes with seemingly impossible DoF - the street just in front of the camera is just as sharp as buildings in the far distance, and the tops of the closest buildings too. No tilt or swing can do this, since the sharp objects are not on a plane. So how did they do it?

Answer: Use a single element behind the stop. The field curvature makes infinity focus in the center coincide with 2-3 meters in the corners!

[Jerevan]

I've attached a quick test shot.

Aaah. The famous Goldfarb view. I can't get enough of it, I think.

[David A. Goldfarb]

Yes the field curvature is fairly dramatic with one cell. I'll have to try that.