Why not just try some glass from a basic old AN glass slide mount? I've got a bunch of 6x7 laying around somewhere, and when I first started out (pre-LF), did
successfully use this in an enlarger.
Why not just try some glass from a basic old AN glass slide mount? I've got a bunch of 6x7 laying around somewhere, and when I first started out (pre-LF), did
successfully use this in an enlarger.
Part of the reason was to use higher quality glass below the negative, and also to explore the possibility that multicoating (to reduce reflection) would help suppress the appearance of Newton rings without having an etched ANR pattern.
Depends on both the room humidity and the specific type of film. Some of these new thin emulsion films are downright slick on both sides. I can't comment on your own climate. Here on SF Bay it's foggy most of the year, and I've never had luck with mere coated glass, except for a older style sheet films. And in the latter case, the best results were with a special Zeiss glass that I've been utterly unable to replicate. Unfortunately, last year I chipped a sheet and had to replace it with another from removed from my contact frame, so don't have any more left from that original box. It must have been surplus from some custom scientific application, and was hell to cut. Odd sheet size too, approx 12x16, but otherwise ideal for 8x10 film. I find 35mm less a pain in the butt than 120 film, which tends to be thinner and have more of a curl, so needs exceptionally even pressure in the carrier. And again long ago, starting out, I used a miniature film punch matched to the alignment pins in the glass slides. Now it's all custom Condit punches and glass or stuff I have personally modified. I always register small film (35mm and 120) using a taped on strip of polyester film and the 4x5 punch pattern. The tape itself needs to be polyester (not acetate) for dimensionally
stability. There is a narrow, thin mylar graphics art tape excellent for this. I wouldn't waste any time on things like Denglas. You need a better coating than that.
What polyester tape are you using? I've wondered about using tape even for 4x5. Obviously that wouldn't be the same system, more like the design Lynn Radeka uses. But I haven't gone there because my stuff works fine.
Re Denglas, I guess your saying any glazing material (Tru Vue etc etc) would be out of the question for you as far as coatings go? The specs on some of the Tru-Vue coatings look pretty impressive.
I find the Schneider MPTV filter glass frustrating. Why is it only single coated???
The standards for picture glass are different than for optics per se. The True Vue I tested was actually a hard clear titanium coating, versus the traditional soft violet magnesium fluoride single coating of Denglas and many early coated lenses. This stuff is also rather fragile compared to true optical flats. But back to tape... Prior to people doing stuff on keyboards, graphics-oriented art stores routinely sold a selection of narrow high-quality mylar tape for creating lines on board. This has been variously marketed under Line A Tape, Chart Tape, Art Line Tape, Striping Tape, etc. Seems to still be readily available on line, though the big art store around the corner still carries a small selection in black and silver. Don't confuse it with narrow masking tape, sometimes sold under similar names. This is relatively tough stuff. 1/8" or 3/16" wide seems best for attaching masks to film. There is a trick to getting good register. You want everything held dead
flat and immobile as you roll and crease the tape edge to edge. For small film (up to 4x5) I life a semi-flexible non-marring polyethylene Bondo spreader for
applying moderate pressure while doing this. If you need to do big film, I can explain that later.
I guess it's all more or less a waste of time, but an interesting excercise nonetheless.
Likely since that's all they needed. It's just for filters, and it's just for TV. Not exactly the most demanding needs. Multi vs. single coating is not a big difference. < 10% improvement generally. There was an article on it in Modern Photography a few years ago. I will try to find the scan/copies of it I have. Fairly extensive and scientific test.
Originally Posted by Michael R
Well, so far this search isn't going very well. Schneider apparently doesn't carry the 2mm thickness anymore. I guess I should have acted on that at the time. So far, that was really the only economically feasible option. I've been looking at the Howard Glass site too. Great resource.
Newton rings occur when a flat, smooth surface, like the base side of film, comes in contact with a flat smooth surface like glass, that is why they use etched or sprayed anti Newton glass, so the glass in contact with the Fl
Lim base is no longer smooth and flat. Coating or multi coating the glass won't prevent Newton rings since, unless that glass is etched or sprayed, it is still a smooth, flat surface. And, since a filter is within the optical path of the lens it has to be as flat and smooth as possible, unless it is a special effect filter.
Newton rings form due to imperfect contact between two reflective surfaces - but reflection is required. Agreed, depending on other variables AR coatings won't totally eliminate the formation of interference patterns, but they can help.
On a more generalized note, I was thinking just about glass quality in carriers. We tend to go nutso trying to get the best enlarging lenses, but when using a glass carrier, give no thought to the quality of the glass between the neg and lens. I don't know of any carriers that come stock with anything other than standard soda lime float glass.
I know we're into minutiae here, but lots of things are.
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