orthochromatic film?

[maltfalc]

maltfalc - I'm very familiar with dichroic coatings. The biggest manufacturer of these in the world was once nearby, and their former catalog would stun you. No, you don't get them at places like B&H, unless its just a mild or "colorless" UV filter (I'm wearing coated "computer glasses" right now). Nor are these kinds of coatings used for ordinary taking contrast filters. Vacuum deposition techniques apply to both categories, but for different reasons. With camera filters, it's mainly to fine-tune only tiny transmission characteristics and control reflections, just like multicoatings on modern lenses. The kind used in enlarger colorheads are incidence-angle specific in terms of transmission/reflection characteristics, so would not be dependable in an ordinary photographic application where a lens accepts light from a range of angles. I built what is probably the only privately-owned true simultaneous additive halogen enlarger in the world using dichroic "sandwich" trimmer filters, which cut off the bandwidth on both sides of the desired RGB peaks. But I'm no optical engineer. I merely consulted with them.

There is a real engineer responding to this thread, if he wishes to describe the distinctions more precisely than I can, or correct me as per my own definition of "dichroic". But as I already noted, contrast filters for black and white photography, which are the kernel of this aspect of the discussion, are primarily made of either dyed-in-mass glass, or via the colored thermo-foil sandwich method that Tiffen uses. Any optical coatings are secondary. As far as laser applications go, I once sold certain industrial lasers, which doesn't make me an expert in that field either, but knowledgable enough to understand a number of basis issues.

i'm seeing lots of talking yourself up and going off on condescending tangents without refuting anything i actually said. "No, you don't get them at places like B&H" https://www.bhphotovideo.com/c/produ...lue.html/specs "Nor are these kinds of coatings used for ordinary taking contrast filters." never said they were, but they are used for separating colours in various cameras. "The kind used in enlarger colorheads are incidence-angle specific in terms of transmission/reflection characteristics, so would not be dependable in an ordinary photographic application where a lens accepts light from a range of angles." have you tried it? yes, the cutoff point shifts as you get further from the center of the image, but you need a pretty wide lens for the shift to even be noticeable on the ground glass, and since it's just shifting to a deeper blue, the only significant effect in the final black and white image is going to be a little extra vignetting. if you really want to be picky, there are options other than rigid, flat filters.

[Nodda Duma]

TBH if I wanted to accurately replicate ortho look with panchromatic film, I wouldn’t limit myself to photo filters. I would look somewhere like Edmund Optics or Thorlabs which has a wider selection, and I don’t really care by what process the filter does its job. Dichroic filters have sharp cutoffs, but that doesn’t replicate the spectral roll off of ortho sensitizing dyes well. Blaschke ended up going to just such a supplier for his Lighthouse filter. I forget which but do recall the choice made perfect sense.

For that level of OCD, however, you also need to know exactly what spectral response the various orthochromatic and panchromatic sensitizing dyes provide. “Orthochromatic” is of course not an industry standard anymore than “Panchromatic” is. In any case, at some point you realize this is just an academic question, as cheap ortho film is readily available.

[maltfalc]

Dichroic filters have sharp cutoffs, but that doesn’t replicate the spectral roll off of ortho sensitizing dyes well.

the actual change in brightness of say green to yellow leaves would still have a gradual taper to it because the colour of the leaves includes a wide range of frequencies. not as gradual as with actual ortho film, but not anything you'd notice in a photo. you could also get a more gradual cutoff by mounting the filter behind the lens, ideally in combination with a wider aperture.

[Drew Wiley]

maltfac - you simply do not seem to understand how dichroic filters work. That's quite apparent. So you might want to do a little serious homework before arguing either with me or someone with an actual optical engineering background. As far a B&H goes, they have any number of links to exotic odds n ends some of their regular suppliers might catalog list; but that does not mean they stock these things themselves, or that their own link, in this case, to Rosco, even made it themselves. Camera stores are not where one looks for that category of item, or for application information. And if you missed what I stated, I outright built a big SIMULTANEOUS additive enlarger, you'd understand why colored sheets of any type in a filter drawer would not convert an enlarger head into that purpose. That would hypothetically work for SEQUENTIAL additive printing, but so would a basic set of decent 29, 61, and 47B glass filters right over the lens. And even if I hypothetically wanted something dichroic for a filter drawer, I wouldn't pay hundreds of bucks apiece from a tertiary supplier either, but just make a phone call directly to the manufacturer five minutes away and ask what random scraps they have, and what they'd charge to trim it down to requested size. It was many years ago that I did just that, in early stages of my own project experimentation, and it was only about five bucks apiece - they had barrels of random dichroic scrap glass laying around! But anything like that would be worthless over a camera lens for taking pictures.

[Michael R]

Hi Jason, slightly off topic but since you brought up EO and Thorlabs, do you know if their products are generally of equal quality? I might need a BBAR-coated optical window so I’ve been looking around. Some years ago I was able to buy some custom glass like this from Schneider Optics (the U.S. arm) but I think it is more complicated to do that now (if still possible) and both EO and Thorlabs are likely less expensive. I’m looking at a few other places as well but figured I’d ask.

TBH if I wanted to accurately replicate ortho look with panchromatic film, I wouldn’t limit myself to photo filters. I would look somewhere like Edmund Optics or Thorlabs which has a wider selection, and I don’t really care by what process the filter does its job. Dichroic filters have sharp cutoffs, but that doesn’t replicate the spectral roll off of ortho sensitizing dyes well. Blaschke ended up going to just such a supplier for his Lighthouse filter. I forget which but do recall the choice made perfect sense.

For that level of OCD, however, you also need to know exactly what spectral response the various orthochromatic and panchromatic sensitizing dyes provide. “Orthochromatic” is of course not an industry standard anymore than “Panchromatic” is. In any case, at some point you realize this is just an academic question, as cheap ortho film is readily available.

[Drew Wiley]

Michael, it's often difficult to tell just when Edmund makes something themselves, and when they order it from someone else. They can be pricey for individual quantities, but send me each issue of their Scientific/Industrial catalog, which I always fun to peruse. I don't know what happened to the coatings division of OCLI when that split apart. My boss at that time lived near them, invested in their stock, and within three years cashed in and made enough profit to pay all of his son's ongoing college tuition. But only about six weeks later, OCLI announced their invention of vac deposition transoxide pigments, which soon became far more profitable than their optical products themselves; and my boss would have probably made millions if he had stuck with them a little longer. Now there are alternate paths for making transoxides. But back then I was early into the game, as a distributor, of vac deposition of clear titanium coatings for metal protective purposes. Being in a marine climate, we were selling tremendous amounts of door and marine hardware subject to discoloring. Some people like the naturally oxidized brass or bronze look, but other's like keeping their brass shiny. Another significant re-adaptation of lens coating technology!

[maltfalc]

maltfac - you simply do not seem to understand how dichroic filters work. That's quite apparent. So you might want to do a little serious homework before arguing either with me or someone with an actual optical engineering background. As far a B&H goes, they have any number of links to exotic odds n ends some of their regular suppliers might catalog list; but that does not mean they stock these things themselves, or that their own link, in this case, to Rosco, even made it themselves. Camera stores are not where one looks for that category of item, or for application information. And if you missed what I stated, I outright built a big SIMULTANEOUS additive enlarger, you'd understand why colored sheets of any type in a filter drawer would not convert an enlarger head into that purpose. That would hypothetically work for SEQUENTIAL additive printing, but so would a basic set of decent 29, 61, and 47B glass filters right over the lens. And even if I hypothetically wanted something dichroic for a filter drawer, I wouldn't pay hundreds of bucks apiece from a tertiary supplier either, but just make a phone call directly to the manufacturer five minutes away and ask what random scraps they have, and what they'd charge to trim it down to requested size. It was many years ago that I did just that, in early stages of my own project experimentation, and it was only about five bucks apiece - they had barrels of random dichroic scrap glass laying around! But anything like that would be worthless over a camera lens for taking pictures.

i know exactly how dichroic filters work. i've clearly explained how in great detail in this thread. you said you can't buy them from b&h, you can, you're wrong, get over it. i don't know why you obsessed over b&h in the first place since i mentioned there are a ton of places to get dichroic filters. b&h was just one example. "And if you missed what I stated, I outright built a big SIMULTANEOUS additive enlarger, you'd understand why colored sheets of any type in a filter drawer would not convert an enlarger head into that purpose. That would hypothetically work for SEQUENTIAL additive printing, but so would a basic set of decent 29, 61, and 47B glass filters right over the lens. " what the hell are you talking about? i never claimed anything like that. i said dichroic filters are used in colour enlargers. they are, i'm sitting 6 feet from a dichro colorhead right now. "anything like that would be worthless over a camera lens for taking pictures" i asked you if you'd tried using dichro filters on a camera. you're dodging the question just like you've dodged or strawmanned everything else i've said, so i assume you haven't. my claims about how a dichroic filter will act in the specific use being discussed in this thread are based on first-hand real world experience. you are completely full of it, incapable of having an honest discussion and not worth wasting another second on. put me on ignore and don't ever speak to me again.

[Drew Wiley]

Indeed. Welcome to my ignore list, temporarily at least. A waste of time. Assume and accuse whatever you wish. It doesn't in the least affect what I already know, and have already done.

[maltfalc]

[Nodda Duma]

Hi Jason, slightly off topic but since you brought up EO and Thorlabs, do you know if their products are generally of equal quality? I might need a BBAR-coated optical window so I’ve been looking around. Some years ago I was able to buy some custom glass like this from Schneider Optics (the U.S. arm) but I think it is more complicated to do that now (if still possible) and both EO and Thorlabs are likely less expensive. I’m looking at a few other places as well but figured I’d ask.

I would use them professionally without question, if they had what I needed. They often don’t (as you may guess), so other sources of a wider variety of stock and custom windows/filters are Rainbow Research Optics, Omega Optical, Semrock. I have used them all.

There are others, but more expensive and specialized. Coincidentally was just talking to a supplier about feasibility of a very challenging filter which will likely cost — no joke — $30k+ for a 7/8” diameter filter. Hoping I don’t need it but I probably will.

As a fun side note, when it comes to technically challenging filters, I talk to certain suppliers not because of the company, but because of the individual coating designer who works there. Coating design isn’t something everyone can do. The companies I mention all have good coating designers, and BBAR vis coatings are almost trivial anyways.

-Jason