Durst Cls 1840 & 2000 Dichroic reflectors Thread

reneboehmer · Dec 12, 2024

Dear Community,

since my efforts in finding spare reflectors for my CLS 1840 failed, I have decided to make them myself.

I was able to gather the following information:

1) There were two different kinds of reflectors, one with a rippled effect inside and one with a smooth finish. Rippled was more common.

2) The reflector needs to be made of borosilicate (or maybe soda-lime) glass, which is less than ideal since it's terribly expensive. I know there are some coaters who will coat on aluminum (which could easily be CNC milled) but aluminum will reflect a lot of heat, whereas glass would let it transmit. Also, oxidization, thermal expansion and general surface compatibility might be an issue. Alumina or zirconia ceramics might also be an option, I have no clue tho who these would be manufactured.

3) The surface is probably steam coated with (guesswork) (Expensive to be done)

High-index: Titanium dioxide (TiO₂), niobium pentoxide (Nb₂O₅), or tantalum pentoxide (Ta₂O₅).
Low-index: Silicon dioxide (SiO₂) or magnesium fluoride (MgF₂).

This will surface should transmit long waves like heat and reflect white light. This will make sure that the parts following the tungsten source aren't damaged by the heat.

Please, if you have some knowledge about these reflectors, share it here! I will try to make this happen and share the reflectors with everyone in need.

All the best,
René

reneboehmer · Dec 12, 2024

I have found a company in Germany who are willing to coat a small batch of reflectors. They mentioned they have done this kind of photographic reflectors before. Depending on the price, I might try finding a Chinese company.

gary mulder · Dec 12, 2024

Maybe you can find someone how is willing to part with his used up reflectors and let them be recoated. In the past I just threw them away.

reneboehmer · Dec 12, 2024

gary mulder said:
Maybe you can find someone how is willing to part with his used up reflectors and let them be recoated. In the past I just threw them away.

Might be hard to find enough, tho. I would probably need a minimum of 75–100 pieces.

koraks · Dec 13, 2024

reneboehmer said:
(or maybe soda-lime) glass

Soda lime is plain old milk bottle, window pane glass. It's common as muck & cheap as chips.
The main reason I can see why borosilicate would be preferred here is its better ability to withstand thermal transients than soda lime glass.

reneboehmer said:
I will try to make this happen and share the reflectors with everyone in need.

That's very generous of you. For now, it's also fine that you continue to engage with the community to find information, receive suggestions etc. Once the project comes to a point where it turns into a product that you'll offer for sale, please use the Classifieds section. It works best if at that point you start a new thread in that section to offer the product for sale; we can then still keep the present thread open for technical discussion.

ic-racer · Dec 14, 2024

Sometimes one can find off the shelf stuff like this on Alibaba. Maybe someone has something that would fit.

reneboehmer · Dec 15, 2024

ic-racer said:
Sometimes one can find off the shelf stuff like this on Alibaba. Maybe someone has something that would fit.
View attachment 385422

Hey IC,
I have seent these too, but they seem a bit sketchy. I think they are too small and have no opening for the ventilation to cycle through.

reneboehmer · Dec 23, 2024

https://zeiss-campus.magnet.fsu.edu/articles/lightsources/tungstenhalogen.html
this is a good resource if anyone is trying to read up on lamps and reflectors

reneboehmer · Dec 23, 2024

Also some images of how my refelctor looks.

reneboehmer · Dec 23, 2024

"If the entire spectrum of radiation emitted by the lamp is required, or in cases where infrared light is useful, metal reflectors or glass reflectors with a thin gold coat are the optimum choice. However, where specific reflection properties must be used to select wavelengths through interference, dichroic thin-film coatings on glass reflectors are optimal. These coatings consist of approximately 40-60 very thin layers, each only a quarter wavelength of light thick and composed of alternating materials having a high and low refractive index. Fine tuning of the thickness and number of layers enables designers to generate a wide variety of spectral output characteristics. Among the dichroic reflector lamps, the most useful for microscopy is termed a cold-light reflector because only visible light in the wavelength region of 400 to 700 nanometers is sent to the optical system (Figure 4(d)). Infrared wavelengths radiate through the rear of the reflector and are pumped away from the lamphouse with an electrical fan. The application of suitable cold-light reflectors reduces the overall thermal load on the illumination system and produces light that can be recorded with film and digital cameras."

Quote from Zeiss Campus

ic-racer · Dec 23, 2024

The reflector looks pretty good compared to some I have.

There are at least two types of deterioration. On the left there is pretty uniform fading. One the left the lining is chipping off.

Both of these still work fine.

reneboehmer · Dec 26, 2024

Update.
I have found a company in Germany that is willing to chemically clean my reflector and recoat it with a different mix of chemicals originally used.
The worker from the company offered me an Aluminium + MgF2 coating. I guess it's better than nothing, but I am a bit unsure about if it would perform better than my damaged reflector. It seems to reflect heat just as well as light. Which in turn defeats the purpose of the original intend, to create a "cold light source".
It also reflects most of the UV light produced. Which is not optimal. There is a UV cut off filter installed in the machine, but I don't know how good it is. I fear this might be a problem for color enlarging, after reading Cteins book. Where he mentioned UV light as a potential issue. I also found that Aluminum MgF2 coatings are very sensitive, in contrast, the dichro coat should be very durable indeed.

Any opinions on this?

gary mulder · Dec 26, 2024

Your reflector, as ic-racer already mentioned, is in a reasonable state. I would not recoate that one. Try to source an other one in less shape.

reneboehmer · Dec 26, 2024

gary mulder said:
Your reflector, as ic-racer already mentioned, is in a reasonable state. I would not recoate that one. Try to source an other one in less shape.

This might be a good idea. I'll try to find one.

koraks · Dec 26, 2024

reneboehmer said:
I fear this might be a problem for color enlarging, after reading Cteins book. Where he mentioned UV light as a potential issue.

Modern Fuji RA4 paper has a rather effective UV blocking filter. When doing color printing with dichroic filters, the latter will also attenuate most of the UV. UV is not really something you need to worry about. If it worries you, just add a regular UV filter to the optical path somewhere.

reneboehmer · Dec 27, 2024

koraks said:
Modern Fuji RA4 paper has a rather effective UV blocking filter. When doing color printing with dichroic filters, the latter will also attenuate most of the UV. UV is not really something you need to worry about. If it worries you, just add a regular UV filter to the optical path somewhere.

Good to know! Thanks so much!

reneboehmer · Dec 28, 2024

Update.
My friend has these old dichro reflectors that were used in Fuji scanners. They seem to have a good size.
I will pick some up tomorrow and check if they might be a viable option.

Durst Cls 1840 & 2000 Dichroic reflectors Thread

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