Making an UV enlarger

[BJ68]

@BJ68 In your results, when you specify "with filter" are you referring to the glass focusing lens that attaches to the LED heatsink?

No...I do not use the supplied glass lens...

For this testing Filter means

a) BP 365/12 https://www.deltaopticalthinfilm.co...sheets/bandpass-filters/BP365-12-LF101653.pdf for the Nightsearcher Torch
b) The filter glass of UV transilluminator Lid e.g. https://help.lumiprobe.com/media/ca...image/57/aed3d76135685d5e76623ed32d25d8c2.jpg with will pass UV
c) Not used, because to expensive to play around (heat problems*): https://www.baader-planetarium.com/en/filters/baader-u-filter-(venus-and-uv---350nm).html?___SID=U
*= Company says filter was tested @80°C and they do not know if it resists more than that for longer time.....
d) Ordered but not arrived: ZWB2 UV Band Flow Filter UV with 42 mm diameter....should fit in the supplied holder....

I want to get rid of any visible light for the "UVivF" (ultraviolet-induced visible fluorescence) photography....which is/was the primary plan....

bj68

 

[ProfessorC1983]

Thanks for clarifying! When I have a chance I'll do some more in-depth testing with and without the lens.

 

[douwe]

I just stumbled on this thread by accident, having built a prototype UV enlarger myself over the past weeks for cyanotype. I use it to enlarge my 6x7 negatives to A3 paper size (11-3/4 x 16-1/2inch, 297 x 420mm)

The key to this game isn't using as much light as possible, but making the enlarger efficient in terms of its light path and its transmission. That means using acrylic fresnel lenses for the condensor, and setting the whole thing up as a point source enlarger. For point source enlargers, the light source should be smaller that the exit pupil of the enlarger lens, otherwise the light cannot pass the lens. So using the latest high power UV LEDs with a quarz lens is the best approach. the dies in the LED I use measure 7x7mm, this allows me to use a regular 100/5.6 enlarger lens.

Using a LED with a larger cross-section is not effective; you'd need a faster lens to pass all the light. There are not many fast enlarging lenses, and fast lenses that do exist are either poorly corrected for near UV, leading to massive focus shift, or optically inferior for the application due to field curvature or poor sharpness for other reasons.

I also found that for the cyanotype process a 385nm wavelength works very well. There is a trade-off between transmission of the enlarger lens and sensitivity of the cyanotype process. Below 380nm the transmission of enlarger lenses falls off steeply. The spectral sensitivity of cyanotype really drops off at about 390nm. So there is an optimum based on the two factors.

Focusing isn't really an issue. There is a focus shift also with enlarging lenses that are corrected to near-UV (they pretty much all are), so a grain focuser is not very useful. I use copier paper on my easel. The optical brighteners fluoresce blue as a result of UV illumination. With a pair of UV safety glasses you can focus by eye. If you print the same format all the time, you can fine-tune with a piece of paper placed on a wedge.

 

[ProfessorC1983]

That means using acrylic fresnel lenses for the condensor, and setting the whole thing up as a point source enlarger.

Interesting! Where did you source the fresnels? I was under the impression that acrylic blocks a fair amount of UV, but based on my tests it seems the condenser lenses are the biggest issue in my current design so I'm eager for an alternative.

What sort of exposure times do you get for A3 (which is ~5-6x magnification by my crude math)? Any issues with heat affecting the negative?

 

[douwe]

I got the fresnels from Aliexpress. You can find a lot of diameter and focal length combinations, but it is a bit of a puzzle to find a suitable combination for your condensor system. As far as I know the transmission of acrylic (PMMA) for ~385nm is about 90%. The transmission drops off at lower wavelengths around 300nm. The big party trick of the fresnel lens is how thin it is. Al things being equal, a fresnel lens will have higher transmission because light passes through less material than with a comparable glass lens. Less material equals less attenuation.

I print 6x7 negatives in a regular Durst negative carrier with glass inserts. Exposure for an A3 piece of paper is 20min-40min depending on negative density. The enlargement is about 5x. I haven't noticed any adverse effect on the negatives. Perhaps this is due to the larger surface area of the negative compared to 35mm and the glass inserts. A regular lightsource would of course also put out Infrared light, but a UV LED doesn't.

 

[AgX]

I searched around and it seems that there are UV bulbs available with the E27 fitting.

Such lamps need a special power supply, thus you would need to put such device into the mains feed of the enlarger. Also these lamps are rather large and thus may not fit.

 

[Andrew Patteson]

I just stumbled on this thread by accident, having built a prototype UV enlarger myself over the past weeks for cyanotype. I use it to enlarge my 6x7 negatives to A3 paper size (11-3/4 x 16-1/2inch, 297 x 420mm)

Wow, very interesting! You sure held off on making your first post for a long time, but it is a good one!

I would love to see images of a print or three. Are there other alt processes that might work with an enlarger like this?

 

[radiant]

I just stumbled on this thread by accident, having built a prototype UV enlarger myself over the past weeks for cyanotype. I use it to enlarge my 6x7 negatives to A3 paper size (11-3/4 x 16-1/2inch, 297 x 420mm)

Just mindblowing. Thank you so much for sharing. I wish I had the understanding how to design the fresnel lens arrangement.

 

[AgX]

You sure held off on making your first post for a long time, but it is a good one!

Yes, 12years of silence and then something like this. And then the idea to use fresnel condensers.

 

[DREW WILEY]

Try not to burn your house down. The subject of properly cooling your lamp housing should be integral to all this. Fresnels are a different topic still; I'd consult a specialty website or Edmund Scientific Industrial division for specifications and temperature tolerances. There are more types than most people imagine. Acrylic is not the kind of plastic generally used.

 

[douwe]

I'm by no means an optical engineer, but a bit of reading goes a long way. If there is enough interest amongst the people in this thread, we could perhaps set-up a zoom call? I don't mind showing some prints, but I mostly do portraits of friends and I do not want to post those online.

 

[DREW WILEY]

At least one optical engineer does contribute to this and certain other forums.

 

[AgX]

Try not to burn your house down. The subject of properly cooling your lamp housing should be integral to all this.

Yes you right about this critical point with common fesnel lenses.
But in this very case the lamp proper does not mainly emmit IR, actually none at all*, it is only its base that does. And this can easily be screened and cooled


*correct me if I am wrong on this, did not look up data sheets

 

[douwe]

It's very important to think about cooling, but it's not very critical in my set-up. I use a 40W LED, that probably emits 15W in UV light. The 25W in heat produced at the chip is carried away by a processor cooler quite efficiently. The chip is mounted on a copper core pcb. The 15W in UV light is of course mostly transmitted. The diameter of the fresnel lenses is 150mm, so any heat is also spread over a large surface area. Everything is cool to the touch. The light does concentrate in the enlarger lens of course, but I haven't noticed a build-up of heat there either.

 

[douwe]

So, I was a guest on the Homemade Camera Podcast, and we talked about my UV enlarger. I thought you'd be interested to see it!

 

[grain elevator]

So, I was a guest on the Homemade Camera Podcast, and we talked about my UV enlarger. I thought you'd be interested to see it!

Thoroughly enjoyed that, very inspiring! Thanks!

 

[douwe]

Thanks guys!

 

[ic-racer]

I watched the video but am still confused about the light source. How did you make it? Are you using water in the heat pipes? Are you letting it boil then closing the ends with a torch? What kind of power supply are you using?

 

[douwe]

Hi ic-racer,

It's much less complicated than you might think. The cooler is a pc processor cooler and the heatpipes are part of it. I just bought one. Every processor cooler has a flat surface that sits on top of the processor to carry away heat. In the enlarger the copper pcb with the LED sits against that surface of the processor cooler.

The power isn't so hard either. I use a 18V power supply that can handle 6 amperes. From that power supply I run two buck boards that can control current and voltage. The first powers the cooler fan at 12V and 0.15 amperes. The second runs the LED at 14V and 2.8 amperes (check the data sheet of your LED).

Hope this helps,
Douwe

 

[radiant]

@douwe thanks for clarifying. Could you help with picking correct fresnel lenses? It is otherwise a completely shot in the dark for me. I would like to build 5x7" enlarger so maybe I could consider doing it for both UV and RGB

 

[douwe]

Hi Jouni, I sent you a message via the contact form on your blog.

 

[radiant]

Hi Jouni, I sent you a message via the contact form on your blog.

I got your message, nice!

 

[seeschloss]

I thought I might chime in.

I also built a UV enlarger for cyanotypes last year (when this thread was still dead). In my case, I simply removed the lamp holder from a Durst M301 enlarger, and fitted a square 100W UV LED array in its place. I kept the original condenser, film carrier, etc, although I added two fans under the film carrier to blow on the film itself in order to cool it down. I use an El-Nikkor 50mm that opens to f/2.8.

It works fine, gets hot but not so much as to be too hot to touch. The enlarger can only do 35mm, which print on 10x15cm in anywhere between 10 to 30 minutes. At that size, even f/2.8 gives sharp enough prints. Larger prints take proportionally more time of course, and can be tricky to focus (I focus using a magnifier on fluorescent white paper) but work fine even if they might take a few hours.

I see alot of speculation and outright fear in this thread, but it's really not that complicated or dangerous to print using UV. Most of the problems in the past used to be around the light source itself, a problem which has been solved today with small and efficient LEDs.

 

[Snowfire]

Many enlarger lenses do transmit quite a bit of UV-A; quite a few photographers on the Ultraviolet Photography website use one of the EL-Nikkors as a macro lens.

The UV transparency of the acrylic Fresnel lenses is due to their thinness; I have seen a similar phenomenon with a pocket magnifier card and even taken a crude UV photo using it.

 

[douwe]

Almost all enlarging lenses transmit quite some UV-A, because black and white paper is sensitive to UV-A to green light. It was a design consideration. I suspect that enlarging lenses for black and white (so not APO lenses for colour) where corrected to focus UV-A to green light in the same plane.

However, a lens suitable for macro photography in UV isn't necessarily good for UV enlarging. For UV enlarging I mostly want high UV transmission. The tests for macro UV photography focus mostly on the image quality and use sensors that are orders of magnitude more sensitive than the cyanotype process.

Some of the more infamous UV lenses, such as the el-nikkor 63mm, really have no higher transmission for UV than a componon or rodagon in my experience.