as big as my FOTAR Baseboard, 40X60"Originally Posted by Peter De Smidt
6 sheets 14X16-XRay for my south windows inside my double steel doors
I was testing fade and stained glass effect
as big as my FOTAR Baseboard, 40X60"
6 sheets 14X16-XRay for my south windows inside my double steel doors
I was testing fade and stained glass effect
Tin Can
I've built / rebuilt a DIY LED 5x7 head for my Durst several times now.
First was with standard RGB LED Strip lights - worked as proof of concept, but the Blue isn't the right wavelength for VC papers - gave about a grade 3 1/2.
I updated several years ago to add 'Pink' LEDs instead of Blue from the RGB set. Everyone is going to say I'm wrong and need to use Deep/Royal Blue, but after much research (and confirmation with a spectroscope) the 'Pink' LEDs I have are really a deep blue LED emmitter with an additional phosphor coat that fluoresces, adding wavelengths making it pink. Deep Blue by itself is terribly hard to see in the dark - the added waves just makes it much easier to see - much like the Ilford MG #5 filter is pink. Easily gives me grade 5 as shown by step wedge. The bottom set is pure pink LED, the one above is Ilford #5 through white light.
I recently rebuilt the head but got rid of the RGB + pink, and updated to individual strips - Green, Pink and White (though the Green + pink together produces a pretty convincing white).
The newest COB strip lights are amazingly bright. For the attached image they are turned down to about 5% output. For a 4x enlargment I run them about 50% with times in the 15-30 sec or so.
I found a 3 channel LED controller/dimmer with digital display from one of the online LED shops, along with a custom relay controller I built for using with my standard darkroom timers, eliminating the time delay LED can have.
It has been working great. Getting the right diffusion and evenness can be tricky but very doable. I have not noticed any banding in enlargements or contact prints.
Even monkeys fall from trees -- Japanese proverb
That's great! I'd be glad to be wrong about how much light is needed.
“You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
― Alexander Den Heijer, Nothing You Don't Already Know
I built a 5x7 with 12 green and 12 royal blue high power LEDs. It could easily be scaled up to 11x14 with 4x the number of LEDs. 40x60 should be doable with reasonable exposure times.
Can you point me to the details of the pink LEDs you are using? They sound interesting and not something I would have thought of.
The item I ultimately got most recently was https://www.amazon.com/gp/product/B09MRK3CHC
When I was first looking at them several years ago, one of the LED retailers has posted the spectrum graphs of all the options, but either I remember the wrong site, or they stopped publishing that info. They matched closely to that of the curve of the High contrast layer of Multigrade.
I used a spectroscope myself on both the Royal Blue and the Pink, and the peak in the Blue was exactly the same. In fact, if I bring the lit Royal Blue LEDs close to the unlit Pink, the pink will glow brightly from the phosphors.
Even monkeys fall from trees -- Japanese proverb
Interesting. I can definitely see the advantage of being able to see the projected image when using a high grade for a negative. I was considering using red LEDs to address that issue in my next iteration of the head. Do you think a lot of the blue wavelength intensity is lost as it interacts with the phosphors? In other words what are the exposure times compared to the same LEDs without the phosphors?
If you want to go the DIY route, lot's of people have built similar light sources to what Larry talks about for reef aquariums.
“You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
― Alexander Den Heijer, Nothing You Don't Already Know
My experience with the Heiland's blue light is that its almost too efficient...so I'd not worry too much about a bit of pink getting in the way if that's what's likely to happen.
...and Larry - thanks for your encouraging words about "scaling up" (from 5x7)...gives me a bit of hope!
I do have another concern about making big (30x40, 40x60 inch) enlargements from 11x14 - which is that I might be quickly reaching a point of diminishing returns (compared to smaller format enlarging) as I will tend to be very close to the "cliff of diffraction," and I may need to change my tune and set my aperture values for somewhat larger openings when compared to those for contact prints...which also means extra care in focussing and courting the likelihood of occasional negative movements/displacements just prior to (or during!) making an exposure.
I've actually been thinking that I might occasionally make pairs of certain images, with one being set back a bit, aperture-wise, for "best compromise for enlarging," and a second a bit more stopped down for contact printing.
I haven't done any exposure testing of the Royal blue vs Pink. If any is lost, I haven't noticed in use. With this latest build I'm getting similar times with the Green vs Pink channel. a typical 5x7 neg enlarged to 11x14 at f/8 is in the 10-20 sec range on a single channel.
BTW - Thanks for documenting your Durst 138 LED build years ago - I recall referring to your site several time when working on mine - a salvaged S-45 Special missing condensers.
Even monkeys fall from trees -- Japanese proverb
Posting Permissions
Reply With Quote
Bookmarks