LED lighting for wet plate collodion

[Punker]

For still life you can just pop a strobe a few times to get exposure. No need for anything fancy.

I was under the impression you need 3,600+ watt seconds of strobe power. I don't own any proper strobes yet (especially ones that powerful); just hot tungsten movie lights which are poor sources of blue light. Doesn't a speedlight have less than 100ws?

It appears quartz halogen lights have a good spike at the right point in the spectrum too. Still, I think I'll try my hand with a bright cool-white LED which has an almost identical spectral output to deep blue, but is more natural and easy to focus with.

[williaty]

I was under the impression you need 3,600+ watt seconds of strobe power. I don't own any proper strobes yet (especially ones that powerful); just hot tungsten movie lights which are poor sources of blue light. Doesn't a speedlight have less than 100ws?

It appears quartz halogen lights have a good spike at the right point in the spectrum too. Still, I think I'll try my hand with a bright cool-white LED which has an almost identical spectral output to deep blue, but is more natural and easy to focus with.

No, the bright cool white isn't nearly equivalent to 450nm blue. You're wasting a TON of electrons producing photons that the collodion can't seen. Who knows what the ratio is but you could easily be spending 90% of your electrons producing light the collodion can't see. Broad-spectrum LEDs both produce photons the collodion can't see and also have significantly lower luminous efficiencies than monochromatic LEDs do. Both of these hurt you.

FWIW, my friend who got me into this just bought one of the 50W 450nm LED+lens+heatsink kits off eBay. We'll let you know how it goes when it gets here


On the topics of strobes, a lot of people say you need 10kJ to make this work. For whatever reason, I'm doing half-length portraits with just 400J.

[Tin Can]

Cool! I await results.

No, the bright cool white isn't nearly equivalent to 450nm blue. You're wasting a TON of electrons producing photons that the collodion can't seen. Who knows what the ratio is but you could easily be spending 90% of your electrons producing light the collodion can't see. Broad-spectrum LEDs both produce photons the collodion can't see and also have significantly lower luminous efficiencies than monochromatic LEDs do. Both of these hurt you.

FWIW, my friend who got me into this just bought one of the 50W 450nm LED+lens+heatsink kits off eBay. We'll let you know how it goes when it gets here


On the topics of strobes, a lot of people say you need 10kJ to make this work. For whatever reason, I'm doing half-length portraits with just 400J.

[cuypers1807]

I was under the impression you need 3,600+ watt seconds of strobe power.

3600+ for a one pop exposure. If you are shooting still life you can pop it over and over until you get an exposure built up on the plate. That obviously is not an ideal situation but doable if that is all you have/can afford.

[williaty]

Keep in mind that "pops" are sub-additive. They have reciprocity failure just like any other way of building total exposure. 1 pop is what the meter says. 2 pops is pretty damned close to a full stop above 1 pop. To get the next stop, you typically need 5 pops, not 4. It gets exponentially worse from there. By the time you calculate you need 12 pops... just forget about it.

[Punker]

Found these 36-watt 450-60nm blue LED lights. seems promising.

[williaty]

Yeah, those seem like they'd work. No idea how many you'd need though. The only real difference to what I found on ebay is form factor. The eBay light is super industrial/mad hatter while what you found on Amazon is a finished product. You pay slightly more per photon for the nicer product.

[Tin Can]

I don't shoot wet plate yet! Never say never...

But I found X-Ray film to work without reciprocity failure with 10 additive pops from my Einstein strobes. The math says to use 8 and I give it 2 more. ~20%. Obviously dead life photography.

Keep in mind that "pops" are sub-additive. They have reciprocity failure just like any other way of building total exposure. 1 pop is what the meter says. 2 pops is pretty damned close to a full stop above 1 pop. To get the next stop, you typically need 5 pops, not 4. It gets exponentially worse from there. By the time you calculate you need 12 pops... just forget about it.

[williaty]

Those extra 2 pops are your reciprocity failure. It just means that the x-ray film you're working with has good reciprocity characteristics for strobe bursts. I wonder if that's a trait of all x-ray film?

[seezee]

I don't shoot wet plate yet! Never say never...

But I found X-Ray film to work without reciprocity failure with 10 additive pops from my Einstein strobes. The math says to use 8 and I give it 2 more. ~20%. Obviously dead life photography.

I use Einsteins with x-ray too; they put out plenty of power with a single pop. Why are you using additive pops? I'm confused.