about light source and duration of exposure

[alentine]

...
What are you trying to enlarge & to what size?

Thanks Lachlan,
I'm afraid that some of my negatives that print well at grade 4 usual print sizes(24"x20" or smaller), will suffer too much from lacking contrast at bigger print sizes of 40"x30" or bigger.

 

[alentine]

i am making prints 70x55 cm up to 140x75.
And i use a 100w led panel (approx 1000w).
exposure times are around 20-35 seconds.
works out pretty well

Thanks Chris.
May I know what type of LEDs you are using.
Appreciate photos of the mixing box from inside.

 

[Lachlan Young]

Thanks Lachlan,
I'm afraid that some of my negatives that print well at grade 4 usual print sizes(24"x20" or smaller), will suffer too much from lacking contrast at bigger print sizes of 40"x30" or bigger.

Registered contrast boost masks might be the best way forward I'm afraid - though there's often a lot more contrast that kicks in between 4 & 5 than you'd expect - depending on paper. Toning the neg in selenium might help a bit though.

 

[M Carter]

Another idea regarding raw power for print exposure; years ago I wanted to dupe 35mm slides onto velvia sheet film. The lab said this was "impossible". I only had a condenser enlarger.

I rigged up a system that aimed a Vivitar flash at the condenser light bulb, illuminating the bulb with the flash. I used lighting gels in the filter drawer to tune the blue-ish flash to daylight color temp. Used the bulb to focus and the flash to expose. Duping to 4x5 and 8x10 film, the flash was on its lowest power and there were a couple layers of ND lighting gel in the filter drawer.

I've always assumed a more powerful flash and CTO lighting gel (get the strobe to tungsten color temp) could work for large prints, even if it needed a pop or two.

Dodging and burning would be difficult with such a setup, and chances are some sort of masking system would be needed to fine tune things. My idea for very-large prints is doing initial prints at 20x24 and re-photographing those with very fine-grained 4x5 film though.

 

[chris77]

Thanks Chris.
May I know what type of LEDs you are using.
Appreciate photos of the mixing box from inside.

i use the 100w cold white version, i have modified the panel, cut it smaller to fit into the head of my durst m800, but beware of the electricity. needs isolation and cannot be turned on for too long, as it gets pretty hot. i use glass carrier. and two layers of diffusing pergamin paper.
magnifying 6x7 10 times @ f5.6 gives about 20 seconds max for a medium dense negative.
cannot show you right now, im on vacation.
cheers

 

[Sirius Glass]

The size of the baseboard is an indication of the maximum size of enlargement, unless one projects on the floor or wall. Even then the lighting may not be even at the larger size.

 

[chris77]

The size of the baseboard is an indication of the maximum size of enlargement, unless one projects on the floor or wall. Even then the lighting may not be even at the larger size.

when the led panel is bigger than the negative even illumination is guaranteed.

 

[Sirius Glass]

when the led panel is bigger than the negative even illumination is guaranteed.

But my enlarger does not have LEDs.

 

[chris77]

But my enlarger does not have LEDs.

..... so?

 

[Sirius Glass]

..... so?

My statement still stands. Furthermore just changing the light source does not change the enlarger optics. The optical system has size limitations which would need changes beyond the light source alone.

 

[chris77]

certain optics are more suitable (optimized) than others. but still, i do not quite understand what you are trying to say?!

 

[Sirius Glass]

certain optics are more suitable (optimized) than others. but still, i do not quite understand what you are trying to say?!

The diffuser or condenser have limitations of quantity of light, quality of life and the light distribution evenness. The baffles and interior design take those into consideration and are not set up for a wider image past a point. On my enlarger, if I were to put a shorter focal length lens on to get a larger print than the enlarger base, I might not be able to get even light with enough power to be useful. When I tried it, I ran into uneven illumination and distortion problems. Yes I could remove the enlarger from the base and put the easel on the floor or turn the enlarger and projecting on a wall, but doing than may not result in even print illumination. The only way to know is to try it and see if acceptable prints can be made. I found that beyond 16"x 20" or 20"x24", it was not worth the work, especially since there are still a number of custom photo finishers nearby. Therefore I have had a number of 24"x36" and 30"x30" color and black & white prints made optically by local talent.

 

[chris77]

The diffuser or condenser have limitations of quantity of light, quality of life and the light distribution evenness. The baffles and interior design take those into consideration and are not set up for a wider image past a point. On my enlarger, if I were to put a shorter focal length lens on to get a larger print than the enlarger base, I might not be able to get even light with enough power to be useful. When I tried it, I ran into uneven illumination and distortion problems. Yes I could remove the enlarger from the base and put the easel on the floor or turn the enlarger and projecting on a wall, but doing than may not result in even print illumination. The only way to know is to try it and see if acceptable prints can be made. I found that beyond 16"x 20" or 20"x24", it was not worth the work, especially since there are still a number of custom photo finishers nearby. Therefore I have had a number of 24"x36" and 30"x30" color and black & white prints made optically by local talent.

thanks for sharing your experience. i understand you now, but still i would like to encourage people to make the effort and try it. out of my own experience it is totally doable and fascinating. to each his own.
regards, c