Using ND gels to reduce exposure time?

[DannyTreacy]

I’m going to be doing some black and white contact printing, using a low wattage bare bulb, with an inline dimmer switch and with a reflector to control the light’s direction. I’ve made a mask with a cutout so that I can insert contrast filters when required.

I’m using standard enlarging papers so, if I find that my exposures are too short, I was considering using some neutral density lighting gels to put between the bulb and the mask.

Does anyone know if this would have any undesirable effects, in terms of contrast adjustment, blocking any part of the negative’s information or anything else?

I know that wrapping tissue paper loosely around the bulb is an option but I’d rather not do this as I’d like to adjust the bulb’s brightness by not having to remove the mask and filter holder I made.

Thanks all.

[Pere Casals]

using a low wattage bare bulb, with an inline dimmer switch and with a reflector to control the light’s direction.

With this ($7) you have the dimmer, the colors for contrast control and a R button for safe light.

Some kitchen aluminium foil may be useful to make a 1cm2 window in the bottom of the bulb, emulating a single point light source that may have some benefits, and will allow better scaled light control.

[scheinfluger_77]

. And where would we find this little gem?

[Luis-F-S]

Can't you use a lower wattage bulb? If you have an enlarger as a light source, it's easy enough to lower the light output.

[pepeguitarra]

I the old days, I used a lot of parchment paper to cover the light bulb and that did it. That is about 55 years ago (there were only incandescent 60 and 100 watts bulbs)

[chassis]

I used ND gels in the filter drawer to increase enlarging exposure. No undesired effects.

[Doremus Scudder]

If your ND filters are truly neutral (or even pretty close), there should be no problem using them to reduce light intensity and they won't affect the color of the light (e.g., a specific contrast filter) either. Go for it.

Masking the bulb like Pere suggests will give you a slightly more collimated light source, but if your negative and paper are in good contact, I'm don't think you'll notice any difference.

Like pepeguitarra, I used to use parchment paper or even typing paper over my contact printing light source to reduce intensity. Never a problem.

Best,

Doremus

[ic-racer]

You can't move the lamp and print frame farther apart? Doubling your distance will increase your exposure time by 4 times. Also, the farther they are from each other, the more even the illumination.

[DannyTreacy]

Some kitchen aluminium foil may be useful to make a 1cm2 window in the bottom of the bulb, emulating a single point light source that may have some benefits, and will allow better scaled light control.

Hi, thanks for the info, do you wrap the foil over the bulb or need to create distance? Thanks

[Jim Jones]

I used a dimmer to extend expensive enlarger bulb life, and never noticed a significant change in its effect on contrast filter performance. However, I never ran accurate tests to confirm this. The specifications of the enlarger lamps I've used mentioned short bulb life. This suggests they normally operate at relatively higher voltage than household lamps, with a shift towards cooler colors. Some LFPF member with precise equipment and extra time might test the effect of varying lamp voltage on contrast filters.

A well-designed filter holder would permit easy changing of contrast filters, and thus easy changing of ND filters. There are several approaches to improvising ND filters. One can expose film to weak room light, develop it, determine its filter factor, and use it in the filter drawer. One could photograph an appropriate fine pattern with litho or other high contrast film to make a ND filter. An appropriate pattern could be laid down on clear film with opaque tape or opaque ink. An old-time print shop may have obsolete half-tone masters.

As to your last question, I would avoid any set-up that encourages heat build-up in the lamp enclosure.