4x5 film as neutral-density filter

[BetterSense]

I need to cut down the light on my condenser enlarger. I don't have any neutral-density gels to put in the filter drawer, but I could just fog a sheet of 4x5 film and use that. Can anyone see a problem with doing this? I think the polyester base will be able to withstand the heat ok.

 

[MartinP]

You could also put tracing paper or white paper in the filter drawer. This would increase diffusion somewhat, but would be a lot quicker to test. Then again, changing out a 120W bulb for a 75W version is also simple. How much of a reduction in light transmission are you looking for?

 

[NB23]

changing a bulb would be the best bet. But I don't see why your 4x5 sheet wouldn't work. As long as it's over the negative, not under

 

[ic-racer]

That would be the expensive option... 4x5 film is 20 sq" at $1.40 while the Rosco ND is 480 sq" at $6.50.
One reason to use film is to make a perfect center filter to take into account lens falloff and condenser unevenness.

 

[BetterSense]

I have some expired film, cheap film, litho film, and xray film. But no rosco gels, cheap though they may be.

I thought about paper, but don't condenser lenses actually project an image of the bulb? Also I would worry about paper yellowing or burning.

I'd like to block 2 to 4 stops of light.

 

[BetterSense]

In a moment of desperation I tried a layer of paper towel in the filter drawer. It seems to work fine and I haven't noticed the embossed pattern in the pictures, although I have yet to do a rigorous test with a blank sheet of paper. For reference, high-quality paper towels are about 5 stops.