DIY ND Filter for enlarger?

ic-racer · Jun 19, 2012

Or Use a longer lens for more distance.

No. (would violate conservation of matter and energy if it were so)

BetterSense · Jun 19, 2012

It will increase the distance between the light source and the paper

Yes

which will increase the time needed to expose, no?

No

Such as when raising the head for enlargements time is increased.

Time is increased for larger enlargements because they are larger.

X. Phot. · Jun 19, 2012

A variable/adjustable ND filter can be had by stacking two polarizing filters. I don't know if this would serve in this specific situation.

Steve Smith · Jun 19, 2012

Newt_on_Swings said:
It will increase the distance between the light source and the paper, which will increase the time needed to expose, no?

No.

For the same magnification, the same amount of light is spread over the same area of paper.

Steve.

ic-racer · Jun 19, 2012

Newt_on_Swings said:
It will increase the distance between the light source and the paper, which will increase the time needed to expose, no? Such as when raising the head for enlargements time is increased.

If you have a very smokey or foggy darkroom this would be the case

Newt_on_Swings · Jun 19, 2012

Man, I think I'll have to try this when I head to the dark room. Whatever happened to the inverse square law in regards of light fall off because of distance? Instead of just yes or no, an explanation would be useful.

from wiki:
"The intensity (or illuminance or irradiance) of light or other linear waves radiating from a point source (energy per unit of area perpendicular to the source) is inversely proportional to the square of the distance from the source; so an object (of the same size) twice as far away, receives only one-quarter the energy (in the same time period)."

Bill Burk · Jun 19, 2012

Newt_on_Swings said:
Man, I think I'll have to try this when I head to the dark room. Whatever happened to the inverse square law in regards of light fall off because of distance?

I think the law of inverse squares breaks down any time you try to use it or explain it. Think of how far away the sun is...
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When you use a longer focal length lens, you raise the enlarger making it dimmer but you decrease the magnification making it brighter.

When you use a shorter focal length lens, you spread out the square so light falls off faster but you move the enlarger lower making it brighter.

Newt_on_Swings · Jun 19, 2012

Ah thank you Bill, got it, I was afraid my brain was going bonkers. =]

Steve Smith · Jun 20, 2012

Newt_on_Swings said:
Whatever happened to the inverse square law in regards of light fall off because of distance? Instead of just yes or no, an explanation would be useful.

The inverse square law works perfectly but only if you keep the same lens on the enlarger.

If you use a 50mm lens to expose a piece of 5x7 paper then change to an 80mm lens, you will get a smaller image on the paper. To get back to a 5x7 image you will need to raise the enlarger head (and re-focus) because the 80mm lens projects a narrower angle than the 50mm lens.

Set up for a 5x7 image with either lens, the magnification is identical. i.e. the light passing through a 36mm x 24mm negative is now spread over a 5x7 piece of paper so the exposure is the same.

Steve.

ic-racer · Jun 20, 2012

Newt_on_Swings said:
Man, I think I'll have to try this when I head to the dark room. Whatever happened to the inverse square law in regards of light fall off because of distance? Instead of just yes or no, an explanation would be useful.

from wiki:
"The intensity (or illuminance or irradiance) of light or other linear waves radiating from a point source (energy per unit of area perpendicular to the source) is inversely proportional to the square of the distance from the source; so an object (of the same size) twice as far away, receives only one-quarter the energy (in the same time period)."

What you posted does not apply to focused light rays. The bare bulb in your enlarger head will respond that way if you take everything out of its path. The focused beam from the enlarger lens (or any lens or laser or collimated light) does not follow that 'rule.'

DIY ND Filter for enlarger?

X. Phot.

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