DIY ND Filter for enlarger?

[Klainmeister]

Hi All,

My C760 is too friggen bright and I need to dodge/burn some images. I was looking at putting a ND filter above the film, so something like a 4x4" should work...except the price. I don't care to spend $75 when the quality of glass really isn't as critical.

Anyone have any thoughts on something that could still get the job done? Looking for about 2 stops.

 

[cliveh]

I don't know what paper you are using, but if multigrade, you could dial in cyan to act as a neutral desity filter.

 

[ic-racer]

Two stops, 21"x24" sheet for about $7.00. You can double it over if you need more. http://www.bhphotovideo.com/c/product/163142-REG/Rosco_102302112124_E_Colour_211_9_Neutral.html

 

[ic-racer]

I don't know what paper you are using, but if multigrade, you could dial in cyan to act as a neutral desity filter.

??

 

[cliveh]

??

Do I take it you think this is bad advice?

 

[ic-racer]

The cyan reduces the light reaching your retina, but the paper does not 'see' any difference. Cyan is anti-red. The paper does not 'see' red. So the paper does not care if there is less red or not. Cyan filtration of the enlarger light would have the same effect on the paper as dimming your safelight.

 

[Steve Smith]

But you could add equal amounts of yellow and magenta minus blue and minus green respectively.


Steve.

 

[ic-racer]

But you could add equal amounts of yellow and magenta minus blue and minus green respectively.


Steve.

Yes that is a nice 'built-in' solution, however, I'd say 80% of "enlarger too bright" posts are from users of condenser enlargers and 80% of "enlarger too dim" are from diffusion users. So my guess is the OP has a condenser enlarger. Am I right?

 

[Bill Burk]

Can you create a "physical filter" like they use in sensitometers and densitometers? Window screen or punch holes in a sheet of steel foil and place it between the light and negative but as far out of the plane of focus as possible. (If it projects a gobo pattern forget it).

 

[wildbill]

Two stops, 21"x24" sheet for about $7.00. You can double it over if you need more. http://www.bhphotovideo.com/c/product/163142-REG/Rosco_102302112124_E_Colour_211_9_Neutral.html

this is the kinda thing you want but get GAM brand, it's the only nd that's completely neutral.
If I could find my stash, I'd mail you a piece. I usually have a bunch from work in every density they sell.

 

[Gerald C Koch]

Equal amounts of cyan, magenta, and yellow produce a ND filter. For example 40M+40Y+40C. So if you need a 20M filter pack and need to reduce the amount of light then use 60M+40Y+40C to lengthen the exposure time. Other than for color printing this is the principle use for cyan filtration.

 

[stillsilver]

I bought a rheostat(dimmer control) at the hardware store. I set the switch to about half-way and that semed to help.

Mike

 

[Nicholas Lindan]

The cheapest, and best solution is to use a lower wattage bulb.

But, if you are set on a filter, then I second Mr. Racer's recommendation. Be sure it is the e-colour (or equivalent cinegel - these things have many names) filter - the other Rosco ND filters aren't as neutral. The curve for the Rosco filter is:
http://www.rosco.com/filters/SED.cfm?titleName=E211:%20.9%20Neutral%20Density&imageName=../images/filters/ecolourplus/211.jpg

I'm sorry, but the GAM filters don't seem to be as well behaved, though they may have a different series buried somewhere on the web site:
http://www.gamonline.com/catalog/cinefilters/cinefilters.php

The Rosco filter will give a little rise in contrast as it attenuates green a bit more than blue/purple.

Neutral density filters are the hardest filters to make - maybe because it is easy to find a lack of perfection in the transmission curve. After all, what is the curve for a #11 yellow filter, and really, what does it matter if it varies a bit.

If you want a filter with a flat transmission curve then the only one to get is sputtered metal - expect to pay through the nose, though Thor Labs makes a reasonably priced one:
http://www.thorlabs.com/catalogpages/V21/833.PDF
The filters are, however, sensitive to the incident angle of the light - a bit of a problem in an enlarger unless you use a longer than usual lens to keep the angle close to vertical.

Solutions from the sublime to the ridiculous...

 

[Gerald C Koch]

The problem with using a rheostat is that it changes the color temperature of the light source effectively adding more yellow. Not something you may wish to do with VC papers.

 

[Yamaotoko]

As a quick and dirty solution, I drop my 77mm ND8 in my lens cone if I'm doing small enlargements. That, as well as use a longer lens to give a bit more working room.

 

[Newt_on_Swings]

You can also stack another piece of film on in the neg carrier to make a two layer sandwich.

Or Stop down the lens.

Or Use a longer lens for more distance.

Or Use a slower paper.

 

[henpe]

My solution to the problem was to remove the cyan-filter in my color head and replace it with an aluminum-plate of the same size. The aluminum plate was drilled with a lot of small holes. Since the "filter" is before the mixing box, the hole-pattern wont affect the evenness of the light. I can now "dial-in" the amount of ND needed by using the "cyan"-dial. This is very convenient since I now have three variables to determine my exposure; time, aperture, and ND-filtration.

PS: The installation was very easy. However, it took me two trials to determine which size of the holes that were appropriate and how many holes I should drill. I aimed for a linear relation between effective ND-filtration and the "Cyan values" on the Cyan-dial, therefore I ended up with drilling more holes at the top of the plate.

 

[Steve Smith]

Or Use a longer lens for more distance.

But that won't reduce the light output.


Steve.

 

[Klainmeister]

Holy moly, thanks guys. The reason I am thinking of a filter instead of a new bulb is that for lith, the extra wattage is quite nice

I don't like stopping down too much because I can begin to see corner fall off (schneider componon s 100mm and el-nikkor 50mm 2.8).

I'll see what I can do, thanks again!

 

[Bill Burk]

My solution to the problem was to remove the cyan-filter in my color head and replace it with an aluminum-plate of the same size. The aluminum plate was drilled with a lot of small holes.

Well, there you go... a physical filter. Simple and neutral.

 

[Newt_on_Swings]

But that won't reduce the light output.


Steve.

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.

 

[kb3lms]

Doesn't the C760 have a slot in the top of the color head to insert a metal screen between the light/filters and the mixing box? Mine does (I think its a C760 head) and came with screens for the purpose. You can probably purchase a small piece of aluminum screen at a hardware store (HD, lowes) that can be cut to fit in the slot. There's thumb screw on top that you loosen to open the slot and insert the filter.

-- Jason

 

[Klainmeister]

I'll have to take a look, but wasn't aware of that feature. Thanks!

 

[Ian C]

This is the Omega C760 light attenuator set for the dichro head.

http://www.ebay.com/itm/Replacement...959?pt=LH_DefaultDomain_2&hash=item1e6b15c617

Scroll down for a larger photo.

 

[Klainmeister]

Ha! I was just about to post that. Funny, I've been using this enlarger for about 9 months and had no clue. Whooooops. I'll have to poke about and see how things are looking. I have access to a machine shop so I might just create my own.

Thanks!