DIY neutral density filters

Hi, I am new to this forum and I have a question.

 

Now I have done a search but could not find what I was looking for. It also

seems (to me) like a strange thing to want to do (but I want to do it anyway) so

I will go ahead and assume it has not been asked before. If it has, I am truly

sorry :)

 

So, I want to make some poor-mans neutral density filters for my p&s camera so

that I can do some daytime long exposure work.

1. Camera does not have a filter attachment system

2. I do not want to invest in real filters just yet (I have my reasons)

3. I want a range of filters, the exact value of them not being that important,

but having varying values to play with is.

 

I have tried using sunglasses and foils but that was quite hopeless, nothing had

neutral colour properties and I had no variation on the amount of light that was

blocked.

 

My proposed solution is to run a roll of b&w film through an SLR at a plain

white object and out of focus with varying exposure settings going from no light

to fully washed out and over exposed. Then developing this roll and using the

developed negatives as my cheap-mans diy ND filter set.

 

2 things...

1. would this work? I don't see why not. (the 35mm stock is plenty big enough to

go over the lens on my p&s

 

2. What sort of exposure settings would be good to go from a fully black

(Overexposed) negative to a fully white (underexposed) one? I could just go from

the maximum shutter speed to the minimum shutter speed in 36 steps and hope that

that gives me a nice range. Any ideas?

 

I have a friend who thinks this could work and I am borrowing his EOS 300. I

just bought a roll of Kodak Professional B&W 400. Now all I need to do is work

out my white screen and my exposure settings.

 

p.s. Posting in the b&w forum as I will be using b&w film and need exposure

advice for said film. It's the closest forum section I could think of for this

question.

 

Cheers for any help!

 

Tom...

It will work. You may experience some loss of image quality but if that is not an issue -- go for it. You may prefer to use a fine grain film. I have used "home made" ND filters for years in non-image forming applications, filtering the light sources of enlargers and a home built sensitometer. They work!

Kim

There are two methods you could use - measure the exposure required for a mid gray card (inside of a cereal packet will be close enough for what you want, and then, using manual, keep these same settings while you take pictures of a number of different coloured gray cards. OR Determine the exposure as above and then increase and decrease the exposure to photograph the gray card at a number of different exposures. Opening up the lens and or a slower shutter speed will give you a denser image, closing down the lens or a faster shutter speed a lighter one.

If you have got Kodak Professional BW400CN you have a dye-image film. This should be better than a silver-image film for use in an image-forming path (ie it should not degrade the image nearly as much as silver-image film would). The maximum density with normal C-41 processing might be equivalent to around eight to ten stops. It is definitely not neutral, however, having an image colour similar to that of a neutral object on colour negative film (ie orange-ish).

 

Ilford XP-2 might be better in this respect. It has a more neutral image, but does not achieve the same density - a maximum of about six stops of ND.

 

Best,

Helen

.30 = 1 f stop. Multiply .30 by the number of stops of exposure increase you wish to create.

 

Use a thin emulsion, high resolution film, frame closely, but focus at infinity.

 

Your Problem is going to be eveness of the density. To get best results I would suggest that you use a rotary drum processor for the best results.

 

I created the neutral density filters for the Calumet SBC Flash/Ambient meter. It was 1.66 +/- .005, I had to get a special densitometer from Welch Densichron and processing at +/- .10F with dilute D76, and gas burst processing. I had to do this myself because no company even knew how to do this!

 

I don't think you have to be that precise.

 

Lynn

Thanks for the tips everyone. it sounds like this Kodak Professional BW400CN will be no good. I read the same stuff about the orange hue on wiki after it was mentioned here. I think I will use this roll of film to take some b&w pics. I have never taken film pics with an slr before so may be interesting :)

 

I'll go out and buy a roll of Ilford XP-2 today and use that instead. I will do a couple of 'nd filter' shots on the kodak as well incase the Ilford creates too much image quality loss.

 

Thanks for the tips!

 

Tom...

Tom,

 

The XP-2 is also a dye-image film, so it should cause less image quality loss than a silver-image film. It doesn't have as great a maximum density as BW400CN, but you should still get about six stops. It has a very long 'shoulder' to its characteristic curve, so it needs a lot of exposure to reach maximum density: at the shoulder you need about three stops more exposure to add 0.3 (ie one stop) to the density. If you give about eight or nine stops over a reflective meter reading you should reach maximum density.

 

If your XP-2 comes back with some pinkish or pinky-brown colour to it, either wash it until the colour comes out (that may take a while) or leave it exposed to daylight (these are Ilford's suggestions - I've never bothered trying to remove the slight brownish colour).

 

Best,

Helen