Lowering ASA of BW Film
I have a 111mm f:1.5 Ektar large diameter lens without shutter or diaphram. I thought it would be fun to give film and lens long exposure times like old timers. My subjects are buildings , textures , my family and may be clouds.
I can access Ilford FP4 and Kodak Tri X 120 Products , D76 , Ilford Phenidone and may be most widely available chemical powders from a Istanbul Seller.
Is it possible to lower the ASAs of these films to 1, 5, or so. Is there a advantage ?
My new camera will be 120,6x10cms back.
I don't know on the film but you could use neutral density filters on the lens.
I read they are expensive and I dont want to wait for summer. Its winter and expenses are great. But for information , if someone knows what is the price of 6cms diameter one when looking at used ones classifieds generally ?
I still want to know the film developer option also.
I don't think it is possible to use a native ISO 125 or ISO 400 film at super low ISO values like you are describing. At least, I've never encountered anyone doing it. You can use neutral density filters as has been suggested, but they are indeed expensive. I'd suggest using a sheet of welding glass (10-15 stops difference). The results may not be as good as with a ND filter, but it does the trick if you don't want to spend a lot of money.
Alternatively, you could just make paper negatives.
You cannot change the "ASA" of film. The ASA is a rating applied by the manufacturer based on industry-standard testing procedures. It is what it is.
You can reduce the EI (exposure index) of film. I routinely rate my film at about half the ASA assigned by the manufacturer. I do that by means of testing under realistic exposure conditions (rather than the idealistic conditions that are the basis for the standard ASA tests).
It is also possible to reduce the EI to less than what would result from practical testing. However - there is a limit. As you reduce the effective EI, you must also compensate with a change in development. A reduction in EI always means a corresponding reduction in development. The problem that you will encounter is that you don't want the development time to be shorter than 4-5 minutes - anything shorter is likely to lead to uneven development. You can also compensate by diluting the developer beyond the manufacturer's recommendations, but you eventually reach the point where the diluted developer doesn't contain enough active ingredients to develop the quantity of film you are working with.
So if you are working with 'off the shelf' films of ordinary ratings, you will need to use a neutral density filter to force your exposure time longer.
You can of course use black paper and cut an aperture to mount in front of the lens. That's the cheapest alternative.
From what I read, certain developers, like Rodinal, can reduce a film's speed. Maybe a 1/2 F stop or so. Microdol-X, when it was around, could lower a film's speed about a full F stop.
If you have two polarizers of the same size you can experiment crossing their axes close to, but not quite, 90 degrees. That gives you a great deal of neutral density cheaply. I did this to photograph a nearly total eclipse of the sun with a 300mm lens on a Nikon loaded with Kodachrome 25 in the 1990s. It worked well.
You’ll have to experiment with a meter, such as that in an SLR, to determine precisely how many stops of light are held back by the pair of crossed polarizers.
When you find the setting you want, you might want to draw a diagram of the relationship between the polarization axes indicator marks of the two polarizers so that they can be positioned in the same way relative to each other on the lens you use.
Even if you don't cross the axes, the combination of the two polarizers will hold back about 10/3 = 3.3 stops lengthening the exposure by at least 8X.
If they can get Ilford FP4, maybe the seller can also get Ilford Pan-F 50, which will give you EI 12 in D-76 or ID-11 at 1+3 dilution, 9 minutes at 20 C (according to the Massive Dev Chart). That's not quite ISO 1.5, but still very slow.
Thank you for all replies . I think I will follow Pan F route , I dont want to use cash as much as possible , so the expenses great. Playing with D76 is the cheapest route and I will look to massive development chart also. Suggestions for necessarty least 4 minutes development or double polarizer are great ideas.