Long Exposures with Welding Filters

giganova

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Today I experimented using "welding lenses" (as they are called) as ND filter for long exposures. I purchased a pair of #10 welding filters from Amazon ($5 for a pair). Since these welding filters don't have a well defined diameter and rough edges, I purchased the cheapest E48 UV filter that I could find, plus a 48-52mm setup ring, removed the UV filter glass, and screwed the welding filter between the E48 and the step up ring, which gave a nice snug fit. Total costs: a whopping $15! 😱

The first pictures had light leaks and reflections all over the place, rendering the photos useless. So I put black electrical tape around the filter and step up ring to light-seal it, and covered the lens and M body with a dark cloth so only the front of the lens would not be covered. Why cover the M body with a cloth? Because -- believe it or not -- there is light leaking through the bayonet (!) when you have the shutter curtains open for a few minutes in bright day light.

Below is the first picture that I took today.

Some technical details: 5 min exposure with M4, 21/3.4 Super Angulon at f/11 on FP-4 developed at box speed. I bracketed the exposures and a 5 min exposure gave me the best result, which would otherwise be 1/500 sec at f/11 ("sunny 16"). This means that the #10 welding glass has an attenuation of 16 f-stops! Surprisingly, this cheap welding filter gives almost no loss of overall image sharpness. The corners are a bit softer and vignetting is more pronounced than before, but I can live with that.

Can't wait to get out and make more long exposure with this $15 contraption! 😀

2017-01-13-0001_2.jpg


P.S.: This will be last photo in Washington, DC, where I live, before I escape the city for the inauguration next week. Maybe you'll see more long exposures from the beach when I am back 😛
 
FP4+ is a good choice if you wish to make very long exposures because, like most of the Ilford films it has a steep reciprocity curve. The vast majority of your five minute exposure would actually be to account for that, rather than the metered exposure time. On the other hand, Acros 100 needs no compensation at all for times under two minutes which can be an advantage when light is low, and you just want to do the shot. The tech data sheet for FP4+ has a reciprocity compensation graph. You've probably already seen it, but, just in case, you can find it via Ilford's own website, here:
Cheers,
Brett
 
Good point! From what I read, a #10 welding glass should have 13 f-stops, but my exposure bracketing clearly showed that it is closer to 16 f-stops, so this must be due to the reciprocity of FP-4. Good, because it works to my advantage.

In any case, I know now that "sunny 16" is f/11 and 5 min exposure with this filter and FP-4 combination.
 
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