Anyone here ever stack two Lee big stoppers (10 stop). A friend has a pretty good deal on his used filter and I am contemplating picking it up... wanted to see if anyone had experience with 20 stops in the past.
Anyone here ever stack two Lee big stoppers (10 stop). A friend has a pretty good deal on his used filter and I am contemplating picking it up... wanted to see if anyone had experience with 20 stops in the past.
That might be useful for looking at solar eclipses. 20 stops is a total density of 6.0, or a factor of ~1 million. One solar filter I found with a quick search (http://www.thousandoaksoptical.com/solar.html) has an overall density of 5, so transmits 10x more light than two stacked Big Stoppers.
Photographically you could change your "sunny 16" exposure of 1/250 at f/16 to 4096 seconds (68 minutes before accounting for reciprocity), or to 512 seconds (8.5 minutes, before reciprocity corrections) at f/5.6 if you wanted to go for shallow depth of field. I personally wouldn't find this very useful, although perhaps it would give effects in bright sun similar to those in some of Michael Kenna's work.
It was just a thought... would be interesting to see how far you could push your exposures. I am terrible at calculating reciprocity failure though, as evidenced in my work.
I'd read the actual density using a densitometer before relying on the published specs, if you have one that will handle that degree of density. In any event, you'll
have to do a net test for actual exposure.
Why not just stop down one more stop from your "given" exposure, using the single 10-stop filter?
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It is an interesting question in many ways but a few practical issues with the Lee holder system. It normally works as the closest filter.if you stacked a second filter side light would get in the interface (with possible unpredictable internal reflection.) It wouldnt exactly be another 10 stops. I suppose you put can black tape around the Lee holder. What were you wanting to capture that ten couldn't stop. Most of the time I reach for the little stopper instead.
Are you sure about that? The stoppers have foam on the inside... I'm almost 99% sure that the second filter would be snug with that foam layer.
At 20 stops, exposures could get out of hand. As in the multiple hours range, depending on your film speed and aperture. This shot (flickr link) was done on a 645 with 17 stops filtration (ND 4.0 plus red 29) on Acros in mid-afternoon. Exposure time was about 20 minutes. I think my aperture was something like f/8. So let's add 3 stops to that to get to your 20 stops. That gets you from 20 minutes to 160 min, or 2 hours and 40 min, without considering reciprocity (something I barely think about with Acros). Stop down to f/16 and f/22 and you could be looking at a whole day exposure. Which could be really cool, but may not be what you're looking for.
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