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dodphotography
29-Oct-2014, 09:39
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.

Steve Goldstein
29-Oct-2014, 12:12
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.

dodphotography
29-Oct-2014, 13:29
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.

Drew Wiley
29-Oct-2014, 13:29
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.

Daniel Stone
29-Oct-2014, 16:18
Why not just stop down one more stop from your "given" exposure, using the single 10-stop filter?

Greg Miller
29-Oct-2014, 16:37
Why not just stop down one more stop from your "given" exposure, using the single 10-stop filter?

Because 10 stops + 1 stop = 11 stops; The OP is contemplating 10 stops + 10 stops which yields 20 stops.

Daniel Stone
29-Oct-2014, 16:40
Because 10 stops + 1 stop = 11 stops; The OP is contemplating 10 stops + 10 stops which yields 20 stops.

Ya, now that I re-think this, my initial question seems a bit stupid :rolleyes:

Deval
29-Oct-2014, 19:35
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.

dodphotography
30-Oct-2014, 02:48
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.

David R Munson
31-Oct-2014, 21:17
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) (https://www.flickr.com/photos/davidrmunson/8275574780/) 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.