ND filters for really long exposures

[Ed Richards]

I would like do some long (10+ minute) daylight exposures. Using my usual TMY-2, an ND 3 (10 stop) filter is only going to get me to about 16 seconds in daylight, even at f32. I can then add a second ND filter, 1.8 or 2.1 or 2.4 to really stretch things out. This would have to be screw in, otherwise light leakage would be impossible to control. I am wondering if anyone has experience with this. I am looking at the Formatt glass filters at BH, they are about 30 dollars less than the B&W. I could use a slow film, but I prefer to stay with one film.

[vinny]

Formatt glassmfilters are made of schott glass as are the b+w's. Unless you are buying a multicoated version, i don't think you'd see a difference.

[Ron Marshall]

Some Formatt ND filters are multicoated, some are uncoated.

[Frank Petronio]

Just throw every filter you have onto the stack and see what you get. I did an hour long on Portra 400NC with a cheap $20 ND 3.0 (10 stops) plus a Polarizer - you're going to stop all the way down so it's not like you need the best quality glass filter in this case. A good deep lenshade is a must.

[AF-ULF]

I have done 30 minute exposures at the beach (in B&W) by stacking multiple ND filters in a lee filter holder with a good hood. No problem.

I have heard that some people use a welding glass for a filter (10 stops). There is some color shift with the welding glass. If you go to flicker and search for welding glass, you can find many images made with the glass. It is much cheaper than buying a designated 10 stop ND filter.

[BetterSense]

you're going to stop all the way down so it's not like you need the best quality glass filter in this case.

Shouldn't it be the opposite? It strikes me that imperfections of the filter will have less effect at larger apertures where DOF is less, thus the filters will be more oof.

[Frank Petronio]

Yeah I guess you have it right. But I didn't want to spend $$$ on one shot so I rationalized ;-) Perhaps once you stop the lens down to f/64 diffraction is going to play a role and lessen the quality....

[brianam]

I've used 6-stop (1.6) and 10-stop (3.0) round filters stacked. Will echo the comments re: using a good lens hood. (I'll use a better one next time)

There is a 20-stop available as a special order item. All B&W's I think.

You could also start with a slow film (e.g. Efke 25), which will of course need a stop or two extra for reciprocity.

[dave_whatever]

How about just using a lens cap?

[Bob Salomon]

If you are currently using a 3.0 and at f32 are at 16 seconds then an ND twice as dense will only get you to 32 seconds.

Why not find a slowe film?

[Bob Salomon]

Formatt glassmfilters are made of schott glass as are the b+w's. Unless you are buying a multicoated version, i don't think you'd see a difference.

So are Heliopan ND filters. And they are available in SH-PMC multi coating.

[Ed Richards]

Why is a lens hood more important with the ND filters - assuming I am using a screw in filter and not a Lee style?

[vinny]

Why is a lens hood more important with the ND filters - assuming I am using a screw in filter and not a Lee style?

They are referring to using multiple filters where all the surfaces add up. Light hittig 3 filters will lower contrast more than just one filter.

[ataim]

I know that if you take two polarizing filters and twist them they will go progressively darker. How dark I don know. Thats my two cents.

[Bob Salomon]

I know that if you take two polarizing filters and twist them they will go progressively darker. How dark I don know. Thats my two cents.

About 6 stops. Some polarizers might add one more stop but they will also have more density at the brightest setting. The problem is that most of these will have yellow or blue shifts or moire or interference patterns or simply not be neutral.
However, the OP is already well beyond this density.

[Lynn Jones]

Remember that long exposures give you lots of reciprocity failure. When I was doing schmidt camera photos averaging 20 to 25 minutes, I would lose as much as 5 f stops of exposure (at that time, TriX, PlusX, and PanX would both be ASA 4 at 20 to 25 minutes, so I always used 25 speed Pan X). Also we made special ND filters for solar imaging at density 5.0, a cool 16.66 f stops (.30 = 1 f stop).

Lynn