Stacking ND filters

Gavjenks · Mar 3, 2014

I need like 20 stops' worth of ND filter. (Want to shoot in midday with like f/2 for minutes of exposure)

1) Will this work with some 2 variable filters on top of one another (each of the 4 sheets basically at 90 degrees to the next), or will they cancel each other out weirdly and/or cause even worse patterns than a typical subtle "X"?
2) If not, will this work with normal flat, non-variable 10 stop ND filters stacked on top of one another?

runnah · Mar 3, 2014

What about two pieces of welder's mask glass? You'll get some color issues that can be corrected in post but at $10 a pop it's pretty cheap.

IIRC one piece is roughly 10 stops.

edit: yes Use Welding Glass As 10 Stops ND Filter - DIY Photography

tirediron · Mar 3, 2014

Never tried this, but my instinct says that you will get better results with non-variable ND filters.

Gavjenks · Mar 3, 2014

That looks like something I would find fun. But I'm concerned about the dark green tint. Especially with 2 in a row, is that beyond the hope of RAW's color range to correct for?

Would make it only able to do B&W if so. Also, using welder's glass it's not exactly optical grade, one is pushing it, two in a row might be iffy.

runnah · Mar 3, 2014

Gavjenks said:
That looks like something I would find fun. But I'm concerned about the dark green tint. Especially with 2 in a row, is that beyond the hope of RAW's color range to correct for?

Would make it only able to do B&W if so. Also, using welder's glass it's not exactly optical grade, one is pushing it, two in a row might be iffy.

I am tempted to try it out myself.

I think if you can find some brand new glass it would be optically as good as a variable filter. They also make different colors for glass.

Gavjenks · Mar 3, 2014

Runnah, SEPTLS101FS5H12 - Filter Plates: Amazon.com: Industrial & Scientific
what do you think -- trust the product dimensions of 5.5x4.5" (one square, need to buy 2 of them)? Or the image that shows a double long single sheet that could be scored and snapped in half to give both that I need (only need to buy one)?

runnah · Mar 3, 2014

I'd go with these.

US Forge 00097 Shaded #12 Welding Lens 4-1/2-Inch by 5-1/4-Inch - Amazon.com

#12 is pretty dark so you might be able to get away with one.

bribrius · Mar 3, 2014

I give up. whats the purpose and why would you have to shoot at f3 for minutes. im totally lost.

Gavjenks · Mar 3, 2014

Guy in article: " My welding glass is grade #12, so I usually have to take a 5-6 minute exposure at f/8, iso 100."
Assume he means a sunny day. Which would be 16 stops below sunny 16.

That would be sufficient, Yes. Okay, I'll try just one of those. Will report back.

(By the way, the guys says to focus and compose before putting it on, but I'm quite confident from previous experience that live view mode would allow composition and even autofocus with the filter in place. More practical than he makes it sound)

Designer · Mar 3, 2014

Gavjenks said:
Runnah, SEPTLS101FS5H12 - Filter Plates: Amazon.com: Industrial & Scientific
what do you think -- trust the product dimensions of 5.5x4.5" (one square, need to buy 2 of them)? Or the image that shows a double long single sheet that could be scored and snapped in half to give both that I need (only need to buy one)?

I don't think I would try cutting these. They are hardened, so unless you know a special trick in cutting these, I think I'd just purchase multiple examples.

Gavjenks · Mar 3, 2014

My sapphire dust encrusted nail file I got for a weird personal care set christmas present way back when would score it just fine

But I'm just getting one square one anyway since it sounds like it's a lot stronger than 10 stops.

480sparky · Mar 3, 2014

I've gotten 18 stops out of my 10-stop (actually is 10 1/3) ND and Sign-Ray VND dialed down as far as it will go without Xing out. I've shot ISO 100, f/11 on a bright sunny day with a 16-minute exposure.

spacefuzz · Mar 3, 2014

Try the LEE Big Stopper. Or stack a few 5 stop filters on top of each other.

480sparky · Mar 3, 2014

bribrius said:
I give up. whats the purpose and why would you have to shoot at f3 for minutes. im totally lost.

Try shooting a scene full of people when you don't want anyone in the shot.

Gavjenks · Mar 6, 2014

Not terribly surprisingly, the welding glass is crap.

* It is 16 stops exactly as I suspected, which is nice, but...
* You cannot recover colors. It blocks everything but green so completely by comparison to green that the other two channels look like the most heinously jpeg artifacted garbage imaginable. You are pretty much obligated to dump both channels and make the green black and white.
* Even then, it does some strange stuff with images across the frame. Dead center is usually normal looking. As you go further out to the left or right (it seems to be a linear pattern not circular), the image starts splitting up and down. Like, it looks as if you jostled the camera up or down halfway through the exposure and it ghosted half and half up and down. But only on the sides of the image. Esentially impossible to get a sharp image end to end.
* Even though I glued it to an empty filter ring it still flares weirdly, so it's coming through the glass with the weird flares, not just from the edges.

Gavin is sad. Back to resigning myself to shelling out way to much money for gray glass.