photodoc16

Ladies and Gents,
My problem is that on the two apps I have for figuring out exposure times with ND filters, neither can handle ND values over 15 stops. I have tried to estimate times by making proportions but it is not very accurate. Is there any app that you know that will get up to 20 stops?
Thanks,
Photodoc

CHG_CANON Loc: the Windy City

What lighting and composition is going to need 15-stops of light blocking?

Quixdraw Loc: x

Unless you are talking about film, it costs nothing but time and attention to record settings and experiment till you hit the results you want. Large changes to start, then small ones when you are close to the outcomes you desire.

CHG_CANON Loc: the Windy City

Our OP will also likely find a stopwatch / timer with a wired-remote and the camera in BULB mode will help in these experiments. They do for me, in the rarely used 10-stop range.

rmalarz Loc: Tempe, Arizona

Exactly!!! I'm always puzzled by the lack of incentive to actually test a camera, lens, combination thereof, or various bits of equipment. Every camera I use has been tested to the point that I know what to expect from it. These are not tests done by walking around the 'hood and taking a few random shots. They are laboratory setups.
--Bob

photodoc16

Hello Paul,
Thanks for answering. The situation is long exposures during a sunny day primarily for clouds. I know overcast skies are probably best but there are some tremendous cloud formations moving around these days. I am still on the LE learning curve so I want to practice and this has been a problem. The longest time available on my calculators is 30" and 14 or 15 stops is the max for their calculations. Looking for a formula but no luck so far.
I can go up to 20 stops but it is a guessing game.
Photodoc16 Richard

photodoc16

I use all of the above but without something approaching an accurate time it can be exhausting.
Photodoc16

CHG_CANON Loc: the Windy City

I'd expect a lot of cloud movement in 30+ seconds, but my long-exposure experience is more focused on the water in Lake Michigan than the clouds, also typically working on clear days so there is no cloud movement. As noted, it's free to test in digital so you can evaluate the results and delete what doesn't work, being out only your time.

htbrown Loc: San Francisco Bay Area

I have a ten-stop ND filter (don't remember the brand) and... it's not ten stops. It's somewhere around nine stops. Maybe the more expensive filters are more accurate, but the odds of them being perfectly accurate are limited. So whatever you do will require some experimentation to get the exposure right anyway. Any calculator will only get you in the ballpark.

You don't need a calculator, only a piece of paper and a little time before your shoot.

1. 1/125 f/2.8
2. 1/60 f/4
3. 1/30 f/5.6
4. 1/15 f/8
5. 1/8 f/11
6. 1/4 f/16
....

keep going until the time column is as long as you like. You can go to minutes or hours if you like.

Now, when you meter, you can find your nominal exposure in your chart and count down until you add the number of stops you need. In the abbreviated chart above, if you meter at 1/125 sec, you can add five stops by going to 1/4 sec. 1 + 5 = 6 and the sixth column says 1/4 sec. If you wanted two stops and your nominal exposure was 1/6o (column two), then column 2 plus two stop = column 4 = 1/15 sec.

If shooting film, reciprocity failure sets in after some seconds (I no longer remember how many) and all bets are off. In digital your problem will be noise. As the camera heats up, the noise will get worse. For my camera (which isn't very good about noise), anything beyond a minute or two is too long. If I needed longer than that for something like a sky picture, I would have better luck taking multiple 30 sec exposures and blending them in PS.

CHG_CANON Loc: the Windy City

You shouldn't see that much digital noise if you leave the camera at the 'base ISO', typically ISO-100. What I've seen over the years is 'hot pixels' where specs of red or white pixels occur in the frame, the longer the exposure and particularly on hot evenings after several long exposure attempts.

jim quist Loc: Missouri

Try setting your camera on full auto to see what settings you get. Make your adjustments from there.

photodoc16

Thanks Jim,
Interesting idea. I shall follow up on that and see what happens.
Thanks,
Photodoc16

photodoc16

Thanks Jim,
Will give it a go.
Photodoc16

camerapapi Loc: Miami, Fl.

Why in the world do you want to shoot a ND filter that requires 15 stops of light? I do not use ND filters very often but a 6 stops is the higher number I will ever use.
If you cannot do it with the 10 stops you do not need the 15.

photodoc16

Okay. You go out on a sunny day and try to create a long exposure of moving clouds and let me know how many stops it takes to do it. (and not with a lens with an f1.2 aperture)
Photodoc16