Calculating 10 stop exposures

Ac1dh0u$3.

Ac1dh0u$3.

Ac1dh0u$3.

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Hi there..

Can anyone tell me the best way to work out how long to take a picture with a 10 stop filter attached.

I'm already pretty sure this is wrong but the light meter app on my phones goes up to like F512, so I so I figured if the cameras at F22 then with the 10 stop filter on the end that would be F32? Gives out a time in my dark room of like 2mins, which really cant be right.

So whats the calculation to work out the shutter speed ?
 
If your using a decent system, as in slide in filters rather than screw on. Use metering to expose shot without filter in. Put filter in. Adjust exposure ten stops.

kd
 
Without the filter attached, set the desired aperture based on the depth of focus required - you don't want to be pushing more than f/16 unless under exceptional circumstances. Learn about hyper-focal focusing so you can try to maximize the aperture and minimise the f-stop. Focus the lens, preferably using live view, typically about 1/3rd of the way into the scene. Switch the lens to Manual focus and be careful not to touch.

At this point it is worth taking a test exposure to see if your focus and DoF is correct.
Examine the Histogram and look for any highlight clipping which will benefit from reduced exposure.

Switch from aperture priority to manual mode at this point, reducing or increasing. exposure to get the desired exposure. This is your base level exposure. Attach the filter and multiple your exposure time by 10 stops (~= 1000x). You can do this in your head/calculator on phone. If the base level exposure is say 1/200th second then multiply by 1000 => 1000/200 = 5 seconds. Alternatively you can just do this by rotating the dial controlling shutter speeds. If you have this set to 1/3rd stop increments then rotate 30 clicks.

Take an exposure (using Mirror up or exposure delay combined with a timer release or remote release). This should be close. Again, examine the image histograms and see what needs to be shifted. Nothing is exact here so it is unlikely that the exposure is fully correct.

Also you might want to exposure to the right as much as possible before highlight clipping to maximise shadow detail and dynamic range, bringing the exposure back to normal in post. generally, the hotter you exposure the lower you reduce the noise floor of the shadows- until highlights get clipped, which can happen at different exposures for different colour channels so don't go too far right.
 
One f stop is multiplying by square root of two (or about 1.4, it's thereabouts just for nice numbers.) not adding or subtracting one from the number.

10 stops off of f/1.0 is 1.0 * 1.4^10 i.e. f/29
10 stops off of f/22 is 22 * 1.4^10 i.e. f/636
 
What ever method you use you cannot work things out precisely because the apertures on still photography lenses are not properly calibrated (unlike t-stop or cinema cameras).
When you take into account the massive change in exposure (factor 1000) then these small errors become really quite big.

Furthermore, not even the filter will be perfectly calibrated.
 
Yeah fair enough but I don't think anyone does long exposures gunning for slap bang on perfect exposures because there is really no such thing.

What I tend to do is do exposure test shots shorter exposure times, wide open at a higher ISO just to see where the exposure is and when I'm happy drop the ISO and aperture in equal measure.

On a somewhat related note, I initially went with a 9 stop instead of a 10 stop (they were cheaper) and to be honest I think it's a more versatile density to use as it means that most of the time you don't need to go into bulbs and for my work at least where I want to be able to do 5 second portrait exposures it's nicer not having to go to 6400 ISO in anything less than midday sun.
 
yeah, i was just meaning that you cannot calculate these things perfectly so there is some trial and error involved.

I described my method above, it is actually very quick and simple. Just get the exposure correct without filter, rotate shutter dial 10 stops worth and test. You typically don't want to be adjusting aperture when you are shooting such scenes.

I actually don't have a 10 stop any more, was borrowing a friends for ages. Don't really miss it because it is a pretty limited piece of equipment (pretty much limited to making those boring cliched midday long exposures seascapes), CPL and graduated NDs are much more useful to me.

My best use for them was daytime architecture/street shots using a long exposure to blur people away.
 
Most people use shutter speed to make the 10 stop adjustment. In which case it's easy. 10 stops means doubling the shutter speed 10 times. 2^10 = 1024. So a 125th exposure time becomes 8.192 seconds, 0.5secs = 512 secs or about 9mins
 
Yeah I use screw in filters so it takes a little longer to do it that way round which is why I do the bumped ISO max aperture method
 
If your lens gos to f22 then either use f16 or f14. Never use the Top f stop on your lens.
What I mean by that is f32/f22...
Try at various seconds. Like 30 seconds or less to start with and go from there.
With Screw on you got a problem. You got to focus first, switch to manual, screw filter on without turning lens, take shot and hope you did not turn lens slightly..
I use a screw in various 10 stop. zero to 10 or more. I screw it on and turn so I get full light, focus, then turn it to 10 and take shot. I'm still learning and do get lots of images where focus is not quite there. So practise a bit.
 
Ksanti said:
Yeah I use screw in filters so it takes a little longer to do it that way round which is why I do the bumped ISO max aperture method
Click to expand...

You can't auto focus with a 10 stop attached so it is usually easier to gt an estimate first without a filter then adjust with the filter on.
 
Thanks for all this information everyone.

I've also found an app on ios which is the same as the one Albaba posted, you take a exposure, put in how long it took without the filter and what filter your going to put on and its tells you how long to do it with the filter. Its called "Longtime"
 
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