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I've a 10 and 11. Has anyone worked out exactly how many stops these are yet?
Question About Welding Glass ND Filters
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Steve Smith
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Why not hold them in front of your lens and work it out from the change in exposure settings?
Steve.
Steve.
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To be honest, Steve, I've not been able to work it out. Just a newbie and they seem so dark nothing much happens. If you could give me an idea how to do it I'll give it a go. Thanks. 
Steve Smith
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Set the camera up, preferably on a tripod so nothing changes between shots and point it towards a fairly standard scene.
Set the camera to aperture priority with the aperture set at about f8 (on a bright day) and and make a note of the shutter speed.
Then put the filter over the lens and take a note of the new suggested shutter speed.
Make sure your ISO is set (to around 100) on manual, not on auto as this doesn't want to change.
Now look at your shutter speeds. For the non-filtered shot on a bright day at ISO 100, you should have a speed of around 1/500.
For every stop of filtration, the shutter will be open for twice as long. i.e. a one stop filter will give a 1/250 shutter speed.
Two stops - 1/125
Three stops - 1/60
Four Stops - 1/30...... etc.
In this example, ten stops would be a two second exposure.
Steve.
Set the camera to aperture priority with the aperture set at about f8 (on a bright day) and and make a note of the shutter speed.
Then put the filter over the lens and take a note of the new suggested shutter speed.
Make sure your ISO is set (to around 100) on manual, not on auto as this doesn't want to change.
Now look at your shutter speeds. For the non-filtered shot on a bright day at ISO 100, you should have a speed of around 1/500.
For every stop of filtration, the shutter will be open for twice as long. i.e. a one stop filter will give a 1/250 shutter speed.
Two stops - 1/125
Three stops - 1/60
Four Stops - 1/30...... etc.
In this example, ten stops would be a two second exposure.
Steve.
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Thanks. It really is as simple as that!
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I don't know what one I have but it's roughly 12 stops from the control.
I would not rely on a camera meter with filter of this density. Plus camera matrix metering can be affected by various factors like colour changes induced by filter etc. So I'd advise to do the following (basically following Steve's advise with small changes):
1) setup the camera on tripod, fix ISO and aperture (aperture priority mode) and take a test shot in aperture priority mode. Note the shutter speed.
2) change the camera mode to manual set the same ISO, aperture and shutter speed as in step 1 and set the filter
3) start taking photos with manual exposure increasing shutter speed in whole stops (doubling the exposure time) until you get the matching exposure to the one that you had on step 1 (compare them visually). When you get a match - the number of stops you moved your shutter speed away from the original is the one you seek.
Steve Smith
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I was going to suggest this method too but I thought I would keep it simple!
Manually adjusting until you get similar hystogram readings would be a good way too.
The simplest method would be to use a hand held light meter but not everyone has one of those.
Steve.
Manually adjusting until you get similar hystogram readings would be a good way too.
The simplest method would be to use a hand held light meter but not everyone has one of those.
Steve.
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Interesting stuff. I've just tested both out on a well lit scene and the 11 came in at 10 stops with the 10 coming in just a 1/3 of a stop less. I'll try your method now, Dalex, thanks.
D
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I would guess about between 8 and 12 stops depending on the strength of the filter the 9 being 8ish and the 11 being 12ish. easiest way is to get someone with a 10 stop to see what the difference is 
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To be certain of getting the right result, it is important to actually take comparison pictures rather than just note the change in meter reading, as this can be affected quite a lot with a heavy ND, by light entering the viewfinder. You can see it changing if you just move your eye to one side. Check the histogram to ensure that the exposure is an exact match.
It is also vital to cover the viewfinder during the actual exposure, as light leaks around the piggy-back mirror during very long exposures in bright light. I guess it varies from camera to camera but both my Canon's do it. On the 40D, deliberately provoking it produces a rather nice sunset effect
This is also a good time to check white balance and experiment to find the right adjustment for that (there will probably be a fair bit). Or just use custom white balance.
It is also vital to cover the viewfinder during the actual exposure, as light leaks around the piggy-back mirror during very long exposures in bright light. I guess it varies from camera to camera but both my Canon's do it. On the 40D, deliberately provoking it produces a rather nice sunset effect
This is also a good time to check white balance and experiment to find the right adjustment for that (there will probably be a fair bit). Or just use custom white balance.
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Interesting experiment. I took a test picture first then started taking filtered pictures from 8 stops until I got to 14 stops, but I forgot to cover the viewfinder so I'll start again.
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RE white balance. There's nothing the camera can do to sort this as it's SOOO green. I'm working on a custom setting in Lightroom for this though.
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Just do a custom white balance with the filter in place - hey presto, pretty much spot on colours. 
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Try custom white balance. It should get you pretty close. Page 57
Edit: beat me to it IRW!
D
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That is all I do but in Canons DPP software, once you have it set, save it and it is just a click to sort it out in the future.
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Cheers!
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The 10 is 13 stops and the 11 is about 14.5. I think the 10 will do, but I might have to get a 9, which must be closer to a 10. God that's confusing!
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That's surely close enough to work with. In practise, the final exposure is done via trial and error in conjuction with educated guesswork using the info above. Or that's how I do it.
To save time with long exposures, I do test exposures at highest ISO and lowest f/number, which reduces an exposure of several minutes down to a few seconds. Saves waiting.
How did custom white balance turn out?
Hmm - this would not quite work unless you place the meter in completely dark enclosure with only filter letting light in. Otherwise too much light leaking will affect the exposure.
Interesting, I have got 10, 12 and 13 grade filters so I wonder now what my 13 will give me...
Apparently according some info on a web, the supplies of thew 14 grade glass seems to go really fast when the sun eclipse is coming up as this one is really good to observe sun directly.
Why are you trying to get closer to 10 stops? I would have thought the longer the better...
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It didn't, but then I was in the shade exposing a shot out into a well lit area so the white card was in the shade too so under exposed even at 30 secs. I needed to play around with it later and have another go now my shutter release cable has arrived. Perfect timing!
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TBH, I don't know. I just had that as a base mark for long exposure shots, but you're right that longer will be more fun.
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I might be missing something here, but why is the White card involved? And why use a 30 seconds exp to set your white balance? Just put the filter on, set the camera to record a custom white balance, take a "normal" exposure and then use that wb setting with your long exposures. Hth?
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I might be missing something here, but why is the White card involved? And why use a 30 seconds exp to set your white balance? Just put the filter on, set the camera to record a custom white balance, take a "normal" exposure and then use that wb setting with your long exposures. Hth?
Because the filter is 13 stops and a normal exposure won't register anything but complete blackness. Surely?
I think by "normal" irw1 means exposure of your subject via filter not the white/grey card.
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It doesn't sound like that's what he's saying. I can't see how that'll work unless the camera knows how to adjust via the white card.
I think you misunderstand it slightly - camera shoots the test shot but then will use the calculated average WB from that shot on any subsequent shots. It does not have to be grey card at all.
This is how it works on Nikon though and irw1 are quite unambiguous for Nikon - may be Canon is slightly different though...
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For custom white balance, exposure isn't very critical - so long as the camera gets a half decent image of a neutral colour. White paper is the easiest thing readily to hand that is neutral, and it also has the advanatge of being bright, which is particularly handy in this application as it keep the shutter speed a bit shorter.
Set camera on Av, lowest f/number and highest ISO, fit filter and cover viewfinder, take test pic. By raising the ISO and lowering f/number, you are just helping to reduce the exposure to a conveniently brief time, which might otherwise run into several minutes.
You will then have a light mid tone image, probably rather green from what I've heard with this filter. Use that frame to set custom white balance and take the shot again. It will come out neutral grey and now you're ready for the real thing.
Don't forget to reset the ISO and f/number, and also turn off in-camera noise reduction which doubles the length of the exposure while it's processing - do that in post.
Edit: it must be a neutral colour for white balance, regardless of camera brand, and it must obviously be illuminated by the same light source as the final subject. Neutral colour means equal quantities of red, blue and green - white is neutral (and easy to use), grey is neutral (but a neutral grey is often hard to find) and black is also neutral come to think of it - equal quantities of nothing
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One other potentially stoopid question. Will I have to do this every time I use this filter or will the camera remember?
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One more clarification. When you say take the shot again, do you mean take the white card shot again or just shoot the scene?
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The camera will remember. You can do what you like after CWB has been set and until you reset it again the camera will always revert to it.
However, if you shoot under different lighting conditions, eg you move from daylight where you set the CWB, indoors to tungsten light, you would have to reset it for the new light conditions.
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That's great, thank you. Let me know when your book is published.
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Sorry, you don't have to take the shot again - it's just to check that the white balance is correct, so yes if you wanted that confirmation you would shoot the white card again and it should come out neutral.
But if you trust it, and I think you probably can, go straight for the real thing.
TBH, while it's nice to get everything tickety boo, if you are going to post process the Raw image as a matter of course, white balance doesn't have to be perfect. By the nature of this kind of photography, you are quite often working in usual light, eg sunset, under street lighting, whatever, in order to get maximum effect from the very long shutter speed.
But it's nice to get confirmation on the LCD of an image that looks most of the way there, and when you go into post processing the chances are that the file will import with the in-camera JPEG settings still tagged to it. You can change them or delete them of course, but if they are already there or thereabouts, that's a better starting point than a hopelessly green, flat and low saturation image that needs working from the ground up.
Hope that makes sense
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That's great, thank you. Let me know when your book is published.
Don't you start
I haven't really started it yet! But no worries, my pleasure and I hope it all works for you. Be sure to post some examples up
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Don't you start
But no worries, my pleasure and I hope it all works for you. Be sure to post some examples up
Will do. We're off to Norfolk for a couple of weeks staying right on the cliffs by Sheringham so I'm hoping to get some cracking shots off the top of Beaston Bump.