10 stop/Welding Glass Question

[realmofconfusion]

I'm trying to get my head around this whole "10 stop" adjustment thingy, and after a great deal of :bang: I think I've finally cracked it, but could you please let me know if my thinking is correct....

1 stop of adjustment is a doubling (of halving if going the other way) of exposure time - assuming that aperture and ISO remain unchanged.

So if I have a metered exposure without a 10 stop filter of 1/125 then the adjustments to shutter speed alone would be as follows:

1 stop = 1/60
2 stop = 1/30
3 stop = 1/15
4 stop = 1/8
5 stop = 1/4
6 stop = 1/2
7 stop = 1 second
8 stop = 2 seconds
9 stop = 4 seconds
10 stop = 8 seconds

If however, I also reduced my aperture by one stop, say from F22 to F16 (is that one stop of aperture???), would the calculated exposure time of 8 seconds above then need to be doubled again to 16?

 

[zeroeseight]

Going to f16 from f22 is an increase, so your time would halve to 4 seconds. Unless you got mixed up and meant to say f22 from f16, then yes your time would be doubled to 16.

 

[realmofconfusion]

Going to f16 from f22 is an increase, so your time would halve to 4 seconds. Unless you got mixed up and meant to say f22 from f16, then yes your time would be doubled to 16.

Sorry, yes. f22 to f16 is of course a wider aperture, so that would halve the calculated time from 8 seconds to 4. :bonk:

Had the original exposure of 1/125 been calculated at f16 (giving a new shutter speed after 10 stop change of 8 seconds) and I changed the aperture to f22, then the new shutter speed would be 16 seconds.

Got it!

I used to know this stuff, but lately my mind has just gone blank!!

 

[Kaouthia]

Yup, you got it. Some of the welding glass isn't quite always what it says on the tin though.

I got one recently from CGeezer that clearly says printed on it "Shade 10", but I'd say it's a good 12 stops in my limited testing so far. I'll know better once I pick up a spare 72mm cokin adapter and some superglue and can do some proper testing

 

[Alastair]

By my reckoning shade 10 is somewhere between 13 and 14 stops. Most people I know that also have a shade 10 estimate their's is in the range 12-14 stops. It's almost certain that the "shade" number is not based on a stop scale - it does exactly what it says on the tin, it's just we don't use the same units of measurement for photography as the welders use for shade protection.

For middle of the day bright sunlight conditions I find that f/16 and ISO100 an exposure of 2 minutes is about right with a shade 10.

 

[Kaouthia]

it does exactly what it says on the tin, it's just we don't use the same units of measurement for photography as the welders use for shade protection.

Fair enough.

 

[TheBigYin]

By my reckoning shade 10 is somewhere between 13 and 14 stops. Most people I know that also have a shade 10 estimate their's is in the range 12-14 stops. It's almost certain that the "shade" number is not based on a stop scale - it does exactly what it says on the tin, it's just we don't use the same units of measurement for photography as the welders use for shade protection.

For middle of the day bright sunlight conditions I find that f/16 and ISO100 an exposure of 2 minutes is about right with a shade 10.

iirc a large amount of the output from welding flash comes as UV light (hence you can get a welding "tan"), so it may well be that the shade 10 is a factor of 10 attenuation, just skewed towards the UV. All conjecture of course, and the main thing is that you really need to "calibrate" the welding glass when you get it, then you'll know exactly what to do in the future.

 

[HoppyUK]

My welding glass is marked 11 and is about 14.5 stops.

To the OP on stops. A 'stop' is any halving or doubling of exposure variables - shutter speed, f/number, or ISO.

The confusing bit if f/numbers are related not by a factor of two, but by the square root of two, ie 1.4. Eg f/4 x 1.4 = f/5.6

 

[AndyB1976]

By my reckoning shade 10 is somewhere between 13 and 14 stops. Most people I know that also have a shade 10 estimate their's is in the range 12-14 stops. It's almost certain that the "shade" number is not based on a stop scale - it does exactly what it says on the tin, it's just we don't use the same units of measurement for photography as the welders use for shade protection.

For middle of the day bright sunlight conditions I find that f/16 and ISO100 an exposure of 2 minutes is about right with a shade 10.

Hi

Using your example - it conforms to the Sunny 16 Rule; quote wiki "On a sunny day set aperture to f/16 and shutter speed to the [reciprocal of the] ISO film speed"

Basically you would be at f16, ISO 100 and shutter value 1/100 + 14 stops = 120secs.

Stops - Tv
0 - 1/125 s
1 - 1/60 s
2 - 1/30 s
3 - 1/15 s
4 - 1/8 s
5 - 1/4 s
6 - 1/2 s
7 - 1 s
8 - 2
9 - 4
10 - 8
11 - 15
12 - 30
13 - 60
14 - 120

If the strength of the filter was unknown, could we not begin by metering a very bright scene - resulting in fast shutter, small aperture and low ISO.

Then drop in the unknown filter - and open up one stop at a time from all the combinations of shutter, aperture and ISO until the exposure meter was indicating optimum exposure?

Then you would know your filter strength/density for future use??:shrug:

My thinking could be way out here, so put me right if thats nonsense


Andy

 

[Alastair]

I tend not to get too hung up on tables of numbers. I think I described my method on the long thread, but basically..

I fit the welding glass, mount the camera on the tripod and compose and focus using liveview. I'm using a fast prime for welding glass shots (Sigma 30mm f/1.4) so liveview is pretty easy to see.. using a slower lens you may struggle.

I meter the scene in liveview using a high ISO and an aperture more open than I intend to shoot (say ISO800 and f/4).

I don't need a table of figures because I know a few basic things about my camera and this lets me keep the maths to a minimum:

• My ISO is set to 1-stop increments
• My aperture dial is set to 1/3 stop increments
• My shutter speed dial is set to 1/3 stop increments

As I reduce the ISO I need to increase the shutter speed by three clicks of the dial for every stop of ISO.

As I move from f/4 (or wherever I metered) I need to increase the shutter speed for one click of the dial for every click of the aperture dial.

Once I get to 30 seconds and need to go into Bulb mode I know that getting from 30 seconds to 2 minutes is six clicks of aperture or two ISO stops.

I call this the "counting clicks" method.. all you need to know is how your camera is set-up for shutter speed and aperture increments. There are no complicated fractions or tables needed. If you compensate as you go you don't even need to hold any numbers in your head.


For welding glass shots the exposures are pretty forgiving.. you could easily manage by changing the settings in-camera to 1-stop increments for all settings. This would make it even easier.

 

[AndyB1976]

Yeah I used a 3-click method to try and explain the 'shutter speed' thread a few days ago

I just posted the table as I find it easier to show the correlation between the stops and shutter value and how it correlated to a 14stop density, for the 'basic thread' users (including me)