How to Use Welding Glass as a Budget Big Stopper
You will no doubt have read about using welding glass in place of and expensive 10 stop Neutral density filter. I decided this was something worth trying before investing in a proper 10 stop ND and I found it pretty successful. Here what to do if you want to try it.
The first step is to buy yourself a bit of welding glass I picked mine up from Amazon for around £2; eBay also has plenty of this stuff available. After having a look on various forum posts etc. about the subject I was clear that a shade 10 glass was the popular choice so that’s what I went for.
Here’s the one I’m using.
Once the glass arrived the next step was to be able to mount it to my lens. For this I used and adapter ring from the Cokin P system which you can also pick up really cheaply on Amazon or e-bay. In order to put the glass onto the ring I place a thin line of blutack onto the adapter ring all the way around so as no light can leak in the pressed the ring firmly onto the glass. In the picture below you can see the blutack ring on the glass after I removed the ring.
If you want to make sure that your new long exposure filter is going to be vertically orientated when on your lens it is worth screwing the adapter ring onto the lens before attaching the glass and marking the top of the ring.
Now that you have built your Welding Glass ND Filter you’re going to want to shoot some shots with it but how do you know how long to expose your photo for. For this there are a number of apps for IOS and android that will calculate this for you. I use android and my app of choice is Exposed. You simply tell it your shutter time without the filter and the number of F-stops that the filter will reduce the light by and it calculates the required exposure time. It also has a built-in timer with alarm which is really handy for exposures requiring use of bulb mode.
Now you know how to calculate the exposure time required but wait how many stops reduction does your welding glass ND filter actually give you. This is easy to calculate using your cameras histogram and an app like I spoke about before.
The first step is to lock the camera in position on a tripod and take a photograph of a plain neutral surface a grey card or sheet of white paper are ideal. Put your camera in aperture priority and shoot without the filter. Raising your ISO to a pretty high level here can really speed up the process as if your initial shot requires a shutter speed of 1/8th sec the some of your subsequent exposures are going to be several minutes, so raise your ISO until you get a shutter speed of around 1/30-1/60th.
Now that you have your initial shot without the filter switch to manual making sure to keep your aperture and ISO the same as you used for your reference shot. Put your filter on and using your app calculated the exposure for a 10 stop reduction. (10 stops is a good place to start as your glass will probably be somewhere in this region) now take another shot of the card/paper. Compare the histogram of the reference shot and your 10 stop exposure if the 10 stop exposure is brighter try again using 12 stops reduction or try 8 if it is darker. Keep Trying different values until you get a shot in which the histogram looks as close as possible to the reference shot, now you know how many stop of reduction you are getting. My welding glass ND filter gives me a 12 stop reduction, fantastic for doing some really long exposures.
Obviously a £2 piece of welding glass is not a high quality photographic filter and there are going to be some issues so what are they.
- The glass isn’t coated so is quite prone to flare
- The glass shows up smudges and fingerprints really strongly
- The edges can be quite sharp.
The biggest downside to your welding glass ND however is the colour cast. Once you try it out you will find that there is a very strong green cast, so strong that it is virtually impossible to completely remove in post however if you convert to monochrome you can still get a stunning final shot. A lot of the types of shot where this type of long exposure filter are commonly used really suit the black and white treatment anyway.
To give you an idea of what possible with your welding glass ND here’s a before and after look at one of the photos I captured with mine.