Experimental Dark Glass…

…or how to make your own 10 stop ND filter for under one 10th the price of a Lee's filters "Big Stopper"

Off the back of my last post where I discussed Neutral Density filters, I finished by discussing the possibility of making your own 10 (or more) stop filter for a fraction of the cost of a Big Stopper. I'd first seen the idea in a magazine, where the idea of using welding glass was explored as an alternative filter material. It was a great idea, but looked a bit clumsy and difficult to use. It did start me thinking though, and I came up with a more elegant and user friendly version that will be far easier to use in the field, without fear of breaking the glass or cutting yourself.

In the original article, they bought a large sheet of weld lens and attached this to the front of their lens with a filter holder ring, by taping the ring to the glass using duck tape. It definitely worked, but the risk of getting a cut was pretty high and spinning the glass pane onto the filter thread has to be pretty tricky. I set to thinking how this could be done better, and came up with this refinement of the original concept:

You will need the following items:

• 1 pane of glass welding lens (for fitting into a welder's mask)
• 1 Cokin P type filter holder
• 1 adapter ring to fit the end thread diameter of your lens
• 1 roll of black (or dark coloured) self adhesive foam weather stripping from a DIY store

1. The lens glass

This is available in a variety of different darkness strengths to suit the type of welding that you would need it for. In the original article they went for a "10" strength piece. I bought 2 pieces from ebay - one "8" strength and one "13" strength so I can experiment with which works best.

You can get these lenses in all sorts of shapes and sizes, but I got this idea when I found a supplier that had lenses cut with one width of 84mm - the exact size to fit into a Cokin P holder. My 2 lenses were £1.39 each - what a bargain! If you try and look through this glass, it's so dark, you can only make out light sources - so it'll give a really long exposure.

2. The holder

This is a standard plastic Cokin copy holder - the kind with 3 filter slots and the rebate for a polarizing filter at the back. The weld lens grass is a great match for the width - the only problem is, the glass is thicker than a standard perspex filter, so it won't slot straight in - you'll need to do some minor surgery (don't panic - nothing complex). I got this holder for £1 on ebay - nice and cheap!

The holder slots have molded in springs that stop the filters from slipping out when you slot them in (the curved bits in the centre) so on each side you need to remove one of the fins from between slots 1 and 2 - to make one double width slot. You can see here, the fin furthest from the front has been cut out. I used a scalpel for this and if you're patient, and keep scoring gently, you'll be able to snap out the fins neatly on both sides, leaving a slot that is now too big for the glass - that's where the foam comes in.

3. The foam strip

 When using a really dark filter to get a super-long exposure, it's important that no light is able to leak around the glass and enter the front of the lens, spoiling the exposure. On a Big Stopper, there is foam attached to the back to stop light leaks, so I've devised a system that takes care of this and ensures that the glass lens stays snug in the holder and doesn't slip out.

By using foam weather stripping - available from all DIY stores, I made a foam rubber gasket, attached to the holder that prevents all light leaks and holds the glass firm - here's how it's done:

 The weather stripping comes on a roll like this, and already has the adhesive on one side. I found a black roll as it made more sense bearing in mind it's going to double up as a light barrier. This stuff also comes in brown and white - I'm sure the brown would be fine as well.

I stuck the foam around the entire face of the holder, making sure it was as neat as possible and there were no gaps. You'll need to trim the foam very carefully around the inside circle to make sire none is covering the lens area as this will show in your image. Again - I used a scalpel for this, but if you're not confident with a sharp blade - or just plain cack-handed, you could try cutting the foam to fit with a scissors first and dry fitting it with the backing still on, before fitting. Any doubts - get an adult to help! This is the most expensive item to buy and it was still well under £10 - if you already have some in the shed, even better!

Then all you need to do to finish is slide in the glass carefully, so the foam doesn't tear. Once it's seated nicely the idea is that you leave it in the holder, so it's easy to handle safely and has a degree of protection against accidental breakage.

4. The adapter ring

This is a standard fit adapter ring, easily available online. I bought a 77mm one to fit the diameter of my Nikkor 10-24mm extra wide angle lens - the rings are available to suit all lens sizes, so you just need to source one that suits the lens you'll be using. This one came in at £4 delivered - I could have taken the ring out of my other holder, but for 4 quid, it's easier to just get another one and leave it on this rig.

The ring snaps into place as usual, on the holder back, and that's everything done!










In use, the whole lot can be easily spun on and off the lens front, without you cutting your fingers off and the holder prevents breakage in your bag - here's the lot spun onto the front of my wide angle lens. Also, even with this dark filter in place, you will probably still need an ND grad to balance the sky, so the remaining 2 slots in the filter holder allow for you to slide in a grad in front of the glass!

It's a neat solution and all in cost less than £20. A big stopper with holder and ring is going to run you just under £200 all in, so a significant saving.

There is a slight trade off for the low price - welding lens glass is green, so all your images will have a green colour cast. If you shoot your images in RAW, this can be taken out in processing to achieve a normal white balance, but there's a much simpler and more satisfying route - shoot for mono images. If you set your camera up to shoot mono - or even better, convert your raw files to mono, the green cast is an irrelevance and you'll be able to shoot dramatic long exposure mono exposures all day long for a fraction of the cost!

To use this system, you're going to need a tripod naturally, along with a remote release of some kind – preferably with a lock off on the shutter button to allow you to take really long exposures. At anything over 30 seconds, you'll need to set your camera to manual, dial in your aperture and set the shutter to "BULB". Then with the remote release, you can leave the exposure as long as you need.

With exposures of around 4 minutes, 10 or 15 seconds either way won't be that critical
so to make timing the exposures easier - I bought a super cheap plastic stopwatch so I could time my exposures accurately. It seemed to be the easiest way to make sure your exposures are all the right length - an ordinary watch would do it though - just not as easily.



So there you have it - bargain long exposure fun ahoy!

I'll be posting how I get on using this in the near future, along with the results, so keep an eye out for that and it might convince you to give this a try - at this price there really is nothing to loose - give it a go! If you do - let me know how you got on - I'd love to see your experiments.


As usual - if you're enjoying these posts, do let me know with a comment - I'd love to hear from you! Keep shooting!