Bill Ward


The set up has always been, more or less…,  the same. Stick a grating in front of your lens and see how it goes!

The plastic grating film now seems to be sold all over the place. The stuff I currently use I bought from Edmond Optics in 2009, £6.99 plus shipping etc. This was the second batch. The first was from the early 90’s. Trying searching for “holographic plastic grating film” or similar combination. Again, the stuff I bought, of US origin was sold in 12 inch x 6 inch sheets with either 12500 or 25000 lines per inch. I use the 12500 version which is just under 500 lines/mm. 

It’s on Amazon and ebay as effect filter, novelty pattern filter, rainbow generator etc etc. You can even buy a 200 foot roll if you want to! 

I should caution that TWO results (this and one other spoardic of almost the same magnitude) might not represent a statistically significant sample but with a bright enough meteor the plastic film seems to have a better throughput at the blue end of the spectrum than my much more costly glass gratings. Given the spec of the glass gratings this seriously surprises me! So I have now come to the conclusion that it’s a much more cost effective way to start should anyone wish to give meteor spectroscopy a go. I think this is pretty much old hat now as lots of stuff is online about it. I gave up on it when I ultimately stopped trying film based photographic spectroscopy which yielded precisely zero over 15 years prior to me using video. I decided to try it out again for financial reasons.

Due to the embossing process the grating is not blazed so equal amounts of light go into the spectrum on each side and because it’s a simple sinusoidal embossing the spectral throughput, overall, is less than a good glass replica. The upshot is you need brighter meteors to produce a spectrum all else being equal. Effectively you get half the light in your spectrum but at 1/20 the cost of a proper grating. It’s up to the prospective observer to decide whether that’s a reasonable cost/benefit analysis.

I used to have quite a bit of the stuff as I bought several sheets at the time but I have given it all away in little bits and pieces to those who wanted some to experiment with. At seven quid, cheaper from ebay, I don’t know if it’s exactly the same stuff though, it’s not going to break the bank.

Bit of a ramble but I hope it helps….