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Alex,
Downloaded the first paper by Steve you listed during my lunch. Interesting read. (Also glad to see my chop rates were in accordance with his determinations too…). I’ve not played with astrometrica for a LONG time. Working with DSLR images looks like it’ll be a bit of a challenge. But he’s laid down the gaunlet for a few arc sec precision to directly measure decelerations.
Ties in really nicely with the demand for high speed chopping (I take it that’s why he made the six slot shutter). This of course open up the challenge of making a 9 or 12 slot shutter for very high mechanical chop rates. The LCD’s start to show their convenience at this point.
Anyway, got plenty of things to do now to fill my staycation this summer!
You mentioned Edinburgh, will you be up for a couple of days? I’ll try and come through (by train this time) so we can finally have a few refreshments! Might even have some results should the weather cooperate for the Persieds.
cheers,
Bill.
Hi,
Tested the rotating shutter at lunchtime. It’s turning at a fair clip. Chop rate is 62.5Hz. This is faster than the LCD rate on the image from the earlier post. I think a shutter with 2 or 3 blades (20.83Hz and 31.25Hz respectively) may be better for more general purpose observing. Need to locate some suitable plastic sheet and get cutting….
cheers,
Bill.
cheers,
Bill.
Hi,
It’s interesting to read that the problems with astrometery are nothing new! It is probably the sole advantage of DSLR imaging over video. The precision is vastly better! Talking to Felix about the LCD shutters he tells me that this issue was one of the drivers for trying them despite their optical limitations.
I ran the LCD system I have for ~2 hours through the wee hours of Sunday morning but didn’t catch anything. Despite the near full moon and essentially twilight conditions through the night at my latitude, the DSLR images looked much better than I anticipated given the sky brightness. The only concession I made was reducing the ISO from 1600 to 800.
We’ll see how it goes.
Cheers,
Bill.
Hi,
After collecting Steve Evans’ old system I gave it the once over. A few loose connections were tightened and I changed the power lead. Seems to work a treat now. Next thing is to determine the rpm and chop rate….
It’ll be interesting to compare the two methods (hopefully during the Perseids…)
Cheers,
Bill.
Hi,
If you have a look at the manufacturer’s website all the figures are there. I’m using a FOSG2 (circular version).
Off the top of my head it’s the transmission that is the problem. It’s only about 37% thus you’re losing ~ a stop. A fast lens is needed. The extinction ration is 1800:1. That’s dark enough for meteor work but whether this is sufficent for other imaging I’m not sure. The meteor image shows quite a clean profile, I pleased with the result (and if I’d paid more attention to the timing diagram on the website the actual chopping rate wouldn’t have been a surprise! ;-)). I’m currently constructing a ye olde fashioned rotating shutter for some other cameras so it’ll be interesting to compare the results….
cheers,
Bill.
A rather late follow up. One of the issues that originally confused me was the duration of the meteor from video compared to the duration determined by the chops in my still. After some tests with my system and an oscilloscope there is an effective doubling of the chops due to the way the crystals in the shutter work.
In this case the function generator was producing a square wave at 20Hz (20 times per sec) HOWEVER the crystals seem to switch with every reversal of voltage so a 20Hz rate from the function generator gives 40 chops per second. What this boils down to is that the meteor was only half as long as I originally thought but now it fits much better ;-))
Further digging around reveals that driving them this way, with a pos-neg-pos-neg voltage etc signal a: makes them work properly and b: if you use, say, zero-pos-zero etc it can cause the crystal to degrade much quicker (according to the manufacturer’s bumff.)
So, beware if you use these LC shutters, they might not give you what you think they should be giving you…!
I am now confident it was the same meteor.
Cheers,
Bill.
Hi,
That’s an excellent example, and indeed a long gap between the light emissions. Must have positively skipped into the atmosphere ;-))
Bill.
PS, Great to catch up with you at Newcastle. I should have taken a chance and got on the train with you rather than waiting for the “direct” later train. Ended up being 1h 30min late!, I’m glad I had driven into Glasgow as I would not have made the last train down the local line.
Hi,
With so many people collecting spectrum now, that’s pretty much where we’re heading. The eminent Czeck meteor astronomer Jiri Borovicka published a paper in 2016, “Representative meteor spectra…” (sorry not sure of the full title) based on many years of his work using spectra colllected via image intensifier and recorded on video tape.
The technology has moved on and even a basic system can exceed the pros now.
The situation has gone from a few (photographic) spectra per year to several per night with video based systems!
Bigger systems with institutional funding now have hundreds of cameras running! The shower meteors are quite well established but it’s the sporadics that provide the surprises!. I’ve recorded several very interesting ones recently. With said technology the amateur is still on a par with the pros regarding sporadics.
cheers,
Bill
Hi Jack/Eric,
Thanks, it’s taken a decade to get it all together and make it fairly routine. If you look through my other meteor video’s on YouTube you’ll see one of the developments over the years. Doesn’t seem like ten years, I can still remember seeing that very first really crude spectrum at 320×240 resolution and thinking this is the future. When you look at the numbers it is staggering the immense jump that has happened. HUNDREDS of hours over decades to record photographically just those few exceptionally bright fireballs producing spectra. Now, even at this time of year I get several per night (when it’s clear ;-() and dozens during meteor showers.
Now that the pros are using my type of video system they get even more since they run a lot more cameras from considerably better sites! Looking at the journals, meteor spectroscopy papers are now regular. The game is now trying to build up classifications with a large number of spectra that all look pretty similar. The first papers on this have already appeared. The differences are there but it’s a subtle game at that.
cheers,
Bill.
Months on I’m still working through the Geminids 2017! This is a crop from the composite video image. 20171215:011300UT. (Correcting the smile is just another little challenge….)
However If you look to the left of the image the first two bright, closely spaced lines are the H and K ionised calcium lines. I am both surprised and extremely please to be getting this resolution with an objective mounted grating. Shows that a good fall of meteor across the fov (pretty much luck) can make a significant difference to the results! Considering some of the comments I’ve been exploring some new reduction strategies. Here’s a non instrument corrected spectrum with the line ID’s as best as I can tell.
If only all meteors were the same mass, traveling at the same velocity and were recorded in the zenith things would be just so much easier (but probably not as much fun!), sigh… ;-))
cheers,
Bill.
Hi,
Nothing has been done with any continuum as such. The graphs were normalised to each other around 4700A where there were few lines so a simple comparison could be made. When full corrections are done, the differences are still there but a lot more subtle. “For exposition only”, I think is the correct expression!
cheers,
Bill.
Hi,
The emissions below 4000A are well know (Fe, Mg and Ca+, running left to right in the spectra). The point is that they are only seen (in this sample) in the Geminid and not the others. When fully calibrated and instrument corrected the Mg peak is the strongest in the entire spectrum. This “line” is actually an unresolved triplet centred around 3833A.
Bill.
Hi,
My tuppence worth…
I’ve been using Compro video cards (C100 and C500) for a decade and counting, Currently I have 8 installed they’ve all worked perfectly. They’re very old fashioned but cheap (£30 new) however I don’t know if they are made anymore.
I’ve also found the latest Climax Digital usb grabbers have proved reliable, again cheap at ~£30 BUT only buy direct from the manufactures website as there are gazzilions of clones that are truly crap. As a test I’ve been running a comparison between the venerable C500 and a usb frame grabber and I can see no difference.
There is also an alternative to UFO capture if you really want to keep costs down. This is handyavi. It is nowhere near as good as UFO (and that’s not a critisism it just not a single purpose entity like UFO Cap) and can’t be used for all the analysis.
I’ve used it in “emergencies” and for plain captures it’s fine when tuned properly (It’s also good for other astrostuff which is where I mostly use it).
So there are a few ways to get up an running on a budget but it all depends on what you want to do long term. You can always invest some more as your experience and/or interests develop.
Cheers,
Bill.
Not really related but just a general comment about the Quadrantids. Apart from ~2 hours on the night of the 3rd Jan I saw nothing else. Caught 8 Qua’s in total on video (and none visually) in those 2 hours. Then the cloud and rain returned…
You win some, you lose some 😉
cheers,
Bill.
Hi all,
I’ve put a short video on YouTube of this fireball and a colourised version as well.
Certainly the best spectrum I’ve had in several years!
The other analysis is progressing but it’s a lot more work than I anticipated… 😉
cheers,
Bill.
Hi,
That sounds like just the ticket! Do you have a copy of the circuit or a URL for such. Mentioning the 350D, I built a timer circuit using the venerable 555 chip so I could use long exposures on my own 350’s.
There’ll be a solution somewhere!
cheers,
Bill.
PS. It’s just occured to me I could probably do it with one of the Arduino’s I have, DOH!!!
HI,
Yep, indeed it does but when taking meteor shots one is taking sequences of hundreds of images. Unfortunately the manual says the mirror lock up works in what it calls “single shot” operation. It needs a two step operation to function and whilst that can be done with the canon remote control it can’t be done sequentially, automatically. Looks like it would need the observer to manually do the two press thing every shot. That would be VERY tedious after a short time let alone 6 hours!
I’ll just need to beef up the tripod and investigate further vibration mitigation for future field operations. IF the weather co-operates I’m going to run the same set up with the Quadrantids just to see how it behaves.
I am just so disappointed this could all be a mechanical resonance ;-))
Cheers,
Bill.
Hi,
I was using two Canon 1000D’s, don’t know if such economy models have this feature. I’ll check the manual just in case.
The peak night was just gorgeous but casual astro-tourism has turned the caldera into a motorway. 12/13th a few cars, 14/15th a few cars but 13/14th was ridiculous until around 0200. Every layby and track had cars jammed in. From the traffic I saw I’m glad I wasn’t actually at the observatory! It must have been chaos up that road.
When I left there was not a soul remaining, this was still an hour before twillight but I was frozen.
More importantly I got 10 viable spectra. Apart from the big fireball (twitter) the fainter ones show some interesting characteristics.
Cheers,
Bill
