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I’d also be interested to hear from anyone who’s getting good meteor captures with the Watec 902H.
If I recall correctly, the AGC only has low and high settings. As Callum says, the low setting is very dim, so you only record fireballs. The high setting is very noisy. If you stack the frames for 30 seconds you can get some nice deep images, but for meteor searching it’s not great, because the meteors are lost in the noise.
My solution was to upgrade to a Watec 902H2 Ultimate, which has an AGC knob, so I could tune the gain to a happy medium. But I do gather others are getting on OK with the 902H. I was wondering whether some kind a pre-amp between the camera and the digitiser would help, but Callum tells me he’s tried that and it hasn’t helped!
Have you tried dropping David Rothery a quick email? I’ve not corresponded with him personally, but I understand he’s very supportive of the BAA.
Hi Dave,
There may be other people here who know more about aviation than I do, so my views are my own and may not reflect the wider BAA!
I’m sure we’re all keen to make sure everybody knows that lasers are dangerous, and have to be used in a safe and legal way. The police have been doing a good job of raising awareness of this in the UK media in recent days.
However, I’m not sure NOTAMs are the way forward.
My personal understanding is that (at present) NOTAMs have to be issued for fixed laser displays, such as the ones that light up the sky at Greenwich and other temporary installations. Those installations are permanently on, so pilots need to avoid flying through the beam.
Star parties are a bit different. There’s someone steering the beam. Planes are easy to see at night time, especially at low altitude. Anyone running a responsible star party should be keeping an eye out for them and make sure laser beams stay well away. In fact, there’s a legal obligation on them to do so (quite rightly!).
If the Civil Aviation Authority wants notification of star parties, I’m sure we’d be keen to help in any way we can. However, I rather doubt the CAA could do anything useful with that information. Laser beams at star parties move all around the sky, crossing vast areas of airspace. The CAA is unlikely to block out such a large area of air space because of one star party!
So, my impression is that we need to urge people to act responsibly within the existing rules, and make sure that everyone knows that pointing lasers anywhere near planes is a very stupid thing to do!
I did at one point briefly consider using an SBIG AllSky-340 camera for my own meteor camera work (instead of a Watec 902H2 Ultimate).
Unfortunately there were lots of reasons why it didn’t really seem to fit the bill. Even though you can set custom exposure lengths, it communicates with the PC via a slow serial link, making quick exposures almost impossible. By contrast, the Watec camera delivers 25 frames per second. As Jeremy says, you really need that many frames to catch fast meteors.
The other issue is that having bright lights in the field of view is a real nuisance. You get blooming and internal reflections. The slightest muck on your glass gets illuminated. A limited field of view actually helps keep unwanted light out — the metal CCTV housing acts as a lens hood.
It was a real shame, because I wanted an excuse to buy an AllSky-340 to play with 😉
We currently offer the videos in two formats: MP4 and OGV. The MP4 is high-quality video that Nick produces with clever compression. I produce the OGV versions from Nick’s files, with less clever compression and generally much poorer video quality.
When you view the video through the player that’s embedded in our website, your web browser is given a choice of which format to play. Firefox and Chrome can play both formats, but will generally pick the lower quality OGV. Internet Explorer will play the MP4, because it doesn’t support OGV. A few platforms will play the OGV because it’s the only format they support — specifically Opera, and some (many?) Linux systems which don’t include MP4 codecs.
It’s a bit like the old VHS vs Betamax video tape wars 🙂
We have various options. We could scrap support for OGV, meaning that most users will see the higher quality video, but a few users may be left out. We could still give them an OGV they can download separately from the web player.
Alternatively, I could double the file size of the OGV files. Currently I aim for 100 MB per hour of video. We’re not close to any bandwidth limits on our server, so we could comfortably serve higher definition videos… providing BAA members are on good broadband links where 200 MB per talk isn’t an issue. Personally I reckon we could double the file size without any problems.
Thoughts?
I also can’t provide a definite answer, but I suspect the answer to both questions is “not really”.
The Julian Day system’s great strength is that makes it really easy to calculate the time interval between two dates/times, which is difficult in most calendars. But unless they’re assembling historical chronologies, or doing astronomy over long periods, how many people actually do much date arithmetic?
The system’s weakness is that its epoch was nearly 7000 years ago, so Julian dates are big numbers. In the past, scribes got lots of practice at writing out big numbers that start 24…. But nowadays it leads to loss of precision in computer programs. Computers typically do calculations to 16 significant figure precision. If you waste some of those figures on 245… you have less precision on the digits that come later. A Julian Date stored in a standard-precision variable in a computer program is only stored accurate to 20 microsecond.
Many of the applications today that involve time arithmetic involve computer operating systems where a lot can happen in a microsecond. They usually use Unix times, stored as the numbers of seconds since 1 Jan 1970. That gives you 0.1 microsecond precision. I think pretty much everyone other than astronomers use Unix times rather than Julian Dates nowadays.
So in short, it’s not clear to me many people outside astronomy would have had much use for Scaliger’s system. And it’s not clear his decision to use an epoch in 4713 BC was ever a useful one. Is it fair to suggest today, even astronomers only use the system out of tradition, rather than because it’s good?
Nice work! Out of interest, is that the Astronomik clip filter? I’ve been wonder for a while whether that’s compatible with full-frame DSLRs, since the list of supported cameras doesn’t include the 6D. But it looks like it is!
Cat 5 cable is pretty amazing stuff. It’s built to carry very high data rates with minimal dispersion over long distances, and it works!
I know somebody who wanted to have a PC they could access in their shed and indoors. He wired the keyboard, mouse and SVGA data signals down 30 metres of CAT 5 cable buried under the lawn. Normally SVGA deteriorates even more than USB over long distances, but his set up worked perfectly.
Then again, I think he paid an arm and a leg for the connectors (impedence mismatches can be a nightmare if you bodge the cables together), so probably best to try a simpler solution first.
Roy is right.
5 metres is right at the limit of how far USB signals can travel without dispersion leading to an unacceptable error rate. So you really need to have something on the end of the cable acting as a repeater.
An active USB cable does exactly this: there’s a small repeater in the plug furthest from the computer. I’ve used cables like this and they seem to work.
I imagine that plugging the far end of a passive 5m cable into a powered (or even unpowered) hub would have the same effect, but I’ve not tried it.
As Jeremy says, Data Protection means that the BAA couldn’t do this without getting permission from members. We could potentially have an opt-in members’ directory, but I fear a lot of our members would be very uncomfortable about putting their addresses in the public domain — especially those with very expensive telescopes in their back gardens!
I am keen to develop the BAA website into a more social platform where are members can share images and send messages each other. Perhaps it would be worth giving members the option of specifying a home town that we could plot on a map…
OK – Yes, I think it was those images I was thinking of. It was something I saw scroll past on twitter a couple of months ago, so I can’t go back and check!
I suppose the selling point of a Goto system for me is that I’m often giving people tours of the sky, and you’ve usually only got half an hour before they get bored/cold, so a Goto system lets me show far more objects in that time than if I was finding them manually. Perhaps I’m just slow at star hopping…
What really annoys me about Goto is not being able to declutch and yank the telescope around without losing alignment. I’m quite tempted by the SkyWatcher FreedomFind thing which solves that by putting encoders on both axes. But I think the cheapest FreedomFind mounts are about £950, and at that price it’s not exactly top of my wish list…
Callum,
That’s interesting to hear! I’d assumed the EQ3 was quite a popular wide-field imaging mount.
If I recall correctly, Ian Sharp uses an NEQ6 as a slightly-overkill DSLR-mount-with-autoguider, and a few people seem to use the HEQ5?
Not seem too many people use an EQ3, but then I guess it limits your options if you want something you can also put a telescope on. And I have no idea how stable it is…
Dominic.
I’d be curious to know how many widefield DSLR astrophotographers do or don’t callibrate their frames. I think a lot comes down to what camera you’re using.
About 10 years ago, I started out (I would imagine like many beginners) doing astrophotography with a very low-end camera. I found a compact Canon Powershot can get you nice pictures of M31, M42, etc, but I absolutely had to callibrate those frames because the sensor was rubbish. The same seems to be true of low-end DSLRs, e.g. a Canon EOS 1000D produces rather scratty frames at ISO 800 or 1600, yet I’ve seen many astrophotos in online forums taken with it. Yes, you can get impressive images without callibration, but you can do a lot better with.
I don’t doubt that if you use a Canon EOS 5D (I think the camera Graham uses?), you can push it to a very high ISO setting and still get nice clean images. But I wonder how many beginners are willing to splash out on such an expensive camera?
When we were talking about this at the Winchester weekend, someone raised the question of what images Astronomy Picture of the Day should or shouldn’t use.
I think yesterday’s image is a rather unfortunate example: <http://apod.nasa.gov/apod/ap140419.html>.
Of course, any astronomer knows this is an artist’s impression. And the discovery of this exoplanet is a big news story that NASA will have wanted to cover. So perhaps with suitable warnings attached, it was reasonable for NASA to choose this (wildly speculative) artist’s impression.
But the general public does not know this isn’t a real observation. Most media outlets were well-behaved in making very clear that this image isn’t to be taken too seriously, so it seems extremely unfortunate that NASA say nothing at all.
Hi Phill,
There do seem to be a few problems with the forum pages as they stand, both to do with the layout of the individual pages, and also that forum posts don’t have “breadcrumbs” at the top to show where they sit in the hierarchy of forum topics. We’re using a standard Drupal forum implementation, but it seems rather rough around the edges.
At the moment, clicking “back” on your browser sometimes works, but it’s no replacement for a proper breadcrumb at the top. I’m trying to figure out at the moment how much needs to be done, but I fear some of this involves rewriting their code… From what I can see, Drupal’s forum implementation has code which is intended to produce a breadcrumb, but it isn’t doing anything particularly useful at the moment…
Dominic.
Thanks for reporting this. I’ve fixed the stray close div tag on the Who’s Who page.
I think you’re right that there are a few problems with the forum pages as they stand. both to do with the layout of the individual pages, and also that forum posts don’t have “breadcrumbs” at the top to show where they sit in the hierarchy of forum topics. We’re using a standard Drupal forum implementation, but it seems a bit rough around the edges. I’m trying to figure out at the moment how much needs to be done, but I fear some of this involves rewriting their code…
