My First Tentative Steps Into Video Astronomy
The idea of sharing my hobby has always been something that appeals to me, hence the creation of this site, and my involvement in my local astronomical society. To me, the sharing of what I see and do is as important as the seeing and doing itself. Don’t get me wrong; I love those quiet nights of solitary visual as much as the next person, but I also like to get others involved where I can.
The idea of video astronomy has intrigued me for a while now. Video astronomy is the use of video cameras (very often modified CCTV security cams) to capture live images directly from the telescope onto either a TV screen, or onto a PC via a video capture card.
The emphasis here is on the ‘live’ part. Astronomical imaging as a whole is a long-winded process, that very often requires a LOT of work to get decent results, and doesn’t really lend itself to a shared experience ‘in the field’. Video astronomy on the other hand is a more ‘real-time’ process. It enables multiple people to view the same image at once, and has the advantage of being able to show objects that may be too faint to view directly visually, especially for the more inexperienced observer.
I first got interested when I saw what some of the live broadcasters on the ‘Night Skies Network’ were producing. The Night Skies Network (www.nightskiesnetwork.com) is an USA-based website that enables users to broadcast their live video feeds and also to provide a commentary whilst doing so if they wish. This potentially opens up the video feed to thousands of viewers.
Many use the relatively expensive ‘Mallincam’ cameras for this. Mallincam are excellent cameras, but are not readily available outside the USA, and are relatively expensive. Others have approached this from another angle, and modified existing (and relatively cheap) CCTV cameras to do a similar job. A common choice for this is the Samsung SCB-2000. This camera has excellent low-light capabilities in that it can take the longest shutter speed of 1/50 sec, and multiply this by various factors, up to 512x, giving you effectively almost 10secs of exposure time. This is enough to pick up many ‘faint fuzzies’ and provide enough detail for a good viewing experience. This ‘integration’ facility is effectively ‘stacking on the fly’.
I got hold of an SCB-2000 for the grand old price of £19 delivered on eBay – they’re readily available if you’re willing to be patient and bid on a used one. You can pick up new ones for about twice that price, so still not going to break the bank.
This, coupled with a C-thread to 1.25″ nosepiece, provides the basis for a video astronomy setup. Add to this a 1.25″ 0.5x focal reducer to widen the view (and increase the ‘speed’ of the system, thereby seeing more in less exposure time). Also required, if you’re to be using the setup with a refractor, is a UV/IR cut filter to avoid ‘star bloat’ caused by out-of-focus IR.
This aspect does confuse the first time you read about it. In order to make the cam sensitive to the red end of the spectrum (produced by many emission nebulae), you need to remove the IR filter that’s built-in – this is an easy process that’s documented in several places on the web – google will help you here… You then need to replace it with a higher quality astronomical one that allows more of the ‘good’ stuff through but still blocks the wavelengths that cause the problems. If you’re not going to use the cam with a refractor, then you don’t need to worry so much about adding an astro IR/UV filter, as reflectors don’t have the same issue with focusing IR light. However, I’d always suggesting having one available anyway, as it stops any IR causing star bloat in instances where that’s a good thing, and if you want pinpoint stars. However, some galaxies emit strongly in the IR, so sometimes its actually good to go galaxy hunting without an IR filter. On a refractor, your stars may be a bit fatter, but you’ll see some very fain galaxies that you may miss with a filter in place. This was pointed out to me on the Stargazers Lounge forum by a long-time video astronomer, and is something I wasn’t aware of at the time.
The use of the focal reducer is important in two ways as previously mentioned. It widens the field of view, which is important when trying to fit in larger objects (M42 for example, is huuuuuge!). Also, it makes the optical system ‘faster’ which means you can capture fainter things in the same amount of exposure. It effectively makes my f/6 newtonian into an f/3 scope.
There are also challenges if using a focal reducer with a Newtonian, in that it makes it impossible to come to focus in many Newts. It moves the focal point closer to the mirror, so you can’t get ‘close’ enough to get the camera to focus on the scope (known technically as a lack of in-focus travel). luckily, the particular model I have has a low enough profile focuser that with a modified (i.e. shortened) adapter, I managed to get the camera to focus. The whole setup, when coupled to the newtonian looks like the photo on the left. In this case, the order is… Camera -> C-mount to 1.25″ nosepiece -> 1.25″ 0.5x Focal Reducer -> UV/IR filter -> 1.25″ to 2″ Orion Self-Centering Adapter -> 2″ Skywatcher Focuser adapter (milled down to reduce the height) -> Focuser. As such, I don’t need the UV/IR filter with the reflector, but I have one for when Iw ant to try it with my refractors.
You can just about see that there’s a tiny bit of the focuser tube still showing – literally 2-3mm or so, showing how close I was to not being able to focus. Luckily, the whole setup like this is very rigid and seems to work well.
So – enough about the mechanics of it – where are the images????
Well, the first object I aimed at in order to establish whether I could get focus was good old Luna.
The moon was at about 50% illumination, so provided a good test of the short er exposure capabilities of the cam. I set the cam to 1/1600 exposure, and found that the image quality far surpassed what I expected. It’s not the best quality shot, but to the right is a quick pic of my laptop screen with that first image on screen.
The output of the camera is a standard composite video signal, meaning that to display it on the laptop, a vide capture dongle was needed. These can be picked up for about a fiver on eBay. However, I want to be able to dispense with the laptop sometimes, so I’ll be investing in a small (cheap) LCD screen that can take the signal directly. This will make it much easier to keep the equipment requirements low if I just want to use the Synscan handset rather than the full EQMOD-based laptop setup.
So now I knew it worked, I did a quick one-star goto alignment and then slewed to a deep sky target. I would have gone for easy pickings with m42, but unfortunately, it was behind the house by the time I got around to this test. Therefore, I went for a slightly more difficult target. M51, the Whirlpool Galaxy provided a good first test. I gradually racked up the exposure, and there it was – live on screen. Unfortunately, by this time, the combination of the bright moon and the arrival of some high misty cloud meant that the image isn;t as good as I’d have liked. There was no doubting though – it was there! The structure was quite evident – something I’ve never seen visually. The image does seem to be in mono however, so I’m going to need to fiddle with that a little, as I think it’s a capture dongle problem – another thing that won’t be an issue with a direct screen.
I slewed to a few more targets (a couple of globs – M3 and m13). M3 looked marvellous, and M13, despite being through cloud and trees, also gave a decent view (if a bit blurry!).
All-in-all I’m really happy with the first light for this cam. Obviously it’s not going to produce astrophotos up to the standard of my DSLR or a dedicated CCD, but then that’s not the point. It’s a way of sharing live views through my Telescope with others, either at an observing session, or via the Internet. I’m looking forward to having a proper session or two with this cam and seeing what I can get out of it. Stay tuned for details of future broadcasts on Night Skies Network – it’s an exciting new feather in my astro hat…