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Mon, 30 Nov 2015 - How to photograph Comet CATALINA US10

While this horrible, horrible weather continues to thwart our attempts to even see Comet CATALINA US10 (which I'll just refer to as CATALINA from now on), this might be a good time to think about how to photograph it if you want to.

Obviously many amateurs are going to be photographing the comet through their telescopes - essentially using their telescope as a huge zoom lens to take close up images of it - but if you just have a camera, and no telescope, can you still get a picture of CATALINA? Well, yes, you can, but it's not quite as simple as that. (It never is, is it?) You have to have the right camera for a start.

You really need to have a modern digital SLR (or DSLR) camera if you're going to take images of CATALINA. Why? Well, the small, everyday digital camera you might use for taking photos at parties, or while out or a walk, just won't cut it. Nor will the camera on your phone. Neither are sensitive enough to capture the faint light of the comet, and neither can take time exposures long enough to capture that faint light either.

It has to be said that many modern "bridge" cameras have a lot of the same functions and capabilities as a DSLR, so you might be able to capture CATALINA with one of those. It's definitely worth a try! But a DSLR is especially useful because you can swap lenses, depending on what you want to photograph. You can use one lens for a wide field photo, and another for zooming in really closely on something. For CATALINA you will want to use either the standard 50mm lens, or a zoom lens of some sort.

But because you'll be taking time exposures, of several seconds, you will need an additional piece of kit too. You might think you can hold a camera steadily enough to photograph the night sky, but you're wrong, trust me. Even the steadiest, calmest contestant on The Cube would not be able to hold a camera perfectly still for the several seconds needed to photograph Comet CATALINA. So, you're going to need some help. You're going to need one of these...

  

If you don't already have a tripod, now is the time to go out and get one. You can pick a good, sturdy one up in a camera shop for under £50, and cheaper, less steady ones in places like Argos for half that. It's also worth going around the charity and second hand shops where you live, because tripods often turn up in those - but a word of warning. If you see one, take a good look at it to make sure it's all there. If there's a square hole at the top, with nowhere to screw a camera onto, don't buy it. You absolutely need a "plate" in there; without one, you simply won't be able to mount your camera on the tripod.

    

So, you have your DSLR, fitted with a 50mm lens (at least to start with) and it's on a tripod. What next? Well, you have to get out there at silly o'clock on the next clear morning and start taking photos!

Having reached your favoured observing site, at around 05.30, you are ready to start. The first thing you have to do is get the comet in good sharp focus and, of course, that's not as easy as it sounds, either...

In the daytime you don't have to think twice about focussing your camera - it does it for you, using "autofocus". But that won't work on the night sky, not when everything is so faint and dark. You have to do it manually. Yes, manually

If your camera has "live view" - i.e if you look at the screen on its back you can see what the camera is seeing - you can use that to achieve a good sharp focus. Just aim your camera at Venus, which is in the east before dawn, and focus on that. When it's nice and sharp that's it, you're ready. If Venus is behind cloud, use a bright star or even a streetlight on the horizon instead they'll work just as well. However, if your camera doesn't have live view you'll just have to use good old fashioned trial and error - taking pictures with slightly different focus until one looks sharp.

With your camera in focus you're going to set the lens aperture next. In the old days that just meant turning a dial on the lens, clicking it on until it read the aperture you wanted. Now, most DSLRs select aperture digitally, on the screen, using a dial on the camera. However your camera selects aperture, you want to be setting it at the smallest "f number" available, something like f2, or f1.8 maybe. That just means you've opened the lens up as wide as it can go, allowing as much faint comet light as possible to go into the camera to form your image.

What's next? You need to set the camera's "ISO number" - what we used to call, back in medieval times, "ASA" or even "film speed".

Because CATALINA is faint you want to select a reasonably high ISO rating - start off with 1000 ISO and go higher or lower if your first images are too dark or too bright respectively. Note: too high an ISO and your images will look really grainy, and the comet will be lost in the background noise. Too low an ISO and the comet's faint light won't register. So, it's a balance, and you'll just have to experiment until you find what works with your equipment at that time.

Finally, the key to the whole exercise - setting the exposure time. Because CATALINA is so faint you will need to take a time exposure of several seconds with your camera. Just setting it on AUTO and clicking away won't work, you'll just get blank images. But how long should you set the exposure time for? Well, here you'll just have to experiment. The correct exposure time will depend on how bright the sky is, how high CATALINA is, how bright the comet is, etc etc. All you can do is try different exposure times and see what works.

Right... you're almost set. Let's go through what you need to do to get a photograph of Comet CATALINA!

1. Point your camera, fitted with a 50mm (or close to it) lens, set at its widest aperture (smallest "f number")  at Venus  (or alternative light source) and focus on it. When it looks sharp, move on to...

2. Set the TIMER DELAY on your camera. This is vital, because if you just ptress the shutter buttin and take a photo right away the camera will still be shuddering and shaking about, so your image will be blurry. By setting the time release you delay taking the photo by several seconds, long enough for all the vibrations to die down. If you have a cable release, use it. That will help even more (but it's not essential).

3. Take a 4 second test exposure of Venus. If there are fainter stars visible around it on your photo, you're set to try for CATALINA itself. If there aren't, then increase the ISO rating until you see stars around Venus. Then...

4. Point your camera at the area of the sky CATALINA is in (and you can use the charts in previous posts here to find that) and take another photo with the same settings as before. If you're lucky you will see CATALINA on your photo, looking like a small smudgy star, maybe with a hint of a tail. If you can't see it, experiment with different exposure times and ISO settings until you capture the comet.

Now, don't expect too much! All you'll see with the set-up described above is something like this... You'll have to enlarge the image by clicking on it, and then you'll see the comet looking like a small, fuzzy, out of focus "star". As I haven't managed to see CATALINA yet this is actually an image of Comet Jacques from last year - it's the tiny fuzzy greenish... thing... just above the centre of the image...

                    

Now, if that appears on your camera back - with signs of one or more tails, if CATALINA keeps behaving as it is right now - you might feel disappointed, but don't be; you've just photographed a comet! There are, however. ways to improve on that.

Firstly, try changing your camera settings. Increase the ISO, and/or the exposure time, and you might get a much better image of the comet. You could also try swapping your standard 50mm lens for a longer one, say a 135mm, or even a 200mm lens. But be aware that the longer the lens the shorter the exposure you can take before the stars look like trails on your photo, so you will hit a "wall" at some point where you get lines rather than dots. Again, just experimenting with different ISO settings and exposure times is the way to go.

Eventually though you will hit a "wall" and there'll be nothing else you can do with single images. Then you caneither accept that as the limit of your abilities, and be happy with what you've got, or you can take your comet photography to the next level.

To take more detailed images of the comet you will need to collect a lot more light, and that means taking longer exposures. To do this you will need to either take a single picture, with a much longer exposure, or take lots of short exposures and add them together to make the equivalent of a single long exposure. If you want to take a single, very long exposure you will need to make your camera track the comet as it moves across the sky, and that means either fitting it to a driven telescope, or mounting it on one of the many "star tracker" camera mounts available now. I have an iOptron star tracker and it is fantastic, it recently gave me excellent shots of Comet Lovejoy, like this. which is a two minute long tracked exposure taken with a 135mm lens...

          

If you don't have a tracker you can get (roughly) the same result by taking lots of short exposures and "stacking them together" using special software, which can be downloaded free from the internet. "Registax" and "Deep Sky Stacker" are the programs most people use, and there are lots of great tutorials available on YouTube to help you get to grips with them once you've downloaded them.

So, there you go, that's how you take very basic photographs of Comet CATALINA - once this awful weather breaks! In fact, you don't need to (and shouldn't!) wait until CATALINA itself is visible. On any clear night you can do all the above but just aim your camera at the starry sky instead. If all goes well your photos will show the stars as sharp points, lots of them, and then you'll know you're ready for the comet.

Finally, don't worry about the technical stuff too much, that will come with practice. Just get out there and, using the guidelines above, start snapping, and keep snapping until you get something!

Good luck!

 

Added by: Stuart Atkinson