Camera Advice

[David Perkin]

After years of soldiering on with celluloid, I have decided to get a DSLR for astronomical use. I thought the Canon EOS 1000D was a good starter camera but Canon have dropped it for the 1100 and now 1200. Does anyone know how either of these would compare to the 1000D for diffuse objects and spectroscopy?

Also, which accessories would I need to get started with both unsteered and steered  camera lens work and prime focus and eyepiece projection? I have everything needed for a standard old-style M52 screw fitting SLR.

 

Thanks,

 

 

David Perkin.

[Martin Mobberley]

Hello David,

There is a book in the BAA shop entitled ‘Introduction to DSLR Astrophotography’ which may well be worth you acquiring, see: http://britastro.org/product/881
I have no experience with spectroscopy, but I would suspect the difference between the cameras cited would be very subtle. The Canon 60Da is optimised for astronomy as it has extended red sensititivity, but it costs about £750. The Canon data is here:
http://www.canon.co.uk/For_Home/Product_Finder/Cameras/Digital_SLR/EOS_60Da/

H-alpha regions will need far shorter exposure times with this camera, but if used for terrestrial subjects any red objects will come out far redder than their visual appearance. The normal cameras you mention both have 30 second and Bulb exposures so clearly can be used for astronomy.

Not sure what you mean by steered and unsteered? If you have a small equatorial mount, and there are some quite nifty ones around, such as the Vixen Polarie:
http://www.vixenoptics.com/mounts/polarie.html
…then you can take wide field shots with standard lenses that are several minutes in duration, quite easily.

However, for prime focus telescope work you need either a great equatorial mount or some form of guiding/autoguiding…. Without somehow guiding the exposure your shots will be limited to somewhere between 15 seconds and 2 minutes on the celestial equator, depending on whether your drive is poor or excellent, and what focal length you are working at. You can stack multiple short exposures using software such as Registax or Deep Sky Stacker. There are numerous handy videos on Youtube explaining how to use this type of software. For an astronomical telescope with a drive you need a camera to drawtube
adapter that will fit a Canon EOS bayonet mount, such as this:
http://www.harrisontelescopes.co.uk/acatalog/Canon_EOS_T_Ring.html

You may have a 1.25 or 2 inch telescope drawtube so you also need a compatible T adaptor to mate with the T-ring. For prime focus photography one problem often encountered with old Newtonian telescopes is not being able to rack the camera in close enough to achieve focus, but if you have achieved focus with a film SLR then you should not have a problem. As for eyepiece projection, well, this is usually used for lunar and planetary work, although most 21st century imagers use Barlows and Powermates for this purpose. For high resolution planetary imaging most imagers would not use a DSLR at all, but a high frame rate USB/Firewire camera that can shoot at up to 100 frames per second to give thousands of frames that can be aligned and stacked in Registax or Autostackert. An example of such a camera is the ASI 120MC, such as sold here (colour and mono versions are available):

http://www.365astronomy.com/zwo-asi120mc-colour-13-cmos-usb20-camera-with-autoguider-port-p-3536.html

There is also a BAA Observers workshop on September 20 which may be of interest if you are thinking about planetary imaging, although I’m not sure if DSLRs will be included:

http://britastro.org/meeting_render/3542

But I would definitely consider buying the aforementioned BAA book.

Other forum readers who have more experience with DSLRs may be able to give better advice about the specific Canon  cameras you have mentioned.

Martin

[Graham Relf]

David,

I suggest you should get the most recent model you can afford, because they continually get better. Since 2001 I have traded up through 5 Canon DSLRs and each has been better in terms of increased sensitivity and yet less noise (analogous to grain on film). So 1200D in preference to 1100D or 1000D.

I concentrate on deep sky and comet photography. So I would go instead for the 100D because it has the highest native sensitivity, at ISO 12800 (the 1200D only goes up to ISO 6400). By native I mean amplifying before digitisation rather by software afterwards (which would be counter-productive for astrophotography). Although the 100D series is considered to be at a higher level than the 1000D series, the 100D costs only about £50 more than the 1200D.

In the good old days of film single long exposures were the only possibility and so very accurate drives and guiding systems were required. Digital cameras enable a completely different approach, needing no guiding. Instead use the highest native (non-menu) ISO setting (in my case ISO 6400). Take many (50 or more) exposures, each of about 30 seconds to 1 minute. As Martin said, that length of exposure should be safe against trailing without guiding on a reasonable equatorial mount driving nominally at sidereal rate (I use a basic HEQ5 with the camera either using its own lens or at the prime focus of a 10″ aperture f/4.8 Newtonian). Take as many exposures as possible, to reduce the noise. Total exposure time is what matters, regardless of whether that is 1 frame or a stack of many. Then stack and post-process using free software.

There are many benefits to stacking, beyond the obvious ones, some of which I cover here: http://www.grelf.net/defects.html

[David Perkin]

Thanks, Martin and Graham, for useful and interesting advice.

I have been trying to photograph the night sky (with film SLR and a homemade webcam setup) for several years, with varying success. I have already got a copy of “An Introduction to DSLR Photography”, which is where I got my original interest in the Canon EOS1000D: the example pictures looked good value for money. I was unaware that the internal IR filters were so strong at the Balmar Alpha (H alpha) line – surely it’s in the visible part of the spectrum. I will certainly get an appropriate T-adaptor.

I think I have a much better sky at this location than previously so it is worth my while setting up to expose for as long as practicable for diffuse objects, to reduce the effect of readout noise, but 30s to 2 minutes should be good enough to start with.

I do wish to attach the camera to my GEM mount either on its own or piggybacked on the telescope – the specialist Camera GEMs seem to be over the top in terms of expense. If I get a new mount for a new telescope, then the existing mount may become dedicated to the camera – if I can find a way of attaching it, that is. There doesn’t seem to be a suitable mounting ring with a camera screw for my tube.

Thanks again,

David Perkin.

[David Perkin]

Dear Graham,

Sorry about the mistake. I have corrected it.

Regards,

David Perkin.

[Graham Relf]

The method I use for attaching my camera directly to my HEQ5 mount can be seen here, with photos: http://grelf.net/piggy-back.html#N656258

Please read the rest of my site because I have put lots of hints and tips like that on it. There is also my book, aimed at photographers: http://www.ypdbooks.com/photography/1050-the-dark-skies-of-the-north-pennines-YPD00983.html

 

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