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Posted by M C Butcher at 10:34 on 2012 Sep 04
I conduct my imaging with a stock Canon 40D. Within those limitations I attempt the best imaging results of which I am capable. My telescope is a 8" Meade LX90. Whole disc lunar is not a problem and I use a f/6.3 focal reducer to shorten exposure time and nicely encompass the whole lunar disc in the single exposure. For individual craters I increase the focal ratio and magnification by performing eyepiece projection using a variable tele-extender. However, this set-up is very susceptible to poor seeing, vibration and any one of other problems and consequently my results are very hit and miss – more miss than hit! The 40D does not have a video capability so I take many images employing the camera’s 2 and 10 second self-timer together with mirror lock-up (to reduce vibration from the mirror movement). Is this the best I can do? Should I be attempting to stack the images, certainly when I try I do not get a crisp result and the sole value of taking lots of exposures is simply to enable me to choose the best. My stacking software is Images Plus, should I be using a different software for this purpose?I appreciate that the best solution is to use a web cam, a CCD or a video camera, however, all of those involve a computer near the telescope and my set-up does permit this. It may of course be that I am already doing all I can to get the best detailed images of craters in which case so be it. Can anyone offer any practical advice?Martin Butcher
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Posted by Roy Hughes at 12:24 on 2012 Sep 04
I would think that using the Self Timer is very much second best to using the Remote Release cable (£6.90 on eBay) – you should be able to squeeze off more and steadier shots, improving your chances.Don’t know Images Plus. I use the classic sony webcam on luna craters. Then Registax for stacking and it works great. Watching it do stacking and alignment in real time is mesmerising. As Registax is free I’ve never felt the need to use anything else. Might be worth a try?
Posted by Andrea Tasselli at 20:52 on 2012 Sep 04
If I remember well the D40 has burst capability so that you can take a number of shots very quickly. I would use it if available. The trick is always to take the greatest number of shots in the shortest time available by the body you’re imaging. For the moon this is set by the speed of the advancing or retreating shadows more than anything else, which should be in the several minutes at least (shortest when the moon is closest to the sun and longest when it’s in opposiiton to the sun). The best way to use the shots you’ve taken is always to allow a program such as Iris or (alas) Registax to quality-filter, align and stack them up. Use the final stacked-up image to do all the contrast enhancements required.Andrea T.
Posted by A R Pratt at 21:08 on 2012 Sep 04
Hi,As well as lunar imaging with colour and mono webcams, I also use my Canon EOS 500D on my 20cm f/20 Mak-Cass ‘scope.Likewise, I use mirror lock and the self-timer delay. The mount is driven at lunar rate, I carefully align and focus on an area of interest using Live View, then I take up to 30 shots with the self-timer option, pausing a few seconds between each shot, to allow vibrations to die down.BMPs are then stacked and processed via Registax.An example is given on page 15 of the 2011 May Lunar Section Circular. (This is just a small crop from the original.)It’s nice to work with large images instead of 640×480 pixels from some webcams. I occasionally add my Apo Barlow lens (with T-mount) to increase the magnification.Clear skies, Alex.
Posted by M C Butcher at 09:35 on 2012 Sep 05
Roy,Many thanks, I forgot to say that I do use a remote control release anyway. But thanks for the rest of the advice, registax would seem to be worth a try.Martin
Posted by M C Butcher at 09:38 on 2012 Sep 05
Andrea,Thank you. The Canon 40D also has the ability to take images in quick succession which I have tried, so far without success as the mirror moves up and down between each exposure. Your point about collecting all the images within a shortish timeframe is understood. Do you know how to calculate the maximum period over which to take the images before the rotation will start to impinge on the image?Martin
Posted by M C Butcher at 09:52 on 2012 Sep 05
Alex, Very many thanks, I’ve had a look at your image in the LSC which is a delight. I can achieve results almost as good but it is more by luck than judgement and my question was aimed at improving my success rate a making my astrophotography more a science than an art. Whilst I realise that your photo was at f/20, was that at Prime Focus or using Eyepiece Projection? I presume the former but it would be interesting to know. Obviously I will need to get a copy of Registax to have a go at the stacking. Many thanks for your help.Martin
Posted by A R Pratt at 11:08 on 2012 Sep 05
Hi Martin,Yes, the photos were taken at prime focus of the 20cm aperture f/20 Mak-Cass. I also have an Apo Barlow lens with built-in T-mount adapter, which gives more magnification.Lunar images at 4000×3000 pixels are beautiful to look at, and are nice to use in presentations.A time delay of a few seconds between exposures shouldn’t be a problem for most lunar images. For example, the shadows cast across Plato during sunrise can be seen to change over periods of 15 minutes or so, but if you can take a series of images within 3 or 4 minutes they should be OK.Registax is free to download and use, and its website has some good tutorials to get you started.Cheers, Alex.
Posted by M C Butcher at 09:59 on 2012 Sep 07
Alex, Many thanks. I’ve downloaded Registax. I now need to learn how to use it! All I need now are some clear skies, never mind we can’t have everything.I am most grateful for your help.Martin
Posted by A R Pratt at 10:44 on 2012 Sep 07
Hi Martin,Some skilled exponents of Registax have written detailed descriptions of how they process their images, but these can be very complicated and confusing for the beginner.Paul Maxson has written a nice tutorial on getting started with Registax 6http://www.astronomie.be/registax/previewv6paul.htmlRegistax 6 runs very quickly on a multi-CPU-core computer.Good luck, Alex.
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