Guest peepshow Posted August 9, 2013 Share Posted August 9, 2013 This may make some groan and some others laugh but here goes......... As dslr Canons have large sensor areas has anyone removed their swinging mirror to reveal the large sensor area and then put this on the end of a suitable telescope which can use a large sensor area ? One might blow cold air onto the sensor too now with the mirror and camera lenses out of the way. So, did you laugh or groan? Link to comment Share on other sites More sharing options...
dawson Posted August 9, 2013 Share Posted August 9, 2013 I'm not sure what you mean? SO I did neither, I had a puzzled look. Do you mean attach the camera to the telescope at prime focus (ie no eyepiece between the telescope and the camera's sensor)? You can attache the camera in that fashion and then when you take a picture the mirror flips up to allow the light traveling through the optics of the telescope to hit the sensor; alternatively you can chose "mirror lock up" somewhere in the settings which locks the mirror up (it's all in the name). Or have I totally got the wrong end of the stick? Have I even got hold of the right stick? Is it in fact a stick? James Link to comment Share on other sites More sharing options...
+Graham Posted August 9, 2013 Share Posted August 9, 2013 Why would you want to remove the mirror ????????????????????????????? Sorry but I am as confused as James on this one. :wacko: Link to comment Share on other sites More sharing options...
andyboy1970 Posted August 9, 2013 Share Posted August 9, 2013 I get what your on about. Most Canon cameras have a Mirror lock setting to stop the mirror causing camera shake. I have never had a problem with it causing shake. The mirror doesn't cover any of the sensor area when it is up. Blowing cold air I think would have minimal effect of sensor temp. as the CMOS sensor is behind a high pass filter with an air gap, people have tried direct peltier cooling which is tricky but quite effective. Link to comment Share on other sites More sharing options...
Guest peepshow Posted August 10, 2013 Share Posted August 10, 2013 (edited) In searching and learning I find that folks use webcams (which have very small sensors), on telescopes for planets/moon. Or they use Canons on their own with camera lenses. I just wondered if there was any advantage in combining the large sensor area of a Canon with a telescope of some form. The top range and expensive CCD cameras have large sensor areas so I wondered why not use the Canons large sensor as a poor man's replacement,( although it is CMOS and not a CCD.) From the replies it seems not, although there is one chap who has put his fast telescope on a Canon 550d and removed the mirror to prevent vignetting. http://www.markshelley.co.uk/Astronomy/Projects/Mirrorless/canon550mirrorless.html Edited August 10, 2013 by peepshow Link to comment Share on other sites More sharing options...
philjay Posted August 10, 2013 Share Posted August 10, 2013 Hi Richard Putting dslrs on the end of scopes has been done for as long as dslrs have been in existance. In the 70s we were putting 35mm film slr cams on the end so its nothing new. The mirror lock feature on most dslrs negate the requirement to remove any mirrors. And as for cooling to increase sensitivity and reduce noise on the sensor, this too has been around a few years as well Link to comment Share on other sites More sharing options...
dawson Posted August 10, 2013 Share Posted August 10, 2013 There are several disadvantages of using a dslr, including: - it is effectively a colour sensor and not monochrome, so that affects resolving ability. - most dslr cameras have filters in front of the sensor which blocks out certain wavelengths of light which are undesired in dy time photography, but which may be desired in astrophotogeaphy (modifications can remove some / all of these filters) - the sensors are not cooled and long exposures result in noise. I've not look at the link, as i'm on my phone, but i'm not sure why the mirror should cause vignetting as the mirror should flip up and reveal the sensor, and not obstruct any of the light hitting it. James Link to comment Share on other sites More sharing options...
philjay Posted August 10, 2013 Share Posted August 10, 2013 All the above disadvantages have been addressed in one form or another, just take a look on various astro imaging sites to see what can be done with a dslr on the end of a scope. There are thousands if not 10s of thousands of folks using dslrs to take stunning images, please be aware that dedicated astro ccd cameras are not the only true way of taking astro images. Each form of camera has its own pros and cons so generalised comments that x cam is better than y cam without pointing out what the cameras can be used for can be misleading and confusing to a newby into the hobby. My advice to anyone interested in imaging through a scope is to go onto dedicated imaging sites and get experienced advice from those who do it Link to comment Share on other sites More sharing options...
dawson Posted August 10, 2013 Share Posted August 10, 2013 Yes, I should have qualified that I wasn't suggesting DSLRs are rubbish for astroimaging, simply they are not necessarily the answer to everything, and having a big sensor might be perceived as a great leap forwards, but this (as with all good things) needs to be offset against other considerations. James Link to comment Share on other sites More sharing options...
glider Posted August 10, 2013 Share Posted August 10, 2013 Astronomy has several questions that are always asked and the discussions go on for ever. Is a reflector better than a refractor? Fast scope or slow scope with reducer? Is a DSLR better than a webcam? Is a cooled CCD better than a DSLR? Should I guide or not? I think the reality is that each idea has its place. For example and not exhaustively; DSLR for wide field, Webcam for Planetary, Cooled CCD for narrow band DSO. The other reality is that when you've been at this hobby for a couple of years you inevitably end up with multiple setups to suit the different jobs. In answer to the original question, a Canon DSLR is a perfectly good camera to connect to the end of a telescope. If you already have the camera it's an ideal introduction into imaging. Its nice wide field means you can get good images without being thrown straight into guiding, processing, etc learning curves. The PC software available to automate the imaging process takes care of mirror lock and bulb exposures so you don't have to worry about it. Enjoy. Link to comment Share on other sites More sharing options...
Astrocookie Posted October 9, 2013 Share Posted October 9, 2013 I've just finished doing the filter removal mod on a canon 300d. I got the camera on eBay for less than 30 quid as the mirror wasn't locking up. As it's almost impossible to focus through the veiw finder this wasn't a problem so I completely removed the mirror and blocked off the eye piece to prevent stray light entering the chamber. Looking forward to some deep sky imaging soon :-) Link to comment Share on other sites More sharing options...
philjay Posted October 10, 2013 Share Posted October 10, 2013 Hi Paul, how are you going to focus? My old 300d didn't have live preview so you should have some fun with no mirror or viewfinder. I suspect you will have to keep taking shots, analysing then adjusting focus to suit. Link to comment Share on other sites More sharing options...
Astrocookie Posted October 10, 2013 Share Posted October 10, 2013 Yeah. I use dslr focus! I've drawn a little marker on my draw tube for rough focus and then use the peak information from the program to get it spot on. I imagine I'll have to make another mark in the drawtube mind, as now there's no filter the focal point may have moved! Btw. What white balance adjustments do you think I should make if any on the 300d At the moment I use it in AWB (auto) Paul Link to comment Share on other sites More sharing options...
xanthic Posted October 10, 2013 Share Posted October 10, 2013 I've read that it ought to be on sunlight, as that's the temperature our eyes are tuned to. It can be altered in processing if it doesn't look right though. Link to comment Share on other sites More sharing options...
Astrocookie Posted October 10, 2013 Share Posted October 10, 2013 Cheers Leigh :-) Link to comment Share on other sites More sharing options...
philjay Posted October 10, 2013 Share Posted October 10, 2013 Leave it awb, i do with the 1000d. Only use custom white balance on terrestrial subjects. AWB sucks in all that luvly ha red and thats what you are after Link to comment Share on other sites More sharing options...
andyboy1970 Posted October 11, 2013 Share Posted October 11, 2013 Take a picture of a white card outside on a sunny day then use the "INFO" function on photoshop to see the white values of the image. For an unmodded camera I would expect 255 for red, green and blue. My modded camera gives something like Red 238, Green 222 and blue 255 so at the start of processing in Ps I bring the right most slider in levels down to these figures for each colour channel and it corrects the white balance. Link to comment Share on other sites More sharing options...
Astrocookie Posted October 11, 2013 Share Posted October 11, 2013 Nice one guys. Thanks. Link to comment Share on other sites More sharing options...
philjay Posted October 11, 2013 Share Posted October 11, 2013 Just a point, taking a pic of a white card is setting the custom white balance to natural light. If you then use a modded cam on deep sky with it set on custom white balance you have wasted your time and money on modding it as the cam will compensate. However leaving it on auto white balance will take it as is without any CWB I use CWB for terrestrial only. Link to comment Share on other sites More sharing options...
Astrocookie Posted October 31, 2013 Share Posted October 31, 2013 Moving on..... OK. I've used the modded dslr for the first time. I'm getting much more in the red part of the spectrum which I expected, but this seems to be compromising quality of the image. I know its an IR filter I removed but do I need to add An IR filter to the light path???? This seem counter intuitive. Perhaps someone could explain this to me. please. Link to comment Share on other sites More sharing options...
Brantuk Posted October 31, 2013 Share Posted October 31, 2013 "this seems to be compromising quality of the image" Do you mean you are now seeing too much red? (there is one heck of a lot of red up there you know). How's about posting up your pic so the imagers can analyse it and make suggestions Paul. I'm not quite sure what you mean by "compromising quality"..... Link to comment Share on other sites More sharing options...
Astrocookie Posted November 1, 2013 Share Posted November 1, 2013 Hi Kim Nice to hear from you :-) Will post an image tonight. Basically I'm getting a lot more noise. Just wondering if this could be too much IR getting in! I was imaging close to a house, plus there was a fairly bright 30% moon nearby. Will try again when conditions are better. My main question is do you still need IR filtering after the camera mod. I've not replaced the dslrs filter with anything. Cheers Paul Link to comment Share on other sites More sharing options...
+RonC Posted November 1, 2013 Share Posted November 1, 2013 I had the same problem so I added a CLS filter from Astronomic and it solved the problem, the red is now just more than pre- filter removal. Link to comment Share on other sites More sharing options...
Sheila Posted November 1, 2013 Share Posted November 1, 2013 yes i had clip in filter too on mine. Sheila Link to comment Share on other sites More sharing options...
Brantuk Posted November 1, 2013 Share Posted November 1, 2013 Yep - a lot of imagers use the CLS filters. I've also heard of the Baader UHC filter being used after a dslr astro mod too. Link to comment Share on other sites More sharing options...
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