New member - Astrophotography question

[robindurant]

Hi

I'm Robin, have been in to Astonomy for 1 year and have just treated myself to a Celestron 8i Secial Edition. Most impressed with the results.

I have a Canon 350d and want use it taking shots of Planets, Moon etc but am totally green to what to do. I have a T Ring, T Adaptor and have ordered a piggy back bracket. How do I go about it. What exposures do I give , what speeds etc etc. Is there a book for beginners to Astrophotograpy that I can buy in the UK. The mind boggles !!

[FLO]

Welcome aboard Rob,

SGL thrives on questions ... as you are about to discover

[Naz]

Welcome Robin, grab a chair, and the answers will flood in

naz

[Greg]

Welcome to the forum Rob....Lots of helpful people her including imagers..

No doubt you'll have the answers soon!!

[Albireo380]

Hi Rob,

Welcome to SGL.

My set up is similar to yours. Meade 8" LX90, Canon 350D, piggy back bracket, etc.

Piggy back will give you wide field views, how wide depends on you lens. I have an 18-55mm and a 80-300mm. At 300mm I get the doubler cluster nicely framed in the shot. Around a 30-45 second piggyback exposure will give you stars down to about 13th magnitude easily - so you can get really good resolution. At 50mm, you get whole constellations - bright stars show on the chip at about 5-15 seconds, dimmer ones take longer. Spend an evening having a play around with exposures - you get different images with shorter or longer exposures. Hint, using a lens on the camera - focus on a distant set of terrestrial lights, then fix to piggy back (careful not to move the focus though). This is easier than trying to focus on a stellar image.

At prime focus you get a 1.6 magnification effect from the size of the CMOS chip in the 350D - so prime focus at a focal length of 2000mm (x40) is increased to x64 effective magnification. This means that you can't quite get a full moon onto one frame - only about 80% of it. It also means, however, that some of the larger Messier objects image nicely - M42 (30-60 second exposures), M13 - (45-80 second exposures).

The moon exposure times is dependant upon the phase of the moon - obviously a shorter exposure at full moon, and a longer exposure at other times. I generally find that (at prime focus) exposures vary from 1/100th second to 1/500th second, depending on lunar brightness. Again, trial and error is a reasonable way to proceed. Take a range of shots at varying exposures and see which is best. Better to go for a slightly dimmer image, cause when you then take 20 of these and stack them using Registax (free software) the brightness tends to increase.

Remember, it is very difficult to focus on a very small dim object. So where possible focus on a brighter, bigger object at infinity, then slew to what you want to image and take multipoles of shots, then select the best.

All I have said above is for unguided imaging, just using the motors on your 'scope to keep the object in the centre of your FOV - so anything over about a minute or so can give you less than pinpoint stellar images.

A great book (almost a bible for astrophotographers) is "Astrophotography for the Amateur" by Michael A. Covington, it will give you lots of food for thought and great guidance.

I am no expert, (and there are several very experienced imagers on this Forum) but have had a great time dabbling around with piggy back and prime focus stuff over the last 6 months.

Hope this is helpful.

Tom

[Ambermile]

WRT to Tom, a dslr is not going to give you planetary shots - the image scale/FOV is just too great. DSO's fine, but you really need a webcam or something with a smaller chip/smaller pixels.

Arthur

[radioactive]

Welcome to the SGL forums Robin good starting question not sure where you live but there are two starcamps comming right up it would be an ideal timr to call into one of the sites and get all the first hand knowledge you could ask for but you will have to be quick its all about to happen

[Albireo380]

WRT to Tom, a dslr is not going to give you planetary shots - the image scale/FOV is just too great. DSO's fine, but you really need a webcam or something with a smaller chip/smaller pixels.

Arthur

Arthur is right - I have struggled to image Saturn or Mars using a DSLR - simply too small an image - even when using a barlow for negative projection (also becomes a focussing nightmare). DSO's do come out quite well though.

I haven't yet dipped my toe in the webcam water, that is next on my "imaging adventure" list. I am looking longingly at the new Phillips 900NC webcam (basically a Toucam mk3) - and wondering if I ought to get one over the Summer, install the software on the office laptop, and take it for some wee imaging trips to dark skies next Autumn. I'm sure the boss wont mind his laptop being used for something useful now and then

Best of luck

Tom