The zoom lens is great for day time work and I have used the Tamron 18-200 for some DSO work. See image below.
What is best for astro work is a Prime lens.
The most popular for the budget conscious is the Canon Nifty Fifty F1.8. It has it's faults, coma being a big one, but you can work around that in Photoshop or just by framing the image around it. But at around $130, you won't find a better, cheaper lens.
My next favourite is the Tamron 90mm Macro. It gives stunning images both in daytime Macros as well as wide field Astro work. You can pick them up 2nd hand, if you're lucky, for around $350.
Thanks jjj. I will be using it prime on the scope of course. But I will be using it by itself first,guided somehow or other. so want a good lens for multiples on say m42 for arguments sake. I had a quick look on the net re. the 90mm macro and was mightily impressed. It always seems counter intuitive to me seeing a macro lens used for other things like portraits etc. http://www.pixel-peeper.com/lenses/?lens=45&p=4 I think i can see which way I'll be going. 550D or 600D body with separate lens. There'll be more lenses later but which one for starters. Do you use zoom at all when imaging nebula's and suchlike? For instance jjjnettie, how much zoom on that cool pic of Antares.
The image above was taken at full zoom.
I'm totally biased toward that 18-200 Tamron.
If I had to get rid of all my lenses, bar one, it would be the one I would keep. (though it would almost kill me to get rid of the Tammy 90mm)
I'm interested to hear what others have to say on the topic though.
As Nettie says, primes are the best option. The manufacturers have to make compromises opticaly to get zooms to work at all focal lengths, but modern zooms are very good.
Another option for lenses is the old M42 mount manual focus primes with an EOS adaptor. All the shots in my link above were shot on 1950's, 60's and 70's glass. With careful purchasing, you can get 5 or 6 mint condition lenses for the same outlay as one decent modern lens.
Obviously they aren't as convenient for terrestrial work being manual focus, but many of them are as sharp as, if not sharper, than what is available today with the exception of $1000+ glass like Canon's L series.
Some of them are still considered excellent lenses today.
Stick to the better known brands like Nikkor, Leica, Carl Zeiss, Contax etc, though there are a few examples of one type of lens that goes by many generic brand names that have a cult following (like the 55mm f1.2 Revuenon/Rokinon/Yashinon/Chinon etc etc, all the same lens, made by Tomioka)
Check out the Manual Focus lens forums Here and Here to get an idea of what is good.
Sadly though, due to the increased popularity of these lenses since the advent of DSLR's and now the the Sony NEX's, demand and therefore prices have jumped considerably, but good clean examples can still be had for a good price on Ebay. Ignore all the way overpriced 'Buy It Now' examples, they are sellers preying on the inexperienced.
Yes, makes a lot of sense. Good quality lenses are always good quality.So it stands to reason there will be a lot of good glass out there at good prices. This is good stuff. I mean I started off simply wanting opinions on what cheap dslr to buy,now I'm happy getting a body and now thinking second hand lenses. I have heard,any old body will do in a pinch but good quality lenses make the camera.. What Simon said is correct I guess . Good glass is always going to maintain value. By the way, those links Simon,jeez, lenses, i never new it was so involved. i'm so used to my point and shoots ,who needs to worry about lenses. This is another world. Kind of exciting.
Simple get a digi 4 1100D if your broke or 550/600 if your got the cash, then a 650 digi 5, after that i would head for a 5d mark II ect, in my dreams. I would not bother with a POS, outdated, flogged out 20D/40D, its old tech loaded with heaps noise... Also note these older camera's have a worse shutter life and a pron to death earlier then there new couter parts.
You can always ask a seller for the shutter count before purchase. Not as straight forward as it should be but I feel if someone wants to sell their camera then they should be prepared to go to the effort to find out.
There's also software which lets you determine shutter actuations.
My point was that if someone was on a budget-conscious path, then, something like the 40D would be stellar. 14-bit system, Live View, decent high ISO performance (particularly when taking many sub-exposures and calibrating accordingly).
If one has the budget to stretch to the newer offerings, then, of course, go for it!
I second MrB's suggestion re older manual focus primes with an EOS adapter. I have recently purchased three inexpensive Nikkor AI manual focus primes (50mm, 135mm, 200mm) & combined with a suitable Nikon-EOS adapter (~$20) the optical quality is superb - for both daytime and astro work - and far far superior to my other standard canon zooms.
An interesting bunch of opinions here. Hadn't realised the 40D had Live View and seemed a good option ( Thanks Humayun). I will check out the prices on that model. As I earlier mentioned my real target here is to get a better focussing method and the bahtinov\bright star\liveview seems the best way to go. My eyes are not what I'd wish them to be and trying to peer at a small LCD screen magnified or not on some silly angle just doesn't work for me. I am lucky I made the UTA on SK II rotatable so I can normally get it at least somewhere comfortable.
I will also motorise and gear down the focusser via probably a stepper motor system so I can control from the desk.
As has been said, $$$ are the governing force here, I cannot justify (afford) $1000's on the latest and risk pulling filters etc out but I'll find $4-500 at a pinch and work from there.
In the meantime the KM 7D is working well enough to experiment and learn.
Hmm, NZ prices ...!! 40D is in the $500 + range as well and that's the reserve !!. This is getting frustrating.
Think I'll have to wait till I've sold the project car, can't afford to roll cage it now anyway.
Well a few questions to go with this thread, where do ppl in Aus generally get their cameras modded? Are they all ship to the US jobs or are their local people who do it?
Also, is the 650D likely to become a new entry level standard now it has the DIGIC5 chip in it which from what I've read is significantly less noisy than the DIGIC4? A Modded 650D I would think would come out cheaper than their 60Da and be much more effective?
Just a quick weigh in. I am the proud owner of a Canon 20D and a 30D, both modded, both performing really well when you treat them as a DSLR and a great way to learn the ropes.
I would though caution against buying anything earlier than a 30D if you are using Windows 7 as there are no drivers available for the 20D which makes integrated capture management, say with APT, Backyard EOS, DSLR Shutter or Nebulosity 3 a no go and whilst Live view is good, if you are pointing straight up at the heavens on the butt of a refractor, its a darned site easier using a laptop to get your focus sorted than live view (unless of course you have the swivel widget for the screen)
There are workarounds to get images onto a PC running Windows 7 with the 20, but its a faff and all you will be able to do is get images onto the PC.
From what I can tell, and from what I knew when I worked for them, Canon has a 7 year obsolesence policy on updates to software and parts manufacture.
So, check first on the Windows drivers website that your Camera drivers for the Windows version you are on are actually available if you are buying pre-loved modded cameras.