My advice, not that it hasn’t already been said, is to go for a 6 or 8 inch reflector. I have a 4.5 inch (114mm) and it is fun to use, but it is limited (especially in the light pollution of Los Angeles). If you want to just look, get a Dobsonian. If you want to photograph, you will want an equatorial mount. One word of caution - many mounts are just not up to the job, and the mount can make or break the experience for you. Also, go for around a f/8 scope. Fast scopes can be more demanding of your eyepieces, slower scopes are more “tolerant”. Don’t go for “super magnification”, you’ll find you get more enjoyment out of the more moderate magnifications (and that is determined by the choice of eyepieces). You will want some sort of finder - Telrads are affordable and very popular.
I found the system at astronomics.com. An extra twenty bucks for a larger mirror? Sounds good to me.
As I said, I’m not even a novice. Let’s see if I have this right: The C8N-GT has an on-board computer control that will automatically point the telescope at a target. Say I want to look at Jupiter or Betelgeuse. I input the coordinates and the motor will move the telescope so that I will see Jupiter or Betelgeuse when I look through the eyepiece, right? And it will track the target so that I can take photograph? And this is all part of the package?
SteveG1: Light pollution is definitely an issue, since I’m planning on moving back to L.A. After spending so many years there, I was stunned to see how bright the stars are up here in the PNW – when it isn’t cloudy. And I was even more stunned when I visited my mom in Arizona before she died, and I found myself on a two-lane blacktop out in the middle of nowhere when I tried to take a shortcut on the way down.
A question about f-stops. With my cinema cameras, I often wish for a larget aperture. I’d love a set of Zeiss Superspeed primes, since my fastest zoom is a T2.8. What do you mean when you say slower scopes are ‘more tolerant’? Also: Why are lower magnifications ‘more fun’? As far as photographs go, would you suggest a moderate magnification, a long exposure, a larger f-stop (or whatever it’s called on a scope) and slow film, and then blow up the image in post? The Celestron says its highest magnification is 400x. Is this too much? What is ‘moderate’?
Well… sort of. You have to do an alignment procedure first. That means using the arrow keys to point the telescope at a bright star, and telling the computer which star it’s pointing to. You have to do this on at least two stars, preferably three. After that the computer knows where it’s pointing to at all times, and point to any object you ask. But you can never release the clamp and move the telescope manually - if you do that, the computer gets lost again.
As for tracking, it tracks well enough for short exposures (up to a minute or so, but really depends on the mount and accuracy of setup). If you use a CCD imager, you can take lots of 30-second exposures and stack them later. This is the most affordable way to get into astrophotography - the Meade DSI imager costs about $300, I believe.
For longer exposures you need to lock onto a star and track it. The traditional method is to mount a second telescope (guidescope) next to the main telescope, point it at a star near the target, and keep the star on the crosshair using the arrow keys on the drive controller. A more modern method is to put an autoguider (a small CCD) on the guidescope and connect it to the drive system to do automated corrections. An even better method is to use a CCD imager that has its own guide system - usually a small CCD next to the main imaging CCD. A self-guiding Peltier-cooled CCD imager costs over $2000. A stand-along autoguider (no imaging, just guiding) costs around $500, but some mounts require modification. I’m not too sure about the Celestron CG-5.
A fast telescope creates a very “fat” (large angle) cone of light. Cheaper eyepieces don’t handle this well. I think F/6 should work well for most eyepieces, but below F/5 you may want to invest in a set of premium eyepieces designed for fast telescopes, such as the Pentax XW series and the TeleVue Nagler/Panoptic series.
For extended objects (nebulae and galaxies), low magnification means higher surface brightness. Also low magnification means wider field of view. Both of these factors can make casual deep-sky observing more “fun”. But of course there are many other objects that should be observed at moderate to high power for the best view.
The concept of “magnification” only applies to visual observation. For photography, think in terms of focal length and focal ratio. Choice of focal length and focal ratio depends on what you want to photograph, and how long an exposure you can tolerate. There’s definite advantage to a fast telescope - it allows short exposures on large, extended objects - but at the cost of small plate scale. Many experienced astrophotographers move up to slower, long focal length telescopes to increase plate scale, but that means using longer exposures. Also, many slower telescopes can be fitted with a reducer to reduce focal length (i.e. make it faster).
You need to tell it what it’s pointing at, twice? Hm. I’d assumed you would align the azimuth with true north, enter your coordinates from GPS, and level the head.
The Celestron C5GT (aka AS-GT) doesn’t have GPS, so you’ll have to enter that info manually too. You can get away with 1-star alignment if the mount is properly polar-aligned, but I think you’re better off with 2-star alignment. And 3-star alignment would correct for the telescope optical axis not being exactly 90-degrees from the DEC mechanical axis.
Heh. I have a hard enough time finding Polaris, let alone telling a telescope where it is!
But I can find Betelgeuse without much trouble, and I can recognise a couple of other constellations.
Well, for starters, you don’t need any onboard help to find Jupiter as it is usually the brightest thing in the sky. Usually, you need “go-to” or setting circles for dim objects that you can’t quite see. What you do is get the scope “zeroed out” on a known bright reference object and then go to the object you want to look at. Of course, tracking is very nice. With a manual system you have to make corrections as the object drifts – a computer tracks it automatically. Of course, everything has to be properly aligned to start out. That’s why so many websites talk about polar alignment and leveling.
The light pollution in L.A. is horrible, and getting worse. Aperture (size of the primary) helps, and so does a light pollution filter. I use a Skyglow filter (different makers call them different names). When I go to Big Bear, the difference is staggering.
As to scope apertures, say f/4 vs f/8… A reflector (and any other scope) sometimes needs collimation (optical alignment). This is more critical and more touchy with very fast scopes. You have to be more exact. A slower scope is more forgiving (wider tolerance), within limits. Also, a very fast scope will have a need to be more tightly focused, a slower scope will have (just like a camera lens) more depth of field as it were. A side benefit is, you can get good results with less expensive eyepieces. I have an f/8 scope, and a few decent Plossl eyepieces do the job for me.
You see, with cameras, aperture usually means the f-stop. With scopes, aperture usually means sheer physical size (to capture more light). Bigger is better, subject to portability and ease of use – You won’t use it if it weighs a ton and you can’t set it up without a derrick.
Here’s my “set-up”
4.5 inch f/8 reflector.
…max resolution 1 degree (based on the size of the primary mirror)
…magnitude limit 12 (minus about 6 for the light pollution around here)
…theoretical max magnification x225 (based on the size of the primary mirror)
32mm Plossl eyepiece (28x magnification)
25mm Plossl (36x)
Generally, I use the 25 and 12mm eyepieces most. the 6 is still OK, and the 4 is way too much. The more you magnify, the worse vibration gets, the harder it is to keep an object in view (or even find it), and you start bumping up against the optical limits of the scope. Also, lower magnifications tend to give a brighter and sharper image. A bright sharp image at say x 72 is far better than a dim “not quite sharp” image at x225. Last, many objects are actually very large (but dim).
The purpose of a scope is not to magnify, but to grab as much light as possible. Do not concern yourself with any claims of magnification, they don’t matter and are decided by the eyepiece used. You will never want to “super magnify” anyway. It is pointless. Physics says any scope of a given size will have a theoretical magnification limit that can be predicted. Physics says that same scope will have a predictable “light gain” or magnitude (brightness) limit. What you care about is that “sensitivity”.
To take pictures, the best/easiest ways are to use a small digital camera, or a manual 35mm SLR. Many people use Canon FTb, Olympus OM1, or other similar cameras with moderate (100-125ASA) of fast film (400ASA and up).
I have a few 35mm SLRs. The OM-1 and K-1000 would be my cameras of choice, since they do not consume power except for the light meters (which I can turn off on the Olympus).
scr4 brought up the 8" Celestron, which is larger and faster than the one you posted just now. Do you have an opinion on it?
Also, how do I learn about exposure for photographing celestial objects?
Either camera will be fine. First of all, keep it simple. Remove the eyepiece. Remove the lens and mount the camera body to the scope, at the eyepiece tube. The scope is now your lens. The cameras you have are fully manual and mechanical shuttered - perfect. Use a cable release to keep vibration down. Various websites have recommended exposure times you can use.
The scope I quoted is mine. It is considered about the smallest starter scope that is still useful for casual observing. An 8 inch is a hell of a lot better. It will have a max resolution of about 0.55 arcseconds and a magnification limit of about 480. The magnitude limit goes up to 14 and the brightness gain is about 1650x (quite a jump).
As far as specific brand names, I will oversimplify a bit and say, any known reputable brand will have good optics. Orion, Meade, Celestron, Hardin, Stellarvue, Discovery, etc. Mine is a Bushnell 4.5 inch, and normally does not get a very good writeup, but I got it for 10 dollars used and couldn’t pass it up
One word of advice based on my purchase, the standard Celestron tracking motor is not good for photography. The motor vibration induces mucho blurring in the viewfield.
Which Celestron mount/motor are you talking about? The ASGT?
Based on what I’ve read in the thread, I’ve ordered a C8N-GT. The seller matched the price at shop.com, and is including an introductory astronomy book gratis.
It’s arrived. Unfortunately, it’s missing the two bolts that attach the quick-release plate to the tube. They also didn’t send the book they promised, and the CD-ROM is for Windows. My laptop is a Mac. Otherwise, it’s all put together. If I have time tomorrow, I’ll go to the hardware store to see about getting a couple of bolts. (I’ve already e-mailed the company, but I’d like to try it sooner.)