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Telescopes are always a compromise. None do everything well. You have to ask yourself how you plan to use the scope. Everyone has different priorities.
I have a 12" Dobsonian. It meets my needs for aperture while still being easy to use and quick to set up. I have looked through 16" and 18" scopes. The views through these scopes do exceed the view through my 12", but the difference is not significant enough to deal with the drawbacks of a larger, heavier and more complicated to set up scope.
I can remove my 12" tube from the base, set up the base in my driveway or back yard, and replace the tube quickly. In less than 5 minutes, I am ready to observe. Truss Dobs are not nearly as easy to set up........and many of the commercially available truss-Dobs seem to require major modifications to make them useable.
I think large truss-Dobs make a great multiple-day star party scope. It takes a while to get them set up and collimated, but once done, the views are superb. But, as a quick, spur of the moment, backyard scope, they are just to big and complicated to set up for short-time observing sessions.
I have looked through a bunch of SCT's, and wasn't terribly impressed. They are expensive and heavy, and I have yet to see one with views that match my 12" Dob. They have compact size, but in my opinion, they have only one real advantage....the availability of computerized tracking.
Refractors (especially the good ones) provide pristine views and pinpoint stars, but the popularly priced scopes just don't have sufficient aperture for serious deep sky viewing. In my opinion, they are at their best for planetary observing and astro-imaging. Aperture isn't as critical in astro-photography, because the camera can store and record long exposures.
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I use an Orion StarShoot II color CCD to capture deep sky objects. This is a bare-minimum camera for this purpose, but it can produce pleasing images with practice and patience. These cameras were recently on sale for as little as $299.
The resolution is it's main drawback.....640x480. Many serious imagers use a CCD or DLSR, and the DSI camera as an auto-guider to help keep the object centered with round star images.
You will need a motorized tracking mount for anything but the very brightest objects. The camera and software that comes with it will record frames up to 30 seconds and automatically align and stack them. You can watch the image 'developing' on your laptop screen as each new frame is recorded. The more accurately your scope is aligned the better your images will be. 'Seeing' is not as serious an issue as it is for solar system imaging......transparency and a dark sky are probably more important.
For deep sky imaging, you generally want a telescope with a shorter focal length so you can get a wider view. Many of the objects are large, so little magnification [just the opposite for solar system imaging] is necessary. A short focal ratio [say f4-f5] allows the camera to capture the light from dim objects faster. The longer your exposures, the more chance there is that tracking errors will crop up.
Most imagers will tell you that they spend an hour on processing [or more] for every hour they spend outside capturing "data". These object are subtle and require more subtle and careful processing.
I like to look at this image to remind me just how far I have come. But I also remember just how thrilled I was to see this image on my laptop screen. Until I aquired my original Meade DSI, my attempts to capture DSO's was unsuccessful. I did get an image of sorts of M42, but it was barely recognizable.
Here a few other early attempts. They aren't very good, but I was thrilled with them anyway. LOL
I have come a long way since these images. * please see my journal entries in 2009.
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If you haven't tried afocal photography through your telescope's eyepiece, you owe it to yourself to give it a try. You will be amazed and delighted with the results! All you need is:
1. almost any telescope
2. digital snapshot camera
3. some very basic photo processing software....that comes with almost every camera and every photo printer.
The moon is the best subject.....in quarter phase. You want a low sun angle to create lots of shadow and detail. A full moon is a poor subject for the novice.
1. center the object
2. hold your camera as close to the eyepiece as possible [grip the camera lens and the eyepiece with your thumb and forefinger to keep them aligned] and leave the camera on full automatic mode to begin with. Make sure you can see the object in your finder or viewing screen and give the camera a second or two to focus. [focus the scope as carefully as possible]
3. start snapping pictures.......take lots of them. Some will be off center or blurred, but some will be centered well and clear.
You might need to do a little brightening, contrast enhancement and sharpening with your processing software, but I think you will be pleased with the results.
Some of my early afocal moon photos:
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|Seeing - Solar System Photography|
Seeing is 90% of the battle. Yes, you need good focus, but unless seeing is at least average, don't waste your time. Your images will be mediocre no matter how good your focus.
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It is very, VERY hard to beat a webcam for solar system imaging. Yes, the resolution is poor on individual frames, BUT do not underestimate the power of stacking hundreds [maybe thousands] of frames. Basically you are capturing a short video clip...2-3 minutes as a rule. That clip is then loaded into a program [Registax 4 is one of the best and free] that selects the best frames, aligns them and stacks them. The results are amazing. There is normally some post-processing [Photo Shop and others] necessary to tweak the final image.
A DLSR or CCD imager can be used, but it is far more laborious to capture 1000 or 2000 frames. The resolution is far superior in these cameras, but, all things considered, the net result of stacking 30 or 40 frames just doesn't compare to hundreds or thousands of frames.
Your DLSR is better [far better] for deep sky imaging......because of greater sensitivity and far better resolution. A webcam is not sensitive enough to capture dim objects.
The webcam is producing frames per second. The DLSR/CCD is producing seconds per frame.
For imaging the planets, you will need a telescope with a fairly long focal length [1000mm or more]. You will also need a 3-5x barlow to increase the size of the object. You want to get as large an image as possible......as large as the 'seeing' conditions will allow. Very long focal length Schmidt or Maksutof Cassegrain scopes are probably the best. Naturally, aperture makes a difference. Get the largest aperture you can afford.
Lastly, don't be put off if the video clip you capture looks fuzzy and featureless. It probably will. This is where the aligning, stacking and enhancing comes in. You have to see it to believe it.
Virtually any webcam will work.....IF it has a removeable lens. The telescope becomes the lens. You need to be able to unscrew the lens and replace it with a 1 1/4" adapter that fits in the eyepiece holder on your scope......the webcam replaces the eyepiece. I use a webcam from Phillips Electronics...the ToUcam Pro....available many places for around $100. Software to control the camera will generally come with it.....to set 'gain', brightness, etc.
Oh, and you will need a laptop with a USB port to capture the video clips and the resulting images. The camera plugs into the laptop via a USB cable....included with the camera.
Some webcam images: