Telescope Reviews: CA ! No color imaging with an ST achro! Really?

In most hobbies once you reach a certain (surprisingly low) quality level in your kit the skills of the hobbiest play a much larger role in success than the cost of the equipment. A good fly fisherman with a basic fiberglass rod will be much more successful than a mediocre fisherman with a handmade, bamboo gem. Lance Armstrong on a Schwinn Varsity would be able to run circles around me no matter what bicycle I rode--and I'm a moderately accomplished cyclist. A good golfer with a mediocre set of clubs is still a good golfer--and her scores will show it.

The same can not be said of long exposure, deep sky astrophotography. No matter how good you are at astrophotography, if your mount can't track accurately you aren't going to capture nice, round stars. If your camera has bad thermal noise you aren't going to be able to capture images of dim objects. If you have an f/5 Newtonian you aren't going to be able to capture wide fields of view with pinpoint stars to the edge. A good photographer, when faced with these challenges, will simply pick a subject that is well suited to her equipment.

Do skills matter? Of course they do. But if you don't have a fairly substantial budget for astrophotography your skills don't need to be that sophisticated before you start running into the limitations of the equipment. You just aren't going to get a picture--any picture--of Stephan's Quintet with an 80mm refractor on a photo tripod!

I don't think you have reached the limit of what your current achromat can accomplish. Longer total exposure time, longer individual subexposures, better tracking, use of a monochrome camera (with re-focus between RG&B frames) could all substantially improve image quality. That assumes you have the interest, the patience, and the budget. After making those changes I think you would be in a better position to determine how large an affect the optical tube is having on your image quality. The local observatory where I volunteer as an 8" Alvan Clark and a 20" Brashear refractor, and those are both capable of taking some superb pictures.

Prior to my current setup, I was imaging with a high quality 110mm refractor, an SBIG 2000 CCD camera, and a Losmandy GM-8 mount. Definitely considered a fairly nice rig for portable astrophotography. The limiting factor in image quality was my own skill set. Specifically, it was my skill with the mount that was holding me back. I couldn't get it adjusted and setup to produce consistently smooth tracking. There was just a little too much weight to get good results without careful adjustment, setup, and balance. I could have been using a 4" achromat and a DSLR and the image quality would not have been substantially different because my skill with the mount was what was holding me back. Eventually, I learned more about the strengths and limitations of the mount and my image quality went up. But I hit a wall. No matter how carefully I adjusted the mount, no matter how carefully I drift aligned the scope, no matter how careful I was in calibrating the autoguider and choosing the right exposure duration I couldn't get my image resolution to approach what I knew was possible with a 4" scope. My gear simply weighed too much for my GM-8 to support. I upgraded my mount and my resolution virtually doubled overnight. No change in my skills, no change in camera, no change in scope, no change in technique. The resolution literally doubled. Situations like this are all too common in astrophotography.

I'd recommend you figure out what the biggest weakness is in your imaging train and address that first. Then move on to the next weakness once you are satisfied you have addressed the first. Imaging skills can be improved in parallel, of course. From looking at the samples you provided, I'd say tracking accuracy and focus are the first two things to be addressed. Focus is probably most easily addressed with a Bahtinov mask or equivalent. Tracking accuracy is going to require autoguiding and perhaps an upgraded mount.

Best of luck with whatever direction you decide to take! I certainly agree that it is possible to take good images with an achromat, and that in your case the scope itself is not the most critical component to address.

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- Jared Willson

TMB 152 f/8 Apochromat
Fluorostar FLT-110 w/ TEC optics
Stellarvue SV80S
Astro-Physics Mach1 GTO
Takahashi Teegul SP Mount
STL-11000