Disclaimer: I am not an expert in this field, the following are derived from internet forum discussions:
“I have had a MX716, a ST-2000XM with color filter wheel and I have an EOS
The SBIG and MX716 were more sensitive, but at f6.3 and below I get much
better results and have more fun with my EOS. I sold the other cameras after
I wrote my Maxim/DL driver for the EOS.
If you just want to have fun and make pretty images, the DSLR cameras can't
be beat. If you are imaging really fair objects and slow f-ratios then you
need a cooled CCD camera and will have to spend 10x the price of a 300D for
The ST-2000XM is not quite a fair apples to apples comparison since it has
an auto-guider, but the chip is so small that it was a pain to find a good
guide star anyway for some objects, a separate guide scope, or wide field
imaging is a great solution and still much cheaper.
If I had all the money and time in the world I would probably have a ST-10
with A07 and a Color filter wheel as well as a DSLR, but given I don't I
pick the DSLR for the fun of it.
I have a friend who has a 30k+ imaging setup. He bought a 300D and now he is
gaga over it and has hardly touches his sensitive, expensive setup all
I'm assuming that A) you have chosen to start with widefield imaging (good choice), and B) you have made a definite decision on the camera..ST2000XM.
First, don't worry about your image scale sampling with either
scopes, because they both have relatively short focal lengths and
with either scenario, you are more toward the undersampled scenario
vs. oversampling. For example typical “hi-res” with the larger
scopes/longer focal length is around .60 to 1 arcsec/pix! Remember
that if you have typical seeing (including atmospheric, mount &
guide issues, etc.) of around 3 arcsec, your _best_ sampling is that
number divided by 3.3 = .90 arcsec/pix.
Now, with widefield, you are obviously aware that you will be
sampling differently…no problem, the images still come out great.
So, I guess it's just a matter of which optics you prefer..the SKY90
or the Televue. I can't speak for the Televue, but I've seen great
images with Televue products. However, some people complain that
the Televue focuser is not quite robust enough. The SKY90 will also
produce great images…you MUST use the field flattener (another
expense), but most people love the Tak focuser. Of course, with
either setup the Robofocus will work great and is a great tool.
Therefore, if I were you, I'd consider two things before making a
final decision. First, check out how Televue users feel about the
stock focuser and make sure you feel it's acceptable. Secondly,
determine how wide a field of view you want. As you said, the TV
will offer a smaller FOV but with slightly more detail, the SKY90
would offer the larger FOV and the detail would still be great.
Personally, I like the TAK products and purchased a SKY90…never
used it because the flat field wasn't large enough to cover the
large chip in my STL6303…replaced it with an FSQ.“
“The ST-7 chip just barely works with the Sky90 without the flattener. That
chip is 4.6 x 6.9mm. The ST-2000 chip is quite a bit larger, around 9 x
12mm. So I would expect the reducer to be essential.
In my experience, you can't use the image circle on film to determine the
useable image circle on a CCD chip. Roughly speaking, film has a resolution
of around 25 microns (but depends on grain size). CCDs are in the 7-9mm
range for the most part, and thus will show optical issues much more easily
than film will.
In answer to your original question, the Sky90 will be a joy to use. It is
easy and forgiving. The FS-102 would be excellent as well, but of course
guiding and tracking will be more challenging.
The issues around the TV focusers are real; I had a devil of a time imaging
with the NP-101, for example. They are designed for visual work. The optics
are first rate, however, and if you don't mind a bit of machining you can
probably rig up something that will be more robust.”
“get the SKY90 (with the reducer/flattener) along with the ST2000…you'll be extremely happy” be aware that you will spend many hundred dollars for so-called “accessories” for the Tak, to make it work for imaging, but they do work, and very well.
“The Sky90 might well satisfy your needs in the near future, but if you wish to quickly move to a larger format detector then you will have problems with its flat FOV.
My suggestion–look seriously at the FSQ106. Huge, flat FOV, similar
focal length, all threaded interface–an imager's telescope. Look at
the spectacular stuff being done right now with the STL11K and the
FSQ106. The 106 isn't that much more money than the Sky90 (not like
the 11K), but you won't outgrow it.” “With all of its specialized adapters, I don't think it is a visual observer's telescope. For that I would recommend the TV/NP101. But for imaging, the choice is different.”