I present here some initial results with two new pieces of equipment that arrived recently. The first is a "toy" Maksutov telescope called the "Maksy" from Acuter Optics. I learned about this little telescope from some posts by Christian Buil (see http://www.astrosurf.com/solex/sol-ex-o ... on-en.html), which he used as a telescope for his SolEx spectroheliograph. This telescope is sold under a variety of different names and sells for around $100 (I got mine at Rother Valley Optics for 75 pounds). The front objective diameter is 60mm and the focal length is 750mm. There is of course a central obstruction so the equivalent unobstructed diameter is probably around 50mm.
There are actually quite a few positive YouTube reviews of this telescope and my impression is the optical quality is very good. There are a number of very useful accessories that come included and they are also of surprisingly good quality. The diagonal, eyepiece and tripod are all really good. I bought an adapter from Amazon that would interface between the 0.965 inch back of the telescope and a standard 1.25 inch adapter.
I used my homebrew CaK filter for initial testing. This consists of a Lunt CaK yellow notch filter behind a Baader Calcium K-line filter. On the front of the telescope I installed a 72mm diameter Hoya NDX4 filter (75% reduction in light intensity). The photo below shows the Masky 60 telescope, NDX4 front filter, CaK homebrew camera filter and ASI camera, all mounted on the included tripod (in this instance, I used an Arca Swiss adapter plate -- these are quite good for small, light telescopes).
The camera in this case was the second new piece of equipment: a ZWO ASI 183MM (the planetary version). I actually bought this camera for spectroscopy projects (because of the small pixel size of 2.4 micron and fairly large 13.2mm x 8.8mm sensor size). The sensor in the ASI 183MM is essentially a larger version of the one in the ASI 178MM.
Below is a quick full disk CaK image, taken through the bedroom window and mounted on a Vixen GP2:
The exposure was 1.9ms, the gain was 114 (25%), binning 2x2, 8-bit. 2000 frames recorded and the best 10% stacked (seeing was quite poor). ImPPG was used for sharpening and PhotoShop Elements for levels adjustment. I think it is not a bad result but my impression is that images from my CaK PST (taken a few days prior) were sharper and had more contrast.
My opinion of the camera is so far quite positive. I did look for noise but did not see any significant "bias" noise and the "amp glow" was much lower than I had expected. The large sensor size and small pixels make this a useful camera for some applications. I have not yet tried it with H-alpha.
The telescope is remarkably small and light and may offer some good travel scope possibilities. The plastic is extremely strong and rigid and appears to be made with quite high precision. The rubber focusing knob on the back turns very smoothly and offers very fine focus adjustment.
CaK imaging with a "toy" Maksutov telescope
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Re: CaK imaging with a "toy" Maksutov telescope
Very interesting result! I used a Meade ETX90 once for CaK imaging and it wasn't great, this seems to be better.
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Re: CaK imaging with a "toy" Maksutov telescope
Wow!! not at all bad for £75. This would be a great product to recommend to young people with a tight budget
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Re: CaK imaging with a "toy" Maksutov telescope
I guess the thick corrector plate at the front of a Mak may cause distortions at 400nm. I'm actually surprised the results weren't better. The results from Christian Buil at 650nm (mentioned above) look very sharp.marktownley wrote: ↑Fri Jan 21, 2022 6:29 am I used a Meade ETX90 once for CaK imaging and it wasn't great, this seems to be better.
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Re: CaK imaging with a "toy" Maksutov telescope
It's a really fantastic educational device. Great for the moon. I'll try do a test in solar white light when there's some sunspots.
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Re: CaK imaging with a "toy" Maksutov telescope
This is really interesting @thesmiths, thank you. I have an old vgc ETX125 which I'm chewing over ideas for. I'm quite tempted to try s/t like this once I sort a few things out. By any chance, do you remember what the camera's temperature reading was when you used this setup? I'm trying to see what sort of front energy rejection would be needed with an ETX 125.
If the Hoya NDX4 worked for you with a 60mm front objective (50mm clear), then an ETX125 has c 2x objective (so 4x flux?) but also has 40% central obstruction so 76mm clear vs the 50mm of the Maksy (so c 2.3x flux although the back of the central obstruction would still be receiving energy). So I'm wondering what a sensible Hoya to use would be (& hence an indication of how hot your 183MM got would be interesting).
Another alternative might be solar film for photographic purposes (3.8)?
Thank you for any more info you can share!
If the Hoya NDX4 worked for you with a 60mm front objective (50mm clear), then an ETX125 has c 2x objective (so 4x flux?) but also has 40% central obstruction so 76mm clear vs the 50mm of the Maksy (so c 2.3x flux although the back of the central obstruction would still be receiving energy). So I'm wondering what a sensible Hoya to use would be (& hence an indication of how hot your 183MM got would be interesting).
Another alternative might be solar film for photographic purposes (3.8)?
Thank you for any more info you can share!