Affiliation
British Astronomical Association, Variable Star Section (BAA-VSS)
Thu, 07/23/2020 - 21:13
Is there anyone out there using a Celestron C11 for photometry with Optec SSP3?
I'm looking to resume my observing and am considering upgrading as I only have an 8" Newtonian at present.
I believe that the C11 package with mount is way too flimsy:
Celestron Advanced VX 11 Schmidt-Cassegrain Computerised Telescope
https://www.365astronomy.com/Celestron-Advanced-VX-11-Schmidt-Cassegrai…
Hence I would also be looking for a mount.
The Skywatchers look a bit sturdier
E.G.
Sky-Watcher NEQ6 PRO Go-To Astronomy Mount
https://www.firstlightoptics.com/skywatcher-mounts/skywatcher-neq6-pro-…
Any experiences, comments or brains I could tap would be most helpful.
Thanks
Kevin
(UK Schmidt-Cassegrain Newbie)
Hello Kevin,
I've been using a C8 on an EQ6-R for photometry and astrophotography. Due to the high focal lengths of SCT telescopes, I reccomend three things primarly:
The NEQ6-Pro which you linked has a weight capacity of 18kg, whereas the C11 OTA weighs in at 12.4kg. Combined with accessories, I'd say this approaches the weight capacity too closely. For optimal performance which is required at the high focal length of the C11 you ideally want the mount to not be near the official weight capacity. There is a severe drop in performance as you reach it, and I've been told a general rule of thumb is 50-65% of the weight capacity for ideal results.
The C11 will be at the limit of what the NEQ6 Pro can handle and still offer precision. I would personally suggest not exceeding a C9.25 for optimal performance and ability to add accessories. Filters, cameras, guiding, perhaps a mini-PC or finder scope, and dew shields quickly add to the weight.
If you plan to take multi-minute exposures this is even more important with regards to pointing accuracy ("Go-To" feature) and guiding requirements. Platesolving is a very large benefit and depending on your sensor size, oftentimes a must.
The AVX mount unfortunately doesn't have a good reputation in imaging circles. It's either a hit-or-miss in quality, with a C6 or C8 being the match for it. A C11 is certainly far too heavy. Comparatively the Skywatcher mounts are better in quality and more robust, which is somewhat confusing considering Suzhou Synta (the producer of Skywatcher mounts) also owns Celestron.
Leon
The SSP3 is a single-channel photometer - platescale does not matter (within reason). A focal reducer will only make transfomations worse.
Hello Leon,
Many thanks for your detailed reply and suggestions. I don’t believe that SSP3 photometry is as stringent in its mount stability as imaging. The stellar image has to be held within a fairly large circular graticle for 3 x 10 second integrations.
I have never tried any imaging so I may be corrected on this by other photometrists.
I’m guessing that many astrophotographers image with a lower gain instrument and guide with the main scope except for the planets.
The SSP3 photometer would add an extra 1.4kg making a load of 13.8kg.
The Sky-Watcher NEQ6 PRO claims 18kg imaging and 25kg visual. I wondered where my photometry sits in that range.
I’m a bit stuck between a rock and a hard place as I was hoping for some portability although I know Tom has advised against this. This would limit me in weight.
Kevin
The other important consideration is the angular aperture size of your SSP3, whic will change significantly if you go to a much longer focal length telescope. You are presumably aware of this. The data is in Appendix B of the SSP3 manual.
Roy
The standard diaphram of the SSP3 works fine with F/10 SCTs.
Agreed. The standard diaphtam is 1mm. Others are available on request, down to 0.5mm. Kevin didn't note in his post which one he had.
Roy
Hi, i've optained a used Orion-Optics Newton 300 / 1200 mm with 15kg.
For variable stars i would not recommend a focallength > 2m, you'll have a much smaller FOV and less compare stars. If you go for exoplanets, than a bigger focal length will be ok, since there only differential photometry is important.
Which stars do you like to observe?
WBEA
Hello Bernhard,
Thanks for your post. The SSP3 is basically a detector which the light of one star is kept on. You use a comparison and a check star which you move back and forth between integrating on each.
Up to now I have only carried out differential photometry on relatively bright stars. Semi-reg, Miras, Eclipsing Binaries plus a few other bright variables that caught my interest. From my previous house I had a smallish scope 20cm, a poor sky and was limited to brighter than about 7.0 mag, so quite limited.
Having moved to a better sky I was looking to upsize a bit. Hence my request for advice. The C11 with its 2.8m focal length is way over then. However are you referring to imaging type photometry in which case the field of view is mucf reduced with higher f number. Sorry I'm not sure what non-differential photometry is. Is this what the CCD observers do?
Regards
Kevin
Hi Kevin,
you can ask yourself the following Qustions:
Which targets do you want to observe?
Which accuracy in mmag do you need?
Which amplitude do you want to resolve?
Which equipment (mount, telescope, camera) can you afford or match the upper needs.
Mhhh.. i have observed with an 4 inch refractor in a Bortle 7-8 zone over a year. 12th mag stars are possible. 13 mag stars are close to the limit. With my upgraded 8 inch reflector, 13-14 mag stars are possible. So far i have no autoguider. So the stars sometimes are moving slightly through the image (due to the polar alignment), but for Muniwin photometry software, this is no problem. (Its a big dithering (-;)
Why would you start with a photometer?
https://www.optecinc.com/astronomy/catalog/ssp/ssp3.htm
Which advantages does the SSP3 have over DSLR or CCDs?
You have to stay up all night with a SSP3 shifting..., while a semi automated CCD, DSLR you can go to sleep, if you have some shelter for the telescope.. (even a balcony with a small visible part of the night sky will do it) (-;
With aperture photometry
https://www.startpage.com/av/proxy-image?piurl=https%3A%2F%2Fastrobites.org%2Fwp-content%2Fuploads%2F2016%2F04%2Faij_aperture-e1460731340188.png&sp=1595761045T086267e12d9f2ad4f355899b513dff73db9850eb677274b14b69c386d6c4184b
you perform the task for one frame, and than the software does it automatically for the other 100 -200 frames of a night...
Aperture photometry does not do shifting, so all the stars (var, comp, check) have to be on the same frames. Therefore, a smaller focal length with a big FOV has more compare and check stars, available for the aperture photometry.
A DSLR with 14 bit, the old Canon 450 D or newer ones, are affordable on ebay or other platforms for around 100 - 200$.
greetings wbea
Hello Bernhard,
Thanks for your reply, comments and clear explanation of aperture photometry.
I already have an old (probably original) SSP3 which I used for about 10 years to make many observations of variables. Yes it is pretty tedious and repetitive but I think I am too old to learn the new methods and instruments now. I have a pretty poor sky as I'm at sea level and have always been forced to observe bright variables (brighter than 7.0) with variations of at least 0.1 ideally much more than this.
This pushed my interest into trying to follow stars for as complete a coverage as possible, aiming for circumpolars. I managed to do this for about 10 years and think I did something useful. In the end I concentrated on 4-5 stars and have just joined AAVSO and uploaded my observations with much help from Tom Calderwood. I aimed for an accuracy of better than 0.02 mag.
I agree it seems to be pretty tedious but I quite enjoyed the hands on, and just being under those glorious night skies. I guess being a bit OCD with numbers also helped me.
Regards,
Kevin