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Just a quick heads up for all CGEM users... Celestron has released version 6.51 firmware update.
So if you have been missing the PEC capability of your mount, this update is meant to fix the PEC problem where the CGEM was not accepting any PEC program, communicating with PECtools (or any PEC software) nor recorded any corrections.
This was bought new back in 2014. It was used for a short time in our observatory before we decided to get a Mesu 200 in late 2015. Following that, it received little use – we would occasionally get it out for visual work. Further purchases have meant that the CGEM is now not being used at all, and it is time to shift it on.
The CGEM is, in most respects, equivalent to an EQ6, although you should be aware that it cannot be used with EQMOD. It comes with the original tripod and a 17 lb counterweight (as shown in the photo). It comes with the 12V cigar plug power cable.
• Payload Capacity: 40 lb (18.14 kg) – visual
• Computer Hand Control: Double line, 16 character Liquid Crystal Display
• 40,000 object database with over 100 user-definable objects and expanded information on over 200 objects
I kept the original foam for storing the mount, but the original box has gone. The total weight of the package is not far short of 80 lbs. I don’t know how much it would cost to ship (or quite how I would ship it), so I think collection would be required. I don’t mind driving a reasonable distance to deliver or exchange (maybe we could meet half way).
Note that I am also separately selling a Sky Q Link which works with this mount and enables you to control it using an IOS or Android device.
The mount is also for sale on UK ABS
This is a 10 hour exposure of the NGC1055 galaxy using a standard Canon DSLR. The image is taken with a Celestron 8" SCT at F10 (2032mm focal length).
The image consists of mostly 600s subs and approximately 2 hours of 90-150s subs, all at ISO 800.
This galaxy is located at about 60 Million Light years distance from us, and at a magnitude of 12.5 is quite a faint object to image, especially when there is a little bit of light pollution with in the par of the sky it is imaged at... Looking at the result, I probably should have used the f6.3 FR to have less over sampling and most likely capturing more light in the same amount of time, or same amount in less time... end result most probably, at worst, would have been the same if not very similar and at best there might have been a bit more detail captured since guiding at 63% of the focal length and not oversamplig the subs would not be as susceptible to seeing/star fluctuations/movement.
I came across the knowledge of NGC1055 galaxy in Cetus by accident while looking at some Hubble images and thought that this Galaxy was possibly a rarely imaged object since I didn't see any images posted of it. Googling this galaxy there are a few amateur images, but still not as many as other galaxies or objects and seems very unpopular.
This galaxy was not in my "Star Walk" app so I thought that perhaps its not in the simpler star map programs that people use? or due to the fat that it is quite faint... it is in Cartes Du Ciel and Star Map HD.
Enough of my google babble, tech specs time... this was imaged using my NexStar 8SE on the CGEM mount at F10 (2032mm) through my unmodded DSLRs. I initially started imaging the galaxy using my Canon 7D to try to get a higher resolution but realised that the 7D is not only as sensitive as my 40D, modded or unmodded, but a 600 second sub heated up the sensor to 43 degrees as reported by APT. Surely this would generate more noise but I decided to allow the rest of this and next night to image using the 7D.
I was curious about the difference between the sub quality between my 40D and 7D so I changed the DSLR used to the stock 40D and the difference was staggering... the 40D only heated up to 21-23 degrees, there was more of the galaxy visible in the 600 second sub but the subs had a noticeable less noise.
Each night conditions were very similar, seeing, temperature etc, so I figure that the reason for higher sensitivity was the fact that the 40D has physically bigger pixels and so more photos hit each of the receptors...
Total Exposure time was:
57 x 600 sec subs (20 subs through the 7D and 37 subs on the 40D)
23 x 150 sec subs (all 40D)
12 x 60 sec subs (all 40D)
The galaxy was mid height in my northern sky and I always started imaging 10-15 degrees east of the meridian until sunrise, so I only really had about 3 hours per night of imaging it before the galaxy was obscured... that includes finding the guide star, calibrating and start the process which took about 30 minutes.
It's not anywhere near the hubble image or most of the amateur images but I hope you like it, thanks for looking...
Now that I have my CGEM on a permanent pier, I figured that I should get much better accuracy in guiding quality, especially at 2032mm (F10) focal length on my 8" SCT.
I spent a bit of time getting guiding results that are at the very least acceptable and thought I’d share my experience with anyone who is looking for info on PHD autoguiding.
In the pasten setting up for each astro session and using PHD I was generally getting RMS about 2.2-2.6ish and after stacking and processing, the soft effects were able to be negated to a great point, revealing detail and with results that I was quite happy with (on a good night) imaging at 2032mm using a modded Canon 40D.
The stars were round and generally I was able to use most (if not ALL) of the subs generated, even when I was exposing through Halpha or SII for 30-40 minutes per sub. That in it self, I thought, was pretty good for the setup that I'm using... or... I'm just easily pleased.
I use a OAG for my exposures so guiding on the same FL as imaging.
That said I did spend a bit of time playing with PHD settings, as well as the backlash setting on the CGEM, along with autoguide rates to try to get better guide graph.
After a spending a bit of time on both polar alignment as well as tweaking the autoguiding parameters in PHD, I was still getting a graph that showed large jumps, see pics… Nowhere near the near flat line that a few imagers were getting. Although the RMS level at 2032mm did improve, now I’m getting numbers of between 0.83-1.3, so it is definitely an improvement but still didn’t look flat.
The test exposures I done at those RMS levels using the 40D at ISO100 on a 40 minute exposure showed round stars and the frame exposure looked good.
I decided to investigate to try to improve the graph, and when turning off the guide commands the graph showed large bumps generated by star movement caused by the atmosphere, the graph was very similar, although slightly higher RMS, due to the star moving around obviously due to seeing.
At this stage I put my larger graph RMS in comparison to other very flat graphs to perhaps me guiding at 2032mm on a 1/4” CCD and others guiding using a much smaller/shorter FL guidescope where such large seeing related star movements are not picked up at a shorter FL, I base this on the fact that when imaging and guiding while using my 80mm/500mmFL frac where I generally got a RMS of 0.3ish.
Using the size of the pixels and CCD on the focal length the results are 0.548 arcsecs per pixel so multiplying that by the RMS I get the guiding is 0.45 – 0.71 arc seconds accuracy (?) which if I’m right, sub arc sec accuracy is OK for AP. I used http://www.celestialwonders.com/tools/imageScaleCalc.html for the calculation.
NOTE That until I had decent backlash set on the handset I was still getting intermittent saw tooth like spikes in DEC and RA, and the guide star did spontanously jump large distances periodically.
The way I adjusted the backlash on both RA and DEC was by centering a star on the laptop screen and at 1X guide speed moving forward, forward, back, forward, back, back, adjust the backlash and repeat until the star responded instantly.
Also my autoguide rate is set at 40% for both DEC and RA.
My PHD parameters that seem to give the best guiding at 2032mm are below:
RA Aggressive: 50
RA Hyster: 10
Max RA Dur: 350
Search Reg Pix: 15
Min motion: 0.15
Calib Step: 500
Time Lapse: 0
Dec Guide Mode: Auto
Dec Alg: Resist Switching
Dec Slope: 4.5
Max Dec Dur: 350
Star Mass Tolerance: 1.00
Dither Scale: 0.05
Hopefully some of this helps someone.
Also if I'm missing something and anyone has advice to improve that graph, please feel free to share.