old guy with new mount going to revisit astrophotography

[John Pierce]

I did some unguided piggyback DSLR astrophotography with an old Vixen SuperPolaris a few years back, got some OK results.  never did get guiding working on it.   Went back to visual for the past few years (10" dobson, 17" dobson)

Acquired a Celestron CI-700 a couple days ago, which is a slightly cheapened version of the venerable Losmandy G11, from 1999.    It has the simple non-Gemini 2-axis control system, with a guide port, which I assume is ST-4 compatible, so I'm thinking I'll dabble some more in DSLR astrophotogging.

Wanting to make sure I'm headed in the rigth direction before I leap off the cliff of no return :)

I just slapped my 80mm f/11 refractor on a losmandy plate, and tested it, simple polar scope based alignment, and things were staying pretty well centered in the FOV for an hour or more, coolio.    Mount has slo-mo 0.3X, 0.5X, 8X, and 16X siderial, also has solar and lunar tracking speeds.   very little DEC backlash, but a fair bit of RA.

I guess my next step is finding my EOS camera adapter and shooting a few unguided test shots, but....

a couple years ago I built a guide scope from a Synta/Celestron 9x50 finderscope objective+tube, a radio shack 1280x1024 USB webcam, and some plumbing parts.   Using the Vixen SP, and phdGuiding 1.x, I was able to graph the PEC by following a medium bright star in my suburban sky.

so I'm assuming if I get a GPUSB, and hook all this up to my laptop with openPHD, I'll be golden ?   the guidescope has a ~ 200mm FL, while the main scope is 910mm.   the pixels are quite tiny on this webcam.   my EOS 60D is quite free of noise on 3-5 minute ISO 1600 exposures, and I have an intervalometer to run timed series (or USB from laptop)

I know putting a 80mm f/11 refractor on this mount is kind of a joke.   the CI700 originally had a C11 on it.   I'm going to need some small counterweights, the one that came with the mount is 25 lbs.

  

[wa5...@centurylink.net]

Hi John,

I use a CI-700 for imaging.  I also use a GPUSB connected to the autoguider port on the hand paddle. The guider port on the hand paddle just parallels the contacts of the 4 push buttons so the relays in the GPUSB do the same thing as the push buttons.  Make sure you run the guide rate at 0.3X when autoguiding.   My guide scope is a 80mm f7 refactor.  I image with a AT6RC, 150mm f9, scope.  I normally run 10 minute sub-frames. 

My biggest problem with my CI-700 is backlash in Dec.  Most of the backlash seems to be in the motor and reduction gears that drive the worm whick can not be adjusted. 

Hope that helps.

Wes

WA5TKU

[John R Pierce]

On 3/28/2017 3:16 PM, wa5...@centurylink.net wrote:
> My biggest problem with my CI-700 is backlash in Dec. Most of the
> backlash seems to be in the motor and reduction gears that drive the
> worm whick can not be adjusted.

mine seems to have significantly more backlash on RA, but I guess as
long as the guide speed is less than 1X sidereal, thats not a
problem. the original owner told me he never tried to adjust
anything, so I may have to break it down, clean it and regrease the
appropriate stuff, and adjust the worms....


--
john r pierce, recycling bits in santa cruz

[wa5...@centurylink.net]

John,

I would recommend cleaning out the old grease since it seems like it has the original.  The original grease gets really stiff when it get sold.  The effect of RA backlash is also reduced by adjusting the balance to be slightly heavy to the East.  Of course good polar alignment really helps in both RA and DEC for the autoguider not to have to make correction. 

Wes

WA5TKU

[John R Pierce]

On 3/29/2017 5:05 AM, wa5...@centurylink.net wrote:
> I would recommend cleaning out the old grease since it seems like it
> has the original. The original grease gets really stiff when it get
> sold. The effect of RA backlash is also reduced by adjusting the
> balance to be slightly heavy to the East. Of course good polar
> alignment really helps in both RA and DEC for the autoguider not to
> have to make correction.

I need to find a much smaller counterweight for this 1.25" shaft. the
supplied 23 lb one would totally overwhelm my 80/11.3 + EOS combination,
hah. its almost balanced with just the shaft, no weight.