Polar aligning CG5 GOTO

[Sam Bo]

Hi all

I have been having fun (sarcasam intended) trying to GOTO and polar align my recently purchased CG5 for imaging. I have updated the firmware and recent attempts have only allowed a 1-2 minute exposure without star trails. At five minuties they were quite obvious which i have put down to using Manchester as my coordinate setting rather than my actual coordinates (i.e. poor initial GOTO alignment affected the polar alignment), bad telescope balance and possibly backlash in the motors.

This evening I am hoping to reduce all of these errors and see how the polar align feature of the scope works. I would like to test it by doing a proper drift alignment. However, I was wondering whether you need to have the RA axis set at a specific setting so that only the DEC axis is moving, or whether it is ok to move to the star (in south/west) using the GOTO hand controls? What I mean is whether the procedure is different for a manual versus GOTO scope? Can you manually perform a drift alignment first followed by GOTO alignment?

My initial steps would be as follows:

1. Rough polar alignment using polarscope

2. Attach telescope/camera and balance weight

3. Check backlash on motors

4. One or two star alignment

5. Polar alignment using firmware or Drift alignment (do you move the scope using the hand control, or undo the latches and move it manually so that the RA axis is in a specific position?)

6. Two star alignment with three calibration stars

Hope this makes sense?

Cheers

Sam

[Chris Rowland]

IMO the All Star Polar Alignment (ASPA) in the HC does a good job, probably enough for 1 - 2 minute exposures. It won't remove periodic error though.

In your schedule I would suggest a two star alignment AND some calibration stars, 3 or 4.

Then the ASPA using a star fairly close to the meridian and not too high. Follw the instructions on the HC, using the HC byttons fo the first sync movements, then the mount adjusting screws for the second alignment stage.

If you want to do a drift alignment you should be in a good position to do so from this. You can goto the star, then adjust the mount using the mount screws but once you do this the scope alignment will be inaccurate.

If you drift align you will need to do a new alignment, if you just do an ASPA you don't need to.

Use a reticle EP. I don't think it's possible to get star positioning accurate enough without it.

Chris

[Sam Bo]

Thanks Chris!

If you do the alignment with an eyepiece reticle, how do you ensure the scope is balanced when you replace it with a camera, as you cant unlock the motor drives to rebalance the mount? Could you return the scope to the GOTO home position, rebalance the mount and return to home position before switching on?

Cheers

Sam

[Chris Rowland]

Balance with the cameras and accept that it's out of balance with an EP and diagonal.

Chris

[astrosathya]

Hi Sam,

Glad to know ou live in Manchester. I lived in Eccles and Salford myself for over 3 years

Alright, my first scope was the C8-SGT-XLT and it came with the CG-5. I would say that after a fairly basic drift alignment I used to get about 90 seconds of tracking if I was lucky. Ofcourse my CG5 had faulty gears resulting in V shaped stars. I then moved on to the kit in my signature and have had no trouble since. As suggested above, you need a two star alignment before you use the firmware to polar align, then you need to power off, on again and do a three star align with two calibration stars. Remember that the CG5 is a real old design and hance that itself is a limitation. If you are able to get 2 minutes, I'd call you lucky. Even mounts costing £££££'s can track unguided maybe for five minutes, only the really expensive ones like Paramount can do more. If you are looking for extended tracking times, Id highly advice a guidescope or even better a new heavy duty mount like the NEQ6-PRO.

[Sam Bo]

Hi astrosathya

Thanks for your comment!

I have been trying everything for the last couple of months and the tracking is still out. I was told by the previous owner that five minute subs were possible. However, I have updated that Firmware and hence performed a factory reset and so all previous settings (i.e. calibrations, backlash settings etc) have been deleted. I think that is why I cant get five minutes.

So I have started from scratch by doing a rough polar align with polarscope, followed by two-star alignment + three calibration stars. At this point the alignment has been way off and my feeling is that the backlash settings may be the cause (still working on this). Then I have done a Polar align followed by turning power off and realigning on two stars + three calib stars. Alignment still seems to be off. I have also tried drift alignment that actually seemed to be pretty good. However, I cannot track for longer than 2 minutes.

I have wondered whether it could be periodic errors in the motors as the star trails appear like a sudden jump (i.e two blobs connected by a thin line) rather than lines. However, I know there is no PEC on the mount and I dont have a guidescope to use PEC tools.

Have run the calibration routines after alignment and polar alignment but that hasnt helped.

Would be great if anyone has any other ideas over what might be causing the tracking to be off?

Cheers

Sam

[astrosathya]

Hi Sam,

I really doubt the CG5 can do 5 minute subs. For you know, and it may not be untrue that the previous owner wanted to sell it off, so just made up a number. Why did he sell it off in the first place if he could get 5 minute subs? Maybe he got 5 minute subs with a DSLR and wide angle lens? The CG5 is from the era of the Dinosaurs. I remember the first time it was introduced as a GOTO mount in Sky and Telescope magazine of year 2000 ish. Even then the reviewer had picked a fault with the design that it could not go to low latitudes because of the RA motor housing. The gears are small, and hence for the price you pay accuracy will not really be the priority for the manufacturers. There is a reason why for example the Losmandy G11 will cost you an arm and half a leg. Today, quality is directly dictated by the Cost. Big brands charge you so much, but their minimum quality standards will be much higher than the maximum standards of the mass producers. I scrapped my CG5 mount after 8 months, because th egears were faulty and it was a pain in my back side. When selling it though, I made sure not to make tall claims of 5 minute subs and so on. I'd say you contact David Hinds, they are the distributors of Celestron in UK. They are by far the best folks to look at it. (though Mr David Hinds himself looked at my mount, it couldn't be fixed).

[Daddystu]

If you go down the guiding route you will easily get 10 min + subs (from what i've read). I think 5 mins unguided would be pushing it even for my pier mounted HEQ5. I have done 3 and 4 mins with usable subs but had to drop most at 4 mins.

[Russe]

I never managed over 2 min unguided with my HEQ5.

Then again, my polar alignment skills are developing only slowly.

My first guided pic was straight away over 5 min with round stars...