Software solution for Cone Error?

[umasscrew39]

Hi Robin

I used ConeSharp and found my cone error to be 0 15'59", with the front of the telescope pointing out away from the mount. I was planning on adding a shim in the back of the scope to correct this but I have 2 issues: 1) my scope is over 12ft up in the air in my observatory and is heavy and 2) it is on a Losmandy dovetail which does not have a set screw or other convenient way/opening to even add a small shim. So, other than doing plate solving when I slew across the meridian to find out where I am, are you aware of a better, non-physical way, to correct for cone error using software (e.g., pointing model)?

Regards,
Bruce

[admin]

Hi Bruce,

I'm not aware of any good way of correcting for cone error in software – in theory if you do a three-point alignment on your go to Mount then it should calculate and correct for cone error but my experience has been that this is a pretty hit and miss affair and that it's better to correct it. In situations where I have difficulty with an adjustable thread I have used one or more washers behind or in front of the dovetail to add some extra spacing.

Hope this helps, Robin

[umasscrew39]

Thanks for the info, Robin. I will play with it some more and see what I can come up with.

[umasscrew39]

Hi Again Robin

One more question which may be obvious to everyone but me. When the error popped up, it also said: ...."with the front of the telescope pointing out away from the mount." What is the front? Where the objective/eyepiece goes or the corrector plate/secondary mirror end (I have a SCT)? And if pointing out away from the mount, I am assuming adding the shim on the opposite end to raise it is the fix.

Thx
Bruce

[saguaro]

Hi Bruce,

The next version of Astro-Physics hand control firmware is supposed to have a new feature that allows cone error correction to be saved so that your AP mount will automatically correct for cone error. I agree that shimming a heavy OTA like yours or my 14Edge is a pain. I saw this new feature mentioned by Roland in the AP GTO Yahoo forums recently.

In the meantime I have used thin stainless steel shims on the rear of my 14Edge OTA, placing them underneath the rear radius block that sits on top of my Losmandy rail. I have also used Conesharp and found it to be a nifty tool.

-Robin Clark

[admin]

Hi Bruce,

By the front of the telescope I mean the bit that points towards the sky

Cheers, Robin

[umasscrew39]

WOW... Two Robins to help me out!! That is what I call service

Thanks much. What makes this so much worse for me is my scope being 12 ft off of the ground in my observatory. So, I have to use a safety ladder to make such changes. That is why I want to get this right the first time and be done with this issue. At least lifting weights 5 days a week should help pay dividends for this fix. I did not see that about the new AP hand controller. I sold mine a year ago as it does not help in the observatory.

Anyway, thank you both for coming to the rescue and I will remember what is the front of the telescope

[admin]

Hi,

I think that if you are using an Ascom driver for your scope that can accept multiple synchronisations and build a pointing model then you will be able to correct the cone error by synchronising in a range of positions in the sky. Personally I've never tried that, but I believe EQMod and other advanced Ascom driver support this idea.

Cheers, Robin