Polar Alignment Meade LX200

[joselito10]

Hello,
A pleasure to be in this forum greetings to all.
I have a Meade LX200 14” telescope i.e. 3550 mm focal length and 355 mm aperture. I would like to use Polar Alignment but my mount is a fork mount and so many magnifications I see difficult to place 10 star. I have a 0.6x focal reducer that I think would not improve much. The telescope is in a fixed observatory and I would like to fine tune the alignment, how can I do it? I rule out putting the camera on the 8x50 finder as it would be too low magnification. I have a 900 focal and 90 diameter refractor that I could mount on top, align and then dismount. is this possible, thanks.

Regards
Jose

[admin]

Hi Jose,

you don't say what camera you are using, but with 3550mm of focal length you would need a camera with a very big sensor (probably 35mm full frame size) to reach the required field of view of about 0.5 degrees in each direction to get polar alignment working. You would be much better off with a shorter focal length.

It's actually surprising how little focal length you need - 200mm focal length (many guide scopes) combined with a typical guide camera with 3.75mm pixels gives a pixel scale of about 4 arc seconds per pixel. That's plenty - there's no need to get the alignment closer than 20 to 30 arc seconds, which is easily achieveable at that pixel scale (providing your physical mount adjustments are nice and smooth).

So, I would suggest trying the shorter focal length options that you have - either a ~200mm guide scope with guide camera or the 900mm refractor with a somewhat bigger camera to get a reasonable field of view.

cheers,

Robin

[joselito10]

Thanks Robin,
I have a RisingCam G3-2300KPC camera which is a color clone of the ToupTek G3-2300KPC. I have read in the Sharpcap requirements an equatorial mount, my mount is a fork mount is that a problem?

Regards
JL

[admin]

Hi,

yes, a fork mount should be fine - to get the polar alignment to work, the real requirement is to be able to rotate around the RA axis with no change to declination, which you should be able to do for any type of equatorial mount.

It looks like the RisingCam/ToupTek 2300 is using the Sony IMX174 sensor, so will be OK for polar alignment up to about the 900mm focal length of your refractor (the FOV comes in at 0.72x0.45 degrees at 900mm, I think the width being well above 0.5 degrees will compensate for the height being a bit low).

cheers,

Robin

[joselito10]

Thank you very much Robin,
excellent explanation.

My Refractor is a SkyWatcher EVOSTAR 100ED Apochromatic Focal 900mm and 100 mm aperture.

Regards
Jose