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Locating targets using degree scales?


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Hi

I am setting up a manual rig for the holidays. I have 360 degree panoramic rotators on the RA and Dec axes as below

P1120415.jpg.448bd4cb5bbc6e9c3f1059a9a036dd94.thumb.jpg.cdbb29367e16ee1e2701aa225b13d36f.jpg

 

If I want to use these to 'star hop' to a DSO target, is the following procedure correct?

Align lens with a bright star, example say Vega,  same side of meridian as target, note the degree readings on RA and DEC angular scales

Work out difference between target RA and DEC and Vega RA and DEC (and convert RA hrs mins sec to degrees). I'd probably do this in advance on a spreadsheet on my tablet and using stellarium web)

Adjust the RA and DEC axes accordingly

I'll be widefield with a 135mm so getting it dead center isn't critical, I'll plate solve as long as I am approximately on target

 

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1 hour ago, Elp said:

Think it'll be far easier and quicker to star hop with a Rigel or Telrad then plate solve.

Not really, my rig is low level so I can't get down low enough to use a finder of any sort. The ASI Air is useful for plate solving for fine adjustment, but I need to get 'near enough' first  

It's less than 1m high..

20230513_132258.thumb.jpg.4539bb7d2c23f56bd63b20a15f9913f6.jpg

Edited by 900SL
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I think that you'll be fine.

Using "settings" circles on EQ mounts is rather limited in precision - because of small precision you get from reading the marks (best you can do on small gauges is something like 1-2 degrees of precision - and that is enough for plossl at x25 or so), but you should be fine if you have several degrees of FOV with short FL lens.

Ideally - easiest way to do it is to "set" the settings circles onto a know target and work from there, but I'm guessing these are fixed and don't rotate freely, so yes, just "mentally" set them to known position and do value subtraction between two targets.

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Thanks VIaiv.  gave it a test run last night. And realised that initial alignment with a bright star was an issue. I'll try from a home position on Polaris next time, or maybe Horizontal - West

Polar alignment is a doddle with the AAP.  Tracking no issues with 3 min test exposures. 

20230515_112947.thumb.jpg.61e5209b244ac4636a76ee9f81fc0974.jpg

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Yes, easier if the degree rings can be set to the co-ordinates of your sync star, but your method should work OK and the degree (no pun intended) of precision you are working to should be fine.

Have a good (imaging) holiday.

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On 13/05/2023 at 10:03, 900SL said:

Hi

I am setting up a manual rig for the holidays. I have 360 degree panoramic rotators on the RA and Dec axes as below

P1120415.jpg.448bd4cb5bbc6e9c3f1059a9a036dd94.thumb.jpg.cdbb29367e16ee1e2701aa225b13d36f.jpg

 

If I want to use these to 'star hop' to a DSO target, is the following procedure correct?

Align lens with a bright star, example say Vega,  same side of meridian as target, note the degree readings on RA and DEC angular scales

Work out difference between target RA and DEC and Vega RA and DEC (and convert RA hrs mins sec to degrees). I'd probably do this in advance on a spreadsheet on my tablet and using stellarium web)

Adjust the RA and DEC axes accordingly

I'll be widefield with a 135mm so getting it dead center isn't critical, I'll plate solve as long as I am approximately on target

 

An easier method if your mount has setting circles and a meridian pointer (which I use with my 14 in fork mounted Newtonian) is via a sidereal clock, although you don't need an actual clock these days as sidereal time for your longitude is available as an app on iPhones. You simply set the meridian pointer to local sidereal time on the RA Circle, and then move the scope to the RA and Dec of the desired object, assuming of course your mount is reasonably well polar aligned.

I find this particularly useful for locating Mercury and Venus in daylight, when you can't star hop. The problem is that most scopes that actually have setting circles these days, is that the circles tend to be too small, ideally you need an RA circle at least 12in in diameter, my fork mount has a 12in RA circle with each hour subdivided into 20 minute and 4 minute segments. 

John  

Edited by johnturley
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Thanks Gents.

 

I have an additional question to do with a manual meridian flip

 

The RA axis is straightforward, a 180 degree rotation assuming the flip is made at the meridian crossing

 

But is there a simple relationship for the DEC axis rotation to ensure that the scope is pointing approximately back on target? 

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OOooooKkkaaaayyy   I think I worked this out. The Dec rotation should be double whatever the Dec angle is from 90 degrees?

 

So for example,  I have a target at DEC +30

At Meridian, I flip the RA axis 180 degrees and rotate the DEC axis 2 * (90-30) = 120 degrees and I should be back on point (approximately)?

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I always use Polaris when i am setting up my circles, but i will admit the ones on my dob are just a bit bigger and easier to use then that.  Get 0 as close to aligned with Polaris as you can and you are halfway home.  

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1 hour ago, 900SL said:

At Meridian, I flip the RA axis 180 degrees and rotate the DEC axis 2 * (90-30) = 120 degrees and I should be back on point (approximately)?

If your target is at DEC 30, after meridian flip, your camera will point to DEC -30 (it mirrors), so you need to move it 60 degrees to bring it back to target.

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