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Excel help needed please


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Hi all,

I have a DIY secondary imaging rig for my HEQ5 Pro, which I often use with a TS ImagingStar 71 refractor (not in the picture), and I can point this secondary scope independently of the main scope.  It looks like this :

IMG_20160219_150411.jpg.4c30387196e1234c222c168e083f8338.jpg

Not visible in the picture is a locking device in the upper end of the CW shaft, so it is not as unstable as it looks. I get decent subs up to 5 minutes with 350 mm FL. But that is another story...

If I shoot the same target with both scopes, everything is fine - no problems at all.  I just align the two on the same star during the mounts star alignment procedure (I always use "1 star alignment" only). But if I want to shoot another object with the secondary scope, it can be very tricky to find it, especially when I have a NB filter attached in this secondary scope. I do have a laser pointer included but it still is very rough and often hard to see. So I came up with a GOTO assisted procedure:

  • Center both scopes on the mount alignment star
  • GOTO a pre-calculated "virtual target" (RA / DEC)
  • Manually re-center only secondary scope on the previously used alignment star, creating an offset between the two scopes
  • GOTO primary target with main scope and secondary scope will magically be spot on the secondary target

I have spent some time now trying to do an Excel spreadsheet that takes three inputs: RA & DEC for primary & secondary targets and the alignment star. The output should be RA & Dec for the virtual target.  Due to my own shortcomings in Excel and mathematics, I only managed something that worked as long as the RA did not cross the 00:00:00 (near NGC7790).

I have a portable setup and do not use a pc in the field so I will need pre-calculated data which I plan to program into the HEQ5 handset "User Objects" to save time under the stars.

Is there anybody out there who can give a helping hand with such a spreadsheet ?

Cheers

Ragnar

 

 

 

 

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Sorry I can't help with the excel problem, but the secondary rig looks amazing.

Have you thought of doing a write-up on this adaption for the diy section of the forum - I'm sure I would not be the only one interested. [Did a quick search and did not find anything - apologies if I missed it.]

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14 minutes ago, Demonperformer said:

Sorry I can't help with the excel problem, but the secondary rig looks amazing.

Have you thought of doing a write-up on this adaption for the diy section of the forum - I'm sure I would not be the only one interested. [Did a quick search and did not find anything - apologies if I missed it.]

Will do.

Ragnar

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I have just seen this...

50 minutes ago, Demonperformer said:

Sorry I can't help with the excel problem, but the secondary rig looks amazing.

Have you thought of doing a write-up on this adaption for the diy section of the forum - I'm sure I would not be the only one interested. [Did a quick search and did not find anything - apologies if I missed it.]

 

38 minutes ago, lux eterna said:

Will do.

Ragnar

...and I was going to suggest the same thing.

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On 23/08/2018 at 17:53, Demonperformer said:

Sorry I can't help with the excel problem, but the secondary rig looks amazing.

Have you thought of doing a write-up on this adaption for the diy section of the forum - I'm sure I would not be the only one interested. [Did a quick search and did not find anything - apologies if I missed it.]

And here it is :

Ragnar

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...and I am now the happy owner of such an Excel spreadsheet ! Thank you @Synchronicity for providing a very clever design with no problems related to the RA 00:00:00 border crossing etc.

Then I added a RA scaling factor, because if you set a fixed offset between the two scopes (assume both are relatively high up in DEC) and then slew the complete setup down in DEC (towards the equator), you will have to increase the RA part of the offset (because the equatorial grid becomes wider and wider as we approach the equator).  This was tricky, and I´m not sure if I have this mathematically correct but it comes close to what I get when testing this IRL.

My latest imaging attempt was what triggered this idea. I was imaging the Cocoon Nebula in Ha with my main scope, and tried to find the Elephants Trunk with an OIII filter in my secondary (TS Imaging Star 71). It takes some fiddling to remove a 2" filter inside the Imaging Star just for framing, and the reinserting it, so I never did that and of course I missed the secondary target. But my next try will be with Excel & GOTO assistance !

If some of you are using an extra camera, maybe with a widefield lens on a piggy-back mounted ballhead, this can be a very quick way to frame the planned secondary target. Just choose a bright (and rather nearby) alignment star as reference.

Here it is :   Offset Calculator.xls

Ragnar

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  • 1 month later...

Just in case someone is using this. Sometimes I was a bit off target using this version of the Excel spreadsheet so I updated with another formula for calculating what impact delta DEC positions have on delta RA with a fixed offset between the two scopes. I have no proof for correctness with this new version, but the last time I tried it it was spot on.

Offset Calculator_V2.xls

Ragnar

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  • 1 month later...

Hi Ragge,

I took a look into your Offset Calculator, but had little bit hard to follow the function of it. But if I understand it works for you now, or?

Otherwise you can have a look into my Excel sheet:

http://www.astrofriend.eu/astronomy/astronomy-calculations/excel-sheets/astronomy-calculations-excel-angleconvert.html

I have angle conversation there and from them you can borrow the matematics if you find them useful.

/Lars

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