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EQMOD alignment accuracy?


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Well finally got a clear night having bought all the new equipment weeks and weeks ago so finally giving everything a go together.

Im using CdC with EQMOD and i polar aligned as normal and the slewed to vega, it was nowhere to be seen so i loosened off the clutches and manually centered and then synced in CdC (i checked and it did EQMOD as well). I then went off to Altair and adjusted with the gamepad by a small amount and the same with Alkaid and synced both in CdC

Since Jupiter was looking nice tonight i then slewed expecting it to be in the centre of the eyepiece, it was way off so i moved with the gamepad (by guesswork as i dont have a finderscope) and then synced that as well (mistake to sync on a planet?)

Having viewed Jupiter for a while i decided to try the autoguiding out and take a few shots of M31, again picked M31 in CdC and slewed. Again nowhere near the centre, lots of manual adjustment required.

I read that slweing is most accurate within the chosen alignment points but i thought that it would have been more accurate than this? Have i missed something?

Thanks.

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Okay packed up for the night but when i went back to the PC everything was guiding fine. I brought up the EQMOD interface in CdC and the words 'LIMIT' were flashing in the RA and DEC boxes.

Scope was pointing effectively straight up at M31, i saw somewhere to turn them off bu couldnt find where just now. Should i leave the settings as they are for safety?

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Im using CdC with EQMOD and i polar aligned as normal and the slewed to vega, it was nowhere to be seen so i loosened off the clutches and manually centered and then synced in CdC (i checked and it did EQMOD as well).

Don't expect your first goto to be accurate simply because you've polar aligned. The goto accuracy of the first goto is defined by your ability to power up with the mount in the "perfect Home position". Just accept that your initial goto will always be off - once you've centred and synched on that first goto EQASCOM will compensate subsequent gotos for any error in home position. Slackening the clutches is ok - all you're doing there is manually correcting your start up position error.

I then went off to Altair and adjusted with the gamepad by a small amount and the same with Alkaid and synced both in CdC.

Since Jupiter was looking nice tonight i then slewed expecting it to be in the centre of the eyepiece, it was way off so i moved with the gamepad (by guesswork as i dont have a finderscope) and then synced that as well (mistake to sync on a planet?)

Having viewed Jupiter for a while i decided to try the autoguiding out and take a few shots of M31, again picked M31 in CdC and slewed. Again nowhere near the centre, lots of manual adjustment required.

It looks to me like the three points you chose for alignment - Vega, Altair and Alkaid are pretty much form a line rather than a triangle that covers the sky! As Jupiter would have been well out side the oblique triangle formed by these three points it is really not surprising that your goto required significant correction. Unless you had waited a couple of hours for M31 to move across the sky M31 still would still put you outside any possible triangle formed by the now four points so again it is perhaps not surprising that your goto was inaccurate.

It is best to stick to syncing on stars rather than planets. Also use a high power reticule eyepiece if you have one. The more accurate your syncs the more accurate your gotos.

If you haven't seen them already check out the EQMOD video tutorials on EQASCOM alignment.

Chris.

Edited by chrisshillito
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Okay packed up for the night but when i went back to the PC everything was guiding fine. I brought up the EQMOD interface in CdC and the words 'LIMIT' were flashing in the RA and DEC boxes.

Scope was pointing effectively straight up at M31, i saw somewhere to turn them off bu couldnt find where just now. Should i leave the settings as they are for safety?

By default EQASCOM applies a limit to the RA when it tracks across the meridian. You can turn this off or set your own limit position. Most folks can quite happily track over the meridian for a number of hours without any problems but it is up to you to determine the safe operating limits of your particular setup and define limits accordingly.

Chris.

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Okay Thanks. Sounds sensible

Something else that i have thought it, when i polar aligned using the RA setting circle i put in 8pm, and did not take off any hour to make it GMT, could this also have caused a problem?

Would it be wise to empty out the sync i did last night and redo the points next time, making more of a triangle?

Also, does anyone know if you can change the onscreen star names in CdC to the common ones instead of having to use the find function?

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Something else that i have thought it, when i polar aligned using the RA setting circle i put in 8pm, and did not take off any hour to make it GMT, could this also have caused a problem?

Its not a problem from the point of view of gotos. Polar miss-alignment is one of the errors measured as part of the initial goto. So once you've synched on that first point that error is corrected for on all subsequent gotos.

If you want to precisely position the polar scope reticule then consider using EQASCOM's inbuilt polar scope alignment tool - there's a video on using it here.

Would it be wise to empty out the sync i did last night and redo the points next time, making more of a triangle?
If you setup a fresh every night then you can't really use the previous nights alignment data. If the mount is permanently sited then you could just remove the last one (wher eyou used jupiter) and the add some more low in the E/SE/S to get better sky coverage. alternatively just add points close to your observing targets.
Also, does anyone know if you can change the onscreen star names in CdC to the common ones instead of having to use the find function?
Yes, you can do that - setup->display; Labels tab

Chris.

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