PA with a dobsonian

Using SharpCap's Polar Alignment feature
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Tiago Ferreira
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PA with a dobsonian

Post by Tiago Ferreira »

is it possible? i can't rotate 90 degrees. precisely. should i do it more or less?
Youtube channel: https://www.youtube.com/channel/UCgR3Ha ... Vmw/videos

GSO 12" 1500 f/5 Dobson on Geoptik Eartha Eq Platform

ZWO ASI224MC + ZWO ASI294MC
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admin
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Re: PA with a dobsonian

Post by admin »

Hi,

Polar alignment only makes sense if you are using an equatorial mount - Dobsonians are Alt/Az mounts, so do not need polar alignment (for completeness, some people mount Dobs on an equatorial platform, which would need PA).

cheers,

Robin
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Tiago Ferreira
Posts: 34
Joined: Sun Mar 21, 2021 10:50 pm

Re: PA with a dobsonian

Post by Tiago Ferreira »

admin wrote: Wed May 12, 2021 1:45 pm Hi,

Polar alignment only makes sense if you are using an equatorial mount - Dobsonians are Alt/Az mounts, so do not need polar alignment (for completeness, some people mount Dobs on an equatorial platform, which would need PA).

cheers,

Robin
I have it on an Equatorial platform. And is drift aligned but i want to know if it's viable to use the sharpcap for it too.Thanks
Youtube channel: https://www.youtube.com/channel/UCgR3Ha ... Vmw/videos

GSO 12" 1500 f/5 Dobson on Geoptik Eartha Eq Platform

ZWO ASI224MC + ZWO ASI294MC
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Re: PA with a dobsonian

Post by admin »

Hi,

Ah, OK.

Right, the amount of rotation is pretty much irrelevant - it can be anything from about 30 degrees up to about 150 and you should get decent results.

The instructions just say 90 because it is (a) the most accurate by a small amount and (b) nice and simple to explain.

cheers,

Robin
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Tiago Ferreira
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Re: PA with a dobsonian

Post by Tiago Ferreira »

admin wrote: Wed May 12, 2021 2:08 pm Hi,

Ah, OK.

Right, the amount of rotation is pretty much irrelevant - it can be anything from about 30 degrees up to about 150 and you should get decent results.

The instructions just say 90 because it is (a) the most accurate by a small amount and (b) nice and simple to explain.

cheers,

Robin
As far as i understand an eq platform usually rotate 15º so that means that from the end (or start) to the middle of that arc, where it position at 90º, the rotation will be only around 7,5º.
Do you think it can work?
Should i try just those 7,5º or should i try rotate all the 15º arc to the 2nd step of sharpcap PA?
Sorry but i searched a lot everywhere for a long time and there is absolutely no info about this experiment anywhere with sharpcap and PA a dobsonian on Eq platform. So i want to try it (if viable). If it works i'll share the results.
Youtube channel: https://www.youtube.com/channel/UCgR3Ha ... Vmw/videos

GSO 12" 1500 f/5 Dobson on Geoptik Eartha Eq Platform

ZWO ASI224MC + ZWO ASI294MC
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Re: PA with a dobsonian

Post by admin »

Hi,

SharpCap 4.0 has a 'reduced rotation' mode for star trackers - however this still requires a minimum 15 degree rotation currently, so from one side of the adjustment all the way to the other and hope... In theory that number could be reduced to (say) 12 or 13 degrees, but I worry about how the accuracy is affected...

cheers,

Robin
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Tiago Ferreira
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Re: PA with a dobsonian

Post by Tiago Ferreira »

Ok, i will proceed with the experiment. I have my set up pretty well drift aligned and always precisely placed on the same position every night so it will be easy to verify if sharpcap PA can match my already drifted set up. Will see if this feature fit these kind of set ups.
Youtube channel: https://www.youtube.com/channel/UCgR3Ha ... Vmw/videos

GSO 12" 1500 f/5 Dobson on Geoptik Eartha Eq Platform

ZWO ASI224MC + ZWO ASI294MC
User avatar
Tiago Ferreira
Posts: 34
Joined: Sun Mar 21, 2021 10:50 pm

Re: PA with a dobsonian

Post by Tiago Ferreira »

Until now the experiment has failed. At 2nd part it always fails because it ask me to rotate the telescope further and i can't.
Could be important to choose a certain region of the sky to try it with my limited set up rotation? Or would be the same no matter where i point to?
Youtube channel: https://www.youtube.com/channel/UCgR3Ha ... Vmw/videos

GSO 12" 1500 f/5 Dobson on Geoptik Eartha Eq Platform

ZWO ASI224MC + ZWO ASI294MC
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Re: PA with a dobsonian

Post by admin »

Hi,

I am going to reduce the rotation limit to 13 degrees in SharpCap 4.0 in low rotation mode, also make it log the rotation so far more frequently at low angles, so we can see how far you are able to rotate. This will be in Monday's update.

cheers,

Robin
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