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Solar Rate on Hand Control

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#1 Tom Polakis

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Posted 03 December 2012 - 02:34 PM

I was doing a time-lapse sequence of the sun, so for the first time ever, I set the tracking rate to solar on the hand control. It doesn't appear to be any differently from sidereal rate, as the sun continues to drift eastward across the chip at a rate of roughly 2 1/2 arcminutes per hour. Is there a sub-menu that I am missing, or does the solar rate not function on my hand control? Mount is a CGE, in case that helps. Thanks.

Tom

#2 Tel

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Posted 04 December 2012 - 05:21 AM

Hi Tom,

For normal observation purposes I think most of us would agree that one can view the Sun or the Moon at Sidereal Rate rather than switching to Solar or Lunar Rates since any such change will go unnoticed to the eye.

On the other hand, if one were to want to make a time lapse sequence of Jupiter, then switching to Solar Rate may well prove significant although personally, I confess I've never tried it.

What puzzles me though is your intended time lapse sequence of the Sun. I presume you're aiming to capture the more fleeting prominences in Ha rather than Sun spots, given that the Sun's average rotational period is a very slow ca. 25 days ?

Also, how do you rate the tracking accuracy of your CGE in general once set up ? Is it permanently sited or do you have to set it up each time you use it ?

Sorry to be so inquiring but I think a little more information might help.

I'm sure there are no sub menus to tracking with the Celestron HC. Certainly my own Skywatcher HEQ5 Pro GEM Synscan HC provides only for Sidereal, Lunar, Solar , PEC plus Sidereal Rates and Stop Tracking. I have never had cause to use anything but Sidereal from this observatory contained permanent fixture.

Best regards,
Tel

Edited a few afterthoughts, Tom, what 'scope and (DSLR ?) camera combination are you using ? Is the set up "Barlowed" ? Conversely, focal length reduced ?

#3 mclewis1

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Posted 04 December 2012 - 09:21 AM

Tom,

What version firmware is in your hand controller?

I change the tracking rate to solar or lunar when I know I'm going to be doing some higher magnification work on either the sun or the moon. It just means to me that I'm not re centering small objects very often, it just stays put ... but the effect is very subtle. Most of the time though I forget to change the rate ... :o

#4 Tom Polakis

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Posted 04 December 2012 - 09:43 AM

For normal observation purposes I think most of us would agree that one can view the Sun or the Moon at Sidereal Rate rather than switching to Solar or Lunar Rates since any such change will go unnoticed to the eye.


Hi Tel,

For visual observing, the departure of solar rate is pretty small (2.5 arcmin/hour, but the moon moves nearly a half degree every hour. Every two minutes, a lunar feature you're viewing at high magnification shifts by an arcminute, so it's not a trivial error if you're looking at a feature at 300x for 10 minutes or so. I haven't checked if the lunar rate works properly yet.


What puzzles me though is your intended time lapse sequence of the Sun. I presume you're aiming to capture the more fleeting prominences in Ha rather than Sun spots, given that the Sun's average rotational period is a very slow ca. 25 days ?



The sun's rotation period is irrelevant to solar rate. The sun moves against the background stars by roughly 1 degree per day due to the arc of Earth's revolution about it, so the solar rate is slower than the sidereal rate by a few tenths of a percent.

The field of view of my Webcam setup is 8.3', so over a 2-hour time-lapse sequence, the part of the sun I am imaging would have moved more than half way across the field if it's tracking at the sidereal rate. It's pretty annoying to have to make those corrections when the mount should be doing it with the solar rate change.

Here is the time-lapse animation from last Sunday (~8 Mb)



Also, how do you rate the tracking accuracy of your CGE in general once set up ? Is it permanently sited or do you have to set it up each time you use it ?


The CGE is permanently set up in the backyard observatory, where it is aligned to within a few arcminutes of the Pole. Tracking is fine for stars, but I need to get this solar rate problem solved.


Tom, what 'scope and (DSLR ?) camera combination are you using ? Is the set up "Barlowed" ? Conversely, focal length reduced ?


The H-alpha scope is a Pronto with a 60mm H-alpha filter. A Barlow lens in the train brings the focal length to nearly 1500mm. Image scale is about 0.8" per pixel. At this image scale, any tracking errors are apparent pretty quickly.

Tom






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