clear sky chart

Job 9:9

Job 9:9-10
9 He is the Maker of the Bear and Orion,
the Pleiades and the constellations of the south.
10 He performs wonders that cannot be fathomed,
miracles that cannot be counted.

Sunday, January 5, 2014

Imaging With a Guidescope

Anyone else except me have this genius idea to image using your guidescope ?  Well, I can tell you that if you use narrowband filters, it does work.  The only problem is... that if you want to guide, you need another guidescope, unless you have an off axis guider.  Therefore, I bought a very inexpensive 50mm guide scope from Orion.  Actually, the FOV of the little scope is pretty wide, and its brighter than the original 80mm Awesome Autoguider scope.  I found literally dozens of stars that were in perfect focus and plenty bright enough to guide on.  And the accuracy was just fine for the 400mm focal length imaging scope.  I'll let you know how it works with a longer focal length.

Now I'm using the old guide scope as an imaging scope.  It is not color corrected - its a simple doublet, and very inexpensive.  I think the price of the 80mm is something like $150, which does not buy a whole lot of refractor.  However, I was looking for a way to increase my FOV with the CCD, and it seemed like a logical choice.

Because it is not color corrected, I dont recommend any sort of wideband or one shot color imaging with one of these.  However, narrowband is a whole nother story.  Stars are pretty small in narrowband, because there is no color fringing on specific wavelength lines.

There is one quirk when imaging with this scope.  The FWHM readout during focusing is actually pretty worthless in obtaining focus.  I had to focus the scope for the roundest possible stars.    If I didnt focus that way, the stars sport a tail, all pointing in one direction.  It looks like a guiding error, but is, in fact an aberration in the low cost optics.  This occurred with MY telescope, yours may act differently.  This first image has oblong stars - caused by the way I focused.

Here you can see the stars are oblong.  It does look like a tracking error, however the next image is even farther South, and therefore farther from the NCP which would cause the stars to streak even more, however I made no changes to the polar alignment or guiding parameters.  In fact, I imaged longer frames - 15 minutes over the 10 minutes I imaged the above image.

In this image, the stars are nice and round.  I purposely focused on Alnitak, attempting to get it as round as possible, even if it resulted in a larger, degraded FWHM reading.  The FWHM actually wasnt BAD in this image, averaging around 1.75.  Best of all however, the stars are nice and round without the trails.  Could the focus be better?  I dont know - the nebulosity seems a little soft focus to me, but it is a pleasing image with the round stars.  But the point is...  I'm imaging using a VERY low cost scope.  Are the optics perfect?  Not by a long shot, but it still takes decent pictures.