Does stacking alignment accuracy ever limit sharpness?

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RonAM
Posts: 38
Joined: Sun Nov 04, 2018 4:39 pm
Location: Midwest US City

Re: Does stacking alignment accuracy ever limit sharpness?

Post by RonAM »

Hi Tim,

Thanks for the excellent detailed description. I appreciate your taking the time to describe the equipment and approaches you are taking. Perfection is great to seek as its the driver for improvement in capabilities. I thank Robin every time I use SharpCap for its current capabilities and look forward to more :)

Thanks for mentioning exact leveling of the base, such an important item I forgot to note. I paid the price a couple times when this wasn’t exactly set.

I guess I am using the FWHM as a gauge and have been doing what you suggest to optimize settings for a given object. I’m finding best settings to be similar to yours. We appear to be in similar light polluted areas, you near London and me near Chicago. An example of not having FWHM limit set tight enough is my m31 image from my deck that is the image of the day today on Astromart website. Something must have moved during the hour long total time, shifting the image so some of the brighter stars have a “companion”. I’ve since set it to avoid this. A perfectionist will cringe looking at that one. It was using an Ioptron skytracker equatorial and 200mm f.l. f4 lens on my ZWO. Except for the shift during the capture the tracking was good. This lens has some flare and chromatic aberration that spoils star size as well.

It makes me appreciate the aperture and contrast of my Zambuto mirror in my Starmaster Dob. Yes it does give bright images on short exposures, which is very helpful.

For really good tracking my brother in western US recently bought a “10 micron” mount from Italy that guarantees 5 minutes unguided perfect tracking. His pictures are incredible. I’m trying to get him started on SharpCap to make his system even better but he is also using a recently purchased Astro modified DSLR and manually post processing his images.

I see how the drift graph shows how good or poor the tracking is, which is very useful. I appreciate the information both you and Robin have shared.

All the best,

Ron
RonAM
Posts: 38
Joined: Sun Nov 04, 2018 4:39 pm
Location: Midwest US City

Re: Does stacking alignment accuracy ever limit sharpness?

Post by RonAM »

Tim - I found this couple year old Andromeda image I took at a dark sky site near me. Unguided single image with Canon T3i DSLR and 200mm f4 Canon FD lens, all riding piggyback on my Starmaster Dob. So this shows the tracking accuracy with no help from guiding or SharpCap stacking. It is a 120 second single exposure at 1600 iso. This is the best tracking my Dob Mount could ever do. I recall taking about 10 exposures and selecting the best one. Most showed some minor star trails. I’m confident up to 60 seconds will produce mostly well tracked images, provided the object is in that 30-70 degree altitude range I mentioned earlier.

All the best,

Ron
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