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Hyperstar Blotchy Stars

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#1 JMac85X

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Posted 02 August 2013 - 12:02 AM

I'm still fairly new with the hyperstar and I think its great. It's like going from dial up to high speed internet, but I have noticed in many images blotchy or stars but in others the stars are crisp and pin point. My question is to those that have achieved those beautiful stars, how is it done? Do you have to collimate your hyperstar itself or is it trial and error with the focuser? I'm also in a fairly light polluted area. I use a light pollution filter and it helps out quite well. I'm also wondering how long should I go on the exposures and at what iso? Do flats, darks, etc? And how many? If I take 30 30 second exposures of lights darks and flats wouldn't I need an autoguider with that amount of time? Much appreciated.

#2 Peter D.

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Posted 02 August 2013 - 09:07 AM

I'm just starting with my Hyperstar too, so I'm a beginner like you. The previous owner of my Hyperstar said that 30 second exposures are optimal, so I doubt if you're over-exposing. Since you have taken some pictures with crisp stars, it's probably not the collimation. So that leaves focus and tracking.

I'll bet it's focus. Focus is real touchy on my Hyperstar; it's apparently a consequence of the low f/ratio. I use the focus utility in Nebulosity to assist focus; it helps a lot, but I still have to wait for the vibrations to settle down everytime I touch it. So yes, for me it's trial and error. Unless you have a carbon-fiber tube you will find that focus changes slightly with temperature change, so the focus probably has to be checked from time to time throughout your imaging session. To get pin-point stars the focus has to be perfect; it's one of the trials of imaging and the reason why the experienced guys generally have motorized focusers.

Another thing to consider is tracking. You have a decent mount and you're not seeing any trails so it's not a drive error problem, but at f/2 any vibration (like from a gust of wind or through the ground) could blotch out your stars.

Good luck with your Hyperstar; I'm real excited about mine.

#3 JMac85X

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Posted 02 August 2013 - 02:12 PM

What camera are you using on yours? Lately I keep hearing about the qhy8l because it has a big chip and its cheap for what your getting. I was also looking into the atik cameras. Right now I have the 1000d unmoddified dslr.

#4 JMac85X

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Posted 02 August 2013 - 02:12 PM

What camera are you using on yours? Lately I keep hearing about the qhy8l because it has a big chip and its cheap for what your getting. I was also looking into the atik cameras. Right now I have the 1000d unmoddified dslr.

#5 JMac85X

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Posted 02 August 2013 - 02:12 PM

What camera are you using on yours? Lately I keep hearing about the qhy8l because it has a big chip and its cheap for what your getting. I was also looking into the atik cameras. Right now I have the 1000d unmoddified dslr.

#6 RedLionNJ

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Posted 02 August 2013 - 03:25 PM

Focus with the faster f-ratio of the Hyperstar is proportionately more persnickety (scientific term). Focus, focus and focus again. If you can use a Bahtinov mask or FWHM measure, that's the way to go.

Oh, and patience :)

Grant

#7 Jeff2011

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Posted 02 August 2013 - 03:56 PM

Bahtinov mask


:waytogo:

#8 JMac85X

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Posted 02 August 2013 - 05:03 PM

I ttriedmy bahtinov mask but the star didnt change. Maybe I did something wrong?

#9 Peter D.

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Posted 14 August 2013 - 04:07 PM

I'm limited to the Starlight Xpress H9C camera with my C8 Hyperstar: the C8 version does not have enough backfocus for my Canon DSLR. The H9C pixels are a little big for the Hyperstar application, but the resulting sensitivity is amazing: with only 10 second subs, no guiding or darks are needed. I wish I could use my DSLR though, the wider field and smaller pixels would be nice. I have no experience with the QHY8, but I've seen some nice images taken with it. Good luck.

#10 Mark72

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Posted 15 August 2013 - 12:07 AM

you'd better using autoguider. I tried initially 30 seconds but the stars were really bloated. With guiding you can go much deeper.

http://www.astrobin.com/20823/B/?mod=

Mark

#11 Peter D.

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Posted 15 August 2013 - 10:11 AM

If I take 30 30 second exposures of lights darks and flats wouldn't I need an autoguider with that amount of time?


No guiding is needed for taking darks and flats: darks have no light coming in, and flats are totally blurred so it doesn't matter.

For 30 second lights the need for guiding depends upon your mount and your focal length; my combination of Atlas mount and short focal length (Hyperstar C8 focal length is only 425mm) is very forgiving for exposures of 30 seconds or less. Guiding won't help if the wind is shaking your mount, especially at only f/2. Your mount is in the same league as my Atlas, so I don't think guiding will be critical up to 30 seconds (maybe a few subs could have short trails, but you could throw those out in the stacking process). Mark was taking 300 second lights (5 minutes; nice picture Mark!), so his was an entirely different situation.

I used to have to guide with 2 minute exposures using my CG5, but without guiding that setup usually yielded streaks rather than bloated stars. I hated the hassle of guiding the CG5, but for really outstanding results guiding is a neccessity, especially at longer focal lengths.

In my case I get bloated stars only on the brightest ones, even on very short exposures, and every sub is bloated equally. I now think that I don't have the backfocus right since I'm apparently not using the correct adapter. That's probably not your problem, since some of yours are not bloated.






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