Atik 420 circles??? Any idea what they are?

[stephen99]

OK Using the Atik 420 mono with a Lum filter and hyperstar on a celestron edge HD8. This is about 45 minutes of 1 min. exps and 20 minutes of 2 min. exps. Guided. What is causing the circles in the image? It starts small at the center and gets bigger at the outside? It really shows up in PS when you adjust levels and curves. I am almost there! Just need to get this fixed. Thanks for the help. Hope I provided enough info.

Thanks

Steve.

[niteman1946]

Hi Stephen,

Let's see if we can get this going.

I have never seen a hyperstar in person, nor the process technique.  But, this does look like vignetting to me.  Are you doing Flats, Darks, Bias (or flat darks)?

If not, you will find they greatly mitigate your apparent problem.

Mark

[Lex]

Hi,

IMO this is vignetting multiplicated by the lenses of the HS...
As told before taking flats will iron out the problem nicely...

Best

[topboxman]

You need to take flats no matter what scope or camera you are using. I can see how tricky it is to take flats with Hyperstar/camera attached to lens corrector.

Starizona has only one tip is to use sky flat at dusk or dawn. Problem with sky flat is you have very narrow window of opportunity to get the right amount of light.

http://starizona.com/acb/ccd/hyperstar/flats.aspx

I use T-shirt flat and it never fails me. You could cut a small hole at the center of T-shirt and if you can sew, put elastic band inside the hole center so that it's light tight from sun light. Or wrap around the center hole with black electric tape. T-shirt flats even works well under cloudy sky, just expose a little longer. Never point the scope toward the sun, point at opposite where the sun points to behind the scope. The best exposure time is when the peak is at the center of histogram.

You also must take bias which is the same as darks except the exposure is 0.000 second. You need to calibrate your flats with bias to remove bias from flats. Dark flats will also work but it's only useful if your flats are over a certain amount of exposure like 5 seconds.

Have fun.

Peter

[Lex]

Hi guys,

Shouldn't this also work with an electroluminescent panel, Neumann type for instance? I really like those panels because of their easy handling capabilities...

Best

[topboxman]

How do you use EL panel with Hyperstar in the way?

Peter

[MikeM]

How do you use EL panel with Hyperstar in the way?

Peter

A friend of mine has an 10" RCOS which has the secondary protruding from the front of the spider which makes it look like a hyperstar - in any event he has an EL Panel mounted on a wall in front of his scope so when he's done he just points it at the panel and takes his flats.

[topboxman]

OK. Sounds like it must be done under a dark sky or in a very dark room with no light leaking or straying in between EL panel and the scope. Maybe make a short dew shield in between the scope and EL panel to prevent from stray light. Sounds doable.

Peter

[Lex]

Hi,

In may case, i take my flats after all my lights. I close my obsy and point my scope to the ELP...
The Obsy itself is then completely darkened...

Best

[stephen99]

Thank you for all the suggestions. I like the light box thing the best! Going to see if I can make one.

Steve

[stephen99]

Could this also be a collimation issue? Really not liking this whole package at this point. Was expecting a lot more with the hyperstar. Still have to take long exps and all that. Oh and for some reason when I take any exp over 3 minutes I get a white screen and no image. I am using the Atik software and the 420 mono. Any idea what settting needs to be adjusted? Still very new using the software.

[Chris]

That looks like a nice image to me. nice round stars and no obvious problem except some vignetting causing the corners to be a little darker.

There's no astro photography system I know of that can avoid having to calibrate the images, using dark and light frames at least.

Darks are easy because you don't need to have the camera on the scope so you can take it off and fit the the CCD cover. Take 15 or 20 frames with the same exposures as you use for the light frames, average them and subtract from the lights.

Flats can be done with an EL panel, or a light box.  It's quite easy to make a light box from foam board with four white LEDs at the corners at the telescope end shining away from the scope so they illuminate the inside of the box but don't shine directly into the scope.

I've managed to get flat frames just by propping up a white panel a few feet from the scope, moving the scope so it's pointed towards it and illuminating it with a torch.

Whatever you do set the camera exposure so you get a signal of about 40 to 60% of full scale, collect a load of frames - 30 or so. and average them.

A good program to start with processing is deep Sky Stacker.  It handles lights, darks and flats and does all the processing aligning and stacking, leaving you to play with adjusting the levels.  I usually do a crude version there and then move to PS for a more detailed tweaking.

Chris

[stephen99]

Thanks for the info Chris. I do take darks most of the time. Never take flats or bias frames. Guess I am at that level now to start doing that. Appreciate the info on the light box. Thanks again to everyone for the input. Hope to get some better images soon. Guess its called a hobby for a reason? haha!

Steve