Saturday, April 20, 2013

First Hyperstar imaging

So, I could finally start imaging with my Hyperstar lens. I tried the Leo Triplet (M66, M65 and NGC3628). I focused manually with my Bahtinov mask (will figure out the @Focus2 parameters later). I then played with the exposure times. I was surprised how quickly the whole image gets saturated (a 6 minute exposure is completely white, a 1 minute exposure is getting into the 50000 range). So, I took 1 min RGB exposures and 2 min Lum exposures.

Exchanging the filters wasn't too bad with the Hyperstar filter drawer. But I can't do it easily with the dew shield on the scope - so, I had to remove it. I'm a little bit afraid if this will bring in some stray light from the side...

Taking flats turned out to be a major pain in the ... I tried with my flat panel, but it was too bright. And even with the dimmer I could not get them dark enough (I later found out about grey filters from Neumann that you can put over the flat panels to dim them). So, I took flat frames at dusk. It took me two evenings to do that as the hyperstar lens is so sensitive, that by the time I was done with 2 series of flats, it was already too dark and too many stars were coming through.

I then went into CCDStack and processed the images. During processing, I could already see that the flat frames weren't very good (they didn't neutralize the background evenly). And that's why the final picture looks like this:

Yikes! This images has everything that you don't want to have: uneven background, vignetting, field rotation, unsharpness... Well, maybe hyperstar imaging isn't as easy as I thought...

Looking at the flat frames:
Blue:
Green:
Red:
Luminance:
Clearly, the blue and green flats are very uneven. So, I chose the 1x1 flat for all images. And this is the result:

By far not perfect, but much better.