The Rosette Star Cluster NGC2244 and the Rosette Nebula NGC2237

[Whitters]

NGC2237 & NGC2244  60 Minutes - MX916 - WO110 - Astronomic IRBlock

[Fay]

Paul I really like this image. Really nice & focused. I have only just seen it.

[Mike]

Nice image Paul. can't wait to see that in colour !

[RobertM]

Yes it's the first time I've seen it too.  A really lovely image, looks almost 3d with the foreground stars.

Just a question in passing really but why have the brighter stars got what looks like a diffraction pattern ?

Thanks for bumping it Fay.

[Rick]

Just a question in passing really but why have the brighter stars got what looks like a diffraction pattern ?

It's a sign that the optics (and the viewing conditions) are excellent that you're only seeing them on the brightest stars.

If you want to determine what imperfections are present in a system, give it a very short high  intensity spike, and see what comes out at the other end. For an optical system a point source is what you want. Stars, being so far away, make good point sources. The brighter the point source, the more of the imperfections and the effects of plain old physics you'll see. So the bright stars are showing up things that the fainter stars aren't bright enough to reveal (because not enough light gets from them to the final detector via the off-axis paths...).

[Fay]

Paul, did you use a Ha filter? How long were the subs?

I'm jealous of your skies!!!!

[Mike]

Weird there is difraction spikes at all as it was done using a refractor.

[RobertM]

Thanks Rick I can understand that.  In this case then it's probable that there is some arrangement of three or six elements intruding into the light path.  I've seen that type of obstruction holding the objective lens in my guide scope.

Yes, I'm jealous too - must find a dark sky location or attend a DSC.  

[Mike]

It's possible it could be the arms holding the glass in place. If they intrude into the glass slightly that would be enough.

[Whitters]

Exactly right Mike, it is caused by the spacers holding the optics to the cell. I was surprised by them the first time I used the scope, but a quick exam of the front end of the scope gave the explanation. Except they don't so much protrude as change the transmission at the edge of the optice at the cell edge. See photo.

[Ian]

well you would go and buy cheapie mickey-mouse optics mate. Still, should be good for your teeth, says it's got fluoride in it. Or something.

Still, it's incredible the effect such a small detail has on the star images. Why don't you just use them tool things to add some more, disguise the real ones?

Actually, I don't think it's detrimental to the image at all.

[Whitters]

Fay, it was with six 10 minute subs with only the IR block Astronomiks filter, just to stop the bloat from IR light which would not be in the same focus point as the visible.

[Whitters]

And the scope was an e-bay bargain. It's always a bit of a sweat waiting for something like that to arrive though

[Fay]

Paul, is it a Megrez or APO Triplet?

[Fay]

OK, I've just seen triplet on the scope image