Uranium235
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Everything posted by Uranium235
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Radial distortion looks like image rotation.
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Its a good sky out there tonight... fill yer boots! (with photons)
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I did mine by eye, its not an exact science. I had the same problem a while back and twisting them straight was the only thing that fixed it. I had it on one diffraction spike, like this:
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Its still the spider vanes, its not a case of them being aligned - but one (or two) of them may be slightly twisted.
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Nothing wrong with the setup, the only thing that might need to be improved is the guide camera - something that has an ST4 port on it (QHY or ZWO). Nowt wrong with the way the DSLR is set up either, as sometimes you need to put it that way in order to make tagets land on the chip the right way up. You might find yourself switching between that and a 90o rotation to suit your target (especially if its big). The guide scope doesnt really have to be pointing at the same patch of sky as your main OTA, just roughly in the same area is good enough.
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Well, whatever you did to fix it - dont touch it again! (or at least remember exactly what you did...lol)
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Looks bang tidy! Only one odd thing, the M101 has a little bit of coma in the far corners - while the M3 has none at all (I pixel peeped both images). Maybe you did something between the two images (slightly different focus or adjustment?).
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Good for a first go! Your flats need sorting out, and a bit of balance on the background to sort out the blueness - but I'd say youre well on the way!
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I see you have discovered the limitations of the SWCC, it is less apparent in narrowband (and non-existant in Ha) - but it is a problem when it comes to handling bright stars. Best way around that is to invest in the Baader MPCC MkIII, that has no reflections whatsoever. You can (as I did) swap and change between correctors according to your target - ie: if you have no bright stars in shot - you can use the SW.
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Great image! But, I dont think I could ever justify a FT focuser as they are horrendously expensive. I'd consider it if I was using an 8" f5 or a quattro, but buying one just for the 130 seems a little bit of an extravagance!
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Depending on what camera you are using (chip size), you will have about a 50% useable field - maybe a bit less (ie: you will end up cropping half of it out) without a coma corrector. It will get real ugly towards the corners.
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Hint: Dont get a VX6, 1/10 wave optics make no difference when it comes to DSO imaging If you want a 6" get the 150pds - or if you want the wider field (for large nebs) get the 130pds. When it comes to small newts, Skywatcher have got it licked.
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Just had a closer inspection of it, and the coma seems worse on the right hand side of the image. That would suggest some tilt in the imaging plane, as a short term solution you can focus your telescope with a star placed on that side of the frame (not centrally placed), that should help balance out the field a bit. I noticed a fair smattering of hot pixels too, but oddly - they dont seem to be travelling in the same direction across the frame. Its almost as if they are subject to a rotational pattern... was your PA good enough? or did you rotate the camera at all during the shoot? Edit: The presence of coma on the right side may suggest that the spacing or placement of the corrector (in the drawtube - ie: tilt) is too close. Fortunately, the Baader does have some tolerance, so you can increase the spacing in steps of 0.5mm if possible (mine turned out to be 57.5mm). You will know when you have gone too far becuase the coma distortion will become a radial distortion.
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The new image looks better, miles ahead of the other
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The star issues seem to be across the entire frame, you need to check the following: Collimation CC Spacing Whether the corrector and camera is seated in the drawtube correctly (no slop or tilt). Also, was the shot taken with any guiding? Becuause trailing can occur easily in 30s if unguided - the smaller stars close to Arcturus give the game away (as theyre all eggy in the same direction).
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Newtonian Astrograph vs refractor
Uranium235 replied to Ohm's topic in Getting Started Equipment Help and Advice
Maybe you should look at the mount first, because whatever telescope you choose - sticking it on an insufficient mount wont be any good. The HEQ5 would be considered the minimum requisite for good imaging. The pecking order for AP is mount>camera>optics. -
Focal Reducer vs Pixel Binning?
Uranium235 replied to The Admiral's topic in Getting Started With Imaging
Thats a question I've been asking myself for quite some time! And it confirms my hunch (ie: in relation to Maxim 2x2 software binning) - no, its not as good as hardware binning. -
Looks pretty nifty.... Im impressed! Its much the same thing for bashing a 130p into imaging. However, you will definitely need to make a cover for the bottom of the tube now, because there will be a substantial light leak around the edges of the primary.
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