billyharris72

Seems like perfect forum. Thanks for posting! Billy

No, it's not too bad. Trick is to shoot an avi or ser file for each, using a different filter for each. Then stack, sharpen etc. Align them in Photoshop or similar (Registax will almost certainly do this too, just have not worked out how) and then combine. That's the way most of the heavily published planetary imagers tend to work, and the approach as significant benefits (better management of seeing, CA and atmospheric dispersion, ability to use IR filters etc). Pretty much a prerequisite for recording detail on Uranus or Neptune. The difficulty, such as it is, is with planets with quick rotational periods, especially Jupiter. Without detotating the image (with WinJupos) you need to keep the overall exposure length short (about 3 min max). While that's easy enough with one shot colour it can be trickier with a filter wheel. You can grab less time for each channel as mono will allow faster framerates, but you probably will need to refocus between each filter (and if you don't you'll be losing some of the benefits of a mono camera). The usual way around that is to use an auto focuser, record the correct focus position for each filter and then set the whole thing up to do its stuff automatically. Can give great results, but starting to get complicated and expensive. In that sense, the easiest option probably is to buy a colour camera. But the best results will come by going the mono route. (P.S. if it were me, I'd go for one shot colour, especially if starting out). Billy.

Hi Tony: Colour is easy enough to do, but you will need to shoot through red, green and blue filters, process each image separately and then combine them into an RGB (colour) image in Photoshop, GIMP or similar. ZWO producesfilters and filter wheels at a reasonable price - you should be able to track them down on the First Light Optics site or similar. Billy.

This was 25 x 300s subs, with 15 darks (matched settings, shot about a week previously). Both shot at 0C. I did shoot flats (and they look fine) corrected with flat darks, but these were not applied to the image - I have an issue with field brightening near the edges, probably due to reflection, and the flats seem to make this worse (I think they are correcting for vignetting that is less than the brightening). I'll get back to you on settings - it's the ZWO software default "zero gain" setting, but I don't know the actual values off hand. Thanks, Billy.

That's a thought. I used 15 darks but more would not hurt. I also think longer subs might help, as these took a lot of stretching (mean pixel value in the calibrated image is lower than in the dark frame).

I've only started guiding quite recently and have not yet used dithering. I guess now is as good a time as any to start. 25 x 300s, stacked in AstroArt using sigma clipped mean. Be interested to hear how you get on. Interesting- I've noticed it before ( I seem to get it some times, not others). Any idea what causes it? Billy

Hi all: After my last post (I'm suffering a weird brightening around the edge of field that is not amp glow, is unaffected by flats etc) I cleaned everythig, turned the filter around and tried again - same result. A bit annoying but some post processing gets rid of the worst of it and I reckon a new filter will sort things out. However, on last night's run I noticed something else that's been bugging me for a while. My Ha images are typically quite noisy (hardly a unique problem) but also, the noise doesn't really look like ... well, noise. You can see what I mean in the shot below. The sky noise to me has a definite pattern to it, like a series of striations running top left to bottom right. I know it's not hot pixels that are drifting - my setup does not have that much drift and I'm using sigma clipped stacking, which (I imagine) should eliminate that anyway. As before, it's a ZWO ASI 1600MM. I don't even know if this is unusual to be honest, just something I noticed and thought looked odd. Any ideas? Billy

You too? I am seriously starting to take the hump with Mr Gates. If I could get my ASI120 (old version) to work under Linux I'd move back without a second thought, but I've had no luck there at all...

I've struggled with the same issues. I bought a collar type dew srtip from 365 Astronomy (wraps around the secondary stalk) but it tended to change the profile of the secondary mirror (which affects star shapes in images). I emailed Altair Astro to see if they have something that would do the trick (the ones on their site are too big) but that petered out. In the end I've gone for the DIY option, with a loop of 4 x 24 ohm resistors that is taped to the back of the secondary mirror. In testing it runs a bit hot, but I'll make a plug to connect it to the dew controller that I use for everything else and vary the voltage appropriately. Othr advantage is that can use thinner wire than commercial dew heaters, which won't unduly increase the profile of the secondary strut that I run the wire across. Not a lot of work and it should do the job nicely. Billy.

Peter knows what he's talking about more than I do. Do what he said!

When you say a smudge, can you say a bit more? Reason I ask is that it's hard to tell from the photo, with the way the light is hitting it - looks to me more like a piece of cloth or a scratch (don't panic, sure it's not!) or something. Assuming it is some kind of material do you know what it is? If it were me I'd be thinking about cleaning it (the corrector coatings are not that delicate) but if it's a big blob of grease or something I'd want to be very careful not to spread it around. If you do decide to clean it I'd start with a blower (not compressed gas) and then maybe a soft brush (a lens cleaning one). After that lens tissues (wipe once with each and disposee) and a spot of Baader optical wonder fluid for stubboorn bits. Just take your time and be very caseful not to rub anything you lift off over the mirror, as little grainy bits of dust can leave scratches. Seriously, it'll be fine. Billy.

Interesting thought Dave, and there is a slightly embarassing story there. Having changed from my Newt to the frac, and from M42 tube for my CC to T2 for the field flattener, I discovered last night that the threads of the Baader adjustable t-tube were fouling the carousel. That's when I reaslised I've been using the whole filter wheel back to front for about a year. Turned it round (in the dark, with much fumbling and swearing) and it worked okay - but of course it does mean that all my filters are now back to front - so yes, that could definitely be a problem! On the plus side, I reckon the data I've captured will be usable if cropped or blended into lumumance or red, so not a wasted night. Billy.

I'm calibrating with matched flats and flat-darks, but the issue appears whether I apply the flat frames or not, so it does not seem to be related to the flats. You're right about the filters - they are 31mm unmounted. I might try blackening the edges.

It's a mono ASI 1600 and unmounted 31mm filters (so pretty much 1.25", maybe a touch larger). Why do you ask - is this a known issue? Billy.

Hi all: An attempt at the Eastern Veil from last night in Ha. Shot with an ED72, Skywatcher FF, ZWO ASI 1600MM. 23 x 5 minute subs at (alleged) unity gain. Overall I thought it was okay until I looked at the whole image stretched and saw this bright ring pattern, almost like the opposite of vignetting (but then getting darker at the corners). I've tried to experiement a bit and have ruled out overcorrection from the flats - it happens even if I don't use flat frames. Neither is it the darks (just stacking the images on their own shows the same effect). Looking at the individual subs, I can't see this issue in any of them - yet picking subsamples of any 10 subs and stacking results in the same thing. Have stacked in both AstroArt (my usual) using additive, median and sigma clipped mean, and SIRIL (mean only). Same result each time. So, does anyone know what might be causing this? My working hypothesis is that this might just be the kind of optical aberration you get in any system and that it is showing becasue the image is over stretched (and that the individual subs lack the dynamic range to allow enough of a stretch to make this onvious). Sampling the dark pixels in the centre of the FITS image gave me a mean value of 172, while the background in the lighter halo is around 228. 50 ADU does not seem like that much. So, thoughts appreciated - do I have an optical issue, a camera issue, or am I just suffering lack of data and overstretching? Cheers, Billy.