BrendanC

Thanks - I think that, if it weren't for APT actually asking me to specify the diameter of the aperture and the focal length, I would assume it's fine too. But the fact that it's asking, so that the Bahtinov aid can do its calculations correctly, makes me think I probably should absolutely get this one right! Otherwise everything might be very slightly out of focus, which I'd rather not realise several months down the line...!

Hi, I have a Bahtinov mask that I originally got for my scope (a Skywatcher 130PDS) before I got a coma corrector. The scope has a focal length of 650mm. The coma corrector reduces this to 590mm. So, in the APT Bahtinov aid, should I specify the focal length for which the Bahtinov mask was intended (650mm), or the focal length now that I use the coma corrector (590mm) - or should I get a new Bahtinov mask?! Or doesn't it matter? Thanks Brendan

Mmmmmmkay, just read up on this, western hemisphere always has negative longitude, so -0.931339 is by definition West, which means I can specify it as 0.931339 West. If I'm wrong, please shout, like this: "AAAAAAAAAAAAAAAAAAAAAAAAAARGH!" Thanks, Brendan

Hi, On every other bit of astro software I've got - Stellarium, APT, EQMOD - I can specify my lat long as either RA and Dec, or using the equivalent decimal versions which comprises a positive latitude and, for my location, a NEGATIVE longitude value. So, I don't actually know how to convert this into the Sharpcap Polar Alignment settings field, which asks for positive decimal versions of both. So, given that my longitude is 00°55'52.8"W, which is -0.931339 in decimal... how would I specify this as a positive value in the Sharpcap longitude field? Would it be 0.931339 East? I know I could just ask Sharpcap to take the ASCOM mount values, but I'd prefer actually to see the correct values in front of me because I'm funny that way. I told you it was a seriously dumb question.

I've had a suggestion this could be backlash, and that I might need to experiment with being east-heavy. Any comments welcome!

So I'm still getting walking noise with my image acquisition - I'm going to ramp up the dithering, make sure it's dithering in RA and Dec, and try and get my polar alignment better. However, on inspecting individual frames it seems I have an even worse problem. Take a look (you get a better sense of what's going on if you click the image below then you can see it 100% size...) I have trails that go horizontal to the right of the image (zoomed-in bottom right section below)... ... but then seem to curve up towards the vertical on the left! (zoomed-in top left section below) The brighter stars also seem to have a 'judder' to them. It's the same for every one of the 155 subs. How can this happen? This is from a 130PDS on an NEQ6 mount, camera is a modded EOS1000D with Skywatcher coma corrector. I'm using DARV for polar alignment in APT. The subs were 30 seconds, just tracking, no guiding. Control was via APT, using APT's own dithering module, via EQMOD directly connecting the laptop to the mount. There is no stretching or processing on this image, other than converting from raw to JPG to upload it. It was a really clear, calm night, no wind. The mount is on the grass, not concrete, and I made sure it was level. I've been able to get 30 sec subs easily before with pin-sharp stars. I'm stumped as to how this could have happened. Tripod not level? Camera not secured? Collimation? PEC? Is it optical, or mechanical? Little goblins coming out at night and shaking the tripod? Any/all suggestions welcome. Thanks, Brendan

In relation to the stored backup image, I believe that's part of a regular week-round backup housekeeping procedure. I found this out (to my relief) when I froze my laptop after a particularly cold photography session! So that might account for the image disappearing after 8 days. I use Macrium Reflect free to back up my Windows partition. Problem is, if updates genuinely do cause problems, you can't really keep returning to the backup. I do know that recent updates have changed my sound and pointer settings, which was not expected. I think privileges is part of this problem. It was suggested initially, but I don't see how it could have changed so many things throughout my system. More research needed I think. Thanks for all the feedback anyway.

Point taken. Looking into other causes now. All alternative suggestions welcome!

Thanks for the heads-up - and in fact you make a very good point about checking the Windows Update History because I just checked, and the last one was in April, which predates my problems. So, something else must be causing bother. Time to run a full av scan and look for other problems. I can't have this happening every month or two...

The other day, I noticed that all my settings had disappeared from APT - my location, plans, preferences. Everything. This had happened once before and the always helpful Ivo suggested it could have been some change due to Windows updates, maybe admin settings. It didn't take long to get it set back up and I've since saved all the settings onto a different drive. So, that was that. I just put it down to 'one of those things'. The next night, my scope wouldn't connect via EQMOD. I've only recently been able to get it to work so my heart sunk. However, a quick look at the setup revealed... all the settings cleared. Location, COM port, everything. As Oscar Wilde might have said: "To lose one set of preferences may be regarded as a misfortune; to lose both looks like carelessness.” But I'm not careless. I have backups of backups. I'm meticulous about antivirus, security, system maintenance. I've built computers in the past so I know what I'm doing. So, as the heavens wheeled above, by the red light of my little headtorch, I managed to get it set up again and continue as if nothing had happened. THEN, today, I had a sudden thought: what about Stellarium? I'm using that to move the mount. I've been experiencing walking noise in my shots, even though I thought my polar alignment was ok, and I've been using dithering and drizzling (although I'm still not using guiding, I know I need to bite that particular bullet sooner or later). I'd also noticed that the past couple of times during alignment, the first two stars I'd chosen were quite far out, by what seemed a similar amount. Could it be that Stellarium's settings had been cleared out too? Indeed they had. Stellarium thought I was in Greenwich, UK, which is 60 miles away. Some fancypants maths would probably prove that the distance the stars were out by, would equal the time differential to Greenwich. If I lived further away this might have been more apparent as a problem. So, something rather drastic happened to my laptop recently, and I think it could have been a Windows update. I'm just flagging this in case anyone else notices anything similar. Or, if not, then it could just be me. It usually is.

Update: APT doesn't dither un-guided shoots automatically, so I've switched that on. Fingers crossed. I'm still going to do the 'blocks' of shots anyway, the idea being that I maximise the chances of success and eliminate stuff until it stops working, rather than keep failing and adding things until it works.

Hmmm, looks like APT does in fact dither non-guided shoots automatically. So, this won't cure it. One thing I used to do with the AZ mount was to shoot in 'blocks' ie use platesolving to get the target in the centre, shoot say 100 subs, then repeat so that the target was back in the centre. It was the only way to cope with the mount's inaccuracy. Now, I totally get that I need to improve my polar alignment, but as an interim fix (ie so that I can make the most of tonight and tomorrow, which are rare good nights in the UK!) would this help?

Thanks for this, plenty of food for thought. So you think they are separate issues? I'm using APT for the acquisition, I should have mentioned, and I think it has dithering features which I'll look into. I'm still getting acquainted with the NEQ6 mount too, so lots of new stuff going on (I had an AZ Goto mount before - so inaccurate that it kind of had its own dithering built in!). New mount, new calibration library, and this is the first time I've attempted photography during summer (started last Feb). So, dithering might fix the walking noise. I'll see what I can do about the banding. Thanks again.

Absolutely no idea, sorry. There are some reviews out there. Generally I think, given the price, it's much more suited either to people who are very rich but don't want the hassle of kit, or community outreach where people want to see electronically enhanced images in real-time.

I'm acquiring images with a modded Canon EOS1000D, with Skywatcher coma corrector, via a Skywatcher 130PDS on an NEQ6 mount, no guiding. The other night I captured part of the North American Nebula and noticed some curious streaking in the image, but didn't know for sure whether it should be there. See below - it's a fairly ok image but you can see persistent streaks going up from bottom right to top left, almost as if it were a pencil shading (this was taken portrait). Last night I captured around 250 30-second subs of M13. As with the above image, I stacked in DSS and applied darks, dark flats, flats and bias frames and noticed the same streaking. Given that this and the previous shot are the first I've taken with my new calibration files library, I wondered what would happen if I removed all the calibration files to see if it was the subs themselves. And it was, see below - stretched image to show the streaks, although now they're going from bottom to top because this was taken landscape. One thing I'm extremely aware of is that this is not the best time to take photos in the UK because we don't reach astronomical darkness until the end of July. So, could this just be an effect of taking shots when it's not really dark enough? Or could there be something wrong with the coma corrector (ie check there isn't any smearing), or the sensor? I doubt it's the mirror. Or is it something to do with Deep Sky Stacker? I've been through all the options and set them as per recommendations for StarTools (which I use for post-processing, and which I used for the nebula shot). These were all 30 second subs taken at ISO800. I've never seen it before. Any ideas?

Anyone fancy using a Stellina with huge amounts of localised light pollution?

Outstanding. Thank you so much for your help. You make a great point about Sharpcap picking out lots more stars so that the logo really doesn't have much impact. I have actually tested plate solving with an image from my setup in Sharpcap and it worked. So, I'll have a play around. Thanks again!

Hmm, just managed to get it to try and plate solve a daytime shot, just to see how it behaved, and it's picking up all the dots in the Sparkocam watermark as stars. So this is almost certainly not going to work unless I pay £40 to remove the watermark and THEN test whether it works. Which I'm not prepared to do. So, if anyone else has used this combination, it would be good to know, other looks like Sharpcap Pro polar alignment isn't for me.

Thanks all - and it's a good point about the SNR for flat light images, I guess ideally they'd be at the same temperature but they're really for removing artefacts such as vignetting, dust etc. So, same flats across all temps it is, but taken at the shoot rather than in a library. Thanks.

I recently created a library of calibration files across a range of temperatures. It is a thing of rare beauty - dark flats, biases and darks at a range of temperatures to match the subs. So, if I have some subs at 24C and some at 25C, no problem, I just use groups in DSS so I have darks, dark flats and biases for the 24C group, and the same for the 25C group, etc. All good. However, I realised the other day that I don't know how this works with flats (ie light flats, not dark) when there's a range of temperatures involved (I use a non-cooled DSLR so I can't control the temperature). I understand that, as opposed to dark frames, they ideally need to be taken with the exact equipment used during the shoot because otherwise orientation, dust motes etc could change. So, that precludes building a library of them. They should be taken during the shoot at some point. But let's say half of my flats are at 24C, and half at 25C. What do I do then? Do I have to take loads of flats at 24C, and another load at 25C? This might not be too much of a problem but what if I really do get a range, like from 20C to 28C or something? What then - are 8 separate sets of flats needed? I'm kind of thinking that, assuming there's not too wide a range, I could just use the same flats for each group. So, if I have subs at 25C, 26C and 27C, I apply the relevant calibration frames, but apply the same flats for each group. Or, is it viable to create a library across a range of temperatures, if I'm very careful to make sure the camera is oriented the same every time? Or is this too risky, as I'd imagine even slight misalignment could cause real problems ie instead of removing artefacts it would in fact double them. Does this make sense?

If it works with the watermark I'd be ecstatic. Sounds fairly robust if it works just by pointing at your screen! I don't have a lens however, it's a DSLR hooked to a 130PDS so I'd probably have to show it the screen from somewhere across the other side of the village where I live, which is impractical. If it doesn't however, then I'd still need to know whether anyone's had any luck with the non-watermarked version ie whether it actually works at all, or whether it's a waste of time/money. From my experience with astro stuff so far, if something works, it's a minor miracle. Still, when some half-decent weather appears, I'll give it a go.

Hi, Has anyone used Sparkocam with their DSLR for Sharpcap Polar Alignment? I tried using the open-source ASCOM driver for my Canon EOS1000D but it didn't work. However, Sparkocam seems to work very well with Sharpcap so far, as in it provides a video feed and I can record it. However, the trial version has a huge watermark on it which I'm sure will confuse Sharpcap's polar align solving. So, before I shell out money for the non-watermarked Sparkocam, can I ask whether anyone has had success using it for polar alignment? Thanks, Brendan

Thanks again. I already tried exactly what you suggest, increasing the timeout and number of tries, with no luck. Even FLO got back to me and said it should work! So, it looks like this is just 'another of those things'. EQMOD is working fine now, I've managed to get Stellarium talking to it too which sorts me out for initial alignment (although I had to use Stellarium Scope to make that work, which I shouldn't have, but still...) Onward and upward.

Thank you!

Errr... success? Tentative, but I just went through the EQMOD setup and it sprung to life. I could immediately hear the high-pitched whine from the mount and everything works. I would still much have preferred the app to have worked, simply because I was so familiar with it. But I guess EQMOD is probably better in the long run. There seem to be more people out there who are more familiar with that kind of setup, than there are using the app. So, I'm if not a happy bunny yet, a slightly less disgruntled one. EQMOD would appear to have given me some of my gruntle back. Thanks everyone for your help again, especially @stash_old.