The Admiral

I second that. I wouldn't worry too much about the stoma, I gather people get on with them OK, and in any case, it does mean that there shouldn't be a recurrence as the badly affected part of the intestine will have been removed. So life might actually be easier. I wish her a speedy recovery. Ian

I hadn't realised that the Evo mount drive now included a worm gear, and it would be interesting to see how it performed in imaging. It's not sold separately however, though it can now be had with the Edge 'scope, so I guess that must say something about performance expectations. The beefy mounts I referred to can be used in both altazimuth and equatorial mode, so there wouldn't need to be any extra work involved. Their software allows for that option as well. What we don't know about them though is how they perform in alt-az mode for AP, 'cos in general they are not used like that. You are correct, in theory one can take say 3x30s subs or 9x10s subs instead of 1x90s, and there'd be more chance of getting an acceptable frame, except that each picture has an associated read noise so one ideally wants to minimise the number of subs. Conversely, I suppose, one might be able stack a greater proportion of frames, and also reduce the risk of saturating bright stars. But an hour or two's total exposure is a heck of a lot of 10s subs! I think blue bloat reducing filters are available I believe, but I'd hesitate to guess what impact that would have on a full colour image. Ian

Thinking a bit more about this, probably the biggest improvement might be in the form of a focal reducer. I bought a 0.79x reducer for my refractor so that I can image larger scale objects, as I always have to crop off the outer parts of an image because of field rotation. I've not had a lot of opportunity to use it yet, but I have found it gives higher scores in DSS, presumably because the mount movements impact the image less and therefore the stars are rounder, and of course an object will be that little bit brighter (i.e. more photons per pixel than without using it). The image of M57 I posted on May 29th used the reducer. The only thing is I'm not sure how well they work with Newts, I think I read somewhere that achieving focus might be a problem. Perhaps someone with knowledge on Newts can come in here. I see that there is a coma corrector for the 130P-DS which has a 0.9x reduction, though that's not a lot. I'm not sure how these would reduce coma either, or whether one could be found that would work with your 150p. Glad to hear that your Mum is making progress. Ian

Well I think I remain to be convinced of that happy-kat. I do find that quite a few of my subs show streaking, and I limit my sub-length to 30s (convenient because I don't need to use an intervalometer, and most of my imaging is towards the south anyway). Nige seems to get good results from his mount. Perhaps I don't manage to get the best out of it. It does have a decent tripod though. Ian

Hmm, that's an interesting way around controlling the field rotation gizmo. But as Calli says, the limitation is going to be the relatively poor quality of tracking provided by the amateur alt-az mounts. If only mount manufacturers would put effort into refining their products to meet this, admitedly somewhat limited, need. Somehow, though, I think we're going to be stuck with what we've got. One of the problems is that folk tend not to use the more expensive/beefier AZ capable mounts for astrophotography, so we get no feedback as to how good or bad they are in this role. I think it needs a well-healed person to experiment for us Ian

I'm sorry to hear that Nige, I hope all goes well. Mum's are far more important than astronomy! Ian

Glad you like it. I think that your pic certainly qualifies I for one would be very interested in how you'd find your AZ-EQ6 for imaging in Alt-Az mode. With the perception that Alt-Az is only going to be used for visual astronomy, the tracking movements of Alt-Az mounts aren't especially refined. One would hope that the AZ-EQ mounts, being dual purpose, might do better in this regards, but I really don't know if that is true. So any feedback that you can provide would be very welcome. Our humble mounts generally provide a mix of images, some with point-like stars and others showing clear streaking, even taking into account the effect of field rotation. It's just that the tracking is somewhat coarse, and it depends whether an exposure coincides with a particularly jerky movement. The effect worsens with exposure time, and 60 second exposures are pushing it. Please let us know how you get on. Cheers, Ian

Yes I think you are right, I'd sort of forgotten about that limitation! What I've yet to find out though is how much better, if any, the more up-market mounts like the Skywatcher AZ-EQ series or the iEQ45 or the new iOptron AZ PRO GOTO are when used in Alt-Az mode, compared to our more lowly steeds. Ian

Hmm, not sure I'd go along with that . It's still using an Alt-Az mount; just an alternative to taking short exposures. It would be an interesting project, and quite complicated to control as the rotation rate varies according to both azimuth and altitude. Steve sent me this link in a PM; I believe the software provides the control http://www.optecinc.com/astronomy/downloads/altaz_server.htm Ian

I'm not sure if that applies to Alt-Az mounts though. I've seen reports of my Nexstar 6/8 being well over-(theoretical) loaded. Balancing is critical though, I believe, as well as the length of the equipment attached, and of course the mount will suffer a greater rate of wear. Still, I think Nige does well with his gear. Ian

Nige, I think that your train of thought mirrors my own to some degree (no pun intended!). First things first, I'm lucky enough to own an APO and I'm very pleased with its rendition of stars in my astrophotos. I know that Steve Nickolls owns a Startravel 102 and he struggles with blue bloat, which he freely admits to having. What keeps coming to my mind, though, is that being limited to short exposures with an Alt-Az mount, I'd like something which has a much greater capacity to hoover up photons, yet with the same sort of focal length (715mm), or may be a bit shorter. But then I come back down to earth, because even if I went from my 4" refractor to a 6" refractor, that is only going to give me just over 2x the number of photons for a given exposure. And a 6" APO is going to be both very expensive and a lot heavier. An alternative would be, say, an 8" (200mm) reflector which would give me about 4x the sensitivity. Now we're cooking, but, an 8" reflector with a ~700mm FL (i.e. f/3.5) is a specialised beast. Cost again, and not to mention sensitivity to poor collimation and fine-ness of focus, i.e. it's going to need special care and attention. Given that I have to drag my gear out each time I want to use it, that's not very practical either. And then all these monsters will be too big/heavy for my existing mount, so then I'd have to look for an alternative mount! Which then raises the question: "EQ or ALT-AZ?" This is where one sees the merits of an EQ mount, 'cos you can use a small 'scope, like an Esprit 80ED, and just lengthen your exposures, and not worry about field rotation. And then, perhaps, add guiding. Hmm, here we go, costs are beginning to escalate. This is all fine of course, if you have an observatory where you can set everything up and leave it, but for me, in addition to having to set up each time, I can't even see Polaris. We get so few opportunities to get the gear out that I just want to get everything set up with the minimum of fuss. Which is why Alt-Az imaging appeals. But at the end of the day it is going to be a compromise. I'm not sure if this ramble helps. As the FL of your 150 is a bit longer than the 130P-DS, there probably wouldn't be much difference in the number of photons per pixel, so their sensitivities I guess would be much the same. It seems to me that if you are getting good results from your 150, and you are, why would you want to change? I think it might be a different answer if you were using an EQ mount , mind. By the way, I like your M31. That's something I've yet to have a good go at, but a bit later in the year I think. Ian

That's come out rather well Nige, the nebulosity is nicely defined. Looking up the specifics,I see that by 03.00 it is at an elevation of 80° and almost due south, at which your exposure time needs to be around 5s to keep field rotation in check! You certainly are pushing the envelope. NGC7000 is a huge object. Are you planning to do a mosaic? Ian PS. Ah I see that in the past you posted images of different parts of NGC7000. I'm losing your plot here! PS2. I take it you managed to get your sensor clean without problem?

Nice one Nige. I went out last night for the first time in ages; the sky seemed beautifully clear but it was rather breezy. My aim really was to visually observe Saturn, though I did try to image it as well. I can't say it was entirely successful as I don't have a lot of magnification available with prime focus imaging, even though I used a 2X extender, and what with it being so low down. It did cross my mind to try a spot of DS imaging as well, but when I tried a frame it was clear it was by no means sufficiently dark. I don't have the staying power for the early morning imaging that you do. But as you say, even that is curtailed at this time of year. Ian

Well, StarTools claims to work on Linux, though I've not tried it. Has anyone here? "StarTools multi-platform processing engine and UI (User Interface) presently runs on Intel Windows 32-bit and 64-bit, Intel MacOSX 64-bit, Intel Linux 32-bit and 64-bit, and ARM Android 32-bit devices. " Ian

Have a look here: http://www.eos-magazine.com/articles/cleaning/partone.html As good an article on sensor cleaning as many others. Ian

And also, don't use any old rubber bulb to squirt air at the sensor, because its interior surface is probably coated in talc and you don't want to give it the grandmother treatment . Apologies to grandmothers everywhere! This is the business http://www.giottos.com/pro_view.aspx?nId=8&TypeId=77 Ian

Nige, I've fortunately not had to clean my sensors, but I know it is an exacting job and folk do get put off for fear of doing damage or making things worse. There is a lot of information on the photography forums on steps to doing it, and I'd really recommend perusing those before tackling the task. I believe it is quite straightforward though, it's just that the methodology is exact, and there is a choice of specific products, some of which are best tried first. The 'rocket airblower' is the first step, and if it works, great. Don't use any old air blast though as it can put more on than take off! The 'rocket blower' is specifically for cleaning sensors. Cheers, Ian

Nige, the sensor probably doesn't have smudges, just bits of dirt. Often the front face of the 'sensor' is some way in front of the plane of the sensitive array, so shadows are cast, making them appear a lot larger than they are. I'm sure you know how to test, but if not, put on a lens and close the aperture to the smallest possible, then take a picture of, say, a blue sky, or a least an area of reasonably uniform light level (much like doing a flat in fact). Best to see if they'll go with a puff of clean air (not air and spit!) before attempting anything more dramatic. Sorry if I'm teaching you to suck eggs here. Good luck with getting it clean, Ian

In principle, yes, but the question is how do you centre for each shot? I think in the 'early days', when film emulsions were used for recording, it was customary to manually keep an object centred over long exposure periods. Nowadays of course that's what we have motorized mounts for. Whether it is an EQ mount or and Alt-Az motorized mount, once set up correctly both will keep an object in the centre of the field of view. The difference is that with an EQ mount the whole image appears fixed within the frame, whereas with the Alt-Az mount only the centre of the image remains fixed and the rest rotates around it. Thus one can make long exposures with an EQ mount, but the Alt-Az limits you to just tens of seconds before the rotation becomes too visible. So the way we do it is to take lots (and I mean lots) of short exposure images and them stack them in a program like DSS. EQ mount users take fewer, but much longer, exposures, and stack those. Hope that helps. That's a good start Peco, but you will find taking multiple frames and stacking will make a big difference. If you take pictures on a static mount, which I guess is what you've done, you probably need to reduce the exposure time to prevent star trailing, and just take more of them! Don't worry too much about underexposing stars, as they're bright points of light and by the time a lot of frames are stacked and processed, you'll have adequate brightness. The same is not true of fainter deep sky objects though, where you need to maximise the exposure time within the constraints of your mount. Ian

Some nice images there both Steve and Nige. I attempted NGC6910 and the surrounding nebula, not far away from NGC7000, last Sunday. It initially looked good, but it was all cut short when some cloud rolled in. I only managed 20 minutes, about the same as for Nige's image, but not having the benefit of a 6" aperture it really isn't up to snuff. Anyway, there was a lot of water in the atmosphere and I think that affected seeing as well. It's difficult to know what is causing those smudges Nige, I've not seen anything like that on my images, fortunately, but from what I've read it could be dust on the sensor. If you've got a 'rocket blower', try a squirt from that to see if it'll shift. I'm not at all familiar with Newtonians, but I guess the other thing is something on the secondary, but wouldn't that be too far away to give such a well-defined marks? I tend to think that counteracting the affects of dust by using flats is a bit of a cludge, far better to get rid of the dust in the first place, as best as one can at least. Ian

Good capture Steve, and well done for having the fortitude for imaging at this time of year! Ian

Thanks for your comment Ken, and yes you are probably right. I always seem to have trouble with star colours and often get pink stars, and M57 should really go blue-cyan-orange and not blue-cyan-magenta. Might have another go tomorrow when I feel a bit less jaded after last night's extended day. Us olduns can't take these late nights like we used to . I hope the house move goes smoothly. Ian

Things have been a bit quiet around here; the truth is I find late nights difficult! Anyhow, I've just acquired a 0.79x reducer/flattener and I took the opportunity late last night to try it out and see if I could optimise the sensor spacing. In order to minimize the risk of trailing I used 15 second subs and only took 10 at each setting. That enabled me to find frames with minimal trailing and look at the distortion of the stars near the corners. Anyhow, as I was looking towards Lyra I also captured the Ring Nebula, so I wondered what I'd be able to get out of those 10 subs. Surprisingly, I thought it worked quite well, considering that the integrated exposure was only 2½ minutes! This is without the reducer/sensor spacing being optimised. Here is M57 enlarged. As usual, the set-up was an Altair Wave 102mm f7 SuperED APO, TS Photoline 2" 0.79x reducer/flattener, Fuji X-T1, Nexstar 6/8SE Alt-Az mount, 28 May 2016. No flats or darks used, though I did use bias frames (~50). Stacked in DSS, processed in StarTools, and finished off in Lightroom and PWPro. Cheers, Ian