The Admiral

You've done well with that Matt, and as Nige said, you've got the core well exposed. That's probably down to the short exposures. M42 may be bright, but it actually isn't the easiest of targets because of its large brightness range. There's a lot of dust around too, which needs longer exposures to reveal, so one often takes a range of exposures and blends them for the final image. The long exposure noise reduction function on the camera takes a second identical exposure but with the shutter closed, and then subtracts this background frame from the first frame. As Nige says, switch this off. For astro images, you do your noise reduction by taking a set of darks, and programs like DSS will stack those separately and subtract the resultant from the stacked lights. I think it would be worth taking at least 50 darks as otherwise you're likely to introduce more noise into your image than it corrects. Ian

Do you think? They're quite short subs, and you're not pointing in the worst direction for FR. Could it be a touch of coma? Ian

Thanks happy-kat. Yes, it was a frosty foggy morn, not long after sunrise. They don't make sunrises like that any more! Ian

The lens is not without it's issues. The early coatings were not as effective as they now are. Here's a pic I took, I suppose in the mid-70's, on film of course, so it's a scanned image. You can see the flare well defined, but then again the sun is quite bright. I was able to remove it in post-processing of the scanned image, not something you could do with an astro image. Incidentally, that's the natural colour, no filters were used. Well, I say that, but I probably had a skylight protection filter on it, so I guess the flare could be from that. It'll be interesting to see how it copes with bright star sources. Takes me back though . Ian

Well I guess whether you achieve infinity focus will be down to your Nikon-Canon adapter. Hopefully it will be sized so that infinity will be slightly beyond the focus range, in order to guarantee it. Ian

I don't think the Q200 was one of Nikon's finest lenses! Anyway, it'll be interesting to see what you get out of it. Ian

Have you looked at this site happy-kat? http://www.photosynthesis.co.nz/nikon/serialno.html#200 Ah, just realized I had one of those until about 5 years ago, but sold all my Nikon gear. I didn't use any of it for astro then. The serial number was 622056. Ian

You might be interested in this photo of Will Hay during a visit to the Edgbaston Observatory. I don't know when it took place. Ian

The link I gave you contains some information on field rotation, but I've used this site: http://calgary.rasc.ca/field_rotation.htm. There are other sources if you Google. This excludes any issue resulting from poor tracking, which it seems you may have as you say you have to re-centre often. I would expect the object to remain more or less centred over a couple hours, not perfectly mind, but drift needs to be slow otherwise you'll get star trailing. I can achieve this using my lowly Nexstar SE. It all comes down to initial alignment. I level my tripod accurately using a proper level, not a button level, and do a 2-star alignment. I guess bright stars will readily saturate your camera, given your aperture. M42 is a difficult target anyway, in that there are some bright regions, and so it is common to take short exposures and blend with longer exposures in order to cope with the dynamic range. There is some star trailing visible - aim for better alignment. Edit. Well, I say star trailing but I see it isn't over the whole field. I wonder if you have camera alignment issues as well. At f/2 I know that camera alignment is critical, but I have no experience to advise on that. Ian

Wayne, welcome to the world of Alt-Az imaging! EQ mounts seem to be king when it comes to imaging, a wedge on your mount would go some way there, but imaging on an Alt-Az mount is by no means without reward. The answer to this is to stack many, and I mean many, short exposure subs. The maximum length of the sub is limited by field rotation, and this will depend on where you are looking in the sky; in some cases it will be seconds, and at the most probably 90s. The other issue you will encounter is the accuracy of the tracking that the mount can achieve during the exposure time, and it is not unusual to find a percentage of subs which show star streaking. You should reject these and not stack them. This would be a severe problem with the C11 because of its long FL, but with Hyperstar you have a very fast, short FL set-up, which greatly helps. The light gathering power of your C11 compared to my 102mm refractor is huge! Might I suggest that you have a look at the long thread "The No EQ Challenge" (https://stargazerslounge.com/topic/228101-the-no-eq-dso-challenge/) where you will find a lot of information about doing Alt-Az imaging, and you can see what others (mainly with short FL refractors) achieve. Good luck, and keep us informed of progress. Ian PS. Visited Cape Town some years ago. Fabulous country.

Ah, in your signature, just realised that Ian

That's nice Shaun. I like the star colours and sharp stars. What equipment did you use for this please? Ian

I think that would be true Ken if field rotation was the limiting factor, but my guess is that in profdann's case it is just that the mount's general tracking isn't sufficiently good for such a long fl. Even at ~600mm fl I get a good proportion of 30s subs showing star streaking over the whole frame. Ian

I think it's come out rather well Shaun, but like Fabien, I too find it strangely noisy. As Neil says though, a bit of noise reduction on the image could work wonders. But, where is the noise coming from? I would guess that apart from benefiting from an increase in the number of subs, you should think about increasing the number of darks significantly too. It is oft said that you should take as many as you can, at least the same number as lights. The reason is that you are subtracting one noisy image from another, and the net result is that the noise will be combined and therefore increase. By taking as many darks as you can the noise introduced from that component will be minimised. Likewise bias frames I think, but to do that takes no time at all given the short exposure necessary. It is a chore I know, and that is why some of us are not bothering with darks and just using the bias frames as a substitute. If you are using a DSLR the value of dark frames is questionable in view of the lack of temperature control and stability throughout the session, and the fact that dark noise is very sensitive to temperature. However, on the other side of the coin its use does allow correction of the gross artefacts such as amp glow. Incidentally, this particular subject benefits from short exposures in my view because of the star brightness could be overwhelming. Ian

Well I think you shouldn't be disappointed with it, the core is well defined and the lanes are visible. But a bit more information about the image would be helpful, such as scope and mount, camera, number of exposures, exposure length, any darks and bias frames, stacking and processing software. If you take darks, make sure that you take plenty otherwise they can add noise. And yes, flats are probably more important. Ian Edit. OK, I see there is some info on the linked image, but it's quite helpful to have it on the post as well.

You've done well to get that Shaun. I didn't find it the easiest of objects, and I should think my Oxfordshire skies are rather darker than yours. Interestingly, your spikes seem pretty sharp considering field rotation and it being a combination of 3 sessions. Ian

What mount is it? As I said before, you won't be able to take long exposures. There are two aspects to this: general mount tracking, which to some degree is determined by how well you set it up, and field rotation, which you can't do anything about except keep exposures short. Depending on what part of the sky you are imaging, exposures will range between 15s and, say, 60s, if the general tracking of the mount is good enough. Have you looked through this thread? Does it raise any issues that you specifically want to ask about? Ian

Yes I did, and suggested he might get a more detailed response here than in the general imaging thread. Ian

That's a nice image Shaun, the dust lanes are showing well and you have colour in the stars. There does appear to be a blue 'wedge' associated with the bright stars so I suspect that is due to lens aberrations and you may never be able to sharpen them up more. A likely problem with a zoom lens with IS I suspect. Is it focus by wire? Sometimes they can be hard to adjust. Was this at full aperture? The chromatic aberration might be improved by stopping down. Ian

Welcome to the thread icebergahed. Sorry, bit of a long answer coming up (never let it be said I don't give value for money . But then I'm not getting paid for this!) First things first, a lot of imagers will tell you nothing less than an EQ mount will do, and then a dedicated astro camera is to be preferred. Totally untrue, but there are limitations doing Alt-Az imaging with a DSLR, but so long as you are content to stay within those limitations, all well and good. The principal limitation is that with an Alt-Az mount, the image will rotate as the target moves across the heavens. You can get around this peripheral star streaking by using short exposure times, say 30s or less, sometimes more, depending on which part of the sky you are looking at. The consequence of that is that you will need to take an awful lot of pictures, many dozens, if not hundreds, in order to suppress the noise in the image. The second thing is that Alt-Az mounts move in two directions to keep a target centred, in a kind of zig-zag pattern, and with the cheaper mounts these movement aren't necessarily very fine, and you will find that some of your frames will show star streaking, even if, on the whole, the target remains centred. You cannot use such frames and so you will end up discarding a percentage. This mount inadequacy is made worse when you have long focal length 'scopes, such as the 6SE. OK for visual, but a bit of a challenge with photography. You can ameliorate this by using a flattener/reducer, such as https://www.firstlightoptics.com/reducersflatteners/celestron-f63-focal-reducer.html. This does three things. Firstly it reduces the FL of the telescope and so it will be less susceptible to mount inadequacies, but secondly, and just as importantly, it will give you a wider field and in doing so will concentrate more photons onto each pixel. In other words, improve your recorded signal of these faint objects, and help improve your image, but at the expense of a wider overall field of view. Thirdly, it will keep the image sharper across the frame, rather than sharpness being confined to the centre of the frame. This isn't an essential accessory, but I think it would be worthwhile. Some others may chip in here. Interestingly enough, the starter of this thread asked a similar question about this back in 2012 (https://stargazerslounge.com/topic/167836-focal-reducer-on-nexstar-6se/). I'm sure that plenty of material on this can be found on this site with a search. Finally, I'd thoroughly recommend reading "Astro-photography on the Go - Using Short Exposures with Light Mounts", by Joseph Ashley. Good luck, and looking forward to see your images on here! Ian

I do very little solar imaging, but I did manage to catch the Mercury transit. I was clouded out initially so it was only a matter of luck that I managed to grab the first contact. Shown here is the transit at about 2 hours in, with an inset showing in a rather cloudy image, between 1st and 2nd contacts. Ian

Is that not a sweeping generalisation? TIFFs can be compressed, either losslessly or lossy, or uncompressed. I think it's an issue related to DSS isn't it? Some applications also won't open some compressed TIFFs I believe. Certainly something to be aware of though? Ian

Ah, me too! Ian

You most certainly can and welcome. Indeed, nice small and round stars, and an excellent 1st DSO. What camera are you currently using, how many subs and what sort of exposure? Certainly processing can't be undervalued, and although Photoshop can and is used for astro work, you might wish to look at other more specialised applications. I'm sure you already appreciate that there are essentially 2 types of trailing with Alt-Az imaging, field rotation which depends on the direction you are pointing the scope, and the degree of tracking. The former you can't do anything about, apart from limiting exposure duration, and the latter seems to involve black magic and in what mood the mount is in! Levelling and aligning are both critical though, but even after taking all the care you can, sometimes things just don't work out. I think if it was me I'd hone your skills with your existing camera. Don't foget that the larger the sensor the more obvious the field rotation will be at the frame edges, so you will end up cropping. Keep posting your images! Ian

I think he uses Regim, Neil. To be honest, I 've not got my head around how these values affect the final outcome, and I certainly haven't done any tests. By the sound of it, you have. Ian