The Admiral

Hmm, that's interesting, I can't see how that works with an Alt-Az. I guess it must assume that the mount is perfectly level, and then if it knows where Polaris is it can make the 'scope rotate around it. I think I'd prefer the synscan unit with it, at least then if you align to a couple of stars it'll take account of any mount not quite levelled. Still, that wouldn't account for the apparent complete lack of tracking. Any ideas why? Do you have a mains power supply you can check it with? I had a quick look on t'internet for this mount, but it doesn't seem widely available, and only then with a 'scope. Ian Edit. Ah, I've just looked at the manual for your scope. I see it depends on setting it to point to true north and the 'scope levelled prior to switching on. So I see what you were saying, that it pointed to Polaris OK after starting, indicating that it had got its alignment right.

Sorry Happy-kat, I didn't quite follow that. I presume that you didn't use Polaris as one of your alignment stars? Ian

Thanks for your response Martin, and for returning to this ancient thread! Ian

Thanks Louise, I can see that they will enable longer exposures as a result of a reduction in apparent sky fog, but to what extent do they reduce the light from white light sources like galaxies/stars? Ian

I'd really like to settle the issue in my mind about whether a light pollution filter will need much by way of increase in exposure time. The Hutech blurb says: Filters increase exposure times. While light pollution suppression filters will slightly increase the exposure times of emission line objects in their bandpass and affect broadband sources somewhat more, they do not require increasing the length of an exposure. However, because they increase the contrast of emission line objects compared to the sky background, it is usually desirable to increase exposure times to make better use of the imaging media's dynamic range. This is a little bit ambiguous about white light sources, but certainly if one looks at the transmission curves, the transmission is nigh on 100%, apart from the notches of course. I find it hard to reconcile that the reduced contribution of light intensity due to those notches could amount to half of the total exposure. So when you say up to double the exposure, I presume that that is from practical experience? Ian

Yes I agree, there seems to be so much more contained in that second image, different processing not withstanding. Looks like that filter could be a winner. Ian

Doh! Why didn't I read it properly? Ian

I don't understand why flats should worsen the detail. The stars are so much less distinct fewer clearly visible in M42. Ian

Indeed! Did you wade into the fray with a suggestion to check out this thread ? In the nicest possible way of course! Ian

That's a lovely combination of nebulae Nige, and it shows just how bright they are. Did you try the HDR module - reveal? As a matter of interest, did you try wiping without using a mask? I must admit that on the occasions when I've tried using a mask it's not been that successful. Ian

I must admit I think that is the direction I'm coming from. Ian

I would really hope not Neil, surely the imaging fraternity can't be that polarised. If it is then I would worry about the mindset of astro-imagers. There needs to be space for all approaches to imaging. Ian

Well I do use an APO, though the mount is a basic Nexstar, and the whole caboodle cost rather more than €1000! I think 'budget' is not really a sufficiently well defined criterion to be honest, and a very personal one at that, and I have my concerns that we should keep the Alt-Az criterion for its own particular demands. It is, after all, a proposal with regards to the "No EQ" thread which we Alt-Az imagers post to, and I wouldn't want it to end up being a catch-all with no particular focus. Ian

Ken I think, at least for me, you've hit the nail on the head. Currently the thread is well defined, and I feel it would cause confusion were it to be "all embracing". Ian

Thanks for interesting reply Neil. I'm in a quandary with this, because as a strictly Alt-Az imager I've found the "No EQ" thread to be engaging, but feel that now it's become a bit of a mess, although quite specific in its remit, and it's quite difficult to find the information and images I want. I think it deserves a place on the Lounge in its own right, to (1) allow a more structured approach to the information contained, and (2) because I think it has sufficient profile now, and traction, to make it viable. I understand clearly where you are coming from in suggesting that perhaps it ought to contain matter connected with short exposure EQ imaging, because it poses some of the problems faced by Alt-Az imagers. Alacant has also suggested, again for perfectly good reasons, that perhaps the new thread ought to cater for achromatic refractors, though presumably that would include such refractors mounted on a well aligned EQ mount. And so I fear we are moving away from our original premise to provide a vehicle for Alt-Az imagers with the prospect of opening up the field. You mention "topic bloat" in your reply, but that is just what concerns me. Anyway, all this may be moot if we can't have a new forum section. Ian

I suppose it also raises the question about the management structure of this site, and to whom or what any requests for a change should be made. Who is ultimately responsible? I take the view that moderators are there to ensure that Site Rules are followed, deal with conflicts, and to refer back any issues, technical or otherwise. They cannot be dictators of core of policy, surely? Ian

Well said everyone, and far more eloquently than I could. It's difficult to know where to go from here without knowing what Admin's response to you was Nige. Nige, I'm not sure if you are aware that all I get in that link is "Sorry, we can't show this content because you do not have permission to see it." I suspect that as it is a private thread that only you can see it. I think you'll have to cut and paste. But I agree with Steve, this needs to be a democratic decision and provided it can comply with the rules of the Board and doesn't cross lines, then I see no reason why our request cannot be granted. At the end of the day, it is our blogging site, and without us it wouldn't exist. But as I said, I do not know why the request was rejected. Ian

Whoops, can't delete a post already posted. See below

I agree it is a promising first effort. There's plenty of star colour there and with 250mm at your disposal you should capture a lot of photons at good resolution. Any reason why you went for such short subs? Is this within what one might call video astronomy? My guess is the definition becomes a bit blurred here. Ian

Not necessarily. This thread already has over 1500 posts and leads the field, never mind how many folk contribute. Also, by focusing on the subject and making it easier for our achievements to be seen, it may attract others into the fold who are teetering on the brink of doing astro-photography but are put off by the thought of what is supposedly required. Hopefully Ian

If I understand things correctly, the large 'scope will hoover up (14 squared)/(5 squared) more photons per second, i.e. ~7.9x faster. However, their respective focal lengths are important too, because the longer the focal length the more magnified the image is on the sensor, and therefore the lower the number of photons per pixel, which governs the sensitivity. However, in this particular case their focal lengths are very similar and so the image sizes on the sensors will be about the same. Hence the larger 'scope will throw ~ 7.9x more photons at each pixel than the smaller 'scope, assuming that the same camera is used. The smaller 'scope would therefore theoretically require ~ 7.9x more exposure. In fact, I believe the sensitivity will be inversely proportional to the square of the focal ratio, so actually the correct figure is 6.76x. That might not seem like a lot of difference if we are talking of 1s subs, but it's the difference between 1 hour total exposure and 6¾ hours total exposure! I penned a short consideration of the factors involved, which I think is correct . I've attached it in case you are interested. Ian Is the F ratio Myth a Myth v3 .pdf

This is something that Steve and I have discussed occasionally, and I'd be up for it. One of the things that prompted me was trying to find images that would reflect our 'art', and trying to find them interspersed in 60 pages is no mean feat. So I'd like to see a thread (? sub-forum) devoted to discussion and a separate gallery thread (or sub-forum) to which we only post the best of our images. That way there'd be a single vehicle that would allow beginners and others to see just what this mode of imaging can achieve, and hopefully dispel any myths about astro-photography with 'basic' equipment. The discussion thread could actually be sub-divided, for mounts and processing for example. SM raises an interesting point in that the approaches used with Alt-Az imaging are equally applicable to using an EQ mount in its most basic form (apart from significant field rotation and altitude limits to accommodate). My only slight reservation I have is that using an Alt-Az mount is clearly distinct from using an EQ mount and is easily categorized as such. I'm not sure how one could categorize his EQ mount situation as it's more of a grey area, but if a suitable definition can be derived then it could be appropriate. Perhaps we would need separate sub-forums, one for Alt-Az and another for other forms of mount? We already have a separate video astronomy section, so I don't see why one for our imaging approach shouldn't be instigated. Just my 2d worth. Ian

I guess it really comes down to whether the SNR is improved, increased exposure or not. I can imagine though there the would be more potential with EQ imaging where it would allow greater sub duration. Still, we are scratching at the limits so any benefit to be had is worth seeking out. Ian

Interesting! Yes that is quite a difference Nige, but to my eyes the curly-whirly appears more visible in the one without! May be an illusion. Does the filter need more exposure? +1 to which filter are you using? Ian

Where there's a will......