ollypenrice

HOORAY!!!! I think that's nailed it... lly

Great images in my view. The Monkey Head is glorious. I might let the black point stay a tad higher, especially in LRGB, perhaps. It's very mild but there's a strange circular artifact passing through the centre of the galaxy. I wonder what's going on there? Olly

I've been happy to let Vlaiv and Alacant fight this corner but I suppose I ought to chime in since I'm probably guilty of having made an issue of the F ratio myth on this forum! Joe, what has been true forever is that, when aperture is the variable and focal length is the constant, an F5 objective has four times the area of an F10 objective so it lets in 4x as much light and so reduces exposure by 4x. Nobody is arguing with that. The first problem arises when focal length is not constant between optics being compared. The Hyperstar would be an obvious example. Point it at a small target first at F10, then at F2. Unlike the first situation we are now getting precisely the same number of object photons from the target. So is it faster at F2 than at F10 when there is the same amount of light in each case? Not in any way that's very useful. All that's happening is that the same amount of light is placed onto fewer pixels at F2, producing a tinier but brighter image in the same time. And so to problem number two: if you bin the pixels at F10 / use a huge pixel camera / resample the the image downwards there will, in the end, be little to choose between the two F ratios. There is a good article on this issue here: http://www.stanmooreastro.com/f_ratio_myth.htm Professionals build big telescopes for a reason. However, they put large pixel cameras behind them for a reason as well. Key point: in isolation from pixel size, focal length and aperture, F ratio is not a very useful term. When dealing with camera lenses there is no problem. When dealing with AP rigs there is room for confusion. Olly

I guess the blue channel has a right to be blurry because it's being dust-scattered. I think this is a tremendous rendition already. The target is an absolute devil of a thing, unlike any other galaxy I've ever imaged. Yours has come out somewhat less yellow than ours (mine and Tom O'Donoghue's. We processed the data individually and got very similar colour but that doesn't prove anything.) Your star colour is convincing and you've controlled them well. I think this is great. Olly

It's hard to keep the stars down in RGB for sure but you can make an understretched RGB to use as a vehicle for Ha to red and OIII to green and blue, adding the NB in blend mode Lighten in Ps. I think this is easier than trying to drop RGB stars into an HOO image. I think the image is going well, Alan. You have the blue well separated from the red in the flaming star feature itself and that isn't always easy by any means. Olly

Hi Peter and happy Christmas to you too. That cluster is an absolute glory! I can understand why Craney asked if it was for real but, knowing you, I didn't have a doubt. It's astonishing and way better than the usual Christmas Tree cluster. I really must have a pop at it. Olly

That's a lovely image. Just over 3 Hrs is plenty for M42 but your image is much more ambitious than that since it goes after the faint outlying dust structures. More data would be a huge help. In Photoshop there are various ways to select just the regions you want for noise reduction but I think the easiest is the dead simple 'Colour Select' tool. Set the 'fuzziness' (the range either side of the specific pixel you happen to hit) to about 10 and then click on the regions containing the noise. You can then apply NR just to those selected regions but I wouldn't do it that way, I'd make a copy layer and apply a fairly heavy dose of NR to all of the bottom layer then go to the top layer and use the eraser at partial opacity to erase the noisy top layer in a series of passes till you have the right amount. None at all looks terrible. At any time you can ditch that selection and make a different one, perhaps concentrating on areas of really stubborn noise. In my own widefield M42 I did pull down quite a few of the brighter stars but mine only had a soft kind of bloat. Here we see hard disk-like haloes which seem to go with the present CMOS cameras for some reason. Processing them out would not be at all easy so they are probably best left as they are? Might be worth a few short subs for the Trapezium and this method for blending them? http://www.astropix.com/html/j_digit/laymask.html You're onto a winner with this image. Olly

In practice visual observers and narrowband imagers may find so little false colour in a really good doublet for it not to matter to them. Exacting deep sky imagers will be very unlikely to be entirely satisfied by a doublet, though. Vlaiv mentioned the fact that faster F ratios are harder to correct. I think it's also true that increasing aperture makes colour correction harder. Some doublets will beat some triplets, such is the overlap in real performance. Olly

The Dobsonian telescope will be by far your best bet at this price. Optically these are classic Newtonian reflectors but the mounting is simple, inexpensive and both stable and intuitive to use. https://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-150p-dobsonian.html OK, this is £19 over budget but it's a grand tradition on SGL to regard stated budgets as negotiable!!! You'll also need maps of the sky to use the scope productively. Stellarium is a free planetarium software which would allow you print paper charts for an observing session. Some take PCs outside, dimmed with a sheet of red transparent plastic but I prefer to keep my dark adaptation by using paper and a red torch. Olly

I'm another who would not try to find a scope capable of doing both planetary and deep sky imaging. The requirements are quite different and grow even wider apart when the mount has to fit within a tight budget and the imager is a beginner. As others have said, the best mount you can find and a prime focus camera lens will get you going very well indeed. Olly

This is an important point. The 'round stars' test is really no test at all. Olly

It takes me two hours, if I'm lucky, to get the background sky acceptable! You must be one of these juveniles with ADHD that we keep hearing about!!! lly

I'm talking about just the processing. I can do a quick 'proof of concept' processing job in as little as five hours... The whole thing is madness. Madness, I tell you!!! lly

It would be unusual for me, now, to spend more than ten hours on a single frame image, I think, but that does sound about right for a single frame image with five filters, Ha, OIII, L, R, G, B. On the other hand, getting it down to ten hours has taken me ten years... lly

Stars may need to be reduced when they are embedded in nebulosity. These are the tricky ones. Stars in pure background sky do not need to be reduced: it is better to replace them with stars not stretched so far in the first place. Olly

SCTs can deliver astonishing planetary detail in fast frame imaging but are notorious for giving large stars in deep sky work. I don't know why that is, but the evidence is overwhelming. This target is surrounded by bright stars, which doesn't help. You will need excellent guiding, excellent focus and excellent seeing to hold them down. And then, if you're looking at good images on the net, you'll be looking at those produced by experienced image processing experts who have a battery of techniques for holding down stars. In this image I wouldn't even bother holding most of them down, I'd just combine two different stretches, one for the galaxy and one for the stars. This is really for a different discussion but my point is that processing plays a big role in star control and there is no single best way to do it. Olly

Pleasingly original and rather spooky as an object... Olly

A sound decision, in my view. A very fast scope which is being tuned on clear nights is not a very fast scope... AP is hard enough without adding the risk of further complication. Olly

You have the option to halt the device. I don't remember exactly how it's worded (mine's in French anyway) but I think it's fairly obvious. Olly

You don't really need any advice from us because your assessment of the choice is perfect. I've used both mounts professionally and consider them both to be outstanding and the pick of the field. Your own analysis is right. If you were not mobile then the Mesu would win. It is certainly more mount for the money and is the better of the two. The 20% price difference makes the Mesu a clear winner on value for money. But is it a mount I'd take put up and strip down on a night by night basis? No. I have a regular guest who sets his up for a week at a time at my place and that makes perfect sense. Night by night? Ouch, maybe not. The Avalon Linear Fast Reverse is one of the best astronomy products I've ever bought. The two Mesu 200 mounts (both bought second hand) are the best. Given that I have a TEC140 that is saying something, believe me. Olly

Sorry, I should also add that it's a great advert for your capture and processing! lly

What I would do would be make a moderate RGB stretch, or an LRGB. If the L is proving difficult you don't have to add it at 100%, remember. I'd be looking for nice clean, properly coloured stars in this as the overwhelming priority. I wouldn't chase the nebulosity in this image. I'd then make an HaRGB out of the above with Ha added to red in blend mode lighten. I'd brutally star reduce the Ha stars because I wouldn't want them in the final image and as long as they are less bright than the red stars they won't be, using 'lighten.' Next I'd make two more images, the new HaRGB with OIII added fully to green, same technique as above, and another HaRGB with OIII to blue, ditto. Then I'd make a three layer construction in Layers: Top HaRGB ( with OIII to blue) Middle HaRGB (with OIII to green) Bottom HaRGB Now you have complete control in real time and don't have to guess how to distribute the OIII between green and blue. You can use the opacity sliders to balance the green-blue components of the OIII while aiming for that teal blue colour which is true of OIII. You can also decide how much of the total OIII you want in the final image. Personally I would beware of Ha as luminance on this target because it will subdue the distinctive OIII outer shell. The method I suggest here is, in reality, Carole's HOO with RGB stars but I think the method is more controllable, easier and will potentially allow a little of the colour subtlety of RGB nebulosity into the final image. An L layer might enhance this possibility by lifting some of the RGB nebula colour above the brightness of the added narrowband but one can't be certain. Olly PS Edit. When doing this I leave the RGB-only image open so I can use it as a colour reference for the narrowband-enhanced image.

I think the image is very good indeed. Colour and depth are there already. I can't help thinking you could get slightly sharper small-scale detail, though. But this is great. Olly

Impressive. A great advert for this filter. Olly

Planetary images in telescopes are very small so it is naturally tempting to want to make them bigger. Personally, I think this temptation is best resisted.* I find it more productive to concentrate on the image I have than to hanker after a bigger one. Olly * I hope my wife isn't reading this since my ability to resist temptation is tenuous at best...