ollypenrice

This is Photoshop, right? Go to Window - Channels and open the channels. If all is normal it will look like this, but you may have an extra channel as indicated by the green arrow. This is often the cause of problems when trying certain operations on an image. Just delete the extra channel if it's there. Olly

Things to check: 1) Are you in Mode RGB? 2) Open Channels and see if you have an extra channel like a star selection or other. 3) Do you have a selection in place, possibly hidden? Ctrl D to deselect. Olly

Oh yes! It's not just about orchestrating the assassination of heads of state... Olly

Very good. I'm pretty sure there are processing tweaks still available to you, as well. Most beginners bring the black point in far too far and clip out faint data. I think your black point could come in a bit and give you more contrast - but softly, softly! Maybe ease the green down a whisper as well? Olly

Spain? Spain? Never heard of it! Olly

To enable important communication along the lines of... Waitrose. Waitrose. I'm in Waitrose. Near the beans. Here, I'll send you a seflie. Hang on. There we go. Oooh, hang on. I missed my nails. I went to Nailgun next to Macdonalds. What do you think? Union Jacks ahead of the rugby semi finals. I wanted to please Darren. Oh, listen to me, I mean Dave. Don't go to B and Q. Their nailguns don't look safe to me. Olly

Capture, stitching and pre-processing by Paul Kummer, my post-processing. About 3 hours per panel, RASA 8, EQ6, ASI2600 OSC. It's a big image but if you'd like to check out the RASA's resolution of nebular detail (which I think is very good) there's a large one here: https://ollypenrice.smugmug.com/Other/Emission-Nebulae/i-CgQFbZK/A Olly

The only adjustable saddle I know of with any hope of holding your OTAs parallel is the Cassady T-Gad, now out of production. I have just sold my own example. There is no problem inherent in the separation between the instruments. It took more than a century of positional astronomy to detect the parallax of the Earth's 200 million mile shift in position over six months of its orbit. Nor is it the end of the world if you don't have perfect alignment: you just have to edge crop. However, this assumes a good alignment device. You have the additonal problem of mirror flop. My honest opinion is that it would be nigh-on impossible to make a long FL dual reflector system work. Peter Goodhew uses twin refractors at high resolution, aligned to each other, one carrying the guider and the other using an active optics unit. I seem to remember his saying on here that it worked and that the slave scope with AO unit actually got the better FWHM. It really might be more productive just to use two mounts. Olly

Indoor plumbing? You mean - ahem - waste products - flowing through the walls of one's house? How disgusting! Far better to stroll outside and empty the body while filling the mind with the perfect Platonic purity of distant starlight. All this while relishing the cool, moist morning air ahead of yet another day of blazing October sunlight under crystal skies. Toy binoculars? How dare you! My loo roll binoculars are quite outstanding and nothing I've ever used from major manufacturers has replicated the naked eye view so perfectly. lly

The use of Ha in green and blue will replicate Hb for the reasons given by Dave and Alan. I did experiment with this years ago but the problem is that all it does is alter the hue of the red channel. It doesn't bring any new structure into play. Being cynical, you can adjust the hue of the red channel without going to the bother of adding a new layer! Actually, I think most imagers will tune the hue of the red channel in any HaRGB image... Olly

The very one! Thanks. The 'silver braid' does imply nebulosity, I think. Very little LP here and, though I didn't measure it, it will have been SQM22. That's the best we get and the night was truly of the best. Olly

Thinking about this a bit further, a useful exercise might be to take a very good amateur image and set yourself the task of identifying ten good points about it. This would oblige you to focus on, and distinguish between, different aspects of the image. Background sky (my personal starting point), stars, colour balance, colour intensity, noise, presence or absence of visible processing (sharpening, noise reduction), framing, depth of faint stuff, originality... etc. Olly

I thought that naked eye observation of nebulosity was recorded a long time ago, but can't remember the source for this. I'm also pretty sure that there's line about it from in one of the Romantic Poets but, to my embarrassment, I can't find that, either! If I'm right, that would be pre-photographic. I've never found aperture to be much help because, with it, the FOV diminishes and you need some background sky for reference against which to detect nebulosity. I think that this is why my view the other morning was so convincing. I had a vast region of very dark, dry sky with the cluster in the middle of it and the cluster itself did not have a dark background. I suppose it could be bloat from the densely packed cluster stars but the bins are good - Leica - and give very pinpoint stellar images. I was convinced, certainly. Olly

You have it in one. I've been running imaging workshops, giving tutorials, demos, whatever you want to call it, for years and I've been trying to improve my images for more years than that. The one thing I insist on is learning to look at the image. When you have learned how to look at it you can see what needs attention. We can all stare at an image and fail to see that it's green. Or clipped. Or over saturated. Or just ruddy hideous!!! To combat this, I built in certain rules in my workflow. 1) Measure the background sky at regular intervals. Ps lets me see its brightness and its colour balance in RGB at a click. I want it between 20 and 23 and equal in R, G and B. 2) Keep looking at the histogram. Is it clipped? 3) Keep doing hard test stretches. You're not going to keep these stretches but is there any faint stuff that you've failed to drag out? 4) Take a break and look at other astrophotos you like, but not of the object you're working on at the moment. You are not trying to replicate existing images but extract the best from your data. I'd also look at good astrophotos and ask yourself what's good about them. This will make you a better critical observer. Olly

An interesting thought. It hadn't occurred to me that the CMOS camera might have altered the demographics of astrophotography but I think you might well be right. Olly

This is never simple for my 70 year old eyes but, getting up for a call of nature at six this morning, I went outside to find a truly sensational sky. The stars were ablaze. I picked up a pair of 8x42 bins and had a cruise. The Pleiades nebulosity was easy, an unmistakable glow around and within the cluster. It was an inspiring little tour and unexpected. Recent weather has been astonishing, too, with clear blue skies and temperatures hitting 32C in the afternoons. Olly

It's a rigmarole but, if you are going to de-star the main image, you could shoot a star layer quickly (short subs and not too many of them) using a much larger overlap which would allow you to discard the bad edge stars. There's not much noise in stars and you want to keep them small anyway, so total integration could be short. Joining them into a mosaic ought to be painless because the joints only show in the background signal and that won't be applied from a star layer. Warning: I suggest this without having tried it! Olly

The discussion has become rather academic since the cooled CMOS chip arrived but that's quite recent. Regarding CCD, though, I was a firm advocate of the long sub. I routinely shot 30 minute subs in Ha and, occasionally, in luminance. In practical comparisons I was entirely satisfied that, when looking for faint signal, the long subs were the winners. When looking for the outer glow around M31 I found it only when I switched to 30 minute luminance subs. I know several very experienced imagers who agree with this and some who don't. With an uncooled DSLR the build-up of thermal noise over long subs is a variable affecting the decision. In any event, I would urge you to experiment since, had I not tried it for myself, I might have believed that 10X15 in CCD equaled 5x30. I found that it didn't. The first gave a smoother result, the second a deeper. Using CMOS in very fast optics we just use 3 minute subs across the board.

Quite simply, this isn't commonly accepted and has been the subject of endless debate. The relationship between 'more and shorter' and 'fewer and longer' depends on the camera technology in question. What are now 'old technology' CCD cameras had significant read noise so you got one dose of this noise per exposure. This made 'fewer and longer' advantageous because you got fewer doses that way. Modern CMOS cameras have remarkably low read noise so the penalty of read noise per exposure is reduced to very little. In any event, signal must overwhelm noise and the 'zero noise' camera does not exist, so that gives us a bottom line. We must also remember that modern cameras have high pixel counts and that a serious image might need twelve hours. Now Alan, above, images with an F2 RASA - as do I. We can go deep in three hours. Turn that into twelve hours and ask yourself how many subs your computer can calibrate and stack. Olly

Imaging at this speed is simply a different world, as you'll see! Olly

Why easier to balance? I think it's the opposite. You can put a guidescope on a sliding dovetail to move it fore and aft for fine tuning in Dec without having to struggle with the main scope. You can also position the guidescope off-centre as a way of getting dynamic balance right. The usual instructions on how to balance assume a system which is symmetrical in balance side-to-side but, with focus motors etc these days, it won't be. I like being able to use guidescope position as a way of reaching balance. It can also offer be a way of moving your OTA up or down in the clamshell, in cases where hitting the tripod/ground or hitting the observatory roof is the issue. Olly

I think there are good reasons not to do so... I say this because I've swapped out so many of the things on the robotics setups I host. Olly

I'd only use an OAG if I had to, and that would be with a reflector and the likelihood of mirror flop. (This is a rather extreme term for small amounts of mirror movement.) Given that many very high-end setups at long FL run on direct drive mounts without autoguiding, flexure can't be that much of an issue. With a C11 I'd err towards an OAG. On small refractors, I'd consider an OAG to be bonkers, quite honestly. You disturb it every time you do anything to the imaging scope. On my refractor rigs I would say that I never touched my guidescope-guide cam once in ten years, other than to scrape spider webs off the lens - when I remembered. Olly

It does suit some people and not others. The reason I'm more at ease in Ps is that I like layers. I can copy an image onto a new layer, modify it and then decide where I do and don't want to keep the modification. I don't have to struggle to make a mask that covers just what I want it to cover, I can just erase small areas of one of the images. Olly

This is looking really good. Olly