ollypenrice

I think that there is plenty of evidence 'out there' to show that Ha does work on modded DSLRs despite the loss of efficiency. There are lots of red filtered pixels on your chip, after all. Regarding processing, at one time imagers regularly used Ha as luminance and regularly produced very pink nebulae dotted with stars with large blue haloes. The problem is simple: Ha filters pass deep red light so it cannot be a good idea to illuminate an entire image, including the green and blue parts, with such light. There is a much better way in which you apply the Ha where it belongs - in the red channel. Process your natural colour image and Ha image independently. If you're going to use the Ha image only as a component within the colour one you can push it very hard for high contrasts and not worry about a little noise in the dark parts because they won't be present in the final blend. In Ps, split the colour channels and paste the Ha onto the red. Change the Blend Mode to lighten. Now the Ha will be applied to the red only where it is brighter than the red. If you want to see if you can push the Ha still harder in this mode give it a try in Curves. Hold the bottom of the curve down and lift the upper parts a little, all the while looking at the result. Flatten the Ha onto the red and merge the channels. If you feel the new HaRGB has too much Ha contribution simply paste it on top of the RGB original and dial down the opacity to taste. On some images a tiny hint of Ha as luminance may be helpful but I never apply it beyond 15% opacity. A final tweak to bring out Ha regions in Ps can be done in Selective Colour. Simply move the top slider in Reds to the left to lower the cyans in red. This makes the Ha pop. Olly

I would begin by reading Making Every Photon Count (by Steve Richards, available from FLO.) So much in AP is counter intuitive that it's easy to buy inappropriate kit. If you're thinking of imaging with a Skywatcher Star Travel refractor - don't! It is totally unsuited to the task because its colour correction is catastrophically bad, being a fast achromatic doublet. It will give you big pools of blue bloat around the stars. It's a fine budget grab and go 'scope but don't image with it. Olly

Could you post 5 images cropped from one single sub: centre and four corners. Post them heavily cropped and at full size, but strictly from one single sub. Olly

Yes, the convenient shortcut with CCD is that a master bias can perfectly well double as a flat dark because the thermal noise built up in very short flat exposures is insignificantly different from that found in a bias. This isn't true for CMOS cameras. Olly

If it's obvious is it successful? I'm not going to knock this image but I will say that, personally, I wouldn't process in this way since there is a huge mismatch in sharpness between the area around the progenitor star and the rest of the field. It looks like two images to me, one wrapped around the other. While it can be a tough decision to sacrifice resolution when blending high res with widefield I think it is sometimes necessary to do so. APOD or not, I'm afraid I don't like this composite image because it looks composite. Olly

Very much what I was thinking of trying should the comet see fit to present itself to the view from my observatories! (We didn't prioritize a low northern view when siting them.) As you say, I'm sure that adding the stars from a single sub (or the stars from a stack stacked on the stars) would take the eye away from any mild artifacts in the starless image. For the sake of accuracy one would want to make all the component images aligned to the same starfield but there's nothing complicated about that provided you know which was the registration sub for the 'aligned on comet' stack. Just use the same sub for reference on the starfield set. It's already a thrilling image. Olly

It might be worth applying a custom stretch to the linear star layer to avoid the 'painted in' look. I haven't tried it but my guess would be to lift the bottom of the curve and restore it to a straight line low down, so softening the stellar edges. I think that just one mild application of such a stretch might be the thing before returning to the standard log stretch. Olly

Have a look at the first post in this thread: Olly

I was initially alarmed by 'Boob of the day' as an imaging challenge on SGL 🤣 but, like the others, I rather like this is well. Olly

I keep the stacks. The individual subs would take too much space. (Stacking old and new stacks is not optimal but still works very well indeed.) Olly

I'll never be able to download those files with the current internet situation here but the initial image seemed oversharpened, to my eye, and I was instantly suspicious of deconvolution. Shock horror but I don't use it at all. I think Ciaran has nailed it, with a result that looks fluffy and yet has all the detail crystal clear. Olly

Good stuff. I think the nebulosity is a great success. The stars, though, as is often the case with SCT deep sky images, are pretty large. Of late I've been seeing what happens when I use Starnet++ to de-star an image and then paste the original linear data on top of that in Photoshop's blend mode lighten before stretching that top layer till the stars begin to appear but in smaller size. It's quite simple and might work well with this data. Olly

Post deleted. I hadn't seen the second page! Nice result. Olly

So would I. I dare say the CMOS niggles (internal reflections, microlensing artifacts, funny OSC stellar colours, stellar haloes) will be sorted out in time but the demise of CCD is rather worrying. Olly

You can't focus on galaxies and nebulae because they are fuzzy, you must focus on stars. You may need to find a bright star to find focus first. Zoom in to pixel scale and focus to get the star as small as possible. Also, just as you hit focus, you'll probably find that lots of tiny stars suddenly appear. That's the spot! You might also try Googling Bahtinov Mask - a much-loved aid to finding focus. Olly

That's a truly cracking rendition. The contrast between acute sharpness in the gas/dust structures and smoothness in the background brings the structures forward and makes them look three dimensional. It also draws the eye towards the features of interest. And all of this is achieved without the image looking processed at all. (The holy grail of processing.) I reckon you've extracted all that your data had to give and stopped a gnat's crotchet short of exaggeration. Spot on. Olly

As everyone will tell you, and with good reason, you first need the best possible mount. If the mount won't track the sky with the necessary precision it doesn't matter what scope or camera you have, your pictures will be blurred. So it's mount first. Now, what is 'the necessary precision?' This depends on the resolution at which you're going to be imaging. The proper units of resolution are arcseconds per pixel (how many arcseconds of sky land on one pixel). The more sky per pixel, the lower the resolution. For a given camera the resolution is controlled only by the focal length since the pixel size is now fixed. You can image at short focal length with only a modest tracking accuracy. As your focal length increases so does your need for accuracy. Not all that far along the path from low to high resolution you need a good mount and and autoguider for it. So the message is clear: on a budget keep to a short focal length, perhaps with a prime lens like a Samyang 85 or 130. (The 130 has a devout following and its own thread on here.) If you stick with lens imaging you might be happy with a Skywatcher Star Adventurer. Personally I would make the HEQ5 the next step up. I can't see the point in an intermediate step which would soon leave you frustrated. I would also make this my first purchase: https://www.firstlightoptics.com/books/making-every-photon-count-steve-richards.html (When I started, Steve hadn't written it. It would have saved me a lot of money had it been available...) Olly

Ah, that makes sense. I thought it was a bit small for a garage unless you drive a Messershmidt Cabin Scooter!! Olly

Thanks, but I meant the building in the background! Now you say you're below road level I can guess that it might be a garage or road-level storage unit? I was just curious about it's elevated position. Olly

I have to ask: what's the elevated timber structure standing on rows of brick? 🤔lly

Sorry, I thought you were using a 130 Newt. My mistake. It's unfortunate that the term 'aperture' is used in normal photography as it is because F ratio and aperture are not the same thing. In the case of a camera lens with a given focal the shorthand use of the term does no harm but it's the source of endless confusion in telescopic imaging. Olly

No, it's important to use terms properly in AP or you'll confuse yourself. Your aperture was the aperture of your telescope, so 130mm. Don't become fixated on F ratio. Once you change a scope's focal length with Barlow or reducer you'll find that the term F ratio does you more harm than good. Olly

Actually you only need one astrophotographer to lift the dome but it does need to be Mike Sidonio (AKA Strongmanmike on the astro forums.) In this link he's only carrying a 150 Kg round stone but there is a pic somewhere of him carrying an observatory on his shoulder... http://mstecker.com/pages/appsidonio.htm Paradoxically, perhaps, Mike's astrophotos are of exquisite delicacy and are certainly among the best in the world. Olly

What an absolutely lovely and classic SGL thread this has turned out to be! Olly

If I thought the technique were unethical I wouldn't use it. Like you, I want to produce good images. There is a PI mentality of being 'true to the data' which I find slightly comical since, if you want to be true to the data, don't process it! I know that's a simplification but it's a simplification which contains some true pointers. Anyway I do what I do and those who don't like it don't have to look at it. I can't cover all the things I do in blending high res with widefield in a post here, but anyone who familiarises themselves with Ps tools can work out how to do it. The key things are these... - Get the background of the high res to match that of the widefield perfectly. Registar will do its best but use Dodge and Burn tools in Ps to get it spot on. - Get the colour balance to match. - Fade in the high res using a feathered eraser so its presence increases towards the area of interest. - Don't obsess over the need to to have the high res at 100% even in the middle of the area of interest. This is an exercise in compromise. Olly