ollypenrice

As high in the sky as possible, wide field EP and an OIII filter. Start by spotting the naked eye triangle marked 1,2,3 below. Star 3 is the one with the WItch's Broom running right through it. Try moving that star just out of view if you can't see anything. Apologies for the digression. Olly

What does this moon filter block? The moon filter I have is just a neutral density visual filter so it blocks a percentage of the full visual spectrum, which is worse than useless for imaging. Olly

To ease neck pain by reducing the time spent grovelling beneath the polar scope, here's a simple trick; shine a laser pointer through the polar scope and see where it's pointing in the sky. The polar scope's optics will align the beam roughly with itself and that gets you close to Polaris before the final grovelling and contorting begin! The usual caveats apply regarding the adult use of lasers. I don't find that the ultra-precise centering of alignment stars using a crosshair improves my GoTo significantly. Any gain is overwhelmed by the amount of image shift involved in refocusing. (This is with an SCT.) Olly

^^ Benjam's image above is a good approximation of the binocular view at our dark site (SQM22 on occasion.) There is little point in chasing M31 at high magnification. There is never going to be any visible detail in the core; the main interest lies in the dust lanes for which you need as much aperture as possible combined with a wide field. Our 20 inch F4 Dob was very good for this because its focal length of 2 metres wasn't too long. However, the dust lanes are still visible in our present visual scope, a 14 inch LX200. The limiting factor with this scope is not so much its reduced aperture as its reduced field of view from a 3.5 metre focal length. Large scopes also make the two satellites into fine sights in their own right. One caveat: dedicated observers with keen eyesight and the right equipment can also go in search of M31's globulars but this is serious stuff! Olly

Wow indeed, that's a rich image and beautifully framed to find one coherent structure in this wide field. A very memorable image indeed. Olly

Nope, just mellowing, maybe!! There's a difference... 😁lly

There are three fundamental problems with using Ha as red. 1) the signal from the stars is tiny in Ha so red is under represented. 2) The background is held down by the NB filter so it's hard to get a balanced background sky. 3) The red you have is highly selective, coming only from only one source of emission and it's almost monochromatic. While you have a broad blue spectrum and a broad green one you have only a highly restricted red one. For all that, the image is attractive and it would be easy to reduce saturation in red if you wanted to. However, I think it would work even better if the Ha were applied to the red channel in blend mode Lighten. There is a blue reflection nebula in the middle part of the cone which has little or no signal in Ha. This means that if you use Ha to illuminate the image you'll kill it. Olly

That's really well resolved, especially the beautiful M66. You'd find a vast improvement in smoothness if you had more data. Olly

Well done and welcome to the mysteries of AP! I'd have a look at your colour balance. At present it's overly green, I think. I suspect that, in GIMP, you'll be able to see the histogram for each separate colour. For a rule of thumb try getting the top left hand side of the histogram peak to the same point in each channel. You do this by moving the black point slider on that channel's histogram slightly to the right. Olly

It's great to see something new and well done for the effort on going after something faint. Very nice processing, too. Superb background sky. To my eye the stars and nebula might be a tad on the magenta side, suggesting a slight lift for the greens as an option. Olly

Could be. I guess you want the signal concentrated in the stars. Most of us in DS imaging are struggling to drag out the faint stuff whereas in a cluster you're probably better off without it. Olly

Not easy to get a good sparkle in cluster images but this has it. Olly

That's lovely, Harry. Something of a change of style for you, too, as it seems to me. A softer processing which certainly suits this dusty, gassy region. Olly

I don't know what that is. Can you expand? Does mine have it? (I won't be offended!!! 😁) Olly

It is, yes. Sorry, I missed the fact that it had been posted already. It's worth emphasizing that it's often necessary to increase the saturation quite considerably on the shorter exposures. Olly

Al, there's a green feature in your image just above the Trapezium which I also found in an image offered up for processing on here recently. I must admit that I took it for an artifact and subdued it but I now think I should try some OIII on the region to see what that gives. I have no trace of it in my own LRGBHa data but it looks as if it might be perfectly genuine. Olly

If you have Layers and Masks available could you possibly adopt this Photoshop method, which I prefer to proprietory HDR techniques? http://www.astropix.com/html/j_digit/laymask.html Basically you paste the processed short subs on top of the processed long ones, create a mask, paste a copy of the processed long subs onto the mask and this will allow the transparent over exposed parts on the mask to let the top layer appear. You need to blur and manipulate the histogram of the mask to get a seamless result. Olly

Because the signal is so strong you need only a few subs so shooting a wide range of exposure times doesn't take long at all. I'd just experiment. Olly

The process I followed with my own image was in every way identical to that I followed with yours. I posted the image on here, screen grabbed it, checked the histogram in Ps, screen grabbed that and posted it below the original. No clipping was induced by this process. Olly

This one? https://www.amazon.com/Orion-13039-Crayford-Style-Telescope-Focuser/dp/B000KKBQKI It looks as if the circular protusion intended to go into the hole in a round tube might pull up flat against a flat surface but you'd still need to be sure you were precisely on-axis and tilt free. I'd much rather start off with the right focuser myself. Olly

I don't think so but let's find out. Here's an image of mine. And here's a screen grab of that image opened in Ps with the histogram displayed. As you can see, the use of a screen grab has not induced clipping though the black point has been affected to a tiny extent, perhaps. So I think the use of a screen grab gave a safe approximation of the original. Olly Edit. For completeness here's the original image in Ps with its histo displayed.

I only took the histo of a screen grab. Have you posted a link to the full linear stack somewhere? If so I've missed it but it would be interesting to look at it in my familiar software. What we haven't considered is that calibration might be eating into the black point. Or maybe even the stacking software is doing something wrong. Olly

That's only a secondary observation in my case. I began by looking at the picture and finding the sky unnaturally dark and smooth or glossy. The idea that it's clipped comes after the observation. There may be another explanation but, as I demonstrated above, the screen grab is showing as black clipped in Ps. A background with very consistent pixel values looks smooth and smoothness is, of course, a property of surfaces. As a 2D object trying to reproduce a 3D experience the last thing a picture wants is a 'visible' surface. It will seem to reflect the observer's gaze back out of the illusory space it sets out to create. Also, when we look up at the night sky from a dark site with adapted eyes, it doesn't look all that dark and it certainly doesn't look glossy. There are, therefore, several different reasons underpinning the common feeling that a natural looking image should have a little grain and a little lightness - but the imager is entirely free to do as he or she wishes. I'm not making up rules. Olly

That's not the background which sparked the conversation. It's much better, as several of us have agreed. The one in question is the first in the thread. When I open a screen grab in Ps S3 I see exactly the histogram I would expect to see from this image. It (the screen grab of the original) is obviously black clipped. How much of this is arising from the use of a screen grab I don't know but I would be surprised if the fact of using a grab accounted for the clipping illustrated above. Olly

We've discussed your backgrounds before and I maintain they're clipped. The JPEG screen grab certainly is but, whatever the cause, I see Francis agrees with me. I do find them a bit dark. Your rework looks much nicer to me. The sky looks lighter, a better colour and not so shiny. I found your original blues rather cyan so I used Ps Selective Colour in blues and cyans, to lower the cyan and increase the magenta. I felt it looked better. Your reds look good to me. I used to find them rather yellow. In the rework I think the blue stars should now be a touch more cyan. (I know, I know... Where's that 'Headbang' emoticon gone?) A by-product of the colour calibration is a reduction in blue bloat. This is a good bit of graphics. Thanks. I normally use the B-V index and a colour graph linked to it but this is easier to use. Olly