ollypenrice

Incomparably better, with crisp details curling right into the core of the spiral. The core is less blown out and there is more faint stuff, the background and stars are better, it's win-win-win.

Olly

I don't normally see any degredation between here and my view of an image in Photoshop. Are you're in the right colourspace? The internet standard is sRGB.  (I process in ProphotoRGB for its better gamut and then go into Photoshop's Edit-Convert to Profile to choose sRGB. Don't confuse this with 'Assign Profile.')

Olly

Hardly anybody uses wedge-mounted alt az mounts, not because there is anything wrong with them in principle, but because the ones on the market are really not up to the task. In most cases we are talking about the American SCTs. The mounts are lacking in stiffness, precision and backlash control and this is particularly problematic because the focal lengths are long, giving high resolution image scales which are extremely intolerant of tracking error.

I struggled for a while with a wedge-mounted Meade SCT and gave up on it, switching to a German Equatorial.

Olly

Lovely job, Francis.

Olly

Maybe type the eyepiece make, model and focal length into Google and see if any pictures come up which would give you a clue.

Olly

Much better background and now you have that tail showing decisively.

Olly.

It's very good. I don't think a focal reducer would add anything, though. The other way to get the same effect is to use bigger effective pixels. At bin 2, you are still highly oversampled so the trick would be to stack to give a still larger effective pixel size. You can also resample downwards before doing any processing.

When I process our Samyang 135 data I know it is optically limited in resolution so I resample it downwards till the image scale matches the available resolution. In your case you will be seeing limited but you can still do the same.

In a nutshell, it is much better to downsample before processing than after, when you discover that presentation at full size is not a good idea.

Olly

7 hours ago, petevasey said:

Thanks for your interest, Olly.    I've had a good play with the image.  Certainly I can improve it to look less noisy overall, but in doing so the tail tends to disappear into the background - it's simply not contrasty enough.    I just hope for better conditions this month.  Last chance for this target under dark skies at my latitude.

Cheers, Peter

4 hours ago, WolfieGlos said:

Another Leo Trio, well done, and the tail is a pain right? 

I found exactly the same, mine looks very similar to yours in the stretched version but any form of NR just kills it off.

Have you tried Noise Xterminator? It's what I use to control the ultra-highly stretched regions in our images over the last year or two. It removes only the noise.

In order to find out what's lurking, unseen, in my initially stretched data I run it through Photoshop's Equalize routine (in Image-Adjustments.) This is a diagnostic filter but it tells me what's in there and, once I know it's there, I'll move heaven and earth to get it into the final image.

Olly

I think the tolerance of guidescope offset is related to the precision of your polar alignment. If you are polar misaligned, the guider will cause the imaging scope to describe a circular path around the guide star during the sidereal day. The position of the guidestar relative to the centre of the image determines the size of this circle - or so it seems to me.

In reality you can point the guide scope considerably off axis. That's what adjustable guide rings are for. They are not there to let you align the guide scope with the main but to search off-axis for a guide star. This used to be necessary when guide cameras were far less sensitive.

Just remember that, if you change the guide scope position, you will need to recalibrate the guiding.

Olly

17 minutes ago, MartinB said:

Thanks Olly.  I haven't got the flattener yet and it's a big chip!

That should sort it. It really is a stunning chip. I'm using it in two OSC iterations, a ZWO and a generic Telescope Service variant. I think it tends to be more sensitive in the blue but it's clean, fast and vice-free.

Olly

Thanks and, yes, that's a good idea.

Olly

Very good separation of the reflection nebulosity.

Olly

Welcome back, Martin. I don't think it's at all blingy. On the contrary, it has a subtle and natural look.

Are you sure about the chip distance, though? Three corners show elongation. 

Olly

On 21/03/2024 at 21:28, pipnina said:

The sky at my home has an Exposure Value (EV) of about -5.5 or so, and it's already dark enough that the ground is very hard to see even once I'm adjusted.

However a place near me is much darker, dark enough to see the MW core and even sometimes the outer spirals, which means it's probably closer to EV-7 or even EV-8, I can see the ground at this level but not clearly. I would guess if it were just the MW core in the sky and no sky glow at all, I'd struggle to see any ground at all as you say. The milky way just isn't that bright!

Dark sites are not dark, a fact which has been discussed on SGL before. At a dark site it is easy to see the ground and easy to walk around without bumping into things. When it hits SQM22 here, and you are dark adapted, you walk around easily and have no need of a head torch. We've even discussed whether or not Jupiter was casting a shadow.

When there's haze or cloud, though, a dark site is dark and a place where you may struggle to see your hand in front of your face. 

Olly

9 hours ago, fwm891 said:

Well done. Agree with @tomato about the redness. I would also lighten the background too that will help you bring out the tidal effects more.

This! I'm sure you have discarded, through black clipping, many of the benefits of your heroic 18 hour run on this target. Lightening the background of this version won't help because, when it's gone, it's gone. But if you go back to the linear and pay great attention never to black clip, I'm sure you'll find oodles of wonderful faint stuff in your data. The histogram never lies:

Olly

Great stuff, Goran.

Olly

With modern processing tools, Peter, you could incorporate a very significant part of that wonderful tidal tail (second image) into the nicely stretched galaxies of the first image. At least, so I believe.

This is particularly true since the second image is superbly flattened and free from gradients.

Olly

I'm with Backyardscope and suspect pinching. The star looks distinctly triangular to my eye and that's a classic consequence of pinching. I'd try to relax the mirror clips just a tad.

Olly

59 minutes ago, TiffsAndAstro said:

Do you think I would be able to get away without guiding?

I seem able to do upto 5 mins unguided if I take care with setting up, but that's at a much much bigger fov.

The need for guiding, and the necessary precision when guiding, depends entirely on your resolution in arcseconds per pixel. The error in your guiding (the RMS in arcseconds) needs to be no more than half your image resolution in arcsecs per pixel. That's actually quite a tall order and a very tall one when unguided with a non-premium mount. People often regard round stars as proof of acceptable tracking or guiding but this is an error. If your tracking/guiding errors are about equal in both axes you'll get round stars however bad your tracking is. They will just be large round stars and all fine detail will be blurred out.

Guiding is a wonderful thing. It allows a £1000 mount to perform like a £10,000 mount.

Olly

I think a DIY fix might be possible. (Low tech, low cost.)

1) Remove the three bolts marked 1 and discard the broken triangular casting (2) they hold in place.

2) Cut out a triangular piece of good thick marine plywood to replace it. This could be the same size as the original or a little larger. Larger would give you more room and convenience for the last stage.

3) Cut six short sections from a square section hardwood baton of a size large enough to let them be drilled to accept the circular pins on the tripod legs as an interference fit. Screw (from above) and glue these to the triangular ply so as to make bushings to hold the legs to the triangular plate. (Obviously you'd attach these to the triangle with the legs in place and everything squeezed up tight.)

4) Bolt this assembly to the pier top in place of the broken casting.

This method would require no metalworking tools or welding. I don't know how the original system braced the legs but you could brace them using a triangular accessory tray part way down the tripod legs. Excuse the sketch quality! 

Olly

3 hours ago, TiffsAndAstro said:

Currently my best lens for ap is a 200mm and with my 1.6 canon crop is effectively 320.

I'm struggling to compute a roughly equivalent crop factor for the zwo859mc. Will plug info into stellarium hopefully for a comparison 

Don't try to calculate crop factors at all. They are entirely meaningless in astrophotography. 'Crop factors' imply that you can improve resolution by reducing chip size, which is pure nonsense.

There are two dimensions which matter:

1) The size of the pixels. These, along with focal length, determine the resolution in arcseconds per pixel. (The pixel count of the chip on its own says nothing at all about the resolution.)

2) The dimensions of the chip in mm.  These determine the field of view.

If you muddy the waters by using the kinds of shorthand used in daytime photography you go right up a gum tree. 

Olly

This looks interesting but, on Kindle, it's rather expensive and has a large file size.  This makes me wonder if the book's format will be appropriate to a Kindle. Pictures, graphs and graphic illustrations don't work well on the Kindle, for me.

Thanks in advance,

Olly

1 hour ago, TiffsAndAstro said:

Im hopping i can just slew and center m87 in nina over multiple nights. dslr dark frames might not be an issue for too much longer. i think its telescope and astro cam time. 

after what i can only assume is a decent 3ppa, it slews and is usually about 4000 pixels out. then it adjusts and is about 40 pixels out, then one last and its a couple of pixels out. 

In that case you'll find nothing difficult about multiple night imaging. Have fun!

Olly

1 hour ago, TiffsAndAstro said:

confession time: i only took 5 dark frames. also i used 'library flats' because i am lazier than cuiv and it was just another test. wasn't really expecting to actually see any galaxies and i gave up counting at twenty. i think i've managed to clean the finger print off the front element that i think caused the black hole.  

its good to know the cause and likely solution. im rushing a bit into more complexity, but so far its been ok. most problems are with niggly usb things. and focus. and clouds. i need time to fail more then fail bit less the next time  

Many DSLR users don't use darks because they add more noise than they remove, and using only 5 will certainly do that. A large dither (12 pixels) is by far the best way to go.

Shooting multiple nights is perfectly simple provided you have the camera consistently aligned. I always align along RA and Dec (either in portrait or landscape) because it is repeatable. Once set up, simply slew slowly in one axis while taking an exposure of about 3 seconds. You'll get star trails and these will show the current orientation of the camera. Once they are horizontal or vertical on the chip you're good to go.

You can plate solve to reframe, though I never used to do this, working manually. I just looked at the star pattern round the edges of the chip.

Olly

More integration is always better but the benefits are very target-specific. If you are chasing faint signal like tidal tails, faint galaxy arm extensions, accretion loops, outlying nebulosity, IFN, etc., then the benefits are enormous. When you are trying to drag something faint out of the background sky, you will never have enough.  If you have a reasonably bright object already but would like to sharpen its brighter details, the benefits are considerable. You need signal to sharpen. Multiply by four and you'll see a difference. If you are imaging an old elliptical galaxy with little structure, more signal will make it cleaner and smoother and, quite probably, a little bigger but the benefits will not compare with the previous examples.

With a screamingly fast F2 system, cooled CMOS camera and a very, very dark site we regard 2.5 hours as a minimum, so that would equate to about 11 hours in a small refractor of comparable focal length.

Olly