ollypenrice

On 10/10/2023 at 15:11, dan_adi said:

 

For mobile use it's another story, but for an observatory there no need to place computers on telescopes

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

40 minutes ago, The Lazy Astronomer said:

Hmm, well I decided I quite liked PI's layout and structure - maybe that says more about me than anything else 😅 

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

I'll just back up praise for Photoshop for post processing.  If it's going out of fashion for others, it ain't going out of fashion for me.

I find Pixinsight wantonly obscure but, if you don't have it, you have a problem: it's the only platform (I think) which supports Russel Croman's BlurXterminator and that is a deconvolution routine like no other I've tried. My routine, after stacking is,

Pixinsight: DBE or ABE.  SCNR Green. BlurXterminator.

Photoshop: Everything else.

Be aware, there is a lot more to learn in processing than there is in capture. It should not take you long to capture data at the limit of your equipment. But you will never reach a point where your processing gets the very best out of it.

Olly

There's no point in using short exposures if you don't need them and it's easy to see if you do. Take a test sub and read off the brightness value of the brightest part. If it's not saturated in linear (unstretched) form there is no need for it to become saturated with careful stretching. Leaving yourself a bit of a margin would be helpful, though.

With globulars, it's all in the stretch if you're not saturated. A handmade Curve with a heavy lift at the bottom and flattening early is what's needed.

Alternatively, you can do two stretches, one gentle to keep the core controlled, the other hard to bring in the outer stars, and blend them using a high dynamic range technique. Just mixing long and short in a single stack won't solve any problems. You do need an HDR blend. Photoshop has one built in, there are proprietory ones available, or you can use layer masking. I use this method in AP: https://www.astropix.com/html/processing/laymask.html

Olly

44 minutes ago, Clarkey said:

Probably a dumb question, but why? The only reason I can see it due to the resolution, but that would be the same on any 400mm scope.

I think it's simply that the spikes are reduced to vestigial extensions close to the star and don't extend into full spikes. We just see the four spike 'bases,' if you like, and these tend to form a square. I haven't knowingly seen any Sharpstar images but I've seen the phenomenon on Tak Epsilon images and also on images from the Vixen Cassegrain which had thick vanes and no corrector plate. I'm absolutely not a pixel peeper and found them pretty obvious.

Olly

Obviously a dew magnet? Certainly not. The RASA 8 is the least dew -prone imaging optic I've ever used. We have never, ever, had any dewing and we have no dew heater. With a short dew sheild (I made this one) the camera warms the air around it and its fan also keeps it circulating. The fact that it is a zero-dew rig is a selling point and, for me, a real luxury. This is not an SCT!

At a given focal length F2 is a hell of a lot faster than F2.8. 4 minutes versus 7.84 minutes. Nearly twice as fast. That's a lot.

46 minutes ago, tooth_dr said:

Depends how fussy you are but nothing beats the resolution and light gathering capabilities of a big fast scope.

I don't agree on resolution. The RASA 8 is not diffraction limited and speed tends to work against resolution anyway. It does not resolve at the level of a slower 8 inch instrument. However, I think the relevant and meaningful comparison is how it resolves against other possibilities offering the same focal length and, in this comparison, it's fine by me.  I maintain that it does better on non-stellar detail than stellar. Vlad insists that this is impossible. Hey-ho. I think the OP can decide by looking at RASA images and seeing if he'd be happy with that resolution.

Diffraction spikes in a FL of 400mm means... a  lot of diffraction spikes.

Tomato is right to flag up the QC issue. I would only buy from a retailer who acknowledged this risk and would offer no quibble returns.

Tilt is fixable, the stars could be better, but I've never had as much fun as I'm having with the RASA, despite having at least 250 clear nights a year.

Olly

24 minutes ago, Lee_P said:

This is a good question. For optimal results it's probably best to alter your times and ratios based on which specific target you're imaging -- but speaking personally, I like to keep things simple and just try to get a little more SII/OIII, given how weak the SII often is. That also helps boost the OIII. Here are some examples:

Cygnus Wall
– Optolong L-Ultimate (Ha / OIII): 540 x 120 seconds (18 hours)
– Askar Colour Magic D2 (SII / OIII) : 570 x 120 seconds (19 hours)
– No filter (RGB): 90 x 120 seconds (3 hours)

 

Butterfly Nebula
– Optolong L-Ultimate (Ha / OIII): 450 x 120 seconds (15 hours)
– Askar Colour Magic D2 (SII / OIII) : 600 x 120 seconds (20 hours)
– No filter (for RGB stars): 15 x 120 seconds (30 mins)

 

Soul Nebula
– Optolong L-Ultimate (Ha / OIII): 300 x 120 seconds (10 hours)
– Askar Colour Magic D2 (SII / OIII) : 420 x 120 seconds (14 hours)
– No filter (for RGB stars): 90 x 120 seconds (3 hours)

 

I don't know about the time balance (though it looks fine to me) but your total integration times are the real thing, and so are the images. All the images have a real 'three colour dimensions' feel to them, the Soul nebula above all. That's a wonderfully broad gamut.

Olly

Scratch this. I wasn't thinking straight. Need a tilt adjuster!

lly

3 hours ago, DaveS said:

OK. After some experimentation I found that I had to do an initial RGB combination, then split into individual RGB components then recombine into RGB before AA8 would allow me to make the fine sub-pixel shifts needed.

Ignore the dark star centres, I was more interested in the overall alignment. I think it's better. This is a Synthetic LRGB 

ETA: I've been blinking between the original and realigned LRGB and the improvement isn't marginal, not only the stars have tightened up, the galaxy structure is much better defined, even though the restacked version didn't have Unsharp Mask applied. Thanks @ollypenrice

Fixed.

Olly

Lovely image.

Do you have a slight channel alignment issue? Stars seem to have a blue upper edge and a red lower one. More precisely, it seems to be on the clock face axis running 11.00 - 5.00.

Original:

Red channel moved up by 0.5 pixel and left by 0.2 pixel:

Olly

I'm terminally old school and would always prefer to ditch all hubs, mini PCs etc., and run a large number of direct USBs into a desktop PC with enough USB ports.

Olly

More Milky Way adventures with Paul Kummer, Peter Woods and the Samyang 135. Paul did the capture, stacking and stitching, taking this as a final crop from 7 panels. Just an hour per panel, wide open at F2. 

Anyone doubting the existence of Nessie can see her strolling along just above the Coathanger.

lly

Nicely spooky, as it should be.

Olly

Once again, beautifully done.

Olly

That looks well resolved to me. 

Olly

Great stuff on all counts.

Olly

Nice croissant!

I might just look at the brightest parts and ease them down a bit since they look a tad over-exposed to my eye.

Olly

10 hours ago, david_taurus83 said:

I'm the same. I find less points works better most times unless I have a difficult gradient or residual flats issue where I need to place more specific points. If struggling with DBE you could also try the free software GraXpert. It has gotten me out of a jam a few times when DBE proves difficult.

Residual flats issues would, in theory, require you to apply the DBE gradient map via division, whereas gradients are removed by subtraction. I've only ever used subtraction since I take flats and find they work with current setups.

Olly

Regarding matt black paint, it must be pigment-based rather than dye based, the dye-based paints being reflective in some wavelengths. Buying stove or BBQ-type heat proof paints will exclude dye-based ones.

Olly

First thing, for me, is not to sharpen stars, so they always need excluding. Indeed, using star removal and replacement, I usually blur them by about 0.5 Gaussian.

Secondly, as Vlaiv says, don't try to sharpen weak signal and, because it's pointless, don't sharpen any regions with no small scale detail in them.

Thirdly, consider the scale of any sharpening. If you set USM with a higher threshold it will only operate on larger scales, working almost like local contrast enhancement. This can be good for structural boundaries in extended nebulosity, for instance. Small scale sharpening, however, works well on small features like galaxy detail. Basically, one USM set of values does not fit all parts of the image.

I do this in Photoshop because it means I don't have to faff about trying to get exactly the mask I want. I can just make a copy layer, sharpen the bottom and then erase the top with a soft brush where, and only where, and exactly where, I want it. The Select-Colour Range tool in Ps is also a very easy alternative to masking. (It is a form of masking but generated differently.)

Finally, I try not to forget what nebulosity means.

lly

I would advise against large numbers of sample points. What you are trying to remove is a broad gradient and the more points you put in, the more you are likely to pick up local brightness variations - or create them. I rarely use more than 8 and, sometimes, half that.

Olly

You can balance the scope at present just by sliding it through the rings. If that gives you enough range, well, it just does!

The saddleplate-dovetail allows the scope to be removed a little more quickly and the rings come off with the tube. Depending on how you set up and tear down, this might be useful or might be a way of spending money for no substantial benefit.

If were using this scope in an observatory, for instance, I wouldn't bother.

Be aware, also, that the dovetail rail should have stop bolts at both ends to stop it sliding through the dovetail clamp. This is a classic way to trash a telescope!

Olly

11 minutes ago, Clarkey said:

Now all I can see is a big dog.... about to eat Nessie🤣

By Gad, yes - though the dog has three ears!

Olly