ollypenrice

13 minutes ago, Gerr said:

Thanks Olly,

OIII extraction with Siri provided a good start but still faint outline that was challenging to bring out in Photoshop! I noticed my star field overlay was inaccurate and I had to re-do the image again (included below). Glad no one noticed!!! 😂.👍

I've had that as well! Grrr.

Olly

8 minutes ago, MichaelBibby said:

While playing with Microscofts generative 'A.I.' model called 'Bard' I thought I would test it with this question and see what it came up with:

Me: "if I were to compare images taken through each of those telescopes using a camera with a pixel size of 2.9um, and was guiding at a total error of 0.5 arc seconds, would I notice the difference in resolution under 'average' to 'good' seeing conditions?"

Bard: "Yes, you would likely notice the difference in resolution between images taken through a 150mm Newtonian telescope and a 200mm Newtonian telescope, using a camera with a pixel size of 2.9um and guiding at a total error of 0.5 arc seconds, under average to good seeing conditions.

The 150mm telescope has a theoretical resolution of 0.8 arcseconds, while the 200mm telescope has a theoretical resolution of 0.6 arcseconds. This means that the 200mm telescope can resolve finer details.

The pixel size of the camera is 2.9um, which corresponds to a sampling rate of 0.12 arcseconds per pixel. This means that the camera is capable of sampling the images from both telescopes at a high enough rate to capture the difference in resolution.

The guiding error of 0.5 arc seconds is relatively small, so it will not significantly degrade the resolution of the images.

Under average to good seeing conditions, the atmosphere will typically introduce a blurring of about 1 arcsecond. This means that the effective resolution of both telescopes will be limited to about 1 arcsecond. However, the 200mm telescope will still be able to resolve finer details than the 150mm telescope, even under average to good seeing conditions.

In conclusion, you would likely notice the difference in resolution between images taken through a 150mm Newtonian telescope and a 200mm Newtonian telescope, using a camera with a pixel size of 2.9um and guiding at a total error of 0.5 arc seconds, under average to good seeing conditions.

Here is a table that summarizes the expected resolution of the two telescopes under different seeing conditions (Please note that these are just estimates. The actual resolution of the images will depend on a number of factors, including the quality of the optics, the observing conditions, and the processing of the images.):

 

Seeing	Expected resolution of 150mm telescope	Expected resolution of 200mm telescope
1 arcsecond	0.9 arcseconds	1.1 arcseconds
0.5 arcseconds	0.8 arcseconds	0.9 arcseconds

Where is the artificial intelligence in all this? It is just a regurgitation of numbers already out in the public domain, with one vitally important number replaced by the adjectives 'average' and 'good.' Since these are the numbers which define everything that the system will produce, what are they and where are they?

I would rate this answer average to poor.

lly

Lovely stuff, Maurice.  I see that people are shaking off their sleep in Lagrand and putting the coffee on!

Olly

7 hours ago, jambouk said:

A friend at my local Society has asked me for some advice on what camera he should get. He has recently got a standard C11. He doesn't want to guide and can reliably get 30-second exposures with his DSLR on his old driven equatorial mount. He is primarily interested in DSOs, but would like the option to capture planetary/lunar data too.  He wants to capture more Ha than his old unmodified DSLR allows, and is keen to get a one-shot colour camera. He lives under a fairly dark UK sky.

Now I presume a cooled camera will still be best, even for 30-second exposures, but which one? Budget under £1000.

Thanks for any replies.

James

 

I'd have to ask what criteria he uses to define 'reliably get 30-second exposures with his DSLR on his old driven equatorial mount.'  My fear is that, in upgrading to a better camera, he would be wanting to upgrade his images and would, very quickly, find himself re-defining what he found to be acceptable tracking.  30 seconds, unguided, at well below an arcsecond per pixel? Science doesn't work by proving negatives but, no, I would need a lot of persuading.

Olly

6 hours ago, Louis D said:

I'd probably suggest you start out spending a fraction of the $2000 budget on a good starter scope that is still compact.  If you find you're not that into astronomy later, you can easily pass it along.

I would suggest either a Sky-Watcher Heritage 130 or 150, but mounted alt-az style on a photographic ballhead on a sturdy tripod:

Or on a Sky-Watcher AZ5 mount:

If you prefer a driven mount, they can also be had on a goto mount in the Virtuoso GTi 150P version which can be mounted on a photographic tripod:

Yes, I understand this argument but the OP has wisely started out with binocular observing already.  The problem with starter scopes, which is common to starter products in other arenas, is that the buyer risks finding, 'Yes, I like this,' and will almost immediately want to take the next step. When they do, the starter setup will be obsolete for them.

On the other hand, many seasoned observers have a 4 inch (ish) refractor along with all sorts of other, more extravagent, instruments and they keep it because it remains a particularly useful tool.

Personally, I have given up on 'starter products' because I invariably find that they have a very short role in my activities. This may just be me, of course.

Olly

For me a small telescope with a very long focal length misses out on what a small telescope can do and a big one can't, which is deliver a very wide FOV. That's why I'd prefer to avoid Maks and SCTs. I also think that, in Norway, you will also want something which does not attract dew. SCTs and Maks are bad for this.

I do like the look of this, mentioned above by Vlaiv. https://www.firstlightoptics.com/stellamira-telescopes/stellamira-110mm-ed-f6-refractor-telescope.html I didn't know about it.

Olly

Aperture is important in visual astronomy but inevitably comes at a cost in terms of portability. Bigger is - well - bigger!  Robustness is another aspect of real portability.

For many, the 4 inch refractor hits their target. This one is an old established favourite. https://www.firstlightoptics.com/ed-pro/skywatcher-evostar-100ed-ds-pro-outfit.html It has a longish focal length for its aperture so isn't going to give as wide a field as a faster 4 inch, but it is very well colour corrected as a result. Being a refractor it is robust and won't require collimation.

For visual observing, alt-az is nice and intuitive, does away with polar aligning and needs no counterweights. This would be one option. https://www.firstlightoptics.com/alt-azimuth-astronomy-mounts/astro-essentials-alt-azimuth-fork-mount.html

On a suitable tripod it would make a kind of budget replica of the Televue 4 inch used by Steve O'Meara to write his classic observing guide to the Messier objects. You'd be on budget for a couple of reasonable eyepieces, too.

( Eyepieces stimulate a kind of mania among astronomers, many of whom have twenty or so. I use two, almost exclusively. Better two good ones than four poorer ones, in my view.)

This is a setup you would pull out of the car, place on the ground and get started. A red dot finder would also be good and you'll need star charts but you could print selected regions from a digital planetarium.

Olly

Yes, if you have a little backlash in RA, then running slightly east-heavy will leave the driven gear resting against the drive side of the driving gear rather than oscillating across the backlash. It does mean that you need to reverse the imbalance after a meridian flip.

There is an equivalent procedure to reduce Dec backlash but which doesn't involve balance weights. You can deliberately polar mis-align the mount slightly then activate only the guide direction which corrects for that. You don't run the guider on the other direction. Trial and error decides which inputs to disable and, again, they need to be reversed after the flip.

While I've had reasonable success with both methods, this was only as a stop-gap measure prior to fixing the problem properly.

Olly

9 hours ago, Icesheet said:

Here's the widefield for reference...

I like them all.

BTW, cropping, of itself, has no effect on resolution. In daytime photography there is a careless tendency to confuse pixel count with resolution but they are not at all the same thing.

Olly

Perhaps a member near you might let you try your handset in their mount?

Olly

Fabulous! Exceptionally deep and yet exceptionally clean with superb levels of local contrast in the Ha. Beautiful processing, too. The result has rewarded your effort.

Olly

Très belle galaxie! Balanced colour and brightness giving a natural look.

Olly

This target really comes to life in NB, with a distinct change in gasses, therefore colour, between body and pincers.

Very deep and clean. A just reward for your patience.

Olly

Your OIII is way better than mine, which had 11 hours at an exceptionally dark site. I was using a mono CCD (Atik 11000) and Baader OIII filter. This was a decade ago and I think we can say that the technology has improved!

Great stuff.

Olly

11 hours ago, gorann said:

For a while I have been running a rig with two RASA8 and a piggybacking Samyang 135. All are at F/2 and the cool thing with the Samyang (FL 135) is the extreme wide field. But when if comes to both resolution and catching the faint stuff, the Samyang is nowhere near the RASA. The simple reason is aperture: 67.5 mm (Samyang) versus 200 mm (RASA). So there is no doubt in my mind that aperture rules when it comes to resolution and depth, as long as both instruments do not get limited by seeing or guiding. This may be an extreme comparison and the difference between a 6" and 8" SCT may not be so clear, but I assume it will be there.

I certainly agree that the Samyang is mightily out-resolved by the RASA but here, we are comparing massively different apertures.

As regards depth, I think it's 'aperture per pixel' which matters. I'll go back and compare our own RASA and Samyang data on the same targets. I've blended the two without paying particular attention to this.

Olly

The theory will be overwhelmed by the practice in comparisons like this. An 8 inch scope has higher optical resolution than a 6 inch if both are diffraction limited. To give the same FL the larger scope has to be faster, making it more susceptible to optical imperfections in the grinding of the mirror, the collimation and the mechanical alignments. Which will be the real world winner? It depends on the specific instruments in use.

In DS imaging, sharpening in post processing has an effect on final resolution and more signal can take more sharpening than less signal. This favours the faster scope.

If you are over sampled the optical resolution comparison goes out of the window because you'll be seeing limited, but the larger, faster scope gets more light. See previous point.

I firmly believe that these discussions are academic and that the success or failure of an image derives from a dozen other things before the niceties we are discussing here have any contribution to make. I also know from experience that not all reducers play nicely with all optics and, given the very questionable wording of Starizona's Hyperstar advertising, I would read anything they write with a high degree of critical distance. For example, 

The HyperStar 8 lens converts a standard Celestron 8" SCT from f/10 to f/1.9, making the system 25 times faster. That means 25-times shorter exposures!   For this to be true, the Hyperstar lens would have to increase the area of the clear aperture by 25 times and then we could consider it to be the same 'system.'

Olly

8 minutes ago, LandyJon said:

 

Nicolai, until you see olly proving this possible with his own rig, I'd stick to a stable platform and try to raise the mount head from the legs.

 

 

For some time I used a Takahashi EM200 mount which has no facility whatever for leveling the top of the tripod. EM200 users at latitudes outside the fairly limited adjustment range of the mount routinely tilt their tripods to reach alignment. 

I'm assuming a reasonable degree of intelligence in not overdoing this. Within reason it is a perfectly normal thing to do to make your mount's adjusters more comfortable. If they are OK when horizontal, then fine.

You can also expect Polaris, if visible this close to the horizon, to be displaced visually by about half a degree by atmospheric refraction.

I have observed on the equator and would not make Polaris my primary means of alignment if I lived there.

Olly

1 hour ago, windjammer said:

I'll go out on a limb and say, yes it is real and you haven't denoised enough.  Looking at my own image of the cave (a smaller FoV) in the area where they overlap, I have the same features as you in the murk.   I posted my pic here if you are interested - it needs to flip vertical to match your orientation.

https://stargazerslounge.com/topic/412672-cave-nebula-update-algorithm-beats-human/#comment-4403775

Simon

 

Can't agree on NR. It already looks like 'vaseline on the lens' and that's the root of the problem. But I do agree that it's a good image.

How about resampling it down to a lower resolution , accepting a smaller rendition, and getting a cleaner image?

Olly

I disagree with most of the advice above.  7 degrees above the horizon is not going to work for any kind of Polaris-dependent PA routine. You'd need a fantastically low horizon and minimal light pollution to see it at all. No design of pier is going to get around this, so forget it. You can Polar align by other means, quite successfully.

Use a compass, corrected for your magnetic deviation, to point the mount north. https://www.magnetic-declination.com/Sri Lanka/Colombo/1481546.html#:~:text=Answer%3A -2.09° (-2°5')  For the purposes of this method, just remember that your compass will be pointing about 2 degrees west of north. That will do. Even just using the compass's magnetic north without correction will do. That gets you in the rough position for Azimuth. Don't use the compass close to anything magnetic, like electronic devices.

The rough position for altitude is going to mean that your polar axis is only going to be about 7 degrees off horizontal. If this is a problem for your mount, don't hesitate to tilt your tripod to make it easier. The base of the mount does not need to be horizontal. Many will say it needs to be horizontal but they are mistaken. I would make a physical wedge with a 7 degree angle and place one side on the the mount and put a spirit level on the other for quick repeatability.

Once the mount is in this position, just use the drift method. It has various versions.  This is a very intelligent one for imagers. https://www.cloudynights.com/articles/cat/articles/darv-drift-alignment-by-robert-vice-r2760

Forget Polaris. It will not help you.

Olly

1 hour ago, Ouroboros said:

Yes. I use SCNR a lot. Usually later and very successfully to remove residual green after background modelisation and colour calibration.  The green I’m referring to above is the bright green colour cast observed in many OSC images immediately after preprocessing and before you do anything else. I have read it arises as a consequence of OSC sensors having twice as many green sensors as red or blue.  

Just out of interest I just applied SCNR to a just processed green image. It goes sepia, and looks yuck! I think it’s better to apply SCNR when you can see what it’s doing in a controlled way, possibly masked too to protect certain areas. 

I regard SCNR as a linear-stage tool. Sometimes I'll run it and not run it, making two versions which I can then blend easily and selectively in Ps Layers.

Olly

On 29/10/2023 at 10:01, Ouroboros said:

Several selective applications of TGV Denoise applied using masks (to protect brighter areas).  

Personally, I'm suspicious of this stage. The effects you describe look like excessive NR to me.

Regarding NoiseXt, or any other NR, I don't know what the official recommendations are but I cannot imagine running NR before knowing where I wanted it and what its consequences were. Hence I run Noise Xt on the starless once it is sufficiently stretched to reveal noise. I apply it to a top copy layer in Ps so I can blink the NR version on and off to see where it's good, where it's bad and whether or not it's over-done. I can then erase it from where it's harmful, retain it where it's good and adjust its opacity. Using layers I can see what I'm doing as I do it.  I don't think anyone could ever persuade me that making a guess at what to mask and hitting 'Apply' was a better way of doing it.

Olly

Edit: regarding green, try SCNR green. I run it on 9 images out of 10. DBE doesn't deal with it for me.

On 28/10/2023 at 23:55, Veloman said:

I'm looking at mini guider scopes and notice that a lot don't have the means to align themselves with the main scope. Is this a thing that is compensated for by the software and if so to what kind of alignment error is tolerable?

ATB

Rob

None of them does. The alignment adjusters you'll have seen were invented for the opposite reason: They allow the guide scope to be moved off axis in search of a guide star. In the past, this was necessary for guiding on a star by eye or when using early and insensitive guide cameras which only picked up brighter stars. They are now redundant and I would far rather have a guidescope bolted down hard than carried in potentially flex-prone adjusters.

Guiding on an off-axis star has one side effect.  If polar alignment is out, the imaging scope will describe an arc around the guidestar. If you guide on a dead central star the chip will rotate on its centre point.  If it's off axis it will describe an arc.  If shooting in old-school 30 minute subs, polar alignment is critical. Since CMOS cameras use only short exposures, and since stacking software will easily align slightly rotated subs, polar alignment is less of an issue.

Nutshell: guidescopes don't need to be precisely aligned, as everyone has said. They do need to be rigidly mounted.

Olly

Dramatic improvement. The processing of dense starfields has been transformed.

Olly

Dust from the city is very good going indeed!

Olly

Good going on a tiny target. Impressive.

23 hours ago, Albir phil said:

 often wonder what is the correct colour in many DSO its down to personal preference really 🤗

If you are shooting in RGB, rather than colour mapping in narrowband, there is a right colour, at least in a reasonably broad sense. It can be checked by looking at your background, which should be about equal in RGB, and your stars, which should match the astrophysics of their spectral class.

I think that, in this image, the colours are a little out in a consistent way, with the reds too yellow and the blues too cyan. I would guess at this arising from too high a value in the greens, perhaps because of the filter. I haven't used this one.

Olly