ollypenrice

Lovely result, Oskari. This is a remarkably tricky galaxy because of its intensely bright core. This is perfectly balanced. Very nice detail in the little barred spiral above it, too.

Olly

Planetary image stacking and deep sky stacking work slightly differently.

In deep sky, the stacking exploits the fact that noise remaining after calibration is random whereas signal is constant, so signal is reinforced and noise cancels itself out. More signal and less noise is the result.

This also applies in planetary imaging but, in planetary, a proportion of the very short subs will have coincided with moments of good, stable seeing. The imager identifies such a sub and asks the software to find and stack other ones like it, ignoring the rest.

In both cases the software will identify key features and align all the subs based on these. In deep sky this will be the stars and, in planetary, it will be features on the disk.

The algorithms used for stacking don't necessarily use simple averaging. They can also be asked to reject outlying pixel values, such as those created by passing satellites, these to be replaced by the average of the other subs.

In other activities we can all obtain more precise measurements by making not one measurement, but several, and averaging the result.

Olly

An inexpensive and intuitive Dob might mean you could have both. The SCT for visual is a little restricted by its long focal length.

Olly

55 minutes ago, Meluhanz said:

 

This is kind of heart breaking. My amateur brain was bigger telescope, better for viewing and better for photos

I'm sorry and many hearts have been broken in exactly this way. Your big telescope is certainly better for viewing so that's OK, and it can image the planets well. A dozen years ago the intensive marketing of SCTs by Meade and Celestron caught out lots of newcomers wanting to image the deep sky. It's not impossible to do so but a look on the forums at what people actually use will tell you all you need to know. At moderate prices the favourites are Newts or small refractors - and by a mile.

You will also read, again and again, that the first priority is neither scope nor camera but mount. This is repeated quite simply because it is true. If you try to shoot a photo with a £12,000 Hassleblad held at arm's length while riding a unicycle, you would get a better result from a Box Brownie held properly while standing on the ground. The sky moves and the scope must move with it, with a precision of about one part in two million. Incredibly, this is possible on amateur budgets.

So much is counter intuitive in AP that exhaustive homework is a must before writing any cheques. Or rather, before writing any other than this one: https://www.firstlightoptics.com/books/making-every-photon-count-steve-richards.html

Olly

Regarding the imaging of the deep sky with this setup, I would not invest in any accessories to make this possible because the scope and mount are fundamentally unsuitable and will remain so. Like many other people I set about converting my alt-az SCT for deep sky imaging, spent a lot of money and never took a presentable picture with it.

Regarding planets, note that 'cropped resolution for imaging planets' does not alter the resolution in any way, though it will probably allow you to run a faster frame rate.

Olly

1 hour ago, Stuart1971 said:

If you do need some sharpening too, then use the normal setting and not correct only, but drop the star sharpen setting way down from the new default of 0.5 to what it was before, 0.25, and that also will stop the double star issue, or you could drop it even lower if needed….not sure why they have changed the default from 0.25 to 0.5

Great, thanks. I've just fixed a physical fault on my processing PC (a miracle!!) so I can give this a go now.

lly

1 hour ago, Stuart1971 said:

It really is only your settings you are using in BlurX that does that Olly, I had the same issue, try the correct only option, that will solve it…👍🏻

Thanks, I'll try that.

Olly

AI 4 is a disaster on our RASA data and I have gone back to 1. We have elongated stars on one edge and it turns them all into doubles. Yes we should fix it but we want to continue a number of projects before disturbing the rig.

Since Sxt gives control over star size I don't feel the need for it there but do like the nebula sharpening. BTW, another sharpening tool I like is, of all things,Topaz denoise!

Olly

The focal plane of an eyepiece is a very long way from the focal plane of the camera so refocus is always needed. There is a device called a flip mirror which lets you flip between EP and camera with both in focus.

You should not be using a diagonal, either, with a camera. You need a camera adapter which will screw into the back of the SCT. Fortunately these scopes have a huge range of focus so you may not need anything else. Sometimes an extension tube is needed to place the camera further from the objective.

I try not to over think mounting issues. I'd be looking simply at bolting a flat alloy plate to the top of  the Vixen rail and drilling a few holes in it so all the components could be bolted side by side onto this plate. Nothing long or spindly and no 3D printing within a five mile radius.

Olly

On 24/12/2023 at 16:56, old_eyes said:

Lovely image Olly. When the target and the conditions are right, and the astrophotography gods smile, OSC can deliver fantastic results.

Nadolig Llawen!

With fast systems we find a higher proportion of dust to emission, which gives a fresh look, I think.

Olly

8 hours ago, newbie alert said:

No idea 💡 as just read the text, can't remember seeing the images , didn't realise any was there🙈

They are in the opening post.

We do see rotation but what is rotating looks unlike a flat to me.

Olly

On 23/12/2023 at 10:59, newbie alert said:

Your flat panel is unevenly illuminated which will cause issues with creating a flat field

You base this on rhe flats as posted? I would not be so sure. I think they are so far off the mark as to suggest a more fundamental problem. I doubt that these flats are recording the illumination at all. I think they might be entirely rogue.

Olly

In my view it would be crazy to let pixel size drive you towards CCD and away from modern CMOS.cameras, especially for OSC. The new cameras make OSC seriously attractive. I'm using two 2600 cameras now.

Olly

Edit: if you want a CCD, buy second hand. They fetch nothing on the used.market.

18 hours ago, Elp said:

If it were easy I don't think I'd do it, much like any hobby.

I agree but it is not the faffing with electronics, software bugs or hardware that bring the challenges I enjoy. I like planning an image and trying to bring something new to it, if possible, usually via processing.

I've nothing against the s50 and can.remember a time when it would have been a good outreach tool for me. I wonder how good these devices will become? I suspect I'd.rather not know.

😁lly

On 19/12/2023 at 09:35, tomato said:

Hey, it’s the faff that makes it pleasurable.😉

NO! I hate the faff. 🤪i love the sky and the picturus, though. I may be the only astrophotographer in the world who does not like or understand removed word computers, too!

😁lly

That's a very nice rendition.

For the record, our cables are routed thus;

Regarding arc-like artifacts, I lasso them fairly closely in Ps CC and then use content aware fill. This seems to work astonishingly well.

Do you ever get a kind of grid-pattern artifact from Star Xt? It only appears on certain images but is a royal pain when it does. (Edit: I always use Large Tile Overlap.)

Olly

Great post! Lovely dusty rendition at the top, an image with something to say.

Pass on my best wishes to Matt.

Olly

1 hour ago, BrendanC said:

Sure, here you go - really stretched master flat (actually taken from the GHS preview cos I think it displays in fewer bits and shows off the artefacts better).

I can see what you're saying (literally) - the two circles do look somewhat like what you'd expect to see when looking down the OTA, complete with a bit of secondary spider for good measure. and therefore could be reflections.

Oh yes, that secondary spider vane is a dead give-away. That is not a dust bunny, it's your telescope.

Olly

On 06/12/2023 at 17:52, bwj said:

Sorry I'm so late to add to this discussion. Here is the SQM to Bortle conversion the Starry Sky Survey includes in the kit for people to report data with.

https://montanalearning.org/starry-sky-survey/

That's an interesting conversion which I find more convincing than most attempts to define the Bortle scale. My own site, on nights on which you'd want to go out and do astronomy, varies between SQM 21 and 22, so Bortle 4 to Bortle 1. The problem with the Bortle scale, as usually presented, is that it seems to assume consistency.

Olly

As ever, Martin, good taste, delicacy of touch, and a little restraint.

Olly

23 minutes ago, BrendanC said:

Thank you for the input Olly.

I've tried reading this several times and I still don't quite understand it: "Could the bright flats-equivalent of the dark patches on the calibrated image be reflections created by some part of the light path illuminated by the panel?"

I'm wondering whether it's reflections too.

This is from a 130PDS Newtonian.

My English was pretty garbled - sorry! I was called away mid-post and was rushing.

You have artifacts shaped like a circle with a with a dot in the middle. This is pretty much what you have when you look down (or up) a Newtonian... This might be a coincidence but it might not.

What is dark on your calibrated image will have been bright on the flats in use. So you are looking for something which created a dark bright ring with a bright dot in the middle of it.  That's why I suspect a reflection, made even more likely by the fact that there are two identical artifacts offset from each other, perhaps by a combination of tilt and refraction.

Could you post the stretched flat used to calibrate the image we are discussing?

Olly

Edit: I haven't used Newt flats so wasn't aware of what ONIKKINEN said about their appearance.

Firstly, can we be sure we are talking about the same thing? The aberrations I see from your flats are arrowed below.

1) These don't look like any dust motes, or any over-correction, that I've ever seen.

2) They do look very like each other. In both cases we see a segment from a circle (from about 3.00 o'clock to about 6.00 o'clock) and, at the circle's centre, we see a dark spot. They are so similar to each other that we have to consider the possibility that they come from the same source. Since they are dark in the flats-calibrated image, they must have been bright in the source. An educated guess would tell us that, if they were not cropped by the edge of the chip, they might look like a full circle with a spot in the middle. What telescope are you using?

Could the bright flats-equivalent of the dark patches on the calibrated image be reflections created by some part of the light path illuminated by the panel? Another argument in favour of this comes from the fact that, the artifacts apart, the image posted here is very well flattened.

I would bet on a reflection.

Olly

On 20/12/2023 at 09:44, aleixandrus said:

Hi! I have an issue with my flats and, after many-many tries, I can resolve.

I have a ZWO ASI183MM Pro with a Samyang 135mm @ f2.8. I also have a ZWO EFWmini with 6.5nm SHO Baader filters. My lights (both subs and master) seems fine. I recently acquired a circular flat panel (3D printed) with a slightly bigger diameter than the Samyang 135mm. What I found is, as I rotate and change the position of the flat panel, the light pattern of my flats also change orientation.

 

 

 

Whatever these are, they are not flats - by which I mean that they are not images of the illumination your optics' illuminated circle. To my mind, these are not really optical in origin so are probably electronic. Your camera reacting irrationally to your panel. They bear no resemblance to the illumination of a Samyang 135. It's also possible that you are getting strong and asymmetrical reflections.

As Oddsocks suggested, I would just try sky flats. One of my robotic shed clients also has a rig in Spain and has discovered that his panel flats were systematically eating into his data, leaving him with far less signal than expected. Switching to sky flats has transformed his calibrated signal strength.

Olly

1 hour ago, Elp said:

 The fish you might struggle with. 

You're right. We've planted them several times with no success.

lly