ollypenrice

3 hours ago, gorann said:

Thanks a lot Olly!

Like with the RASA, you are usually up for a pleasant surprise when you point a Samyang 135 towards the sky😁

That's the fun of it in a nutshell. You are likely to find something you weren't expecting, or a slightly different perspective on an old friend.

Olly

Love it! The field gives a wonderfully shapely composition.

Olly

13 hours ago, Richard said:

Going a bit off-track, but my first view of the Veil, through a 16” Dob and Lumicon UHC, was the first time I’d seen something that looked something like the observatory images available then (~25 years ago). Even from pretty dark skies (Bortle 2/3), the UHC filter made a big difference. Without it the Veil was clearly visible, but with it I could see quite a lot of detailed structure.  

My experience, precisely.

Olly

9 hours ago, tomato said:

In a previous life I was often required to do training presentations on a whole variety of topics which for the most part, was quite enjoyable. What I didn’t like was presenting on a subject which I knew little about, even if my audience knew even less. I have heard the adage about the one eyed man in the kingdom of the blind, but I always felt I was on a rickety rope bridge and my next utterance would send me crashing onto the rocks below.

Yes, in my previous teaching life I always felt that, when required to take charge of a classroom in which I was not properly informed, the best place to start was, 'I don't know about this, so let's try to find out.'

Olly

Even in a 20 inch at our exceptionally dark site (and a good deal south of the UK) I have always found the Eagle disappointing, visually. There is certainly nebulosity to be seen but I never found much to link the EP view to the photographic. (Obviously I wasn't hoping for the tiny Pillars of Creation either.) On the other hand the Swan is spectacular, visually, and the Swan shape is clear and insistent.

Olly

I dug this out with a view to using it to enhance our Cepheus to Cygnus megamosaic but, uncharacteristically, Registar refused to co-register the images. However, I reprocessed it anyway, using the X suite. 16 hours Ha OIII RGB with Paul Kummer a few years ago. Dual Tak FSQ106N/Atik 11000s/Mesu 200.

Olly

Nice. This has a moody, dusky look and the blue nebulosity hovers dreamily over the scene.

Olly

I'm impressed by the image. It's strongest feature, for me, is the way it distinguishes between different levels of very dark, sooty dust. Often they are all clipped down to the same level but here they lie in clearly distinguished layers.

What I'd want to work on would be getting it less monochromatic-looking. Most of the image is the same colour. I think this is largely a result of the filter cropping the blues. One thing to try would be increasing the contrast in the blue channel.

Regarding playing with ill-understood sliders, I do try to avoid it and we all do it to some extent, no doubt. Just don't make an instructional video saying, 'This is me thrashing about with sliders I don't understand and hoping to find something I like!'  There are way to many of those videos already...

Olly

Just now, Clarkey said:

I think the point @ollypenrice is making is that the mount is the most important part of any set up and should be the bulk of the budget, which is quite right. If you were to buy a second hand mount (HEQ5 / 6), if you decided to give up on the AP you can re-sell with minimal losses. You already have a DSLR and you can use this with a prime lens or a widefield scope. You should be able to get this within your budget. You can run this from a bog-standard laptop using free or cheap software. If you then want to advance you already have the mount to do it.

That's right, but I'm also suggesting that, if you go for the very minimum on all three components (mount, optics, camera) you won't want to keep any of them if you upgrade along the line.

I agree that a second hand HEQ5 would be a sound investment.

Olly

If you respect your first budget, very few of your first purchases will pass to the second level. It's best to know this from the start.

If you want to build for the future, start with the mount. The rest will follow. This is a fairly sophisticated image but the mount was a basic EQ6 - and a very old one.

Olly

25 minutes ago, powerlord said:

Don't use ps, but in affinity photo it would be an Add blend layer. The opposite of how you get the star layer in the first place (by flipping the starless layer to subtract, set above the original image and merging the visible layer into a new 'stars' layer). Screen can give a milder result, but Add is the 'as it started' way.

What I tend to do is start with either it set to Add or Screen as I feel best suits, then apply curves, levels and saturation to that layer as appropriate. I usually do end up 'normalising' a little by reducing the bright stars.

What's the equivalent process in Ps ? Or I suppose rather, what do you do in Ps ?

Oh, and how long did starx take on the whole mosaic ?? How many mp is it in ps ? Must be Giga pixels ?

Stu

I use a mathematically more complex system in Ps but I don't do the maths myself! Essentially it's invert and divide.

1 Log stretch the image to about 80% of full stretch and set the black point not too dark. Save as Stretch1.

2 Run StarX. Save as Starless. Process Starless as you see fit. I use Noise Xterminator as a bottom layer and erase the bright, sharp bits which don’t need it. I also fix the background and stretch a little more above that, using Curves. Do all contrast enhancement and sharpening to the starless image. Save.

3 Paste Starless over Stretch I. From here on I have made an Action:

4 Ctrl I to invert both layers.

5 Top layer active, set blend mode to Divide.

6 Stamp down. (Alt Ctrl E) This gives a new top layer.

7 Ctrl I to invert that layer.

8 Flatten image. (Do this under the layers palette from the top toolbar. Ctrl E does not work for me.)

9 Save as Stars. End action.

10 Paste Stars onto the processed starless, blend mode screen.

11 Use Levels mid-point slider to reduce stars.  Small stars benefit from contrast reduction. Large soft stars benefit from contrast increase.

We were working with an image of 552MB after stacking in super-pixel at 80%. This is much smaller than huge telescopic mosaics in which I've participated.

StarX worked reasonably quickly. I wandered off and came back, but 20 minutes would cover it, I'm sure. No big deal.

Olly

On 29/09/2023 at 16:55, symmetal said:

Thanks Olly. It's possible that SXT is not preserving all the individual stars when the density is very high and may be combining or omitting stars when creating the star layer. In the 'normal' stretch above the stars above Deneb are much denser than those in the dark patch below it but in your separately star stretched composite image the density is very similar. it would be interesting to see what it looks like if you gave the separated stars image the same stretch as the background and added it back in. Does it look like the image above? 🤔

Regarding the background stars all having a similar brightness, at short focal lengths several faint stars will fall on the same pixel and register as one brighter star Certain image scales may show this effect more than others.

When rescaling to 80% the algorithm used will affect the star shape/size too along with jpeg compression of course. 

Alan

 

Good points. However, I wouldn't say that SXT has any role in preserving or discarding stars. In order to create the starless layer it obviously removes them. However, when they are replaced, they are replaced by stars from the original image, untouched by SXT. There are different ways of doing this but the simplest (which I no longer use) just involves putting them as a top layer in blend mode lighten. If Photoshop is doing what it says it is, these stars will come into view as the stretch renders them brighter than the background. This means that the imager is likely to halt the stretch before the faintest stars have become visible. I'll see if this method gives a greater range of stellar brightness.

One thing I have done is experiment with ways of varying the star stretch according to the brightness of the background around them. While this is not true to the data, it may be more true to the visual impression since stars of a given brightness otherwise look way brighter against a dark than a light background. I didn't do that on this image.

Olly

20 minutes ago, GasGiant said:

Also, this guy recons he has taken all these incredible images using the ASI120 MC @ 158 gbp. Is this possible or is it clever stacking/post processing.

This is a false dichotomy.  It's both.  Almost all astrophotos that you'll see anywhere will have been made from stacked and post-processed multiple exposures. It is possible to shoot something as bright as the moon in a single, untracked exposure provided the focal length is not too long and the F ratio fairly fast. (F ratio is a simplification, here, but it will do for now.) 

This was with a Canon 400L lens, a 250D body and hand held at F5.6, braced against a house wall.

Your focal length is more than three times this, meaning that the moon's apparent movement will make it track across more pixels in a given time, introducing blur. While your telescope can resolve more detail with its longer focal length, it will lose what it has gained because of the motion problem.

Basically, astrophotography is not a point and shoot activity. If that's what you want, I'd stick to a conventional camera and appropriate lenses. They don't have to cost as much as the Canon 400L!

Olly

12 minutes ago, aleixandrus said:

Oh god, you made my mosaic bite the dust! Impressive work. I'll save that image (for personal use) as a map of that region of the sky. Love it!

 

No, yours is a great image - as I said at the time and repeat here.

Olly

9 hours ago, symmetal said:

Well done to all involved on such a large endeavour, but can I ask what happened to the Milky Way stars? On the large image the background stars are all pretty much the same size and brightness, and there's no change in star density throughout the whole image. 🤔

Alan

Interesting question. The stars have been given an absolutely bog-standard log stretch using the mid point slider in Ps Levels, so the size/brightness range should be perfectly normal and typical of most astrophotos. (Indeed, since there has been no star reduction*, it should be a classic AP stretch.)  However, the stretch itself was much lighter than that given to the background. If  you use one stretch for all you end up with this:

Now some people might like or prefer this and, as an image demonstrating the richness of the MW starfield, it's fine. It's just not what our image is about. Modern processing allows a telescopic look to be extracted from a lens image, meaning smaller stars and more visible nebulosity.

A consequence of the separate stellar stretch is that small/faint stars will not reach the level of the widespread nebulosity and will remain invisible, so diminishing the range of the stars we can see. This is exaggerated when faint nebulosity is lifted well clear of the background sky but, again, that is the whole point of an image like this. Perhaps this accounts for what you are seeing?

Olly

*By star reduction I mean the reverse-processing of a star of a given size to make it smaller. Our stars have simply never been stretched far enough in the first place to need it.

17 minutes ago, vlaiv said:

Do be careful with such assertions.

You have a lot of sky covered in such mosaic and there must be some level of distortion present when you project large part of sphere onto a flat plane.

One of projections used has a consequence of enlarging objects that are close to the edge versus those that are in center.

This is well known in map of the world vs globe for size of landmasses (for example Svalbard looks larger than Madagascar on google maps - but in reality it is only 1/3 of the size - ~1500km vs ~500km)

I realize that there are such distortions, inevitably, but I was only speaking approximatively.

Olly

23 minutes ago, tomato said:

Amazing, you surely must go on and fill in  rest of your hemisphere (as and when). 

How are you coping with projection effects? I seem to recall APP does something clever with these but I have never come close to doing a big enough area of sky to worry about them.

 

 

It's put together in APP which is very clever with the geometry.

32 minutes ago, powerlord said:

that is truly one to be proud of. I'd love to see the full resolution version. You should get it printed 300cm wide or something for a wall!

stu

The printer's running as I type.  My largest option is 'extended A3' but I'm thinking of joining two A3s together. I no longer have a friendly neighbourhood printer with a roll paper machine, unfortunately. He's retired.

Olly

New image from our Samyang here.  Love that lens! 

Our largest mosaic to date. Capture, pre-processing and construction by Paul Kummer using gear jointly owned by Paul, myself and Peter Woods. (Avalon M Uno, Samyang 135 wide open at F2, TS 2600 OSC CMOS camera. My post processing. I gently gently enhanced ten extensive regions of interest using existing telescopic images but only the nebulosity was enhanced. All stars are Samyang, for consistency.

Paul's construction of the linear data was outstanding and this was remarkably easy to process.

I do like finding out unexpected relationships between well-know objects and also seeing their relative sizes. The North America, for instance, is smaller than I thought.

The target per panel was 21x3 minute subs, captured between Aug 21st and Sept 23 this year. Stacking was in super pixel and then downsized to 80%.

Larger verison here.  https://ollypenrice.smugmug.com/Other/Emission-Nebulae/i-TL48wrC/A

Olly

5 hours ago, JonCarleton said:

Alacant and Olly,

Alas yes, the ASI178MC is a very noisy planetary camera.  I frequently find myself clipping to battle noise, even with NoiseXterminator and some other tricks in GIMP.  I also lose a lot with the conversion to .JPG from the .FITS imaging for posting.  Probably though, I should just buy a deep sky camera . 

 

There are better ways to beat low signal than clipping. This is a big subject but it is worth looking into.

Olly

I agree with Alacant: I think your black point is very low, suggesting the clipping of faint data. However, the resolution of the Bubble itself is excellent.

Olly

9 hours ago, alacant said:

 

🤩Nice stars.

May I ask if this was taken using a filter? 

I've a feeling it is best done without a filter. The UHC, as well as relegating the stars to a secondary role, is probably considered cheating.

Cheers 

Why cheating?  

(BTW, no AI on mine, either. It predates StarXt and I don't think it would benefit from further star reduction. I'll certainly have pulled down the outer glow of the larger stars in Ps, though.)

I think you just need more signal for the brown, dusty feature. (Great image from tooth-dr.) You have the emission gasses.

Sh2 126 Two panel. ( Olly Penrice ) - AstroBin

Olly

14 minutes ago, GasGiant said:

Just purchased the 10 "   😀 

That's a serious scope and a good choice.

You now need to be able to navigate the sky. There are free PC planetaria like Carte du Ciel and Stellarium but I don't ever use screens outside, not even under red acetate sheeting, because good dark adaptation is vital. You can print paper charts from the planetaria at different scales.

I'd suggest that you familiarize yourself with a rendition of your present night sky and then go outside and try to pick out the bright stars shown on the planetarium. It's easy for experienced observers to forget how tricky this is for a beginner. You can look for fainter stars and brighter non-stellar objects using binoculars, too. Learning your way around is both essential and rewarding.

Olly

I love the picture and would also like to try a glass of whatever it is that you're having!

lly