Magnum

On 19/12/2022 at 13:01, ollypenrice said:

I would struggle to do without PI's ABE, DBE, SCNR green and now BlurXT. I also use LHE but as a layer in Photoshop!   That's all I use but I rate them as 100% essential.

Olly

its funny ive tried the pix insight trials about 10 times now but still cant make myself purchase it due to the hideous user interface and crazy workflows ( im sure it was designed by monkeys. 😛 ). or maybe im the Monkey 😛 

I still do all my stacking and pre processing in Maxim DL including Gradient removal, DBE and ABE in Maxim DL, though they are called flatten Background and auto flatten background & remove gradient. and in direct comparison still give as good of a result but are much simpler to use in my opinion. Then do all the final processing in Photoshop + Noels & Annies actions plus Starnet++V2.

I wouldnt mind trying this new BlurX but shame it's only available as a Pix insight plugin. 250 for pix insight plus 80 for the plugin sounds a huge amount to me just to sharpen. 

I will look through this whole thread and decide if I want to lay out that much as a late Christmas present to myself, but will probably decide id rather buy a new Scope or camera, as I always have trouble spending money on new software compared to new hardware 😛 

Lee

On 15/12/2022 at 18:42, ollypenrice said:

Has to be worth looking into. I do have Pixinsight but consider it a barbaric environment of tyrants fresh from the Spanish Inquisition. If you do something of which they disapprove (which I do all the time in Photoshop) there is a roar from the heavens of 'Die, heretic!'

lly

Brilliant 😛 spot on there Olly. 

ive replaced the image with a less sharpened version as it looked awful when I just revisited it LOL

17 hours ago, vlaiv said:

13ms is too long.

There is something called coherence time related to the seeing - it is period in which atmospheric distortion is almost non changing / frozen.

Look at this paper:

https://articles.adsabs.harvard.edu//full/1996PASP..108..456D/0000456.000.html

This is important graph:

It shows how "similar" (correlated) are wave fronts at time 0 and time t0 (being - atmospheric coherence time).

In another words - if coherence time is 0.5 - and you sample at 10ms - you get 0.1 similarity between start and end wave front - substantially changed

But if coherence time is 10ms and you sample at say 5ms - you get correlation loss factor close to 1 (good correlation).

And this is interesting part:

Atmosphere changes on very short time scales and if you want to avoid motion blur - you really need short exposures - like 5ms or less.

That an interesting and good to know, luckily by chance I have been using 5ms as my default in colour images of Jupiter and 2-3ms on Mars. Can get get that speed at any f ratio ive tried upto f25 with the 12" scope, I remember previously I had a C9.25 but always felt limited by the amount of light that could put onto the sensor so had to use longer exposures and higher gain. Since moving to the 12" scope I don't have to worry about using slow shutter speeds except for Uranus and Neptune or imaging in deep IR and Methane.

Lee

thanks Geof, I should have done a few captures for derotation. not sure why I didnt.

25 minutes ago, vlaiv said:

Here is what I find interesting in this comparison.

First two images are supposed to be F/11 vs F/18, right?

This means that Jupiter in one image should have 18/11 = x1.6363.... larger diameter.

I've measured following diameters in two images:

If smaller Jupiter has 470px diameter - larger should have 470 x 1.63636 .... = ~769px and not 524

Difference between two images is much less than F/11 and F/18.

Noise difference is very large indeed, and I wonder if images where manipulated in some other way?

If we check the native image, at F/11 it should have sampling rate of 0.153"/px and that would make 46.2" diameter Jupiter be ~301px

Maybe drizzle x1.5 was used for that image? It would be much better fit if drizzle x1.5 was used to F/11 and F/18 integrated normally (accounting for small FL change due to primary - secondary distance change when focusing).

 

If the f11 one has not been resized then yes its coming out at about f16.5 for me rather than f11

Id forgot I took this wider field shot on Sept 29th of Jupiter and 3 moons close by, going out from the planet we have Callisto, Europa & IO.

This was a single 2 min capture with the Meade 12" LX200GPS @ f15 with the QHY5iii462C.

Moderate seeing, Kent, UK

Lee

4 minutes ago, geoflewis said:

I'll round of my set of Jupiter images from last night, with my first attempt at Methane band (CH4). This is at F11 with the GRS just rotating into view and some other detail coming through too.

Thats very good for your first methane band Geof, 

7 minutes ago, johnturley said:

Do you find the ASI 462 with its smaller pixel size a definite improvement over the 224.

John 

I dont think the pixel size made any difference as I adjust the focal length with the barlow spacing to compensate. Well except at prime focus then the smaller pixels are an advantage, come to think of it, I wouldn't mind a 1.5um pixel camera then I could do away with the Barlow altogether and lose the extra glass from the equation 

The main reason I upgraded was my old Altair 224 was only USB2 and was limiting my frame rate, and as I was upgrading I thought I would go for the newer sensor which is more versatile as its  more sensitive in IR

Just now, geoflewis said:

Nice images and good comparison Lee. Yes, I agree,  the right hand images is far superior.

on the Down sides  the f25 image took much longer to stack and takes up much more disc space and was dimmer so had to use higher gain, yet the final image still looks smoother to me. 

I found this comparison I did on Sept 4th with my old 224C, colours is slightly different between the 2 as it was only a quick comparison, and I really cant be bothered to process it again from scratch.

Anyway the left image is at prime focus with my 12" LX200 but with extra spacing the disc measured 250 pixels which works out to be F13, the right image is using my 2.5x Barlow measuring 480 pixels and is bang on f25. I have enlarged the f13 image to match the f25 image size. They were taken about 30 mins apart and conditions were pretty consistent throughout the session. To my eyes the f25 image is way more refined.

Ive since upgraded to the 462C with smaller 2.9um pixels compared to 3.75um on the 224C so ive dropped my working FL down from f25 to f21 now to get me similar scale.

the ideal sampling maybe somewhere between the 2, but I would conclude same thing Neil said, its better to oversample than to undersample

Lee

by the way, nice post Geof, and nice images

11 minutes ago, neil phillips said:

And dont forget higher sampling will likely work best under good seeing

That's the key point, and ive been trying to say in other threads, the top imagers capturing from Barbados or Singapore with perfect seeing can consistently use very high sampling ( some would say oversampled ), and ive also been able to gain advantage from doing that in the UK when its a perfect night, by imaging at f21-f23, but on average and poor nights I then drop down to lower sampling say f15. Some say we that ideal sampling doesnt change with seeing conditions, well in theory no but in practice it definitely does. 

very good result, and nice to see real world examples of different sampling, as you say being oversampled doesn't seem to be an an issue in real world use.

Lee

8 hours ago, Kon said:

Mine is in the post so it is waiting time 😀.

Thanks Lee. I did not want to hijack your post on the filter. Like Geof, I also have the 462mc. So we are talking very low fps, close to what i am getting for Neptune (30fps) so it will be even lower. Thanks for the tip on the dark frame. How do you go by focusing, I assume it is a fairly dark image and you rely on the GRS showing as white?

Slower than that actually. With the 462c which is the most sensitive camera for methane band it needs 100ms so thats 10fps and a gain of 400-500. Its easy enough to see the bands to get rough focus but not sure i got it spot on, here is a still from the capture to show how it looked with histogram around 40%

8 hours ago, geoflewis said:

How do you take a dark frame with this camera? I've never done any calibration frames for lunar or planetary, so really have no idea.....

Take 5 still frames then use them in registax or AS3 when you stack the avi,

8 hours ago, geoflewis said:

Thanks Lee, this is very helpful. I did take a look with the CH4 filter and the ASI462, but all I got was a screen full of what looked like a noise, albeit Jupiter shaped, i.e. a speckled mess. I think was at 8ms, with the gain pushed all the way, so quickly gave up. Also, how do I set the RGB histograms for capture, is it the same as with colour, i.e. try to get them all equal, or doesn't it matter?

You need to use around 100ms in methane as its a narrowband fikter

10 minutes ago, Kon said:

Lee do you also aim for a histogram of 70-90%?

well in visible light yes, but in methane I only go to 40% and the histogram jumps around a lot more.

7 minutes ago, geoflewis said:

I'll look out for that, but I can't help you with methane band imagin as I've never done that. I did just get a methane filter with the ASI462MC, but like you I have no idea where to start with it.....🤷‍♂️

I can answer regarding settings for methane band. it's same as normal capture but is a very dark filter so need longer shutter speed and higher gain, also helps to use Lower F ratio to get brighter image and that wavelength responds better to lower f ratios anyway. if using 290 mono then you will need to bin 2x2, but the 462C is much more sensitive in that wavelength so doesn't need binning.

with the 12" scope I have to use about 100ms shutter speed with gain quite high about 475, using gain this high causes a quite a bit of colour noise and hot pixels to show so they recommend taking a dark frame for stacking. Chris go with his C14 says he does 12fps with similar gain.

Lee

6 hours ago, neil phillips said:

When i read Kons report i didn't bother. You still got some good detail out. Can see you had to push the processing a bit. No doubt a consequence of the seeing. 

Yes probably pushed it too far, that what happens when I process too late at night LOL

Lee

1 hour ago, Kon said:

Some nice details coming through the IR filter. I take it the colour was suffering from the jet stream?

How was your CH4 on Jupiter? I just ordered a cheap set to try. I might have to borrow your brains on how to go with imaging and processing with the methane filter.

thanks, yes the colour one was much softer, so I didn't bother to process it.

My CH4 filter was is only 10 or 12nm wide and was bundled with my QHY462C camera along with an IR850 and IR block, was a very good deal at £250 for the camera and 3 filters.  It works but have never got much real detail to show with it but that could be because it's so hard to get perfect focus in Methane band. Christopher GO uses the same camera but he has a wider 18nm Chroma filter.

Lee

Mars at 23:24UTC on Nov 9th. seeing was pretty poor tonight, Jupiter was rather featureless and not worth even capturing but had a quick go on Mars before packing up as its considerably higher in the sky. Used a lower focal length than I normally do as I forgot I had removed a spacer last time I imaged as was on Jupiter in CH4. So this is at around f15 instead of my preferable f21, so had to upscale by 200% before posting.

Surprisingly it came out better than I expected, probably as this camera can capture so fast at 320x240 I ended up with a massive 77,500 frames in 4 mins then stacked the best 25%.

Pole is at about 1 o'clock but very low contrast in IR.

Single 4 min capture @ 350 fps.

Stacked best 25% of 77,500 frames.

Scope: Meade 12" LX200GPS @ f15

Camera: QHY5III462C

Filter: Astronomik IR742

Shutter speed: 3ms

Gain: 250

Location: Kent, UK

Lee

On 07/11/2022 at 16:40, vlaiv said:

 

F/ratio is fixed for critical / optimum sampling.

Why?

Because as you put it 1m telescope being F/7 will give you same sampling rate as say 333mm at F/21 - but 1m has 3 times more resolving power than 333mm aperture scope and can thus utilize 3 times higher sampling rate.

If you double the aperture - you can double the sampling rate - which means double the focal length for same pixel size

2 x aperture / 2 x focal length = aperture / focal length = constant F/ratio

Sorry I didn't type that out very well, I understand how aperture effects sampling.

I didn't mean sampling of the scope I meant oversampled for the seeing, even with lucky imaging there is a practical seeing limit ( somewhere between 0.06 & 0.1"/pixel ), I know you previously said that seeing doesn't effect optimal sampling, but in practice I think  the seeing does limit how high we can sample no matter how short the exposures.

I may be wrong on this, im just talking from my experience.

all the best 

Lee

27 minutes ago, vlaiv said:

Here are test simulation files that compare F/14.5 to F/21.75 on C14 under "regular" conditions:

- 200fps / 3 minute capture - total of 36000 subs captured

- stacked top 10% subs, so 3600 subs stacked for each

- Peak signal strength for optimum sampling is 200e (for oversampling it is 2.25 times less as light is spread over 1.5 x 1.5 = 2.25 larger surface).

- Poisson noise was use to model shot noise

- Read noise was modeled with Gaussian noise of 0.8e per stacked sub.

- Each image was first blurred with telescope PSF (same used for both, adjusted by sampling rate)

- Each image was additionally blurred with Gaussian blur (again adjusted for different sampling rate - so same in arc seconds) to simulate seeing effects.

optimum.fits 950.63 kB · 1 download

oversampled.fits 2.1 MB · 0 downloads

Images are normalized in intensity and saved as 32bit fits. Green channel from above HST Jupiter image was used as baseline (I'm hoping that 8bit nature of baseline image won't have much effect given all the processing that went into making simulation as it was all done on 32bit version of data).

I don't understand why you are doing simulations, why not do it with real captures? 

1 hour ago, vlaiv said:

.

I just don't see why would you aim for F/22 or F/24 if you can sample optimally at F/14.5 given your pixel size. If you use barlow - then you can "dial in" magnification by changing barlow to sensor distance.

Maybe best approach is to just give it a try one way and the other and just choose what you feel is giving you best results. Most others are using that sort of an approach and don't really care that their images are over sampled, if it is easier for them to work that way.

 

Well you have asked the same question as I have, but my conclusion is the top imagers have already tried it both ways, and all seem to have settled on what you consider to be over sampling, if they could get as good results using the lower sampling that your calculations suggest ,then why aren't they doing that? its not like they would choose to oversample for no benefit is it?

I myself have tried using lower sampling then upscaling it in post, but my side by side results against the higher sampled images are worlds apart in terms of detail.

Also loss of SNR from oversampling is a non issue if using a large aperture, with my 12" scope I can still get 200fps at f24 on Jupiter and never have to go over gain 275 with the 462C sensor and the limit is the speed of the camera at that ROI not the shutter speed. So even if thats oversampled im still capturing more data than I can handle, 90 sec captures are 18,000 frames each. with Mars at the same scale with smaller ROI im getting 350 fps and 31,500 frames in 90 secs. 

if I go down to f15 I can max out the camera using a smaller ROI box but then the images don't look as good to me anyway so seems pointless.

If using a smaller aperture scope then it would be an issue to get a decent SNR, but if I had a 6" scope I wouldn't be trying to image at the same scale anyway.

Also we have to remember we can't use the f ratio number universally in these conversations, whenever I state the f number im using, it's only relevant for other 12" scopes.  If I ever get 1 metre scope then f7 would be all I need to get the same sampling with the same camera, or if I buy myself a 1um pixel camera then my current scope would be very over sampled at its native f10, its all relative. The only number we should really be quoting is the pixel scale of the system, and I like to be at around 0.1"/pixel. 

Lee