geoflewis

13 minutes ago, tooth_dr said:

Highest I’ve ever seen at 500 earlier but unfortunately heavy rain here 

I had the same alerts here in Norfolk and the same cloud covered sky.....

Sorry Vlaiv, what are we meant to do with these?

1 minute ago, johnturley said:

I agree with you Geoff, imaging at the supposed optical focal ratio often results in far too small am image, which makes it more difficult to focus on the laptop screen, and to set align points in Registax or AutoStakkert.

John 

Thanks John, this has been a very enlightening discussion for me.

3 minutes ago, neil phillips said:

Cheers Geof. Had high hopes for a good saturn this year. But after the council installed a floodlight over my garden that doesn't go off until 12 summer 1 O'clock winter. I gave up. 

I had a couple of goes at Saturn with the 462MC, but they were worse than I got last year with the 290MM, however, I had left it until well past opposition this year to even try, also I think I was applying IR as lum last year, so not a fair comparison.

Just now, vlaiv said:

Your logic is not wrong - if you want to capture all the detail that is potentially available - it is better to over sample than it is to under sample.

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.

Thanks Vlaiv, I think you may have hit the nail on the head. It may just be that it is easier to dial the focus with a bigger 'oversampled' image on screen. I certainly found this to be true when Mars was last close to us in 2020. I was operating at ~F22 for Mars in 2020, but only F12 for Jupiter and Saturn last year, but of course Jupiter and Saturn were much lower down and imaging them at all was very challenging. So far this year I have imaged all three at F12, but I am going to experiment with different amplification to see what differences I get, especially with Mars smaller diameter this year, but up at ~60° elevation.

Thanks for all your advice on this complex (to me anyway) topic.

5 minutes ago, vlaiv said:

There is no detail loss due to over sampling - at least not one explicit one.

You are quite right - it is far more difficult to model detail loss due to SNR loss and inability to sharpen as much as one would like.

I don't think there will actually be detail loss - only more noise at the same level of detail as no detail is really lost if one over samples - it is just that it can't be shown without showing the noise as well.

Ok , so if there is no detail loss due to oversampling, then that suggests that I'm definitely better to 'risk' oversampling versus undersampling, which is what I think I may be doing without any amplification in my image train - I think we calculated I am currently at <=F12 or 0.14"/px. There may be worse SNR at F22 v F12, but will I actually see it, especialy if in excellent seeig I can stack >10k frames? However, maybe at F12 I am not fully utilising the optics and I can't ever recover what I didn't capture - is my logic still wrong?

2 minutes ago, vlaiv said:

It is HST image that I just googled as high resolution Jupiter image.

It is much larger (and still sharp) than one I used for comparison.

Here is original link:

https://stsci-opo.org/STScI-01FM5S4SWQQ9M5A15BHBMG0NW4.png

Ok, now you really lost me. How is comparing HST image with ground based image relevant to this discussion?

3 minutes ago, vlaiv said:

I don't think that you need to look at math at all - just look at first two images and you will clearly see the difference.

Left is level of detail captured by over sampling, right is level of detail that is possible at that resolution. When you properly sample - you capture level of detail that is possible at given resolution.

Who produced the image on the right and what equipment were they using please?

That's a cracking good Saturn Neil

@vlaiv Thanks again for the additional analysis and supporting images. It is beyond my ability to understand what you are saying, sorry. Well I understand what you are saying, but not the maths that 'proves' your analysis. It still leaves me questioning why the expreience of Chris Go, Damian Peach, et al, differs from your mathematical analysis. I think that they fine tuned their approach based on experience, so when experience/observation challenges the maths, I have to question the maths - it's almost like Ptolemaic v Copernican arguments. OK I know it's not, but hopefully you will understand my reasoning for doubting the maths....

48 minutes ago, vlaiv said:

In any case - if image is over sampled - that is easily identified in the image. High frequency components will be missing and there is simply no cheating of the physics - one cannot capture what is not there.

Thanks Vlaiv, I am not a physicist, so can't challenge the theory on any basis other than experience, but I still contend that there must be something going on. We are not talking about hack imagers, but the world's best, so IMHO there must be a 'real' reason why they chose to sample at F22, F24, etc., with small pixel cameras like the 290 and 462 sensors. Look at the image from 5 Nov and more so the comments by Christopher Go.

http://astro.christone.net/jupiter/

He clearly considers it an extremely good image displaying very fine detail, so I am curious what 'high frequency components' he may have lost by imaging at F24  rather than F12-F14 that you contend is optimum for his configuration, which is essentialy the same as mine and Avani's?

Please know that I'm not just rejecting your analysis, but I can't for the life of me understand why the field evidence of these very experienced, talented imagers doesn't tie with the theory....

6 hours ago, astroavani said:

A beautiful result, geoflewis friend!
Interesting that I only get good results using the C14 at f/22 with the PM 2X. I've tried many times in bad seeing night to use native d/f but the results were not good.
I think it must be related to sampling and ASI 290 which is very close to the 462 you use. As it has a very small pixel, it seems that a larger image makes the final result more pleasant.

Thanks Avani, it's very good to hear from you. The topic of correct sampling is indeed very interesting; I'll add you to the growing list of planetary imagers who find that sampling well below (ie. much finer) the theoretical numbers as calculated by @vlaiv, just works. There must be something in the maths theory that just isn't correct as all the best planetary imagers get their best results imaging at 0.1"/px or lower, where the maths is saying optimum for C14 is ~0.14". It's a huge difference in sampling rate and I'm at a loss to fathom why the theory is not supported by evidence in the field.

Wow Neil, I've only just seen this, absolutely superb detail. I'm estimating down to <2km comparing with LROC quickmap....👏

17 hours ago, Avocette said:

Some distance away from Tenerife I was busy capturing Jupiter and these three Galilean moons at the same time. Here is a GIF of the transit and occultation event…

SkyMax 150 Pro Maksutov-Cassegrain operating with a 2x ED Barlow with shortened spacer at focal length of 2762mm (f19.7). ASI533MC ROI 300x300 pixels. FireCapture 2.7.10, AutoStakkert!3 & Registax 6.

The twenty or so still images which make up this GIF were 25% stacks of 10000 frames from one minute of captures every second minute. So the original 20GB of captured files were squashed into a 600kB GIF - with some inevitable quality loss of course.

Excellent animation and as others commented, it really deserves its own thread.

Excellent image NV. I was clouded out for this event and travelling for the similar transit the previous week, so good to see your high quality version.

On 03/11/2022 at 17:10, Nigella Bryant said:

Hi all, this has probably been asked before but I have a question about using de-rotation software from planetary imaging. Do you apply wavelets before de-rotation or after? Sorry for the question I've only just got to imaging Jupiter this October and produced one image so far but not that brilliant so I've taken a number of images over several mins of 2min intervals. So i'm hoping I'll be able to de-rotate them. Also do you use autostakker first which is what I've done with the following image. This is just my second effort. Thanks for any help. Attached is one of the ten processed images in autostakker with wavelets applied. 

 

Hi Nigella,

I guess it’s an ‘it depends’, question. If de-rotating the SER/AVI then that will be unsharpened, though you may use a sharpened image as a reference frame. If I’m stacking each SER first, eg via AS3!, then yes I will sharpen with wavelets in Regustax, but I’ll hold back a bit to leave something on the table, so that I can take the de-rotated stack out of WinJupos, back into Registax for a final tweak. I think WinJupos handles a lightly sharpened TIFF better than unsharpened, but don’t overdo it as that could introduce artefacts that WinJupos  might treat as real features.

Nice Jupiter image BTW.

21 minutes ago, Magnum said:

I just added a bit more to my last reply while you were typing yours

Just read the extra comments  - all excellent info, thanks

16 minutes ago, Magnum said:

Oh that's a good chart, yes the 2x does seem to have a negligible change doesn't it.

OK, so I would go straight for trying the new Baader at 1.3x, but I would put the ADC and or  filter wheel in front of the Baader 1.3x . if you keep the ADC in the middle like you have it now the spacing will be too much for the Baader and make it act at something like 2.5x. You will need to have a play around while previewing Jupiter, a quick and rough way to check is to adjust your ROI box in the capture program if given ROI is just touching the edges of the planet then you know thats how big it is. You can set any custom sized ROI in sharpcap. I like Jupiter to be around   500 pixels at the moment.

Lee

Thanks Lee, that’s the configuration I was thinking to use . I’m going to try the Baader lens on its own, screwed into the nosepiece of the camera (I’ve already confirmed that it fits ok). So the configuration will be scope -> ADC -> FW -> Barlow lens -> camera, but I’ll be experimenting as you suggest. I use FireCapture for capture, but can set the ROI in the same way you describe to measure the planet - I can’t believe that I never thought to do that previously 🙄. I’ll then reset the ROI with a bit to spare around Jupiter for the capture itself.

28 minutes ago, vlaiv said:

339.8px and 0.1407"/px seems about right. That gives diameter of Jupiter to be 339.8 * 0.1407 = 47.80986" which seems right.

Stellarium is giving apparent diameter at the moment to be 47.27" and this image was probably taken some time ago.

These two criteria have nothing to do with sampling rate. They give rule of the thumb for visual separation of two equally bright stars.

Sampling rate is determined by maximum frequency of the image in frequency domain by applying Nyquist sampling theorem. There is cutoff frequency due to nature of light (waves and interference). This is "hard" cutoff frequency - meaning it is indeed maximum frequency that the optics of given aperture can produce. There are no higher frequencies.

This limit is given by simple expression:

https://en.wikipedia.org/wiki/Spatial_cutoff_frequency

but actual math behind deriving that expression is a bit more complex (involves Fourier transform of aperture to get Airy disk function and then another Fourier transform of Airy disk function to derive low pass filter resulting from Airy pattern).

Formula that I presented above directly derived from above formula on wiki page:

and application of Nyquist sampling theorem (which states that you need to sample at twice max frequency - or that pixel needs to be half of shortest wavelength associated with max frequency).

By the way - when we speak of frequency and wavelength in this context - it is not frequency and wavelength of light / photons - but rather Fourier transform of image represented by 2d function (so FT of that function).

There is really simple way to check that.

0.1407"/px implies that your setup is at effective:

0.1407 = 2.9 * 206.3 / focal_length => focal_length = 2.9 * 206.3 / 0.1407 = ~4252mm

C14 has 356mm of aperture so effective F/ratio is F/11.96

For 400nm wavelength you want to sample at x5 pixel size, so F/ratio should be 2.9 * 5 = F/14.5

If you go by that criteria, then you are slightly under sampled, but I don't think that you are, as I often say that it is better to use 500nm as baseline and instead use x4 pixel size (from above mentioned formula F/ratio = pixel_size * 2 / 0.5um = pixel_size *4), because of seeing effect on shortest wavelengths and fact that most sharpness (perceived) comes from green part of spectrum - which is 500-550nm.

Going by that criteria 2.9 * 4 = F/11.6 - so you are spot on.

 

Thanks Vlaiv, this is helpful, even if I don't fully understand all of it. Regarding my Jupiter image, WinJupos measured it at 349.8px, not the 339.8px that you used in your calculation and yes, it was when Jupiter was displaying a disc diameter of 49.2".

28 minutes ago, Magnum said:

Yes I think if you weren’t using an ADC then you could use the 2x powermate, but the adc will push it a bit too far so the Baader barlow will get you something in between. 
rember though that with barlows extending the spacing increases the magnification, but with power mates it’s the opposite, extending the spacing decreases the magnification. So you could theoretically back of the mag with your power mate by using a bit more spacing.

do you have the ADC before the barlow or between the barlow and the camera? As that makes a big difference too.

Lee

Thanks Lee, yes, I'm aware that the change in magnification for TV PMs is different than how it works for barlows. As the below chart of the TV website, shows there is definitely a reduction with the x2.5 PM the further it is from the sensor, but for the x2 PM the change is very marginal.

It's one of the main reasons I moved from using the TV Barlows to the x2 PM. I have the ADC between the PM and camera as the ADC is 1.25" diameter, whereas the PM is 2" diameter. I'm also using a FW, so that increases the distance to sensor a bit too.

9 minutes ago, Magnum said:

From UK 0.07” will be pushing it, but around 0.09 - 0.10” is doable

Thanks Lee. This whole discussion the last couple of days has been eye-opening for me. I've just fairly blindly followed the px_size x5 rule of thumb, then watched the on-screen image to see what worked. I felt including the x2 PM with an ADC was too much and I think last year I took the PM out when imaging Jupiter which was still very low down. On Anthony Wesley's (Bird's) advice I'd taken the ADC out for Mars in 2020, but I was happy with my results still including the x2 PM. As I discussed with @neil phillips yesterday, I think I was too hasty to give up on the x2 PM with the 462MC sensor, but with the Baader barlow I have some options to increase amplification without going as far as 0.07" / px. It will be good to experiment some more, as Mars moves towards opposition over the coming weeks.

31 minutes ago, Magnum said:

In Damian’s talks he classes anything below 0.07” pixel as oversampling, 0.08” - 0.10” as ideal sampling , and 0.14” as under-sampling. 
this is for scopes in the 30-40cm aperture range.

im attaching screen shots from his talk to demonstrate.

this is of course under perfect seeing In barbados, but  I still find 0.1 works best for me.

remember those calculators aren’t taking into account unsung lucky imaging with 10s of thousands of split second exposures.

 

Thanks, that's great to know.....

41 minutes ago, Magnum said:

Yes sorry I typed it wrong 

Phew....!! So I've checked my images with the ASI290MM from 2020 and see I was very similar to Go & Peach at 0.07"/px and according to FireCapture FL = 8500mm, equivalent to F23.

That worked really well, so I'm definitely going to try again with the ASI462 at greater amplification.

6 minutes ago, Magnum said:

My jupiters measure around 500 pixels with my current sampling with the 12” scope, I’ve found that about the ideal. So about 1”/pixel Damian and GO are a bit higher than that around 6-700 pixels or around 0.8-0.9”/pixel but that’s with 14” scope and perfect seeing.

Do you mean 0.08" to 0.09" per px. Jupiter at say 49" / 500px = 0.1" / px not 1" / px - or what am I doing wrong please?

18 minutes ago, Magnum said:

Yes and to measure a simple way is to just crop the image in photoshop until it’s just touching the limbs the go to image size to see how many pixels it is.

though first make sure it’s rotated so the equator is level and wack up the mid level slider to expose the limb darkening enough to see the true edge.

alternatively win jupos can do image measurements precisely.

Thanks, I just did that and got 345 px, so very similar to the 349 that WinJupos gave me. I did the maths myself based on Jupiter's diameter at 49.2" on that night which confirms the ~0.14"/px (49.2/349). So am I actully then already oversampled without any further amplification....?🤷‍♂️