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Mars 12th Nov


neil phillips
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10 minutes ago, neil phillips said:

Even at A exposure of 2 versus an exposure of 4 on the oversampled image.

If I'm reading this correctly, you used

2ms exposure on ~F/14 and higher gain and 4ms exposure on ~F/26 image?

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1 hour ago, Space Cowboy said:

Looking at these again on my 32" monitor and the oversampled image is much sharper, showing finer detail. If you shrink it down 50% it kills the f14 shot for sharpness. I've always thought you can get a more accurate focus with a larger image, even if it looks a bit noisy. I remember years ago using my 5x powermate with the qhy5L-ll on Mars at nearly f25 and although the images initially looked noisier the detail was far sharper.

The polar cap detail on these are awesome Neil, with such a 3D effect.

Cheers Stuart. As mentioned there can be reasons why someone may get a better oversampled image. Its never a given. But yes, agree it can happen. There is something about seeing a image at larger scale the helps two close points be easier for the eye to resolve perhaps? just a guess. 

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7 minutes ago, neil phillips said:

Look forward to seeing them Geof. I initially setup. but cloud came over as soon as i started the first capture ( dont you just love the UK ) I waited and it all cleared again. So my timestamp of the first usable capture was 02:04 UT

Ah, so much later. I went to bed at around 2am, but looked out first and it was still solid cloud here.

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3 hours ago, johnturley said:

Fantastic image Neil, Mare Erythreaum and North Polar Hood showing up really well.

I could see the North Polar Hood quite clearly visually at about 12.30 last night, I was just about to take a few images, but then it clouded over.

I regularly use a 2.5x Powermate with my Esprit 150 (f17.5), which gives reasonably good results, yet some observers suggest that I should be aiming for around f9 (1.25x Barlow) to optimise the sampling rate, and Astronomy Tools ridiculously suggests that under O.K. Seeing Conditions I should be aiming for around f5 (0.7 Reducer).

John 

Cheers John all i can say is don't under sample as that could lose information

What is the sampling ? (planetary-astronomy-and-imaging.com)

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2 hours ago, vlaiv said:

One thing is sure - over sampling won't make image (at focal plane) sharper as laws of physics don't allow for that - any perceived sharpness is due to difference in processing - and as we have just seen, simple tweak can make properly sampled image look sharper.

I think seeing and lucky imaging is being forgotten.  In planetary imaging, everything is oversampled.  Seeing changes by the second, so it is very possible that the F14 Is sharper than the F26 due to micro seeing conditions--and vice versa.  Lucky imaging is different than deep sky imaging.    

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3 hours ago, vlaiv said:

Here is an interesting thing:

image.png.09cf830d84aff5055fbc34203734309a.png

these are both F/14 versions - but one on the left is sharper than one on the right - because I just ran a bit of sharpening on it.

Compared to resized oversampled image - it now looks sharper, doesn't it:

image.png.8e14ba10252037fc10df31ae4e105d8c.png

(left sharpened F/14 image and right downsampled over sampled image).

I guess there is a lot to how the image was processed.

One thing is sure - over sampling won't make image (at focal plane) sharper as laws of physics don't allow for that - any perceived sharpness is due to difference in processing - and as we have just seen, simple tweak can make properly sampled image look sharper.

The processing depends on the individual's preferences regarding the finished result. Neil doesn't like to over-sharpen his images, so the comparison is based on his preference, i.e., a natural appearance. I'm sure I could add extra sharpening to the oversampled image to reverse the difference again. What we produce in theory and practise are not always the same. Some conditions and setups will favour one sampling over the other. Experimentation is how we find our own sweet spots 🙂

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2 minutes ago, Space Cowboy said:

The processing depends on the individual's preferences regarding the finished result. Neil doesn't like to over-sharpen his images, so the comparison is based on his preference, i.e., a natural appearance. I'm sure I could add extra sharpening to the oversampled image to reverse the difference again. What we produce in theory and practise are not always the same. Some conditions and setups will favour one sampling over the other. Experimentation is how we find our own sweet spots 🙂

I'm always surprised that people think that they can produce detail that is not there by over sampling.

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2 minutes ago, neil phillips said:

Was running a second capture at F26. 3 mins in the scope went out of travel needing a meridian flip. So added the 3 mins I got onto the existing 6 min capture i had. Did a video de rotation. Slightly harder processing and contrast. reduced to 70% in size. 

 

2022-11-12-0303_0-DeRoT 70.png

Well done Neil, very creative and well worth the effort.

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