Mars 12th Nov

[neil phillips]

Some single runs. may try de rotation later 

Orion 245mm Newtonian QHY 462C no ADC. EQ5 PRO

Optimal sampling F14.175 Baarder Q 2.25x RGB

100%

resample

 

Oversampled F26.775 Baarder 2.25x + Celestron Ultima 2x 

100%

Personally think too much is made of sampling rate. As can be seen not much advantage correctly sampled. And seriously oversampled isnt really hurting the image that much. Long discussions over pretty much minimal effect, I think. As long as your not under sampled and not ridiculously oversampled. It doesn't really have a huge effect. Not one i am seeing anyway. 

 

 

Edited November 12, 2022 by neil phillips

[CraigT82]

Fantastic work Neil, best I’ve seen  anywhere yet this year. 👍🏼👍🏼👍🏼

[neil phillips]

5 minutes ago, CraigT82 said:

Fantastic work Neil, best I’ve seen  anywhere yet this year. 👍🏼👍🏼👍🏼

Been waiting a while because of bad weather. Just got focus ready to capture. Sky completely clouded over. Anyway waited. And it cleared again. Which I didn't think it would.

Cheers for the positive comments Craig.

[CraigT82]

53 minutes ago, neil phillips said:

Been waiting a while because of bad weather. Just got focus ready to capture. Sky completely clouded over. Anyway waited. And it cleared again. Which I didn't think it would.

Cheers for the positive comments Craig.

It’s absolutely spot on Neil the processing is just perfect to me. Bravo! 
 

Was thinking of having a go on Mars tonight if the forecast holds and was debating if I should go OSC or mono and you’ve just made up my mind… going to go with OSC.

Edited November 12, 2022 by CraigT82

[Space Cowboy]

Those look good on my phone. Look forward to seeing them on my pc later! 

[neil phillips]

7 minutes ago, CraigT82 said:

It’s absolutely spot on Neil the processing is just perfect to me. Bravo! 
 

Was thinking of having a go on Mars tonight if the forecast holds and was debating if I should go OSC or mono and you’ve just made up my mind… going to go with OSC.

Good seeing and the OSC will do well. You will nail a belter with your experience I have no doubt. Thanks again on the processing comments

[neil phillips]

1 minute ago, Space Cowboy said:

Those look good on my phone. Look forward to seeing them on my pc later! 

Having to snatch chances lately. Nearly didn't get anything.  It's good to be imaging Mars again

[Simon128D]

One word review here... Stunning!

[Magnum]

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

[neil phillips]

Many thanks Simon.

[neil phillips]

Cheers Lee. It's not the night and day issue its made out to be. Slight focus inconsistency is probably more damaging. As is seeing. Falling temps. Non cooled scope. Collimation. Sampling is way down the list of damaging, as long as you're not under sampled. Slightly over even seems to have benefits I've found. I've said this before.  

Edited November 12, 2022 by neil phillips

[johnturley]

5 hours ago, neil phillips said:

Some single runs. may try de rotation later 

Orion 245mm Newtonian QHY 462C no ADC. EQ5 PRO

Optimal sampling F14.175 Baarder Q 2.25x RGB

100%

resample

 

Oversampled F26.775 Baarder 2.25x + Celestron Ultima 2x 

100%

Personally think too much is made of sampling rate. As can be seen not much advantage correctly sampled. And seriously oversampled isnt really hurting the image that much. Long discussions over pretty much minimal effect, I think. As long as your not under sampled and not ridiculously oversampled. It doesn't really have a huge effect. Not one i am seeing anyway. 

 

 

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 

Edited November 12, 2022 by johnturley

[chiltonstar]

Nice Neil. I always think Mars start to get interesting when the Tharsis trio start to appear.

Chris

[vlaiv]

Excellent images.

It faithfully shows many features (to resolving capability of the scope of course).

I managed to find similar high resolution image for comparison - and yes, everything is where you expect it to be - nothing is processing artifact:

 

[geoflewis]

Those are cracking good Mars images Neil. What time were you out there. I set up earlier to do some sampling testing on Jupiter, including my 1st try at CH4 imaging, but was fighting clouds. I did slew over to Mars later and grab some data, but it was shrouded in brightly illuminated fog and by 11pm I had pretty much total cloud cover so gave up. I haven't processed my dats yet, other than play with the CH4 Jups, so will post everything up later.

[Kon]

Fantastic set of images, so natural looking without being pushed too much. Nice comparison on sampling.

As I am still getting my head around things, is resample just a resize? What is usually a good resize? I usually try 120 or 150 if I feel it's a nice capture.

[Space Cowboy]

3 hours ago, neil phillips said:

Having to snatch chances lately. Nearly didn't get anything.  It's good to be imaging Mars again

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.

Edited November 12, 2022 by Space Cowboy

[vlaiv]

3 minutes 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.

Really? I'm not seeing it

Here is comparison at ~F/14 scale

and here is comparison at ~F/26 scale

In both cases - ~F/14 is on the right side.

And to tell you the truth - I'm finding ~ F/14 to be maybe just a tiny bit sharper on some features while F/26 might be said to be sharper on other

Here we see that F/14 is sharper / has better separated and more contrast on the feature that I marked.

~F/26 looks just a tiny bit sharper in this feature.

[Space Cowboy]

18 minutes ago, vlaiv said:

Really? I'm not seeing it

Here is comparison at ~F/14 scale

and here is comparison at ~F/26 scale

In both cases - ~F/14 is on the right side.

And to tell you the truth - I'm finding ~ F/14 to be maybe just a tiny bit sharper on some features while F/26 might be said to be sharper on other

Here we see that F/14 is sharper / has better separated and more contrast on the feature that I marked.

~F/26 looks just a tiny bit sharper in this feature.

To my eyes the oversampled shot looks far sharper on the f14 size comparison.

[vlaiv]

9 minutes ago, Space Cowboy said:

To my eyes the oversampled shot looks far sharper on the f14 size comparison.

Here is an interesting thing:

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:

(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.

[Sunshine]

A fantastic Mars image!

[neil phillips]

The fact that we are even debating this proves my initial point. I think sampling rate has its uses. But getting bogged down in it, to the level we do is quite distracting. It doesn't hurt to experiment. There can be reasons why oversampled image may look better. one reason often mentioned is, it can be easier to finely focus. On the correctly sampled images I had to use 150% zoom as the image was difficult to see at 100%. No such problem on the oversampled image. So regardless if the image is sharper or not here. On some occasions I can see why it could be. The oversampled image likely had less read noise, as the gain was higher. And quite low on the correctly sampled image. Even at A exposure of 2 versus an exposure of 4 on the oversampled image. Anyway, I say experiment generally. Oversampling does not always hurt the image as much as one might expect. There can be reasons why it might turn out to be the better capture of the night. Everything from getting correct focus. to having less read noise on a bright target like mars. Of course, it could also go the other way. And be the inferior capture of the night. But it doesn't hurt to experiment. Lets not keep getting bogged down in theory as Christophe Pellier correctly says 

This means one thing: evaluating the sampling before imaging is a matter of experience. In astronomy, it is nice to know a bit of theory, but we must not become its slaves ;).

 

[neil phillips]

Right back to replying Many thanks Chris. it certainly is getting interesting now.

[neil phillips]

Cheers Vlaiv forever the scientist. 

[neil phillips]

11 hours ago, geoflewis said:

Those are cracking good Mars images Neil. What time were you out there. I set up earlier to do some sampling testing on Jupiter, including my 1st try at CH4 imaging, but was fighting clouds. I did slew over to Mars later and grab some data, but it was shrouded in brightly illuminated fog and by 11pm I had pretty much total cloud cover so gave up. I haven't processed my dats yet, other than play with the CH4 Jups, so will post everything up later.

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

Edited November 12, 2022 by neil phillips