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Classical cassegrain 10th July Jupiter


neil phillips

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Thought it was worth looking at some captures from the 10th July under good seeing. Will process a few and see what comes out here is a early one from the night 

 

03_22_36_july 10th .png cc.png 125.png

Seriously oversampled. using a 2.25x Baader Q barlow screwed  straight into a ZWO ADC it was a experiment to see how the scope coped. This is capture size

03_57_32 10th july best.tif ps.png b.png

 

2022-07-10-0314_2-DeRot last.tif r.tifdone.tifsg.png

Edited by neil phillips
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15 minutes ago, Kon said:

Very nice details Neil.

I wanted to have a relook at this data. It was the best night of recent times. I kind of rushed looking at it back then. So always worth having another more careful look. 

I must admit. its surprising how these cassegrains can be pushed to this level. It could be forgiven thinking the images came from a much larger scope. Not sure what others think. But thats my impression. The focal length on these larger shots are around 5000 mm 

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1 hour ago, neil phillips said:

I wanted to have a relook at this data. It was the best night of recent times. I kind of rushed looking at it back then. So always worth having another more careful look. 

I must admit. its surprising how these cassegrains can be pushed to this level. It could be forgiven thinking the images came from a much larger scope. Not sure what others think. But thats my impression. The focal length on these larger shots are around 5000 mm 

I agree your images from the 10 and 11 July seem the best so far this summer. I can't comment on the telescope as I only have experience with my Dob.

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34 minutes ago, vlaiv said:

But also seriously sharp and detailed when you resample it to proper size.

Lol trust you vlaiv it is already proper size. I think it looks better full size. As two points are easier to see in my opinion. Each to there own 

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Very nice images Neil, definitely a keeper that CC.  Would be tempted myself had I not just bought a mount (beans on toast for the rest of the year for me!)

Looking at your image and doing the calcs it looks like you were operating at F/31 ish, so your barlow power was around 2.6x

Purely for info here is the capture image (0.09" PP) and the downsized images together (downsized to 0.22" PP or F/13.6 - not saying this is the correct sampling, just a comparison 😄)

 

 

neil jup comparison.png

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57 minutes ago, CraigT82 said:

Very nice images Neil, definitely a keeper that CC.  Would be tempted myself had I not just bought a mount (beans on toast for the rest of the year for me!)

Looking at your image and doing the calcs it looks like you were operating at F/31 ish, so your barlow power was around 2.6x

Purely for info here is the capture image (0.09" PP) and the downsized images together (downsized to 0.22" PP or F/13.6 - not saying this is the correct sampling, just a comparison 😄)

 

 

 

Its interesting. What's weird is i took a number of shots correctly sampled. But ended up preferring the oversampled shots. Not exactly sure why ? Could be a number of reasons I guess. As i said to vlaiv. I think they look better full size. Certainly not as sharp but that's obviously going to happen. But i do think two close points together are easier to see full size, that on the correctly sampled image is harder to see, maybe its my old eyes.  Yes when i mentioned 2.25x i meant the native power of the Q Barlow. With the ADC even screwed  directly into it. is increasing the power more. One annoying thing about ADCs generally. 

 

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35 minutes ago, si@nite said:

Splendid detail on display Neil, the storms also showing up well in the southern region, nice work!

Cheers Simon i kind of get the feeling  I might prefer  sampling a little higher. Not as high as these larger shots but. higher than using no barlow at all. Even though that's close to good sampling. On the smaller shots

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39 minutes ago, neil phillips said:

But i do think two close points together are easier to see full size, that on the correctly sampled image is harder to see, maybe its my old eyes. 

That part is down to display device rather than sampling rate.

When image is properly sampled, one still needs to match resolving of their eyes as well as display device pixel pitch and viewing distance.

Similarly - over sampled image can look rather sharp when viewed from a distance.

Proper sampling is just ensuring that minimum number of pixels (or rather sampling points - better to think of it that way) is used to record all information needed. This helps with SNR and in turn that helps with sharpening as we need good SNR in order to process and sharpen data properly.

I can make over sampled image look good - just by simply moving away twice the distance to my display device.

For example - I use computer screen that has 92ppi (1920x1080 resolution on 24inch computer screen - that is ~2202 pixels on diagonal for 24 inch diagonal 2202 / 24 = 91.75ppi). That makes pixel ~0.246mm in size

20/20 vision is resolving about 1 minute of arc.

If I'm 80cm away from my computer screen - I perfectly match pixel size to minimum resolving size of good vision (I actually sit a bit closer at something like 60-70cm).

In above conditions, viewing at 1.5m away, overs sampled image will look similarly sharp as correctly sampled image at optimum viewing distance (of ~80cm).

People viewing on mobile devices will have different experience as pixel pitch on those devices is quite different - often going up to 400-500ppi, and older people have trouble focusing as close as 20-30cm, so often hold their devices further away - which makes image at 100% on such device that is x2 over sampled - just right.

 

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28 minutes ago, vlaiv said:

That part is down to display device rather than sampling rate.

When image is properly sampled, one still needs to match resolving of their eyes as well as display device pixel pitch and viewing distance.

Similarly - over sampled image can look rather sharp when viewed from a distance.

Proper sampling is just ensuring that minimum number of pixels (or rather sampling points - better to think of it that way) is used to record all information needed. This helps with SNR and in turn that helps with sharpening as we need good SNR in order to process and sharpen data properly.

I can make over sampled image look good - just by simply moving away twice the distance to my display device.

For example - I use computer screen that has 92ppi (1920x1080 resolution on 24inch computer screen - that is ~2202 pixels on diagonal for 24 inch diagonal 2202 / 24 = 91.75ppi). That makes pixel ~0.246mm in size

20/20 vision is resolving about 1 minute of arc.

If I'm 80cm away from my computer screen - I perfectly match pixel size to minimum resolving size of good vision (I actually sit a bit closer at something like 60-70cm).

In above conditions, viewing at 1.5m away, overs sampled image will look similarly sharp as correctly sampled image at optimum viewing distance (of ~80cm).

People viewing on mobile devices will have different experience as pixel pitch on those devices is quite different - often going up to 400-500ppi, and older people have trouble focusing as close as 20-30cm, so often hold their devices further away - which makes image at 100% on such device that is x2 over sampled - just right.

 

In this case i think its both sampling rate and display device, I am fully aware of the advantages of correct sampling Vlaiv. Anyway cheers for the input.

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9 minutes ago, chiltonstar said:

Nice detail! CCs seem to be a bit like marmite at the moment I think.

Chris

Yes i noticed that. But is that the fault of the telescope or the hands they are in ? When the results come in from a well collimated CC And you realize the asking price per performance. Then the extra care needed with collimation. Is more than worth it in my opinion. But of course this may be different for different people and i get that. But i still think they are probably one of the best 7" scopes per £ money can buy. 

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10 minutes ago, neil phillips said:

Yes i noticed that. But is that the fault of the telescope or the hands they are in ? When the results come in from a well collimated CC And you realize the asking price per performance. Then the extra care needed with collimation. Is more than worth it in my opinion. But of course this may be different for different people and i get that. But i still think they are probably one of the best 7" scopes per £ money can buy. 

7”?  Isn’t it a 203mm aperture? 

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31 minutes ago, neil phillips said:

Yeah they are all at it. Maks do similar. 

Only some Maks - the 150 and 180 are full aperture with o/s mirrors I believe. My 180 returns a clear aperture of 179mm on a test bench.

Chris

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