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Old 28-05-2016, 06:38 PM
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144s vs 480s - what's what?

Thought this was an interesting comparison.

Each of these are a single calibrated sub (flat and bias). They were both stretched to roughly the same point using the histogram transformation tool in PI.

One of these subs was 144s long and taken before the moon came up. The other was 480s long and taken when the moon was about 90% full and up in the sky during capture.

Can you guess which sub is which?
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  #2  
Old 28-05-2016, 06:44 PM
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i would guess the first one is 144
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Old 28-05-2016, 06:51 PM
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Atmos (Colin)
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From my phone I would say that the first is the 480s.
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Old 28-05-2016, 08:19 PM
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Ray's on the money this time. The first image is 144s, the second 480s. I'd never done a comparison like this before so I didn't really know the impact the moon had on targets like this... opened my eyes a bit.
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Old 29-05-2016, 07:47 AM
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I didn't get a chance to guess!

Yes, your comparison shows very clearly that dark skies rule.

Even with 3nm filters, there is a significant reduction in data quality collected when the moon is up, particularly for fainter objects.
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Old 29-05-2016, 08:34 AM
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Interesting comparison. Of course I would I have thought the first one was the longer.

A might also add various scopes perform differently in high moon. I would not blanket assume all are the same in this regards.

For example my AP Honders Riccardi has the best ability to cut through light pollution of any scope I have ever used. It has lots of baffling and an oversized tube for the size of the mirror (14 inch tube, 12 inch mirror great for thermal currents as they drop off to the side where a fan sucks them out, very clever).

But yes there is no substitute for a dark site most noticeably when you go for the fainter objects. Bright objects are still very accessible from light polluted or moon skies.

I find as long as the scope is not pointing towards or near the moon narrowband with 5nm Astrodons is quite workable. But near the moon nothing saves you until someone comes out with a .5nm Ha filter!

Even then how much of the moonlight has Ha in it?

Greg.
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Old 29-05-2016, 10:11 AM
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codemonkey (Lee)
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Quote:
Originally Posted by Slawomir View Post
I didn't get a chance to guess!

Yes, your comparison shows very clearly that dark skies rule.

Even with 3nm filters, there is a significant reduction in data quality collected when the moon is up, particularly for fainter objects.
I'm good like that. I also like to give people presents early, even if they don't want them early.

Dark skies definitely rule!

Quote:
Originally Posted by gregbradley View Post
Interesting comparison. Of course I would I have thought the first one was the longer.

A might also add various scopes perform differently in high moon. I would not blanket assume all are the same in this regards.

For example my AP Honders Riccardi has the best ability to cut through light pollution of any scope I have ever used. It has lots of baffling and an oversized tube for the size of the mirror (14 inch tube, 12 inch mirror great for thermal currents as they drop off to the side where a fan sucks them out, very clever).

But yes there is no substitute for a dark site most noticeably when you go for the fainter objects. Bright objects are still very accessible from light polluted or moon skies.

I find as long as the scope is not pointing towards or near the moon narrowband with 5nm Astrodons is quite workable. But near the moon nothing saves you until someone comes out with a .5nm Ha filter!

Even then how much of the moonlight has Ha in it?

Greg.
Ah, now there's an interesting point and one I hadn't considered. Thanks Greg. It would be interesting to see comparisons with other kits to see how they might differ.
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Old 29-05-2016, 12:58 PM
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Quote:
Originally Posted by gregbradley View Post

For example my AP Honders Riccardi has the best ability to cut through light pollution of any scope I have ever used. It has lots of baffling and an oversized tube for the size of the mirror (14 inch tube, 12 inch mirror great for thermal currents as they drop off to the side where a fan sucks them out, very clever).

Greg.
I am a bit unclear, but how does one scope “cut” through light pollution. I thought the sensor was purely a passive device catching photons directed towards it, acquiring signal. The result contains light pollution, noise, and the intended target signal. How is the light pollution signal removed from the acquired sub in the OTA?

Terry
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Old 29-05-2016, 01:19 PM
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Quote:
Originally Posted by TR View Post
I am a bit unclear, but how does one scope “cut” through light pollution. I thought the sensor was purely a passive device catching photons directed towards it, acquiring signal. The result contains light pollution, noise, and the intended target signal. How is the light pollution signal removed from the acquired sub in the OTA?
Some scopes will do a better job than others of rejecting off axis light pollution. I agree that there's not much you can do about LP that's inherent in the FOV though a fast scope, like Greg's RH, will allow you to achieve a high SNR faster for both wanted (target) and unwanted (light pollution) signal. The LP can then be removed as a gradient.

Cheers,
Rick.
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Old 29-05-2016, 04:43 PM
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I thought this thread was going to be about trouble with youtube given the 144 vs 480 premise. Anyhow, I believe I'm seeing more detail in the first pic. Going after anything other than planets near full moon is never a good idea imho.
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Old 05-06-2016, 09:05 PM
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astronobob (Bob)
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Just looked at this, trick question huh so concluded that the 2nd image had a courser noise signal so guessed it be the longer sub
Interesting read further on tho - out smarting LP, we're all at it
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