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Ok, I am going bonkers : What can I really do with this scope

Catanonia

By Catanonia
in Imaging - Discussion

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Catanonia

Catanonia

Posted
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The TS SuperNewt @f2.8 is proving to be about 3 - 4 times quicker than the Skywatcher MN190 @ F5.3

My 10 min subs in ha are looking pretty good, much much better than other scopes as you would expect.

So after gathering 17 subs of 10 mins Ha (equivalent to 30+ mins each sub on the MN190), I have just set the timer to 20mins subs.

By my calcs, that will be give or take 1 hour+ subs on the MN190.

Excited to see what comes out if the guiding holds.

Obviously there is a limit and these calculations are subjective and not precise, but it is a fun game.

20 mins on a 200mm Newt @F2.8... LOL :D:D:D 18 mins to go

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Catanonia

Catanonia

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sort off. Well got the 1st image and to tell you the truth, there was not much difference between 20min subs and 10 min subs. Even though the data should have been twice as good with of course noise, but being a cooled CCD that would have been limited.

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jgs001

jgs001

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Okay newbie question I guess - would that not be about right. I seem to remember that speed goes to the square of the f-number ratio - so (5.3/2.8)^2 = 3.6

You've lost me with the subs. Is that there the subjectiveness comes in?

Sub in this context means sub exposure from a sequence of the same image that gets stacked (combined to improve the SNR) into a single resulting image.

It's probably easier to think of in terms of photographic stops... I think I've got the numbers right... that it's one stop from f/2.8 to f/4, then another stop f/4 to f/8. For each stop larger (smaller number), you actually let in twice as much light as the previous one. So... if you start at f/4 and go to f/2.8 you let in twice as much light. So f/5.3 to f/2.8 is about 1.3 stops (ish)... errmm.... :D 2.5x as much ??

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cloudythoughts

cloudythoughts

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Does signal to noise will reduce to the root of the optical power on CCD ? That would make the S/N improvement linear with f-number ratio. I guess noise floor also creeps in somehow

How low a temperature is the CCD? I really must do some research rather than asking daft question, but is it on a Peltier cooler?

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cloudythoughts

cloudythoughts

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It's probably easier to think of in terms of photographic stops... I think I've got the numbers right... that it's one stop from f/2.8 to f/4, then another stop f/4 to f/8. For each stop larger (smaller number), you actually let in twice as much light as the previous one. So... if you start at f/4 and go to f/2.8 you let in twice as much light. So f/5.3 to f/2.8 is about 1.3 stops (ish)... errmm.... :D 2.5x as much ??

But I thought f/4 to f/8 was two stops. What about f/5.6. If f/5.6 to f/2.8 is 2 stops the f/5.3 to f/2.8 ought to be closer to 1.8 stops so about 3.6x :(

Thanks for the info on what subs mean - I've so much more to learn

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jgs001

jgs001

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But I thought f/4 to f/8 was two stops. What about f/5.6. If f/5.6 to f/2.8 is 2 stops the f/5.3 to f/2.8 ought to be closer to 1.8 stops so about 3.6x :D

Thanks for the info on what subs mean - I've so much more to learn

You could be right I get easily confused by one stops, two stops and having my slr work in third stops. thus my errrrmmm :(. I'll dig out a list later when I'm on a proper puter

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Catanonia

Catanonia

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double the f-number, double the stops and quadruple the light :D

It all depends on your terminolgy of what a stop is. People use different methods.

But double the F ratio and the rough rule of thumb is you quadruple the time it takes to gather the same light with all things such as apeture being equal. The old square rule

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Catanonia

Catanonia

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Here are two single subs that have been calibrated and leveled only.

10mins vs 20mins @F2.8 Not a lot of difference in them at the single sub level.

I have posted them as TIF's so you can play with them without compression.

There are some star shap isssues at the corners that I am still trying to fix.

Have fun.

Cone10m.tif

Cone20m.tif

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