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Uggg RASA

astrophotography Celestron
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#1 rcamikes

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Posted 07 December 2019 - 08:46 AM

Like the rest of you, I have had a steep learning curve with imaging.  I have had success with a Stellarvue and a Meade 10" LX90 mounted to a HDX110.  I have been moderately happy with my imaging "success" with those scopes.  I am imaging with a ZWO ASI 183 Color Pro and 1600 Pro mono.

 

I cannot figure out WTH I am doing wrong with the RASA 11" I just bought and mounted on the HDX.  Are my exposures too long, too short, too much gain, do I need a better LP filter.  I have F2 filters on the way and have only used the color 183.  The stars come into focus unbelievably fast and I am imaging in no time.  I know its user error, but I have no idea what I'm doing wrong.  I am attaching a pre-processed image, with the hopes of some telling me why I cannot process the Bubble Nebula and why the stars look great in raw mode but all of it looks blown out after preprocessing.  I used AstroPixelProcessor for one pic and Nebulosity for the other.  Not much difference whenI bring into PS.  Blown out and no nebulosity.  Help

 

54 Lights x 180s, Gain 60, Offset 20

15 Darks

15 Flats

15 Bias

183 Color Pro -20 degrees

RASA 11"

PHD2 Guiding

Orion SkyGlow Filter

(I have used no filter and pretty much same results)

Bortle 8, Clear Night

 

https://1drv.ms/u/s!...BpWDKa?e=NEGVDV

 

https://1drv.ms/u/s!...jm2VPqgUwksg7yV

 

First link is preprocessed with AstroPixelProcessor and second link is preprocessed with Nebulosity.

 

HELP!!!   Any feedback greatly appreciated

 



#2 ChrisWhite

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Posted 07 December 2019 - 08:52 AM

The RASA is a very fast system, and 3min subs are waaaayyyyyyyyy  too long for it, especially with that huge aperture.  You're just blowing out the stars like crazy. 

 

If I had to take a wild guess, you should probably be taking 20 second exposures... maybe 30 second at the most.


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#3 John Miele

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Posted 07 December 2019 - 08:56 AM

You might overexposing a bit using 3 minute subs at f2 with these sensitive CMOS camera. I would start by checking your mean ADU values in the subs and see if they are close to what is recommended for  the camera you used (183 or the 1600).



#4 OleCuss

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Posted 07 December 2019 - 10:17 AM

I tend to agree.  Shorter subs and more of them is likely the better answer.  You could probably be doing 10 second subs and by stacking a bunch of them have excellent results.

 

Also remember that the IMX183 does not have a lot of bit depth - especially if you turn up the gain.  That means fairly limited dynamic range and quickly blowing out your brighter stars.


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#5 Dynan

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Posted 07 December 2019 - 10:59 AM

I had to put a UV/IR filter in front of my 183MC-Pro to get ANY star color. The sensor is very sensitive to light outside the visible spectrum, so stars were so swamped as to be nothing but white. I use an Astronomik L-3 (narrowest band UV/IR) of the L series.

 

And as stated above, watch the exposure time for 15k well capacity pixels. I've had great results imaging M42 (yes, a brightness beast) at 3 seconds. That was with a 127mm aperture refractor.

 

https://www.cloudyni...zium/?p=9737236

 

Back off on the powder and let the big dog eat! waytogo.gif


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#6 SonnyE

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Posted 07 December 2019 - 11:52 AM

I'm an experimenter.

I tend to run up, and run down the time.

So experiment... a LOT.

Don't think what worked before will apply to something entirely different.

Apparently it does not.

But get out and have fun.

And with digital, use the delete button a lot.



#7 rcamikes

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Posted 07 December 2019 - 12:42 PM

Thanks everyone. With shorter subs will I even get any nebulously?

#8 Dynan

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Posted 07 December 2019 - 01:01 PM

Thanks everyone. With shorter subs will I even get any nebulously?

With enough of them!


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#9 ChrisWhite

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Posted 07 December 2019 - 01:03 PM

Thanks everyone. With shorter subs will I even get any nebulously?

Plenty.  What matters is how much TOTAL integration time you have.  For an hour of total time whether you have 20, 3 min subs or 180, 20 second subs really doenst make any difference in the final image... as long as you expose long enough to swamp read noise.  At f2, you wont have any trouble with that using short exposures. 


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#10 ChrisWhite

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Posted 07 December 2019 - 01:10 PM

Here is an example taken with 30 and 45 seconds at f2.8 with an 8in Newt:  https://www.astrobin...page=2&nc=&nce=

 

F2 is twice as fast as 2.8....

 

In the image here, I couldnt see anything at all in the single subs.   Its super faint and dusty...


Edited by ChrisWhite, 07 December 2019 - 01:11 PM.

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#11 rcamikes

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Posted 07 December 2019 - 01:20 PM

I’m using the 1600 with NB tonight. I’ll prob do 90 seconds with NB filters unless some tells me otherwise ??

#12 ImaLibra

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Posted 07 December 2019 - 01:21 PM

I was going to make a separate thread asking about RASA and Hyperstars at F/2. However, this post should be a great place to ask!

 

Question for you all: Can I achieve the same speed as a RASA or Hyperstar with a Starizona .4 Night Owl Reducer and larger pixels?

 

Here's the comparison: Using 12Dstring calculators, it appears that an 11" aperture at F2 = 560mm FL. Combine that with the small pixel size of an ASI 1600mm and you get 1.40"/pixel.

 

I have an old C11 F10 = 2800mm FL, put on the .4 reducer to get to 1120mm FL. I have an older model Nikon D700 with pixel size of 8.45 microns and a sampling of 1.56"/pixel. Not counting the Bayer Matrix inefficiency, shouldn't the speed be nearly the same between the two systems? Both buckets are gathering the same amount of photons, and although my scope is twice the FL, the 2x pixel size means that it cancels out that "slower speed" of F/4 compared to F/2, right? 



#13 ChrisWhite

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Posted 07 December 2019 - 02:00 PM

I’m using the 1600 with NB tonight. I’ll prob do 90 seconds with NB filters unless some tells me otherwise ??

What gain are you gong to use? What filters?  At unity, you might do 90 seconds or 60 seconds. 

 

Review your image without ANY stretch.  Do you see a bunch of white stars?  If so, your exposure is too long.  You should not see the stars in an unstretched image, with the exception of a few.  I use the baker's dozen rule.  If I have more than 12 stars that are saturated, I reduce my exposure time. 

 

Make sure you dither frequently and aggressively.  When you flirt with low exposures, you want to do everything you can to prevent fixed pattern noise in your final result.  The curse and blessing of imaging with 11in of aperture at f2. 


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#14 bugbit

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Posted 09 December 2019 - 01:21 AM

Just a fyi: I have been playing with a 11" rasa for a bit over 4 years and 99.5% of those shots are/were at 30 seconds.I should say of the photo's I kept.A bright star like Alnitak will blow out in just a few seconds. Once in a while a 5 minute shot at the horsehead just to show someone what it looks like when they come over.

 

fwiw




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