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Got my first light with the ASI533 - need some tips

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#1 DRK73

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Posted 19 October 2020 - 05:05 PM

Hi all,

 

The camera is SOOOO much more sensitive and faster with downloads than the SBIG - focusing was such a snap, aligning, etc. Wow.

 

I wanted to try M31 as my first attempt because it was a new moon night and I was just going to use an L-pro filter, but framing was pretty tight in the AT72 (I just have a flattener, here I definitely need a reducer which is currently OOS at Astronomics). 

 

I don't know how to really figure out a good exposure time, so I just picked 2 minutes and planned to do a lot of them. The plan was working for a little over an hour until the sky became a really soupy, hazy mess, and all but the brightest stars (and Mars) were wiped out. Oh well...so here's 45 2-minute exposures calibrated with flats (probably not great ones), bias, and darks. 

 

CzsyHEJ8deDa_620x0_MhYR8GmW.png

 

In the bottom right and top left are these regions where the background illumination seems...hazy? As if there are variations in the brightness? It may be kind of hard to see here because I tried to hide that in processing. 

 

I've also got these random little speckles here and there that are red, green, or blue. Are these stuck pixels? What's the best way to handle them?

 

Also, even though the camera comes with precisely 55mm of spacing, it looks like the AT2FF flattener needs a bit more...



#2 DRK73

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Posted 19 October 2020 - 05:10 PM

Here's a pic of those green, red, and blue spots. I've not dealt with this kind of thing before.

 

 

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#3 zxx

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Posted 19 October 2020 - 05:19 PM

Here's a pic of those green, red, and blue spots. I've not dealt with this kind of thing before.

I get them RGB spots when my darks temp don't match the lights.



#4 DRK73

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Posted 19 October 2020 - 06:13 PM

I get them RGB spots when my darks temp don't match the lights.

Well, I went and checked the FITS headers for my lights and darks and they're just about the same. The darks (taken indoors) were bang-on -10C, the lights kind of varied between -9.7 to -10.2degC.

 

I haven't used dark flats before, should I be doing this?


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#5 zxx

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Posted 19 October 2020 - 06:25 PM

Well, I went and checked the FITS headers for my lights and darks and they're just about the same. The darks (taken indoors) were bang-on -10C, the lights kind of varied between -9.7 to -10.2degC.

 

I haven't used dark flats before, should I be doing this?

I never tried dark flats. I couldn't say.



#6 sn2006gy

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Posted 19 October 2020 - 07:04 PM

Be sure to dither! If you dither and bayer drizzle it should remove the hot pixels.

When I had the 533 (moved to 2600) I just did flats, dark flats and lights and dithered between frames. Not hot pixels
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#7 jewelsdean

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Posted 19 October 2020 - 07:11 PM

My understanding is that this camera touts not having any amp glow.  Wouldn't that negate a need for darks?  I use 100 gain on the 533 and 10 offset and I seem to get fairly good exposures guiding.  I also use a L-pro filter in my image train and have not noticed the blue spots you mentioned.  I certainly don't see them when using narrowband filters.  Don't know if this helps or not just throwing more information out there....  I do believe if you adjust the gain appropriately you will see less noise according to this chart.  The last chart shows the read noise at 1.5 and 100 gain.  This is the setting I use the most.  Also the Gain(e-/ADU) chart shows 100 as the optimal gain setting.....

 

ASI533 Performance1

Edited by jewelsdean, 19 October 2020 - 07:22 PM.

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#8 DRK73

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Posted 19 October 2020 - 07:34 PM

My understanding is that this camera touts not having any amp glow.  Wouldn't that negate a need for darks?  

 

I don't actually know - to be clear: were you asking me this in a way to remind of what I should know? I was doing darks mostly because I always do them and figured that, at worst, they couldn't hurt?
 

I've been doing some more research and see that people are not even doing bias, but using dark flats instead. I need to get a better handle on what I'm doing...


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#9 BinoGuy

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Posted 19 October 2020 - 07:57 PM

AFAICT (I'm a noob at this) you take the Bias out of the Darks and use those for calibration (some smart folks don't use them again all but for now that's my process).  Even though our 533s don't have amp glow there can still be hot pixels.  One of my free tools, Siril, gives you the coordinates for individual pixels.  You could look at other images and see if the same pixels are consistently lit.
 

I'm just over a month with my 533, and I have maybe 5 nights out with it. 

 

clear skies, BinoGuy


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#10 jewelsdean

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Posted 19 October 2020 - 10:37 PM

AFAICT (I'm a noob at this) you take the Bias out of the Darks and use those for calibration (some smart folks don't use them again all but for now that's my process).  Even though our 533s don't have amp glow there can still be hot pixels.  One of my free tools, Siril, gives you the coordinates for individual pixels.  You could look at other images and see if the same pixels are consistently lit.
 

I'm just over a month with my 533, and I have maybe 5 nights out with it. 

 

clear skies, BinoGuy

Now you've got me curious if I can remove some of the noise in my photos with a good set of darks added to my post processing.  This is an example of a photo taken with the settings above that I mention.  This was with a narrowband filter:  (I'll add some darks and reprocess it to see if it improves the image and report back)

NGC 6992 RGB session 1 St

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#11 BinoGuy

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Posted 20 October 2020 - 01:03 PM

I should have included this last night, but I was pretty sleepy.  I think Bias frames also help remove the read noise, as per Trevor:

 

https://astrobackyar...trophotography/

"Bias is an offset that occurs when a pixel is read from the CCD or CMOS camera sensor. Your camera inherently has a base level of readout noise as it reads the values of each pixel on the sensor, called bias. Basically it’s an inherent pattern to the sensor.

Like the other calibration frames we use, Bias frames are meant to capture this so it can be removed.  The Bias noise pattern can vary across the image. In many cases, if the bias frame is not corrected then flat-field calibration will not work accurately.

A bias frame is essentially a zero-length exposure or to the shortest exposure time possible on the camera, with the shutter closed. We are interested in the fixed noise pattern of the electronics, therefore keeping the exposure short as possible helps prevent other noise creeping in, such as dark currents."

"



#12 sn2006gy

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Posted 20 October 2020 - 03:00 PM

I don't use Darks on this camera.  Just flats and flat-darks.   If you don't use flat-darks, then you calibrate your flats with bias - which may be the easiest route as the only thing you need to do to take each time your out is your regular flats. Bias can be a master bias.

 

The best way to get rid of the hot pixel noise by dithering. Dithering wipes it clean and fixes other issues as well as gives you  bayer-drizzle which helps recover signal from your bayer matrix that would otherwise need to be inferred.

 

Darks work too, but i find i enjoy the flexibility of changing my time without worrying if i have a matching dark library and since i have a flip-flat i don't mind taking flats and flat darks for the temp/gain i'm using for the night.


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#13 lesleyrgreen

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Posted 20 October 2020 - 04:07 PM

I have the same red and blue pixels in my images from my 533 and never noticed them with my 294mc pro. I believe it is because the 294 requires you to do good calibration frames due to the amp glow and I have been less than lazy with calibration frames from the 533. I have had good results (for my standards anyway) with the Light Vortex Astronomy preprocessing tutorials using PixInsight (specifically cosmetic correction) in the absence of calibration frames. This is the step which has really helped me get rid of the red/blue pixels (skip to the CosmeticCorrection process) .

 

https://www.lightvor...t.html#Section4

 

Probably not the way you are supposed to do it, but it does work. 

 

Les


Edited by lesleyrgreen, 20 October 2020 - 04:09 PM.

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#14 Wookiee

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Posted 20 October 2020 - 05:02 PM

I had the same issue with my 533 and dithering with enough frames completely resolves the issue.

I usually dither every 2nd to 4th frame depending on how many subs are planned.

As mentioned above, dithering also allows you to drizzle which has benefits.

As for darks, I've tried various combinations and settled on lights, flats and bias frames. Including darks gave no visual improvement for me, not to say it doesn't help somehow but I couldn't see an improvement with my beginner eye.
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#15 AhBok

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Posted 21 October 2020 - 12:59 PM

And here is my first light with the ASI533MC P. Frankly, I was just working on getting my spacing correct from the field flattener and only captured 2.7 hours of exposure. All the processing was done in APP. I expected a lot more noise, so was surprised at the result. Now I'm excited to find out what this camera can do when I get all the issues of gain, exposure, temp and spacing worked out with a bit more exposure time.

 

Skywatcher 72ED

ASI533MC Pro

80 x 120 sec lights

50 darks

50 bias

30 flats

101 gain

10 offset

Medium dither every 4th frame

APT for capture

APP for stacking and post

 

 

Not an APOD image, but the camera shows promise.

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  • Messier_031-web.jpg

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