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Slow Beginnings: ASI 294 help please

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#1 Owk

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Posted 05 May 2019 - 09:27 PM

G'Day!

 

Very much a beginner with EAA.

I have a C925/Meade 6.3 Reducer/AZEQ6/ASI 294 MC Pro/Sharpcap 3.2 Pro/EQAscom.

 

These are some images ive taken, all 4-15s.30-60 subs. No calibration frames. 294 is cooled to the max: gets to about -10 max, as I live in the tropics.

Im getting a lot of hot pixels. Is this normal at this length of exposure?

Can someone tell me what the finger print like smudge is, the optical train appears clean.

Should I expect vignetting with this setup? Or do I need to alter the spacing? currently reducer is directly on the SCT, then a Baader click lock, with 1.25 adapter and then the nose piece of the camera.

Lastly, I am bewildered on how to properly get the WB settings correct. They clearly have a great effect on the stacked image, but how do I set them correctly so the colours are accurate?

 

Thanks in advance.

 

 

Hemi

 

 

 

 

 

Attached Thumbnails

  • Centaurus A.jpg
  • M83 copy.jpg
  • M4_00001_WithDisplayStretch.jpg
  • Trifid.jpg

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#2 cshine

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Posted 06 May 2019 - 09:11 PM

Hey Hemi, here are my thoughts, hopefully they help until someone more experienced chimes in:

 

>> No calibration frames. 294 is cooled to the max: gets to about -10 max, as I live in the tropics.

 

Flats will obviously help with vignetting, it's always worth taking a few mins to capture those. Simple twilight sky or t-shirt flats are fine to start with. I tend to avoid running the cooler at max power although that's more of a gut-feel thing, doesn't seem right to run at max for several hours.

 

>>Im getting a lot of hot pixels. Is this normal at this length of exposure?

 

What gain are you using? I tend not to use Darks and don't have an obvious problem with hot pixels at 300 gain and 60s exposures. If you post a few sample dark frames (at different gains and exposure lengths) then we can take a look. 

 

>> Can someone tell me what the finger print like smudge is, the optical train appears clean.

 

It looks like slight condensation to me. Did it appear toward the end of the session or permanent fixture? High humidity at your location?

 

>> Should I expect vignetting with this setup? Or do I need to alter the spacing? currently reducer is directly on the SCT, then a Baader click lock, with 1.25 adapter and then the nose piece of the camera.

 

I think the 1.25 adapter is causing the vignetting, suggest switching to a T-adapter behind the reducer and then T2 extensions all the way to the camera. I don't know the correct spacing for the Meade .63 but the Celestron is 105mm from back of reducer to the sensor. The Celestron .63 will give you a corrected field at that distance. 

 

>> Lastly, I am bewildered on how to properly get the WB settings correct. They clearly have a great effect on the stacked image, but how do I set them correctly so the colours are accurate?

 

There are 2 schools of thought it seems. Some folks use the R and B sliders on the camera Image Control panel (1 below) to get the RGB peaks aligned in the live view and stacking histograms. Robin (SharpCap developer) has advised against using these camera-level controls and instead advises using the color sliders in the live stacking window (2 below) to adjust the color: 

 

InkedM42 10mins_LI._2.jpg

 

These 3 color sliders move the color peaks relative to each in the DISPLAY histogram only. The 4th slider is saturation and should probably be set lower than I have it here.. worth playing around with while stacking.

 

InkedM51-2_LI_2.jpg

 

The idea is to get the peaks roughly aligned although you may get more pleasing results when slightly misaligned depending on the target. You could try both approaches to see what works best. Keep in mind that accurate color balance is somewhat display-specific. The M51 above looks ok on my laptop but is far too red on my desktop monitor. 

 

Cheers

 

Edit: corrected panel name, explained 4th slider and added link to Robin's post on color correction


Edited by cshine, 06 May 2019 - 10:13 PM.

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#3 Alien Observatory

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Posted 07 May 2019 - 08:44 PM

G'Day!

 

Very much a beginner with EAA.

I have a C925/Meade 6.3 Reducer/AZEQ6/ASI 294 MC Pro/Sharpcap 3.2 Pro/EQAscom.

 

These are some images ive taken, all 4-15s.30-60 subs. No calibration frames. 294 is cooled to the max: gets to about -10 max, as I live in the tropics.

Im getting a lot of hot pixels. Is this normal at this length of exposure?

Can someone tell me what the finger print like smudge is, the optical train appears clean.

Should I expect vignetting with this setup? Or do I need to alter the spacing? currently reducer is directly on the SCT, then a Baader click lock, with 1.25 adapter and then the nose piece of the camera.

Lastly, I am bewildered on how to properly get the WB settings correct. They clearly have a great effect on the stacked image, but how do I set them correctly so the colours are accurate?

 

Thanks in advance.

 

 

Hemi

Hemi, I also have a 9.25 and a F6.3 Focal reducer and have used it very successfully with a ZWO 294 cam.    My first observation / question is, are you using a Light Pollution Filter and if not what are your local LP/seeing conditions?

 

My second observation is that you are getting significant Vignetting using the Bader 1.25" Click Lock.  It is much better to use a Celestron SCT to T thread adapter and a  40 mm to 50mm T spacer to have the correct Focal Reduction backspacing (106mm) which produces very little vignetting with the 294 cam....  Pat Utah smile.gif

 

https://agenaastro.c...ter-93633a.html


Edited by Alien Observatory, 07 May 2019 - 10:51 PM.


#4 Owk

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Posted 08 May 2019 - 12:31 AM

Thanks Pat and Cshine for your time,

 

Firstly no flats, they seem very daunting to get right. Will try and get some, white t shirt and daytime sky.

 

Im using a gain of 300, even 8s exposures get me a lot of hot pixels: they look worse as the polar alignments is off a little so their is hot pixel creep I think.

 

Ive started a small dark frame collection, it seemed to help last night, but still got the occasion hot pixel trail coming through, but significantly better.

 

I think the finger print happened quite early on, I live in the tropics and the dew point is quite high at the moment. I will try to cool down in stages.

 

I will attach the Camera directly using a t Adapter. It seems very obvious now, but why do ZWO provide the nose piece with this sensor then?

 

Fantastic info about the White balance: ive been using all the sliders!! did not appreciate the Histogram trails shifting as I moved the RGB sliders, will try again tonight.

 

Im not using a LP filter, I live in the suburbs of Darwin, Australia: Bortle 5 according to the FLO app.

 

Thanks again for the help, will post again to let you know how I get on.

 

Cheers

 

 

Hemi



#5 cshine

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Posted 08 May 2019 - 06:07 AM

Thanks Pat and Cshine for your time,

 

Firstly no flats, they seem very daunting to get right. Will try and get some, white t shirt and daytime sky.

 

Im using a gain of 300, even 8s exposures get me a lot of hot pixels: they look worse as the polar alignments is off a little so their is hot pixel creep I think.

 

 

Hey Hemi, no worries, happy to help. SharpCap makes flats pretty easy, just use the Capture -> Capture Flats menu option and adjust the exposure until it says "Histogram Status OK" . Turn on the image histogram (icon next to the Zoom box) and get your peaks roughly around 50% by adjusting the gain/exposure.

 

If you take some screen captures that show your stacked images, histograms and SharpCap settings we can probably give you a few more pointers and it will help to see that hot pixel issue. 

 

Cheers


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#6 Alien Observatory

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Posted 08 May 2019 - 09:51 AM

Thanks Pat and Cshine for your time,

 

 

I will attach the Camera directly using a t Adapter. It seems very obvious now, but why do ZWO provide the nose piece with this sensor then?

 

Im not using a LP filter, I live in the suburbs of Darwin, Australia: Bortle 5 according to the FLO app.

 

Thanks again for the help, will post again to let you know how I get on.

 

Cheers

 

 

Hemi

Hemi,  Here is an image of my set up (Focal Reducer...T adapter...20mm spacer...ZWO cam) that results in a FR of ~0.7X.  I add another 20mm T spacer (40mm total) to get FR of X0.63 (see image of spacing v.s. total reduction).  You might look for a light pollution filter for the future as the sky glow can alter the colors being imaged  and make it harder to white balance...I use an IDAS LP2 filter as it works very well with the 294 cam...Pat Utah smile.gif

 

p.s.  I just noticed the correct back spacing for a Meade 6.3 lens is about 90mm, for a Celestron back spacing is about 106mm

Attached Thumbnails

  • F7.1.jpg
  • FR Spacing.png

Edited by Alien Observatory, 08 May 2019 - 10:38 AM.

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#7 descott12

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Posted 09 May 2019 - 06:32 AM

 

Firstly no flats, they seem very daunting to get right. Will try and get some, white t shirt and daytime sky.

 

As was already mentioned, flats are pretty easy to create and they work really well. I put off making them for a long time and I had horrible vignetting. The flats almost eliminated that so I encourage you to try.

 

I make them using just a gray sky as the sun is going down.

 

Also, after a little experimentation, I discovered that old flats work reasonably well. While fresh ones are clearly best, older ones do a good job for our purposes in EAA. So you don't have to necessarily remake them before every session - as long as your setup doesn't change much.


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#8 RazvanUnderStars

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Posted 11 May 2019 - 10:04 PM

Some suggestions:

 

  • read Sharpcap's excellent documentation (online, PDF) at leisure, I think it's essential to get the full power out of Sharpcap and even to use it properly. If it's cloudy outside, it's a great read. 
  • cooling the camera to the max can be stressful, thermally speaking, to the circuits of the camera. Within minutes, they get cooled down a few tens of degrees, so the thermal contraction of the material is fast. It's not the temperature but its fast change that's the issue. I remember reading (probably here on CN) the advice of an electronics engineer to avoid cooling to the max for this reason as it potentially shortens the lifetime of the camera. Of course, only the manufacturer can test this hypothesis. With less cooling you'll save some power as well, in case it matters.
  • For the optimal exposure combination (gain & time) for a given sky condition, see Robin's detailed explanation at https://forums.sharp...b62468dcd057520 or if you prefer a video exposition, see https://youtu.be/3RH93UvP358 (it's Robin again).

Enjoy the setup!



#9 39.1N84.5W

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Posted 18 May 2019 - 01:08 AM

I take flats, at sunset, with the scope pointed about 15 degrees east of the zenith. No t shirt needed. Exposure time ranges from 10ms-30ms and I capture 10. Adjust the time so the peak of the white histogram is at 50%. (You need to turn the histogram on by clicking at the upper right corner icon.)
Oh... and you can't capture flats if you have darks already applied.
This will greatly help with your donut shaped illumination.
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