Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_30_second_exp_2_winners.thumb.jpg.b5430b40547c40d344fd4493776ab99f.jpg

uhb1966

Now that's what i call a dark frame

Recommended Posts

Hello girls and guys,
just out of curiosity i tried to get a grip on the noise of my new used QHY8. I'm sharing a 30 sec sub with a low gain setting that would somehow translate into ISO 100-400 with a Canon (roughly):dark30secs.png

The frame is completely pitch black, even with heavy stretching! With the only notable exception being 4 hot pixels (all of them green). I stretched it 3 times in Gimp with no visible noise.
I guess as long as the Gain is kept so low, i even might ignore the darks completely (?). I will try my first DSO's ASAWA(as soon as weather allows), process them with and without darks, and will share the result here.

Dark skies!

 

Share this post


Link to post
Share on other sites

Yep use that to make a bad pixel map to get rid of those pesky hot pixels and forget about the dark frames :)

  • Like 1

Share this post


Link to post
Share on other sites

Hello guys and girls,

just in case somebody stumbles upon this thread, this would be the steps i should have done before taking darks:

Quote from the doc (the procedure should be the same for QHY9,QHY9L, and possibly other units as well):

Setting the GAIN and OFFSET

Unlike many other manufacturers, QHYCCD leaves the the internal settings of the camera ADC GAIN and OFFSET settings so that you can get the absolute best performance out of your CCD.

GAIN is the pre-ADC programmable gain amplifier gain setting, the range is from 0 to 63.

OFFSET is the ADC voltage offset setting.

The correct setting of OFFSET and GAIN can change the CCD camera system gain, which match CCD output signal range and scope of the quantitative ADC to get the best dynamic range.

Usual Calibration Method:
1. Set the Gain=0
2. Set the exposure time to 0 and cover the lens-this is a BIAS frame .
3. Watch the local average of the captured images (can use the Noise Analyze function of EZCAP)
4. The ideal average value is around 500 to 1000. If the value is higher, then you should reduce the OFFSET. If the value is lower then you should increase the OFFSET.
5. Repeat steps 2-4 to obtain the ideal OFFSET value.

6. Open the lens cover and increase the exposure time. Use a uniform light source, such as light boxes or an LCD screen, and take a saturated exposure of the image.

7. Watch the local average value of the captured images if the value is is less than 60,000, you need to increase the value of GAIN, if the value is 65535, then reduce the GAIN .

8.Repeat steps 6-7 to obtain the appropriate GAIN value.
9.Under the GAIN, repeat steps 2-4, and obtain more accurate OFFSET

 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

  • Similar Content

    • By Demonperformer
      I have been reading the PHD2 manual and have noted the statement: "The settings for 'Use Dark Library' and 'Use Bad-pixel Map' are mutually exclusive - you can use one or neither, but not both at the same time".
      So, in order not to reinvent the wheel, a question for those of you who use PHD2. Which, if either, do you find works best? Or. if it isn't that simple (and when is it ever?), what are the main things I should consider in making the decision?
      Thanks.
    • Guest
      By Guest
      QHY8 OSC and QHY6 Mono £400 (+postage UK mainland only)
      Selling to move to LRGB imaging, the QHY6 is thrown in as a bonus :-)
      QHY8 One Shot Colour - Cooled CCD Camera 
      QHY6 Mono Cooled CCD Camera
      You can see pictures I've taken with the QHY8 on my website
      David
       
    • By uhb1966
      Hello guys and girls, these are the first adventures of a new CCD user.
      I hope you'll have a bit to laugh
      i bought a used QHY8 from a fellow stargazer. It arrived yesterday. It was missing the documentation (but in the documentation was not part of the deal, so that's okay). After quite a while I got everything running (the Camara needs two power sources). As the weather was good for the first time in years, I immediately set up in my garden at 11 PM. First I was struck by a faulty USB cable - it took me about an hour and a half to isolate the problem as it was not constantly failing but intermittantly freezing the software and/or windows.
      But after that, i was able to shoot a few short moon sequences with APT. However, the result was less than optimal. I was getting pesky little black squares. I suspected something with debayering and asked APT's Ivo and the qhyccd forum for help.
      Ivo answered within about 30 mins, and after 2 or 3 messages everything was clear: the debayering settings in APT refer only to the display within APT, not to the saved images ! (I hear the more experienced SGLers ROFLing)
      After some updates and mouseclicks, i got nice little stacked images of the full moon.
      The next problem was the cooling: the unit cooled very well when connected straight to a power source, but with the QHY power converter in-between the cooling was mediocre (guessing from the outside temp of the casing). Also, the unit stubbornly said it was running at 25C, but the pictures were ok (yes, i know, moon pics dont have to worry about SNR, but still, they were ok, some test darks at 30 secs were also very ok).
      Well, to cut a long story short: the QHY8 does not have a temp sensor!!! Its supposed to cool straight away at max power. APT (and other software) is somehow getting wrong temp values.
      Finally, i used the QHY power converter for the sony chip and a second power supply for the cooling. The finding: the cooling via the QHY power converter was much weaker- even the fan went at a little lower rotation speed. Running through the second power supply, the unit cooled great. Possibly one of the cables was mistakenly sent instead of the original one- it looks suspiciously thin for a cable that is supposed to be transferring 36 watts at 12 volt.
      So, after several hours of silently swearing, everything works! Yay!!!
       
      PS: the suspiciously thin 36 watts cable (the cross diameter of the plug is 2.5mm):

    • By stevebb
      After seeing some absolutely incredible widefield and through telescope results from a good friend in Brazil using the QHY8L this is the logical upgrade I have been considering from a modded Canon 450D.
      Now I do know a few SGL members have the QHY8L and I have recently seen a QHY8 for sale.

      Comparing the QHY8 against the QHY8L, the imaging capabilities "appear" similar, I appreciate the physical design is different. But aside from the latter, are there any other differences that would say put the QHY8L at a level above the 8 ?

      Searching for images of the QHY8, they are few and far between and to be honest, I have not seen any that match ones I have already seen taken with the QHY8L. Now I know the skill in bringing out the image is arguably the most important aspect on the final result but I do need to be certain I am making the right decision regarding the capabilities of the camera ..... or "Bank of wife" will kill me, again 

      Many thanks in advance,
      Kind regards,
      Steve
    • Guest
      By Guest
      I hope all of you were able to get out last night.
      I managed to capture 10x15min on the Rosette Nebula.
      Teleskop Service 65mm, QHY8, EQ6 Pro, AS120MC guiding through an Altair 60mm, processed in Pixinsight
      David

       
      this compares the 1 hr of data I got on the 2nd to the 2.5 hours captured last night - big difference :-) 

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.