#1  
Old 25-09-2009, 03:53 PM
toryglen-boy's Avatar
toryglen-boy (Duncan)
Scotland to Australia

toryglen-boy is offline
 
Join Date: Jan 2009
Location: Canberra
Posts: 1,645
The great QHY8 flats mystery

Yeah me again, whinging that i cant get this sorted ...

ok, taking flats, in MaximDL i take an exposure of around 0.025 secs, and i get the first image, i would have thought it would have been a bit more uniform, instead of black with white splodge, anyway, the second image is how it appears if i save it as a PNG and dont do ANYTHING to it ..

image 3 is what the flat looks like, if i take a sub of any longer than about 0.3 seconds, image 4 is a sample image i took to test with, and image 5 is what the sample picture is like with the flat filtered through it..

what am i missing? remember image 1 & 2 are the same thing, just saved to different formats. i dont mind getting slaughtered if its something stupid, as long as i get it going ....
Attached Thumbnails
Click for full-size image (flats.JPG)
103.2 KB64 views
Click for full-size image (CCD Image 22.JPG)
14.2 KB102 views
Click for full-size image (flats2.JPG)
124.9 KB54 views
Click for full-size image (pic.JPG)
114.0 KB44 views
Click for full-size image (combined.JPG)
126.7 KB48 views
Reply With Quote
  #2  
Old 25-09-2009, 05:06 PM
DavidU's Avatar
DavidU (Dave)
Like to learn

DavidU is offline
 
Join Date: Jul 2007
Location: melbourne
Posts: 4,835
Gawd damn ! I can't wait for the expert replies
Reply With Quote
  #3  
Old 25-09-2009, 05:32 PM
marki's Avatar
marki
Waiting for next electron

marki is offline
 
Join Date: Mar 2008
Posts: 2,427
Duncan, what did you use for a light source? Is this a single image or a stacked master (averaging). Have you applied your dark flats/bias frames to this flat. The exposure time seems very short. It also appears maxim has applied a pretty funky stretch to that first flat.

Mark
Reply With Quote
  #4  
Old 25-09-2009, 05:52 PM
TheDecepticon
Registered User

TheDecepticon is offline
 
Join Date: Feb 2008
Posts: 1,223
Step 1Ditch MaxIm. Step 2:Get Nebulosity2. Step 3PM me when you have completed step 1& 2!!

(The opinions expressed by the author of this post regarding MaxIm are a personal opinion and are not open to debate or war)
Reply With Quote
  #5  
Old 25-09-2009, 06:03 PM
mtodman's Avatar
mtodman (Matt)
Registered User

mtodman is offline
 
Join Date: Oct 2007
Location: Arcadia, NSW, Australia
Posts: 189
Hi Duncan,
Have you focused the camera before taking flats? You need to ensure that your flats setup is EXACTLY the same as your imaging setup.
Also, open your information & histogram windows. Use the histogram window to perform a screen stretch to better view the image. Your information window will tell you the value of the pixels (you need to aim for about 20,000 - 30,000).
Matt
Reply With Quote
  #6  
Old 25-09-2009, 06:06 PM
marki's Avatar
marki
Waiting for next electron

marki is offline
 
Join Date: Mar 2008
Posts: 2,427
Quote:
Originally Posted by TheDecepticon View Post
Step 1Ditch MaxIm. Step 2:Get Nebulosity2. Step 3PM me when you have completed step 1& 2!!

(The opinions expressed by the author of this post regarding MaxIm are a personal opinion and are not open to debate or war)
I am not sure that buying more software is gonning to fix Duncan's problem. He is doing something wrong, lets see if we can work out what it is first.

Mark
Reply With Quote
  #7  
Old 25-09-2009, 06:37 PM
gbeal
Registered User

gbeal is offline
 
Join Date: Oct 2004
Location: New Zealand
Posts: 4,345
Tricky huh?
I'll disagree with the comment about ditching Maxim, if there is a better program out there then it must be good. My problems with maxim related to the QHY8 not playing well with it, and this to me was a software issue.
No matter. Couple of comments. Why an offset of 137? Did you arrive at this by trial?
In respect of an ADU count, I went with the "multiweb method" and kept my ADU to about 9000, worked for me.
The first shot is what I used to get, just use the screen stretch box to give a more accurate look and I think you will find it is OK. Plenty of donuts but OK. I also wonder if the slight darkening in the centre is a shadow of your secondary and spider vane??
When you say "filtered through it" in image 5, did you use "Process/Calibrate?
Gary
Reply With Quote
  #8  
Old 25-09-2009, 06:42 PM
Bassnut's Avatar
Bassnut (Fred)
Narrowfield rules!

Bassnut is offline
 
Join Date: Nov 2006
Location: Torquay
Posts: 5,064
Pic 1 looks about right, but a bit contrasty. pic 2 is what, a PNG?, isnt that an 8 bit format?, why bother at all with PNG?. pic 3 is what happens when you overload a sensor, it goes very weird. and which flat did you use for pic 5?.
Reply With Quote
  #9  
Old 25-09-2009, 08:31 PM
Hagar (Doug)
Registered User

Hagar is offline
 
Join Date: Oct 2006
Location: Australia
Posts: 4,646
Duncan , I think this is one of those easy ones. Maxim has an auto stretch feature built into it's screen display. If you open an image it will always try to stretch the image to whatever the preset is. If you open the stretch display window you can select range and you might find your images don't look so bad.
Just one of the reasons I only use maxim for basic capture but better still is Nebulosity.

A few things you must remember when taking flats with a QHY8.
1. The full well depth of the QHY 8 is approx 27,000E ADU therefore your flats should be taken with a maximum pixel intensity/ ADU count of between 9000 and 13500. This is taken accross the entire image not just a point you pick.
2. To achieve reasonable results you must take Bias frames or at least darks at the same duration as your flats to calibrate the flats correctly.
3. Capture your Flats at the same Gain, Offset and Focus and camera position as your light frames.
4. Talking about Gain and offset settings. Lots has been said about both but the easiest way to set them is to use whatever gain setting you like. I personally never went above about 12. Take a bias frame and adjust your offset until the peak of the histogram is just to the right of the left side, sounds a bit Irish but it works. As long as the same gain is used, well in most cases it doesn't matter to much, your offset is now set and should never need to change unless you use some NB filters and then only a small change is required.

Good luck with it all, it's really not that hard, it just seems like it is.

Last edited by Hagar; 25-09-2009 at 08:53 PM.
Reply With Quote
  #10  
Old 25-09-2009, 08:39 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Sydney
Posts: 22,060
Quote:
Originally Posted by toryglen-boy View Post
Yeah me again, whinging that i cant get this sorted
Don't worry about what your flats look like visually (for now). Make sure you reach the right ADU levels. And remember that you will need bias frames to subtract from your bias prior to divide in the sub or you'll get inverse vignetting like your las two pics show. Doesn't matter what capture or processing software you use so don't worry about maxim or other programs. Use what you've got.
Reply With Quote
  #11  
Old 26-09-2009, 02:05 PM
TheDecepticon
Registered User

TheDecepticon is offline
 
Join Date: Feb 2008
Posts: 1,223
How did you go?
Reply With Quote
  #12  
Old 26-09-2009, 03:19 PM
toryglen-boy's Avatar
toryglen-boy (Duncan)
Scotland to Australia

toryglen-boy is offline
 
Join Date: Jan 2009
Location: Canberra
Posts: 1,645
Quote:
Originally Posted by TheDecepticon View Post
How did you go?
I think Hagar has something, i noticed that when i open anyfile, it automatically gets stretched to some degree, when i take the flat, and stretch it to "normal" it looks like how a flat would look, that explains why if i take the same image and save it as a different format, then it looks completely different from how it does in Maxim.

I think over the next 2 weeks, i need to experiment with getting, bias, lights, and flats all calibrated, although this excercise has been a good way for finding my way around Maxim.

although i might invest in Nebulosity.

Reply With Quote
  #13  
Old 26-09-2009, 03:32 PM
TheDecepticon
Registered User

TheDecepticon is offline
 
Join Date: Feb 2008
Posts: 1,223
Cool, as long as your moving forward!
I must admit, MaxIm does have some not so well understood ways of doing things. I wouldn't say Nebulosity is "better" but it is "easier", and this can be the difference at times. I have used MaxIm quite a lot over time, trying to utilize its features, and while it is very good and essentially quite a complete package, Nebulosity and PHD are still "easier".
Cheers.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 06:57 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Advertisement
Testar
Advertisement
Bintel
Advertisement