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Old 18-10-2009, 08:11 PM
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toryglen-boy (Duncan)
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QHY8 - Still cant get it.

ok, still i am trying with the QHY8 and Maxim DL, still i cant get it. Here is a screenshot of what i get,the histogram seems like a complete puzzle, any comments welcome, before i bounce this thing of the wall
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Old 18-10-2009, 08:34 PM
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sheeny (Al)
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hmmm... I don't have one, but I don't see anything too unusual about your histogram for what I'd expect with a 16 bit camera... Maybe clipping both ends a bit, but that's just an adjustment.

Can you be more specific about the problem?

Al.
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Old 18-10-2009, 08:38 PM
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Originally Posted by sheeny View Post
hmmm... I don't have one, but I don't see anything too unusual about your histogram for what I'd expect with a 16 bit camera... Maybe clipping both ends a bit, but that's just an adjustment.

Can you be more specific about the problem?

Al.

Yeah, i dont understand it, and cant take a decent image

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Old 18-10-2009, 09:04 PM
jase (Jason)
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Yes. Takes a little getting use to Maxim's screen stretch. Quite powerful and useful.

In the minimum field enter 0 (zero) and hit enter. This will place the red triangle (black point) as far left as possible. Then hit the + magnifying glass to zoom into the histogram more. As you zoom, you'll be able to raise the red triangle and lower the green triangle (white point) to display the data you want to view.

I'm not sure what you've taken an image of, but the signal is weak. Imaging is a numbers game. Despite what many believe, FITS files aren't conventional image binary files, but series of numerical values. This provides incredible flexibility allowing the imager to multiple/add/subtract values to all pixels to fill the bit space (16bit or similar).

If I was to judge your data, I'd say you need more exposure time. 3 minutes isn't going to cut it. The info window shows that the minimum pixel is 1063 counts with the average 1433 counts. This will change where ever your cursor points, but for an average to be so low is probably a good indication more exposure time is needed. The maximum of 65k will be hot pixels or saturated stars. The info window are real values i.e. you can screen stretch the data as soft or as hard as you please, but the pixel values remain the same. Screen stretch does not manipulate the image data itself, just how its presented on the screen buffer.
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Old 18-10-2009, 09:08 PM
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thanks for that Jase, its NGC 300, here is a single 45 mins shot (ignore the guiding going mental)

i think i might fire up the 1000d, it was sooooooo much better than this
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Old 18-10-2009, 09:18 PM
jase (Jason)
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The data is all there.

Just need to play with the sliders. Please keep in mind that the screen stretch function is performing a linear stretch on the screen buffer data. This is the reason why you're highlights look saturated and your shadows black clipped. Obviously you need to adjust the red and green triangles to reduce the clipping. The point however is that the data is all there. linear stretching does not show the mid-tones well hence the contrasty look.

Now, take a couple more sub frames and combined them and save it as a 16bit tiff. Use photoshop or gimp to do a non-linear stretch. Or you can use MaximDL's DDP and log stretch functions to fill out the bit space.
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Old 18-10-2009, 09:46 PM
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How have you set the gain and offset values for your QHY8 Duncan? This can make a big difference to the final image with a QHY8.. when I had mine, the default values in Nebulosity 2 were Gain 50, Offset 124. after working out what settings I needed by taking bias frames and adjusting the values so that I had an average of between 800~1000 ADUs in a bias frame, the settings were Gain 0, Offset 64. This always provided me with a very nice image..

As Jase said, the screen stretch is not manipulating the data in any way, just changing how its displayed on the screen, it is also not indicative of what the final stacked, processed image will be...

Are you shooting RAW or Colour? I would recommend shooting RAW..
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Old 18-10-2009, 09:48 PM
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Hi Duncan! Have you tried the image capture program that comes with the camera, CCDCap, just for s**ts and giggles? Just to see what you can get. MaxIm doesn't present your image as it actually looks. Can you check the image in Photoshop as a fits using fits liberator, just to see what it looks like in there? I really feel for you, it is a great camera and you should be getting some cool pics. What about just trying some of the easy, boring regular objects to get to know how the camera works? Also, some aren't gonna like this, however, I would go over to Nebulosity, it is a lot easier. If you want to, PM me, and I'll give you my home number and see if I can help a bit while your in front of your PC.
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Old 18-10-2009, 09:48 PM
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Quote:
Originally Posted by AlexN View Post
How have you set the gain and offset values for your QHY8 Duncan? This can make a big difference to the final image with a QHY8.. when I had mine, the default values in Nebulosity 2 were Gain 50, Offset 124. after working out what settings I needed by taking bias frames and adjusting the values so that I had an average of between 800~1000 ADUs in a bias frame, the settings were Gain 0, Offset 64. This always provided me with a very nice image..

As Jase said, the screen stretch is not manipulating the data in any way, just changing how its displayed on the screen, it is also not indicative of what the final stacked, processed image will be...

Are you shooting RAW or Colour? I would recommend shooting RAW..
Numbers came about through trial and error, i am shooting in RAW, although whe i debayer it, its colour ?

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Old 18-10-2009, 10:08 PM
dpastern (Dave Pastern)
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*carefully taking notes of all of this*. (and trying to learn).

Dave
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Old 19-10-2009, 12:07 AM
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Duncan,
Here's a guide to setting gain and offset - http://www.lightstorm.at/pdfs/QHY8_settings.pdf You will need a different offset for each gain setting you want to use. Start with a gain of 0% to get going.

I use the maxim sequence section to capture lights, bias, flats and darks. I use the focus section, set to continuous, to frame the shot. With binning set to 4x4, a 5 sec exposure and screen stretch set to high, I can see the target on screen to frame it.

I use Deep Sky to stack all these files, maxim often won't stack qhy8 images correctly for me. In DSS, under Raw/Fits DDP settings, go to FITS tab, tick monochrome and select QHY8 from the camera list. The first attached image is what I see in PS after stacking in DSS. The second is the same image after curves and levels. I sometimes use ddp in maxim to stretch before going to PS but for me it's not always successful with qhy8 images so normally I'll stetch the image in PS.

Don't give up, they are pretty good cameras for the cash.

I've added a single 10minute sub, shown in maxim and shot from a dark site, from that image set.
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Old 13-11-2009, 03:23 PM
Steve
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It looks like you might have some fogging or ice on the camera window, that can cause the gradient you see in your images. I'd check it with a flashlight while you're in the field to make sure it's clear. There's a few ways to fix it if you are getting it.
Steve
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Old 13-11-2009, 03:43 PM
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Originally Posted by toryglen-boy View Post
QHY8 - Still cant get it.
Duncan you're not QHY8 compatible. Pack it up and take it back to the shop.
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Old 13-11-2009, 03:45 PM
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Duncan you're not QHY8 compatible. Pack it up and take it back to the shop.

actually, and dont hold your breath, its starting to make sense!

its my own fault, i thought it would be much easier than it was, and i should have done my own research, instead of posting absolute drivel on here ..


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Old 13-11-2009, 04:13 PM
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Originally Posted by toryglen-boy View Post
actually, and dont hold your breath, its starting to make sense!

its my own fault, i thought it would be much easier than it was, and i should have done my own research, instead of posting absolute drivel on here ..


I'd suggest to put the camera aside for a little while and do a lot of reading. You'll save yourself a lot of time and confusion. There are absolutely stacks of info on processing or data acquisition with the QHY8 in many many forums. Have a look at the QHY8 forums, CCDware forums, Yahoo groups: stark-labs, QHYCCD. That's a good place to start from.
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Old 13-11-2009, 04:44 PM
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Whatever you do, don't give up, keep asking. The "get the DSLR out" idea has merit, as it will show you how easy it is to get an average shot, but the QHY8 will give you better.
First thing you really need though is the "proper" offset and gain, so work on this. I did the same as what was described in the "lightstorm" link Robin posted. In my case I ended up with Gain 1, Offset 114, but each camera is different, so trial and error it, and get this sorted first.
Then tuck into some more subs, longer being better, or if the skyglow intervenes, more of them.
Gary
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Old 13-11-2009, 05:40 PM
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As others have said... Expose longer... If the skyglow is a problem, either get a Hutech IDAS LPS filter, or take plenty of shorter subs... I would say 5min is the minimum exposure time for any target out there (apart from M42 which always requires some short subs to tone it down a bit) when I'm at dark skies, I don't bother with anything less than a 20 minute exposure, unless im capturing colour information for a Ha lum or something like that. with an LPS, 10min subs should be doable from suburban skies... I would strongly recommend doing this over taking heaps of 3 min subs...

As Robin and Gary said, the gain and offset can be different for every camera, Gary's was Gain 1 Offset 114.. My QHY8 was Gain 1 Offset 66... So follow that guide that Robin linked...

Also, with a 16bit CCD, you can expect to have to do quite a few itterations of levels and curves to pull out data... Unless you're taking very long subs, the data will not be clearly visible in an unprocessed image like it is with a DSLR.... It will only be clearly visible in 15~30 minute subs without applying some stretching...

I have an unprocessed 30x20min shot of M8 and M20 on the HDD, I can upload a JPG copy of how it looks pre-processing for you to show you what I mean... even with the epic exposure times, its still not much to look at...
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Old 13-11-2009, 11:29 PM
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The Idas LPS filter does OK for light pollution, but you will lose a heap of sensitivity on galaxies and the like.
Here an image from the QHY-8 with my CDK-20, its a stack of 20 x 5 minute subs, with NO darks, No Flats etc, so you can get the feeling of what the image is like thru the IDAS LPS filter. I have also attached an image without the LPS, and notice the light gain.


Theo
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Old 14-11-2009, 12:06 AM
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The gain and offset for my QHY8 was 1% and 65, respectively.
Its different for each camera.
Keep in there Duncan - you will finally twig to it all and then you will be off. I felt the same in a way with my flats until Marc put me on the right course.
We'll help, so don't give up.
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Old 14-11-2009, 01:06 AM
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