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Yes, I can easily do that, but 2200 gain is a lot. I've gotten to the conclusion through experiment and reading that gain 100/offset 50 is a good place to be for me. At least on the RASA. The wells get filled very fast.

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The Rosette Nebula and Cluster ( NGC 2237 and 2244 ) in the constellation Monoceros edit:  updated 30th Dec with improved colour balance and slightly increased brightness ...   ..

It really should be red - the Hα wavelength is bang in the middle of the red part of the spectrum. It's weird that the light passing through looks magenta; I'll have to try that! It shouldn't look mag

No not really - the combination is performed using masks.  Only the saturated parts of the image are replaced with the unsaturated portions from the less exposed images.

Posted Images

 

2 hours ago, Datalord said:

Yes, I can easily do that, but 2200 gain is a lot. I've gotten to the conclusion through experiment and reading that gain 100/offset 50 is a good place to be for me. At least on the RASA. The wells get filled very fast.

You may well be right. I am just going off their website

http://www.qhyccd.com/QHY247.html

A1D19962-22D6-41B2-A905-7648B2A5D082.jpeg.2d9521c5473e0cb1008813fd3e1c41a9.jpeg

Their diagram shows unity gain as 2200 on a 0-4095 scale.  Does your capture tool have that range ( ie. 0..4096 )?

I would like unity gain so I can do a like for like comparison as my darks for the D5300 were taken at near to unity gain and a lower than unity gain will of course show a lower noise value but I won’t know how to compare it.

And the offset, well I think I might be wrong there.  I was assuming that the offest is set in relation to a 16bit data range.  Thinking about it some more, the offset would I guess be applied at the analog to digital conversion stage and I understand that the converter is 14bits so the offset should be 600 if it is to match the offset value ( 14bit scale ) of the D5300. Having said that, as long as there are no zero value pixels in the dark, a lower offset is fine as I can simply add an additional offset to align the darks from the different cameras.

Oh and I did not mention cooling, what do you think, would -20deg C be a good figure to go for?

Thanks again but I hope this is not too much trouble

cheers

Mike

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Not at all. Yes, the camera has that range. To my knowledge, the offset pushes the beginning of the well "up" in the range, which gives you more room to stretch the bottom, but less overall range. I see no point at all doing that with the lightbuckets we own. For the same reason I would be very, very cautious with using 2200 gain in the camera. Unless you want to take very short exposures.

I can do -20. I shoot at -15, which people seem to regard the point of diminishing returns.

What exposure length?

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Too much theory in this for me... If I thought it related to the real pictures I'd buy into it, but I never have. On another thread at the moment we have elongated stars being judged fine by an assorted collection of analysing programmes. The stars are elongated, the programmes are wrong.

Olly

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2 hours ago, Datalord said:

Not at all. Yes, the camera has that range. To my knowledge, the offset pushes the beginning of the well "up" in the range, which gives you more room to stretch the bottom, but less overall range. I see no point at all doing that with the lightbuckets we own. For the same reason I would be very, very cautious with using 2200 gain in the camera. Unless you want to take very short exposures.

I can do -20. I shoot at -15, which people seem to regard the point of diminishing returns.

What exposure length?

Please see private message ...

Cheers

Mike

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1 hour ago, ollypenrice said:

Too much theory in this for me... If I thought it related to the real pictures I'd buy into it, but I never have. On another thread at the moment we have elongated stars being judged fine by an assorted collection of analysing programmes. The stars are elongated, the programmes are wrong.

Olly

Sorry, you are right, the conversation has moved on from the image to cameras and I have taken it off line.   And yes it is only the end result that matters.  The reason I am discussing the camera with Datalord is that the end result of the images produced by my new D7500 are significantly less attractive ( due to pattern noise ) than my old D5300 and I do not want to repeat the mistake by buying another new camera that does not improve my photos.  But a conversation for elsewhere ...

Cheers

Mike

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2 hours ago, MikeODay said:

Sorry, you are right, the conversation has moved on from the image to cameras and I have taken it off line.   And yes it is only the end result that matters.  The reason I am discussing the camera with Datalord is that the end result of the images produced by my new D7500 are significantly less attractive ( due to pattern noise ) than my old D5300 and I do not want to repeat the mistake by buying another new camera that does not improve my photos.  But a conversation for elsewhere ...

Cheers

Mike

Haha, it's an ok conversation to have and I'd prefer if we take it to conclusion in this thread now that we started it. Think of some poor guy googling about that camera in 6 months, hitting this thread and then it just abruptly stops. So please, let's continue in the open and end it with your conclusion about the camera. 

And Olly, I agree. I actually didn't care about all this gain - offset stuff until I realised the RASA hits full well to fast because of it. And my meager experiments have shown low gain to be the way forward for me. 

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10 minutes ago, Datalord said:

... I'd prefer if we take it to conclusion in this thread now that we started it.

Ok.

Thanks for your reply.   The settings I am after are just for comparison purposes.  That is, for the same sensor, with the same approximate settings, what difference does cooling make and is there a difference in processing between Nikon and QHY.   If I get the camera then I would then seek to further optimise the results with settings closer to yours.   
 
With regard to the gain; most discussions I have read on using OSC CMOS cameras recommend using unity gain or higher in order to avid the quantisation issues one gets with less than unity gain.  For example, if a particular faint object taken at unity gain has a captured brightness range of say 20ADU then at half unity gain the same galaxy would only have a brightness range of 10ADU.  These ten values when stretched are more likely to show quantisation bands than the one with 20ADU.  Having said that, I believe that the quantisation issue is perhaps somewhat overstated when one is taking many images in a noisy environment as the resultant integrated image will have more levels than just the 10 that are present in any one image.   
 
Anyway, back to the settings ... 
 
So if you can, I would like: 
 
16bit raw,    gain: 2200,    offset: 600,   Exposure: 240 seconds,   Temperature: -20C,    No white balance adjustment ( ie. Just the raw pixel values ),   And no calibration,    
 
Thanks again 
 
Cheers 
 
Mike
 

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WRT comparison, wouldn't it be better to compare on the basis of real usage? Every fiber in my body says that 2200 is A LOT, especially with a 12" f4.  

Regardless, I will take that picture for you and post a link to the original here. Probably going to be tomorrow night. It will be the raw fit file output from the camera, approx. 48MB.

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11 minutes ago, Datalord said:

WRT comparison, wouldn't it be better to compare on the basis of real usage? Every fiber in my body says that 2200 is A LOT, especially with a 12" f4.  

Regardless, I will take that picture for you and post a link to the original here. Probably going to be tomorrow night. It will be the raw fit file output from the camera, approx. 48MB.

Thanks that would be great.

Cheers

Mike

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  • 2 weeks later...

Hey,

Got back from travels yesterday and camped out with the scope. I tried to get a session with the Rosette nebula at 2200 gain, but the gods of hardware (Microsoft) decided to work with the gods of clouds to mess up that plan. But I managed to get the darks and bias shots. I did them at 300s and -15C, so that's what is available. I placed a raw dark, a raw bias and the masters produced with DSS. 20 darks and 40 bias in those. 2200 gain, 50 offset.

https://www.dropbox.com/sh/nwipcrqwvvg8c2x/AADVNjFincjPhPKwX0BVWov6a?dl=0

 

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5 hours ago, Datalord said:

Hey,

Got back from travels yesterday and camped out with the scope. I tried to get a session with the Rosette nebula at 2200 gain, but the gods of hardware (Microsoft) decided to work with the gods of clouds to mess up that plan. But I managed to get the darks and bias shots. I did them at 300s and -15C, so that's what is available. I placed a raw dark, a raw bias and the masters produced with DSS. 20 darks and 40 bias in those. 2200 gain, 50 offset.

https://www.dropbox.com/sh/nwipcrqwvvg8c2x/AADVNjFincjPhPKwX0BVWov6a?dl=0

 

That is wonderful, thank you very much, I will download them today.

Cheers

Mike

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2 minutes ago, Datalord said:

Let me know what you find.

Will do.  I downloaded them over the weekend and I’m off work for a couple of days from tomorrow so I plan to have a look then.

Cheers

Mike

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On 21/01/2018 at 03:07, Datalord said:

Hey,

Got back from travels yesterday and camped out with the scope. I tried to get a session with the Rosette nebula at 2200 gain, but the gods of hardware (Microsoft) decided to work with the gods of clouds to mess up that plan. But I managed to get the darks and bias shots. I did them at 300s and -15C, so that's what is available. I placed a raw dark, a raw bias and the masters produced with DSS. 20 darks and 40 bias in those. 2200 gain, 50 offset.

https://www.dropbox.com/sh/nwipcrqwvvg8c2x/AADVNjFincjPhPKwX0BVWov6a?dl=0

 

Thanks for uploading the files.  Sorry to be a pain but are able to upload the raw unprocessed 300s individual dark in the format output by the camera.  Or is that what you posted?  I am confused because the FIT file is loading as grey only and I can’t seem to be able to extract the individual colour channels for comparison purposes.

Thanks

Mike

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1 hour ago, MikeODay said:

Thanks for uploading the files.  Sorry to be a pain but are able to upload the raw unprocessed 300s individual dark in the format output by the camera.  Or is that what you posted?  I am confused because the FIT file is loading as grey only and I can’t seem to be able to extract the individual colour channels for comparison purposes.

Thanks

Mike

That is the output. Unlike RAW, the FIT files have to be de-bayered. To this day I don't have a simple method for doing that on the individual file, but the debayering done in DSS is plenty good for me.

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24 minutes ago, Datalord said:

That is the output. Unlike RAW, the FIT files have to be de-bayered. To this day I don't have a simple method for doing that on the individual file, but the debayering done in DSS is plenty good for me.

Sorry, not sure I understand.  Are you saying that the file you uploaded is straight out of the camera or did you process it in DSS?

Thanks

Mike

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I came back for another look at this one and wasn't disappointed! One thing that is interesting is the colour. If you hold an Ha filter up to the light it looks pretty magenta, yet many imagers steer their Ha-reds away from magenta in post processing. Maybe we shouldn't. OK, you have the inner part of the nebula here and that is also rich in OIII which does take the colour that way. You might have a more conventional and 'redder' outer shell from your setup. Even so I think your colour is great, not just in the stars (which are outstanding) but in the nebula too.

Olly

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3 hours ago, Datalord said:

The FIT file is straight out of the camera. That is what you get. The masters are from DSS.

Thanks, my problem then.  I’ll need to try to figure out how to open it properly in Pixinsight.  At the moment is just opens as a grey image without any channel information.

Cheers

Mike

 

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1 minute ago, MikeODay said:

Thanks, my problem then.  I’ll need to try to figure out how to open it properly in Pixinsight.  At the moment is just opens as a grey image without any channel information.

Cheers

Mike

 

Yeah, it's super funky. And I haven't found a good tool to just "debayer this one file and make a tif". If I REALLY want to see that single file, I asked DSS to stack it (WITH THE RIGHT DEBAYER SETTINGS!!!)...  :-|  

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3 hours ago, ollypenrice said:

I came back for another look at this one and wasn't disappointed! One thing that is interesting is the colour. If you hold an Ha filter up to the light it looks pretty magenta, yet many imagers steer their Ha-reds away from magenta in post processing. Maybe we shouldn't. OK, you have the inner part of the nebula here and that is also rich in OIII which does take the colour that way. You might have a more conventional and 'redder' outer shell from your setup. Even so I think your colour is great, not just in the stars (which are outstanding) but in the nebula too.

Olly

Thanks Olly.

This one has been a bit tricky due to the lack of any neutral background.  I use Pixinsight’s dynamic background extraction tool to try to remove the orange skyglow and, when the background is not neutral, it can be hard to determine if the background is “real” or if it may still contain some residual skyglow.  Of course with my unmodified camera the Ha regions are relatively dark and I need to pull these out of the skyglow, hence the difficulty.

Anyway, it is good to know that the colours are close to what one would expect for this target.

Much appreciated,

Mike

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17 minutes ago, Datalord said:

Yeah, it's super funky. And I haven't found a good tool to just "debayer this one file and make a tif". If I REALLY want to see that single file, I asked DSS to stack it (WITH THE RIGHT DEBAYER SETTINGS!!!)...  :-|  

I’ll have another go tomorrow.  There must be a setting somewhere in Pixinsight to make the program load the file as a CFA image.  I’ll figure it out!

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On 25/01/2018 at 09:24, ollypenrice said:

If you hold an Ha filter up to the light it looks pretty magenta, yet many imagers steer their Ha-reds away from magenta in post processing. Maybe we shouldn't.

It really should be red - the Hα wavelength is bang in the middle of the red part of the spectrum. It's weird that the light passing through looks magenta; I'll have to try that! It shouldn't look magenta unless some violet is leaking through, but that's at the opposite end of the spectrum.

Normally, with a modified DSLR or CCD the blues are overpowered by the strong Hα reds. That's why I think there are some really nice, colourful images like this one from unmodified DSLRs.

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