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pshepp1890

Altair hypercam 183c

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Update on the grey bias frames... 

They appear as grey and fuzzy in Astrophotography Tool but when I open the file in say deep sky stacker its black and looking normal. 

Any ideas? 

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Each software package applies its own degree of stretch to an image when displaying it - some none. You would need to use a package where you can apply your desired degree. Are your bias frames in FITS format?

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1 hour ago, prusling said:

Each software package applies its own degree of stretch to an image when displaying it - some none. You would need to use a package where you can apply your desired degree. Are your bias frames in FITS format?

Yes they are saved as fits. I'm sure it's just the software showing me a "preview" that is stretched. 

Is there a program that I can load the fits file up without any stretching? Just the base image? I've been doing this in deep sky stacker for the time being. 

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There are a number of programs that can view and manipulate FITS files - the ones I use are FITS Liberator 3 (ESA/ESO/NASA basic image stats), Fitswork 4 (a number of useful functions), IrfanView (a lite photo processor that can convert TIF to JPG for sharing) and GIMP (full-functioned photo editor). All are free or donation.

Most will not show colour (unless a debayering function is used). Bias files (and darks) have extremely low pixel values so will display as black unless stretched a lot.

My main personal recommendation would be StarTools which is an excellent post-processing program that is very reasonably priced - there's a free trial as well which disables saving.

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1 hour ago, prusling said:

There are a number of programs that can view and manipulate FITS files - the ones I use are FITS Liberator 3 (ESA/ESO/NASA basic image stats), Fitswork 4 (a number of useful functions), IrfanView (a lite photo processor that can convert TIF to JPG for sharing) and GIMP (full-functioned photo editor). All are free or donation.

Most will not show colour (unless a debayering function is used). Bias files (and darks) have extremely low pixel values so will display as black unless stretched a lot.

My main personal recommendation would be StarTools which is an excellent post-processing program that is very reasonably priced - there's a free trial as well which disables saving.

I download fits liberator last night but that's was also showing the bias as a fuzzy grey image. The exposure was confirmed as 0.0001s in the meta data tab. 

I also see alot of people saying set gain to 50 or 60% or to 300 or 400 but my gain control works as a multiplication ranging from 1x to 50x.

How does that translate to what everyone else is using? As in what percentage is the same as the X that I'm getting. 

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Fuzzy grey is good for bias and dark frames as it shows the signal that is present. Other software won't stretch them as much and you'll just see black but that won't really tell you anything.

Sorry I can't add anything more to the gain query - what software are you using and someone else may be able to help?

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2 minutes ago, prusling said:

Fuzzy grey is good for bias and dark frames as it shows the signal that is present. Other software won't stretch them as much and you'll just see black but that won't really tell you anything.

Sorry I can't add anything more to the gain query - what software are you using and someone else may be able to help?

I'm using Astrophotography Tool via Ascom. It's the ascom dialog box that opens when connecting camera that has the gain as a multiplication rather than a percentage. 

Thanks so much for your help prusling, you have taught me alot. 

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You're welcome, I may not live far from you so I'll drop you a pm.

I believe that the latest APT beta has native support for Altair cameras (rather than ASCOM) though you may want to check with Ivo the product owner.  There's also a good facebook group for Altair products if you haven't already found it.

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So what is everyones thoughts? Does a 400 gain seem the right ball park or am I reading it wrong? Cheers.

 

 

image.png

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And with a gain of 400 and black level of 40, a bias frame come out like this in fits liberator..

image.png.041d4d046765c393759115c2577092cd.png

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Looks good to me, though it depends on what you are doing - i.e. whether you need more gain or not. e.g. if you are taking long exposure images of DSOs it's probably fine but if you are wanting to live stack lots of short exposures you'd need to wind up the gain (in my limited experience!).

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4 minutes ago, prusling said:

Looks good to me, though it depends on what you are doing - i.e. whether you need more gain or not. e.g. if you are taking long exposure images of DSOs it's probably fine but if you are wanting to live stack lots of short exposures you'd need to wind up the gain (in my limited experience!).

Thanks Prusling, that's my intention to be honest. Its just to get me in the ball park area so im not messing around with settings in the cold and dark when I could be getting images.

Does that grey output from the bias look normal to you then? I thought a bias was supposed to be dark? thats with a shutter of 0.000264s (fastest camera will go)

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It is very dark. It's the stretch that is moving the very dark pixels up to brighter levels so you can see them. You have a mean/median pixel value of around 656 out of a possible 64k. That represents the unwanted signal from the electronics that needs to be subtracted from the pixel values to give you the real signal.

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1 hour ago, prusling said:

It is very dark. It's the stretch that is moving the very dark pixels up to brighter levels so you can see them. You have a mean/median pixel value of around 656 out of a possible 64k. That represents the unwanted signal from the electronics that needs to be subtracted from the pixel values to give you the real signal.

Perfect. I can't thank you enough for your help. 

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On 18/10/2018 at 01:10, pshepp1890 said:

So setting my offset to 45 gives me an average of 750 when taking a bias frame. 

I am having problems setting the gain though. I've got it as low as posse but everything still comes out at max exposure, even at just a 2 second sub. 

Also if I set my shutter speed below 0.1 to try and get a bias frame, the end picture is fuzzy grey, like it's been stretched. I'm using Astrophotography Tool. 

Never use bias with a CMOS camera. Use dark flats.

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21 hours ago, Adam J said:

Never use bias with a CMOS camera. Use dark flats.

Hi Sub Dwarf, Any reason for this? I'm still learning at the min.

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2 hours ago, pshepp1890 said:

Hi Sub Dwarf, Any reason for this? I'm still learning at the min.

Its Adam lol, Sub Dwarf is a forum rank thing.

Yes its because the bias is not stable in CMOS for short exposures so you cant calibrate it out and might even make things worse.

Edited by Adam J
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47 minutes ago, Adam J said:

Its Adam lol, Sub Dwarf is a forum rank thing.

Yes its because the bias is not stable in CMOS for short exposures so you cant calibrate it out and might even make things worse.

Adam would you also use the dark flats to calibrate light frames in place of bias?

Edited by jjosefsen

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5 minutes ago, jjosefsen said:

Adam would you also use the dark flats to calibrate light frames in place of bias?

Lights should be calibrated by Darks and Flats

The Flats should be calibrated by Dark Flats (even more important with the IMX183 due to the amp glow)

At no point should Bias be used.

Adam

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7 hours ago, Adam J said:

Lights should be calibrated by Darks and Flats

The Flats should be calibrated by Dark Flats (even more important with the IMX183 due to the amp glow)

At no point should Bias be used.

Adam

Hmm alright..

I used to remove the bias signal from my darks, and then calibrate lights with flats, darks and bias. But I guess that doesn't make much sense since I'm not scaling darks anymore, due to the amp glow you mention.

So uncalibrated darks it is..

I think I need to put something in front of my EL panel so i can shoot longer flats. I'm well under 1 second as is on some filters.

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