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Old 03-07-2021, 01:05 AM
baj (Brad)
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In search of larger pixels

CCD cameras although still available are slowly being phased out and being replaced with small pixel cmos cameras with software binning. I am wondering what owners of larger longer focal length instruments are doing or planning to do in the future to achieve reasonable image scales.

I have a 300mm f4 newtonian and my main interest is imaging asteroids and comets so my preference is to image around 2 arcseconds per pixel. CCD cameras with hardware binning meet my requirements but cmos cameras are with large pixels are very hard to come by. The ultra expensive QHY42 (11 micron pixels) is suitable. The IMX432 sensor with 9 micron pixels is the only cheaper option which is used in Toup Tek cameras.

To achieve the image scale that I want with cmos cameras I have purchased a hyperstar for my EdgeHD 11. This combined with a QHY174 (5.86 micron pixels) gives me an image scale that I am happy with and allows me to image without autoguiding. The newtonian is basically moth balled.

So are owners of larger instruments with longer focal lengths using ccd cameras with hardware binning or going down the path of higher resolution imaging with cmos cameras? I would be interested to hear what approaches are being used.
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Old 03-07-2021, 01:49 PM
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QHY600M 3.76 microns binned 2x2 is hardware binned not software binned. Gives 7.52 micron pixels at 90% QE.

It works just fine on my CDK17:

https://pbase.com/gregbradley/image/171682364

The other advantage of 2x2 is 30mb files instead of 120mb for 1x1 which are slow to process.

Greg.
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Old 03-07-2021, 02:41 PM
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Binning of the IMX455 (aka QHY600M) is actually done in software, with in the case of 2x binning, the signal from 4 pixels being combined after each individual pixel has been read.

This is not the same as CCD binning which reads the combined output of four pixels as one “superpixel”. That said, there are small gains and file size reductions to be had by using 2x binning with the IMX455.

For users with long focal length systems large CCD options are still available, the SBIG Aluma CCD77-00 has 24 micron pixels and 93% QE making it one of the most sensitive cameras available, but would not be a great “pretty picture” camera due the small 512 x 512 pixel array.

I have found comparing data from my STX-16803 camera to the QHY600 when using a 3400mm focal length that the IMX455 does not fare very well on low brightness targets due its significant oversampling and low level noise structure which overcome any QE advantages. At that focal length, the KAF16803 when correctly calibrated has an ultra-smooth noise profile making it far easier to tease out hidden details.
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Old 03-07-2021, 03:48 PM
baj (Brad)
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I would be happy with binned 2x2 7.52 micron pixels so long as that was the pixel size during capture time and not at readout time. If the signal from 4 pixels is combined after each pixel is read as Peter has stated then from what I understand the pixels are 3.76 microns when data is being captured.


This is my problem with software binning in relation to pixel size and calculating the image scale for my setup. Do you use the 3.76 micron pixel size when determining your image scale or the 2x2 7.52 micron?



It probably seems like its not important but for moving targets like asteroids and comets I think you need know. For example if you are making astrometric measurements or want to avoid trailing.
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Old 03-07-2021, 07:38 PM
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If you're software binning anyway, just pick a combination of pixel sizes that matches with your desired resolution... then click "resample"

There's no magic to the binning when it's not done in hardware.

Bin 3x3 with 3.76 micron pixels => 11.28 microns.
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Old 07-07-2021, 07:39 AM
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Quote:
Originally Posted by Peter Ward View Post
Binning of the IMX455 (aka QHY600M) is actually done in software, with in the case of 2x binning, the signal from 4 pixels being combined after each individual pixel has been read.

This is not the same as CCD binning which reads the combined output of four pixels as one “superpixel”. That said, there are small gains and file size reductions to be had by using 2x binning with the IMX455.

For users with long focal length systems large CCD options are still available, the SBIG Aluma CCD77-00 has 24 micron pixels and 93% QE making it one of the most sensitive cameras available, but would not be a great “pretty picture” camera due the small 512 x 512 pixel array.

I have found comparing data from my STX-16803 camera to the QHY600 when using a 3400mm focal length that the IMX455 does not fare very well on low brightness targets due its significant oversampling and low level noise structure which overcome any QE advantages. At that focal length, the KAF16803 when correctly calibrated has an ultra-smooth noise profile making it far easier to tease out hidden details.
Just looked at the QHY website again which has been updated. It originally said there was some hardware binning on the QHY600 but now says it is software binned.

I did a test image the other night to see the visual difference between 1x1 and 2x2. 2x2 seemed to have less noise, was a bit brighter but a bit less resolution, details not quite as contrasty but it was minor. SNR was 3.76 whereas with 1x1 it was 2.8.

The 120mb 1x1 files though really slow down processing and takes 4 times as long as the 2x2 30mb files.

Greg.
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Old 07-07-2021, 10:28 AM
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Originally Posted by baj View Post
CCD cameras although still available are slowly being phased out and being replaced with small pixel cmos cameras with software binning. I am wondering what owners of larger longer focal length instruments are doing or planning to do in the future to achieve reasonable image scales.

I have a 300mm f4 newtonian and my main interest is imaging asteroids and comets so my preference is to image around 2 arcseconds per pixel. CCD cameras with hardware binning meet my requirements but cmos cameras are with large pixels are very hard to come by. The ultra expensive QHY42 (11 micron pixels) is suitable. The IMX432 sensor with 9 micron pixels is the only cheaper option which is used in Toup Tek cameras.

To achieve the image scale that I want with cmos cameras I have purchased a hyperstar for my EdgeHD 11. This combined with a QHY174 (5.86 micron pixels) gives me an image scale that I am happy with and allows me to image without autoguiding. The newtonian is basically moth balled.

So are owners of larger instruments with longer focal lengths using ccd cameras with hardware binning or going down the path of higher resolution imaging with cmos cameras? I would be interested to hear what approaches are being used.
Hi Brad,

If you want LARGE pixels, and are OK with colour you could always try an early Canon or Nikon DSLR which would put you in the 7-9 µm pixel range for a full frame sensor. If you go to very early models you can get close to 12µm pixels, but they are in smaller APSc type sensors. Even by current DSLR standards the earlier full frame DSLRs still have reasonably good noise performance.

Examples of some early Full Frame DSLRs with large pixels...
Canon 1Ds - 11 Megapixel sensor (Y2002) has 8.8µm pixels
Nikon D3 - 12 Megapixel sensor (Y2007) has 8.5µm pixels
Nikon D4 - 16 Megapixel sensor (Y2012) has 7.3µm pixels
Best
JA

Last edited by JA; 07-07-2021 at 10:43 AM.
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Old 07-07-2021, 12:27 PM
baj (Brad)
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Thanks JA


This is a path I have recently gone down. Tossing up between the Nikon D700 and the A7s both with 8.4 micron pixels.



I have gone with the more modern A7s and will use 30 second exposures to avoid bulb mode and the star eater problem that you hear so much about with these cameras.


30 seconds at f1.9 is more than enough exposure time and the colour sensor will be excellent for comets.



The A7sIII looks impressive since it is supposed to have a back side illuminated sensor and 8.4 micron pixels. Don't know if it will be suitable for astrophotography though.
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Old 07-07-2021, 04:44 PM
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Thanks JA

This is a path I have recently gone down. Tossing up between the Nikon D700 and the A7s both with 8.4 micron pixels.

I have gone with the more modern A7s and will use 30 second exposures to avoid bulb mode and the star eater problem that you hear so much about with these cameras.
Oh I forgot about the more recent models. The Sony A7s is an excellent choice and should you need it will also do excellent 4k/30P video from virtually the entire sensor at 1:1. I can't see for astro or your specific applications any further benefit of the A7sII or to go crazy with the A7sIII with 4k/120p. The A7s should be just fine and even if it did exhibit some minor star eater effects (in Bulb mode) , there are too many stars anyway

You can also, with any of them, given their maxISO of ~100,000 turn up the ISO like crazy to help find dim stars for focus and/or gauge composition directly on the LCD display or take a quick high ISO snap.

Best
JA

Last edited by JA; 07-07-2021 at 05:39 PM.
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