Monochrome A7s CMOS Sensitivity Test

Debayered A7s CMOS

Gold wirings on 4 sides of sensor ares was covered by epoxy to protect from chemical solution. CMOS sensor is  having several defected points in debayering process. And these made Horizontal rows and vertical columns in image.

 

Test condition:

Astro A7s camera 1 set.

Low pass filter was removed, Hoya clear filter window on airtight chamber + Hoya UV IR cut filter in Drop-In filter holder.

Indoor table , 50mm F1.4 lens +white cover plate.

ISO100, 1/20sec electric shutter (Silent mode) exposure. sony RAW image format(ARW) was taken.

Original JPG images

1.Taken from color CMOS

2.Taken from mono CMOS

ARW file was processed to 16bit B/W image in RawDigger.

1. Image from Original Color CMOS

2.Image from Debayered A7s CMOS sensor( This sensor is the one extracted from another A7s camera and debayered by chemical solution.)

Level stretched image comparison.(255 ->30)

 

Center Area cropped, 16pixels x 15pixels area

 

Luminance Level Comparison (Black=0, White=100)

We can see the difference of pixel brightness  in Color CMOS :G1,G2 is more bright than Blue or Red pixels. It caused by the color filter character. In mono CMOS the bright level of pixels are very stable. I expected to see the level of mono CMOS pixels exceed to green pixels’s luminance value, but it’s  20% lower .  it’s most equal to Red value and 25% over  level of Blue pixels.

Average Luminance Level is Color CMOS =41, Mono Debayered CMOS= 39,  Monochrome sensor is slightly lower. But in resolution aspect, Monochrome sensor is 2 times higher compared to Color sensor.

 

 

RAW File Loading in Photo shop ( using Camera Raw )

File > Open.. > Choose your CR2 file.

Check factors in [Basic]  and set the values as below.

Check factors in [Detail]  and set the values as below and press [Open Image] Button.

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Image Processing for Nebula Object

There are so many ways to make astro images from Raw File .

Here is one way using RawDigger + Photoshop. Read more

Q: How can I change the reddish astro images taken by my modified camera to the natural colored astro images?

A:  The camera modification for astro photography aims to  maximum H-alpha (Hα)  656nm recording. Camera modification for astro photography make the regular camera to High Ha sensing camera, it’s about 3 times more compared to unmodified digital cameras.

But the color of background will become so reddish, because the increased red light amount.

There are many ways of image processing to correct the reddish colors to natural colors.

Here are 2 simple ways.

A. Take the shots using Custom White Balance

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Monochrome Camera

WHAT IS A ‘DEBAYERED CAMERA’ ?

To convert the color image sensor of a generic digital camera to a monochrome sensor, we must remove the bayer filter layer(= Color Filter Array=CFA) on the image sensor. This is called “Debayering”.

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Astro A7s System Chart

1. Active Cooling with EXcooler
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Astro 6D System Chart

1. Active cooling with EXcooler
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Astro A7s (Cooling modified SONY A7s)


The launch of Sony’s A7s this year is remarkable because of it’s very good low light performance and 4K movie mode with it’s Full Frame image sensor.
 The A7s 12 megapixels is small compared to other full frame digital cameras but this camera is special to amateur astronomers because of it’s ultra high iso (up to 409,600).

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