Teaser: Nikon DSLR Black Point Hack for Astrophotography

Heads up Astrophotographers, Canon is no longer the best camera in terms of image quality in astrophotography. Today, we, the Nikon Hackers, are first able to extract the real, authentic RAW image from the Nikon D7000. The last hurdle towards serious astro-imaging. Especially for people doing narrow band where background is very dark. It will also promise greater bias and dark calibration.

This is an exciting moment, for me as an amateur astronomer at least. Here’s a quick peak of the dark frame image.

Preview

Here’s the image straight out of the camera. The DSP engine is still treating 0 as black point thus it’s pink on the screen. The histogram also looks weird due to its X-axis is gamma corrected for JPEG preview.

statistics

Average will now be brought back to around 600ADU, the setting for on sensor black level.

As for image quality, Sony Exmor CMOS has far less readout noise and FPN compared to Canon. Dark current is also in the range of 0.15eps stablized under room temperature. Under a typical winter condition, dark current is so low and comparable to cooled CCDs.

Now 2 options are available to get sensor data without any pre-processing. One, get the firmware patch called “True dark current”. The drawback is camera will not use calibrated data. Gr and Gb pixels will not be at the same conversion gain. And currently it is only for D5100 and D7000 as we don’t have time to dig into the assembly codes for other DSLR models. Second option is to get my “Dark Current Enable Tool”. The downside is it’s only transient. Camera will return to normal once power cycled or metering system went asleep.

Thus if you have computer during imaging and use your camera for daylight photography, the second option will be the best. Otherwise if you travel like me, go for the first option and keep 2 copies in the smart phone. Copy the desired version with USB OTG and flash the camera with a charged battery.

5/17/2015 Update:

We released a new firmware patch for D5100/D7000/D800, which trades a menu entry called “Color Space” into one that can activate the original sensor data. Thus you can use your DSLR during travel for both astrophotography and daily photography without the need to flash different firmware or with a computer tether. And here’s a demo:

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