Page 1 of 3

Monochrome D5100 and true dark current

PostPosted: Sun Dec 14, 2014 11:50 am
by Herra Kuulapaa
I have a monochrome modified Nikon D5100 with no bayer filters. You can check the project here: http://kuulapaa.com/home/astrophotography/nikond5100mod.html. There has been an unfortunate pattern in NEF files that looks like some kind of bayer matrix remains. Or at least I have thought so.
Like this:
Image

Today I was experimenting with no NEF compression and true dark current mods and made an interesting discovery.

There was the same pattern in no NEF compression file:
Image

But no pattern in true dark current file:
Image

Is this because the pixel colors are subtracted with different values or something? Anyway I'm pretty happy finding the reason and solution to remove the checkerboard pattern :)

Re: Monochrome D5100 and true dark current

PostPosted: Sun Dec 14, 2014 12:25 pm
by astronomer
Hi Herra,

What you had observed is due to Nikon's digital scaling on Red and Blue Bayer channel in stock firmware.See this post for detail. Thus even you strip all the bayer filter and microlense array, the pixels at original red and blue locations are still scaled up by firmware.

In the true dark current hacking, I had disabled all the digital processing on the sensor data including the digital scaling. That's how you ended up with the uniform background. Just use the firmware hack with "True Dark Current" if you are mounting a B/W converted sensor.

Astronomer

Re: Monochrome D5100 and true dark current

PostPosted: Mon Dec 15, 2014 3:00 am
by Herra Kuulapaa
Great work :)

It’s interesting how strong the pixel scaling actually is.
Is it by the way possible to introduce same option to the 1.02 firmware?

Re: Monochrome D5100 and true dark current

PostPosted: Mon Dec 15, 2014 9:22 am
by Herra Kuulapaa
Here's a small comparison between original firmware, true dark current patched and a stacked 5 frames of original firmware:
Image

Re: Monochrome D5100 and true dark current

PostPosted: Mon Dec 15, 2014 9:25 am
by astronomer

Re: Monochrome D5100 and true dark current

PostPosted: Tue Jan 27, 2015 4:02 am
by Herra Kuulapaa
Couple of examples with mono D5100 and dark current mod:

Image Image

Re: Monochrome D5100 and true dark current

PostPosted: Tue Jan 27, 2015 1:08 pm
by mutofuto
Jumalauta! :clap:

Re: Monochrome D5100 and true dark current

PostPosted: Wed Jan 28, 2015 12:08 pm
by Herra Kuulapaa
Yes, like my fellow countryman nicely summarized, it's a very good mod (dark current one) :)

Re: Monochrome D5100 and true dark current

PostPosted: Sun Feb 08, 2015 1:00 pm
by Herra Kuulapaa
One more test with D5100 dark current firmware.

Image

Keep up the good work guys :handgestures-thumbupleft:

Re: Monochrome D5100 and true dark current

PostPosted: Mon Feb 09, 2015 7:43 am
by astronomer
Hi Herra,

Those are really great images!
Can you share with some exposure time, scope details?

best,
astronomer