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UltravioletPhotography

Nikon D5100 full spectrum vs monochrome


Herra Kuulapaa

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Herra Kuulapaa

Referring to my previous posts of Nikon D600 monochrome, I have two Nikon D5100 cameras I'm planning to do a comparison. One of the cameras is filterless full spectrum and another full modified monochrome (without any RGB filters). So far I've used them in NIR and narrow band imaging and idea is to check if a budget monochrome camera such D5100 makes or breaks it.

 

http://www.kuulapaa.com/UV/Cameras.jpg

 

Plan is to use a modified firmware disabling all pre raw write data manipulation such as dark current and RGB channel scaling. This way the monochrome data stays as pure raw as possible. One of the issues remain, the lack of a proper UV lens and I'm using the same Nikon 50/1.8G in all of the tests. If anyone has ideas for a budget UV lens (hilarious, I know), please let me know :)

 

But let's consider this as a budget approach and in that perspective also the UV dim lens 50mm/1.8G is justified.

 

Ps. I link Oleksandr's mono NEX 5n thread here as well: http://www.ultravioletphotography.com/content/index.php/topic/758-sony-nex-5n-monochrom-conversion-results/

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Herra Kuulapaa

So far with 50mm/1.8G (f/3.5, 1/50sec, ISO200), Yongnuo YN560-III, UG1 + unspecified IR block the pure raw of white wall looks on pixel level like this:

 

Full spectrum D5100

http://www.kuulapaa.com/UV/Bayer_1.jpg

 

Monochrome D5100

http://www.kuulapaa.com/UV/Bayer_2.jpg

 

I failed to save debayered RGB file to attach it here, but at the moment it looks that the sensitivity increase cannot match the 6X with a regular lens due to the internal UV absorption. The measured D5100 response curve (taken with the same lens) shows the same effect:

 

http://www.kuulapaa.com/Spectra/D5100_resp.jpg

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Perhaps a Nikon 50 mm f/1.8 SE is a viable substitute? should do better in UV than the more modern multicoated Nikkor.
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Herra Kuulapaa

Perhaps a Nikon 50 mm f/1.8 SE is a viable substitute? should do better in UV than the more modern multicoated Nikkor.

 

I happen to have this kind of lens available. Single coated, aged but not old.

http://www.kuulapaa.com/UV/NikonE.jpg

 

It may be it's the glass type that matters, but it's interesting to see if there is any difference to modern 1.8G.

I have also a newly finished 4x3W (yep, at least they make some heat) 365nm led setup I can use to create even lighting conditions.

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Herra Kuulapaa

Thanks for the tip Bjorn! I'll look into the E vs G comparison soon.

 

I did some brief testing with the modern 50/1.8G-model yesterday and it's not that bad in UV. At least I don't have any experience on better lenses at the moment ;)

I appears that the monochrome D5100 gains roughly +1.25 - +1.50 ev boost compared to the full spectrum RGB D5100. It's not much, but helps in certain situations to get better exposure and of course the sharpness is better if the lens supports it.

 

E vs G test incoming :)

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Herra Kuulapaa

My plan was to measure sensor UV response curve of both lenses to evaluate transmission difference between them, but nothing is that easy with UV I've learned :(

The issue is that lenses focus both UVA and VIS in single point much worse I anticipated rendering my spectral measurement tries invalid.

 

Below is a response curve with 365nm UVA led. Visible spectrum focuses nicely, but UVA section becomes a huge blob. I can measure the total intensity from this, but the both lenses "blob" different way creating interesting shapes when I move focus closer the UVA section.

http://www.kuulapaa.com/UV/spectra.jpg

 

EDIT:I would like it to look something like this (this is a Xenon lamp):

http://www.kuulapaa.com/UV/Xenon.jpg

 

 

If I however make a plain photographic test between versions E and G, I notice a small but measurable transmission difference. 50/1.8E is +0.5ev brighter at UVA range than G model. It may be because of the coatings or just the number of glass elements.

 

Where am I then? Not very far, but so far I can achieve +2ev difference switching from a full spectrum D5100 and G model to a combination of monochrome D5100 and older 50/1.8E.

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