Low Light Photography

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Rich Feldman
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Joined: Mon Dec 21, 2009 6:59 pm
Real name: Rich Feldman
Location: Santa Clara County, CA, USA

EV Limbo (Re: Low Light Photography)

Post by Rich Feldman »

Using the Nikon D750 of my friend Craig Foster, we got almost 4 stops lower.
Here's a screen capture of one JPEG he "printed" from raw NEF file without any so-called enhancement.
resamp_14.JPG
Exposure was 30 seconds at f/1.4 and ISO 12800, for EV(100) of -10.9.
When we can retrieve actual pixel brightness numbers, we can figure the luminance of that glowing dot in cd/m^2, or footlamberts, or nanonits. Anybody here ever done that for some dim subject, e.g. a radium clock dial? The strong blue color here introduces a manageable complication.

You can see this and other full-size jpegs here on flickr: https://www.flickr.com/photos/r_k_f/alb ... 4520881252 I need to get credit for Craig into the captions. For the image tagged "16", the fluorescent screen was reversed so the ZnS(Ag) layer is on the camera side. We also took some 3-minute exposures with shutter set to Bulb, holding finger on the button for that long. One with lens cap on, but we haven't yet tried subtracting it. Our dark-adapted eyes could see the glowing spot, and make out large features in the room, which was lit by leakage through space between door bottom and carpeting.

Further work on spinthariscope construction belongs in a new thread. Before Richard mentioned telescope eyepieces, I'd already probed my 26 mm Plössl with a fingertip. Verified that its object plane is accessible (not between or within any glass elements). But screen will have to go in past a 0.85" diameter field stop, for slightly myopic viewers like myself.

[edit] Looks like when EV of -11 is "proper" for a whole scene, the average luminance is on the order of 0.06 mcd/m^2. In more practical terms, 0.06 ncd per square mm. Some standards for luminous watch dials use ncd "per dial". Here's a great reference about luminous instruments and their visibility: http://kronometric.org/article/lume/
lume.JPG
lume.JPG (21.58 KiB) Viewed 2611 times
All models are wrong; some models are useful. -- George Box
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