(first - full photo scaled to 20 MP, second - crop of 64 MP original at 1:1, third - The Contraption)
📷 Ciro-flex B (1947)
🔎 Wollensak Velostigmat 85mm f/3.5
🎞️ Kodak Ektar 100
🖨️ Nikon Coolscan 8000, custom motherboard
the good
- picture! in color, too
- better than my epson flatbed for sure
- the electronics and firmware pretty much work which i have to remember was not a given going into this project
- i have the only coolscan 8000 in the world that has a native USB interface. what the hell have the rest of you been doing
the bad
- the photo is out of focus. i believe (having inspected my other scans) that this is because the original is out of focus; i can see some film grain in the punch-in that i think is distinct from digital noise
- also, like, i know for damn sure the scanner is in focus (i've got a simple script to run contrast-detection AF and nothing moved the focus motor between that and the scan) and i don't believe there's anything i could be doing on the electrical side to make it look like it wasn't
- there's a lot of digital noise though. a few categories of that:
- general background noise like you get in any analog system (probably not worth worrying about)
- the occasional random high-level glitter spot (???)
- a few barely-noticeable vertical stripes because i'm currently only doing a single linear regression for calibration
- and most obviously those giant glittery stripes every 85 pixels. these are essentially an artifact of my duct-taped together analog block so i'm fairly confident they'll go away on the next hardware rev
- no IR cleaning yet. not only did i not produce an IR channel for this scan, i wouldn't be able to do anything with it. gotta write the software and all that
the ugly
- this scan (which is not even full-frame on the scanner) took over thirty minutes. it should be about 60 seconds for a 6x6 scan
- that's mostly because the analog block on this board is completely fucked
- only one input channel works. there should be three, the CCD has three rows of pixels which are supposed to be used for 3x faster scanning
- the one working input channel is just the ADC, there's no frontend. the preamplified CCD output off its daughterboard is going straight into the ADC. this is very not good for noise performance since the input impedance is all out of whack and there's no filtering, plus no ability to offset the input signal means i have to use a voltage divider to get it within the ADC's input range, so the signal hitting the ADC has an AC gain of about 0.75 instead of the ~110 it really wants
- so i've had to make that up with a combination of ~20x the normal exposure time (hence slow scanning) and a ~5.5x effective digital gain ("on paper" it's 22 in software but there's always going to be a 4x in there to get it to the full scale 16-bit output). both of these suck huge; exposure time for obvious reasons and that much digital gain is also not very good for the image performance. we're looking at roughly codes 4400 - 9200 on a 14-bit DAC here
- it's also because the firmware is inefficient
- in theory, with 18 ms exposure per channel i should be able to scan a 6x6 frame in about 8.5 minutes. i should be able to get this version of the firmware to do that with relatively little work, but 60 seconds will need serious hardware and firmware rework (which i am already planning)
- the digital stuff on the board also isn't all working but it's much easier to tape that back together. in fairness it has been over a year since i last did any SMD work and it was a much simpler project
- i probably should not go spend $200 on the next hardware rev of this while i'm unemployed but that might not stop me
anyways, quite happy to see it start coming together. definitely can't call it done yet but still going that direction
