7. More test photos

A project log for SPUD - A self-contained scanner camera

"Scanning Photodiode-array captUre Device" - a digital camera based on TSL1406RS array to capture medium format 0.8MP images.

Kevin KadookaKevin Kadooka 07/02/2016 at 19:220 Comments

Had some more time to take some photos this morning (just from the top of the apartment complex). I think the sensitivity of the sensor is somewhere around ISO 400-800.

Seattle skyline, f/2.8, 1/15000s: Lots of vignetting around the edges. The lens (which by the way, is very cheap), is meant to cover about a 56 x 42mm frame. Here the frame is 65 x 48mm. It improves as you stop down, however.

Some construction on Stone Way, f/8, 1/2000s: Not particularly exciting, but you can see the moire patterns in the crane. Expected, as the pixel count is pretty low and there is no low pass filter. The dynamic range is OK, around 10-11 stops (according to the datasheet) - but everything tends to take on kind of a film noir look - heavy shadows and somewhat limited highlight detail. The datasheet, again, suggests that the response is pretty linear. However, it also notes that the "white" level is somewhere around halfway between 0 and VCC, while saturation is closer to VCC. I'm not sure what the response between "white" and "saturation" is, but to me the highlight rolloff is pretty sharp.

To draw a parallel to film, the sensor has a "short toe" and a "long shoulder" - lots of shadow detail, but limited highlight.

f/2.8, 1/4000s: Some photos of foliage shows another weird quirk of the TSL, namely that its sensitivity extends pretty far into NIR. Plants tend to reflect a lot of IR light, so they show up as gray/white, as shown below. You can but UV/IR combo filters, but they tend to be pretty expensive.

f/2.8, 1/2000s: The thing is pretty hard to compose with! For now it's mostly guess-and-check. I'm working on a few methods to make focusing easier. As far as viewing I may just tack on a 35mm viewfinder. Not the prettiest or most elegant solution in the world but it could work.

f/2.8, 1/30s