How are you measuring the output? The LEDs in the left of the picture look like the ones I wound up using.
Here comes the photo of both LEDs I get, the new arrival on the left and previous one on the right.
I used a Minolta F spotmeter shooting directly agaist the center of the diffuser panel. It reads in 0.1EV step. I also had a closeup len on my spotmeter and it didn't make any different w/wo this close-up len. I'm thinking about borrowing a Luminance meter from a friend to measure it with higher accuracy.
I also noticed that the spotmeter reading was the same with my Nikon DSLR. However, the readings of all my manual focus body (FM2 F3 F5, etc) were one stop lower than the spotmeter and DSLR. In the light source section on wiki, it says "Because of the Color Correction Factor of LED, old light meters like selenium meters, photoresistors or LDR, and some photodiodes read exactly 1 stop lower. More modern light meters, including digital cameras, read LED lights correctly." So I surpose that is expected, right?
Make sure the K is set correctly. For Nikon it is K= 14.03. Some meters (like Sekonic) are K = 12.5
Also, when testing Nikon, I use center weigh mode rather than Matrix. A complete illuminated field might confuse the matrix meter.
That might be for older classic Nikon. I'll try to find the reference.
Since the light unit is using PWM pulse to drive the LED, I think it is possible to insert another Arduino Nano to measure the PWM signal output from the shield board and then output a corrected PWM signal corresponding to my light unit. The code should be fairly simple and I would like to give it a try.
That might be for older classic Nikon. I'll try to find the reference.
ic-racer, In your test table I see mix of old and new cameras, which were designed to meter differently. For example, Nikon F100 calibrated to K14.03, and it uses modern photodiodes, so Light Source should be set to K14 and 0EV shift in settings. Also, pay attention that F100 has different metering modes, you might need to switch it into average mode, not centered. And when calibrating, you should use 50mm lens on your Nikon f100, and place it directly against the screen at the center. --Serhiy Rozum
Exactly, I was going to suggest the same thing but wasn't sure people would understand it. You should try it!
My interest in doing that would be so I could use my REAL CREE lamp with closer to 4700k output. The intensity was ok in the middle range but the linearity was off.
All right, I managed to finish my very first version of the "Tuner" before my vacation.
I guess the dev has already accomplished what he needed for his own use. I doubt he will advace the project any further.
I remember now that he mentioned the limited memory space on the nano:
"The thing is, the firmware takes so much space that it doesn't fit into regular Nano board. For example, v2.5 uses 31380 bytes of flash memory."
I'm not even sure if any more code additions would be possible.
(source: https://github.com/srozum/film_camera_tester/wiki/Firmware)
. I figured out why he had to combine PFM/PWM together to control the light unit only until I started to calculate the actual requirement which required quite a high resolution for the dynamic range.
"Sensor 6"
I noticed that it needs to be in it's enclosure to calibrate. I tried to test it (before fitting it in the enclosure) but just a little stray light messes up the calibration making it appear dead or non-functional.
After fitting it in the enclosure, it worked perfectly.
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