I’m using an incandescent bulb for my scanner, but I’m not sure whether it’s the right approach, as it’s not as bright as I want it to be and it won’t give me much control when scanning colour negatives.
Ideally, I’d like to be able to dim the RGBW leds with an Arduino. I’m struggling to understand how to wire LEDs, I’ve never done it before and it’s so much more complicated than incandescent!
I’m using a Nano for stepper motor control, camera trigger, and LCD screen (number of feet, frames). Do you think it might be a bit much to add LED control to it or is the Nano powerful enough? Do you recommend I use a separate Arduino nano for this?
Thank you very much for your help! This forum is amazing!
I have to agree with @Manuel_Angel here. For me at least, going simple with an off-the-shelf LED bulb was absolutely the right way to go. This way you don’t have to worry about a driver and you can literally just hook it up to an adequate voltage power supply and be done with it. If your scanner is built around a projector, mounting the bulb is much easier as well, because it will probably fit right where the old bulb went.
The most important thing to look out for, I think, is colour accuracy. You probably want a CRI 90, better still 95 or even 99. Otherwise, I would recommend a warm white LED for scanning reversal film and a daylight balanced LED for colour negative film. If you are scanning in RAW and your CRI is high enough, I personally believe you can get away with either, though, and just fix the colours in post (as you do in negative conversion anyways).
For my own scanner, I ended up buying an LED that was bright enough and otherwise relying on the camera for controlling exposure as I found that easier to do than to dim the lamp. If you want to dim the lamp (LEDs in particular), you have to make sure to avoid things like PWM-related flicker etc.
To give you some pointers: I’m using this fairly cheap LED bulb. I also tried this probably higher quality one by Philips, which was great, too, but actually turned out to be too bright in my setup at the time. The MR16 form factor covers 8mm perfectly when diffused adequately and I think 16mm should be fine, too.
Especially regarding colour accuracy and negative film scanning, there is a lot to learn from this excellent video by Hashem of Pushing Film.
Here is a posting of the machine I assembled, the last posting illustrates that the light source quality (the LED) is an important contributor to the quality of the scan.
The simple answer:
An incandescent bulb light is driven by the voltage (V) across the lamp. The bulb is acts as a resistor, and it has no polarity. It would work with alternating or direct voltate (AC or DC). Although for scanning it may be best to use DC.
The LED light is driven by the current (I), the LED is a diode and will illuminate when the current has the appropriate polarity. It also has a minimum voltage to make the diode work (Vf in the specifications). What the drivers typically do is to regulate the current, which can also be achieved by a resistor.
As part of the quality there are a couple of aspects to consider: the spectrum of the light source (AKA the CRI), and also as important, how even the light is across the film surface. Here is an article (in spanish) on the subject of making the light source even.
As previous comments suggest, intensity and color control have significant complexity and are not necessary required to start.
Hope it helps.
PS. by intensity I mean the ability to dim manually or controlled; by color the ability to mix color LEDs for color correction.
Yes the YUJILEDs are the best white light LEDs you can get for scanning. You want the 5600K one, and then you diffuse the light using your chosen diffusion method (that can take some time and tinkering to get right).
Cine2Digits no longer sell the commercial-grade RGB light to hobbyists, and at a certain point the Film Society would be better off investing in one of the entry level commercial film scanners - in particular they could look into the Lasergraphics Archivist which they’d be able to use for paid work as well to bring in some money and pay it off.
What do you think? is it worth going for the Yuji or the Nicha 2,080 lm? Or will the cheaper Nichia be enough? This LED would be inside the bulb compartment of an Eiki projector, so I haven’t got much space for a big chip + big heatsink.