silverdr

It will have to drive many more LEDs to _much higher_ light output and it's not so much about overheating (overloading) the power supply (although this has to be double-checked too and possibly bypassed with a new supply path if needed - the external PSU should be more than enough to handle it though) but about overheating the plastic elements of the light duct (and its surroundings) itself. As for the CRI stuff - I believe that you are mistaken (or misunderstood my intentions). While good results can in fact be achieved with three RGB light sources or one having good output in the RGB range (not CMY as you originally suggested), tuned properly to the sensor's characteristics, this means quite a bit of fine-tuning. I believe that's what Nikon did and achieved excellent results, others are now measured against. Since I don't have the means Nikon engineers had and you can't balance in post-processing what you didn't sample properly in the first place, therefore I opt for high CRI. Using high CRI light source, more or less guarantees that there will be no "holes" in the frequencies, where they must not be. This is not to have the film lit so that it looks "correct" to human eye. It is in order to have closer to continuous light spectrum being emitted. So that what passes through the film can be sampled with enough dynamic range and S/N ratio at the frequencies the scanning sensor is sensitive to, regardless of what they actually are.

Which are six variables to match, varying from film to film and led to led. And then you sample CMY into RGB. Well, I disagree. Oh really? That would be why the original light source was so botched then. Honestly, does it look as of the designers had 'high end' in mind when they created that mess of lenses to try and even out the light from 3 inadequate LEDs? They clearly screwed it. They apparently went the way Bose pioneered in audio domain: "we don't care much how the hardware performs, we'll make up for everything in software". This "mostly" works. Until it stops. But all that doesn't change the fact that this scanner is one of five worth spending one's time on, short of some drum machines and Imacon's X range. If that doesn't make it "higher-end" then I don't know what does. It has better film handling than Nikon 5000, it has better glass than Nikon 5000, subjectively it has better Dmax than Nikon 5000/9000. Except intrinsic differences in edge-to-edge performance caused by drum scanning, either virtual (Imacon) or real (Heidelberg) it outperforms both (I have only older Imacon) on 135 in terms of outcome quality and I don't even start talking about total mount and scan time per frame. So yes, "really" :-)

COB increases efficiency/lumen density but does not affect CRI. We're talking about a higher-end film scanner here. That means I am rather convinced that none of the typical bar type units as can be found in cheap keyring lights will have CRI even close to acceptable for the purpose of accurate colour reproduction we strive for.

The thing is that you can't freely regulate the light intensity. Reducing current beyond what the LEDs are designed to work with will heavily affect chromaticity/CRI. So they need to work within the specs limits and the final intensity needs to be reduced by ND filter. Of course I can't tell for sure what they meant but to me it looks like a light beam shaping design. They used only three LEDs there (presumably highly expensive back then) and tried to shape the beams to get something close to uniform coverage of the target area. Please note that three "D"s on the lens are aligned with the three LEDs on the adjacent board. A kludgey substitute for a wide, well diffused light source. Since this approach can probably never give 100% accurate results, they introduced additional software calibration process to make up for hardware deficiencies. This "mostly works", but… Anyways, LEDs arrived. I plan on taking one of the scanners apart in a fortnight.

That's what I hope for… deep inside ;-) The thing is that even if they're twice TDP efficient now, it may not be enough if I replace three with twelve or fifteen. This may be needed in order to be able to get rid of that extra lens. The other thing is that getting rid of the lens calls for extremely good diffuser pretty close to the LEDs themselves, which means less circulation, more heat accumulation etc. But I'll get answers to those questions once I try and measure things. As I have more than one of those scanners I am not too scared to experiment. Those are flat SMDs but they surely need to be diffused heavily to eliminate hotspots, even if I put twelve of them.

White. That's what OP began with. The problem with this is that there's that bubble-shaped plastic lens on the way. We'd probably need to get rid of that and build a much different board with many LEDs covered by a very good diffuser. I just ordered the highest CRI LEDs from the manufacturer OPs linked to (the newer ones) and shall see what I can do with it. There's many questions to be answered before declaring that it can be safely done with many LEDs. Power consumption, thermal considerations are the first that come to mind. Shall see if I can eventually get somewhere with those.

One of the two main selling points for 5400ii was that it's LED lit and the light source doesn't age, etc. The original, metal encased 5400s I have use CCFL lamp, which is prone to ageing and needs a warm-up but then didn't need that bubble-shaped lens and don't produce this kind of side-effects. It would be ironic if the older ones lasted actually longer. My old LED lit Nikons don't have any of these problems either so they are the obvious "goto" devices. But Minoltas have superior optics, better film handling/holders (than 5000 and its predecessors – the 9000 holders are OK) and the 5400ii is on a par in terms of scanning speed (the original 5400 is dog-slow) with the NIkons. It'd be a big pity not to be able to utilise their potential due to a faulty design of the light path…

I eventually brought to the table six 5400II units I've got and spent almost whole day today checking them out in various settings and combinations. The first thing I must say is that I was at least partially wrong in my original post. With some units (mostly two) similar (stripes) result can happen also using original software. So, while I thought that I might have eventually found a solution, this is unfortunately not true. With both Vuescan and Minolta software it is a hit'n miss but the two units produce the stripes virtually every time on both. The remaining ones tend to do it much more often when driven by Vuescan (practically every time) but it can also happen from time to time with Minolta. Obviously I'd need to spend weeks full-time to gather proper, statistically valid sample but for one day this is the result. So when I checked the original software last night, after reading a comment in this thread, I was lucky, it seems. Checked also multi-sampling as suggested here - no change. Once the stripes are there, multisampling doesn't help. Back to Nikon…

Maybe you can put it up somewhere and post a link to it here? Please do, if you can. Would be grateful.

I know it's an old thread but it does not become outdated. A few years later the same problem is plaguing the 5400II users. I have a large number of different scanners, including several 5400IIs, and all the units I can put my hands on, do exhibit the problem this thread is about. The pattern and intensity varies slightly from unit to unit but all units have it. I spent countless hours trying to find the element that needs to be cleaned in order to get rid of the stripes. Then I tried the original software rather than Vuescan. And guess what? Yes, it seems like just another nuisance of Mr. Hamrick's overrated software piece. Don't get me wrong - I appreciate him supporting tons of scanners and doing mostly good job on them. But it's not the first time when I lost indecent amount of time troubleshooting a non-existent hardware/setup issue only to realise that it's Vuescan's inability of this or that. As for dmitry_shijan (OP) case - it might be that your device actually developed some real problem that can't be compensated by the calibration procedure, this scanner model requires before every session. For the rest of us - switching to the original software may be the only move that's needed. For what it's worth, it looks like sometimes Vuescan's calibration works better and the dreaded stripes are less pronounced. Another session a few days later may produce completely unusable results.