Why did drum scanners give way to other technology?

[pkr1979]

{moderator note: this post was split off from the original thread here: https://www.photrio.com/forum/threads/scanning-with-the-emulsion-facing-the-wrong-way.215263}

Also not so relevant to the question of film orientation, but Ive also been comparing my drum scans with scans Ive been doing with my CoolScan 8000... same negatives. The resolution is about the same but the drum scans are indeed significantly better. Considering drum scanning is such a hassle I had a strong bias for the CoolScan... I wanted it to be better, as good, or unnoticeably inferior. This isn't the case though. I also scanned some 8x10 E100 and it is spectacular.

And this made me wonder... why did they quit this PMT technology? Couldn't this be 'transferred' to a flatbed-kind-of-scanner?

 

[koraks]

That's an interesting question, and while it's easy enough to ask, answering it is actually quite complex.

Ultimately I think it boils down to two rationales: (1) productivity and (2) discontinuous technological trajectories.

As to (1), drum scanning essentially boils down to digitizing the film one single pixel at a time. This means that if it needs to be done fast (which you'd done to cut down wait times and increase human operator efficiency), the process needs to be accelerated to pretty insane levels. This is exceedingly complex and expensive to do due to a couple of fundamental technological challenges involved. At the time other scanning concepts arrived at the scene, it's doubtful that the technology even existed or was feasible to create to get a drum scanning concept at a similar productivity level as currently common concepts using strip CCD's.

Concerning (2), photomultiplier tubes (PMT's) are essentially vacuum tube technology and as such are rooted in the early 20th century. By the 1960s, solid state/silicon-based electronics started to replace vacuum tube tech at a large scale. The latter has the obvious advantages (in general) of being more compact, allowing for simpler circuitry, lower cost and lower energy consumption. Combined with (1), the overall simpler, more compact and cheaper design of a solid-state/silicon-based scanning concept turned out to be more attractive.

Taken together, apparently the higher cost, complexity and lower productivity of a PMT-based approach just wasn't justified by the higher quality. Keep in mind that silicon-based approaches can be pretty high quality as well; for instance, the FlexTight concept realized fairly high quality levels using silicon pretty early on in the era of CCD-based scanners. The fact that we're working with often less capable CCD-based machines has more to do with cost and size requirements than with the capabilities of the concept as such.

Of course, in recent years, single-pass capture using a 2-dimensional array (e.g. 'camera scanning') has logically continued the direction that was already initiated when PMT mostly gave way to CCD.

Any of these points could be expanded with considerable backstories; I summarized in a bit of a haphazard way for brevity.

 

[pkr1979]

Thanks for this! When drum scanning boils down to digitizing the film one pixel at the the time I assume this is because the PMT is only able to do one pixel at the time? Which means that if it has to be done quick (haha) it needs to be done wit a drum. But in theory the film could have been digitized on a flatbed using PMTs?

 

[koraks]

When drum scanning boils down to digitizing the film one pixel at the the time I assume this is because the PMT is only able to do one pixel at the time?

Yes,that's correct. A PMT knows no pixels. It's just one signal. So you direct some light into it and record that signal, and call it a pixel. Do that 20 million times in succession, and we call it a 20 megapixel image.

Which means that if it has to be done quick (haha) it needs to be done wit a drum. But in theory the film could have been digitized on a flatbed using PMTs?

Yes, the drum is just a mechanical solution to the problem of having to scan (hence the name) a single beam of light across the entire surface of the film in a matrix fashion. A rotating drum happens to be one of the effective ways of performing that trick, but it's not the only conceivable concept. You could theoretically build a PMT based scanner of a flatbed type using an x/y moving carriage. It wouldn't surprise me if such devices have been in fact built, although no popular devices for scanning photos or negatives come to mind.

 

[Pieter12]

Drum scans have not gone away. Maybe flatbed and camera digitizing has improved, but drum scans are still the benchmark.

 

[calebarchie]

It wouldn't surprise me if such devices have been in fact built, although no popular devices for scanning photos or negatives come to mind.

Have a look at flying spot scanners.

 

[Pieter12]

Have a look at flying spot scanners.

I have employed many, many state-of-the-art and ridiculously expensive telecine (flying spot) rigs during my career. They don't hold a candle to a good drum scanner for still images.

 

[calebarchie]

Didn't say anything about drum scanners, just that this technology existed. I think have about 8 of those now, so I do agree with you.

 

[MattKing]

The last drum scanner I saw in the flesh, needed as much space as a medium sized chest freezer.
That of course included all that accompanied the scanner, but still ....

 

[brbo]

I think that most of the drum scanners still in use today are of the “mini” (desktop) breed - sub 100kg.

Proper ones needed a space of a medium sized room and weighed 500+ kg.