Don't Worry, Be Happy + Flatbeds

From "How VueScan Works"

"If single-pass multi-scanning is enabled, each line of data from the CCD is read multiple times and combined (averaged) while being stored in the memory buffer. If multi-pass multi-scanning is enabled, the whole scan area is read multiple times and combined (averaged) in the memory buffer."

Unlike the Dimage 5400 film scanner - the Epson 1600 is not capable of "multi-pass scanning" - so what VueScan is set to do is "Single-pass multi-scanning."'

Nor, from what I've read is the 4990 capable of multi-pass scanning. There is an interesting line in the manual for the 4990 where it says: Hardware Resolution: 4800 x 9600 with Microstep Drive Technology

I'm not sure what that means either. I don't even know what the scale of 4.0 means. I see that the Dimage 5400 has a higher optical d-max. I see some very large numbers for high-end drum scanners. Is it a straight linear scale where each decimal point is just a little bit better, or is it like the earthquake scale where you are talking about magnitudes of improvement? I have no idea.

At any rate - I looked through the 4990 manuals and screen shots and don't see anything about multi-pass (or focusing for that matter).

So here's the hub of the question: I have setup VueScan with the 1600 to do single-pass "multi-scanning."

And the results are that more detail in the shadow areas (by far) are picked up using say 4 samples than 1 sample. The results are by far the best I've ever gotten for the MF and large negatives out of the 1600.

So - what does this mean? Does it mean that VueScan has effectively increased the Maximum Tonal Range the 1600 can pull from a negative? The empirical answer to that is - yes.

So if you began with a scanner capable on its' own of picking up higher d-max (the 4990 is listed as 4.0, the 1600 is listed as 3.3) - you would need less sampling to achieve the same results.

And to further confuse you (as well as myself) in several tech. sheets for the 4990, the d-max of 4.0 has next to it the phrase "computed."

This is one of those posts where you just want to say to yourself - oh get the damned thing and see how it works. But I have to admit - I have learned a little bit in the process so maybe that's not such a bad thing - though you know what they say about that, a little knowledge being a dangerous thing. But that's a dumb phrase since you always start with a little knowledge at some point and like the aforementioned scanner - you apply micro-stepping to improve on it.

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BILL EMORY EMAILED ME THIS EXCELLENT LINK EXPLAINING DMAX which answers a good deal of my somewhat fuzzy post:

Dynamic Range

By Bob Atkins

"Since the dynamic range of solid state detectors is limited to something like 3.4-3.6, that's all you get. The better the sensor and the better the electronics, the better the dynamic range, so it could be anywhere from 2.8 to 3.6. You just don't know because the manufacturers don't publish measured numbers, just "theoretical maximum" numbers based on a perfect noise free sensor and perfect D/A converter - which of course don't exist!" - Bob Atkins

A lot of fascinating - clarifying info in this article. Explains why, for example the Epson 1600 lists dynamic range at 3.6

Also - explains that without either reading a hands-on-review - or testing it yourself - you can't really know how good (low noise) the sensor is.