What settings are needed to achieve maximum resolution from an Epson V850?

[Peter De Smidt]

First off, I'd be happy to be wrong about this. My understanding about the types of line sensors currently used could be mistaken.

"1 inch", "6400 spi", "8 inch".... were simply examples. I didn't say that any given sensor was 1" long.

I did talk about the various kinds of flatbed scanners, right?

My scanner (Screen Cezanne) does have a hard limit to resolution over a given area due to to the nature of the sensor. It can scan at higher resolutions over a narrower area, as per Screen's documentation, and my own experience using a Edmund Optics' chrome-on-glass high resolution target. It is an xy zoom scanner. See: http://www.screen.co.jp/ga_dtp/en/ne...ewsbox_7_2.pdf

But perhaps Epson has made some huge strides in linear ccd maximum size over the years that I don't know about. The way to confirm one way or the other, other than to have an Epson engineer specify which sensor is used, and it's specifications, or someone tearing apart their scanner to find a part number, would be to scan a resolution target two times. First, scan as if it was a 35mm negative. Second, scan as if it was a larger negative but use the same settings for all other aspects of the scan. If I'm wrong, then the resolution resolved would be the same in both cases. If the resolution resolved is less with the larger area scan, than my suspicion would be confirmed.

Consumer scanner manufacturers are cagey about true hardware specifications, and so it can be challenging to know what's really going on in a scan.

[Jim Andrada]

Why would the sensor have only 6400 photosites?

To save money and make a bigger profit????????????????????

[williaty]

$50 pocket camera has ~10M photosites now, I'm sure in a $1k scanner they can afford 1/20th that many (6-line full width).

[axs810]

But that's what it sells for not how much it costs to make

[Jim Andrada]

From the Epson site

Scanner Type: Flatbed color image scanner

Photoelectric Device: Alternative 6 lines color Epson MatrixCCD®

Optical Resolution:

Epson Dual Lens System
4800 dpi and 6400 dpi
Hardware Resolution:

4800 x 9600 dpi
6400 x 9600 dpi with Micro Step Drive™ technology
Maximum Resolution: 12,800 x 12,800 dpi

Effective Pixels:

40,800 x 56,160 (4800 dpi)
37,760 x 62,336 (6400 dpi)
Color Bit Depth: 48-bits per pixel internal / external1

Grayscale Bit Depth: 16-bits per pixel internal / external1

Optical Density: 4.0 Dmax

High Pass Optics:

Anti-reflective optical coatings
High-reflection mirror
Maximum Scan Area: 8.5" x 11.7"

Light Source: ReadyScan LED technology

Scanning Speed:

High-speed mode: 4800 dpi
Full color: 10.8 msec / line (approx.)
Monochrome: 10.8 msec / line(approx.)

[Ken Lee]

Most of the online reviews estimate the true optical resolution as somewhere between 2000 and 2400 dpi.

See this resolution test of an Epson V750 by Nathan Potter.

The test shows that once we get past 1500 dpi the contrast drops below 50% - a sort of practical cutoff point for usable resolution.

I routinely scan at 2400 dpi (because the menu gives either 1200 or 2400 and I'm reluctant to type in an intermediate number) knowing that there's no usable resloution beyond that point. I tested the higher settings and found no discernible advantage.

One way to get slightly better data is to scan in 48-bit color, discard the Blue and Red channels and use only the Green channel. See http://www.kennethleegallery.com/htm...nningGreen.php.

My guess is that the scanning lens and/or sensor is optimized for the frequency of green light.

[Peter De Smidt]

$50 pocket camera has ~10M photosites now, I'm sure in a $1k scanner they can afford 1/20th that many (6-line full width).

Yep, but that's an area cmos sensor, a type of sensor that's had tremendous development over the last decade. We're talking about ccd line sensors, and area with much less development. Epson scanners have been made for over two decades. While they have made their scanners faster, changed the light sources, added different holders, and a few other tweaks, people who've scanned resolution targets haven't seen significant improvements in resolution over that time, excepting, possibly, the new scanners with the second lens. That would seem to indicate no huge advance in the line sensors that they use, at least from a resolution standpoint.

[Jim Andrada]

And the pixel count is just part of it - the performance of the lens(es) and the whole optical path, vibration, alignment, etc etc etc all enter into it. I don't know the size of the sensor, but the overall area is a big determinant of cost, as is, of course, the technology. CMOS is more common than CCD because among other things things there are more sites on a CCD array - the actual photo site as well as a holding site that holds the charge until the entire sensor is read out globally, as opposed to CMOS where each site is read out "on the fly" which is why you get the infamous "Jello-cam/rolling shutter" effect for video. CCD is more expensive because it takes a much larger footprint on the wafer for the same"resolution" compared to CMOS and as Peter pointed out the Epson uses a "line" type sensor which is much less common than an "area" sensor which also raises the cost significantly, to say nothing of the vastly lower volume of Epson scanners vs point and shoot cameras. I'd be surprised if the sensor is not a fairly large component of the total cost (and price)

By the way, re Peter's comment about "zoom", the Epson doesn't "zoom" since it only has two scanning resolutions - one for the 5.9 inch central strip, and a lower one for the full width provided by a wider angle lens, so the experiment of scanning a resolution target at 35mm size vs larger size wouldn't show anything - the equivalent test would be to scan the central stripe vs the full width, and we already know that the full width scan is at lower resolution as a consequence of the design.

[Peter De Smidt]

Good stuff, Jim. Thanks.

[The Joker]

given that the rayleigh limit says

at F5.6 327 cycles/m
at F8 229 cycles/m
at F11 166 cycles/m
at F16 114 cycles/m
at F22 83 cycles/m

then given that a LF neg may frequently be created using f22 or smaller and then also considering that normal film is only able to resolve upto 200 cycles/m but more typically 100 cycles/mm and given that only happens at high contrast ratio so in normal everyday use the max reslution you ar ever likely to get on film is say 80 cycles/m but more typically 40 cycles/m, then it seems that you would only ever require 2000 spi from a scanner since you are never likely to have more than that in the neg to start with. And infact the vast majority of your images will only have 40 cycles/m so a scanner that can do 1000 spi should be adequate most of the time.

So why do people go on and on and on about resolution targets which bear no resemblance to real world photography and why are they worried about whether their scanner scans at 4800 spi or 6400 spi when their negs aren't good enough(capable) to warrant that high level of scanner resolving power anyway?