DPL users/owners of Howtek/Aztek scanners

[Rich14]

Perhaps the drawing can show better what I have on mind.

That's what I thought you had in mind.

It's not surprising that Howtek used a lens designed to focus the image at 160mm. They were essentially duplicating the dimensions of a standard microscope optical path and had a universe of available optics to chose from. I wonder how they deviated from the 160 mm measurement, though, in the optics box. Maybe they figured there wouldn't be any abberations to worry about when futsing around (an industry term) with the image plane position. Or maybe they just flat out goofed. After all, the Hubble telescope was sent into space after the wrong curvature had been ground into the primary mirror.

The penta prism "fix" seems like a good idea. However, it will alter the available range of focusing adjustment. The lens will focus just slightly further away from the drum than it currently does. Shouldn't matter as there should be enough lens travel to accomodate the fix. What's its Focal Length? 12.5 mm?

How do you know that the LCA you're seeing applies to every 4000/7500 with the short optical path? Maybe some have lenses that hold up even when short focussed?

Rich

[onnect17]

That's what I thought you had in mind.

It's not surprising that Howtek used a lens designed to focus the image at 160mm. They were essentially duplicating the dimensions of a standard microscope optical path and had a universe of available optics to chose from. I wonder how they deviated from the 160 mm measurement, though, in the optics box. Maybe they figured there wouldn't be any abberations to worry about when futsing around (an industry term) with the image plane position. Or maybe they just flat out goofed. After all, the Hubble telescope was sent into space after the wrong curvature had been ground into the primary mirror.

The penta prism "fix" seems like a good idea. However, it will alter the available range of focusing adjustment. The lens will focus just slightly further away from the drum than it currently does. Shouldn't matter as there should be enough lens travel to accomodate the fix. What's its Focal Length? 12.5 mm?

How do you know that the LCA you're seeing applies to every 4000/7500 with the short optical path? Maybe some have lenses that hold up even when short focussed?

Rich

The variation in the focus should be minimal, less than 1mm closer to the drum, easily handled by the mechanism. Yes the focal lens is close to 12 mm The focal length of each doublet is near 25mm so half of that is 12.5mm. Each contributing 5x magnification for a total of 10x.
If the error was 1 or 2 mm perhaps could pass unnoticed. 26mm is a different story. The parts in the path between the drum surface and the aperture wheel are accurately placed so the error among the scanners should be in the order of few tenths of mm, at most. Unfortunately I am quite confident the performance is similar across the models mentioned.

I am sure I am not the first one being aware of the issue in the past 20 years. It will be interesting to find out who new what and when.

[ah693973]

Rich and Armando,

You guys are obviously more studied on this than I am, but there is something about the lens conversation I don't understand.

Why does LCA matter? Since the scanner is only looking at one pixel at a time, the PMTs only care about the average color levels, not their positions in the image from the lens.

Similarly, the focus on the film is what seems important to me. There is no image required for the PMTs since they are only concerned about the average color at that pixel.

Could the 134mm have been an attempt to lessen grain by "averaging" a little of the surrounding area?

Andy

[Rich14]

Rich and Armando,

You guys are obviously more studied on this than I am, but there is something about the lens conversation I don't understand.

Why does LCA matter? Since the scanner is only looking at one pixel at a time, the PMTs only care about the average color levels, not their positions in the image from the lens.

Similarly, the focus on the film is what seems important to me. There is no image required for the PMTs since they are only concerned about the average color at that pixel.

Could the 134mm have been an attempt to lessen grain by "averaging" a little of the surrounding area?

Andy

Andy if LCA is there, it's going to affect any sensor filtered to record that color. Yes, the sensor is an integrator, caring only about the amount of light it receives from the spot on the film it's recording at any particular instant. But that spot will not have the correct representation of the light that left it on the way to the sensor. LCA robs color from what should be the central focused spot and smears it over a wider area. So the sensor is not recording the true image. That degrades the image no matter how it's recorded.

I've yet to confirm the problem on any of my machines. But I intend to try. Got a spare USAF target lying around?

Rich

[onnect17]

Got the prism but I am getting inconsistent results. More testing to do.
Rich, check post #60 in this thread for info about a target.

[Rich14]

Rich, check post #60 in this thread for info about a target.


Thanks. Ordered.

[onnect17]

Got the prism but I am getting inconsistent results. More testing to do.

Some preliminary observations of the tests results:
(Each image evaluated was picked as "the best of" from a sample of 4 to consider variations in the quality introduced by the autofocus system.)

== In the 4500 (Celsis 240)
- The 4000, 4500 and 7500 lens perform better and the premier worst in the extended path (with prism). Not by much, but it can be noticed.
- The lens in the 4500 are by far the worst in the group, showing some chromatic aberration. The 4000, 7500 and premier lens are showing a cleaner image.

== In the Premier (only tested with the short path, for now)
- The 4500 lens shows again as the worst performer.
- Not major differences between the 4000, 7500 and Premier lens.

[fishbulb]

Not to change the topic too much but I learned something today. Don't use your computer too much while scanning or you'll get weird banding in your scans (running around the drum, not lengthwise down the drum).

I was doing a lot of Photoshop work, lightroom work, and had about 20 tabs open in Firefox. Kept running out of ram in Photoshop and crashing ligtroom to the desktop. Stupid 32bit Windows 7 only can use 3gb of ram even if you have more. Scans during the crashes had weird banding and artifacts. Rescanning and leaving the computer alone = clean scans. Can't wait til Aztek releases a 64bit-compatible version of DPL. But that would also require an SCSI card upgrade, since the one I have has no drivers available for windows 7 64bit. Oy vey.

[onnect17]

Never got any trouble of that kind. Still using XP. No Firefox here. Too many updates for just an app is not a good sign. Probably in a couple of years the version number will be 75.

Make sure you have extra space in disk. A small SSD dedicated as the scratch disk will help also. If possible, try to use an Intel CPU. Good quality RAM is also important.

[ah693973]

Armando,

I wouldn't trust the autofocus. With DPL the scanner always seems to focus on a specific drum area, this is not necessarily where you have mounted film. Not sure if this is a machine issue or a flaw in the program but it is worth a double check (maybe by comparing to a manual focus) no matter which program you use. See my thread about this on the High End Scan group.

Andy