Geometrical distortions on belt drive scanners

[8x10 user]

I don't know. You have to be careful about generalizations with this type of tech. One scanner could be off in some way or another while another might be perfect. Also I don't know about how the scans were made, if all the scans were fluid mounted, if they were scanned at another resolution then interpolated or what, ect. There are just too many factors to for me to take this evidence of geometrical distortion in all Eversmart scanners. Maybe when my scanner comes back from service I will run some tests of my own.

The supreme's are also used for scientific research.

[SURF]

I don't know. You have to be careful about generalizations with this type of tech. One scanner could be off in some way or another while another might be perfect.

I found it on february. Now it's august. At first I didn't believe my eyes cause nobody never in my life thought that it was possible. Finally I am sure in what I am saying. While scan the computer think that scanner mechanics is perfect and if it is not we get distortions. I believe that those scanners were not made by the fools and while new they scanned more or less OK. Also those scanners were made for printing industry where nobody ever cared about such things. I know what I am talking about. While the size of the scan is OK then no problems. And the sizes are always OK, but what happens inside those sizes... You can see now.

Another nice picture: Screen Cezanne_vs_Tango. You see - no good for screen too.

[SergeyT]

Exactly my point. There are so many unanswered questions and variables...
I wish that "distortion" (even if it present indeed) was my biggest concern with producing quality scans

SergeyT.

[SergeyT]

Another nice picture: Screen Cezanne_vs_Tango. You see - no good for screen too.

Have you found two scanners which produce identical scans on pixel level?

Thanks,
SergeyT.

[SURF]

Have you found two scanners which produce identical scans on pixel level?

Yes. Tango, Scitex Smart 3XX, Topaz, Nexscan. They are perfect in that terms. May be Nikons with glass holders, but I had no chance to test that setup. Without glass holders they distort and tend to be unsharp. Anyway Nikon distortions feel better because it is close to lens distortion. They own lead screw. Not sure do Nikons have problems in size proportions or not. I have not tested them.

[SURF]

And it happens not only on transparencies. Look at the reflectives scan. The picture is from the summer of 1945 btw. Nice print, not from the family album though. I see the face changes. I do not like the faces to change. That's why I scan my family pictures only on the lead screw driven scanner. I feel better when I am sure that proportions of dear faces remain intact.

Smart vs Eversmart (eversmart that is in average state, before I made it better)

[Valdecus]

The issue became apparent to me for the first time some years ago when I tried to scan a single large format film with different exposures to be used as input for HDR processing. None of the scanners I tested (from the Epson V750 flatbed to Imacon's 848, Hasselblad's X5, and various drum scanners like Howteks) were able to scan *the same* image twice with absolute pixel accuracy. Even with drum scans, certain pixels along the long axis of a file 20,000 pixels wide were off by as much as 10 pixels when compared to the first scan.

For HDR processing, this definitely wasn't accurate enough as the scanned images need to be aligned perfectly. Distortion of the scanned results made this impossible, and even Photoshop wasn't able to properly align the results with its advanced alignment algorithms.

Cheers,
Andreas

[SURF]

Even with drum scans, certain pixels along the long axis of a file 20,000 pixels wide were off by as much as 10 pixels when compared to the first scan.

It's a good remark, Andreas. And we have to mention repeatability now. It's a different animal which also lives in the precision land. The scanner can have a perfect repeatability of the distortions. That's why Eversmarts stitch periodically distorted images on the fly and can pass all the calibrations.

Tango vs Imacon949:

[SURF]

Well... I can add that Screen 1045AI and 1030 also distort. These guys managed to make drum scanners without lead screw. OMG.

[The Deer Gunter]

Well, alomst 5 years later ... can I still throw in a couple of questions? I will begin to try and master an iQsmart3 and its oXYgen scan software somewhere in the next couple of weeks, and stumbled upon this page while Googling. It's my first post on LFP by the way :-)
I already have some experience with the iQsmart, but it is only now I will be able to study it properly. An example:

https://www.flickr.com/photos/thedeergunter/6250812458/

1) Does the geometrical distortion affect image quality in any other way? I'm particularly concerned about loss of sharpness.
2) Is it inevitably inherent to each and every belt driven scanner, even when you're talking about a brand new out of the box device?
3) Does recalibration have an influence on the degree of distortion?

Thanks for your time! Cheers.