The iSiS has a lot of great qualities. It is an exceptionally stable instrument yielding significantly more repeatable results than my I1Pro 2. But there are a few areas where it is less than ideal. I've attached an photo of a chart showing the inside of an opened iSiS. For reference, there are two rows of rollers. The first set of rollers are spaced 42 mm apart, the second (driver) set are spaced 21 mm apart. The first row of rollers rotate freely but only if there enough friction with the paper surface. The second set grabs and feeds the paper.
The first roller sits about 0.3 mm above the surface. If the paper is thinner it may still contact the roller if it has the slightest curl. This is a pretty stiff roller and the paper has to make good contact for it to roll rather than just slide across the rollers which I've seen smear black matte ink. My glossies at .25mm touch this roller at times but never enough to rotate it. Same with 210 gsm Canson Rag Photo. However, the 310 gsm Canson Rag Photo (.45 mm) has to be pushed past the rollers and they do grab and rotate.
The second set of rollers is on a much larger diameter spindle and is much closer to the surface so it can engage thin paper like office paper for a LaserJet (.08 mm). A stepper motor drives these rollers to align the paper with the spectro head. They tend to squish the surface of some luster type papers and can mark glossy paper as well even when well dried. It depends a bit on the paper.
The worst case I've seen was before/after variations as high as 3 dE76 on a few patches with Finestra Baryta fine art, a luster paper, whichc showed strong roller impressions. The effect is to increase saturation. The higher the color saturation, the greater the shift. Fortunately, the effect on dE00 is much less because it also decreases in sensitivity with saturation.
Here's the way I deal with it:
1. Some papers/inks have minimal effect. For those I just use standard (6 mm) patch sizes and ignore the problem.
2. Some papers show higher sensitivity. The worst ones are the Canson Rag Photos with Matte black. Oddly though, when using Photo black the Cansons show virtually no track marks and have remarkably repeatable scans.
For all papers, I place a spacer (magazine the right thickness) so that the paper feeds directly into the iSiS otherwise even thin papers can rub against the first roller set just from the paper bend entering the instrument.
For sensitive papers I set the patch width exactly at 10.5 mm. This allows aligning the paper so that both front and back rollers transit the patch edges and stay away from the center. The rollers will mark the paper but as long as the marks are less than +-2 mm from the patch edge the patch colors are suppressed.
As for aligning the paper, there are two approaches. I usually print targets with Photoshop so I just note the horizontal offset that aligns the patch edges when the paper is inserted against the left guide. For targets printed from the I1Profiler, I mark an offset from that edge on the iSiS feed lip to achieve edge alignment.
A few odds and ends:
In order to view the alignment you need to open the cover. From the middle, pull the housing forward just under the I1 logo then lift up. It flexes enough to unsnap then it rotates backwards. You can run it with the cover up so it's easy to see the feed alignment.
Also, no worries about ambient light in the iSiS. It has zero affect. The spot illuminated is quite intense and orders of magnitude brighter than any light leaking in from the room or internal LEDs. Also, unlike the incandescent lamp in the I1 Pro, the lifetime of the LED is very long and not shortened by turning on and off.
