The three things that matter in photography of edges

[Larrin]

I understand that it has been proposed that the SET tester is dulling the edge by rolling, I'm just wondering what the evidence is that it is doing so. Running a steel roller over an edge can certainly lead to wear.

[EOU]

Maybe we can help there Larrin and it never hurts to revisit these things. First the indicators that the edge has been rolled are;

1. If the roll is severe enough (250 points or so) often a fingernail or the corner of a business card can be snagged on the rolled side of the edge.
2. 250 point rolled sections of edges are visible to the naked eye with reflected light (edge on)

3. Before rolling the edge was sharper i.e. 150 and after rolling duller i.e. 400 (equals 250 point roll)

The indicator to us that the edge has been rolled as opposed to abraded or smashed is that most 25-250 point rolls can be returned to at or very near their original sharpness levels by a few simple stropping strokes (with some pressure) on a plain piece of leather. In addition, post stropping, now the visible roll section will have disappeared and no longer can you hook a fingernail. Rolls of 300 points are dicey. They can sometimes be brought all the way back and sometimes not. Above 300 points, mediation of  the roll can occur with stropping but not returned to original sharpness level usually. The thinking here being that the roll originates so deep in the metal that a solid leather surface can't apply enough force to straighten it. Perhaps a steel could, we don't know because we, apparently, don't know how to use a steel properly.

Of course, all this is hardly new science since any butcher or barber could have told us most of this a hundred years ago.

[Larrin]

Thank you for providing that information.

[EOU]

Our pleasure and thank you for the question Larrin.

[grepper]

Another way to verify roll is visual inspection with a microscope.  You can actually see the roll.

   

[Larrin]

Another way to verify roll is visual inspection with a microscope.  You can actually see the roll.

That edge is post-SET tester?

[grepper]

Doh!  Caught me!  No sneaking anything past you eh?   No, that particular roll was not created by a SET.  It’s just a good example your basic rolled edge.  Even rolls too small to hook a fingernail on will show up under the scope, and a roll large enough to actually hook something on look like a log on the edge. 

The point is that looking at a magnified view of an edge is one way to verify the existence a roll.
 
Mr. EOU, will you please get me out of trouble here and post a microscope image of a SET rolled edge?

[EOU]

Love to help if we could Grepper but I don't think that we have any. We may have thought that we had some in the past but we don't have any confidence now that the micro photos we took portrayed the roll accurately. That's why we're working with Cyrano and his Dinolite now. He'll have the knives early next week so, with luck, we'll be able to show you something later next week.

[Cyrano]

Mr. Cyrano, you said, "I've found Dino-Lite's embedded EDOF algorithm is good, and usually yields results comparable to stacking in Photoshop." 

I have a couple of questions:

Does the Dino-Lite produce a stacked image automatically or does it simply automatically produce a bunch of focus bracketed images that then require stacking in post processing with it's software the same as you would do in PS?

How many images is the focus bracketing?

The Dino-Lite EDOF software produces a finished stacked image with one click. Upon exporting images, one can choose whether to export only the final stacked image, or to export all the individual exposures which form the stack. 

Automatic focus bracketing is adjustable from a minimum of 5 exposures to a maximum 13 exposures. Automatic mode provides a visual preview of the results by scanning the plane of focus through the range which will be compassed in the EDOF. 

Manual focus bracketing will accommodate up to 20 images.

[grepper]

Thanks for the info. Pretty cool little scope.

Gotta hand it to Dino-Lite for addressing the major problems with USB microscope photography; shallow DoF, touchy focusing and exposure. I've been doing some searching around and have yet to find any other scopes with those features.