Thread: Progression DMT 1200->8000-> 1um film

The two pictures were taken with a similar setup, only the light direction was different. It is the same section of the edge, same magnification, same "microscope" (DSLR with a reversed lens). There is a little more motion blur in #1 but even if it was razor sharp, it would not look much different.

Ok, let's establish that using wave motion to judge edge condition only works given that angle, light source, and measuring device remain constant. And having serious blur effect in one pic and not another makes it very hard to compare anything.

Once you jump those hurdles, it's an absolute science (given the use of a computer algorithm) with a generally decent capability for estimation under careful examination.

Originally Posted by IanS

Once you jump those hurdles, it's an absolute science (given the use of a computer algorithm) with a generally decent capability for estimation under careful examination.

What is a science? I don't understand what you are referring to here. Are you talking scratch pattern or level of polish or something else or more than one?

It has been discussed in lots of other threads (and I have seen in my own experience) that the level of polish on a razor does not necessarily correlate to the sharpness of an edge or how well that edge will shave. I am asking you to clarify with that in mind.

We all know that light and angle can be manipulated to hide, show, lessen the effect of, etc. scratches through a microscope. The same can be done when showing razor blades for sale too. Because it can be manipulated doesn't mean we shouldn't use or comment on these images. I, for one, love the detail shown by microscope images. They don't tell the whole story, but what they do show is quite interesting.

What I'm saying is that given a constant angle of source light, and a constant angle of light collection. If you are able to get a reading of light intensity at the collection point, as well as reading the width of the surface scratches there are exact calculations available that will tell you the depth of the scratch at any given angle (of the scratch) within a certain threshold (outside the threshold, accuracy becomes an issue, so the more angles you can measure at the greater accuracy achievable). But even without these calculations, if you understand the behavior of light, you can estimate acceptably well.

OP's pics certainly appear to be very similarly lit and angled similarly, so this is a viable comparison. Obviously taking two random, unrelated images makes a direct comparison much less useful. However, that is not the case in this thread. So I don't understand why those cases are becoming such an issue for people looking at this case.

Holli: Anything you want to measure becomes an exact science, you simply have to weight the effects of different elements. You could go so far as rating edge condition if you wanted to use some sort of formula where length of a cut is weighted as X, depth as Y and width as Z. It wouldn't be an extremely simple formula (involving one or more summations), and there would have to be a standard accepted weighting, but it's definitely possible. My comparison of op's would relate to the integral of the space (the missing steel) between the center of the face of the edge and the top extreme (pictured side) of the face of the edge, extending back to the bevel (or in this case the extreme of the image).

Originally Posted by IanS

What I'm saying is that given a constant angle of source light, and a constant angle of light collection. If you are able to get a reading of light intensity at the collection point, as well as reading the width of the surface scratches there are exact calculations available that will tell you the depth of the scratch at any given angle (of the scratch) within a certain threshold (outside the threshold, accuracy becomes an issue, so the more angles you can measure at the greater accuracy achievable). But even without these calculations, if you understand the behavior of light, you can estimate acceptably well.

OP's pics certainly appear to be very similarly lit and angled similarly, so this is a viable comparison. Obviously taking two random, unrelated images makes a direct comparison much less useful. However, that is not the case in this thread. So I don't understand why those cases are becoming such an issue for people looking at this case.

Wouldn't that also depend on how the hone cuts, not just it's grit. for example, it looks like the DMT's leave very uniform scratches, but not all hones do this. Naturals are one example, especially those that slurry. My Japanese natural will not put a mirror finish on a razor, but I can assure you it is extremely sharp. I'm not saying that using a microscope is useless, just that you have to know what you are looking at (what you and others said about lighting and angle and such) and also what you are looking for (based on what hone you've just used and what hone you used before that).

That's why the calculation will almost certainly involve summations. You are essentially figuring the missing metal that would be present in a perfect edge of that edges dimensions. It's a much easier calculation if you are able to assume that the scratches will be uniform, but it's still definitely possible in other cases. And they will be directly comparable (excepting the argument that uniform or non uniform imperfections may be more comfortable for X user or Y user, we can only establish divergence from perfection, not final user satisfaction).

Originally Posted by IanS

What I'm saying is that given a constant angle of source light, and a constant angle of light collection. If you are able to get a reading of light intensity at the collection point, as well as reading the width of the surface scratches there are exact calculations available that will tell you the depth of the scratch at any given angle (of the scratch) within a certain threshold (outside the threshold, accuracy becomes an issue, so the more angles you can measure at the greater accuracy achievable). But even without these calculations, if you understand the behavior of light, you can estimate acceptably well.

OP's pics certainly appear to be very similarly lit and angled similarly, so this is a viable comparison. Obviously taking two random, unrelated images makes a direct comparison much less useful. However, that is not the case in this thread. So I don't understand why those cases are becoming such an issue for people looking at this case.

Holli: Anything you want to measure becomes an exact science, you simply have to weight the effects of different elements. You could go so far as rating edge condition if you wanted to use some sort of formula where length of a cut is weighted as X, depth as Y and width as Z. It wouldn't be an extremely simple formula (involving one or more summations), and there would have to be a standard accepted weighting, but it's definitely possible. My comparison of op's would relate to the integral of the space (the missing steel) between the center of the face of the edge and the top extreme (pictured side) of the face of the edge, extending back to the bevel (or in this case the extreme of the image).

I don't think you can use a regular microscope to make those measurements. You need a white light interferometer (I have one of those back in the lab too!)

Well it sounds to me like you just volunteered to find the "scientifically proven" best finishing hone for us. We're all counting on you!