High Magnification Loupe for Ground Glass?

[neil poulsen]

I'd appreciate recommendations for a high magnification loupe for a finely ground, ground glass that I've been using. (Actually, it's not glass, it's plastic.) I've been using a Nikon 7x loupe on this g.g., and I know I can do better. Accurate focus is essential for this application. Maybe something like 15x?

Since I need it for a ground glass, it needs to be adjustable, so that it can focus on a surface that's beneath the surface on which it's resting.

It would also be nice if it has opaque sides; but, that's not essential. (Since it's under a darkcloth.)

[Jac@stafford.net]

Neil, degree of magnification is something you have to trial yourself. Really, perception varies very much. For example, I cannot use anything stronger than 4X whether on an old coarse ground glass or over a Satin Snow glass. You probably recognize the profound differences.

For super critical high magnification please consider aerial focusing.

[Drew Wiley]

I find that going higher than 7X just makes the grind pattern more annoyingly apparent at the expense of the image itself. A waste of time unless your have some means of achieving true film plane flatness, which an ordinary holder won't give you. Although the Peak/Nikon/Horseman 7X loupe is my standard choice, I sometimes carry an Emo 10X loupe as an emergency spare due to its very small size in the kit; but it's optically excellent if hard to find. Some types of glass be difficult to drill, so you have to be careful; but some people drill a pattern consisting of several small holes into an optional ground glass, plus one in the center, for sake of aerial image focus, like Jac describes. I'd do that if it were a critical macro or scientific application. But you'd need to match it with a vac film holder if you want true precision. You can also go to Edmund's industrial division catalog to see their excellent options of magnifiers. Their website is a scaled-down selection for amateurs with nowhere near as many items.

[Bernice Loui]

How does one know or can absolutely verify film in film holder distance is within a few thousands of an inch identical to the ground glass center to all edges involved?

Then there is the film flatness problem.

IMO, higher magnification is of much lower value than excellent resolution, contrast, color rendition, low distortion and ... than simple higher magnification number.


Bernice

[Jac@stafford.net]

Some types of glass be difficult to drill, so you have to be careful.

I buy economy glass burrs and use them once (maybe 5 holes) then throw them away.

[Jac@stafford.net]

How does one know or can absolutely verify film in film holder distance is within a few thousands of an inch identical to the ground glass center to all edges involved?

We cannot.

[LabRat]

To elaborate on Bernice, just using sharpness is one of the more difficult ways to focus...

Let's say you were trying to focus a scene and we're looking for a sharp object to focus on, as you get closer to focus point, fine items get smaller and can vanish (like power wires, or the stems on leaves etc) because these objects become very small on the gg... (And we tend to focus on fine details...

But when a lens is in focus, other things happen too, like maximum image contrast, there is greater color saturation, deepest hues, greater contrast between edges of objects, blacks become blacker, objects stand out better etc... So there are other cues to notice as well... These don't require too much magnification to spot...

There is no "one size fits all" approach from the above list, but there will be one or all that can aid you, but just learn to scan your gg to confirm that there is something else there to help you...

Steve K

[neil poulsen]

. . . Although the Peak/Nikon/Horseman 7X loupe is my standard choice, I sometimes carry an Emo 10X loupe as an emergency spare due to its very small size in the kit; but it's optically excellent if hard to find. . .

Thanks for the input.

10x is good; it's almost 50% greater magnification than what I have.

But if someone knows of a higher magnification that would work for a g.g. application, I'd appreciate learning about it.

[Jac@stafford.net]

But if someone knows of a higher magnification that would work for a g.g. application, I'd appreciate learning about it.

10x is far more than is practical. With greater your challenge is to narrow depth to the focus plain. Ain't gonna happen on ground glass. Read back to aerial focusing.

[Drew Wiley]

Any serious machinist or optical engineer could easily verify plane flatness far more accurately than a mere few thousandths. In the optical lab up the road from me, they routinely do so in measurement units FAR LESS than MILLIONTH's. But they have reasons and gigantic budgets for doing so, while anything even remotely near that kind of precision would be both ridiculous overkill and vastly too expensive for any of our own purposes. I once sold a lot of precision tools to a lot of ordinary machinists. You can establish a reference plane quite easily and compare. Even a decent engine shop knows those basics. I have the ability to do it in my own modest shop. The bigger problem is film itself. Triacetate base potentially sags more than polyester base. Some people substitute thin ortho-litho films. Some people put actual print paper into holders instead of film. There are slight variations between even standard films. Sometimes older film holders are warped, and even wooden camera backs. All of these issues can be realistically addressed on a case by case basis, and cured on a modest budget if someone is innovative.