Visoflex Warning

[lars_bergquist]

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I have two Viso III rigs. When using one of them with the prism finder, I was recently irritated by an unsharp spot, as it seemed on the screen. The screen, when checked, was found OK. The trouble was in the finder.

 

When I removed the finder, held it upside down and used it like a brilliant finder, with the eyepiece forward acting as the lens, I could clearly see three circular 'lesions' in the internal optics. They were 1.5–2mm across and shaped somewhat like a daisy, with a central little circle surrounded by small 'petals'. It is not clear where in the works these 'lesions' occur, nor what they are, maybe degrading cement. But there is nothing of the opalescent fogging this usually causes, the structures are sharply delineated. There is no discernible damage to the outer optical surfaces of the finder.

 

Thinking that I just had to change to the other Viso, I dug it out, made the same test – and found two of the structures there! I would advise all owners of Viso III prisms to check this. I would be amazed to find this to be a manufacturing error. But the phenomenon is disturbing, at least when it occurs at the center of the field, where we usually do the focusing. It would also be reassuring if there existed a way of curing the disease, if indeed it is one.

 

The old man from the Age of Extension Rings

[jaapv]

You can open them up to see what is going on. No adjstments to disturb, so it is easy.