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Geological Thin Sections > Granite Greisen with tourmaline, Cornwall, UK by Ian Butler

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About This Gigapan

Taken by
Ian Butler Ian Butler
Explore score
0.35 Gigapixels
Date added
Jul 18, 2012
Date taken

Greisenised granite from Cornwall. Not the prettiest rock, but one for the teaching collection. Some nice feldspar alteration textures here. Greisenisation is alteration assocaited with hydrothermal fluid flow and, in Cornwall, Sn and W mineralisations around granites.

228 images using a Zeiss Luminar lens on a Meiji microscope stitched using PTGUI.

Gigapan Comments (2)

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  1. Ian Butler

    Ian Butler (February 10, 2013, 09:04AM )

    The modification is very simple. A linear polariser was added under the binocular head (which is the most demanding because for this particular microscope the diameter had to be pretty close to 19mm - found on ebay!) and another larger linear polariser was placed over the light source. Unlike normal petrographic work, it was the substage polariser that I removed or rotated. A 23mm T2 threaded eyepiece tube was fitted to a Nikon T2 threaded bayonet adpater to permit the camera to be used in place of the eypiece. This changes the focal plane and make focusing more difficult through the camera viewfinder, but works OK. The Luminar was used at maximum aperture and has an RMS thread, so replacing the objective was simple. Smaller apertures on the luminar caused quite a lot of image degradation, I presume by diffraction. So all in all a pretty easy modification with all the bits available on ebay, and no cutting or alteration needed - in fact the base microscope need not be anything special because all the important bits are changed. I'm glad to say I already had a luminar objective because they're a bit pricey on ebay these days. The advantage is a very flat focal plane, which isn't possible using objective projection with low-end optics - or at least I've not managed to get it to work!

  2. PhotoS

    PhotoS (September 17, 2012, 11:10AM )

    Ian- In the descriptions of your work you mention a modified Meiji biological microscope and both zeiss and direct objective projection under cross polarised light. Would you consider describing the microscope modifications you found to be suitable? Could you share a diagram? I would like to try to do this, as well. Thanks, SM

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