An Article In Meteorite Times Magazine
by Jim Tobin

 

Irghizites and a Little Photography

Its been a while since I wrote on my favorite tiny impact glasses; Irghizites. Fine crater glass is found at several craters on Earth. But many of the most elaborately shaped specimens come from the Zhamanshin crater and are called Irghizites. Black, usually shiny, they testify to the fact that the air must have been a mist of fine melted glass particles. Many Irghizites have tiny round bumps on the surface. Even as the ribbons and drops of glass were stretching and flowing they were being covered by microscopic drops that adhered to the larger glass forms. Similar glass forms are found at Wabar and to a lesser degree at Henbury and other craters. But, those from Zhamanshin are numerous and beautifully shaped. They occur in a range of sizes from several grams to a small fraction of a gram.

I got a new camera just yesterday and have used it to take macro shots of some nice Irghizites. I'll take this opportunity to do a small amount of instruction on close up photography which some readers might find interesting. I am still getting used to the camera, it is really feature rich. I will work in to some of the really advanced options soon. But, enjoy these pictures of very small Irghizites taken up close.

I remember using film cameras with special macro lenses, bellows attachments and reversing rings in the old days to get close up shots. None of that today. I do wish I had higher f-numbers for greater depth of field but the f8 that I have has worked pretty well for these. I was working at a distance of about four inches. Which sort of the zoom end of the macro range of the lens.  I can get as close as 1 inch (.4 cm) but I have to make some lighting arrangements for that close. And at one inch distance from subject the rounded and bumpy Irghizites do not focus up all over with f8. On a film camera I would have been using f16 or f22 even f 32 for such shots depending on available light, film speed and whether the subject was still or might have movement.  If a flower was the subject and it was out side in full light on a still air day I might use f32 if the film was fast enough. That would give tremendous depth of field. Most parts of the flower would all be in sharp focus. On a poorly lit flower on a day with a breeze I might not be able to get away with a longer exposure time at f32. I might have to sacrifice a little depth of field for a shorter exposure time and use f 22 or f16. Each f-stop is basically equal to half or twice the exposure time depending on if you are opening the lens wider or stopping it down. In close up or macro photography a small lens opening is everything. But in most point an shoot digital cameras of today you have only the range built into the lens. Those digitals with a macro option will still not have a very high f-number.With DSLRs you have the same flexibility of lens options that were always available in film cameras. If you think about depth of field as using two very different cones of light to make the exposure you can understand what is happening. A wide open lens uses a very fan shaped cone of light with a great difference in distance for the light to travel from the subject to the flat sensor or film plane. In the tiny aperture opening of a high f-number you are using rays of light that enter nearly parallel and strike the flat film or sensor at the same angle. Much sharper focus over the whole depth of the subject. Meteorites like my Irghizites have bumps and valleys. If you are taking close up photos you want the foreground, middle and background to all be in the best possible focus. Using the highest f-number you can will get you a long ways to that goal.

Built in camera flashes are also pretty much useless when the lens is that close to the tiny subject. The lens blocks the flash pretty effectively. I will make up some color corrected lights to illuminate the one or two square inch area in the near future. For right now forgive the little bit of off color in the background of these shots. I did not have the time to play around with the numerous options of white balance and differing light sources in the camera's menus.

I have noted the fractional grams of each specimen under the photos. None of the specimens if longer than about 3/4 of an inch. Some are much smaller than that. And being pure black picking the detail is a real problem. May try different background colors to help manage some of the camera's automatic exposure control also. It is going to be fun learning this new camera.


.121 grams

 


.15665 grams

 


.493 grams

 


.255 grams

 


.355 grams


.384 grams

This picture was taken with the camera selecting the aperture automatically. At the f4 setting it picked you can see the poorer sharpness and softer overall focus. However it may have picked up more overall detail through better contrast.