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FORVM`s Classical Numismatics Discussion Board  |  Numismatic and History Discussions  |  Coin Photography, Conservation and Storage  |  Topic: More on best lighting - Axial Lighting Test #1 0 Members and 1 Guest are viewing this topic. « previous next »
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Author Topic: More on best lighting - Axial Lighting Test #1  (Read 226 times)
PtolemAE
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« on: April 29, 2019, 03:26:43 pm »

Wanted to try 'axial lighting' method so turned a small cardboard box into a basic lighting contraption that has diffuse light enter from one side, get reflected straight down on to the coin by a piece of glass tipped at 45 degrees which rests above the coin, then photo with camera on a copy stand, from above 'through the glass'.  Sort of uses the natural reflective nature of glass to direct light evenly straight down from 90 degrees orientation above the coin.  And, lo and behold, it works.  Coin is simply resting on a sheet of white paper and the axial lighting orientation leads to minimal shadow and a pretty even distribution over the coin's surface.  

Another reason for trying the axial lighting is to compare images from a couple camera/lens combinations to see if 'more megapixels' will make any difference, given that the lenses are macro lenses at or near their close-focus limit so getting close to 1:1 magnification. 

The coin was just handy, not distracting, and small enough (about 17mm) to be a modestly demanding macro photography subject.

So here's the first image from this two-part test suite:

First Pic:

Sony A6000 camera (APSC, 24 megapixels)
Classic Canon 100mm 'FD' manual-focus macro lens with adapter for the Sony camera, manual focus
axially lit with $10 home-made kit
shot in 'fine JPEG mode' at 6000 x 4000 pixels
1/3 second, ~f16 (seemed to look the best), ISO 100, auto-white-balance

The coin fills 2200x2200 pixels of the 6000x4000 pixel field, and is reduced here to 800x800.  No sharpening or smoothing, just minor white-balance, saturation and gamma adjusted.  Note that the macro lens actual magnification for this setup isn't quite as good as it would be on its native SLR type camera.  Between being 'adapted' and the camera being APSC (with so-called 'crop factor' that, in practise, boosts focal length here from 100mm to 150mm) the overall magnification achieved is only about 1/2, which nevertheless gives a lot of detail to work with.  The APSC sensor is about 15mm high and this coin would fill it completely at 1:1 true macro magnification.  In this setup it fills a little over half of the sensor's height, hence the 2200 pixel coin image size.  One nice thing about old 35mm film camera lenses like this is they can be found in excellent condition for about 1/10 the cost of something comparable made for today's digital cameras.

Been using this camera and macro lens setup for a few years for coin pix and pretty happy with the detail from 24 megapixels with decent lens.  2200 pixels wide image on a 17mm coin almost 130 pixels per millimeter (resolution about 65 line pairs per mm).  When shown on a web page they may be typically 320 to 640 wide so the appearance seems it might be about as good as it could be.

Your thoughts, please.  If there are any comments and anyone wishes to see a comparison from a different cam/lens setup I'll post it shortly.

Thanks,

PtolemAE
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FORVM`s Classical Numismatics Discussion Board  |  Numismatic and History Discussions  |  Coin Photography, Conservation and Storage  |  Topic: More on best lighting - Axial Lighting Test #1 « previous next »
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