A recent topic on a coin forum lead me to investigate the use of diffuse lighting when taking some coin images. My experience suggests that diffuse lighting is only useful for imaging coins of a particular type. It tends to produce low contrast images, hide design details and bagmarks, and suppress coin lustre. On the plus side it gives a very even light source which means a consistent light level across the entire surface of the coin. I've found in the past that the best coins to image using diffused lighting are proofs with a cameo contrast between the devices and the fields.
I've taken images of three very different coins so we can examine the effect of using diffused lighting compared with our normal imaging setup.
Coin 1 : Australian 1959 Penny
Australia 1959 Penny - diffuse lighting left, normal lighting right
As you'd expect the normal lighting setup produces a far superior image for this sort of red/brown bronze coin with minimal lustre. The lack of lustre means the diffuse light produces virtually no contrast and the design features are largely lost in the background of coin. The normal lighting setup gives a much more realistic image, with the coin lustre apparent and full design detail visible.
Coin 2 : Australian 2010 20c
Australia 2010 20c - diffuse lighting left, normal lighting right
Lustrous copper nickel coins with wear like the 20c above are difficult in the extreme to image correctly. The reflectivity combined with the bagging and wear typically makes the coin appear much worse when imaged that it actually is in hand. Seen above neither the diffuse nor normal lighting setup has done a good job of representing this coin. If anything I'd suggest that the diffuse lighting has produced a superior image but it is still a poor image. I've found that a variation of the tilted coin imaging technique I wrote about previously is the best way of imaging these lustrous copper nickel coins so I am not entirely surprised both lighting techniques used here performed poorly.
Coin 3 : Canadian 1971 $1
Canada 1971 $1 - diffuse lighting left, normal lighting right
Above you can see a lovely, toned Canadian silver dollar. These coins have typically been stored in the felt lined cases they were issued in and this has lead to all sorts of coloured toning through the mirrored fields and frosted devices. The toning in the fields can often be quite blotchy and the mirror of the fields can wreak havoc on image quality if any direct lighting is used when imaging them. The image taken with the diffuse lights shows excellent cameo contrast and highlights the mirrors of the fields well. The normal lighting setup still shows the frosted effect on the devices, however the contrast with the fields is not as strong and the fields look blotchy and unattractive. The diffused lighting image is a much closer representation of the actual coin in hand.
Conclusions
Diffused lighting can be a useful tool in the coin photographers arsenal. However it is only suited to some types of coins and time must be taken to understand when it should be used. If used incorrectly it can produce unattractive images that do not represent a coin correctly. It can also hide lustre, coin detail, coin damage, wear, and bag marks. As a coin buyer you should learn to recognise images taken with diffuse lighting and be aware the coin may not be exactly as it appears.
Posted by mnemtsas at May 11, 2011 9:07 PM
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