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The date on an old coin.

 
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mgoodm3



Joined: 08 Sep 2008
Posts: 273
Location: Southern OR

PostPosted: Wed Sep 10, 2008 2:11 pm    Post subject: The date on an old coin. Reply with quote

Nothing fancy, likely a D200, 28mm reversed lens, f8. about 2:1 mag. The crud in the 8 is the remains of a 7 - an overdate. 1808/7 half dollar.

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rjlittlefield
Site Admin


Joined: 01 Aug 2006
Posts: 20370
Location: Richland, Washington State, USA

PostPosted: Wed Sep 10, 2008 2:33 pm    Post subject: Reply with quote

Nicely done.

Lots of people have trouble illuminating shiny metal subjects, but it's obvious that have a great method.

I'd be interested to see & hear what it is, if perhaps you have time to show us, over in the Technical forum.

BTW, what's the story on that "overdate"? Did they actually stamp the coin twice, or rework the die? I'm clueless about coins.

--Rik
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Cyclops



Joined: 05 Aug 2006
Posts: 2968
Location: North East of England

PostPosted: Wed Sep 10, 2008 2:50 pm    Post subject: Reply with quote

Yea nice shot! Its great revesring lenses huh! First did that with my old Zenith-cheap and cheerful macro (Tho not so cheap with a modern AF camera!)

So they made an error making it and the coin was re-minted from 07 to 08?
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Canon 30D | Canon IXUS 265HS | Cosina 100mm f3.5 macro | EF 75-300 f4.5-5.6 USM III | EF 50 f1.8 II | Slik 88 tripod | Apex Practicioner monocular microscope
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mgoodm3



Joined: 08 Sep 2008
Posts: 273
Location: Southern OR

PostPosted: Wed Sep 10, 2008 3:11 pm    Post subject: Reply with quote

For most coin closeups they tend to benefit from lighting at a high angle to the coin (almost axial), but keeping it directional.

For higher mag images you generall can't get lighting at a really high angle (unless you are using true axial lighting through the lens, but I haven't tried it yet). In this case I bring the light in from one side - I typically use a daylight fluorescent source so I can get it in close. The fluorescent tube makse a fairly diffuse light already, but you may need to back it off to soften it up a little. The highlights can be pretty viscious from a low angle.

Regarding the coin - There are two typical ways for an overdate in a coin this old. Most of the elements were placed on the dies individually back then. In more modern times they have master dies that are used to make working dies - this adds all new ways to mess things up. There were lots of overdates in the early 1800's.

1) Die steel is expensive and you have a peefectly good 1807 die. Grind the 7 off and sink an 8 into it.

2) You screw up with the date stamps and put a 7 first.
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Graham Stabler



Joined: 20 Dec 2007
Posts: 209
Location: Swindon, UK

PostPosted: Thu Sep 11, 2008 3:20 am    Post subject: Reply with quote

Assuming the die is a negative how do you grind off the & and sink an eight into it?
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lauriek
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Joined: 25 Nov 2007
Posts: 2404
Location: South East UK

PostPosted: Thu Sep 11, 2008 4:31 am    Post subject: Reply with quote

That is nicely done! The lighting is really excellent!

What are those radial lines of 'grain' I can see there, I just looked at a coin in my pocket (admittedly a modern UK coin) and I don't see that effect...
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mgoodm3



Joined: 08 Sep 2008
Posts: 273
Location: Southern OR

PostPosted: Thu Sep 11, 2008 10:37 am    Post subject: Reply with quote

To grind the date out you also gotta grind a fair amount of the fields to get rid of the number.

the radial lines are called flow lines. The metal flows into the die during striking under high pressure and gradually grinds these lines into the die. As the dies wear, those lines will get much more prominent and elements on the die will also start getting distorted.
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