Classical Numismatics Discussion
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FORVM`s Classical Numismatics Discussion Board  |  Numismatic and History Discussions  |  Coin Photography, Conservation and Storage  |  Topic: Shiny coins, bracketing photos and merging images 0 Members and 1 Guest are viewing this topic. « previous next »
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Author Topic: Shiny coins, bracketing photos and merging images  (Read 278 times)
Anaximander
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« on: September 09, 2020, 09:06:52 am »

Shiny, lustrous coins are notoriously hard to photograph, since they can reflect light like little mirrors.  I read in a post hereabouts that one solution is to shoot them in High Dynamic Range mode.  Makes sense.  I’ve used HDR for outdoor photography from time to time.  My camera can do HDR in-camera (taking multiple shots and then merging them into one photo) or can give you several shots and let you perform the HDR magic in post-production.  I choose to do the latter, as it gives me more more control.  I usually don’t mind taking the time and effort. HDR tends to the more extreme exposure differences, +1 ev to -1 ev, which is why I use the poor-man’s HDR: just “bracket” several shots (each at a different exposure, + or - 0.3 ev) and then merge them, HDR-like, in software

Below is an example of three photos for each of the obverse and the reverse of a rather shiny coin of Gordian III. I bracket using exposure correction of +1.3, +1, and +1.7 ev.  Yes, I’m overexposing them all, my basic point of departure for all silver and gold coins.  I wouldn’t do that for bronze coins, but I find it necessary to overexpose silver coins, otherwise automatic light metering takes my bright coins and damps them down.  Undecided


* HDR.example.GordianIII..jpg (565.66 KB, 3000x1496 - viewed 29 times.)
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Chris “Anaximander” Thomsen. Member Since 2019.
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Congius
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« Reply #1 on: September 09, 2020, 12:43:56 pm »

Certainly a significant improvement from the HDR stacking !

A couple other options for highly reflective coins (depending on what result you are looking for), are either to have highly diffused lighting or to light from the side (almost parallel to the coin) to avoid reflections directly into the lens. Attached photo is one I recently took using latter approach - was difficult to get it looking same as in hand with any other lighting. Not the best photo, but it does capture the silvered appearance while avoiding major over-exposed blowouts.

I've seen people on modern coin forums using axial lighting for mirrored proofs, but not sure how well that works for ancients with less regular surfaces.

Ben


* Licinius II CAES VOT X ET XV F Rome 320 (Eros, RIC VII Rome 205 R4) 19x18mm.jpg (242.91 KB, 800x386 - viewed 25 times.)
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Anaximander
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« Reply #2 on: September 28, 2020, 04:59:41 pm »

I have since experimented with both my camera and with my photo imaging software, and I've smoothed the way to use High Dynamic Range (HDR) on all types of ancient coins, silver, gold, and bronze.  My collection of third and fourth century Roman coins is a medley of metals, and a good testbed.  

Below are examples of automated merging of photos of gold and bronze coins using "bracketed" shots from the camera and HDR processing in PC software.  All photos are unretouched here.
 
The camera has several settings that, when used in combination, allow me to shoot three photos at different exposures with a single press of the shutter button. KISS.
The software has a batch mode that allows me to take my usual complement of a dozen coins and, with a single command, photomerge the 72 photos (3 each of the obverse and reverse) into twelve pairs of HDR photos.  I find the effect to be stunning.  

I'm shooting everything using axial lighting, bouncing LED light off clear glass, with some additional soft direct lighting. The rather diffused glow doesn't make for deep shadows anywhere, so features like legends do not tend to stand out much.  The HDR seems to help increase detail, compensating for the flatness that comes with the axial lighting. Congius manages to use side lighting effectively, so there's clearly more than one way to overcome bright reflections. 


* HDR.example.Theodosius.AV..jpg (1019.34 KB, 1749x1114 - viewed 30 times.)

* HDR.example.AeliaFlaccilla.jpg (387.36 KB, 1971x921 - viewed 27 times.)
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Chris “Anaximander” Thomsen. Member Since 2019.
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« Reply #3 on: September 28, 2020, 09:00:14 pm »

Very nice, I've got to try this.
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