focus stacking

[JBF]

At the February DAWN meeting (Denver Area World Numismatists, first Friday of the month, Calvary Chapel Gino Gerasi minister.) we had a speaker on focus stacking in photography for coins.  Really cool stuff were everything is in focus on high relief coins because each 'level' of the topology of the coin is photographed in focus, and then they are all combined by a computer.  The image is as it appears, and doesn't degrade on "magnification".  See "focus stacking" on wikipedia.  This method is also used to photograph large bodies in space, (galaxies, etc), "image stacking" is a term used there. 

I don't know anything about coin photography, but I can tell that this kind of stuff is coin photography's future.

[dougsmit]

Image stacking can be done with several programs.  I use the freeware CombineZ.  Certainly there are some high relief coins that can benefit but my main use was to handle coins shown at an angle.   It is really miraculous for flowers!  I played with this a lot back in 2007 but let it drop as more trouble than it was worth for most coins.  I'll have to try it again now that I'm reminded of it.

[SC]

Wow.  The result, especially on the bottom tetradrachm, is like a 3-D image!

Shawn

[JBF]

The speaker at the club used it for both straight on, and at an angle coin photography.  He said he had a photo of a bee that was stationary for 10 minutes (he says it takes awhile to do the photographs for the stacking), that was amazing.  Have to get him to show that next time.  It is an amazing technique, but given the time and memory constraints, probably not ideal for photographing an entire collection.

dougsmit, I would love to see more (whether coins or not).  Of course, I don't know how much memory is needed for the photos.

John

[dougsmit]

Since it had been a long time (over 6 years) since I played with this, I decided to try a couple more.  What I learned is that some coins benefit from the technique more than others.  I shot four and threw out two not because the stacks didn't work but just because they added nothing to the image over a flat shot.  These two were thicker coins and gained more.  Worth the effort?

One question with tipped coins is which way to tip.  Here the turtle looks better facing into the camera but the reverse made no difference so both were tipped the same way.  The Philip Alexandrian required tipping opposite ways to make the reverse figure face into the camera but I failed to make both tips the same angle. This shot shows how this coin is not of even thickness.  This is common with ancients but does not show well with flat photos. 

This is easily done with CombineZ freeware.  I know there are expensive programs but, at least for coins and flowers, I see no problems with the freeware.  Here I used four images for the Philip and the reverse of the Aigina but used 7 for the Aigina obverse hoping to capture finer detail.  I generally have just guessed how many to use and have no data on how these would have been improved or wrecked had I used more or fewer.

There will be more when I decide what coins would benefit from the technique. 

[JBF]

I think that it would be neat if dealers included some image stacked pictures with each (high relief) coin they sold.
Of course, it is probably not worth their time or effort, even if the former owners of the coin already had the pictures done.  Stiil, you sell a $5000 dollar coin, you should be willing to do a little extra and keep a file of old photographs on the coin.  I also wish dealers would preserve provenance of the coins they bought and sold.

[Nemonater]

Doug, these are some outstanding images.  I wonder though, couldn't the same be achieved with a single shot using the smallest aperture and longer exposure?

Nemo

[dougsmit]

The smaller apertures carry a price.  Below a certain point which changes according to the size of the sensor (physical size, not megapixels) sharpness is lost to diffraction.  Recognizing this, many point and shoot cameras don't even have the capability to stop down fast f/8 or so.  When a subject is deeper than it is wide, the required aperture could be well beyond reasonable.  Also, stopping down does not make an image evenly sharp but just better across a wider area.  There still could be a noticeable difference between the point of best focus in the middle and the extremes at front and back. 

I shoot many photos of coins at F10 which is on the cusp of the diffraction limit for my camera.  That is enough to get acceptable sharpness for most coins I shoot flat but sometimes need to be changed for something like a high relief obol.  Unless you are making large prints, this difference is not going to be noticed.  When I want a really big photo, I switch to my better (full frame) DSLR which allows huge prints.  I never have tried it with a tilted coin. 

[Jaimelai]

My first attempt at focus stacking using CombineZP:



Easy (after playing around a bit)! Three photos chosen, selected "All Methods"  and picked out my favorite.  Thanks for all the tips!

[dougsmit]

Good job!  'All Methods' is a perfectly good option.  I usually find best results using a two step process starting with 'Align and Balance Used Frames' followed immediately by 'Do Stack'.   If this fails to produce what I want, I play with the others or reshoot with a greater number of images.  I am not experienced enough to predict whether a coin or flower will benefit from using a dozen images rather than just four or so but my guesses seem to be good enough for my standards.   Did you compare this image to the best you could do with just a single shot? I rarely feel the need to use it on coins except for the tilted angles but it is great for flowers.

[Jaimelai]

Here is a comparison using incandescent lighting (other was with ring lights).  I was trying to get the face and boarder dots in focus at the same time.