The importance of keeping things parallel

[dougsmit]

When photographing coins we usually want to keep the coin surface parallel to the 'film' plane to avoid distortions but some coins have edges that just need to be shown if we are to get a feel for what the coin is really like.  This Alexandria tetradrachm of Herennia Etruscilla is 24mm in diameter and 4mm thick.  The angle shot shows this fact to advantage.

[Jay GT4]

Wow!  Is that a stacked photo too?

[dougsmit]

Eight images per side were stacked with CombineZ freeware. 

[Joe Sermarini]

Nice work!

[dougsmit]

For those not familiar with focus stacking software (there are several programs that do this - I use CombineZ which works for my needs and is free):

Focus stacking software analyzes images that were shot with the plane of sharp focus moved between shots but that are otherwise identical.  This can be done with two images or dozens as is required by the shot. If you use too few, there will be areas of less than sharp detail somewhere in the final image.  If you use extra, you are working harder for no gain.  Most I have done have used three to six but my first attempt with this coin using six images showed a fuzzy area so I reshot it with eight.

The first image was made focused on the nearest point of the coin (right edge).  Each image after that moved the focus back a small amount until number 8 was focused on the farthest point (left edge).  The software finds matching details in the images and selects the one of the eight that was sharpest.  These selections were blended into a single image and the 7 loser images for each point were eliminated.  The program has many controls that address problems that can arise with some subjects (insect antennae can be difficult for example) but coins are really easy and usually work well for me on the first attempt. 

The image below shows the 8 numbered images that were combined into the central image.  If you click on the image and enlarge it you can see how some images are sharper in some places while others are sharper in others. If you have trouble seeing this, compare only image 1 and image 8 which are the most different.  This software is usually not needed for coins shot flat on to the cameras but I have seen improved results with some very small and very thick/high relief coins. My example here is an obol of Aegina which has a very high relief turtle.  There was no reason to use stacking on the relatively flat reverse.

I hope some reading this will be encouraged to give it a try.  I started using focus stacking for flower photos before deciding to try it on coins.  It is a fun toy for those who consider photography part of their hobby rather than just a tool for making ID photos.

[Jay GT4]

Thanks Doug, I've been wanting to try this for a long time.  What kind of aperture are you finding gives the best results or does it matter when using this software?

[Martin B3]

I didn't know this existed, thanks for posting!

[Carausius]

My eyesight is bad enough that I have a tough time getting an entire coin side in focus for one photo. I can't imagine focusing on particular points accross the plane.  Great results though.

[dougsmit]

Thanks Doug, I've been wanting to try this for a long time.  What kind of aperture are you finding gives the best results or does it matter when using this software?

Using a larger aperture will require more shots.  I usually use f/11 with my Canon 5D mk II and f/9 with my 1.6x 'crop' cameras.  Smaller apertures can start losing sharpness to diffraction so I avoid going past f/11. 

[PMah]

Belated thanks for this useful post with a new for me technique!

[stevex6]

Nice ... very cool, Mentor (your photography skills are very sweet)

 

[peterpil19]

Thanks Doug, I've been wanting to try this for a long time.  What kind of aperture are you finding gives the best results or does it matter when using this software?

Using a larger aperture will require more shots.  I usually use f/11 with my Canon 5D mk II and f/9 with my 1.6x 'crop' cameras.  Smaller apertures can start losing sharpness to diffraction so I avoid going past f/11. 

Some of the best advice you ever gave me was to look up the f-stop at which diffraction becomes noticeable for my camera. I was using a higher f-stop than I should have been and was oblivious to the effect it was having on my image quality. I rarely (if at all) go past f/11 now and my photos are better for it!

Doug - do you use the focus-stacking for situations other than for photos of coins at extreme angles? Have you noticed any improvement to quality by using it for conventional top-down photos?

Peter

[dougsmit]

I'm sorry I never saw this reply/question so I did not reply.   Focus Stacking is great for microscope work and nature close ups of things that do not move.  Flowers that do not blow in the wind can work but insects can be a problem.  As far a straight down shots, the usefulness is mostly for very small and very high relief coins like he Aigina obol I showed above.  Rather few ancient coins fall into this category.  It could be great for artifacts but I do not collect those so have nothing to offer there.  In the past decade my photo hobby has centered on coins with less and less in the way of flowers and other macro nature.  I don't spend as much time crawling in the garden as I did once.

Whether flowers or coins this software 'trick' allows a lot of control.  You have to learn how to decide how many images to shoot and how to space them for the effect you want.  With flowers you need to be careful not to get too much background sharpness.  Depth of field limits the amount of sharp area obtained in one image but you can stack 3 images each having a lot of depth or 12 each with very little and achieve more or less the same end. The software has a lot of very specialized controls that are needed for some subjects but not others and coins use less of the power of the program than anything I have tried.  Those who think they could improve their results by buying expensive software might be right if shooting microscopic jellyfish but the most simple programs with default settings do what needs to be done with coins.  There is a lot to learn and many redo's will be needed. Below is a test cut Athenian tetradrachm which is sharp in the near parts but gets a bit fuzzy on the far left edge.  This could have been improved if I had added an image or two more (perhaps eight total instead of six?) providing the software with sharp detail information for that region of the coin.  Focus stacking is not for those who take snapshots with their phones but it allows us to do some things that a small percentage of us will appreciate.  Coins offer a number of side specialty interests.  Some clean coins.  Some research the history that goes with the coins.  Some like to run coin clubs and organize shows.  Some like to buy and sell for profit.  Some live to post opinions on our Forvm.  Coin photography is just one more side specialty.



Rather than take up all of Joe's resources with non-coin examples I will offer a link to a page of my stacked images.  Few are coins; most are flowers; some are better than others.  Anyone interested in the subject is welcome to contact me privately for discussion.
http://www.pbase.com/dougsmit/image_stacking

[peterpil19]

Hi Doug,

No need for you to ever apologise!

I will test focus stacking with some of the coins I am having difficulty with and share the results. Roman Imperials are typically always in focus but for some greek coins, especially silver ones, I fail to get the sharpness I desire.  I have started using manual focus instead of automatic focus with improved results for these coins, but still not completely satisfied.

Here is a relatively recent example which will serve as an ideal candidate for this testing. The coin overall is in focus but despite using a higher f-stop (11) some of the outer parts of the coin are less than sharp. I tried taking the photo from higher above, so I could use a higher f-stop with less diffraction kicking in but the results were not materially better. The image should have zero sharpening applied (other than what the camera might do without telling me) as I found a setting which turns that off in the software which came with the camera.  I also found applying sharpening in post processing did not improve this coin.

Peter

[dougsmit]

One thing we gained when we entered the digital photography age is a camera that thinks for us.  Being able to turn off that feature when necessary is a good thing.  My camera does a good job with auto focus but I use manual exposure and white balance.  We do what we can to make the best results.