How well do lenses really work up close when you use extension tubes or an achromatic close-up lens? I have always had good results with them, but recently I decided to do some tests to see what I needed as I expand my GH3 system (my budget is not unlimited!). In working with Art Wolfe on a book about composition (that will be out this fall), Art shared that he never travels anymore with a macro lens. He just uses extension tubes.
One reason I wanted to do a test was because of my Tamron 90mm macro that I really liked with the Sony gear I had been using. I got an adapter for it to use with Micro Four Thirds (GH3 format), but it did not have any automation. The internal aperture does not work. The adapter has this interesting work-around -- it has its own built-in aperture. The problem with that is that it cannot have actual settings on it (since it could be used with different focal lengths), and it is obviously not designed into the camera, i.e., some sharpness is likely to be lost. But how much?
So I decided to test it. I also decided to test and compare my 12-35mm f/2.8 lens with extension tubes and achromatic close-up lens (a Century Optics +7 optic). Unfortunately, I no longer have any Sony NEX cameras so I could not compare the macro at its best with the use of the adapter.
The results were really fascinating. The photo at the top of this blog is a shot of a piece of petrified wood. I have never been fond of test charts. My friend Chris Robinson (editor of Outdoor Photographer) says that we don't photograph test charts in real life, so they don't tell us everything. When I do a test, I like to photograph something real. You then see how the lens handles things like tonality, depth, gradations, as well as sharpness, in a real-life situation. Hence the petrified wood.
The macro results were not as good as I had hoped, though they were not bad. That is a challenge with this adapter. It just is not allowing the macro to be at its best. However, I was blown away by the results from the 12-35mm lens with extension tubes and achromatic close-up lens. The following cropped details from the larger shot of the whole piece of petrified wood give an idea of what I saw. These are all from the center area of the photo.
These shots are all mid-aperture range (not sure what that would actually be for the macro, but these are at f/8 for the other shots) which is where I expected to see maximum sharpness. None of the shots have been sharpened. I shot the 12-35mm at 35mm because short working distances make other focal lengths less likely to be used and extension tubes are problematic. Everything was locked down on a solid tripod and focusing was done with a magnified view on the LCD.
12-35mm at 35mm with extension tubes
12-35mm at 35mm with achromatic close-up lens
The results with the 12-35mm with both extension tubes and achromatic close-up lens were both remarkable and surprising. You really never can predict this, but I did not expect these results. They are really good. This lens with both extension tubes and an achromatic close-up lens does really, really well, as well as most macro lenses. Since the original lens was never designed to be used with either extension tubes or an achromatic close-up lens, you never know how good it was.
I had hoped that the macro lens would do better with the adapter than it did. Not being able to use the aperture of the lens as it was designed is a problem.
That said, what is the difference then between the 12-35mm and a macro lens. Wide-open, it is not as sharp -- I would expect the macro to hold sharpness well from the widest to smaller f-stops (not smallest -- I'll get to that in a moment). In addition, at wider apertures, the edge sharpness is definitely not as good as center sharpness (though in a lot of nature photography, that really doesn't matter).
Since I was checking, I decided to check the whole range of f-stops (I did this, sort of, for the macro, but that really isn't a good test since I could not use its "real" f-stops). As expected, sharpness peaks in the mid-range (f/5.6-8 is outstanding, f/11 is excellent, though a little less) and drops off at smaller f-stops (f/16 gets worse and f/22 gets bad).
That problem of f/22 is so very common yet I find most photographers don't realize that they are often losing sharpness when they stop the lens down below f/16. This is due to something called diffraction. The f-stop gets small enough that it starts to affect how the light goes through the lens. This diffraction effect can significantly reduce sharpness. It is rare to find a lens as sharp at f/22 as at wider apertures (and smaller apertures can be awful), and often I have found that there is a very distinct drop in sharpness from f/16 to f/22. Check these results: