The constant maximal f/4 aperture of the Sony Alpha 7R’s two standard zoom lenses – SEL-2470Z (24–70 mm) and SEL-70200G (70–200 mm) – allows for a wonderful amount of light and great bokeh. However, one area where it’s not terribly useful is macro photography with screw-on magnification lenses, in my case the Marumi DHG Achromat +5. The macro lens itself already greatly compresses the focus depth, and coupled with a high aperture you may end up with a focal plane that’s literally a tenth of a millimeter deep before visible blurring begins.
Seeing a largish spider (~4 cm leg span) that did me the courtesy of hanging out in a convenient location, I decided to take a few comparison shots at apertures of f/4, f/6.3, and f/10 with increasing ISOs to compensate. All shots use the SEL-2470Z at its full 70 mm extension with the Achromat +5. Shutter speed is 1/100 sec to allow for hand-held shooting. You can find the gallery with the original pictures at the end of this post, in case you like spiders. Here are cropped details from the same two front legs for each of the three settings:
The embedded image is a small scaled-down JPEG. Click to see the original 1.4 MB image, saved as PNG to avoid recompression errors. As usual I enabled lens correction and punched up the colors in Adobe Lightroom but performed no other post-processing, in particular no smoothing to eliminate grain. From left to right, these are the parameters and results:
- f/4, ISO 800 — Only a short section of the legs is in focus at all. The web strands in the background are barely visible.
- f/6.3, ISO 2000 — The majority of the visible leg area is in focus. You can see high-ISO grain starting to creep in but it’s not bad yet.
- f/10, ISO 5000 — Technically the focus depth is extended further, but that’s only apparent from the web strands in the background. Severe grain obliterates most details on the legs.
My takeaway is to shut down the aperture as much as possible for macro photography, except if that would drive the ISO above 2000 or so. I recommend that users of macro lenses should take a few test shots with their own cameras to determine the ISO limits for keeping fine details.
You can find the original three spider pictures in the gallery below. Click on each picture for a full-screen view with Exif data. These are big pictures with little JPEG compression so as not to smooth out the image grain that’s part of the demonstration. Right-click on a picture and open the URL in a separate window to bypass the gallery view and obtain the original JPEG.
2017-03-10: Moved gallery from Google Photos to my own host, and changed originally attached (and completely unrelated) Metten & Osterhofen gallery to a separate post.