Macro Photography Experiment

I have a 105 mm f/2.8 EX Sigma macro lens that takes quite sharp photos and will go to a 1:1 magnification ratio. I would like to be able to get a larger ratio for some photos and decided to try a couple of options.

I obtained a set of three auto focus extension tubes made by Kenko. The set includes 12 mm, 20 mm and 36 mm tubes in Canon EOS mount. They are supposed to be auto-focus, but I don't know, I seldom use auto-focus for macro photography and forgot to try. The aperture control does work.

I also have a Tamron SP 1.4 AF Pro converter. This is not really intended for lenses as short as 100 mm, but I thought I would give it a try.

I selected a small patch of lichen on a handy rock face, loaded my Canon Rebel G with Fuji Velvia and mounted the camera on a Manfrotto tripod. ISO was set at 40. I set the lens on the closest focusing distance and proceeded to focus by moving the tripod. This was awkward, but I found that by moving the rear leg in small increments I could control focus. This test has made me really appreciate why focusing rails are so popular with people who do a lot of macro photography. All photos were taken in aperture priority with the aperture set at f/16. The effective aperture would have been less than this due to the extension and magnification, even with just the macro lens at closest focusing distance. The images were scanned by London Drugs using their scan to internet service. The quality of the scans does not do the photos justice so I will also describe the results. The following are the results of my test.

Sigma 105 mm macro lens, no extension tubes, no teleconverter. Exposure time was 1/4 second. The image is quite sharp. This is aproximately 1:1 maginification so the image on the slide is about the same size as the lichen on the rock.

Sigma 105 mm macro lens plus 1.4 x teleconverter. Exposure time is 1/2 second. Magnification is approximately 1.4:1. The image is acceptable, but is definitely softer than the image taken without the teleconverter. This teleconverter will take sharp pictures with telephoto lenses, so it appears that it does not function as well at macro distances with the 105 mm lens. This will not be my favorite combination.

Sigma 105 mm macro lens plus 68 mm extension tubes. (12 + 20 + 36). Exposure time is 1 second. I did not include a scale in the photo, so I cannot measure magnification, but it appears to be slightly less than 2:1. The image is quite sharp, comparable to the lens without extension. The macro lens combined with combinations of extension tubes will be useful in the future.

Sigma 105 mm macro lens + 68 mm extension tubes + 1.4 x teleconverter. The extension tubes were placed between the lens and the teleconverter so they would have the most effect. Magnification appears to be about 2.5:1. This image is too soft for my standards. I do not intend to use this combination very often unless I absolutely need to have the magnification.

Sigma 105 mm macro lens + 68 mm extension tubes + 1.4x teleconverter. I took this shot of a patch of lichen close to the patch where I did the above series of tests. It is definitely sharper than the shot taken with the same combination in the test. A larger aperture and faster shutter speed were used. I am now wondering whether vibration from the mirror flipping up contributed to the softness of the preceding photograph. I have ordered a camera with mirror lock-up and will repeat the test. I would rate this image as acceptable, but not overly sharp.

Index; Petroglyphs park; Frontenac park; May wildflowers; Shooting stars; Spring flowers; Summer flowers; Mushrooms and lichens; Butterflies; Animals; Fall colours; Winter colours; Yukon landscapes; British Columbia landscapes; Shadow; Macro test; BC Champs - Classic; BC Champs - Relay