Saturday, January 23, 2010

January 23 2010: Experiment with Kenko Extension Tubes

For several years, I have been curious about the use of Extension Tubes. Arthur Morris in his Birds As Art bulletins has used Extension Tubes with his telephoto lenses, occasionally with a teleconverter added to the stack.

For Christmas, I purchased a set of Kenko Extension Tubes in these sizes: 12mm, 20mm, and 36mm. These are straight tubes, with no glass or optics inside. They have the connections to allow for your AF functions to still work. I conducted an experiment to see what the effects and benefits were to their use. I used these sizes individually; they may be stacked for additional gain. I wanted to see how I might be able to use this lens for macro work.

Conditions: Canon Rebel Xsi body with a Canon 55 - 250mm IS EF-S lens on a tripod. I set the focal length to 100mm. Aperture was fixed at f/6.3. ISO = 800. Using ambient lighting from a nearby lamp. Used a 2 second delay to take the picture. Note, the closest distance to an object in this scenario is 1.1m or 3.6 feet. I used a Christmas ornament as my object.

Initial findings: as you increase the length of the tube and move closer to the object, you get an increased object size in exchange for requiring a longer shutter speed (less light).

This first shot is taken with no extension tube. Aperture is f/6.3 and shutter is 1/40 sec, and the distance from the hot shoe to the front of the object is 43.5".

This second shot is with the 12mm extension tube. Aperture is f/6.3, and the shutter is at 1/25 sec. The distance from hot shoe to object is now 39". Can't really see a benefit or improvement in object size.

This shot is taken with the 20mm extension tube. The aperture is f/6.3, and the shutter is now 1/20 sec. The distance from hot shoe to front of object is now 27". Note the signficant improvement in object size.

This shot is taken with the 36mm extension tube. Aperture is f/6.3, and the shutter speed is 1/8 sec. Note the greatly magnified object size. Distance from hot shoe to front of object is now just 18", compared to the earlier 43.5" with no tube.
Conclusion: Assuming that I have good lighting and possibly a tripod, I can use this technique to magnify object sizes. Note, that with extension tubes, they will fit my other telephoto lenses--unlike magnifiers placed on the front of the lens, which must match the size of the lens filter.
Next experiment will be with my 30mm lens, with and without a 1.4 teleconverter to see the benefits and restrictions of this combination.

Dec 14 2009: Green Spring Garden Park, Alexandria, va.

Green Spring Garden Park in Alexandria, Va., is one of my favorite places to take pictures. This Fairfax County Park strives to have flowers and plants growing and visible year round. If freezing has already occurred, the greenhouse on the premises is also available.

I decided to pack my camera and stop by this Park on my way to work. These are the highlights of what I saw 10 days before Christmas. It was sunny with a light breeze. I stayed for about 30 minutes. Next time I'll check out the stream below.

I love the bright red pyracantha, with the old country house in the background.

A winter cabbage with last night's rain having beaded up.

A few berries are in bloom here.
Even with a recent freeze, this plant was reasonably intact.

I like the water droplets on this frozen rose.

I love "explosions in nature"

Another cabbage

I particularly like the texture and color of these leaves.
I like the look of grasses

More flowing, wispy grasses