Sunday, November 10, 2013


I have a wonderful Tamron SP 500mm Catadioptric (AKA reflex, or mirror) lens that I use for the NASA rocket launches. It's also pretty good for shooting the moon (for large definitions of "pretty good") but getting a solid moon shot is somewhat of a trick.
See a reflex lens trades length for portability and weight saving. A normal 500mm lens, like Nikon's latest 500mm f/4 lens, weighs in at 136.9 ounces. That's 8.5 pounds, or equal to carrying a one gallon jug of water your entire photoshoot session. This is in addition to carrying around all your other camera gear...
Then you have the length of the lens, it's 15.4 inches. Quite a beast and not that portable. In contrast, the reflex lens weights a mere 595 grams (1.3 pounds) which is a huge savings in weight, so you can carry it around all day without breaking off your arms. In addition, it's only 3.6 inches long, (with the Nikon mount) so another savings. Unfortunately, the light weight contributes to camera shake since it's not enough weight to help dampen motion, and given the 500mm focal length, you need a fast shutter speed to avoid blurred shots. And because the light path is folded in on itself (the reason it's so short) motion blur is really evident unless you use a tripod. 
But the trade-offs become a non-issue when shooting the moon, since a tripod is going to be mandatory anyway. But there are other disadvantages, and one is a killer:
It's an absolute nightmare to focus properly. Because of the folded light path and trick construction, the lens is hypersensitive to minute adjustments in focus, so it's almost a guarantee your shot will be out of focus unless you are super careful, have lots of practice, or have a camera that has focus confirmation. Actually, you need all three of those to get a good shot out of a reflex lens. Reflex lenses are more than capable of producing great shots, but because they are so finicky, very few people *get* the shot, and as such, reflex lenses have a reputation of being poor substitutes for the real thing.
So, to the moon shot at hand. Contrary to what I had expected, the moon moved at a good pace through my viewfinder, and the initial shots exhibited motion blur. Not much mind you, but enough to dull the image. So, back to research, and try again. I upped the ISO to 800 and changed the shutter speed to 1/1000 of a second. The aperture remained at f/8, since it's fixed anyway (a feature of the folded light path of a reflex lens, you get one aperture only) and took a few shots. 
Unfortunately, what I reduced in motion blur, I gained in noise, which reduced the overall sharpness, so the final result, even after some post processing work, was an image that wasn't to my satisfaction. So, back *again* to try new settings. I reduced the ISO to 200, making noise non-existant, and reduced the shutter speed to 1/200 of a second, which introduced motion blur, but I was able to compensate a little in post, and more importantly, the details remained. 
So to make a long story short, I feel I can get better out of this lens, I just need to find the right combination of settings. Meanwhile, enjoy the shot. More to come as long as the weather co-operates, that is.

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