Monday, August 18, 2014

Pentax 645Z And Shutter Shake Updated

No examples this morning because frankly we're talking subtleties here, but on the weekend I did get to play further with the 300 mm. lens (equivalent to 240 mm. on full frame 35 mm. - ie. quite long). I did a single image at 1/200 second and that was fine but I'll need to do more tests at this speed - I'd previously tested at 1/400 and found it good, so perhaps I can drop the short limit of questionable speeds.

At the other end I did several images at 1.3 seconds long and to my surprise these too were tack sharp, so it looks like for now the range for watching exposures is anything shorter than 1.3 seconds and anything longer than 1/200.

Remember that all the images with the 300 and 200 mm. lenses are now done with the 12 second self timer, while the 2 second setting seems to be fine with the 120 mm. lens, and that's handy for focus stacking.

So, if I had an exposure that fell between 1.3 and 1/200 second, what would I do? If a modest boost to ISO can get me to 1/200, then that's what I would do - on the weekend, I simply had to bump to ISO 800, a non issue quality wise. On the other hand, if the base ISO exposure had to be something like 1/2 second, bumping upwards isn't practical (that would be ISO 12,000) so the only option is going down the way and there's only three ways to do that, open up the lens (but usually I'm controlling the amount of depth of field I want), move closer to the subject and use a shorter lens (possible sometimes), or to put a neutral density filter in front of the lens and that's what I'll do.

Shooting suggests that blurring with the 300 mm. from the shutter is minimal but real, but in common with all lenses, , the least wind on the lens hood, movement of a foot anywhere near the tripod (unless you are standing on cement), or brushing your leg against the tripod even lightly can have a huge impact in sharpness. I learned this with my Canon cameras and sometimes would even take off the lenshood if there was a cross wind, and in really strong wind would sometimes take multiple shots with me hanging onto the camera and bearing down.

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