January 3 2010 - Photo Jottings

January 3 2010


Howdy!  2010 is here—thankfully, and this year I’ll have even more controversial reviews coming up, which leads me to the newest entry below!
Due to recent inquiries concerning testing methods (relating to the 28-75mm comparison review below), I thought I might give concerned people some insight into my typical lens sharpness test methods to try and avoid any misunderstandings in the future.  Some folks are having a tough time dealing with the results from the latest comp review.
Since the last posting, I’ve been getting email from people wanting to know what kind of tripod I use, length of sections, what type of head, date of manufacture, weight, feet type, locking mechanism, cable release type, length of cable, insulation thickness of said cable etc.  Well, by
golly I’m going to answer some of those questions, and I hope I can answer them to your satisfaction.
1950s very large studio Star D made out of cast (Reynolds) aluminum in Los Angeles, CA.  Of course I don’t just put the tripod on the ground, I built a massive concrete hard-stand extending below the frost line, with heavy stainless steel brackets on top for the tripod feet to lock in to. I mount the camera directly to the tripod, (no sloppy quick release) with thin, high-tack rubber between the head and camera bottom.  Screw torque used to fasten the camera to the tripod is a nominal
1.58 ft/lbs, (2.14 joules?)
Temperature stabilization;
I let the camera and lenses stabilize in temperature at the test site, then become familiar with the best focusing at that temperature for each lens.  With the 28-75mm comp review, I believe the temperature was a static 64.36 F or 17.97 C (with a possible calibration error of ± .1 F) during the actual lens testing procedure.
The shutter release process;
Steady shot off.  I use mirror lock up, and allow ample time for the mirror-slap absorption gaskets to expand/contract fully before releasing the shutter, not allowing the gaskets to fully expand/contract results in inconsistent energy releases, and may cause slight sensor movement at a critical time.  Furthermore, I use a custom made (electronic type) cable release that has a dedicated support harness secured to a separate steel bracket on the concrete pad, so there is no possible camera jitter because of expansion-contraction cable movement from temperature fluctuations or wind. The shutter release cable is approximately 60′ (19m) long so I can minimize camera movement caused by my shifting weight on my feet near the concrete hard-stand/tripod area.  Most importantly, I check to make sure there are no rolling vehicles or pneumatic equipment being used in the area, as they could cause minute ground movements or sharp air pressure waves, resulting in blurry pictures and inconsistent results.  Also, though not a huge everyday concern, occasional massive solar flare-ups can cause an electrical spike in the steady-shot sensor system, (even if turned off) causing the sensor to move a little, making the image blurry.  If you follow the International Space Station on a daily basis as I do, you know when this kind of stuff happens, and what the projected problems will be, and whether or not you should be out shooting a digital camera with sensor-shift type stabilization, or a stabilized lens for that matter.
One last thing I do when testing any lens over 50mm in focal length is to check with the USGS and make sure there is no seismic activity (earthquakes, tremors etc) over magnitude 1.0 within 300 (480km) miles, and 1000 miles (1600km) at magnitude 3.0 at the time of testing.  I also factor in travel speed of said activity, so I can make sure the time of activity listed in the website above could not have effected the images during my test session; and yes I do compensate for the different time zones and lack of daylight savings time for southern AZ.
Unfortunately, I’m just scratching the surface of my lens testing procedures, and don’t have time now to get to the real specifics. I hope the information above will help you people out that have questions regarding my methods, and allow you to appreciate the high level of effort I put into testing and comparing lenses.
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