Vibration reduction on DSLR camera lenses

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Here is an answer to a photography question I had for a while: If vibration reduction (VR) on DSLR lenses results in sharper images a low shutter speeds, why would you ever want to turn it off? I remember once checking the Nikon manual, which recommended turning off VR when using a tripod, but did not offer much explanation. Last week while on a ski trip to Lake Tahoe I experienced the importance of this recommendation. While exploring Donner Pass on an off day, I tried taking this picture of me and my dad. I used the timer and rested the camera on a post for the shot. Here’s the final result:

View of Donner Lake from the top of Donner Pass. Truckee, CA.

It was a bright day, so I used a small aperture and fast shutter speed. After attempting the shot I noticed that our faces were slightly blurry. Thinking I had somehow missed focus, I tried again with similar results. Then I tried manual focus, same result. Finally I noticed that the background was about equally blurry. Feeling a bit confused, I tried turning of VR. Below is a 1:1 comparison with and without vibration reduction:

Pixels viewed at 1:1 while using a tripod, with and without vibration reduction.

I was surprised to find vibration reduction was make the shot worse. Lesson learned – turn off vibration reduction when using a tripod. It sounds like a feature you should never turn off, but apparently it was over-correcting for handheld vibrations which weren’t happening, since the camera was on a stationary object. I was using an older Nikon AF-S DX ED 18-55mm F3.5-5.6G lens, and it’s possible this issue is not as severe on newer VR II lens.

Comprehensive comparison of pore-scale models for multiphase flow in porous media

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My phase-field simulation of viscous fingering in porous media.

A paper that I contributed simulations to was recently published in the journal PNAS. The contributors were asked to simulate the pore-scale oil/water displacement pattern in a radial Hele-Shaw cell with posts, under different injection rates and wettability conditions. Experimental data was provided and the idea was to compare the pros and cons of different modeling techniques. It was a challenging task.

I submitted phase-field results which were accurate for several of the cases, but like many techniques struggled with strong imbibition. I would like to point out one correction that never made it into the final paper. Fig. 4B shows my results, PF2, producing a very inaccurate finger width of Wf=93. This value was calculated from my original submission, which stopped well before the injected fluid reached the boundary. During revision I ran the simulation to completion (see results in supplementary information) which produced a finger width of Wf=20, close to the experimental value. Unfortunately I missed that Fig 4B was not updated with the correct Wf in the final revision, and the paper was published with the old value.

Judges sermon series

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Several years ago Gordon Hugenberger gave an excellent series of sermons at Park Street Church on the book of Judges, which is one of the most violent, disturbing, and confusing books in the Bible. Since Judges is not a popular book for study guides, I found the sermon series to be a valuable reference for understanding the most difficult parts of the book. Gordon makes a convincing case that although the Israelites are in a downward spiral, the Judges actually build toward Samson, who is a prefigurement of Christ.

Unfortunately the sermons were given over several years and are difficult to find on the church website. Below I have collected the sermons and put them in scripture order along with a link to the audio with the hope of making this valuable material accessible to others. Enjoy.