Focus foibles

denimadept · Oct 10, 2011

During the Albuquerque Balloon Festival last Saturday, I went to the top of Sandia Peak at night, with a D90, a Nikon 70-300mm f/4-5.6G lens dating around 10 years ago, and a new heavy tripod. Temperature was around 21F, wind was light. I used a remote trigger for everything.

While I missed the Glow due to an unexpected ticket line, I got the whole fireworks sequence. Camera was set at ISO 200, exposures between 10s and 2s (faster as time passed) and f/16. Focus was set at infinity and the lens was at 300mm (450mm effective) most of the time, with a slightly shorter setting toward the end.

EVERY PICTURE WAS OUT OF FOCUS!!!!!

WHY?!? What'd I do wrong? Might I have a problem which requires some kind of technical fix? Or was it something I should have foreseen? The distance between where I was and the event was measured in multiple miles, so I can't imagine that "infinity" was wrong. But maybe that's my problem?

Help, please!

Big Mike · Oct 11, 2011

Can you show us some examples? The first thing is to confirm if they were actually out of focus, or just blurry.

Also, with many lenses, if you just turn the focus ring 'all the way' it can actually go past infinity focus. I believe that lenses are made to do this, to allow for expansion & contraction due to temperature.

KmH · Oct 11, 2011

Unfortunately, the Nikon AF Zoom-NIKKOR 70-300mm f/4-5.6G lens is an inexpensive, low quality, CPOS that has serious image quality issues, particularly when used at it's extremes of adjustment.

A large part of your problem was turbulent air roiling, and moving during the long exposures.

denimadept · Oct 12, 2011

Big Mike said:
Can you show us some examples? The first thing is to confirm if they were actually out of focus, or just blurry.

Yes, and I'm sure you're right about the past-infinity.

Sw1tchFX · Oct 12, 2011

denimadept said:
Camera was set at ISO 200, exposures between 10s and 2s (faster as time passed) and f/16. Focus was set at infinity and the lens was at 300mm

That's why. The D90 has live view, you can use it to focus on something that's on a similar plane of focus.