Tuesday, April 24, 2012

Bluebird and Lens Calibration

Nikon D3s; Nikon 600 f4 with 1.4tc F6.3, 1/800 ISO 320 Better Beamer +2

I spent some time with Joan last week calibrating her camera body and lens.  We also calibrated it with the 1.4 TC mounted.  The calibration was done using FoCal Pro Software. The lens and camera body calibrated quickly and with very low variability in focus performance.  

Here is a graph of the calibration results. X Axis is AF Fine Tune setting (would be MA setting for Canon), Y Axis is quality of image. Note the very tight variability around the curve for the multiple shots taken at each setting.

The 1.4 TC never quite calibrated as the lens with the 1.4 TC mounted is still back focusing when the MA is set at -20.  The TC will be going back to Nikon for Warranty repair.  However, it provided us with an opportunity to demonstrate how some folks work around not having their lenses calibrated with their camera body.  Joan took the above Eastern Bluebird picture with the TC mounted and she took it at f6.3 at a distance of 50 feet.  So, she had a depth of field of about 5 inches.  Notice how the branch behind the Bluebird is in focus and the branch in front is not. Admittedly this technique works-but it is a compromise as the lens can not be used successfully wide open. I believe that is why there is so much talk about having to find the sweet spot f stop for a lens.  What is actually being done is compensating for not having a lens and camera body calibrated for the focal plane. 

Here is a graph of the FoCal Results for the 1.4TC plus 600 lens:
You can see that the lens is just starting to get lower variability and that the focus is starting to get closer to being on plane at the -20 MA setting.   Bottom line is that the FoCal Software was instrumental in determining what the issue was with this TC and we now have quantitative info to give Nikon to demand repair. 

On Saturday, our friend Bob Adamowicz from Massachusetts visited to problem solve some issues with his wife's Nikon Camera and Lens.  We used FoCal to help problem solve and resolve the issues.  He and I also tested the Long Lens Support System I am manufacturing and we determined that it improves variability of focus  (pictures and a dedicated post coming in near future). 

We also did some tripod testing and will be writing a separate post about the details.  This type of testing really helps debunk some myths about tripods, leg extensions and mounting systems. 

Until Next Time.

Jim Borden

Also-we have revamped our Photography website.  Stop by for a visit by clicking here


Coy Hill said...

Good info Jim. You leave no stone unturned! I have suspected for some time that the sweet spot issue was related to focusing error. Lucky for me that my 600 is reasonably sharp on my 60D at F4 as the 60D has no user adjustment.

Willard said...

Excellent article, Jim. This has confirmed my thoughts about the sweet spot thing. I find that with my 500mm calibrated it now actually works the best at F4, but previously I had to stop down to get acceptable sharpness because of missing the exact point of focus. It is not good with the extenders ; however--probably need to try the new version. The old ones work well with the 300mm F2.8 though.

Altax said...

Excellent shots. Thanks for sharing the tips.

Preschool Games

Lindsjö taxar said...

Great picture, loveley colurs..hmm I will read that after my 3 times photo sessions to learn. I´m a beginner..