Long Lens Auto-focus Check

One of the great challenges of working with long telephoto lenses is getting the focus where you want it.

The inherent nature of a telephoto lens produces a comparatively shallow depth of field (relative field of focus). The longer the lens, the less depth of field.

So where precision focus is important with a wide angle lens, it is critical with a long lens, unless, of course, your intent is to make soft images.

Placing focus is important to me, as I’ve learned various visual tricks for directing the eye within an image by clever use of sharpness. Sometimes when photographing trains, the optimal focus point is not at the front of the locomotive; however, in this case, that was precisely my objective.

One of the reasons I’ve embraced auto-focus cameras, was that about ten years ago I concluded that I couldn’t trust my eyesight to make precision focus, especially when I had to do it quickly.

Test photo looking toward Platform 10 at Heuston Station, view from Conynham Road.
Test photo looking toward Platform 10 at Heuston Station, view from Conynham Road.

Using my new Fuji X-T1, I made this image on Friday February 20, 2015 of an Irish Rail continuous welded rail train crossing the River Liffey at Islandbridge in Dublin.

Exposed with a Fuji X-T1 with 18-135mm lens set at 135mm; ISO 800, f5.6 1/500th second, ‘Velvia’ color profile.
Exposed with a Fuji X-T1 with 18-135mm lens set at 135mm; ISO 800, f5.6 1/500th second, ‘Velvia’ color profile.

I arrived at my location a bit winded and had only a few moments to make a test photo and set the focus point (the Fuji allows for easy adjustment of the desired focus point) before the train came into view.

The equipment performed perfectly! The front of the 071 class locomotive is razor sharp. Hurray!

Very tightly cropped portion of the above photo to check for sharpness. Considering  that I made the image hand-held of a moving train, I'd say the autofocus worked admirably.
Very tightly cropped portion of the above photo to check for sharpness. Considering that I made the image hand-held of a moving train, I’d say the autofocus worked admirably.

 

Exposed with a Fuji X-T1 with 18-135mm lens set at 135mm; ISO 800, f5.6 1/500th second, ‘Velvia’ color profile.

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