Railfan Technology > Autofocus agony

Here are two images through the rear window on the trailing sleeper on No 5, the Zephyr, in Wyoming on the detour move.
Due to the need to charge my sole battery on my main camera, I am using a Canon Power Shot A1200 pocket camera on my backup for some parts of the trip.
For many of the images the camera did focus through the glass but for about 10-15% it locked on to the dirt on the glass and gave me a "macro" of the grease spots.

On one memorable trip years ago, either the conductor or the car attendent cleaned the rear glass exterior without my even asking, but this is a typical rear window for all other trains.
To Amtrak's credit they do wash the side windows of No 5 at Denver.

Watch the Western Board, I am slowly posting more images of this trip.


 



Edited 1 time(s). Last edit at 06/07/15 20:41 by railstiesballast.

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Most autofocus systems will 'lock in' on whatever is closest to the camera.  In this case, the dirt on the outside of the glass.  Not having a manual-focus capability on a point-and-shoot type camera such as the Powershot, creates the necessity of 'creativity'. 

Perhaps the easiest solution is to set the camera to 'scene' mode and then select the 'landscape' option on the menu screen.  In general, the landscape mode forces the camera to focus at infinity and thus 'ignore' the dirt on the nearby window.  However, for this to work best, the key is to place the camera lens directly against the glass.  This is like shooting through a chain-link fence with your DSLR.  The dirt (or chain links) are too close to focus upon and may show up in the picture as a slightly blurred or underexposed area that can be cropped out or Photoshop 'cloned' to repair or removed.

With a DSLR, the obvious choice is to set the lens to manual focus and set it for infinity.  Unfortunately, the split-ring or fresnel focusing screens standard on 35mm film cameras of days gone by are lacking in the auto-focus DSLR days.  So manual focusing, even at infinity can be difficult.  One of my tricks has been to let the AF focus on what I think it should focus upon and then switching the lens to MF.  Depending on circumstances, I've not only done that but then performed 'bracket focusing' taking 2 or 3 shots while after moving the focus ring slightly left a couple of degrees for each shot from where the AF set it, and then 2 or 3 more shots slightly right of where I think the original AF position was.  In extremely low light situations where AF will not work at all, the 'bracket focusing' technique has served me well, capturing a standing person with a small 4" candle in hand as the ONLY illumination in an otherwise completly dark room...with a hand held camera!