Window Glass and Bokeh

My bird feeders are set up so that I can enjoy them from my kitchen window.  As long as I don't make sudden movements, the birds ignore my presence.   I'm content to work there. I can leave my camera set up while I'm doing other things and return when the right birds are present.  The birds are undisturbed and I'm cozy in the warmth of the house.

If I were asked about photographing behind glass, I would have recommended against it.  The glass at the zoo is a problem because it is dirty and has reflections that are difficult to control. I would have been concerned that the glass would cause a slight color shift.  

My attempts to photograph birds in flight were bad enough that the window glass was the least of my problems.  Spraying and Praying didn't help much.  Half the time, I didn't even have a bird in the frame.  When the bird was present, it was usually out of focus.   When the bird was in focus, the wings were in the wrong position.  

If you read the photography forums,  you will find that sharpness can become an obsession.   Photographers will pay thousands of dollars for a difference in sharpness that can only be observed under heavy magnification.  Regardless of the lens sharpness, dozens of other things need to be correct before the expensive lens produces the sharpest possible image.

Digital photography actually forgives some problems that made cheap lenses inferior to the expensive ones.  Photoshop can correct color shifts.  It can remove lens distortions and vignetted corners.  Canon's DO technology was criticized for having less contrast - this is no problem with Photoshop. With this in mind, today's test is intended to show how little difference a window makes when Photoshop is used.

I used my 400mm lens in today's tests.  I used Live View to focus the lens.  My camera was on a tirpod and I used a 10 second delay to allow vibrations to settle before my exposure.  I used ISO 100 for less noise and f 8 to get the best possible resolution from the lens.  The only difference in the tests is that the window in front of the lens is open or closed.

 

In this highly magnified sample you can see that the shot taken through the window lacks contrast.  I found that when I used contrast and brightness controls in Photoshop, I could make them look very similar.  There was less color shift than I expected.  Resolution suffered, but it was close.

Much to my surprise, the unfocused portions of the image didn't fare as well.  Look at all the extra detail in the image on the left.  The bokeh is horrible compared to the image on the right.  The window added detail that didn't exist.

Even though the open window produced better results,  it isn't the complete answer.  As I watched live view as the camera counted down, I could sharpness come and go. Heat for the house was escaping and caused distortion.  My results would have been even better if I and the camera had been outside in the cold.