Initial Test Results- 4/29/08

Here is the initial testing of the new Sony 24-70 SSM lens for Bokeh.  I have so far only tested at 70mm focal length, which I prioritized due to being more likely to use the longest focal length for portraits, and shorter focal lengths I will most likely use for landscape photography or travel photography, and will be less likely to want large out of focus areas on the image.  Therefore, testing still has to be done for 24mm and 50mm fovcal lengths, as well as a 2 foot range for the out of focus blur circle.

Prior to testing, I had used the lens for some shots around the house and have extremely mixed feelings about the bokeh of the lens.  Sometimes it delivers creamy bokeh even with harsh backgrounds that are difficult for any lens to make pleasing.  Other times it has harsh mirror-lens-like severe circular artifacts with backgrounds that I did NOT consider to be difficult tests of bokeh at all.  The truth is, I can’t make heads or tails of the situation by looking at the pictures.  Based on my limited rigorous testing (below) so far, at 70 mm and f/2.8, bokeh seems to be neutral to slightly good.  However, ring artifacts appear to pop up minimally at f/4 and get bad by f/8.

Based on limited testing at 70 mm focal length, there seems to be a bokeh sweet spot at the center of the lens when focused at 10 feet and at f/2.8 for background objects.  The unfortunate part of this is that at the same settings above, the bokeh at the side of the lens is horrible.  At 5 feet and f/2.8, the center is still brighter than the rest but the light falls off more steeply, but you gain better (although still not good) bokeh at the edges of the lens.

I will revisit this page and update when I have more data available.  I am including the pictures from the formal testing in tabular format.

Here are some shots showing the bokeh conundrum of this lens.

                                Random daughter shot- bad one at that

                                                                                                                                                            Closeup of the red Boxed area

Here we see very bad bokeh from this lens  an admittedly difficult situation.Note that this is close to the 10 foot focal length “sweet spot” for bokeh, but unfortunately, it has terrible bokeh to the side at this focal length.  Look however, at the next picture, showing what I would consider very neutral bokeh with in the background flowers and specular highlights on the house in the background.

                     Flower with blurred flower in background

                                                                                                                                            Closeup of blurred flower in background

But just as I thought maybe the bokeh isn’t so bad after all, I got the following image:

                                                                                      Simple shot of my daughter (out of focus)

                                                                            Close up of out of focus area in red box above

And now for the formal testing results.  Again, these are preliminary and not complete in any way.  The tables show specular highlights from either the center of the image or from the far left side of the lens.  Each table is for the lens focussed at a certain focal length, with varying distances between the camera and a single point source of light (fiber optic source).  The infinity results were done instead with a light bulb across the street, as the fiber optic was not bright enough for longer distances.  In fact, you will notice that there are actually 2 light bulbs across the street.  THe pictures are small enough to see 3 on a page, but you can click on an image to get the 100% files.

So far, it seems that at 70 mm and shorter focal distances, bokeh is quite good, with a little optical vignetting when wide open that becomes worse the further the focal point is.  At 5 feet focal distance when wide open the bokeh becomes a bit more harsh on the edges, and by 10 feet significantly.  This fits very well with my subjective testing, as well as the images above.

Further testing still needs to be done with blurred point of light at shorter ranges as well, and I will make a 20 feet focal length as well, and possibly 40, too.

70mm Results