Sony α290 spot exposure measurement design flaw
yesterday I stumbled upon a (in my opinion) heavy design flaw of the Sony α290 DSLR camera. The camera has nine auto-focus fields in total, see the illustration below:
Within the options menu of the camera, you have the possibility to select a specific auto-focus field. This allows you to focus a specific point, e.g. when composing a picture and your motif is not in the center of the picture. When choosing a spot auto-focus field, the selected auto-focus field is illuminated during the focus process, see the illustration below:
So far, so good. You also have the possibility to select spot measurement for your exposure. This allows you to measure the correct exposure for one specific spot. This spot is not shown in the viewfinder. For illustration purposes, I’ve drawn the spot that is measured in light green, see illustration the below:
Maybe you already get the point… If you combine the spot auto-focus and the spot exposure management, your viewfinder would look like illustrated below:
The problem that now occurs: You focus on a specific part of the picture, but the exposure is always measured in the center. In the best case, you have a homogeneous motif with consistent light. You focus on the right spot, and the picture is still properly exposed.
Worst case, and I think that this is also the most common case, you focus on the right spot, but the exposure of the picture is messed up. Yesterday I made a picture of a heron that was stalking around a nearby creek. I used the settings described above (spot auto-focus and spot exposure measurement) and got the following result:
I focused on the head of the heron, using the auto-focus point on the middle left. The exposure of the background is OK, although a bit dark (Damn, just noticed that I had exposure correction still set to -0,7 EV from another shot!). But the heron is displayed in dark grey. For me this ruins the picture, as the heron should have been the main motif. Even though I have the raw picture data, it is hard to correct wrong exposures in Photoshop without drawbacks (e.g. increased noise) to other parts of the picture.
I would have expected that the exposure measurement spot is synchronized with the auto-focus spot. This way, it is not possible to properly expose a picture when you are not using the center auto-focus spot. There are several possibilities to solve this, ordered in decreasing recommendation:
- Use the spot exposure measurement to measure the required exposure and use the values for the manual camera mode. This method allows you to use specific auto-focus spots without worrying about wrong exposure or wrong focus. This method probably offers the best picture quality, but comes with the drawback that more steps are required to take the shot. Depending on the motif (e.g. animals), these additional steps kill your picture.
- Always use the center auto-focus spot when using the spot exposure measurement. After pushing the trigger half way down, arrange the picture the way you like it in the viewfinder. The problem with this method is that I have heard this may cause problems. The camera focuses the spot you are currently looking on. Changing your view angle by composing the picture now may change the viewing distance to the spot you were looking. This can lead to a wrong picture focus and blurry pictures. I don’t know how severe this is, but I’ve read you should use the correct auto-focus fields whenever possible.
- Don’t use spot exposure measurement at all. There are two alternative settings to use for exposure management: multi segment and center weighted. Multi segment calculates the average value of the whole picture. Center weighted is a mix between spot and multi segment – it calculates the exposure similar to multi segment, but the exposure in the middle of the picture is taken into account more than the edges of the picture.
The best solution however would be to synchronize the exposure measurement with the auto-focus spot.
I have experience with the Sony α290 system only and I’d like to know if Nikon/Canon/other systems suffer the same problem. It would be great if you would share your experience with me!
Kind regards and successful picture-shooting,
Disclaimer: The viewfinder picture was copied from the official Sony α290 manual. I made minor edits for illustration purposes in the pictures above. All copyrights belong to their respective owners.