Quick Tip : Checking for a Dirty Sensor

It has been about 6 months (shooting 3-4 days a week) since I last cleaned the sensor on my Canon 5D Mark II.  I have started to notice that it is taking more of my time to clean up those little dust bunnies appearing throughout the frame.  Especially on shots shot with a small aperture (high f-stop) against light fields of color.

So here is a quick test I do to see if it is time give the sensor a cleaning:

• Take a well-exposed shot of something light colored, a painted wall or the sky works well for me.  I want to use a high f-stop, usually f/18 or so, so it needs to be a bright enough scene and I will use Aperture Priority mode.  I don't crank up the ISO, leaving it at 100 or 200.
• Make sure your shot is in focus, and  shoot a few.

Here is my test shot - I could have overexposed it a little to make it lighter, but that wasn't really necessary.  Notice that the sensor spots are no very obvious (See it larger here Dirty Sensor Test-Unprocessed):

Dirty Test Shot - Unprocessed

After I have a few shot, I import them in Adobe Lightroom 4 for some processing that will help bring out those sensor spots that always seem to show up when you don't want them.

Developing to bring them out in Lightroom is not very difficult.  I like to convert to black and white then boost the contrast - especially in the middle range.   Here is the result of my develop changes for this same image (See it larger here Dirty Sensor Test - Processed):

Dirty Sensor Test Shot : Processed

I know that on this blog post, the spots may not look obvious in the relatively small JPEG, but if you do this in Lightroom, then Zoom in 100% and pan around your image, the dust spots will be pretty easy to see.

For reference, here is what the Develop Module settings I used.   I also save these as a User Preset in Lightroom so I can do this test with very little effort in the future.  I have also exported these settings so they may be imported as a User preset into Lightroom.  Get that file here: Lightroom Dirty Sensor Test - Sky