Every time you swap a lens you risk dust getting inside the body of your SLR. It can settle in front of the sensor and appear in every image that you take thereafter as an indistinct spot (dust on the lens apparently makes for a more defined dirty spec, although it depends on aperture). While many of these artifacts can be effectively dealt with using Photoshop's invaluable healing brush (working at 100% image size), sometimes they fall on an image zone that makes correction difficult. At some point they become to numerous to ignore; that's when I decided to get some CCD housekeeping organized.
If you search the D70 manual for "cleaning", it refers to the mirror lock-up control and describes the protective role of the low pass filter—recommending that it be "cleaned only by Nikon-authorized service personnel". That's all I needed to know, although DIY instructions are given. Thom Hogan's Complete Guide to the Nikon D70 goes as far as including a specific disclaimer:
In particular, the author and publisher shall not be responsible for any damage to the CCD of the camera of any reader who follows the cleaning instructions contained in this book.
Using Nikon Capture (which I don't own) to create a "dust reference photo" is imperfect alternative option discussed by Thom. Lacking the experience, nerve, and equipment, I took my D70 into a local photographic store. WPS charged $NZ150 for a next-day cleaning service and provided before and after pictures to demonstrate its effectiveness.
Click thumbnail to enlarge image
Before and after sensor cleaning
Most of the spots in the "before" photo I could match up to imperfections in recent raw images, particularly those taken on a long (10-20 sec) exposure. In terms of prevention, I'm going to make more of an effort to keep my camera in its shoulder bag—away from flying dirt and sand. When you live in Windy Wellington, there's lots of flying debris that could find a way into the camera. I regularly clean my lens ("The horse"), which I leave permanently connected to the camera body (18-200mm is ideal for general use).
On an unrelated note, this post marks the demise of Image of the Week (IOTW). Instead of an image from any period posted at the beginning of the week, I'll be posting an image from the preceding month at the end of each month. Instead of just a few descriptive sentences, I'll explain a bit more about the context and technical aspects of the shot. In making this change my hope is that those of you with an interest in photography (amateur or professional) can help me refine my skill in capturing a scene from both the artistic and technical perspective. I want to get better, and to do this I need your feedback. So please consider yourself encouraged to comment.
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