I remain a fan of the Sigma MV-95 magnetic viewer despite its slowness at times. I discussed it at length here in June of 2007. It has helped analyze many problematic tapes and has helped me understand the issues enough to apply the correct solution to transfer damaged tapes.
An example is here.
Last October, when my friend Christopher Campbell visited to exchange knowledge** with me, he brought along a Quasar Sensor Loupe from VisibleDust. I had to have one. It is designed for showing dust on digital SLR camera imaging sensors, but its built-in lighting and 7X magnification make it perfect for looking at the magnetic viewer. This link appears to be a new and improved version. They also make a smaller version (called the Mini) which I have never tried, but you can look at it here. It is a little bit less expensive as well as being smaller.
Details about this system can be found here.
When I am not using the VisibleDust viewer, I use my older Surefire L4 LED flashlight for illumination of the viewer, although any good LED flashlight, such as those from 4Sevens and Fenix, would work. I still think the Zebralight in the full-flood mode is the ultimate headlamp for hands-free working—there is no hotspot.
Finally, a note about the viewer images. The majority were made with a Nikon D100 digital SLR camera (6 MP, APS-sized sensor) and a Nikon 60 mm f/2.8 autofocus Micro (macro outside of Nikon-speak) lens. Although the reticle of the B&L magnifier is shown in some of the images, the lens of the magnifier was removed and only the Micro-Nikkor lens was in the image-forming path.
**Christopher is an artist, photographer, large-format image printer, and is involved in tape restoration. I helped him with tape recorder and electronics skills and he helped me with colour profiling, Lightroom and Photoshop tricks and techniques, and camera image sensor cleaning. It was a good time, I think we both learned a lot from each other. Funny thing about knowledge…when it’s shared both parties win!