Adjusting the Tension on Nikon Right-angle Viewfinders
A right-angle viewfinder makes it much easier to work close to the ground. The Nikon DR-4, DR-4, DR-5 and DR-6 rotate 360 degrees so you can orient your camera at any angle needed for your composition, but this isn't always as easy as it should be. Mine used to be so tight it would barely turn while others I have talked to say theirs rotate so freely they just flop around. But there's an easy fix that Nikon doesn't tell you about in the instructions that come with these things.
I first figured out the answer as a result of sheer desperation. Back when I got a D100, I started using the DR-4 right-angle finder that attaches using the Nikon #2370 adapter. These small plastic adapters are cheap, but often out of stock at camera stores and online retailers. Unfortunately, my DR-4 was so stiff in turning that it took less force to break the plastic legs off the #2370 than it did to rotate the viewfinder. Even when I was careful, I would often break a #2370 during a single morning's shooting in a field of alpine wildflowers. I used to buy them half a dozen at a time so I had enough spares to not run out. I even tried reinforcing the adapters to make them less likely to break, but nothing worked.
Finally, I asked another Nikon shooter what they did and to my surprise their DR-4 rotated smoothly. To determine what exactly was going on, I sat down one afternoon to disassemble mine. While it's always fun to tinker with things, I began to wonder if doing so in this case was such a good idea as the number of parts arrayed out before me continued to increase and the solution continued to elude me.
Then, it dawned on me how the mechanism worked. As you've no doubt already guessed, I had taken more than one wrong turn on my road to figuring things out. It turned out I didn't need to disassemble it at all.
Here's the secret of adjusting the tension:
On the end of the of the right-angle finder that connects to your camera, you may or may not have some form of adapter attached. Different adapters are needed for connection to different camera models with some requiring no adapter at all. If you have one on yours, remove it so you can get at the end of the finder itself.
Once you do, you should see something like the picture here. Inside the remaining silver screw threads there should be a black ring with two radial slits. You may have noticed similar slits in the construction of other lenses and components. Such slits are designed to fit a tool known as a spanner wrench that enables ringed fasteners to be loosened or tightened even when they may have glass in the middle as they do here. By turning the ring only a small amount one way or the other, you can adjust the tension on how the finder rotates on its axis. The best spanner I know of is made by SK Grimes, a great machinist and photographic repair service provider located in Rhode Island, but if you don't have one I know of several people who have adjusted their Nikon right-angle finder using two small jewelers' screwdrivers in a coordinated motion. It shouldn't take much force to turn the black adjustment ring and you likely won't need to this but once to get things the way you want them, so feel free to save some money unless you want to invest in a spanner wrench for any other future uses.
These days, I'm shooting with the Nikon D2x so I no longer need to mess with the #2370 adapters. I've also upgraded my DR-4 to the new DR-5 right-angle finder but it adjusts the same way my DR-4 did, although I have as yet not needed to do so. I've also checked out other models of Nikon right-angle finders and the DR-3 and DR-6 have the same adjustment.
Right-angle finders from other camera makers may or may not work similarly. My old Minolta Anglefinder VN didn't, but if you brand does, let me know and I'll make note of it here.
By the way, some folks may be wondering why Nikon has so many different models of right-angle finders — a legitimate question indeed. The current models are the DR-5 that fits models such as the D1 and D2-series, the F5, F6 and similar bodies that use round screw-on viewfinder accessories, and the DR-6 that fits models such as the D200, D70s, N80 and similar bodies that use rectangular slide-on viewfinder accessories. As such, Nikon has finally stepped up to equally supporting both types of eyepieces. These two replace the previous DR-4 finder and feature a nice switch to toggle between showing you the full viewfinder image and a 2x magnified view of the central potion to help with critical focusing. The DR-4 worked natively with bodies with round eyepieces but needed the #2370 adapter to work on rectangular-eyepiece equipped bodies as mentioned at the outset here. If you are fond of #2370 adapters, they also work with the new DR-5 on rectangular eyepieces. That leaves us with the older DR-3 that was functionally a virtual clone of the DR-4 but did differ somewhat in terms of construction. The DR-3 natively fit older non-AF bodies and needed the DK-7 adapter to fit newer High Eye Point bodies while the DR-4 natively fit HP type viewfinders used on newer AF bodies and required the DK-13 adapter (included) to fit the older, slightly different diameter non-AF bodies. Long story short: thing change, so so do right-angle finders. For the bargain hunter, you can generally find used, perfectly good DR-3 finders cheap from folks who have upgraded to the newer models. With the right adapters, it should fit whatever Nikon SLR body you have.