Misc M42 2x Teleconverters

Misc 2x Adapters




Here’s the thing about 2x converters. I hear a lot about how crappy they are, how you shouldn’t use them, how they degrade your image, espcially the dime-a-dozen single-coated three or four element ones like we have here. Mmmmmmaybe. Think about this for a moment. OK, they may take the edge off your image more so than a UV filter or a nicer 7 element MC 2x would, but seriously, if you were going for the gold you wouldn’t be using a 2x converter at all, would you? You’d be using a prime lens in that focal length.

What a 2x is good for: lightening your walking kit for close pics in a pinch. What a 2x is not good for: getting the best out of your best prime lenses. That’s it in a nutshell. I do think every SLR kit should have one. If your lens is good and your 2x is clean, your 8×10 print is not likely to have any noticeable difference.

The ones I have were all made in Japan and are of surprisingly distinct designs. The Royal seems to be the best constructed physically, with nice knurled exterior and snappy aperture return, while the Vivitar seems to have the best glass and coating. The Montgomery Ward and the Royal have a flatter bluish coating, the Vivitar is multicolored if not multicoated in green, yellow and blue. Still, they’re all pretty simple and solid and any one of them would be good in a pinch to pull out of a pouch or pocket for a quick close up.


It goes between your lens and the camera: screw the female side of the converter onto the back of your M42 lens, then screw the male side to the camera. (Please don’t make me explain that terminology…) The doubled focal length generally comes at the cost of the loss of 1 1/2 to 2 stops of exposure, easily compensated for by a TTL meter, but if not then set your hand meter to 1/4 the speed of the film you’re using. (400 becomes 100 = two stops)

The other thing you might easily forget is that the handholding rule of thumb is to shoot at 1/focal-length as the slowest shutter speed, eg 1/60 if you’re handholding and shooting a normal 50mm lens. Add a 2x and your focal length becomes 100mm, suddenly you should be shooting at 1/125 or faster to avoid camera shake. Add the 2x to your 200mm and… get your travel tripod out!


Bit of a shock when I tried to dismantle the Royal one to better count the elements (3) – the group is held in place with an outer spanner ring that actually also determines infinity focus. Took a little adjusting to get it back right once I put it back together.

Special Notes

Funny thing I noticed when trying to set infinity focus with the Royal: with a 2x extender, your focus limit becomes slightly longer than what normally passes for infinity with the lens alone. I verified this with three other 2x extenders on two different cameras with different mounts. Curious! Optical effect? Design necessity? The stuff I was smoking that afternoon? If you know, let me know.

This should go without saying, but even though they seem more or less the same, some are better made than others, with either better or worse spring action in their aperture pins, and better coating on the lenses. When possible, try before you buy or get a couple to choose from, they’re pretty easy to come by.

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