Lens Bubbles: Vivitar 24mm f2.8 TX Mount

Thursday, January 24, 2013

Using a Focusing Helicoid as a Lens Adapter

One of the most annoying problems with old manual focus lenses, is that over time, some of them would fail to attain infinity focus, due to wear or misalignment. The Vivitar 24mm f2.8 TX lens I looked that the other day was an example. The normal course of action is to get it repaired/adjusted, but this could get expensive. Worse, sometimes after a lens repair, it would have other issues like de-centering or other problems. The solution is to use a focusing helicoid in place of a lens adapter.

Helicoid as an adapter on NEX-5N. Click for larger.

My focusing helicoids were originally purchased to be used with odd ball lenses that don't have focusing mechanisms of their own, like enlarging and projection lenses, but they are equally good, and often better, when used as a lens adapter, because a focusing helicoid would make the lens focus closer than its minimum focus distance, but at the same time allows the lens to focus past infinity. The 18-35mm Yeenon helicoid is just slightly thinner than a dedicated NEX to M42 adapter when not extended. This means all M42 lenses mounted on it will focus pass infinity. This solves the problem for lenses that can not focus to infinity by itself.

Allen Garden - NEX-6 & Vivitar 24mm f2.8 TX & Yeenon Helicoid. Click for larger.

Currently, I can only use M42 lenses on the Yeenon Helicoid, as the helicoid has an M42 mount when fitted with a 52mm to 42mm step-down ring. In actual use, there is almost no different than using just a lens adapter, except you focus with the focusing helicoid or the focusing mechanism on the lens. When using the lens for close-ups, you can rack out the focusing on both the helicoid and the lens to simulate the effect of an extension tube to achieve macro magnification.

So yes, the helicoid is a very flexible tool.

True Love Cafe - NEX-6 & Isco-Gottingen Westagon 50mm f2 & Yeenon Helicoid.

Monday, January 21, 2013

Vivitar 24mm f2.8 Auto-Wide Angle TX mount

Of all the interchangeable mounts I have used, the Vivitar TX mount is the hardest to use. In fact, I despise this mount. I only have a few lenses in this mount, and luckily, I have enough mounts for each lens that I don't have to keep changing them, which saves me a lot of frustration. The Vivitar 24mm f2.8 Auto-Wide Angle is my latest addition to the TX mount. This lens is almost identical to the Vivitar 28mm f2.8 TX mount, which I looked at here. Both lenses are about the same size without the mount, and share the same filter thread size. Both lenses were made by Tokina (Serial starts with 37).

One thing becomes apparent is the very poor flare resistance. With light coming from the side, flare quickly reduces contrast and makes the picture look washed out. Effective multi-coating is one advantage modern lenses have over the old lenses. Other than the flare issue, this lens performs quick nicely. Distortion is well controlled, and sharpness is quite good, but lacking the "bite" (micro contrast) of the best (expensive) lenses have. At f8, the edges on APS-C is quite respectable and shows good sharpness. No, it's not as sharp as the center, but not many low cost lenses are. It's definitely not a soft lens, especially with some post processing, the pictures exhibit good colour and sharpness.

A 24mm lens provides a comfortable 35mm field of view on the NEX cameras, and this Vivitar lens is a good choice for its low cost, but decent optical quality.