Most of you probably already know what AI and pre-AI lenses are. To spare you the technical details, basically they're two old kinds of Nikkor lenses, with the big difference being that pre-AI lenses cannot be safely used with many modern DSLRs. As a result, owners of pre-AI lenses convert them (or have them converted) to the safe-to-use AI kind.
The thing is, is it worth it?
|Some older lenses, like this 200mm f/4 can offer very high optical quality. Still, you should always ask yourself if the trouble is worth it.|
Clearly, to answer that question we need some cost data. Having your lens converted is not very expensive, if you have access to a cheap service point. Here in Finland, I suspect most places would charge you $70 just as you enter their front door; in the USA, I'm sure the situation is better. The part itself (basically just a new aperture ring) costs between $25-40 or something like that. The absolute cheapest "conversion" would be to simply rub off (using a file) a portion of the aperture. Assuming you know how to do it and you have the tools already, it costs nothing and takes 15 mins. BUT, it's not a proper conversion. It's proper alright in the sense that it's safe to use. But it will decrease the resale value of the lens.
If you want a proper conversion, to estimate whether the cost is worth it,you must compare the price difference between a pre-AI and an AI lens. In many cases, the difference isn't that much. Examples: micro-Nikkor 55mm f/3.5: Pre-AI $60, AI $90. 105mm f/2.8: Pre-AI $75, AI $115. Prices are indicative, and they can vary greatly. Which, in a sense, makes it even LESS worthy to have a pre-AI lens converted. Imagine, having just sent your lens for conversion, you notice the AI model being sold somewhere for the same price!
So, bottom line, I don't favor AI conversions. If you really want an older lens, search for the AI variety, as it will save you the trouble. Of course, if your camera can take a pre-AI lens (check, but basically any entry-level body), you're in luck.