Ok, right........ I knew that part. But I was thinking that there would be ones made out of quality glass........ so other then the quality of the lens what are the disadvantages ?
Thanks !
It would be awesome if these little attachments worked well. Too bad they don't.
From my understanding, there are many factors at work that make these pretty undesirable.
Of course, there are the problems that have already been mentioned -distortion, chromatic abberation, and flare- which are the glaring difficulties.
That they aren't made with quality glass is really only part of the problem, though. Even a model that
IS made with relatively high-quality glass would likely still produce a major degradation of image quality.
The problem is that you are essentially adding another glass element to your lens which A) was not anticipated by your lens manufacturer and B) is not matched to the specs of that particular lens. Even relatively inexpensive lenses -like Nikon's 18-55mm kit lens, for example- are still manufactured with tight specs and involve 7 lens elements that all work in cooperation to produce a good image. When you drop a piece of glass in front of them that drastically changes the direction and qualities of the light entering the lens, you sort of change the whole game... and those built-in elements simply aren't going to perform as well.
Now, if Nikon released a "matched" screw-on wide-angle attachment that it specifically advertised as being geared towards an 18-55mm kit lens... it'd probably be much nicer than the ordinary attachment you'd find on
eBay. The glass would be specifically shaped to provide the best match to the lenses elements. Judging by the fact that Nikon has never made such a product (as far as I know), however, it's really more trouble than its worth... and even when carefully matched to a lens would probably
still produce all kinds of image quality issues.
That being said, it'll work... it just won't produce great images. Not bad if you're just trying to take some photos of the family on vacation... but nothing you'd want to get involved with if you're sincere about your photography in its own right.
