Kenko (et al) wide angle limitations?

[jimdesu]

'allo all,

 

Question for anyone familiar with wide-angle (non-fisheye) auxiliary

lenses. Is there a limit to how wide one can go with these? If I

put a .42x lens on front of a 20mm lens, will this really give me an

8mm lens, or will I get something else instead?

 

thanks!

 

James

[joseph_ho]

surely, you will have a fuzzy black cornered photo if your putting it on a 20mm for a 35mm camera..

[jimdesu]

Well, maybe, but for the price of these things used, it's tempting -- my concern is if the vignetting would become serious enough so as not to cover the negative or not....

 

// James

[jimstrutz]

I've used several .42x auxiliary lenses and found that they are all about the same on a 35mm film camera. With a 60-65mm lens setting on a small zoom they become something like a full frame fisheye lens. It's not 180 degrees corner to corner, closer to 150 degrees. But there's no denying the fact that the fisheye effect is in play.

 

With a 50mm prime lens the corners are black, and the fisheye effect is stronger. With a wide zoom lens setting of about 28mm they become a circular fisheye, still with the 150 degree vision. Using a shorter lens just makes the circle smaller.

 

In all cases, as soon as you move away from the center of the image it gets very soft. At the edges it's much worse. Stopping down to f/22 helps but does not fix the problem. Still for under $50 (ebay) they are fun to play with. Some of these lenses are better than others with reguard to soft corners, but it's really just a matter of which is less worse.

 

I have also used .50x, .65x and .75x and the image quality gets progressively better, and the fisheye effect (barrel distortion) is reduced but not gone. Of course so is the wide angle effect.

 

On a digital SLR with a smaller than film sensor, the effect is reduced, as it is when using a real fisheye lens.