35mm Fisheye

[steve_rasmussen]

I just got a 35mm and remember the specs saying that it covers 180

degrees. Even with TTL blocking out the frame margins, it still does

not look like it will cover 180 degrees in the full frame. My guess is

around 160. Has anyone verified this on film?

 

Also, has anyone used the rear filter clip for a gel polarizer? Do

they even make a gel polarizer?

[stephen hazelton]

The 180 degrees is measured across a diagonal, I assume- is this the way you're looking at it?

[WJT]

Hi Steve. I believe Edmund Scientifc (Optics) has sheets of various polarizing material. Shouldn't be too hard to fabricate a filter. Regards.

[carina]

Though I have never made a filter for this particular lens, if you decide to do it, check ebay auction center for sheets of filters. A friend recently bought two 8x10 sheets of military surplus polarizer. It had no real label or identification on it, but it was made and labeled "Polaroid Polarized PP1-11". It was military surplus. A friend -I think- wedged it between two sky filters glass, and put it in a mount to use on the old 55mm, which used the old, BIG, odd sized filter. Anyways, he is quite pleased with the material and it cost less than 10$ with free postage. Just a thought. I have seen similar products at photo shows, often made my Polaroid, and also some which I think were Bausch & Lomb. Might be the same basic material as Edmunds, and may or may not be a better price. The infrared stuff is VERY expensive, but the polarized much much less so.

[steve_rasmussen]

Walter, I bought some of the Edmund Sci polarizing sheet when I tried to make a front polarizer for my 400mm Takumar. I was successful in fabricating the filter but the test for sharpness of the finished product proved that the sheet was not high enough optical quality to be used. The resulting photos were all soft. But, front filters on long lenses have to be very flat or it can be seen on the film. A rear filter on a short lens is not nearly as critical. I will try it since I still have some of the sheet.

[steve_rasmussen]

I re-checked the angle of view by removing the TTL and viewing the screen. It does appear to be 180 degrees. In rectilinear lenses, angle of view is a linear function of the focal length. If the 35mm were rectilinear, it would cover around 130 degrees. Since it has a moderate amount of barrel distortion, it covers 180. This lens could have been made with even more distortion and the coverage would have been even greater(but the front element would have to be even more steeply curved). So, there are all different degrees of fisheye effect/distortion, based on mathematical formulas such as the Sine Law and the Fisheye Law. The more barrel distortion there is in these lenses, the more the field of view will be.

[steve_rasmussen]

My investigation of fisheye lenses and distortion has led me to the conclusion that several lenses with differing focal lengths can have the same angle of view! You can have a 45mm, 40mm, 35mm, 30mm and 25mm lens, all with the same angle of view, and differing amounts of barrel distortion. The 45mm would have the most, the 25mm the least.