P67 f4.5 75mm lens surprising design ?!!

[dpurdy]

I just got one of these 4.5 75mm lenses and it is not what I expected in that I thought it would be a very small light lens.

With the Rolleiflex the 3.5 75mm lens is quite a bit smaller and lighter than the 80mm f2.8, so I thought the Pentax 75 f4.5 would be smaller than the 90 f2.8 or the 105 f2.4.

But instead it is a relatively enormous lens with a much larger filter diameter and a big round (like half a globe) front element. I don't get it. 5 elements in 4 groups.

I have researched all the Pentax lens info I can find including reading the Pentax lens book I have and I haven't found one bit of information on it or if it is special in some way.

Any one here have some lens design knowledge and could share why this lens is so seemingly different than the other P67 lenses and so big?

Thanks
Dennis

 

[archphoto]

The difference between a 2.8/80mm for a Rolleiflex and the AP lens is to start-out the image it has to cover (6x6 versus 6x7)
The 75 AP lens is a retro-focus wide angle lens and therefore bigger than the standard 105.

In a bit more modern times lensdesigns have evolved into something that was not held possible 20 years back.
Have a look at the latest 7-14mm lens for Olympus: it looks more like a hefty tele than an ultra wide.

The 75 AP is a nice lens though and will give you good pic's.

Peter

 

[david b]

The Pentax 75mm 2.8 Asphyrical is a 67mm filter thread. The one you bought is a 82mm thread if I remember correctly.

 

[dpurdy]

Yes it is 82mm and bigger than the 77mm on the 55mmlens. I guess the answer is in the retro focus bit.
Dennis

 

[bagdad child]

The old 75mm f/4.5 is actually one of the sharpest P67 lenses and probably the least expensive one of the lot. Yes it's quite big but the build quality is exceptional.