So, if I buy the 67 to K mount adapter so that I can cut down on the number of lenses I need to carry in the field, I assume that you need to double the focal length of the 67 lens when you want to know what focal length it represents on a 35mm K mount body.

Given this, can I also halve the maximum aperture?

For example, my 55mm f4 67 lens becomes a 110 f2 K mount lens? (Even better, a 135 f4 67 lens becomes a 270 f2 K mount lens?!)

Seems too good to be true. Enlighten me folks.

-- Deron (dchang@choate.edu), March 02, 2000

Answers

The only thing that changes is the effective magnification of the image, due to the smaller film size. It should be remembered that the K-mount adapter does not allow for open aperture metering so your shooting aperture must be used to meter. This can cause focusing problems because of the finder being fairly dark. SR

-- Steve Rasmussen (srasmuss@flash.net), March 02, 2000.

Technically, the term telephoto is a lens design type and does not apply to image magnification. The 90mm is not a telephoto design but since it magnifies the image nearly 2x that of a normal lens on a 35mm camera, I can understand why people would call it a telephoto. There are some view camera lenses that are 400+mm that are not telephoto designs. SR

-- Steve Rasmussen (srasmuss@flash.net), March 26, 2000.

The 35mm Pentax that might be what you are looking for could be the LX. Winders can be attached to it but I don't believe the LX is a manual camera like the FM2n. The LX is no longer made but was truely a pro 35mm. The KX is Pentax's manual 35mm but I have never seen a winder attached to one. SR

-- Steve Rasmussen (srasmuss@flash.net), March 26, 2000.

You have got it wrong, the focal length and aperture stays the same so your P67 55mm f/4 wide angel lens will be a 55mm f/4 normal lens on your 35mm body, you only use the center of the lens wich is the best part of it.

-- Sigurdur H. Stefnisson (shs@mmedia.is), March 02, 2000.

Nope, you'll be using all of the lens, not just the center. But, your are only using the center of the image circle.

-- tam (tam@smartt.com), March 12, 2000.

Let me put this another way:

55mm lens stays a 55mm lens all the time. OK so far. A 55mm lens on a P67 body covers an angle similar to 28mm lens on 35mm body. A 55mm lens is a wide angle lens on a 6x7 body. But if you put the 55mm lens on a 35mm body you get...a 55mm lens!!! It's just a little more than a normal focal length. So there.

-- Alex B. (samedobrefotke@hotmail.com), March 23, 2000.

Alex: so my 6x7 90LS becomes a telephoto for a 35 mm Pentax (i.e., is still a 90mm lens)?

-- shawn gibson (SeeInsideForever@yahoo.com), March 24, 2000.

Yeah. The focal lengths are measured in milimeters; on the 6x7 a 90mm is "normal", but when put on a 24x36 it becomes a telephoto due to 4,5 times smaller format. But the good part is, you know exactly the focal length - a 90mm is a 90mm in 35mm format.

-- Alex B. (samedobrefotke@hotmail.com), March 26, 2000.

Amazing. Next question, then, though possibly at the wrong forum, is: what's the Pentax 35mm equivalent of a Nikon FM2n? I want to augment my 67 system with a motordriven 35mm system that either has high sync speed (1/125 or so), or will allow me to use my LS shutter...

-- shawn gibson (SeeInsideForever@yahoo.com), March 26, 2000.