[Bcrary3]

Recently came across a Pentax-A 80-200 f4.7-5.6, just curious if anyone else has used one of these lenses before, I am encountering when I put the lens on the camera that I must manually input focal length, and even at 200, it displays f4.5, not 5.7/ Any suggestions on this?

Thanks

[PJ1]

I have no experience with this lens, but perhaps you could clean the contacts (camera and/or lens) and see if that makes a difference.

[jatrax]

Pentax-A lenses do not communicate the focal length to the camera, you will need to input that.

[PJ1]

Pentax-A lenses do not communicate the focal length to the camera

Well, I learned something. Thanks for that and I am sure the OP will appreciate it too.

[jatrax]

Thanks for that and I am sure the OP will appreciate it too.

You are most welcome. Pentax-F lenses are I believe the first series to communicate with the camera. But that doesn't explain the aperture reading being wrong. Perhaps cleaning the contacts would help that. The possible aperture values that a lens has is read using a pattern presented by the lens contacts. If they are dirty or damaged it could (I think) display that behavior.

[jslifoaw]

A series zoom lenses cannot communicate variable maximum aperture by focal length. So you need to mentally compensate for the fact that at 200mm the actual f number is 2/3 stop higher. You don’t need to do anything special to get the correct exposure but your depth of field will be deeper than indicated.

[StiffLegged]

My 70-210 A series is exactly the same, although the constant f/4 aperture is a bonus.

[othar]

As mentioned, the lens has no way of communication with the camera and therefore can't report the changing aperture accross the focal range back to the camera.
There are multiple ways to deal with the variable focal length the lens offers regarding correct exif data and SR though.
-You could correct focal length everytime you change it, but this is inconvenient and the lens is harder to identify afterwards if you have more than one A-lens with overlapping focal lengths.
-Input the widest focal length, SR will slightly underperform at the long end but the lens is easy to identify because it's always the same focal length in the exif data (I use this option)
-Focal length set somewhere in the middle (~135mm) -> SR will somewhat overreact at the wide end and somewhat underperform at the long end.
-Focal length set at the long end -> SR will overreact at the wide end

[aslyfox]

. .. I am encountering when I put the lens on the camera that I must manually input focal length, and even at 200, it displays f4.5, not 5.7/ Any suggestions on this?

Thanks

as stated, the information you input affects the SR system of the camera

nothing more

I raised this question in another thread the OP may want to review

SR and zoom lens what do you set SR for ?

https://www.pentaxforums.com/forums/58-troubleshooting-beginner-help/422089-...ml#post5238249