K_50 aperture block issues / 55-300 PLM lens

karoly7603 wrote:

DougOB wrote:

karoly7603 wrote:

My Pentax 55-300 PLM has strange aperture behaviour between 98mm-200mm roughly. I set to f4.5 but when I dial it immediately jump to f5.6 I cannot set to f5.0. Below 98mm doesn't have any issue. Does somebody has similar problem? Is it normal?
Thanks.

Uhh.... I think I remember this, it came up a few years ago but I can't remember what it was (I haven't had my coffee yet). I remember testing it though...

What camera body or is it multiple bodies? What shooting mode? Auto ISO?

Let me try to engage my brain/memory...

Doug

Pentax K-70 and I use TAV mode with Auto Iso.

It means is it camera body or lens issue? Funny that I saw a Pentax K-70 photo with the same 55-300 PLM lens here on dpreview gallery at 108mm f5.0, but how is it possible?

I found the old discussion I was thinking of, it was with a 55-300 PLM & KP and the buggy behaviour was when the camera had Program Line set to MTF.  Since the K-70 doesn't have this option I won't pursue that any further...

I tried my 55-300 PLM on my K-70, KP & K-3. I put it in Av mode and dialed down the aperture at different focal lengths. All 3 cameras are set to 1/3 EV stops. I tried it with both fixed ISO and Auto ISO. All cameras behaved exactly the same.

From 55mm to approx 100mm I could dial in 4.5, 5.0, 5.6, 6.3, ...

From approx 100mm to approx 150mm I could dial in 4.5, 5.6, 6.3, ...

From approx 150mm to ... something... I could dial in 5.6, 6.3, ...

I am guessing that between 100mm and 150mm the maximum aperture is (close to) 5.0 but it is displaying 4.5.  I didn't take any test pictures to see what was actually being recorded in the image file exif data.

Doug