I started with the Pentax ME Super in 1983, and have an old 28mm f/2.8 lens that I still use today with my K-5, and I use it on TV mode, i.e. aperture priority mode, and it works good.
I persuaded my nephew to give me the 50mm f/1.7 lens my dad used on his old Pentax ME Super. Dad delivered it to me last week, and I used it on TV mode, but the results were awful. I reviewed the EXIF and saw that indoors at f/1.7 or slightly above, the shutter speed was way too fast, as in 1/800, and 1/640. The images were blurry, orange, and unusable.
Tonight I experimented in manual mode and was able to get a decent image in limited light by slowing the shutter speed, and setting the ISO a bit higher, and putting the aperture near f/1.7 or f/circa 2.4.
I looked in the lens, and I see sort of bubbly material but no fungus.
Why won't it work in TV aperture priority mode, whereas my equally as old f/2.8 28mm lens does work in TV mode?
I experimented tonight to see if I could figure out if it is the settings, or dirt in the lens. The first photo is in TV mode. The second photo is after I experimented in manual mode. (I am not proficient yet at manual mode - my ME Super spoiled me).