I always did suspect that I hadn't got the same lens that AP tested
The trouble is finding one without the separation problem? Mine is only noticeable with a torch and I'm not 100% sure if it is that ? Shining a torch into any lens does make it look a lot worse than it actually is

The best I've found of this range of lenses is the Pentax-A 35-70mm f/4.

I was never happy with the performance from my FA 28-70 f4 and just looking at it now with a torch it could have a slight problem with the cement, but it's never performed very well from new. It did OK in AP tests though.

Slightly heavier the Pentax-F 28-80mm f/3.5 - 4.5 is a decent performer which received high marks in MTF tests in Practical Photography Mag. Nov. 1990. I've found that at 35mm it's almost as good as a decent prime. Very underrated lens IMHO

All the 50mm Nikons were poor compared to the 50mm Omicron's
The 63mm Nikon was a different beast.

Some Nikonite's tried to claim the Omicrons were made by Nikon,
but it was disproved in this post link They were probably made by Tomioka. I have a (rare) 75mm Yashica enlarger lens that
looks similar.

Sadly Omicron's aren't much use as macro lenses, they flare up!

Nikkors are usually OK, but do usually have illuminated scales.
The 50mm f/4 was a dog

And they aren't designed to resist flare and flare up
at the drop of a hat!

A lot of enlarger lenses are poorly built suffering mostly
from misalignement or decentering See 5th post down : link

Rodenstock Eurygon's aren't too bad though, I've got a recent 40mm
f/4 and some Eurygon's were used as camera lenses even macro lenses.
link

I'm not sure what you do about the illuminated scale on an enlarger lens
It will let light though the other way.... needs blanking off somehow.

Edit: This is the same as the one I've got. link
-

A Super Multi Coated Takumar 35mm 3.5 Lens + Caps M42 Screw Fit
went for £81.99 yesterday??? What sort of idiot puts on £81.99
anyway he would have lost to someone bidding £82.00

link

No snipes either (probably too high) just a few idiotic bidders

If you click on Bid History then show Automatic Bids you can
see that someone put a big max. bid on of £80 the day before
and a bidder with 95 wins kept coming back putting on bids a
few pounds higher each time and not winning any of them.

Just cut the aperture lever off any 'M' lens and you can use it like a
pre-set with Av

Up to f/5.6 it's as bright as most zooms so no need to open up.
At f/8 open up to f/5.6 to focus and then back to f/8.
Sometimes you can focus at f/8. I do that with my Russian
135mm pre-sets and only use f/4 ot f/5.6.

Exposure is usually correct from f/4 to f/16
I use manual exposure all the time rather than Av.

I've only cut the aperture lever off a damaged 28mm
and it was very usable afterwards.

A sharp M 100mm f2.8 will beat almost any other Pentax lens around the same focal length You might find this thread interesting .... link it deals with facts not myths and links to MTF tests showing the 'M' beating 3 top macro lenses Plus users who have the 105 and 'M' say the 'M' is sharper.

I'm in the middle of some thorough testing of six 35mm lenses inc. zooms and some of the old mythical stuff is really poor. The 'A' 35-70mm f/4 is on top so far Surprisingly the F 28-80mm is also doing well.
Old Taks (same optically as K) poor with low contrast

As Spike Milligan once said......
I'm a Vegetarian!... I only EAT COWS that EAT GRASS!!

If you don't like kids..... just push them to one side
of your plate!!