Recently Rob Studdert wrote:
>
> If the FA 20 mm f/2.8 and A 20 mm f/2.8 have the same optical formulations
> (as per Boz's site) why then does the Pentax Screen-lens compatibility chart
> indicate differing behaviour between these two lenses using the same
> screens? Any ideas.
Now I know what you are refering to. You've got a new LX screen, and you
are looking at the lens compatibility chart in the screen manual. I
received my new screens too (SC-69 and SG-60), but had not yet looked at
the manuals. I now did, and I saw the differences between these two
lenses:
With some screens the FA 20/2.8 is indicated as "matte gets too dark" and
the A 20/2.8 as "screen corners darken". I would imagine that the
difference results in different people doing subjective evaluations at
different times. I imagine that Pentax assembled the compatibility tables
from existing tables, and didn't care to correct the differences.
As to how sure I am that the A and FA have the same optical formula, I
would say about 70%. Pentax usually mentions when they develop a new
optical formula. Also, when there is a different formula between and MF
and an AF lens, then it is usually that the FA lens is IF, and therefore a
new optical formula is used.
That's my guess anyway. Hopefully someone has a bettwe explanation.
Cheers,
Boz
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