[drypenn]

I know that the DA 21 is not as well acclaimed as the venerable 35/2.8 nor the much-touted 15/4, but how will it fare against the much rarer and quite expensive ancestor the FA 20/2.8. At the moment, there's a big hole in my "wide" focal length but I'm leaning towards the 20/2.8 despite the older coating. (Besides, it's FF )

Am I thinking it right?

[Jannis]

I don't own FA, but for about 1 year I'm using HD 21 ltd - And I must say that it perfectly fits to my needs. It is not as sharp as 35ltd or 100Macro, but it has character - nice color redention, vibrance, clarity. I mus say that I'm very pleased with results and finally had choose DA21ltd over DA15ldt.
My 2 cents.

[pathdoc]

Practical considerations may override optical ones. It depends on how strongly you as an individual are planning for a full-frame future. If your heart is absolutely set on the FF and you want a lens that will make full use of it, you need the FA 20/2.8; don't you? If you trust in the FF to have a good DA-compatibility mode or you're happy to stay with crop for the foreseeable future, the DA21 is probably more the way to go.

[bdery]

At the price it does for, the more desirable DA21 is a bargain (over the HD). The FA20 is very, very good, but to me it lacks the character of the 21 (I don't own it, mark me). I think the 21 has a "less than stellar" reputation mainly because it's f3.2. But it's fully usable even wide open, and really delivers consistently.

[grahame]

I think the 21 has a "less than stellar" reputation mainly because it's f3.2.

IMHO, F3.2 is fine for this lens. I played with F3.2 on DA21 sometimes, but most time I stop down to 5.6 or smaller.
Color is great, very sharp in the center or most part of the frame. But the biggest issue is the boarders never gets sharp enough even at F8 for city or landscaping.

FA 20 is much better in corners, but still not as good as I thought it would be as an FF lens. I tried FA 20 on A7. FA20 also has to be stopped to 5.6-8.0 to get good performance at corners. Not bad for landscaping, but it might disappoint someone.

i have to say, the lens design has been changed so much in the past decade (or maybe film vs COMS?). Modern lenses are designed to perform better at larger aperture, and older lenses leave bigger space to improve from wide open to optimal aperture.
an other example is FA 501.4 and DA 55/1.4. 55 is much sharper at f1.4 than the older FA 50. At f 1.8-2.0, DA55 is already excellent, stop further to F5.6 improves only slightly; FA 50/1.4 is not comparable at larger aperture, it has to be stopped to 2.8 to get close performance as DA 55. however, at F8.0, my FA 50 is sharper than DA 55.

I used to shot F11 on film, but like to use f2.8 or bigger aperture on DSLR, although I can easier put ISO on SDLR at 800, much more sensitive than 100-200 film I used most. Why? I don't know.

[tvdtvdtvd]

I think the 21 has a "less than stellar" reputation mainly because it's f3.2.

2.8 vs 3.2 is really not a big deal in this age of uber-ISO.

For me, the DA21's less than stellar reputation has nothing to do with speed but rather, reliability. Or at least
my perception of it's reliability. I keep moving the DA21 to the top of my want list but then ultimately pass on
it after re-reading the numerous reports of spontaneous disassembly. Common sense tells me there are
more non-problematic copies than bad and yet I hesitate. In the meanwhile I continue to keep my eyes open
for a 20mm despite the fact that they're much larger and heavier.

[grahame]

spontaneous disassembly

Actually there are also reports about DA 70, and maybe DA 40. I owned and used all of them quite a lot, and never had any problem. I guess this is quite rare, but is very dramatic and catches a lot attention. it is much more reliable than SDM :-(.

[tvdtvdtvd]

Actually there are also reports about DA 70, and maybe DA 40. I owned and used all of them quite a lot, and never had any problem. I guess this is quite rare, but is very dramatic and catches a lot attention. it is much more reliable than SDM :-(.

Yep, I've seen those other reports as well, though the DA21 seems to have appreciably more incidents than any other Limited.
As I said, the rational side of me knows it's an irrational fear. If I understand the problem correctly, it's simply a matter of
three screws that were not glued in place and can loosen over time. The fix is simple: a little thread lock and problem solved,
and I'm comfortable enough with lens repair to tackle something like that. I suppose the core of my fear is that the front element
will come loose and separate without warning just as I'm leaning over a cliff or parking garage wall and then the 'fix' will involve
a bit more than cementing three troublesome screws. You see, I told you it was irrational.

I shy away from SDM enabled lenses as well, though in truth that has more to do with the lens characteristics than the
failures. There's not a one of them that is high on my want list, not even the primes. It's hard to prioritize a $600 fast fifty
when the world is chock full-a inexpensive alternatives. Same for the DA200.

[seventysixersfan]

Have you taken a look at the PF comparison between these two primes?
Pentax-FA 20mm F2.8 Review - Review | PentaxForums.com Reviews

[bdery]

For me, the DA21's less than stellar reputation has nothing to do with speed but rather, reliability. Or at least
my perception of it's reliability. I keep moving the DA21 to the top of my want list but then ultimately pass on
it after re-reading the numerous reports of spontaneous disassembly. Common sense tells me there are
more non-problematic copies than bad and yet I hesitate. In the meanwhile I continue to keep my eyes open
for a 20mm despite the fact that they're much larger and heavier.

I've personally heard of one such event. It doesn't worry me.

IMHO, F3.2 is fine for this lens.

I agree. I was not saying it was bad, just that it contributed to the reputation.

[Driline]

I owned a NON HD 21. Honestly my copy was not that sharp wide open, but I used the lens outdoors at higher F stops anyway and that's where it really shined. It was sharper than My DA*16-50 at 5.6 I think if you're going to use the lens indoors than I would buy the FA 20, if not the DA 21 non HD version can be had at bargain prices plus it provides fantastic starbursts if your'e into that sort of thing

[savoche]

2.8 vs 3.2 is really not a big deal in this age of uber-ISO.

For me, the DA21's less than stellar reputation has nothing to do with speed but rather, reliability. Or at least
my perception of it's reliability. I keep moving the DA21 to the top of my want list but then ultimately pass on
it after re-reading the numerous reports of spontaneous disassembly.

I guess I haven't been paying too much attention since I haven't heard any such stories about the 21. The only lens that has fallen apart on me is the FA31. A real bummer whichever lens does that

[kh1234567890]

IMHO, F3.2 is fine for this lens. I played with F3.2 on DA21 sometimes, but most time I stop down to 5.6 or smaller.
Color is great, very sharp in the center or most part of the frame. But the biggest issue is the boarders never gets sharp enough even at F8 for city or landscaping.

I beg to differ - https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/293019-diff...ml#post3223774

[dms]

From what I have seen and heard the 20mm f/4 smc (M) may be be something you want to also consider.

[PKMike]

From what I have seen and heard the 20mm f/4 smc (M) may be be something you want to also consider.

I sold mine and ended up buying the 21. No regrets.