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02-16-2014, 12:05 PM   #1
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Difference between FA50 1.7 and F50 1.7?

Is there any measurable difference between these lenses? I see cosmetic differerences, but is one actually different from the other? Based on the reviews going back to the 1970s, both these lenses seem to be electronic versions of the Pentax-M 1.7, at least if performance is measured. Is that right?

The F line was updated to be the FA line, so there must be *some* difference. But what?

02-16-2014, 12:21 PM   #2
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Some are going to argue my point here, but there are minor differences. I find the older M lenses sharper. I also thing the F line is sharper than the FA line. Technically the two lenses are the exact same optically. In my experience the F is more prone to finging but gets sharper as you stop it down. I dont think the coating is any different. I think mainly what I am seeing is copy variance.

That being said, the DA50 1.8 is said to outperform the older lenses by a small margin and is less expensive.

Last edited by j2photos; 02-16-2014 at 12:31 PM.
02-16-2014, 12:24 PM   #3
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I find the F series a bit snappy as well as noisy during AF. The FA seems to be dampened a bit.
02-16-2014, 12:44 PM   #4
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The FA can set the MTF program line on cameras that can use it (K-20D, K-7, K-5, K-5 II/IIS, K-3), the F can't.

The FA line has a lighter build than the F line.

I got my FA for $100 so I might be a bit biased...

02-16-2014, 01:07 PM   #5
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QuoteOriginally posted by boriscleto Quote
The FA can set the MTF program line on cameras that can use it (K-20D, K-7, K-5, K-5 II/IIS, K-3), the F can't.

The FA line has a lighter build than the F line.

I got my FA for $100 so I might be a bit biased...
That was your lucky day!
02-16-2014, 01:20 PM   #6
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QuoteOriginally posted by ramseybuckeye Quote
That was your lucky day!
I also got a PZ-70 and a Tamron 28-200 with it, so yes, I was lucky.
02-16-2014, 01:23 PM   #7
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While I love my F50, it is a loud beast. Some of my best shots have been with the M50 1.7 and I just received the DA50 1.8 so I still need to do more testing with it.
02-16-2014, 01:25 PM   #8
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They are equally good, optically.



02-16-2014, 02:06 PM - 2 Likes   #9
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First of all, be aware that lenses like the FA43, DA*55, and K or A50/1.2 are in a whole (higher) class by themselves. If you're considering one of those lenses, the differences between these F and FA 50s are moot.


When you say "measurable differences," you realize that none of the tests which are commonly run account for all of the differences that you will actually see when you look closely at the resulting photos. In some cases they measure a quality inadequately; in others they omit it completely. Also the glass changes slightly with each generation, so even though an F and an FA may use an identical optical formula, the end products aren't "optically identical."


With this in mind, there are small differences in optical quality (as well as handling, like previously mentioned). If you read the reviews you know that the FA50/1.7 is considered slightly better than the F version, while with the f/1.4 models the F50 is considered the better one. Additionally, many people prefer the 1.7s to the 1.4s.


So I picked up an F50/1.7, an FA50/1.7, and an F50/1.4. I didn't bother getting an FA50/1.4, because I could already tell from both other's reviews and the images I wouldn't like it as much. If I was going to get one of the f/1.4s, it only made sense to get the one I was already 90% sure I'd prefer.

It turns out (unsurprisingly) the reviewers aren't crazy. It was hard for me to decide between the FA50/1.7 and the F50/1.4. Each had its unique, desirable qualities. In the end the F50/1.4 seemed slightly more special in it's image qualities, and it already had fairly nice IQ at f/2. Bear in mind they all need to be stopped down to either f/2 or f/2.2 (depending on the lens) in order to avoid a significant loss of IQ, and are really better at f/2.8 or narrower.


Soon afterward I got the FA43. It beat all of them at any aperture. Game over - I sold all 3.

Last edited by DSims; 02-16-2014 at 02:34 PM.
02-16-2014, 03:50 PM   #10
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QuoteOriginally posted by DSims Quote

Soon afterward I got the FA43. It beat all of them at any aperture. Game over - I sold all 3.
Agreed. The FA43 is a miracle of a lens. In terms of total package (all things considered) I find it impossible to beat in this range.
02-17-2014, 05:07 PM   #11
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Thanks guys! Information here helped me make a very informed choice!

I realize that there are better lenses out there, but this will occupy a "let's goof around" role for me more than anything else. I use my old K f/1.4 from time to time when I want to do isolation shots or other artsy stuff, but I rarely consider these shots essential. I love the K lens, but manually focusing it is a pain and makes it unsuitable for anything that moves, or even people--I try their patience with my slow focusing. (Have to be super precise at f/2!)

If I find myself using this lens a lot more than I expect, then I will look to step up to something more fancy.
02-18-2014, 09:42 AM   #12
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I owned 2 copies of each, F and FA version and did some compare test.

Frist of all, copy variation plays more in terms of sharpness if you compare two versions. And I guess we should always keep that in mind. Photozone post their test result from only one lens is not reliable. They might got a good one or bad one.

Back to these two versions, the biggest difference is color. F version is cooler and FA version is warmer. I guess pentax upgraded/changed SMC coating formate.

F version has bigger copy variation and the two FAs are more consistent. Although that could just be my copies, the build quality is better on FA version. F version is less dampened and a little more wobbly.

F version could suffer from blade oil much easier that FA version. I had one mounted on camera, left in the car for about 2 hours in Texas summer, come back and had oil on blades. Had to send it to Eric for cleaning.

Sharpness is very hard to say, both versions are very sharp in center even at F/1.7, but maybe slight better aberration control on FA makes it looks a little better than F version.

Can not tell any difference in bokeh.

F version has nosier AF.
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