F28 2.8 versus FA28 2.8

Wild Mark · 10-30-2015, 10:21 PM - **3 Likes**

Ever wondered what the differences are? A quick test to see if they differ.

Background is the F28 was the first AF Pentax 28mm. It had the same optical formula as the A28/2.8 with slightly different coatings (apparently). The FA28mm was the next AF Pentax lens. The optical formula changed to include an aspherical element. SO, there should be differences, but where and how much?

I snapped these two lenses onto my K5iis planted on a tripod out on the street. Shot with no shake reduction in P mode. Shot from f2.8 to f10 in quick succession.

Results? Surprising!

FA28 @f10

FA28 @2.8

F28@ f10

F28 @ f2.8

Findings:

1. F28 sharper through all apertures to f10
2. F28 better contrast
3. FA28 marginally better CA control, but very little in it - very little
4. F28 better more accurate colours

In this simple test I can clearly demonstrate that the F28 is a better lens, and substantially so. Pixel peeping really shows the differences. No doubt about it, the F28 copy I have is superior to the FA28 counterpart.

Gray · 10-30-2015, 10:41 PM - **1 Like**

A possible reason for the difference in optical qualities between the F 28 and FA 28 is that the FA has an almost identical layout to the FA 28 SOFT lens. Pentax may have done this for manufacturing efficiency, to share lens elements between the normal and soft FA 28s. Creating a soft 28 lens using the older F / A / M (ver 2) series layout may have been impractical.

FA 28 / FA 28 SOFT (from Bojidar Dimitrov's Pentax K-Mount Page)

F 28 / A 28 / M 28 (version 2)

Wild Mark · 10-30-2015, 10:49 PM

Hey that is really interesting and I didn't know that little fact. Makes sense too as there are clear differences in sharpness. There could be copy variation in play, but, I do think the 7 element design should perform better.

The FA28 is not a slouch of a lens, just not in the same league as the F28.

npc · 10-31-2015, 03:03 AM

When I tested my two copies on my kolari modified A7R (along with I think every possible 28mm Pentax lens ever made ) I've found the FA to be better than the F and probably the best of all 28mm at least at infinty. Differences were not that big between the two, but as others have mentioned FA has better CA control which is more apparent in the border/corners areas that are outside of the APS-C zone and also better sharpness there. I've found the two to be more or less equal in the center. I've kept the FA and the K 28 f3.5 which was the best of the manual focus ones ( and it is more pleasant to use on A7R)

zapp · 10-31-2015, 04:22 AM

Sorry, but I don't think that your test shows anything.
Did you notice that the FA lens has autofocus. This is the main difference.

fwcetus · 10-31-2015, 05:39 AM

Originally posted by zapp

Sorry, but I don't think that your test shows anything.
Did you notice that the FA lens has autofocus. This is the main difference.

And doesnt' the F lens have AF too ? [Not a difference.]

fwcetus · 10-31-2015, 05:41 AM

Originally posted by npc

When I tested my two copies on my kolari modified A7R (along with I think every possible 28mm Pentax lens ever made ) [...]
I've kept the FA and the K 28 f3.5 which was the best of the manual focus ones ( and it is more pleasant to use on A7R)

Are you dismissing the K 28/2 when you say the K 28/3.5 is the best MF 28, or are you saying so just for your own lenses ? (Was the K 28/2 one of the "every possible 28mm Pentax lens ever made" that you tested ?)

Last edited by fwcetus; 10-31-2015 at 06:01 AM.

pathdoc · 10-31-2015, 06:05 AM

I think npc's point is well made. Wild Mark's pictures indicate to me that there's nothing lost by buying either version for APS-C; I can't pick the difference on the pics here, though I accept that he's describing the findings as he interprets them, and I don't question their validity. It's just not what I'm perceiving at this resolution.

Gray's development history is interesting. Many thanks for that.

**UncleVanya** · 10-31-2015, 07:44 AM

Originally posted by zapp

Sorry, but I don't think that your test shows anything.
Did you notice that the FA lens has autofocus. This is the main difference.

F and FA series lenses are functionally similar, the main difference being that the F series has no MTF information to share with the camera. Both are screw drive autofocus, have fully automatic aperture control from the camera, have aperture rings, etc. The F series is often heavier due to more metal vs plastic construction.

audiobomber · 10-31-2015, 08:19 AM

I had an F 28 2.8 followed by an FA 28. I found CA on the F lens to be objectionable and preferred the colours from the FA. I didn't own them at the same time but I didn't notice any other IQ differences.

The FA 28 is a nice landscape lens, but the FA 35 f2 murders it for anything else, similar colours and much sharper at wide apertures.

troika · 10-31-2015, 10:04 AM

Originally posted by audiobomber

I had an F 28 2.8 followed by an FA 28. I found CA on the F lens to be objectionable and preferred the colours from the FA. I didn't own them at the same time but I didn't notice any other IQ differences.

The FA 28 is a nice landscape lens, but the FA 35 f2 murders it for anything else, similar colours and much sharper at wide apertures.

Thanks to the OP for posting this. I feel that Pentax is really missing a wide/fast prime right now. No 28mm or 24mm prime and the 21 is a bit slower than 2.8.

I bought a new FA 35/2 on-sale a few years ago, without much enthusiasm and like audiobomber, I'm very happy about what it can do. I borrowed an F28/2.8 a few years ago and found it a perfectly factional lens, but compared to the 35/2, it wasn't close in terms of image quality or usefulness.

Too bad there isn't a wider option available to us in production that can match it.

**Just1MoreDave** · 10-31-2015, 11:34 AM

Originally posted by UncleVanya

F and FA series lenses are functionally similar, the main difference being that the F series has no MTF information to share with the camera. Both are screw drive autofocus, have fully automatic aperture control from the camera, have aperture rings, etc. The F series is often heavier due to more metal vs plastic construction.

The FA has 6 blades vs. 5 for the F - probably not a big deal either way. I like my F enough to stop shopping, assuming that the FA might be better but not better enough.

elementdtlop · 10-31-2015, 12:04 PM

Originally posted by troika

Thanks to the OP for posting this. I feel that Pentax is really missing a wide/fast prime right now. No 28mm or 24mm prime and the 21 is a bit slower than 2.8.

I bought a new FA 35/2 on-sale a few years ago, without much enthusiasm and like audiobomber, I'm very happy about what it can do. I borrowed an F28/2.8 a few years ago and found it a perfectly factional lens, but compared to the 35/2, it wasn't close in terms of image quality or usefulness.

Too bad there isn't a wider option available to us in production that can match it.

the fa 31 is close and the sigma art or the older 30 are 1.4. i know its not quite as wide. unfortunately the samyang 24mm isnt af but its a pretty nice looking lens even though its prob the least liked of their lineup from what I've heard.

jddwoods · 10-31-2015, 12:06 PM - **1 Like**

Originally posted by pathdoc

I think npc's point is well made. Wild Mark's pictures indicate to me that there's nothing lost by buying either version for APS-C; I can't pick the difference on the pics here, though I accept that he's describing the findings as he interprets them, and I don't question their validity. It's just not what I'm perceiving at this resolution.

Gray's development history is interesting. Many thanks for that.

If you look at the sign on the left side that says School Days and the yellow fence to the right of the School Days you can see the difference in resolution. Actually I would be happy with either lens and it just so happens that I have the F 28mm 2.8 that I bought new back in 1990. I cannot recall though, how much I paid for it, but it still gets use on my K-5 and K-3 bodies.

Wild Mark · 10-31-2015, 02:18 PM

Originally posted by jddwoods

If you look at the sign on the left side that says School Days and the yellow fence to the right of the School Days you can see the difference in resolution.

Well picked up and that is what I noticed with the benefit of 100% enlargement.

Thanks to all comments. I am no guru tester and I am sure there are many errors in my ways. That said, I tried to keep things as honest as possible and in so doing found a difference. It could be that the F28 is a super good copy and the FA28 a super bad one. Or the FA28 is bad, or the F28 is good and the FA28 is within spec. You chose the possible reasons. My reality is the F28 performed better and noticeably so.

Anyway, there is resolution difference. Quite noticeable. And, the F28 has no worse CA performance than the FA28, although slight improvement in the FA28 was discerned. I found the differences surprising as I was lead to believe the FA28 was superior (hence my reason buying one).

I will try and post some 100% crops for viewing.

10-30-2015, 10:21 PM - 3 Likes	#1
Wild Mark Veteran Member Join Date: Jun 2013 Location: Newcastle Photos: Gallery \| Albums Posts: 1,954	F28 2.8 versus FA28 2.8 Ever wondered what the differences are? A quick test to see if they differ. Background is the F28 was the first AF Pentax 28mm. It had the same optical formula as the A28/2.8 with slightly different coatings (apparently). The FA28mm was the next AF Pentax lens. The optical formula changed to include an aspherical element. SO, there should be differences, but where and how much? I snapped these two lenses onto my K5iis planted on a tripod out on the street. Shot with no shake reduction in P mode. Shot from f2.8 to f10 in quick succession. Results? Surprising! FA28 @f10 FA28 @2.8 F28@ f10 F28 @ f2.8 Findings: 1. F28 sharper through all apertures to f10 2. F28 better contrast 3. FA28 marginally better CA control, but very little in it - very little 4. F28 better more accurate colours In this simple test I can clearly demonstrate that the F28 is a better lens, and substantially so. Pixel peeping really shows the differences. No doubt about it, the F28 copy I have is superior to the FA28 counterpart.

10-30-2015, 10:41 PM - 1 Like	#2
Gray Veteran Member Join Date: Oct 2011 Location: Cape Town Photos: Gallery Posts: 536	A possible reason for the difference in optical qualities between the F 28 and FA 28 is that the FA has an almost identical layout to the FA 28 SOFT lens. Pentax may have done this for manufacturing efficiency, to share lens elements between the normal and soft FA 28s. Creating a soft 28 lens using the older F / A / M (ver 2) series layout may have been impractical. FA 28 / FA 28 SOFT (from Bojidar Dimitrov's Pentax K-Mount Page) F 28 / A 28 / M 28 (version 2) Last edited by Gray; 10-30-2015 at 10:47 PM.

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10-30-2015, 10:49 PM	#3
Wild Mark Veteran Member Join Date: Jun 2013 Location: Newcastle Photos: Gallery \| Albums Posts: 1,954 Original Poster	Hey that is really interesting and I didn't know that little fact. Makes sense too as there are clear differences in sharpness. There could be copy variation in play, but, I do think the 7 element design should perform better. The FA28 is not a slouch of a lens, just not in the same league as the F28.

10-31-2015, 03:03 AM	#4
npc Veteran Member Join Date: Apr 2013 Posts: 313	When I tested my two copies on my kolari modified A7R (along with I think every possible 28mm Pentax lens ever made ) I've found the FA to be better than the F and probably the best of all 28mm at least at infinty. Differences were not that big between the two, but as others have mentioned FA has better CA control which is more apparent in the border/corners areas that are outside of the APS-C zone and also better sharpness there. I've found the two to be more or less equal in the center. I've kept the FA and the K 28 f3.5 which was the best of the manual focus ones ( and it is more pleasant to use on A7R)

10-31-2015, 04:22 AM	#5
zapp Pentaxian Join Date: Jul 2011 Posts: 2,385	Sorry, but I don't think that your test shows anything. Did you notice that the FA lens has autofocus. This is the main difference.

10-31-2015, 05:39 AM	#6
fwcetus Site Supporter Join Date: Sep 2006 Location: New England Photos: Gallery \| Albums Posts: 1,286	Originally posted by zapp Sorry, but I don't think that your test shows anything. Did you notice that the FA lens has autofocus. This is the main difference. And doesnt' the F lens have AF too ? [Not a difference.]

10-31-2015, 05:41 AM	#7
fwcetus Site Supporter Join Date: Sep 2006 Location: New England Photos: Gallery \| Albums Posts: 1,286	Originally posted by npc When I tested my two copies on my kolari modified A7R (along with I think every possible 28mm Pentax lens ever made ) [...] I've kept the FA and the K 28 f3.5 which was the best of the manual focus ones ( and it is more pleasant to use on A7R) Are you dismissing the K 28/2 when you say the K 28/3.5 is the best MF 28, or are you saying so just for your own lenses ? (Was the K 28/2 one of the "every possible 28mm Pentax lens ever made" that you tested ?) Last edited by fwcetus; 10-31-2015 at 06:01 AM.

10-31-2015, 06:05 AM	#8
pathdoc Pentaxian Join Date: Mar 2015 Photos: Gallery \| Albums Posts: 6,381	I think npc's point is well made. Wild Mark's pictures indicate to me that there's nothing lost by buying either version for APS-C; I can't pick the difference on the pics here, though I accept that he's describing the findings as he interprets them, and I don't question their validity. It's just not what I'm perceiving at this resolution. Gray's development history is interesting. Many thanks for that.

10-31-2015, 07:44 AM	#9
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,401	Originally posted by zapp Sorry, but I don't think that your test shows anything. Did you notice that the FA lens has autofocus. This is the main difference. F and FA series lenses are functionally similar, the main difference being that the F series has no MTF information to share with the camera. Both are screw drive autofocus, have fully automatic aperture control from the camera, have aperture rings, etc. The F series is often heavier due to more metal vs plastic construction.

10-31-2015, 08:19 AM	#10
audiobomber Veteran Member Join Date: May 2008 Location: Sudbury, Ontario Photos: Albums Posts: 6,806	I had an F 28 2.8 followed by an FA 28. I found CA on the F lens to be objectionable and preferred the colours from the FA. I didn't own them at the same time but I didn't notice any other IQ differences. The FA 28 is a nice landscape lens, but the FA 35 f2 murders it for anything else, similar colours and much sharper at wide apertures.

10-31-2015, 10:04 AM	#11
troika Pentaxian Join Date: Dec 2012 Location: Seattle, WA USA Posts: 1,753	Originally posted by audiobomber I had an F 28 2.8 followed by an FA 28. I found CA on the F lens to be objectionable and preferred the colours from the FA. I didn't own them at the same time but I didn't notice any other IQ differences. The FA 28 is a nice landscape lens, but the FA 35 f2 murders it for anything else, similar colours and much sharper at wide apertures. Thanks to the OP for posting this. I feel that Pentax is really missing a wide/fast prime right now. No 28mm or 24mm prime and the 21 is a bit slower than 2.8. I bought a new FA 35/2 on-sale a few years ago, without much enthusiasm and like audiobomber, I'm very happy about what it can do. I borrowed an F28/2.8 a few years ago and found it a perfectly factional lens, but compared to the 35/2, it wasn't close in terms of image quality or usefulness. Too bad there isn't a wider option available to us in production that can match it.

10-31-2015, 11:34 AM	#12
Just1MoreDave Site Supporter Join Date: Feb 2007 Location: Aurora, CO Photos: Gallery \| Albums Posts: 6,340	Originally posted by UncleVanya F and FA series lenses are functionally similar, the main difference being that the F series has no MTF information to share with the camera. Both are screw drive autofocus, have fully automatic aperture control from the camera, have aperture rings, etc. The F series is often heavier due to more metal vs plastic construction. The FA has 6 blades vs. 5 for the F - probably not a big deal either way. I like my F enough to stop shopping, assuming that the FA might be better but not better enough.

10-31-2015, 12:04 PM	#13
elementdtlop Forum Member Join Date: Feb 2015 Posts: 97	Originally posted by troika Thanks to the OP for posting this. I feel that Pentax is really missing a wide/fast prime right now. No 28mm or 24mm prime and the 21 is a bit slower than 2.8. I bought a new FA 35/2 on-sale a few years ago, without much enthusiasm and like audiobomber, I'm very happy about what it can do. I borrowed an F28/2.8 a few years ago and found it a perfectly factional lens, but compared to the 35/2, it wasn't close in terms of image quality or usefulness. Too bad there isn't a wider option available to us in production that can match it. the fa 31 is close and the sigma art or the older 30 are 1.4. i know its not quite as wide. unfortunately the samyang 24mm isnt af but its a pretty nice looking lens even though its prob the least liked of their lineup from what I've heard.

10-31-2015, 12:06 PM - 1 Like	#14
jddwoods Pentaxian Join Date: Nov 2012 Location: Newark, Delaware Posts: 1,035	Originally posted by pathdoc I think npc's point is well made. Wild Mark's pictures indicate to me that there's nothing lost by buying either version for APS-C; I can't pick the difference on the pics here, though I accept that he's describing the findings as he interprets them, and I don't question their validity. It's just not what I'm perceiving at this resolution. Gray's development history is interesting. Many thanks for that. If you look at the sign on the left side that says School Days and the yellow fence to the right of the School Days you can see the difference in resolution. Actually I would be happy with either lens and it just so happens that I have the F 28mm 2.8 that I bought new back in 1990. I cannot recall though, how much I paid for it, but it still gets use on my K-5 and K-3 bodies.

10-31-2015, 02:18 PM	#15
Wild Mark Veteran Member Join Date: Jun 2013 Location: Newcastle Photos: Gallery \| Albums Posts: 1,954 Original Poster	Originally posted by jddwoods If you look at the sign on the left side that says School Days and the yellow fence to the right of the School Days you can see the difference in resolution. Well picked up and that is what I noticed with the benefit of 100% enlargement. Thanks to all comments. I am no guru tester and I am sure there are many errors in my ways. That said, I tried to keep things as honest as possible and in so doing found a difference. It could be that the F28 is a super good copy and the FA28 a super bad one. Or the FA28 is bad, or the F28 is good and the FA28 is within spec. You chose the possible reasons. My reality is the F28 performed better and noticeably so. Anyway, there is resolution difference. Quite noticeable. And, the F28 has no worse CA performance than the FA28, although slight improvement in the FA28 was discerned. I found the differences surprising as I was lead to believe the FA28 was superior (hence my reason buying one). I will try and post some 100% crops for viewing.