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12-11-2016, 07:40 PM   #1
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Lens Reviews A28 vs F28

A little puzzle that perhaps the users here can resolve for me. For background, I recently acquired a m42 SMC 35/3.5 and found the colors out the camera to be superb. So I wondered if a 28/3.5 was worth getting and started poking through the reviews for the 28mm lens variants. There have been a number of threads on which is best and why etc. and I don't really want to get into that. My question is what might distinguish the A28 from the F28 that even though they have the same optical formula they get such different overall scores

A28 based on 48 reviews:
Sharpness 8.8, Aberrations 8.3 Bokeh 7.9

F28 based on 34 review:
Sharpness 9.5, Aberrations 9.0, Bokeh 8.9

The A28 did not come with a hood and I suspect from the comments the F28 didn't either. As mentioned above they share the same optical formula. They also should share the same coatings, and there was a period of overlap where both lenses were in production so they come from the same time period.

I realize reviews are highly subjective, and it is quite possible that early reviews of each of the lenses biased the scores of subsequent reviewers. But maybe there is something else that makes them different, or maybe users of A lenses are a different bunch than F lenses.

I've been somewhat underawed by my copy of the A28; hence my occasional quest to look for something better. But if the F ratings are to be believed, they should both be excellent lenses that leave little for the user to desire at this focal length (except not being a F2.0). Hence my query and openness to hypothesis and speculations, if not concrete reasons why these two essentially optically similar lenses should be viewed so differently.

12-11-2016, 07:46 PM   #2
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More sharp pics because of the presence of AF perhaps?

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12-11-2016, 07:55 PM   #3
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I've never had any trouble getting sharp pics from the A28 even without AF. The pentagonal bokeh can be distracting, but the F has 5 aperture blades too.

My theory is that the A carries over some of the reputation of the M 28/2.8. And the F, being AF, gets a pass on that reputation...
12-11-2016, 08:13 PM   #4
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Most likely a matter of micro-contrast differences giving the appearance of sharpness due to difference in coatings. People also tend to rate on a curve based on expectations and price paid. The 28mm optical formula is not known to produce particularly sharp images, but they tended to be priced fairly low. Certainly the 24mm and especially 20mm film lenses were more highly valued.

12-11-2016, 08:20 PM   #5
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I am a happy owner of F28, and agree with the Auto-focus factor. It could help increase number of keep for users, therefore it got a bit higher satisfactory vote.
An owner of both 28 might be able to give you a better review.
12-11-2016, 09:50 PM   #6
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QuoteOriginally posted by pakinjapan Quote
An owner of both 28 might be able to give you a better review.
I'm hoping such owners might respond. I did wonder if the design of the lens housing might have changed a little. For example, if the distance from the front lens to the edge of the filter thread ring was a little larger on the F lens, it might be sharper without a hood. It may also be that F users rarely shoot at F2.8, whereas A users might, as this might explain the sharpness difference. But the lenses have the same optical formula and same coatings...
12-11-2016, 10:20 PM   #7
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QuoteOriginally posted by MSL Quote
it might be sharper without a hood. It may also be that F users rarely shoot at F2.8, whereas A users might, as this might explain the sharpness difference.
talk about hood, F28 didn't come with a hood. if you not already have done it, It might help if you put on a hood for your A28. I got a cheap metal hood from eBay which work very well on K-5. I select the one with a similar size to hood from FA43.

I shoot at f2.8 many time and it really sharp. on my copy, f2-8 to 16 are good, and it is very good at f4 to 11
12-11-2016, 11:03 PM   #8
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I think you're reading too much into the scores - there's not much between them.
88% vs 95% & 83% vs 90% & 79% vs 89% - taking into account the subjectivity of the reviews, that's practically a tie in my book.
The F would push ahead due to being a generation younger and having AF.

12-12-2016, 03:40 AM   #9
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All of the above.
a) Ratings are completely subjective, and can be heavily skewed. Some people are more critical, some have higher standards, some are more relaxed, some have irrational expectations, etc. All of this together gives you a score which is a good indication, but not enough to allow scientific analysis and comparisons.
b) Even though the optical formula might be the same, there might be differences. Maybe the materials changed a little, maybe the inner barrel is less reflective, maybe one has a better lens hood, maybe the coatings were tweaked a little, etc. The DA 50mm f1.8 is not completely the same lens as the M 50mm f1.7, even if they share optical lineage.
c) Differences in manufacturing. I don't know if this happened for that specific lens, but sometimes over the years machines get upgraded, new techniques get evolved, new product lines open, factories might get moved, a piece of the lens might get outsourced, etc.
d) AF can help people get things in focus and get more consistently sharp photos.
e) Price and look are a factor in the ratings - if a lens looks cool, it will be more beloved. If it comes at a good price, it will be more beloved.
f) Odd connections can happen: For example, it might be that people who buy older lenses are of the type that is more relaxed; or people that love the F series might have different expectations, etc. These things can be invisible, but still affect the rating/polling results

So there are many factors that might be part of this. Its like polling or any kind of market research - there are many variables, and you just hope that the sampling and sample size will drown out the noise

I have first version of M 28mm f2.8, one of the worst-rated Pentax 28mm lenses, and it is good enough on my cameras, so I doubt the A or F versions will be disappointing.

Last edited by Na Horuk; 12-12-2016 at 03:45 AM.
12-12-2016, 04:49 AM   #10
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QuoteOriginally posted by Na Horuk Quote
I have first version of M 28mm f2.8, one of the worst-rated Pentax 28mm lenses
i don't know if that is the worst, the optical performance of the SMCP-K 24mm f/2.8 leaves a lasting depression. Which is probably why the lens never made it to the M lens line up, despite its small size.
12-12-2016, 07:26 AM   #11
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I think the simple explanation is 'mathematics'...or specifically statistics. These sample sizes (34 & 48) are too small by orders of magnitudes to give any degree of (statistical) confidence in the result.
To accurately represent the views of all owners, to within a few percent of certainty, you would need hundreds if not thousands of reviews (depending how many owners there are). The difference there is well within the confidence you can expect with that sample size and so they are essentially the same.
12-12-2016, 08:25 AM   #12
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QuoteOriginally posted by Digitalis Quote
i don't know if that is the worst, the optical performance of the SMCP-K 24mm f/2.8 leaves a lasting depression. Which is probably why the lens never made it to the M lens line up, despite its small size.
It made it up to the A series... Same optics.

Yes it's a lens that is weak in the borders, but I think it was created as an alternative to the larger/slower K 24 3.5... it was created and meant for a time before test charts were all that matter. Some older photographer views on it (from stans-photography.info):
Yoshihiko Takinami - "very sharp, good color saturation/rendition, scarce distortion"
Paul.Stregevsky - . . . "The lens makes me look like a better photographer than I am. What color! And it feels oh so nice in the hand. . ."

I had what I believe was a good copy of it and it was capable of taking very nice pictures, even wide open, especially at closer range. At a longer range sometimes if felt like it wasn't quite as sharp, but it was still very acceptable for me - I don't usually do much pixel peeping. The colors were fantastic and I actually miss that lens more than I thought I would - I traded it for a Cosina made Vivitar counter part because it allowed me to also get a Pentax-M 50 f4 Macro. The Cosina/Vivitar is just as sharp - maybe even a bit sharper, it's a good design from that standpoint, it was even sold branded as a Zeiss Jena. But the colors aren't nearly as nice, and the flaring/loss of contrast in bright situations kind of takes the joy out of it.

Regarding the A 28 2.8... I've had it and wasn't awed by the pictures I took with it under f5.6. From f5.6 on, very sharp and contrasty. But I had a Rikenon 28 2.8 XR that was sharp and contrasty wide open, so I sold that (and also the Version 1 M 28 2.8, which I actually liked better than the A version).

Now recently I got the Sigma 30 1.4 Art so I'm mostly set in that range. I did consider the F 28 2.8 as well, but now that the Sigma 30 1.4 Art is selling used in the 300 dollar range, I don't see why even consider the old F and FA 28 2.8 anymore, unless you need full frame of course, and can't afford the FA 31.

Last edited by ChristianRock; 12-12-2016 at 09:20 AM.
12-12-2016, 09:06 AM   #13
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If you go to some of the older Pentax sites, those who were around before Pentax Forums, you'll see some comments on lenses that differ from the DXO style of review you find here. Read both and you'll get a better all around ideal of what folks think of older glass.
12-12-2016, 09:20 AM   #14
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QuoteOriginally posted by thazooo Quote
If you go to some of the older Pentax sites, those who were around before Pentax Forums, you'll see some comments on lenses that differ from the DXO style of review you find here. Read both and you'll get a better all around ideal of what folks think of older glass.
Like the sites that all hate on the A 135/2.8...there is an old review site where they said it wasn't a sharp lens. This site says sharpness is a 9.5...

For example...Brief Comments Though most of the comments on that site praise the 28/2.8s. Even the M...

Last edited by boriscleto; 12-12-2016 at 09:30 AM.
12-12-2016, 09:36 AM   #15
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QuoteOriginally posted by boriscleto Quote
Like the sites that all hate on the A 135/2.8...there is an old review site where they said it wasn't a sharp lens. This site says sharpness is a 9.5...

For example...Brief Comments Though most of the comments on that site praise the 28/2.8s. Even the M...
Yep and like I said if you read both you'll get a better idea what folks think of a lens.
And I haven't found a 28/ 2.8 that I didn't like....except maybe the Soligor.....
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