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05-13-2012, 05:18 PM   #1
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Lens Review Math

I've seriously got to wonder if some people just want to skew the averages on some lens reviews to make themselves feel more important or vent their anger at Pentax for other perceived slights:

SMC Pentax-FA 31mm F1.8 AL Limited Reviews - FA Prime Lenses - Pentax Lens Reviews & Lens Database

Sure, not everyone is going to adore the 31mm Limited (I personally don't like the 77mm), but without any Pros or Cons listed - how does the math of averages on this work?
  • Sharpness: 5
  • Aberrations: 5
  • Bokeh: 7
  • Autofocus: 6
  • Handling: 6
  • Value: 1
  • Overall Rating: 3

Seems like it's time for the lens reviews section to have a little "built in calculator" for the math-challenged.

05-13-2012, 05:31 PM   #2
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So much for the honor system...
05-13-2012, 07:06 PM   #3
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Not every review weights each category the same. People make excuses for a lens' shortcomings - "AF is slow, I don't care 'cause I'm an MF guy anyway" - and give a correspondingly higher score than the average of the 6 categories anyway, so why not?
05-13-2012, 07:24 PM   #4
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Meh, at least it somewhat balances all the 10s pretty much any Pentax lens seems to get.

05-13-2012, 07:38 PM   #5
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A super high value lens might be perfectly sharp and feel like heaven with no aberrations whatsoever, but if you don't like it you don't like it. Sometimes you just don't like a lens.

And I can imagine after paying the price of the FA 31 and finding out you don't like it, you'd be pretty miffed.
05-13-2012, 08:30 PM   #6
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I don't necessarily agree with his position, however in about 9 paragraphs of explanation, he does provide a reasonable and rational basis for his evaluation and grading. That is a lot more than others have done. So, his overall rating will essentially be averaged (rinsed) out in the wash. Its the spin cycle that will get you every time.

05-13-2012, 09:40 PM   #7
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This is a problem from which many sites that try to rank stuff suffer: is a score representative if every lens has a 8 or 9? Some sites solve this by switching to simpler mechanisms, e.g down- and upvoting.

In the case of gear, perhaps it would be better if you could score them comparatively. Say, you get to sort your zooms, your wideangles, your macros, etc., by preference, then use the ELO system to assign a score.
05-13-2012, 10:15 PM   #8
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Well, I don't really care about the ranking system by numbers - when reading reviews the most important is what they write in description. This guy had done good job explaining his views on FA 31 - I find his opinions similar to those of LensTip review. It's always good to have also a critical review of the lens, if you are deciding to buy it - I had FA31 and it is A great lens....but for the premium price it could be tiny bit better.

05-13-2012, 10:28 PM   #9
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These reivews are more useful than the "10" rating ones with no or little description.

However there is some significant copy variation for this lens, much more so than the other limiteds for whatever reason. For the money paid it's worthwhile getting from a place that has a option to return bad ones. Buyers rightly come to the FA31 with high expectations, and a good copy can meet and surpass those expectations IMHO.
05-13-2012, 10:30 PM   #10
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someone would be foolish to make any purchasing decision based on the numeric ratings in the review pages. thus, the scores are somewhat meaningless but the discussion is invaluable. I respect that he explained his reasoning.

ok, that said, an overall rating of 3 is clearly off target for this lens; at least, it is not within any existing standard of evaluation. I'd have to assume he got a bad copy but if he bought it over time from a friend as he states, wouldn't he have gotten the feeling it was a dud before he paid for it? If i were going to spend that kind of money and the lens was not close to perfect, i would wait to find another copy. so, yes, he is probably sandbagging his review.
05-13-2012, 10:38 PM   #11
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well he stated in review that he borrowed and tried another FA31 with similar results....so more likely he was just expecting more from the lens...
it seems to be demandingv pentaxian - see his review of da 35 macro
05-14-2012, 06:51 AM   #12
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QuoteOriginally posted by mikeSF Quote
ok, that said, an overall rating of 3 is clearly off target for this lens; at least, it is not within any existing standard of evaluation.
I think the larger point is that if you add up the various individual characteristic ratings, and then divide by the number of characteristics, you get an overall rating of "5" not 3. This reviewer goes on and on about Nikon primes and how expensive the 31mm limited is compared to the Sigma 30mm 1.4, but never says why, overall, the lens scores lower than the average of its other ratings...

So, with this obvious numeric disparity, I'm left to imagine the Overall Rating given is a "stomp my little feet" reaction to being disappointed in the price-performance ratio of the lens... which was apparently also "tried out" for a long time, and paid for over an equally long time (don't we all wish we could do that?). That's just confusing, so I can see where a calculator might help.
05-14-2012, 07:02 AM   #13
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Evaluating, rating, weighting and scoring are a science in and of itself. So many folks have their own evaluation and rating criteria, and then through the translation in to a score, who knows what you wind up with. You have here a 0-10, poor to excellent scaling. Folks are also so ingrained to the A=10, B=9, C= 8 - or what ever numerical system you want to assign.

I was working on a very large project, and was tasked with selecting a COTS display system. The customer was spending a very large sum of money on collecting the data/information, and need a very intuitive way of displaying it. The selection method also needed to be shown that the correct / best approach was actually being selected. We setup a criteria and scoring system. No one liked the results. We went through several methodologies - same result, same problems. Hate and discontent. We finally did a 0-10 system, however for meeting the main criteria for each category (with an appropriately weighting), the value of 5 was given. For exceeding, additional points could be given beyond 5, or for not meeting the criteria points could be deducted, and all of this was standardized. The winning selection won with a score of something like 7.2 on the average across all the categories and evaluators. The main criticism was that the score itself was too low. If the selection was the perfect choice it should have a near perfect score of 10. A Bo Derick's perfect 10.

We spent a couple of week with 20 some engineers, and with the customer involved - no one wanted to be left out. Categorizing, evaluating, weighting, rating, scoring, arguing that whatever the system was - the results were being cooked. Changing, redefining, and redoing the whole evaluation multiple times. In the end we went through the exercise with about 8 to 10 approaches and methodologies. It was funny that they all came to the same conclusion and selection. With so many rating systems, we could perform a sensitivity analysis across all of them and that showed that we were essentially making a very reasonable selection.

In the end, we produced a system with this selection as the front end. Everyone felt that the selection was the best, most appropriate for the task. So it was a winner. We had buy in from across the board - and a happy and satisfied customer.

05-14-2012, 07:47 AM   #14
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Hi,
Everyone's entitled to one's own opinion. But what puzzles me is this guy was renting this lens and then bought it out. If you rate the lens at 3 and don't recommend it to friends why to put so much time and money into it? It's not like he bought it on ebay and got stuck with it. It's not like this lens was great at the beginning and then, all of a sudden, became bad.
Something's fishy with this guy...
05-14-2012, 07:50 AM   #15
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Can someone with a grade A copy post a wide-open shot of a test chart? I am curious as to what a good copy of this lens should look like.

I also understand probably 50% or more of the FA31mm produced have some degree of hood wobbleness; the reviewer's copy may have had a slightly more wobbly copy.
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