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Forum: Pentax SLR Lens Discussion
08-12-2015, 03:57 PM
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Which 40 ltd are you using, SMC or HD? Mine is an SMC and feels like it's in focus closer than that, though it could just be that I'm a worse judge of distance than I think!!
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Forum: Pentax SLR Lens Discussion
08-11-2015, 06:44 PM
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You need to fit the 35 Macro somewhere in between those. Now how are you looking? :p
Still, you make a valid point - there must be a lot of people whose use of zoom lenses lies at or near the extremes, and/or for whom the ultimate question is one of space in the camera bag. Or if you're not financially challenged, get yourself Tilley's Vest of Many Pockets and find out just how many Limited primes you can stuff in there.
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Forum: Pentax SLR Lens Discussion
08-11-2015, 12:19 PM
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Because, to be humorous, they need to take all the glass from all those primes and shove them inside the zoom casing... :p
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Forum: Pentax SLR Lens Discussion
08-09-2015, 09:04 PM
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And in that case it's your call as to how much smallness and lightness you are willing to sacrifice for the zoom's flexibility. For some, the answer is "none"; for others it's quite a bit!
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Forum: Pentax SLR Lens Discussion
08-09-2015, 05:43 PM
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The trouble lies in how you reproducibly quantify such things. If they can be quantified all the better, but it seems to me that bokeh is hopeless in this regard - it's a aesthetic quality, after all, and what is pleasing to some may be displeasing (or insufficiently pleasing) to others.
If you want true macro capability, buy a true macro lens is my call. People who don't want macro capability do not NEED to buy a macro prime, and their otherwise excellent prime doesn't need to be judged as wanting if pitched against a zoom that has this feature. If your zoom lens has macro capability, that needs to be judged against a dedicated macro prime that falls within its focal length range.
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Forum: Pentax SLR Lens Discussion
08-09-2015, 04:51 PM
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I chose this in order to keep things on an even technological playing field - it wasn't fair IMO to ask primes with previous generations of coatings, or those designed with slide rules rather than computers, to match zooms (and design teams!!) which had all the tech advantages. Nor was it fair to ask a zoom to always beat a * rated prime.
Resolution is the first one that comes to mind, whether in line pairs/mm or line widths/picture height or whatever it is. What the peak is, how it varies across the field of view at various focal lengths and apertures. The camera body, sensor, processing algorithms and firmware iteration involved would have to be specified to allow the figures to be reproduced independently if so desired.
Ultimately whether you believe in peak resolution or best average resolution across the field as the ultimate measure is up to you, but it must be remembered that even this has different meanings in different settings - a portrait photographer is willing to sacrifice resolution at the edges because the important part of their subject is in the centre, whereas the landscape photographer would want constancy from edge to edge with "no alarms and no surprises, please".
The other measure that comes to mind is distortion. The less of this, the better, of course - and even in the case of fisheyes and other lenses where distortion is a feature rather than a bug, I'm sure there are fisheyes with good distortion patterns and those with bad. (Perhaps someone with experience with fisheyes can chime in and explain how this might work.)
Things like wide aperture or macro capability do not, in my opinion, make any zoom "better" than a prime that doesn't have them - in the end, it still comes down to how those lenses deliver the designed features at their super-duper wide aperture or with the front element practically rammed up the bug's nose, and in this respect the performance is the leveller. It doesn't matter if your zoom lens is a 10-600mm f/0.9 macro if the image quality is worse than a shoebox pinhole camera using 70's vintage 110 film that the owner dug out of their grandfather's broom closet in the hottest part of the monsoon.
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Forum: Pentax SLR Lens Discussion
08-09-2015, 07:53 AM
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Alternative definition of S.O.P.: "A zoom lens which - in reproducibly measurable ways - equals or outperforms all consumer level primes of the same vintage from the same maker across its focal range."
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Forum: Pentax SLR Lens Discussion
08-09-2015, 06:24 AM
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I wasn't looking for science; I was looking for philosophy. But there's been a fair bit of wisdom among it all. Thank you.
I seem to have started a p#ssing contest between lenses. :( My apologies to you all. That was not my intent.
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Forum: Pentax SLR Lens Discussion
08-09-2015, 02:11 AM
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The trouble with the 50-135 is that there is no contemporary 135mm (I.e. DA HD DC) prime to compare it to at the long end. Clearly one is required! Come on, Pentax; fill that gap! :)
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Forum: Pentax SLR Lens Discussion
08-07-2015, 11:05 AM
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Thanks for the clarification, boriscleto. :)
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Forum: Pentax SLR Lens Discussion
08-07-2015, 10:36 AM
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Sorry to seem ignorant, but can you please explain what the abbreviations MTF50 and LW/PH mean?
In the last chart/table, you compare the 60-250 at 135mm to the "70 Macro" (which company? I didn't think Pentax made one) and then there is a table listed at 100mm. Did you in fact mean the 100 WR Macro?
By your own definition, it seems that if you're going to compare a zoom to a prime, surely you need to at least make the comparison at the same focal length (and apertures where these are common), NOT the focal length and aperture which is most advantageous to the zoom.
In the end, the issue is which primes you are exceeding. There is a difference between being better than a DA50/1.8 and being better than the DA*55/1.4, isn't there? And it's probably not hard for even a run of the mill zoom lens of today to be better than a third-rate, third-party prime of yesteryear. There has to be some sort of yardstick, otherwise you're comparing apples and oranges.
One thing I will accept from your argument, and that is that it's probably only objective indices like this which enable any sort of comparison. Also, standardisation of testing is important, and it seems to me that not all testing authorities out there agree on the metrics!!
Ultimately there is that mysterious quality called "rendering", which I'm not sure we will ever be able to quantify, any more than we can hope to quantify any aspect of human art. And that's what stops us all from ending up with the same basic lens (or set thereof) on the same basic system. Which is no help at all for LBA sufferers, but it does keep things interesting. :)
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Forum: Pentax SLR Lens Discussion
08-07-2015, 08:16 AM
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I've heard it applied to the Sigma 18-35/1.8, with good reason, and if only the AF didn't suck so much for some owners and for our forum testers it might have gone on to supplant the 35-105 in that regard.
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Forum: Pentax SLR Lens Discussion
08-07-2015, 08:01 AM
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You hear the phrase used, but what does it mean?
Back in the day, it was accepted that a prime lens was better than a zoom lens - that gap has now closed significantly, and if you're willing to pay enough then I'm sure you can find zooms which are better at any FL than a competently built consumer prime at that same FL.
Back in the day, a K mount prime typically carried a wider maximum aperture than a zoom. Some of the Takumars were relatively slow, e.g. the 28mm f/3.5 and the 135mm f/3.5 version) while these days, some of the limiteds (especially the DA15/4.0) are also on the sluggish side, although it has to be acknowledged that their slower apertures are a deliberate sacrifice in the interest of compactness on the APS-C format.
SO it seems to me that a good rule-of-thumb definition of a "stack of primes" zoom is one which...
a) Has image quality at least equal to a consumer-level prime of approximately equal vintage from the same manufacturer (e.g. no-one's asking it to outdo an FA Limited or * prime, although it's a bonus if it does, and it's not fair to pit yesterday's lens formulae and coatings against today's). IQ to be judged on the basis of sharpness, resolution, resistance to CA and flare, minimal or easily correctable distortion, but NOT Bokeh, as this is IMO more a matter of individual taste.
b) Has a relatively fast maximum aperture, which it retains throughout the zoom range (f/2.8 seems a reasonable yardstick here, although f/3.5 might be acceptable if IQ is particularly good).
What are the thoughts of others? I'm not necessarily asking for candidate lenses (that's a direct road to the hell of heated arguments); I'm more interested in your views on criteria.
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