Olympus 17/1.8 review

Started Nov 17, 2012 | Discussions
Jorginho
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Re: Here my tests with 20 mm on EPL5 and Gh2
In reply to Anders W, Nov 18, 2012

Thanks for the link. I have this setting on all day and during daytime it focusses more consistently. I will look at it, these are the standard EPL5 settings I think. I will do another test, but as my black EPl5 is going back tomorrowand the silver arrives on friday it may take some time...

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noirdesir
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Re: SLow focussing seems body reltated mostly
In reply to Jorginho, Nov 18, 2012

Jorginho wrote:

Well, was that not my suggestion after I tiold him what my findings were?

You expected him to amend his review after you had provided him with additional information. But that required Ming to consider your information as accurate and relevant. But how could Ming know whether your estimation of 'fast enough' matches his estimation of fast enough? And focussing speed is not just a single number. And how could Ming know how relevant your information was? There are many camera-lens combinations and if for a few combinations somebody else reports a different experience in relative AF speed (and subjective judgement of), is that such important information that Ming should change his review because this should have convinced him that his report would mislead people?

If for Ming it goes without saying that AF speed experience is subjective and influenced by a lot of parameters, a request to point that out explicitly might easily seem unreasonable.

Again: you say the slow focussing is so well known...I should know that, isn't it? How come that you do not demand the same from Ming when it comes to the behavioru of this lens on Oly bodies? Is that not also well known?? That is my thought on this.

My comment about what is well known and what is not was about why my gut feeling told me that Ming's findings are more relevant and representative than your findings. It is you who is making requests (that Ming change his review), you have the burden of proof why we should believe you.

We have this polemic it seems over what? I wrote this "So I think it is important to note you tested it (most likely, I did not read it) on an Olympus body. On a Panny body, the story is different."

Well, don't you think the phrase 'I did not read it' could be understand as you saying that you didn't actually read the review? Or that the fact that in your reading of the review you did not find the information that his remarks refer to Olympus bodies, when in Ming's mind it was pretty obvious that this information was in there, indicating that you had not really read the review?

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noirdesir
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Re: Macrocontrast vs. Microcontrast
In reply to Anders W, Nov 18, 2012

Anders W wrote:

noirdesir wrote:

Anders W wrote:

Didn't you mean to say somewhere between the 100% and the 50% mark here rather than between 0 and 50%? If yes, then I am all with you.

I think there might be different definitions of microcontrast, as you said that "at least some people use it in reference to contrast at fairly low frequencies rather than very high ones", thus it could be contrast at resolutions between the 0 and 50% mark (but closer to the 50% mark) or it could be the contrast a bit above that.

Yes, but I was thinking about your example with the hypothetical MTF curves and Zeiss versus Leica. In that example, the "Zeiss" (with a presumed focus on microcontrast) beats the "Leica" (with a presumed focus on resolution) at contrast criteria higher than 50 percent whereas it is the other way around at contrast criteria lower than 50 percent.

Ah, I see where the misunderstanding is: when I said below 50% I meant to the left of the MTF50 resolution. Between 0 target resolution and a target resolution corresponding to the 50% contrast mark.

One further question: Would you agree with my assessment that, as far as Ming's images let us judge, the 20 has a better MTF curve than the new 17/1.8? I must admit, I am a bit disappointed at the showing of the 17/1.8 here. I hadn't really expected it to beat the 20 in this regard but I had hoped/expected that it would do about as well. If that had been the case, I would probably have been ready to exchange my 20 for the 17/1.8. Now, I am not so sure.

I'm not sure, my general impression from his review is that the two lenses are relatively close (with a few notable differences like LoCA and vignetting that favour the 17 mm), and closer than I though they would be. But evaluating MTF from a few crops is something I am not really comfortable with, I'd put more weight on his overall comments which I would assume to be based on a lot more (test) images than the ones shown.

OK. Then we simply have quite different perceptions. To my eyes, there is a very clear difference in contrast in favor of the 20 not only at very low frequencies (macro contrast) but also at higher ones. Look at the crops from the bottom-right corner, for example. The individual lines in the grid below the window is clearly visible in the shot from the 20, even wide open, whereas they nearly disappear into a gray patch in the corresponding shot from the 17/1.8. Similarly, the joints (lines) between the concrete blocs in the same corner crops are clearly visible in the shot from the 20 but hardly visible at all in the shot from the 17/1.8.

You see, I simply have very little confidence in a single test image being relevant and accurate. Show me 50 test images taken under varying conditions (and with the greatest care taken to equalise exposure, focus and processing not just for each image globally but also locally for each position in the image) and I might start to have some confidence in the conclusion drawn from them.

For example, if a lens shows vignetting, any crop from the corners will have received a different dynamic range compression during the raw conversion depending on the amount of vignetting making a contrast evaluation on the final image null and void.

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Jorginho
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Re: SLow focussing seems body reltated mostly
In reply to noirdesir, Nov 18, 2012

noirdesir wrote:

Jorginho wrote:

Well, was that not my suggestion after I tiold him what my findings were?

You expected him to amend his review after you had provided him with additional information. But that required Ming to consider your information as accurate and relevant. But how could Ming know whether your estimation of 'fast enough' matches his estimation of fast enough? And focussing speed is not just a single number. And how could Ming know how relevant your information was? There are many camera-lens combinations and if for a few combinations somebody else reports a different experience in relative AF speed (and subjective judgement of), is that such important information that Ming should change his review because this should have convinced him that his report would mislead people?

If for Ming it goes without saying that AF speed experience is subjective and influenced by a lot of parameters, a request to point that out explicitly might easily seem unreasonable.

I only suggested this based on my findings. He wrote is was done on an OMD. Oke. So someone on a forum notes clear differences. I would expect a reviewer at least to ask more about it instead of reacting somewhat irritated. I have arguments with respected reviewers and they did not respnd that way at all. And I really was not easy on them, not like with Ming. This is what I do not understand: it is a lens review, one of the main advantages he mentions IS the AF speed in that it is a night and day difference. BEcause other than that, the differences seem to be minute. It seems to be an essential poiint in his conclusion. Would it not be reasonable to at least ask more about it. Indeed, may be ask me for proof etc. Instead of cutting a discussion on this short by some remakr on an unimportant point. At least to me.

Again: this was a comparison of lenses I feel. Now: if you only read his review, would you not conclude that the 20 mm 1.7 is a slow lens or a much slower lens (significantly slower) than the 17 mm? And, if you have a Panny Gh2 or G5 or whatever, would that be a correct asumption? I think not at all. So I feel my remarks at least shoudl lead to some second thoughts. And that is what I get from other reviewers.

Again: you say the slow focussing is so well known...I should know that, isn't it? How come that you do not demand the same from Ming when it comes to the behavioru of this lens on Oly bodies? Is that not also well known?? That is my thought on this.

My comment about what is well known and what is not was about why my gut feeling told me that Ming's findings are more relevant and representative than your findings. It is you who is making requests (that Ming change his review), you have the burden of proof why we should believe you.

Again: the pint here is not my demand. The point is my response to hjim cutting this short. Personally I would be much more inquisitive as a reviewer and would be thinking of the service I deliver to my readers. If there are indications some findings need further explanation or research, I would personally note it. Of course he could ask me to show this. I could or could not comply. I would have done it immediately. And he could than argue my methodology is not oke etc....Taht is fine. We learn that way.

We have this polemic it seems over what? I wrote this "So I think it is important to note you tested it (most likely, I did not read it) on an Olympus body. On a Panny body, the story is different."

Well, don't you think the phrase 'I did not read it' could be understand as you saying that you didn't actually read the review? Or that the fact that in your reading of the review you did not find the information that his remarks refer to Olympus bodies, when in Ming's mind it was pretty obvious that this information was in there, indicating that you had not really read the review?

I did notr actually read the review nor did I comment on the review. I commented solely on the AF speed of the 20 1.7. I do not need to read the whole review to note that these conclusions are not to be generalised to all m43 cams. I also noted his PF and CA remarks but okey I really read the AF part. With "I did not read it" I solely want to imply that I missed something, I could be wrong when it comes to what he did or did not add to this subject. How is it negative that I wholeheartedly admit I did not read everything??? Suppose he in another section mentions that Panasonic bodies may behave very differently. He could reply that to me and I would said "Oh, okey, then I have no comments at all." I wrote clearly that I did not read all, that I browsed so to make clear I could have missed somehting. But if not, than my findings might be important. I can't see what is wrong with that one bit. But he indeed seemed to take it that way.

Anyways: do think the 20 mm 1,7 on my GH2 was slow in anyway? It was very consistent and indeed, occasionally it will hunt. It just did not show up in my test. But like Anders noted: in general it is not slow at all. On a side note: when I go out during the day with EPL5 and the 20 mm it is not slow either. It is less consistent and indeed slower, buit it focusses between 0,2 and 0,5 s (my estimation).

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Anders W
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Re: Macrocontrast vs. Microcontrast
In reply to noirdesir, Nov 18, 2012

noirdesir wrote:


Anders W wrote:

noirdesir wrote:

Anders W wrote:

Didn't you mean to say somewhere between the 100% and the 50% mark here rather than between 0 and 50%? If yes, then I am all with you.

I think there might be different definitions of microcontrast, as you said that "at least some people use it in reference to contrast at fairly low frequencies rather than very high ones", thus it could be contrast at resolutions between the 0 and 50% mark (but closer to the 50% mark) or it could be the contrast a bit above that.

Yes, but I was thinking about your example with the hypothetical MTF curves and Zeiss versus Leica. In that example, the "Zeiss" (with a presumed focus on microcontrast) beats the "Leica" (with a presumed focus on resolution) at contrast criteria higher than 50 percent whereas it is the other way around at contrast criteria lower than 50 percent.

Ah, I see where the misunderstanding is: when I said below 50% I meant to the left of the MTF50 resolution. Between 0 target resolution and a target resolution corresponding to the 50% contrast mark.

OK. Then we agree after all.

One further question: Would you agree with my assessment that, as far as Ming's images let us judge, the 20 has a better MTF curve than the new 17/1.8? I must admit, I am a bit disappointed at the showing of the 17/1.8 here. I hadn't really expected it to beat the 20 in this regard but I had hoped/expected that it would do about as well. If that had been the case, I would probably have been ready to exchange my 20 for the 17/1.8. Now, I am not so sure.

I'm not sure, my general impression from his review is that the two lenses are relatively close (with a few notable differences like LoCA and vignetting that favour the 17 mm), and closer than I though they would be. But evaluating MTF from a few crops is something I am not really comfortable with, I'd put more weight on his overall comments which I would assume to be based on a lot more (test) images than the ones shown.

OK. Then we simply have quite different perceptions. To my eyes, there is a very clear difference in contrast in favor of the 20 not only at very low frequencies (macro contrast) but also at higher ones. Look at the crops from the bottom-right corner, for example. The individual lines in the grid below the window is clearly visible in the shot from the 20, even wide open, whereas they nearly disappear into a gray patch in the corresponding shot from the 17/1.8. Similarly, the joints (lines) between the concrete blocs in the same corner crops are clearly visible in the shot from the 20 but hardly visible at all in the shot from the 17/1.8.

You see, I simply have very little confidence in a single test image being relevant and accurate. Show me 50 test images taken under varying conditions (and with the greatest care taken to equalise exposure, focus and processing not just for each image globally but also locally for each position in the image) and I might start to have some confidence in the conclusion drawn from them.

Oh, I certainly agree that we want to see more comparisons before drawing any more final conclusions. I was just curious what you saw as far as this particular piece of evidence is concerned.

For example, if a lens shows vignetting, any crop from the corners will have received a different dynamic range compression during the raw conversion depending on the amount of vignetting making a contrast evaluation on the final image null and void.

Vignetting might of course pose problems of comparability. However, based on what I see in Ming's test images, there is very little variation in average image brightness across the three lenses, regardless of whether we compare center or corner crops. The difference in contrast is what strikes my eye.

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DaveWo
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Re: Just a side note
In reply to brunobarolo, Nov 18, 2012

brunobarolo wrote:

DaveWo wrote:

brunobarolo wrote:

DaveWo wrote:

brunobarolo wrote:

Once you increase global contrast in PP for the 17mm f1.8 (which seems necessary since it's so low, as compared to the 20mm) you will also increase noise. An 800 ISO shot with the 17mm lens processed to the same global contrast may have as much noise as a 1600 ISO shot with the 20mm lens. No?

May I ask if you shoot raw or jpeg primarily?

RAW

And you increase the contrast in something like Adobe Camera Raw?

Lightroom

I suppose if you increase the contrast too much, the noise may become more visible. I don't think it would add more noise than it is though. Noise reduction should help.

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Ming Thein
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Re: Macrocontrast vs. Microcontrast
In reply to Anders W, Nov 19, 2012

The problem is the whole MTF thing is misleading - firstly, it's often theoretical, not measured (i.e. doesn't take into account sample variation, mfg tolerances etc) and secondly, it doesn't say anything about field curvature. You could have a wickedly sharp/ highly-resolving lens that has a touch of field curvature, and if measured wide open, would show terrible dropoff into the corners because DOF would be insufficient to cover the curvature. The Zeiss 2/28 Distagon is one such lens - yet I've never found it wanting in resolution, even on the D800E.

Anders W wrote:

noirdesir wrote:

Ming Thein wrote:

I think there may be some confusion between microcontrast, macrocontrast and resolution here. On the full size images, the 17/1.8 has slightly better microcontrast in the center than the other two, but macrocontrast is definitely lower.

Ming,

A few years back I tried to figure out a definition for the term microcontrast. Since the most comprehensive way to measure contrast of a lens is a full MTF curve, lenses with different amount of microcontrast should have characteristically different MTF curves. To this day, I keep being surprised that I have not seen a single person talk about this (how microcontrast is reflected in a MTF curve).

I showed a generic example of two lenses with very different character in this post:

http://forums.dpreview.com/forums/post/35584548

and discussed it further in this post:

http://forums.dpreview.com/forums/post/37010026

Of note is that all full MTF curves that I have seen, eg, from DxOmark, always start at one, ie, 100% contrast. That is obviously not really correct as every lens + camera system has some internal flare. While one naturally can normalise all MTF curve to one, this would clearly paint 'foggy' lenses in a much better light than it should be. My idea of what you mean with macrocontrast would be the contrast at essentially target resolution of zero, whereas microcontrast would be the contrast at finer resolutions, whether that is the contrast below the resolution of the MTF50 value as I insinuated in the first post I linked to above or the contrast just above that resolution, I don't know.

And since nobody has rigorously defined microcontrast to my knowledge yet, so far I can only answer that by comparing lots of full MTF curves of lenses which are claimed to either have good or bad microcontrast to see whether there is a pattern (or whether the term microcontrast either covers a wide array of lens behaviours or is just not used very consistently).

It is certainly true that the usage of the term "microcontrast" is not well defined. However, it is obvious to me that it must originally have been coined in contradistinction to global contrast or macrocontrast, and thus refers to contrast at frequencies (resolution criteria) some distance away from zero. At the same time, I have the impression that at least some people use it in reference to contrast at fairly low frequencies rather than very high ones, lower frequencies arguably being more important for perceived image quality at ordinary display size.

Like you, I have come to the conclusion that we need to consider the entire MTF curve for a better understanding and I have therefore, like you, looked with interest at the curves now regularly published by DxOMark as part of their lens reviews: one curve at each aperture and FL (if it's a zoom we are talking about) for each of four distances from the center of the frame (dead center, one third away, two thirds away, extreme corner).

My conclusion after having gone through this exercise for quite a few lenses is that good lenses tend to have MTF curves rather similar to the red curve in the hypothetical diagram you link to, i.e., the curve is fairly close to a line sloping downwards at an angle approaching 45 degrees. Bad lenses tend to have curves more resembling a hyperbolic function (1/x), i.e., they decline very rapidly as the resolution criterion increases from zero to some 10 or 20 lp/mm and then taper off more slowly as the resolution criterion increases further. I can't remember seeing a curve resembling the blue graph in your hypothetical diagram. Would you agree with this somewhat schematic description of mine?

What I have seen has left me more comfortable with the MTF-50-percent criterion used by most test sites. While the result at that contrast level (which, as you probably know, is said to be chosen because it correlates well with human perception of image quality although I have seen no description of the research that this contention presumably rests on) won't tell us everything, it is likely to be strongly correlated with the results we would see if the contrast requirement were set a bit higher.

I am less happy with the fact that DxO themselves set the contrast criterion used for their lens scores significantly lower than other sites (they use 20 percent rather than 50), both because the differences between lenses are likely to be less clear-cut in this contrast region and because I think it is less important for perceived image quality how a lens does in this contrast region at anything resembling normal display size and viewing distance.

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Ming Thein
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Re: Macrocontrast vs. Microcontrast
In reply to noirdesir, Nov 19, 2012

noirdesir wrote:


Anders W wrote:

noirdesir wrote:

Anders W wrote:

Didn't you mean to say somewhere between the 100% and the 50% mark here rather than between 0 and 50%? If yes, then I am all with you.

I think there might be different definitions of microcontrast, as you said that "at least some people use it in reference to contrast at fairly low frequencies rather than very high ones", thus it could be contrast at resolutions between the 0 and 50% mark (but closer to the 50% mark) or it could be the contrast a bit above that.

Yes, but I was thinking about your example with the hypothetical MTF curves and Zeiss versus Leica. In that example, the "Zeiss" (with a presumed focus on microcontrast) beats the "Leica" (with a presumed focus on resolution) at contrast criteria higher than 50 percent whereas it is the other way around at contrast criteria lower than 50 percent.

Ah, I see where the misunderstanding is: when I said below 50% I meant to the left of the MTF50 resolution. Between 0 target resolution and a target resolution corresponding to the 50% contrast mark.

One further question: Would you agree with my assessment that, as far as Ming's images let us judge, the 20 has a better MTF curve than the new 17/1.8? I must admit, I am a bit disappointed at the showing of the 17/1.8 here. I hadn't really expected it to beat the 20 in this regard but I had hoped/expected that it would do about as well. If that had been the case, I would probably have been ready to exchange my 20 for the 17/1.8. Now, I am not so sure.

I'm not sure, my general impression from his review is that the two lenses are relatively close (with a few notable differences like LoCA and vignetting that favour the 17 mm), and closer than I though they would be. But evaluating MTF from a few crops is something I am not really comfortable with, I'd put more weight on his overall comments which I would assume to be based on a lot more (test) images than the ones shown.

OK. Then we simply have quite different perceptions. To my eyes, there is a very clear difference in contrast in favor of the 20 not only at very low frequencies (macro contrast) but also at higher ones. Look at the crops from the bottom-right corner, for example. The individual lines in the grid below the window is clearly visible in the shot from the 20, even wide open, whereas they nearly disappear into a gray patch in the corresponding shot from the 17/1.8. Similarly, the joints (lines) between the concrete blocs in the same corner crops are clearly visible in the shot from the 20 but hardly visible at all in the shot from the 17/1.8.

You see, I simply have very little confidence in a single test image being relevant and accurate. Show me 50 test images taken under varying conditions (and with the greatest care taken to equalise exposure, focus and processing not just for each image globally but also locally for each position in the image) and I might start to have some confidence in the conclusion drawn from them.

I'm commenting based on all the 500 or so test images I shot, plus the other thousands I've shot in the past with the 20. Definitely not making conclusions from the single crops (which are meant to be for illustration only). It would obviously be impractical to show crops from all...

For example, if a lens shows vignetting, any crop from the corners will have received a different dynamic range compression during the raw conversion depending on the amount of vignetting making a contrast evaluation on the final image null and void.

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Ming Thein
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Re: Just a side note
In reply to brunobarolo, Nov 19, 2012

Not a straightforward question to answer. I don't think the amount of extra contrast you need (mostly in highlights and mids) would make that much of a difference to noise.

That said, at higher ISOs dynamic range is limited anyway, which inherently increases contrast - it may be too much in some cases with the 20.

Ming

brunobarolo wrote:

Once you increase global contrast in PP for the 17mm f1.8 (which seems necessary since it's so low, as compared to the 20mm) you will also increase noise. An 800 ISO shot with the 17mm lens processed to the same global contrast may have as much noise as a 1600 ISO shot with the 20mm lens. No?

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Ming Thein
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You're welcome. I suppose they could have made it flatter without the focus clutch...nt
In reply to Hen3ry, Nov 19, 2012

Hen3ry wrote:

Cheers, geoff

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Ming Thein
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Agree. nt
In reply to bluelemmy, Nov 19, 2012

bluelemmy wrote:

Nice review. I have the 20mm 1.7 and there seems no great reason to replace it with the Olympus.

On the other hand, if I didn't have the 20 and was looking for such a lens, this 17 would be the one to go for.

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I tried it briefly a few times...
In reply to sansbury, Nov 19, 2012

They're not available yet (still) in Malaysia so my impressions are based on about half an hour at Yodobashi in Tokyo. The 12-35 is so big that it somewhat defeats the point of a compact system in my mind - and you lose a stop of aperture compared to say a 12 and 45 combination. It also has rather odd double images in the bokeh, which I don't find appealing at all.

Agree on the kit lens - presume you mean the 14-42, not the 12-50 - it's a surprisingly good performer.

I'd go with the 12 and 45, personally (and did).

sansbury wrote:

Ming, have you ever looked at (through?) the Pany 12-35? I'm considering the 12 and 17, but the same money gets me the 12-35 and a bottle of good Scotch whisky, not to mention focal lengths from 17-35, weather sealing, and IS in case I decide to get a Pany body someday. The slower aperture and size don't really bother me.

The thing that does bother me is that Oly can clearly make AWESOME primes, like the 60 and 75, and even the 45 deserves some mention, while the new 17 appears to be merely "good." The stupid little kit zoom which nobody likes is already a good lens by any absolute standard--I've been printing a wall full of 17x22 prints taken with it. If I am going to bother with primes that each cost 3-5x as much, I want a clear difference and not just in aperture. The 45/60/75 all do that.

The 17 is a nice piece of jewelry but for nearly 50% more than the 20/1.7 I feel like I'm paying for bling rather than lens. 17 is such a basic length for me--I grew up with a 35/f2 Nikkor so my brain is wired at this length--that I am going to give it a try since the 20 often is just not quite enough, but I can't shake the feeling that buying this lens is encouraging Oly to make more overpriced black lens hoods rather than awesome sweep-the-field lenses.

And yes, if the announced Schneider 14 lives up to the reputation of S-K lenses, I'll be opening my wallet.

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noirdesir
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Another 17 mm f/1.8 review: faster AF than 20 mm f/1.7
In reply to Jorginho, Nov 19, 2012

http://robinwong.blogspot.be/2012/11/olympus-mzuiko-17mm-f18-review.html

"This will be a user experience based review, sharing on what I think and feel as I use the Olympus M.Zuiko 17mm F1.8 lens (mounted on Olympus PEN E-PL5) in real life shooting situations."

"I am sure many micro 4/3 users are dying to find out how this Olympus M.Zuiko 17mm F1.8 performs against Panasonic 20mm F1.7. (...) However, two strong advantages the Olympus 17mm F1.8 has would be the much faster and reliable autofocus performance, and also more solid built quality."

But the guy also lives in Malaysia...

I hope you will feel it to be your civic duty to also remind Mr. Wong that is irresponsible (and unfair) to make such outrageous statements about AF speed without (a) having researched whether things might be different on different bodies and (b) clearly prefacing that statement with an appropriate disclaimer.

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Ming Thein
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Re: Olympus 17/1.8 review
In reply to captura, Nov 19, 2012

You're welcome. It's a final production sample, so yes, it's representative. Of course there could be QC issues etc - it's not practical for me to test every lens and a few samples thereof...

captura wrote:

Ming Thein wrote:

Hi everybody,

I've had a final version of the 17/1.8 for a couple of days now and just posted my review:

Comparative lens review: The Olympus M. Zuiko Digital 17/1.8

As usual, leave a question here or on the site and I'll do my best to get back to you.

Enjoy and have a good weekend!

Ming

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Thank you kindly for your interesting review, and same to the commenters.

I was a bit concerned about the pre-production version of the 17-1.8; was it un-representative?

Can some of your test results be quickly re-checked at a later date, using a production lens?

I would also love to see a comparison with the 14-2.5, which is my personal favorite lens.

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noirdesir
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Re: Macrocontrast vs. Microcontrast
In reply to Ming Thein, Nov 19, 2012

Ming Thein wrote:

noirdesir wrote:

You see, I simply have very little confidence in a single test image being relevant and accurate. Show me 50 test images taken under varying conditions (and with the greatest care taken to equalise exposure, focus and processing not just for each image globally but also locally for each position in the image) and I might start to have some confidence in the conclusion drawn from them.

I'm commenting based on all the 500 or so test images I shot, plus the other thousands I've shot in the past with the 20. Definitely not making conclusions from the single crops (which are meant to be for illustration only). It would obviously be impractical to show crops from all...

Ming, to be clear I was responding to Anders who asked me to make a judgement based on the crops you have shown. I declined as I am convinced that your judgment based on a much larger set of images is much more reliable and relevant than mine based a single test image.

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Anders W
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Re: Macrocontrast vs. Microcontrast
In reply to Ming Thein, Nov 19, 2012

Ming Thein wrote:

The problem is the whole MTF thing is misleading - firstly, it's often theoretical, not measured (i.e. doesn't take into account sample variation, mfg tolerances etc) and secondly, it doesn't say anything about field curvature. You could have a wickedly sharp/ highly-resolving lens that has a touch of field curvature, and if measured wide open, would show terrible dropoff into the corners because DOF would be insufficient to cover the curvature. The Zeiss 2/28 Distagon is one such lens - yet I've never found it wanting in resolution, even on the D800E.

Nothing wrong with MTF per se. It can be measured (which is what the lens testing sites do) as well as theoretically calculated (which is what most manufacturers do for the charts that accompany their lens specs).

Sample variation is a problem in all practical lens tests (yours too) but that problem has nothing to do with MTF per se. One way of overcoming it is to do as LensRentals (Roger Cicala), who often tests quite a few copies of the same lens.

As to field curvature: Yes, a lens can behave like you describe and if it were a WA and had serious field curvature at longer focus distances, that would be a reason for me to reject it. Obviously, the amount of field curvature can if desired be tested, by reporting the center and corner MTF values observed when focus is set so as to optimize center performance as well as when focus is set so as to optimize corner performance.

Anders W wrote:

noirdesir wrote:

Ming Thein wrote:

I think there may be some confusion between microcontrast, macrocontrast and resolution here. On the full size images, the 17/1.8 has slightly better microcontrast in the center than the other two, but macrocontrast is definitely lower.

Ming,

A few years back I tried to figure out a definition for the term microcontrast. Since the most comprehensive way to measure contrast of a lens is a full MTF curve, lenses with different amount of microcontrast should have characteristically different MTF curves. To this day, I keep being surprised that I have not seen a single person talk about this (how microcontrast is reflected in a MTF curve).

I showed a generic example of two lenses with very different character in this post:

http://forums.dpreview.com/forums/post/35584548

and discussed it further in this post:

http://forums.dpreview.com/forums/post/37010026

Of note is that all full MTF curves that I have seen, eg, from DxOmark, always start at one, ie, 100% contrast. That is obviously not really correct as every lens + camera system has some internal flare. While one naturally can normalise all MTF curve to one, this would clearly paint 'foggy' lenses in a much better light than it should be. My idea of what you mean with macrocontrast would be the contrast at essentially target resolution of zero, whereas microcontrast would be the contrast at finer resolutions, whether that is the contrast below the resolution of the MTF50 value as I insinuated in the first post I linked to above or the contrast just above that resolution, I don't know.

And since nobody has rigorously defined microcontrast to my knowledge yet, so far I can only answer that by comparing lots of full MTF curves of lenses which are claimed to either have good or bad microcontrast to see whether there is a pattern (or whether the term microcontrast either covers a wide array of lens behaviours or is just not used very consistently).

It is certainly true that the usage of the term "microcontrast" is not well defined. However, it is obvious to me that it must originally have been coined in contradistinction to global contrast or macrocontrast, and thus refers to contrast at frequencies (resolution criteria) some distance away from zero. At the same time, I have the impression that at least some people use it in reference to contrast at fairly low frequencies rather than very high ones, lower frequencies arguably being more important for perceived image quality at ordinary display size.

Like you, I have come to the conclusion that we need to consider the entire MTF curve for a better understanding and I have therefore, like you, looked with interest at the curves now regularly published by DxOMark as part of their lens reviews: one curve at each aperture and FL (if it's a zoom we are talking about) for each of four distances from the center of the frame (dead center, one third away, two thirds away, extreme corner).

My conclusion after having gone through this exercise for quite a few lenses is that good lenses tend to have MTF curves rather similar to the red curve in the hypothetical diagram you link to, i.e., the curve is fairly close to a line sloping downwards at an angle approaching 45 degrees. Bad lenses tend to have curves more resembling a hyperbolic function (1/x), i.e., they decline very rapidly as the resolution criterion increases from zero to some 10 or 20 lp/mm and then taper off more slowly as the resolution criterion increases further. I can't remember seeing a curve resembling the blue graph in your hypothetical diagram. Would you agree with this somewhat schematic description of mine?

What I have seen has left me more comfortable with the MTF-50-percent criterion used by most test sites. While the result at that contrast level (which, as you probably know, is said to be chosen because it correlates well with human perception of image quality although I have seen no description of the research that this contention presumably rests on) won't tell us everything, it is likely to be strongly correlated with the results we would see if the contrast requirement were set a bit higher.

I am less happy with the fact that DxO themselves set the contrast criterion used for their lens scores significantly lower than other sites (they use 20 percent rather than 50), both because the differences between lenses are likely to be less clear-cut in this contrast region and because I think it is less important for perceived image quality how a lens does in this contrast region at anything resembling normal display size and viewing distance.

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noirdesir
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Re: Macrocontrast vs. Microcontrast
In reply to Ming Thein, Nov 19, 2012

Ming Thein wrote:

The problem is the whole MTF thing is misleading - firstly, it's often theoretical, not measured (i.e. doesn't take into account sample variation, mfg tolerances etc) and secondly, it doesn't say anything about field curvature. You could have a wickedly sharp/ highly-resolving lens that has a touch of field curvature, and if measured wide open, would show terrible dropoff into the corners because DOF would be insufficient to cover the curvature. The Zeiss 2/28 Distagon is one such lens - yet I've never found it wanting in resolution, even on the D800E.

For a theoretical discussion it does not matter whether measurements exist or not, in effect it might be even better if no measurements exist because one can be unbiased in developing a theory and if after one has postulated a theory somebody else confirms your theory with measurements, this is usually a better confirmation of the theory than the other way around.

But there are actual measured full MTF curves (from DxOmark) though it is unclear whether or how they account for field curvature, thus maybe it is safest to restrict ones evaluation of them to the central point.

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Anders W
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Re: Macrocontrast vs. Microcontrast
In reply to noirdesir, Nov 19, 2012

noirdesir wrote:

Ming Thein wrote:

The problem is the whole MTF thing is misleading - firstly, it's often theoretical, not measured (i.e. doesn't take into account sample variation, mfg tolerances etc) and secondly, it doesn't say anything about field curvature. You could have a wickedly sharp/ highly-resolving lens that has a touch of field curvature, and if measured wide open, would show terrible dropoff into the corners because DOF would be insufficient to cover the curvature. The Zeiss 2/28 Distagon is one such lens - yet I've never found it wanting in resolution, even on the D800E.

For a theoretical discussion it does not matter whether measurements exist or not, in effect it might be even better if no measurements exist because one can be unbiased in developing a theory and if after one has postulated a theory somebody else confirms your theory with measurements, this is usually a better confirmation of the theory than the other way around.

But there are actual measured full MTF curves (from DxOmark) though it is unclear whether or how they account for field curvature, thus maybe it is safest to restrict ones evaluation of them to the central point.

I am pretty sure the DxO data are for a single, central focus point. One reason DxO do their measurements is that they develop RAW converter software that tries to compensate for "lens softness". From that point of view, it wouldn't make sense to focus the corners separately. I am sure the same holds for most other lens-testing sites. If I recall correctly, however, Andy Westlake said something about Photozone doing it differently, with separate focus points for center and corners if the lens showed field curvature.

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noirdesir
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Re: Macrocontrast vs. Microcontrast
In reply to Anders W, Nov 19, 2012

Anders W wrote:

I am pretty sure the DxO data are for a single, central focus point. One reason DxO do their measurements is that they develop RAW converter software that tries to compensate for "lens softness". From that point of view, it wouldn't make sense to focus the corners separately.

That's quite possible but since the active AF point is reported in the image metadata, they could in principle account for that (but is probably unlikely as that would require a lot of measurements).

I am sure the same holds for most other lens-testing sites. If I recall correctly, however, Andy Westlake said something about Photozone doing it differently, with separate focus points for center and corners if the lens showed field curvature.

Photozone definitely do re-focus to account for field curvature. They have repeatedly mentioned that in their tests and in posts on these forums as well. For a few lenses they even showed measurements with and without the refocussing.

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Amin Sabet
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@Anders
In reply to Anders W, Nov 19, 2012

Anders W wrote:

MTF: I find the 20 distinctly superior to both 17s in the center and the corners alike. Not only is global contrast better. I'd say the same goes for what I'd refer to as micro-contrast.

I see the same thing. The 20 is resolving more detail, especially in the corners, but also slightly more in the center. It isn't just the impression due to global contrast.

Lateral CA: Yes, the 20 has more of that than the 17/1.8...

Longitudinal CA in the in-focus area: Yes the 20 has more of that...

The 17/1.8 has more red/cyan lateral CA. The 20/1.7 has more purple/green fringing, which I think is a combination of longitudinal CA and spherochromatism (definitely not sensor blooming - everywhere you see the purple fringing, you also see green fringing. Clearly some sort of optical aberration).

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