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09-08-2009, 12:36 PM   #1
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lens comparisons - what am I missing?

I have said here repeatedly over the years that I'm not a lens connoisseur. I have also said (more than once) that I think zoom lenses these days can rival the quality of primes and frequently do.

I would like the second proposition to be proved false, and I would like to become a lens connoisseur if I could. But I'm having a lot of trouble. I simply can't see very significant advantages to the primes that I have.

I have four primes right now: Sigma 28 f/1.8, Pentax 35 f/2 (not the 2.8), Pentax 40 F/2.8 limited, and Pentax 50 f/1.4. I'm afraid I can't see huge differences between the results I get with these four excellent primes, on the one hand, and on the other hand, the results I get with my best zooms that cover the same focal lengths, to wit: Pentax 16-45 f/4, Pentax 18-250 f/3.5-6.3 and Sigma 17-70 f/2.8-4.5 DC Macro.

Here's a link to an album with a few test photos I shot today.

Picasa Web Albums - William - 20090908 lens...

You can use the magnifying glass button to enlarge the photos, if you want. I won't tell you what lenses were used for what shots. I would like to know if the connoisseurs here can see a significant difference (without looking at the EXIF info).

I can see little differences but I would not call them "significant."

What am I missing? Am I going about my comparisons wrong? Or have I been right when defending the excellence of new zooms?

Will

09-08-2009, 12:45 PM   #2
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QuoteOriginally posted by WMBP Quote
What am I missing?
If you want to see significant differences, don't go around shooting at f/5.6 or f/8. You're right, differences will generally be pretty subtle, espeically when comparing brick walls rather than photos in which one can judge things like reproduction of skin tones, etc.

But even shooting brick walls, I think it apparently that the primes will when over your zooms when shooting in the f/1.4 - f/2.8 range.
09-08-2009, 01:35 PM   #3
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The relevance of primes are:

1-larger apertures

2-better control over distorsion and other aberrations (not always visible, but try shooting a traight line near the edge with the Sigma at 17mm). Less aberrations means, by the way, that contrast and saturations will be better.

3-usually sharper. That's ususally what people look at when evaluating a lens' IQ. But this is where zooms (current) will compare best with primes.

My sharpest lenses are the Pentax 50 macro, the Pentax F 50 f1,7, then probably a close run between the Sigma 17-70 and the Vivitar series 1 70-210. There is no contest : the primes are sharper.

The lens with the most contrast is the Vivitar. The most pleasing colours come from the Sigma. The most realistic colours come from the two 50s.

The least distostions come from the macro, the f1,7, the Vivitar and the Sigma (in that order).

Remember also that a larger aperture means more light for the AF system to operate. That means faster and more accurate AF.
09-08-2009, 01:44 PM   #4
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QuoteOriginally posted by Marc Sabatella Quote
If you want to see significant differences, don't go around shooting at f/5.6 or f/8. You're right, differences will generally be pretty subtle, espeically when comparing brick walls rather than photos in which one can judge things like reproduction of skin tones, etc.
Thanks for the reply, Marc.

I shot the brick walls in part because I don't have any humans around at the moment, but also because I was trying to test for the acuity of each lens, and it seemed to me that shooting something texture was a good way to do that.


QuoteQuote:
But even shooting brick walls, I think it apparently that the primes will when over your zooms when shooting in the f/1.4 - f/2.8 range.
I take it you meant to say "that the primes will WIN over [my] zooms when shooting in the f/1.4-f/2.8 range."

OK, I'll try that. But this makes comparison difficult. The Pentax 40 has a max ap of f/2.8. That means I can't really compare it to ANY of the zooms I've got, since they don't go to f/2.8 at 40mm. Well, I could compare it to my Sigma 18-50 f/2.8 but I won't bother as I'm already convinced that's not one of my very best zooms.

It seems to me that you are saying that, except at the maximum aperture or near it, the difference in image quality between primes and (good) zooms is going to be small, perhaps negligible or even non-existent. Am I understanding you?

If I am, then this also seems to confirm what I've thought for a good while: that the best modern zooms really do rival primes in image quality nearly everywhere, and of course zooms win hands down in terms of versatility.

Am I making sense?

Will

09-08-2009, 02:05 PM   #5
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I think was the point he was trying to make - that even the best zooms are only constant f/2.8.If you need faster, the only option is a prime. Even at f/2.8 the prime should be better because it's stopped down where as the zoom is wide open. The other advantage is size and weight compared to most zooms (especially the fast ones).

Personally I would have fun using a standard prime for night shooting or something like that, but wouldn't pay for it over a zoom. The constant f/2.8 and very good IQ of top zooms works for me.
09-08-2009, 02:56 PM   #6
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Also, it's very difficult to see a difference when the image is scaled down so small. It's like judging "noise" from a camera at a given ISO.. and then scale it down. The images look very clean even if large amounts of noise was visible in the original.

I will agree though, to see much of a difference between a prime vs. low end zoom's will not be noticeable if scaled to 1/5th it's original size or smaller.
09-08-2009, 03:23 PM   #7
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QuoteOriginally posted by Marc Sabatella Quote
If you want to see significant differences, don't go around shooting at f/5.6 or f/8.
By the way, four of the five shots I posted were taken at f/4, and the fifth at f/4.5.
09-08-2009, 03:26 PM   #8
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To me, the largest difference between zooms (I've used a Sigma 24-70 f/2.8 that has very good IQ at f/5.6 or smaller, as well as Canon L zooms for smaller periods of time) and primes happens in the out of focus areas.

Zooms almost always render OOF stuff in a harsh, displeasing way. This includes the portions of the image that are just OOF, and not completely blurred like the BG in a typical portrait. Also, microcontrast (the "detail") in pretty much every zoom I've ever seen/used has been lower than the vast majority of primes I've shot with.

EDIT: Of course, you can post a bazillion images that disprove this, but it's been my experience: EDIT

Sure, zooms can be sharp, but almost any lens can (look at all the kit lens shots at f/8 or f/11 that prove that to be true), but get into a less than ideal situation, and your primes will hold out better IQ far longer.

Most people don't need or want to see the difference, and you have to look for it, and know what to look for. Myself, I hate shooting with the zoom but it is versatile and I get a lot of shots I probably wouldn't have gotten with the required lens change...but I try to use primes whenever possible.

09-08-2009, 03:32 PM   #9
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QuoteOriginally posted by designinme_1976 Quote
Also, it's very difficult to see a difference when the image is scaled down so small. It's like judging "noise" from a camera at a given ISO.. and then scale it down. The images look very clean even if large amounts of noise was visible in the original.
Thanks.

I've looked at the pictures at 100% and even 200% and I really have great difficulty discerning any differences that I can take as evidence that one lens is superior to the others. I tried to post the photos as large as Picasa Web Albums would let me. If you click the magnifying glass you can see them at a resolution that's 1600px on a side - about 1/4 res.

But in any case, that's how the images get viewed. I don't really care how images look at 100%, since I don't take photos to be viewed at 100%.

Will
09-08-2009, 03:54 PM   #10
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QuoteOriginally posted by WMBP Quote
I can see little differences but I would not call them "significant."
Whether or not you can see differences between excellent and lesser lenses on prints depends on the print size. If you use small print sizes then the resolution advantages often offered by primes will not be apparent.

Since I don't shoot for reproduction in poster size and can deal with distortions / vignetting, the main difference to me when shooting my primes is that they give me more DOF options. I typically don't use f/1.8 to get a faster shutter speed (I'd first increase the ISO) but I use it to achieve shallow DOF. Most zooms don't give you a lot of DOF options and as CWyatt has pointed out, those which do offer f/2.8 will then give you their wide open performance which is not as good as, say a stopped down performance of the FA 50/1.4 @ f/2.8.

EDIT: If you want to compare images reliably make sure the light doesn't change in between, that the perspective / framing doesn't change, and that the focus point is the same. In particular the focus becomes critical when comparing images at 100% (or large print sizes). It may well be that not all of your lenses focus on the same point even if you AF on to the same spot, due to BF/FF issues. But as I said above, for small prints and higher f-ratios this typically doesn't matter.

Last edited by Class A; 09-08-2009 at 04:13 PM.
09-08-2009, 04:04 PM   #11
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QuoteOriginally posted by WMBP Quote
By the way, four of the five shots I posted were taken at f/4, and the fifth at f/4.5.
Why are there two photos of one scene and three photos of the other? Did you use a tripod? If you want a serious stab at this, you should provide as closely as possible the same photo from each lens. The best test of resolution is fine print. I've found some cereal boxes are ideal for this type of test, because they have a variety of print sizes and a good range of colours.

My 16-45 is very nearly as sharp as my primes at F4 and up, has low distortion, great colour & contrast and is sharp across the frame. I switch to a prime for a specialty use; e.g. low ambient light, narrow dof, 1:1 macro.
09-08-2009, 04:11 PM   #12
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QuoteOriginally posted by Fixcinater Quote
To me, the largest difference between zooms (I've used a Sigma 24-70 f/2.8 that has very good IQ at f/5.6 or smaller, as well as Canon L zooms for smaller periods of time) and primes happens in the out of focus areas.

Zooms almost always render OOF stuff in a harsh, displeasing way. This includes the portions of the image that are just OOF, and not completely blurred like the BG in a typical portrait. Also, microcontrast (the "detail") in pretty much every zoom I've ever seen/used has been lower than the vast majority of primes I've shot with.
I understand the importance of bokeh and the out of focus areas - that's why one of my test shots shoots an outdoor wall at the corner and includes a lot of out of focus area. I know that brick walls are pretty uninteresting photographic subjects and generally speaking I don't like test shots that have no interest except as test shots. But the brick wall receding from view on the left, when viewed up close, provides a fairly nice test of the way that the lens transitions from in-focus to out-of-focus areas. (Click image to see larger version.)



But honestly, these pictures were taken at f/4 and I can't see a difference - I mean almost ANY difference at all - between the out of focus areas of the two shots here that were taken with zooms and the one that was taken with the 40mm prime.



QuoteQuote:
EDIT: Of course, you can post a bazillion images that disprove this, but it's been my experience: EDIT
Point taken. But I'm not trying to do anything tricky here. Those who've been in this forum for years know that I'm pretty straightforward. I'm honestly seeking to understand this issue better. I do have a hypothesis: that high-quality zooms can take shots whose image quality is the equal of similar shots taken by primes. But I'm trying to test that hypothesis and if it's wrong, I'd like to know.



QuoteQuote:
Sure, zooms can be sharp, but almost any lens can (look at all the kit lens shots at f/8 or f/11 that prove that to be true), but get into a less than ideal situation, and your primes will hold out better IQ far longer.
Well, let me say it again: The shots I'm looking at were taken at f/4....


QuoteQuote:
Most people don't need or want to see the difference, and you have to look for it, and know what to look for.
I WANT TO SEE THE DIFFERENCE. That is why I started this thread. I'm asking what I need to look for and where to look for it. I've looked - HARD - and I'm not seeing it.

And for the benefit of folks who don't know me: I've been a photographer for decades. I've been shooting Pentax digital only for the last few years and as I said up front, I don't claim to be a lens expert. But I make a fair bit of my income from photography, doing weddings and portraits. My technical knowledge isn't what I'd like but I do have a pretty good idea how to tell a good photo from a bad one. And this isn't the first time (or the second or third) that I've taken a stab at this particular issue.


QuoteQuote:
Myself, I hate shooting with the zoom but it is versatile and I get a lot of shots I probably wouldn't have gotten with the required lens change...but I try to use primes whenever possible.
YES YES this is the point here. Zooms are indeed very versatile. And if the image quality of a good zoom is indistinguishable from the image quality of a prime 99% of the time (or 95%, or 87%) - as I continue to suspect it is - then good zooms are a perfectly responsible choice for a serious photographer.


Will
09-08-2009, 05:29 PM   #13
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Will,
I could not see much difference in your test shots.

Of all the lenses you have in your arsenal, the 18-250 would be the only one with disputable image quality in the lower f-stops I guess.

Much has been said by my pre-posters already and these are all valid points - depends on personal preferences if those things prove important.

Here's my personal take on it: Modern zooms have come a very long way. To get a 'sharp' picture, in fact an excellent digital pocketable camera like the Panasonic/Leica
Lumix LX (1-3) will get you stunning pictures any time with decent lighting - I'd love to have such a cam alongside my K100D.

Now why would I drag the DSLR with my big fast manual lenses along ? Here's two pics for you to decide yourself.


To me this is about the blurred background - I love that :-) 180/2.8 at f5.6 ISO400


55/1.4 at around f2, 1/15sec. ISO800 handheld. Low light shot +colors +bokeh :-)

Best, Georg (the other)
09-08-2009, 06:15 PM   #14
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QuoteOriginally posted by WMBP Quote
I shot the brick walls in part because I don't have any humans around at the moment, but also because I was trying to test for the acuity of each lens, and it seemed to me that shooting something texture was a good way to do that.
Indeed, but other things have texture too, and in any case, there is more to performance than sharpness.

QuoteQuote:
I take it you meant to say "that the primes will WIN over [my] zooms when shooting in the f/1.4-f/2.8 range."
Yes.

QuoteQuote:
OK, I'll try that. But this makes comparison difficult. The Pentax 40 has a max ap of f/2.8. That means I can't really compare it to ANY of the zooms I've got
That is indeed my point. The advantage of a prime isn't necessarily that it can do the things a zoom can do but do them better; it's that it can do things the zoom cannot do.

QuoteQuote:
It seems to me that you are saying that, except at the maximum aperture or near it, the difference in image quality between primes and (good) zooms is going to be small, perhaps negligible or even non-existent. Am I understanding you?
Probably not non-existent, but indeed, hard to see in reduced size shots of brick walls.

QuoteQuote:
of course zooms win hands down in terms of versatility.
Only if you define "versatility" in an very peculiar way: to refer only to the ability to change focal lengths. It's true a zoom has that advantage. But there is a sense in which the DA40 is more versatile than your zooms, in that it can shoot f/2.8 and hence produce more usable shots in low light. OK, so you also have an f/2.8 zoom, but it is unlikely to match the DA40 in IQ at f/2,8, and of course it is *huge* compared to the DA40, meaning their use is further limited to situations in which you have that much space to allocate to lenses of that focal length and don't mind

Which is to say, you're still slanting the comparison in favor of "zooms" by defining "versatility" to mean ability to change focal lengths only, rather than all the other things it could mean.

I'd put it this way: zooms are great if you're mostly shooting in good light and thus don't need f/2.8 or better, if you've got room in your bag to cover the focal length you want to cover, and don't mind the fact that one of these zooms may double the weight of the camera. But if you also value low light shooting, being able to travel with a smaller bag, and working with a lighter camera, those are some important advantages to primes right there, totally independent of how good a picture they take of a brick wall.
09-08-2009, 08:06 PM   #15
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QuoteOriginally posted by audiobomber Quote
Why are there two photos of one scene and three photos of the other?
Because one of the shots was taken with only 2 different lenses (the 40mm prime and the Sigma 17-70), and the other shot (the corner of the outside wall) was taken with those 2 lenses + the Pentax 18-250.


QuoteQuote:
Did you use a tripod?
No, I didn't. I seldom shoot with a tripod and I don't really want to test with a tripod. I'm not really trying to do laboratory tests. However, what I do is take several shots with each lens - making sure that shake reduction is enabled. I review the shots carefully and, for each lens, pick the 1 best shot.



QuoteQuote:
My 16-45 is very nearly as sharp as my primes at F4 and up, has low distortion, great colour & contrast and is sharp across the frame. I switch to a prime for a specialty use; e.g. low ambient light, narrow dof, 1:1 macro.
Yes, my 16-45 is very good too - seems to be one of my best lenses.

Will
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