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10-13-2009, 08:44 PM   #31
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You can only decide this for yourself.
Ask yourself - what will I be shooting with this new lens? Is one more appropriate than the other for what I want to shoot?

To me, it's less of a worry that the Sigma is of 'lesser quality', which I don't quite appreciate. Is the IQ good? Yes? Then just get the focal length you need...

10-13-2009, 08:47 PM   #32
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QuoteOriginally posted by Marc Sabatella Quote
No need to rely on a test done in the past. Anyone can do this test right now. Look straight ahead, fixating on a particular object in front you. Make a mental note of the further object you can see on either side. Now put some lenses on your camera and see which gives you that field of view. For me, on my APS-C camera, my 18-55 doesn't go wide enough to encompass what I can see. So unless I'm just a freak of nature, or human evolution has resulted in the field of view doubling over the last century, the idea that the field of view of a 50mm lens (on FF; 33mm on APS-C) represents human field of view is just ludicrous.

At best, it's some sort of subjective wet-finger estimate of the field of view we might be able to perceive an "acceptable" amount of detail in. But it's also possible to do tests showing that the real peak of visual acuity is found only within the field of view of around a 100mm lens on APS-C. Choosing 50mm as somehow best representing the "natural viewing perspective of the human eye" is just plain arbitrary.



Depending on how you define "normal", sure. But any definition of "normal" that results in 50mm being chosen can have little or nothing to do with the human field of vision, and can only tangentially relates to what can be called "natural viewing perspective" (that term has relevance only with respect to making prints of a "typical" size and then viewing them at a "typical" distance.

I'm not saying statements like that weren't commonly tossed around. I'm saying when you actually examine the matter, they turn out to not be very meaningful. Never were then, but people bought into them without giving it much thought. It would have been just as possible to debunk these notions 50 years as it is now; it's just that no one bothered to then (or if they did, they've been long forgotten). Just as for decades anyone who wrote about photography, would tell you that perspective was affected by focal length, and that different lenses therefore had inherently different perspectives, and that a 35mm lens on APS-C therefore somehow has a different perspective than a 50mm lens on FF. The fact that many people believed this doesn't make it true.

Anyhow, I really could care less how anyone wants to use the term "normal" or "standard". I'm just pointing out that there really is no universally agreed upon One True Defintion.
So then by your definition, there is no such thing as a wide angle lens?
C'mon Mark, you know better than that.
I just looked intently at the painting on the wall beside my computer. It's about 10 feet away from me.
Without moving my eyes, I paid some attention to what was clearly identifiable on the periphery of my vision. I then lifted my K-7 with the 31 mounted to my eye and looked to see what was on the edges of the viewfinder.
I was seeing slightly more than what my 31mm lens saw.
Do the math and you'll find that the normal lens on this camera would be about 28mm (28.12329994861911..mm if you want to be a bit pedantic).
So, I think it's safe to presume that a 28mm is probably a standard lens, presuming that I have fairly average vision.
All of the photographers I know agree with this.
All the camera manufacturers whose literature I've read have agreed with this.

Last edited by Wheatfield; 10-13-2009 at 09:25 PM.
10-13-2009, 09:13 PM   #33
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QuoteOriginally posted by Wheatfield Quote
So then by your definition, there is no such thing as a wide angle lens?
First, I never said there was "no such thing" as a normal lens - just that the definition is extremely vague, and the usual one offered doesn't exactly make sense.

With "wide angle", it's clear enough what is meant, the only uncertainty is what the cut-off would be..

QuoteQuote:
I just looked intently at the painting on the wall beside my computer. It's about 10 feet away from me.
Without moving my eyes, I paid some attention to what was clearly identifiable on the periphery of my vision. I then lifted my K-7 with the 31 mounted to my eye and looked to see what was on the edges of the viewfinder.
All I can say is that you must have defined "clearly identifiable" a lot more narrowly than I do. I can look at the painting on the opposite wall and "clearly identify" my cat sitting far enough to my right that, as I sai, an 18mmlens wouldn't encompass her. how clearly can I identify her? Well, I can tell it's a grey cat; I might not notice if someone substituted a different gray cat. Maybe you are defining 'clearly identify" to mean something else. But like I said, i could then turn around and define it even more narrowly - there is a very real sense in which 100mm is actually the cone we can see best.

This is what I mean about all this being subjective.

QuoteQuote:
Do the math and you'll find that the normal lens on this camera would be about 28mm (28.12329994861911..mm if you want to be a bit pedantic).
So, I think it's safe to presume that a 28mm is probably a standard lens, presuming that I have fairly average vision.
All of the photographers I know agree with this.
What part do you think they'd agree with? Yes, they'd all agree that 28mm is about "normal" or "standard" for APS-C, because we all know the common definitions - equal to the diagonal, or the conventional wisdom that 50mm is "normal" / "standard" on FF. Again, I'm not questioning any of this - yes, we all know that's the commonly accepted focal length. What I'm saying is that the criteria that is generally offered for *why* this is the commonly accepted focal length doesn't really stand up to close scrutiny.

QuoteQuote:
All the camera manufacturers whose literature I've read have agreed with this.
Then, along comes someone with no credentials outside of a fine arts degree comes along and tells me otherwise?
Sorry, you don't have the credibility to pull this one out of your @ss.
I see no reason for insults or profanity. But feel free to believe that 28mm on APS-C really is the field of view of the human eye if that makes you happy.
10-13-2009, 09:25 PM   #34
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QuoteOriginally posted by Marc Sabatella Quote
For me, on my APS-C camera, my 18-55 doesn't go wide enough to encompass what I can see. So unless I'm just a freak of nature, or human evolution has resulted in the field of view doubling over the last century, the idea that the field of view of a 50mm lens (on FF; 33mm on APS-C) represents human field of view is just ludicrous.
I would respectfully disagree that there is no such thing as a normal perspective that approximates the human eye. I believe there is.

Perhaps what confuses the issue is that firstly, the human eye is never still and moves continually; Secondly, there are two eyes, and thirdly, what we see is actually a composite image 'stitched' together in the brain (much like the way we can stitch together a panorama in photoshop from multiple images).

Having said that, The best way to illustrate a 'normal' perspective is with an image that has an 'abnormal' perspective (ie. this one taken with a DA15/4):




Last edited by Spock; 10-13-2009 at 09:30 PM.
10-13-2009, 09:26 PM   #35
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QuoteQuote:
I see no reason for insults or profanity.
Your right about that. Not over this anyway...
Comment excised.
Your still wrong though
10-13-2009, 09:29 PM   #36
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DA 35 2.8 macro

I've been pleased with the DA 35 2.8 macro as a walk around lense including closeup work. With stabilization I can hold 1/15 with un-steady hands and it's fine at 2.8.
10-13-2009, 10:04 PM   #37
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A good definition of a "standard" lens is a lens whose focal length is within cooee of the image sensor's (whether it be digital or film) diagonal length.

For example, the diagonal of 35mm film is 43.27mm. (Pentax's) APS-C is 28.26mm. This is just a guide.
10-14-2009, 05:57 AM   #38
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I'm looking for an inside/outisde/walk around/all purpose lens, I think the Sigma 30mm will serve that purpose 100%, I like more the Pentax 55mm for the WR properties, but I am concern about the very "narrow" angle of view of an almost 83mm lens, with the Sigma lens the angle of view will be equivalent to a 45mm lens, any previous experience with 83mm lens (equivalent) ?, thanks

10-14-2009, 06:07 AM   #39
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QuoteOriginally posted by lithos Quote
A good definition of a "standard" lens is a lens whose focal length is within cooee of the image sensor's (whether it be digital or film) diagonal length.

For example, the diagonal of 35mm film is 43.27mm. (Pentax's) APS-C is 28.26mm. This is just a guide.
It seems to me, that in order to be 'normal' the focal length must both fit the diagonal width of the film plane and match the flange distance to both approximate 'normal' perspective, and 'normal' angle of view.


My FA 28mm has a great angle of view, but because the flange distance is still 45.5mm, my FA 50mm clearly has the most 'normal' perspective.

In short, there is no 'normal' for APS-C cameras unless you made the flange distance closer to 28mm.



Anyway, to the original post. If you can find a FA 28mm used, I recommend the lens. Not terribly fast, but quite sharp wide open, and it takes pleasing photographs IMHO.
10-14-2009, 08:36 AM   #40
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QuoteOriginally posted by Spock Quote
Perhaps what confuses the issue is that firstly, the human eye is never still and moves continually; Secondly, there are two eyes, and thirdly, what we see is actually a composite image 'stitched' together in the brain (much like the way we can stitch together a panorama in photoshop from multiple images).
Well sure, but that's my point. Of course the eye (or eyes) have a field of view that is pretty much fixed; it's reducing that to a single number in light of the above factors is that is pretty subjective and arbitrary. There *is* a sense in which the filed of view of a "normal" lens seems to mimic something about how we see, but it's an extreme oversimplification to say that there is a single number that represents the field of view of human vision.

QuoteQuote:
Having said that, The best way to illustrate a 'normal' perspective is with an image that has an 'abnormal' perspective (ie. this one taken with a DA15/4):
Yes, but this exactly what I was referring to - the effect you are showing here is not dependent on focal-length, but *distance to subject*. The dog looks weird because you shot from an abnormally close distance. Step back to the ame distance you'd be likely to shoot from using a "normal" lens, and the perspective is *exactly* the same. And I mean exactly - if you crop the 15mm shot taken from the same distance as the 50mm, there would be no difference between it and the 50mm shot.
10-14-2009, 08:40 AM   #41
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QuoteOriginally posted by Wheatfield Quote
Your right about that. Not over this anyway...
Comment excised.
Your still wrong though
Apology accepted. I think we're really arguing slightly different point here. I am not disagreeing that it commonly accepted that the "normal" field of view has some special significance. I'm simply quibbling with how exactly that significance is defined. And FWIW, it's not my "fine arts" degree (music) that informs this, but rather, my in math that makes me want to be precise. All I'm saying is that there are *lots* of ways of measuring "natural viewing perspective of the human eye", and depending on which way you choose, you'll get wildly different answers. That's why I say that phrase is too imprecise.
10-14-2009, 08:52 AM   #42
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QuoteOriginally posted by ordinaryimages Quote
I've been pleased with the DA 35 2.8 macro as a walk around lense including closeup work. With stabilization I can hold 1/15 with un-steady hands and it's fine at 2.8.
I agree. Of all the lenses discussed here, this one has the best combination of build quality, optics, reputation, and IQ for an APS-C digital. IMO it whups the Sigma 30, and for price/performance is close enough to the 31 Ltd. I have been sorely tempted by the latter, but I don't need the super-thin DOF (2.8 is functionally excellent), and the price..........

The 1:1 macro capability also makes this lens stand out from others discussed here. The DA 35 is an exceptional value.
10-14-2009, 09:42 AM   #43
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QuoteOriginally posted by Marc Sabatella Quote
if you crop the 15mm shot taken from the same distance as the 50mm, there would be no difference between it and the 50mm shot.
What do you mean?
10-14-2009, 12:04 PM   #44
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Originally Posted by Marc Sabatella
if you crop the 15mm shot taken from the same distance as the 50mm, there would be no difference between it and the 50mm shot.
QuoteOriginally posted by konraDarnok Quote
What do you mean?

If you take a picture with (as an example) a 15mm lens, and then, without moving the camera, replace the 15mm lens with a 50mm lens and take another picture, you will be able to crop a section out of the image taken with the 15mm lens that will be an exact match to the one shot with the 50mm lens, with the exception of noise or grain due to having to magnify one image to match the other one.
10-14-2009, 12:34 PM   #45
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Should have realized there were 2 more pages before commenting.

Last edited by c.r.brown; 10-14-2009 at 12:42 PM. Reason: Should have realized there were 2 more pages before commenting.
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