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07-08-2012, 03:05 PM   #61
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QuoteOriginally posted by Marc Sabatella Quote
All telephoto lenses will create a compression effect, all wide angle an expansion effect.
No it won't per definition, even if if you don't except that when you crop the image the perspective does not change you do except that the viewer can change his perspective relative to the image.
If you look up close to an image created by a wide angle lens then that so called effect is gone.

07-08-2012, 08:11 PM   #62
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QuoteOriginally posted by timo Quote
. . .

All this stuff about 'standard' lenses is a lot of hooey - the old 50mm standard is a convention which happens to be quite convenient from a compositional point of view on 35mm film, and was simple to make. There's nothing magical about it, and to claim that 50mm on an APS-C sensor has analogous qualities (as some have done on occasion) makes no sense at all. And the size and/or magnification of the viewfinder is irrelevant.
Actually, it isn't. The diagonal of 135 is ~ 43mm and the diagonal of Pentax aps-c sensors is ~ 28mm. The closest lens to the latter that is currently in production is the FA 31 LTD.
07-09-2012, 08:01 AM   #63
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QuoteOriginally posted by Anvh Quote
So why does if you move closer as a viewer change the perspective of the image but if you move closer with a camera it doesn't?
Huh? Do you believe that, or are you still misunderstanding me so co pletely thst you think I believe that? I have siad over and over and over sgain: linear perspective depends on shooting position only. It doesn't care what focal length lens you use, what sensor format you use, whether you crop the image, or whether you even take a picture at all. It doesn't even care if you own a camera. Linear perspective depends on position and position only.

It is only the separate optical illusion known as perspective distortion that is dependent on angle of view.
07-09-2012, 08:14 AM   #64
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QuoteOriginally posted by Anvh Quote
No it won't per definition
Yes it does, per definition of the actual phenomenon i question: perspective distortion, which by defi itionis dependent on angle of view. Once again, you are failing to understand that linear perspective and the optical Illusion known as perspective distortion are *different phenomena*.

I realize you are completely convinced you are right and therefore have no interest in actually learning about perspective distortion. But if you would put that attitude aside for a moment and actually read my posts and try to understand rm, I have no doubt you'd be capable of it.

QuoteQuote:
even if if you don't except that when you crop the image the perspective does not change you do except that the viewer can change his perspective relative to the image.
Cropping does *not* affect linear perspective; on this point you are correct. Again, you are still failing to understand me *at all* if you are not getting that I agree with this. Cropping doesn't affect linear perspective. Changing focal length and reshooting doesn't affect linear perspective. Changing cameras and reshooting doesn't affect linear perspective. Only changing shooting position changes linear perspective. How many times must I say this before you realize that I do understand linear perspective?

However, while cropping an image will not chsnge its linear perspective, it will change the angle of view depicted in the image. And this affect the optical illusion known as perspective distortion just as surely as anything else thst would afrect AOV would. That is, the effect is the same as switching to a longer focal length and re-shooting, or switching to a smaller format and re-shooting. And it is this optical illusion known as perspective distortion that is what you are failing to understand, for the most part. Except that:

QuoteQuote:
If you look up close to an image created by a wide angle lens then that so called effect is gone.
True - so this much at least it appears you may be understanding. As I have observed over and over and over and over, the optical illusion known as perspective distortion depends on the angle subtended by the print from the viewing position to xactly the same degree as it depends on the AOV depitced in the image. The notion of what defines "normal" (ie, lack of perspective distortion) depends onthe assumption of "typical" print sizes and viewing distances. Again, I have explained all this many times before; this is not new information.

07-09-2012, 12:00 PM   #65
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Marc you're the problem not me.

here is an example what the problem is.

QuoteQuote:
Originally posted by Anvh
So why does if you move closer as a viewer change the perspective of the image but if you move closer with a camera it doesn't?

Huh? Do you believe that, or are you still misunderstanding me so co pletely thst you think I believe that? I have siad over and over and over sgain: linear perspective depends on shooting position only. It doesn't care what focal length lens you use, what sensor format you use, whether you crop the image, or whether you even take a picture at all. It doesn't even care if you own a camera. Linear perspective depends on position and position only.

It is only the separate optical illusion known as perspective distortion that is dependent on angle of view.
QuoteQuote:
Quote:
If you look up close to an image created by a wide angle lens then that so called effect is gone.

True - so this much at least it appears you may be understanding. As I have observed over and over and over and over, the optical illusion known as perspective distortion depends on the angle subtended by the print from the viewing position to xactly the same degree as it depends on the AOV depitced in the image. The notion of what defines "normal" (ie, lack of perspective distortion) depends onthe assumption of "typical" print sizes and viewing distances. Again, I have explained all this many times before; this is not new information.
So what is it now?

Do you now understand why i don't understand you
07-10-2012, 10:46 PM   #66
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QuoteOriginally posted by Anvh Quote
Do you now understand why i don't understand you
Not really. In the first quote, I am making a statement about linear perspective. In the second, I am making a statement about the optical illusion known as perspective distortion. How could you think these two different statement about two different topics could somehow be in conflict? Again, linear perspective is not perspective distortion. I don't know how to say that more plainly. Linear perspective depends on shooting position and nothing else. Perspective distortion depends on the relationship between the angle of view of the image itself and the angle the print/display subtends from the iewing position. Everything in the quotes you reproduced is 100% consistent with those smole acts. So, no, I don't yet understand exactly what you don't understand.

Perhaps you were confused by my statement (quoted in your post) that "it is only the separate optical illusion known as perspective distortion that is dependent on angle of view". Maybe you misinterpreted my use of the word "only"? Pay attention to where in the sentence that word appears. I said that of the two phenomenons under discussion - lonear perspective and perspective distortion - "only" the latter is dependent on angle of view. But I did not say that perspective distortion is dependent "only" on angle of view. That would be an incorrect statement. Perspective distortion is dependent on *two* things - angle of view, and angle subtended by the print itself from the viewing position. Which is why the second quoted passage is not in conflict with the first - indeed, it is just clarifying the fact that indeed, angle subtended bu the print itself from the viewing position *is* a factor in perspective distortion.
07-11-2012, 03:19 AM   #67
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Here is a little treat for you guys

Pentax DA 35mm F2.4 vs 40mm XS vs 40mm Limited - Introduction - PentaxForums.com

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07-11-2012, 08:48 AM   #68
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QuoteOriginally posted by Adam Quote
Awesome, that's perfect. Gave me confidence in the 40mm XS.

I thought I read that the "XS" had something to do with improving the lens' suitability for contrast detect (and hence the K01) - any truth to that?

Also, is flare the only reason lenses have hoods? So the XS has no hood, but it handles flare well - so it still produces good contrast anyway?

07-11-2012, 09:24 AM   #69
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QuoteOriginally posted by SenorBeef Quote
Also, is flare the only reason lenses have hoods?
Optically, yes (including the blocking of less aggressive stray light that might not be enough to provoke clearly visible flare).
However, hoods also provide varying degrees of physical protection as well,
like keeping raindrops off the front element, or absorbing minor impacts.
07-11-2012, 09:45 AM   #70
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Are there any hoods made that would screw into the 27mm filter thread of the XS? The comparison linked above didn't touch on that, but from what I gather that's a really odd and rare thread size.
07-11-2012, 09:50 AM   #71
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QuoteOriginally posted by SenorBeef Quote
Are there any hoods made that would screw into the 27mm filter thread of the XS?
You'd have to search the online retailers or auction sites.

However, if you don't find hoods that size,
you might be able to get a step-up ring
to get you to a size (like 37mm) where it's easy to find hoods.
07-11-2012, 11:09 AM   #72
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QuoteOriginally posted by Marc Sabatella Quote
Not really. In the first quote, I am making a statement about linear perspective. In the second, I am making a statement about the optical illusion known as perspective distortion. How could you think these two different statement about two different topics could somehow be in conflict? Again, linear perspective is not perspective distortion. I don't know how to say that more plainly. Linear perspective depends on shooting position and nothing else. Perspective distortion depends on the relationship between the angle of view of the image itself and the angle the print/display subtends from the iewing position. Everything in the quotes you reproduced is 100% consistent with those smole acts. So, no, I don't yet understand exactly what you don't understand.

Perhaps you were confused by my statement (quoted in your post) that "it is only the separate optical illusion known as perspective distortion that is dependent on angle of view". Maybe you misinterpreted my use of the word "only"? Pay attention to where in the sentence that word appears. I said that of the two phenomenons under discussion - lonear perspective and perspective distortion - "only" the latter is dependent on angle of view. But I did not say that perspective distortion is dependent "only" on angle of view. That would be an incorrect statement. Perspective distortion is dependent on *two* things - angle of view, and angle subtended by the print itself from the viewing position. Which is why the second quoted passage is not in conflict with the first - indeed, it is just clarifying the fact that indeed, angle subtended bu the print itself from the viewing position *is* a factor in perspective distortion.
Nope that excuse won't work, he is the conversation.
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/191518-35mm-2-...ml#post2016756
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/191518-35mm-2-...ml#post2016795
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/191518-35mm-2-...ml#post2017534

Anyway basically what it comes down what i'm saying is that the difference between linear perspective of the camera and the viewer is what creates the effect of perspective disorder.


About the rest what a normal lens is, as far as i know a normal lens is the lens that gives you a normal perspective or better yet AOV for the print relative for the viewer. We take as standard that the viewer is standing away a typical distance but if you know that isn't the case and know the distance viewers stand and the print size you can actually calculate what the normal lens will be right?
Besides telephoto is about the construction/formula of a long focus lens and 50mm is actually a long focus lens on 135 and most of Pentax 50mm f/1.4 and f/1.7 lenses are actually telephoto lenses.

Last edited by Anvh; 07-11-2012 at 11:28 AM.
07-11-2012, 11:45 AM   #73
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Not a depth of field scale to be found on these three. It's a shame how craft has been discounted - prices, not so much.
07-11-2012, 12:08 PM   #74
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QuoteOriginally posted by civiletti Quote
Not a depth of field scale to be found on these three.
The DA 35mm Limited Macro has one but only has marks for f/11 and f/22. To get a good DOF scale you have to look to the FA Limiteds in this focal length range, the FA31 and FA43.
07-11-2012, 12:45 PM   #75
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QuoteOriginally posted by TomTextura Quote
The DA 35mm Limited Macro has one but only has marks for f/11 and f/22.
Any more, and the marks would all merge together!
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