Wide DA lims (15 vs 21) - which one is better

mikeSF · 12-29-2012, 07:20 PM

Originally posted by lytrytyr

If the sensor is held parallel to a rectangular subject,
a good wide rectilinear lens will project a rectangular image.

aha, that is why you don't seem to think it is a distortion. a parallel sensor would likely need to place the verticals at the center of the frame. all other times when the verticals are out near the edge of the frame, the distortion is pronounced.

DA15 corrected (CROP)

DA15 straight from camera (CROP)

my original point was that I don't find as much need to correct the very slight barrelling of the DA21 as I do the perspective distortion(converging verticals) of the DA15.

Last edited by mikeSF; 12-29-2012 at 09:15 PM.

timo · 12-29-2012, 07:59 PM

Originally posted by Na Horuk

I'm just interested.. I looked at some of the online reviews of these two lenses.. how can the 21mm have more distortion than the 15mm?.

You may be confusing barrel distortion with the 'converging verticals' effect intrinsic in any rectilinear wide-angle lens used at any angle other than horizontal.

A fish-eye demonstrates extreme barrel distortion. If you were a fundamentalist, you could reasonably argue that this represents less distortion than than a conventional, rectilinear wide-angle lens. Rectilinear correction does the same job as our brains do in 'correcting' - i.e. distorting - what we see.

lytrytyr · 12-30-2012, 12:34 AM

Originally posted by mikeSF

a parallel sensor would likely need to place the verticals at the center of the frame. all other times when the verticals are out near the edge of the frame, the distortion is pronounced.

No, look at the barrel distortion chart on Photozone for the DA 15:

Pentax SMC-DA 15mm f/4 AL ED Limited - Review / Test Report - Analysis

The only thing making the grid squares not square on the image
is the slight barrel distortion of the lens.

Originally posted by mikeSF

my original point was that I don't find as much need to correct the very slight barrelling of the DA21 as I do the perspective distortion(converging verticals) of the DA15.

That's a personal aesthetic decision.
Of the two cropped images you show,
I like the lower one better myself: It seems more dynamic.

mikeSF · 12-30-2012, 08:17 AM

Originally posted by lytrytyr

That's a personal aesthetic decision.
Of the two cropped images you show,
I like the lower one better myself: It seems more dynamic.

so you prefer the rendering that looks nothing like the actual bridge? ok.

Last edited by mikeSF; 12-30-2012 at 08:30 AM.

lytrytyr · 12-30-2012, 08:30 AM

Originally posted by mikeSF

so prefer the rendering that looks nothing like the actual bridge? ok.

It gives more of a sense of where you are, looking down on the bridge. YMMV.

SpecialK · 12-30-2012, 08:53 AM

Originally posted by lytrytyr

...chart on Photozone for the DA 15:

Pentax SMC-DA 15mm f/4 AL ED Limited - Review / Test Report - Analysis

Funny that the MTF section of the chart uses bars of various colors, and the legend uses all different colors :-)

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12-29-2012, 07:20 PM	#46
mikeSF Pentaxian Join Date: Jan 2009 Location: East Bay Area, CA Photos: Gallery Posts: 6,622	Originally posted by lytrytyr If the sensor is held parallel to a rectangular subject, a good wide rectilinear lens will project a rectangular image. aha, that is why you don't seem to think it is a distortion. a parallel sensor would likely need to place the verticals at the center of the frame. all other times when the verticals are out near the edge of the frame, the distortion is pronounced. DA15 corrected (CROP) DA15 straight from camera (CROP) my original point was that I don't find as much need to correct the very slight barrelling of the DA21 as I do the perspective distortion(converging verticals) of the DA15. Last edited by mikeSF; 12-29-2012 at 09:15 PM.

12-29-2012, 07:59 PM	#47
timo Veteran Member Join Date: Nov 2006 Location: former Arsenal football stadium Photos: Gallery Posts: 431	Originally posted by Na Horuk I'm just interested.. I looked at some of the online reviews of these two lenses.. how can the 21mm have more distortion than the 15mm?. You may be confusing barrel distortion with the 'converging verticals' effect intrinsic in any rectilinear wide-angle lens used at any angle other than horizontal. A fish-eye demonstrates extreme barrel distortion. If you were a fundamentalist, you could reasonably argue that this represents less distortion than than a conventional, rectilinear wide-angle lens. Rectilinear correction does the same job as our brains do in 'correcting' - i.e. distorting - what we see.

12-30-2012, 12:34 AM	#48
lytrytyr Pentaxian Join Date: Nov 2011 Photos: Gallery \| Albums Posts: 4,310	Originally posted by mikeSF a parallel sensor would likely need to place the verticals at the center of the frame. all other times when the verticals are out near the edge of the frame, the distortion is pronounced. No, look at the barrel distortion chart on Photozone for the DA 15: Pentax SMC-DA 15mm f/4 AL ED Limited - Review / Test Report - Analysis The only thing making the grid squares not square on the image is the slight barrel distortion of the lens. Originally posted by mikeSF my original point was that I don't find as much need to correct the very slight barrelling of the DA21 as I do the perspective distortion(converging verticals) of the DA15. That's a personal aesthetic decision. Of the two cropped images you show, I like the lower one better myself: It seems more dynamic.

12-30-2012, 08:17 AM	#49
mikeSF Pentaxian Join Date: Jan 2009 Location: East Bay Area, CA Photos: Gallery Posts: 6,622	Originally posted by lytrytyr That's a personal aesthetic decision. Of the two cropped images you show, I like the lower one better myself: It seems more dynamic. so you prefer the rendering that looks nothing like the actual bridge? ok. Last edited by mikeSF; 12-30-2012 at 08:30 AM.

12-30-2012, 08:30 AM	#50
lytrytyr Pentaxian Join Date: Nov 2011 Photos: Gallery \| Albums Posts: 4,310	Originally posted by mikeSF so prefer the rendering that looks nothing like the actual bridge? ok. It gives more of a sense of where you are, looking down on the bridge. YMMV.

12-30-2012, 08:53 AM	#51
SpecialK Pentaxian Join Date: Dec 2006 Location: So California Photos: Gallery Posts: 16,481	Originally posted by lytrytyr ...chart on Photozone for the DA 15: Pentax SMC-DA 15mm f/4 AL ED Limited - Review / Test Report - Analysis Funny that the MTF section of the chart uses bars of various colors, and the legend uses all different colors :-)