Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
06-01-2014, 02:44 AM   #16
Veteran Member
OregonJim's Avatar

Join Date: Mar 2009
Location: Willamette Valley, Oregon
Posts: 1,329
QuoteOriginally posted by stevebrot Quote
28mm is a wide angle focal length on my 35mm film and will provide a very satisfactory duck face when mounted with my KX film camera. The same 28mm lens on my smaller APS-C K-3 provides a fairly flat and boring "normal" perspective.
Is that not because you had to move the K-3 backward to create the same image (FOV) as seen on your KX? The camera-to-subject distance is what counts for creating the duck face.

If both cameras were shot at exactly the same distance from the subject, would they not have exactly the same level of distortion?

The only advantage here is that the KX would capture the whole face, while the K-3 would only capture the nose. But that nose would be just as distorted.


Last edited by OregonJim; 06-01-2014 at 02:53 AM.
06-01-2014, 07:16 AM   #17
Site Supporter
6BQ5's Avatar

Join Date: Jun 2013
Location: Nevada, USA
Photos: Albums
Posts: 3,109
QuoteOriginally posted by OregonJim Quote
Ok, this I don't buy.

Lens abberations don't change just because the capture area in the focal plane is smaller. If anything, abberations "go away" because most are near the outer edges of the projection circle, which is no longer near the sensor.
I agree that most aberrations are in the outer corners but there will also be some in the center. This may not be the best way to look at it but let's take two extremes. With a 6 MP sensor the aberrations could be smaller than 1 pixel and they blend into (or average into) a pixel. However, with a 36 MP sensor the aberration may be 1 to 2 pixels in size and can finally be resolved. You may have to zoom in to 100% which would be the equivalent of looking at a mural size print 6" away from the surface but they are there. Zoom out or stand back and your eye probably won't resolve them.

The stuff in the outer edges may be 1 to 2 pixels in size relative to a 6 MP sensor to begin with. When the sensor goes up to 36 MP then the aberrations are monstrous in pixel size and are easily resolved.

I think this sort of behavior is what people mean by when they say a lens was good enough for film but not good enough for digital. Personally, I don't like that statement by itself because IQ is more than just about pixels but it's a starting point for a conversation about lenses, film/digital, and IQ.
06-01-2014, 09:06 AM   #18
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 27,438
QuoteOriginally posted by OregonJim Quote
If both cameras were shot at exactly the same distance from the subject, would they not have exactly the same level of distortion?
You are correct. Thank you for adding the clarification. I hate using the word "distortion", however, because there is a tendency to confuse a distorted perspective with an optical aberration. As for camera position, I did mean both cameras at the same position relative to the subject. The APS-C version is quite literally a crop of the wider view and appears more "normal" simply due to the crop.

This type of discussion and example is usually applied to debunk the common notion of long lenses somehow compressing relative distance between objects. Doing a crop of from a "normal" lens will yield the same compression at the same camera/subject orientation as with a longer lens.


Steve

---------- Post added 06-01-14 at 09:09 AM ----------

QuoteOriginally posted by OregonJim Quote
Ok, this I don't buy.
Me neither, though it may be that I am too tender hearted to admit to applying undue stress to my legacy lenses by pairing them with a smaller format camera.

All joking aside, I should probably do the comparison test that has been nagging at me ever since I took delivery of my DA 50/1.8. I own both the Pentax-K 55/1.8 and Pentax-M 50/1.7, both of which are reputed to be among the best Pentax fast 50s. The DA 50/1.8 shares a similar design, but is supposedly optimized for modern digital sensors. Any "pixel smearing" or amplified aberrations should be readily apparent with available lens test targets. I might also extend the test to a roll of Ektar 100, though it might prove stressful to the DA 50/1.8

BTW, if anyone living in the general Portland, Oregon area has a copy of the DA* 55/1.4 they wish to lend to the cause, I would be pleased to add that lens to the mix as well.


Steve

P.S. I was disappointed that the PF "Nifty 50" shoot-out elected to compare the DA 50/1.8 to the FA 50/1.4 rather than the DA* 55/1.4.

Last edited by stevebrot; 06-01-2014 at 09:31 AM.
06-01-2014, 11:08 AM   #19
Site Supporter
6BQ5's Avatar

Join Date: Jun 2013
Location: Nevada, USA
Photos: Albums
Posts: 3,109
QuoteOriginally posted by stevebrot Quote
All joking aside, I should probably do the comparison test that has been nagging at me ever since I took delivery of my DA 50/1.8. I own both the Pentax-K 55/1.8 and Pentax-M 50/1.7, both of which are reputed to be among the best Pentax fast 50s. The DA 50/1.8 shares a similar design, but is supposedly optimized for modern digital sensors. Any "pixel smearing" or amplified aberrations should be readily apparent with available lens test targets. I might also extend the test to a roll of Ektar 100, though it might prove stressful to the DA 50/1.8

Thankfully most film lenses will perform really well, especially when you consider their age and low cost compared to new lenses. Personally, I found that the lower end zoom lenses, like the kit lenses, perform poorly. Primes, even the older Taks, work really well!

06-01-2014, 02:00 PM   #20
Veteran Member
OregonJim's Avatar

Join Date: Mar 2009
Location: Willamette Valley, Oregon
Posts: 1,329
QuoteOriginally posted by 6BQ5 Quote
The stuff in the outer edges may be 1 to 2 pixels in size relative to a 6 MP sensor to begin with. When the sensor goes up to 36 MP then the aberrations are monstrous in pixel size and are easily resolved.

I think this sort of behavior is what people mean by when they say a lens was good enough for film but not good enough for digital. Personally, I don't like that statement by itself because IQ is more than just about pixels but it's a starting point for a conversation about lenses, film/digital, and IQ.
Ok, this is pixel-peeping level stuff, and has no value to me, but I do understand where you were going now.

I'm trying really hard not to turn this into a rant. Not at you, Boris - just the subjuct in general. What these people are saying relates to the size of individual photosites, NOT the overall sensor size. FF sensors, right now, generally have larger photosites than APS-C sensors of the same generation. But, trust me - this is only temporary. Photosite size on FF sensors will contunue to shrink as the relentless marketing cry for more needless megapixels marches on.

So, at some point in the near future, ALL sensors will be able to resolve microscopic lens defects (and defects are different from abberations, another rant ). The only thing this does is drive up lens prices as manufacturers try to make their new lens designs match the new sensor resolving power, and our images become more cold, sterile, and cutting like razors.

Last edited by OregonJim; 06-01-2014 at 02:25 PM.
06-01-2014, 02:48 PM   #21
Veteran Member
OregonJim's Avatar

Join Date: Mar 2009
Location: Willamette Valley, Oregon
Posts: 1,329
QuoteOriginally posted by stevebrot Quote
BTW, if anyone living in the general Portland, Oregon area has a copy of the DA* 55/1.4 they wish to lend to the cause, I would be pleased to add that lens to the mix as well.
I don't have the DA* 55/1.4, or I would gladly let you borrow it.

What I do have:

Pentax 50 1.4 P/K
Pentax 50 1.7 P/K-A
Pentax 50 1.7 P/K-A
Vivitar 50 1.7 M42
Yashica 50 1.7 M42
Yashica 50 1.7 M42
Chinon 50 1.9 P/K
Vivitar 50 1.9 M42
Pentax 50 2 P/K-A
Ricoh 50 2 P/K
Sears 50 2 P/K
Pentax 50 4 M42
Chinon 55 1.4 M42
Rexatar 55 1.7 M42
Pentax 55 1.8 M42
Pentax 55 1.8 M42

My personal favorite is the Chinon 55/1.4.
06-01-2014, 03:22 PM   #22
Site Supporter
6BQ5's Avatar

Join Date: Jun 2013
Location: Nevada, USA
Photos: Albums
Posts: 3,109
QuoteOriginally posted by OregonJim Quote
Ok, this is pixel-peeping level stuff, and has no value to me, but I do understand where you were going now.

I'm trying really hard not to turn this into a rant. Not at you, Boris - just the subjuct in general. What these people are saying relates to the size of individual photosites, NOT the overall sensor size. FF sensors, right now, generally have larger photosites than APS-C sensors of the same generation. But, trust me - this is only temporary. Photosite size on FF sensors will contunue to shrink as the relentless marketing cry for more needless megapixels marches on.

So, at some point in the near future, ALL sensors will be able to resolve microscopic lens defects (and defects are different from abberations, another rant ). The only thing this does is drive up lens prices as manufacturers try to make their new lens designs match the new sensor resolving power, and our images become more cold, sterile, and cutting like razors.
You hit the nail on the head here. It is indeed pixel peeping stuff. The camera/lens companies of the world have a marketing and engineering strategy centered around pixel peeping! Like you said, pixel peeping gives them a hook to release new lenses with incremental improvements that chase after the ever increase pixel/photosite density. One day we'll have 100 MP sensors of every format and size and today's high end lenses will be considered junk because of pixel peeping. "Look, there's a 2 pixel red shift!"

There was a time about 10 years ago when lenses were chasing after the resolving power of the sensor. Now lenses are chasing after the sensors. I worked through the math at one time and calculated the equivalent pixel size for different sized sensors and resolutions. One pixel seems to be between 3 and 5 microns in size. It would not surprise me to see equivalent pixel sizes of 1 to 3 microns in the next 5 to 7 years. What kind of lenses will we see at that time? How will the older lenses (or even lenses of today) perform? Who knows?
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
28mm, 35mm, angle, aps-c, camera, cameras, crop, distance, factor, field, film, fisheye, fov, length, lens, lense, lenses, pentax help, photography, size, steve, subject
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
35mm FF vs 35mm crop angle of view on APS-C camera QCdude Pentax SLR Lens Discussion 3 01-26-2014 11:16 AM
What is special about APS-C specific lenses. Catscradle Troubleshooting and Beginner Help 9 11-17-2013 01:40 PM
Whats the crop factor for a 6x7 lens on a APS-C K-mount camera? 2her0ck Troubleshooting and Beginner Help 8 06-16-2013 11:45 AM
No one talks about the new Canon APS-C mirrorless? LFLee Non-Pentax Cameras: Canon, Nikon, etc. 2 07-22-2012 05:24 PM
Question About Crop Factor With Pentax FA 50mm f1.4 chrisrussell Pentax DSLR Discussion 35 12-13-2010 08:08 PM



All times are GMT -7. The time now is 10:58 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top