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LENSES: Facts and Fallacies - Part I
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PostPosted: Wed Apr 09, 2014 3:39 pm    Post subject: LENSES: Facts and Fallacies - Part I Reply with quote
This is an excerpt from the article "LENSES: Facts and Fallacies" by Lester Lefkowitz, which was published by Modern Photography in September 1983. Thirty years ago, digital photography was a dream and the lenses were all manual focus. The lens technology evolved since then, but I believe this article remains essentially valid.

The article is not overly technical, and I hope it's an enjoyable reading. Mostly, I hope it helps younger member to understand better the behavior of manual focus lenses.

Everyone feel free to comment and tell their personal experiences.






to be continued...

Last edited by Gerald on Sun Mar 05, 2017 5:55 pm; edited 1 time in total


PostPosted: Wed Apr 09, 2014 6:52 pm    Post subject: Re: LENSES: Facts and Fallacies - Part I Reply with quote
Gerald wrote:

to be continued...


Great stuff. Very informative. Thank you for posting.

Cannot wait for next installment!! Smile


PostPosted: Wed Apr 09, 2014 7:02 pm    Post subject: Reply with quote
Great info in plain language, thanks!

But I'd like to note that contrast issue with digital is not such prominent as with film.


PostPosted: Wed Apr 09, 2014 8:19 pm    Post subject: Reply with quote
Well I always thought the contrast dodge was used by cheaper lenses to appear sharper....but then always wondered how do you make a lens more contrasty Confused


PostPosted: Wed Apr 09, 2014 8:34 pm    Post subject: Reply with quote
Well, lens problems can be formulated into certain groups:

1. Low sharpness (digital can't help)
2. Low contrast (digital will help in most cases)
3. Sperical distortions (digital will help)
4. Vignetting (digital will help)
5. Chromatic abberations (digital might help, sometimes)
6. Flaring/ghosting (digital rarely will help)

So, in modern era #1 and #6 are main enemies, other can be easily fought in most cases, even automatically.


PostPosted: Wed Apr 09, 2014 10:18 pm    Post subject: Reply with quote
+1

The future is now :p


PostPosted: Wed Apr 09, 2014 10:26 pm    Post subject: Reply with quote
Excalibur wrote:
Well I always thought the contrast dodge was used by cheaper lenses to appear sharper....but then always wondered how do you make a lens more contrasty Confused


Cheap nasty lenses usually have poor contrast, especially in tricky lighting where veiling flare is often an issue.


PostPosted: Thu Apr 10, 2014 2:46 am    Post subject: Reply with quote
Good stuff, pure awesomeness. Saved for safe keeping. Keep these coming!


PostPosted: Thu Apr 10, 2014 3:00 am    Post subject: Reply with quote
Edited

Last edited by bernhardas on Tue May 10, 2016 7:40 am; edited 1 time in total


PostPosted: Thu Apr 10, 2014 3:12 am    Post subject: Reply with quote
Part of the trick with cheap nasty lenses is to look for situations where they can look their best, or find their special features. A good lens can spoil me, so I don't try to get something special. I somehow get blah stuff out the best. I am looking guiltily at my Biotar 75, which I rarely use.
On the other hand I have a completely awful 300mm (Kaligar branded Itoh) that has totally charmed me.
There's always a good side to any lens, it just needs to be found.


PostPosted: Thu Apr 10, 2014 3:23 am    Post subject: Reply with quote
luisalegria wrote:
Part of the trick with cheap nasty lenses is to look for situations where they can look their best, or find their special features. A good lens can spoil me, so I don't try to get something special. I somehow get blah stuff out the best. I am looking guiltily at my Biotar 75, which I rarely use.
On the other hand I have a completely awful 300mm (Kaligar branded Itoh) that has totally charmed me.
There's always a good side to any lens, it just needs to be found.


I am frequently reminded that "Lens don't make great pictures, photographers do". Very Happy Very Happy Very Happy Very Happy Very Happy Very Happy


PostPosted: Thu Apr 10, 2014 3:53 am    Post subject: Reply with quote
Edited

Last edited by bernhardas on Tue May 10, 2016 7:41 am; edited 1 time in total


PostPosted: Thu Apr 10, 2014 7:59 am    Post subject: Reply with quote
iangreenhalgh1 wrote:
Excalibur wrote:
Well I always thought the contrast dodge was used by cheaper lenses to appear sharper....but then always wondered how do you make a lens more contrasty Confused


Cheap nasty lenses usually have poor contrast, especially in tricky lighting where veiling flare is often an issue.


H'mm well I'm sure I read the contrast dodge i.e. less resolution but more contrast so the shot look sharper.... in a magazine about 45 years ago, but I suppose you can't always rely on memory.


PostPosted: Thu Apr 10, 2014 1:10 pm    Post subject: Reply with quote
The article from Modern Photography is interesting - and thanks for showing it. But somehow I'm left wanting more. The article tells us that Sharpness is more than Resolution - it has something to do with Contrast. And then the idea of a Modulation Transfer Function (MTF) is introduced, but we are not given an explicit relationship between Sharpness and MTF.

Norman Koren ( http://www.normankoren.com/Tutorials/MTF.html ) discusses these ideas with many more technical details. However much of the maths can be glossed over and we can look at his conclusion ( a short way down the first page of the link) ...

Perceived image sharpness (as distinguished from traditional lp/mm resolution) is closely related to the spatial frequency where MTF is 50% (0.5)— where contrast has dropped by half.

You may not agree with the MT50 number, but I think it's important to to remember that quoting resolution without knowledge (if only implicit) of the contrast level can be very confusing.


PostPosted: Thu Apr 10, 2014 2:55 pm    Post subject: Reply with quote
sichko wrote:
The article from Modern Photography is interesting - and thanks for showing it. But somehow I'm left wanting more. The article tells us that Sharpness is more than Resolution - it has something to do with Contrast. And then the idea of a Modulation Transfer Function (MTF) is introduced, but we are not given an explicit relationship between Sharpness and MTF.

Norman Koren ( http://www.normankoren.com/Tutorials/MTF.html ) discusses these ideas with many more technical details. However much of the maths can be glossed over and we can look at his conclusion ( a short way down the first page of the link) ...

Perceived image sharpness (as distinguished from traditional lp/mm resolution) is closely related to the spatial frequency where MTF is 50% (0.5)— where contrast has dropped by half.

You may not agree with the MT50 number, but I think it's important to to remember that quoting resolution without knowledge (if only implicit) of the contrast level can be very confusing.


Indeed, the perception of "sharpness" of an image appears to correlate well with the MTF50 value.

Thirty year ago, the Modulation Transfer Function, MTF, was very difficult to measure. Hence traditional tests measured the "limit resolution" or "ultimate resolution", which gives the number of lines per millimeter in which the lines are mixed into a blur. Nonetheless, people were well aware of the difference between sharpness and limit resolution. You've surely noticed the article author heavily emphasizes the difference between perceived sharpness and resolution. Incidentally, the "limit resolution" is given approximately by the point at which the MTF drops to 5~10%. That means also the "limit resolution" is always higher than MTF50.
Interestingly MTF50 depends largely on post-processing while "limiting resolution" is practically independent of PP.

After all, which is better to characterize a lens, the MTF50 or the "limit resolution" (MTF10)? Both measures have their values but the current trend is to use more the MTF50, which can be easily calculated by a computer. I intend to post in the coming days a simple procedure to measure MTF50, what could be useful to all who want to test their lenses in a more scientific way.


PostPosted: Sun Mar 05, 2017 5:21 pm    Post subject: Re: LENSES: Facts and Fallacies - Part I Reply with quote
Gerald wrote:
This is an excerpt from the article "LENSES: Facts and Fallacies" by Lester Lefkowitz, which was published by Modern Photography in September 1983. Thirty years ago, digital photography was a dream and the lenses were all manual focus. The lens technology evolved since then, but I believe this article remains essentially valid.

The article is not overly technical, and I hope it's an enjoyable reading. Mostly, I hope it helps younger member to understand better the behavior of manual focus lenses.

Everyone feel free to comment and tell their personal experiences.








to be continued...


PostPosted: Sun Mar 05, 2017 6:28 pm    Post subject: Reply with quote
Just looks like the difference when I bought a Elicar rf 300mm 5.6 (10 times cheaper) to replace my old Minolta RF 250mm 5.6 I lost in a park in Lisbon in September 2015.


PostPosted: Sun Mar 05, 2017 11:45 pm    Post subject: Reply with quote
Antoine wrote:
Just looks like the difference when I bought a Elicar rf 300mm 5.6 (10 times cheaper) to replace my old Minolta RF 250mm 5.6 I lost in a park in Lisbon in September 2015.


Hoping for a good story about how about how a 250mm lens gets "lost in a park"...


PostPosted: Mon Mar 06, 2017 12:07 am    Post subject: Reply with quote
http://math.ucr.edu/home/baez/physics/General/Glass/glass.html

seems to echo much of what is said here...


PostPosted: Mon Mar 06, 2017 5:30 am    Post subject: Reply with quote
Rockwell had something about MTF too, he used it to explain why low-res digital looks crisper than film.

Digital having near 100% MTF steadily until it drops sharply to zero (actually, often softened by aliasing filter), people then talk about lenses outresolving sensors (and vice versa), suggesting a simple < > order relationship, while it is the product o the MTFs.

You still can have a hazy lens, or many of them.


PostPosted: Mon Mar 06, 2017 9:16 pm    Post subject: Reply with quote
This has been my favorite page(s) for a very long time .. this tutorial and a lot of others on these pages ...

http://www.normankoren.com/Tutorials/MTF.html
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