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LENSES: Facts and Fallacies - Part XI
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PostPosted: Mon Apr 21, 2014 4:07 am    Post subject: Reply with quote
That's great conspiracy theory. If a zoom looks like an average prime in terms of MTF, it will look like an average prime in terms of lp/mm too. In reality, MTF and lp/mm are just complimentary ways to measure the lens performance. For instance lp/mm are always measured at specific MTF, e.g. MTF 50 and MTF 20. All lens testing sites report lp/mm because they are easier to interpret for a layman.

Coming back to the topic, in my experience modern zooms still lose to primes (both modern and old) in performance, pop, speed, character, pretty much in everything except the convenience, but zooms has become good enough to make that convenience count and often be the main factor.


PostPosted: Mon Apr 21, 2014 7:58 am    Post subject: Reply with quote
I have a few high quality zooms and they perform amazingly well, but I still prefer to use primes because they tend
to be faster, smaller, lighter, and even higher quality image.


PostPosted: Mon Apr 21, 2014 1:03 pm    Post subject: Reply with quote
mo wrote:
Quote:
From what has been said, it is clear that neither resolution, sharpness,graininess, nor tone reproduction is of itself the determining factor for good definition in a photograph. In order to combine these properties in the simplest way, it has recently become customary to express the performance of a lens by its modulation transfer function (MTF), on axis and at several points in the field.

As its name implies, MTF is a measure of the ability of the lens to form an image that is an accurate reproduction of an object


I grabbed this quote from Rudolf Kingslakes book "Optics in Photography". I added the bold.

If MTF is just about showing how a lens reproduces an image by expressing it in a chart format, that can be easily read and understood by lens technicians to help them on how a lens will perform, or if it is worth while going ahead with a lens design...it is only a small drop in the bucket as to why we use a lens. I believe we enjoy seeing the result of a particular lens regardless of what the MTF charts say,there are so many factors an MTF chart can not cover.

This is a discussion that can get lost in mind numbingly small details....although the discussion can be interesting.



Excellent quotation! Kingslakes was one of the greatest experts in photographic optics in the world.

MTF is a fundamental tool for analysis and design of lenses. That's why MTF is so used by optical engineers and technicians in their work.

A photographer concerned only with the artistic aspects of photography does not need to know anything about MTF, but as you know, there are many photographers who are very interested in the technical aspects of lenses, cameras, sensors, etc. This explains why the lens manufacturers usually provide information on the number of optical components of a lens, type of coating, MTF, etc. This information is usually ultra simplified and not always technically true, but serve the purpose of creating a fantasy in the minds of many photographers. In fact, the technical information provided by lens manufacturers is basically an advertising element of their products.


PostPosted: Mon Apr 21, 2014 1:15 pm    Post subject: Reply with quote
Nordentro wrote:
"... zoom lenses have much more glass for the light to travel through in order to reach the sensor; extra elements are required to zoom in and out, and even more are needed to correct the aberrations created by all the extra elements. With the light altered so many times, it is bound to degrade..."


Oh, my... People have a bad experience with cheap filters and then come to bizarre conclusions...

By that "logic", a Domiplan with 3 elements is a better lens than a Zeiss Otus with 12 elements. Or that a $11,799 Canon EF 200-400mm f/4L with built-in 1.4X extender is a crappy zoom. After all, the Canon zoom has 33 elements!


PostPosted: Mon Apr 21, 2014 2:52 pm    Post subject: Reply with quote
I speak in general. The Canon 200-400mm f/4 you refer to is only a meassured 6.9 lens.


PostPosted: Mon Apr 21, 2014 3:25 pm    Post subject: Reply with quote
Nordentro wrote:
I speak in general. The Canon 200-400mm f/4 you refer to is only a meassured 6.9 lens.


I think you are talking about the T-number of the Canon 200-400mm F4. Note that the T-number 6.9 was measured with the extender ON!

The F-number is F5.6, so the loss is little more than 1/2 stops (0.6 stops to be exact). In comparison, the prime 50mm F1.4 loses 0.39 stops. That is, the zoom loss is about 0.2 stops higher than the prime. Not bad for a zoom with 33 elements, compared with a prime with only 7 elements.


PostPosted: Mon Apr 21, 2014 11:07 pm    Post subject: Reply with quote
Yes, mesured is always T stops and F stops is the theoretical speed. As you say, with the extender is 6.9T and 4.7T without. I have no doubt about this being a fantastic lens.


PostPosted: Thu Apr 24, 2014 1:44 am    Post subject: Reply with quote
Okay, so we have the fantastic Canon 70-200/2.8 with nice sweet zoom spot at 200mm -- i.e. designed to be best at maximum zoom, where most users will set zoom...and... the fantastic Sony 14-24mm, along with something or two from Zeiss. What other newer zoom lenses are there which are better than primes.

I will concede that a few modern zoom lenses give as good or better performance at a sweet zoom spot than corresponding prime, but that leaves the entire remaining zoom range...can we say that Canon 70-200mm/2.8 gives as good or better performance at 135mm, at 85mm? No.
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