Comparing sharpness of 16-80 to other lenses

Started 9 months ago | Discussions thread
koweb Contributing Member • Posts: 524
Re: Questions

Steve Bingham wrote:

koweb wrote:

Steve Bingham wrote:

For a complete understanding of these two terms, look up MFT. They are a measure of contrast and resolution (together) taken 90 degrees apart (diagonals). There is MUCH more to learn - as you will find out! Some manufacturers use theoretical and wide open. Others use both wide open and f8 (Canon). Still others test actual lenses. Many variables, including distance. Some use 15 lines per mm, others use 10, 15, 30, and 45. The closer the M&S lines are (at a given lines per mm), the sharper the lens is - well sort of.

"Modulation Transfer Function or "MTF" is a measurement of the optical performance potential of a lens. MTF charts can give you a better understanding of the optical quality of various lenses." You CAN NOT compare brands due to the many methods used.

Steve, not sure I understand your comments underlined above.

My understanding is that the thicker lines measure contrast (Fuji's 45 l/mm), while the thinner lines (Fuji's 15 l/mm) measure resolution. Is that true?

Nope. I wish it was that simple! However, as a general explanation it will suffice. You see that "sharpness" is really determined by both contrast AND resolution. The thicker lines are used to measure contrast and the thinner lines to measure resolution. Sounds simple, right? Actually, there is much more. Bokeh, might be considered the difference between the line pairs - as one measures accutance one way while the other measures it at 90 degrees. The separation might produce excessive coma which in turn affects bokeh. At least, that's how I understand it.

As the lines (fat and thin) become closer together you approach better alignment between contrast and resolution. A VERY good thing.

Maybe that's what you said, but I misunderstand??

Then, can you explain further the italicized comments above? I thought that if they are closer together it is more a predictor of bokeh, sort of...

Curious to learn more.

Thanks,

Thanks Steve, very helpful,

So, is this correct? It would seem that not all is good in the MTF charts for the 16-80? At the tele end especially, the lines are not very aligned at all. Thoughts?

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Bradk

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