Is there a need for F1.4 lenses....

Started 4 months ago | Discussions thread
AiryDiscus Senior Member • Posts: 1,930
Re: Is there a need for F1.4 lenses....
1

fferreres wrote:

AiryDiscus wrote:

fferreres wrote:

Philnw2 wrote:

I won't mention any brands, but there have been chronic reports of decentered f1.4 lenses for some. Perhaps specific facilities are not all equipped to deal with accurate mfr of these kinds of lenses.

HEre are some examples of sample variation. You buy a lens, and itmight be trash or diamond. It it a lottery? Apparently, yes,

https://www.lensrentals.com/blog/2016/06/the-sony-fe-lenses-mtf-and-variance-summary/

https://www.lensrentals.com/blog/2015/08/mtf-and-variation-an-example/

The longer the FL and the faster, the worst this is.

https://www.lensrentals.com/blog/2015/06/measuring-lens-variance/

This ones give an idea over 2D surfaces. It's not just less sharp...

https://www.lensrentals.com/blog/2016/11/fun-with-field-of-focus-ii-copy-to-copy-variation-and-lens-testing/

In all honesty, I don't think the principal and unavoidable cause is a faster aperture. A faster aperture, with good glass, may not necessarily be harder to align.

It takes an optical designer of extraordinary skill to produce a design of a larger aperture that is easier to align than one of a smaller aperture. Larger apertures almost by necessity have larger ray angles, which are more sensitive to small perturbations than small angles.

I am always humbled, grateful when you chime in. I hadn't thought for a second how it could be even more difficult, even if in absolute terms, a larger element may seem to intuitively easier; but now I know it's not as the tolerances get stricter and the other things you mention. Thanks!

It is not just bigger - it is also less flat.  When it is more appreciably not flat, the ray angles get larger, and thus the alignment sensitivity does too.

The difficulty is that producing small nm layers and layers (3? 5? per side) perfectly even

Antireflective coatings can be anywhere from a few angstroms (airsphere or whatever Canon calls, it nano or whatever nikon calls it, and so on) to 10s of nanometers thick. As a race, we figured out how to deposit atomically thin layers of these compounds decades ago. It is challenging, but very much a solved problem. Coating [uniformity, layer thickness, ...] are a nonissue in modern optics.

If all coatings are generally uniform, I'll cross that out from my list...this is probably more so for higher quality lenses, maybe, but I take it at straight value to not worry about coating uniformity (ie. what was designed, and what ends up being deposited, being largely the same).

The "high quality" lens is going into the same chamber as the "low quality" one.

at that scale and also aligning what, 20 elements, grows in complexity exponentially. Anyone that ever played Yenga can have an intuitive way to visualize it.

More elements does not mean harder to align. Often, the number of elements is increased to trade production cost in terms of grinding, polishing, etc, for production cost in alignment tolerances.

I had no clue about that scenario either. Does this also mean, in your understanding, that a 30 element lens then, may be as easy to align as a 3 element lens? I am simplified general case I mean.

3 would be universally easier than 10 (no matter how hard, your attention is much less divided).  But comparing 12 to 15, which is far more likely, 15 could certainly be easier than 12.

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