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

Started 4 months ago | Discussions thread
fferreres Veteran Member • Posts: 3,746
Re: Is there a need for F1.4 lenses....

Philnw2 wrote:

fferreres wrote:

Philnw2 wrote:

F2 on a 135mm lens: focus distance about 100ft, DOF abt 20 ft, man with red backpack

You bring an interesting point. it is not new, especially to most here, that the DOF is in some way closely related to the subject distance from the lens. In the example above, you have a fast aperture with a large DOF as it's at 20 ft. Here's the inverte table, where I want for what I am thinking a 1 meter DOF.

This table lists all distances (and corresponding Aperture) that result in a a 1m DOF for an 85mm FL lens. Of course, if we set 20/20 vision and not camera maker assumed, the 1 meter may now be 50cm, or if we pixel peek or allow exploring from closer distance, may be 20 cm. But let's say 1 meter:

Subject Distance and f-stop resulting in 1 meter DOF for an 85mm lens

In this case, the fantastic advantage of the f1 lens is being able to place the subject 11 meters away, and f1.2 allows it to be 10 meters away, and an f2 lens, 8 meters. They all produce the same DOF. At f5.6 distance should be 4.5 meters. Of course, the faster lens is still more flexible, but this should that minimal differences (eg. 11m vs 9 meters) is the cost between an f1.6 lens vs f1, and the f1 lens surely will have a lot more aberrations.

Does this means an f1 lens is not useful? Or what if I really want that and need the subject 11m away, and not 9 meters? Well, this is the awesome advantage of going from a $50 to one $5000 with lower quality at max aperture.

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. Actually, it could be even easier to do precisely. The difficulty is that producing small nm layers and layers (3? 5? per side) perfectly even 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.

The only solution?

1) Test and return many times

2) Buy from brands with higher cost but much better QC

3) Get used to it

4) Buy slower lenses that don't need a huge army of elements with brutal numbers of coating layer. The more elements a lens has, the more it needs more and more layers, and the more and more they compound.

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