Search for the cheap new aps-c to adapt

Started May 25, 2020 | Discussions thread
petrochemist Veteran Member • Posts: 3,056
Re: Search for the cheap new aps-c to adapt

Tom Caldwell wrote:

walter g1 wrote:

Tom,

Neewer 85mmf1.8 is a 6/6 design.

Opteka 85mm f1.8 is a 10/7 design.

There are also cheap 85mm f1.8 lenses with a 9/7 design.

Not that I care that much but this Opteka thing has me a bit puzzled:

Looks like 6x6 in the illustration

Yes it looks like 6x6 but I suppose a few of the apparent elements could be a bonded group without the boundary between elements shown. Certainly no more than 6 groups.

It seems to be found at reduced prices when I look closer. I can only find them in Nikon mount that might account for some small weight discrepancies. One vendor claims that they are full frame capable - all others just list the Nikon dslr bodies that they will mount on.

Visually they are the spitting image of the Kelda/Jintu/Neewer lens and hood apart from "Opteka" finishing.

The illustrated Optekas have the same crazy stops 22-10-6-4.5-3.5-3-2.5-1.8* and the same focus scale markings in feet and metres*. They both have minimum focus distance of 0.85m.

FWIW those apertures fit well with a constant increase in aperture diameter (smallest 4mm then 5mm increase each stop till wide open which gets a bigger jump) rather than the more useful proportionate change. To give our usual stops each aperture diameter should be 1.4x the previous one.

The drawing does show a wider gap between f/1.8 & f/2.5 than for any of the other 'stops', so it looks to be more accurate than the optical elements suggested. Perhaps the wrong optical layout accidentally got overlaid on the lens drawing - I suspect that would be more likely to be missed than the wrong value being added to the specs.

An intriguing puzzle Tom, thanks for sharing it.

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