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12-08-2018, 04:56 AM - 1 Like   #121
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QuoteOriginally posted by ivanvernon Quote
Thanks for this detailed explanation. I will have to read it a few more times to know if I am more confused or less confused, but everything you state seems well reasoned. :>)
Forgot to write one more thing.
When you read that an f/whateveritis lens would behave on another format as an f/0.9 lens, of course it doesn't mean that the lens gets faster by magic.
It simply means that IF you keep the subject size the same, the bokeh would look similar to the result you'd get from a much faster lens, simply because of a change in perspective.
To affect the physics of a lens we need optical means: they are called Booster Adapters.
The elements of the adapter concentrate the information (the photons) to a smaller area. A full frame lens used with an m4/3 booster actually increases the theoretical aperture. It's the opposite way a teleconverter works.
DOF and bokeh are affected, cause the actual focal length has changed.
However, the effective max aperture could be a little slower than expected cause more glass means more dispersion. The change in F stop is not met by the same increase in T stop (the real amount of light that reaches the sensor). It is a detail, though. If you use a lens designed for a larger format, and want to have a real increase in speed, the boosters are they way to go. You can shoot from the same place, and the bokeh won't look different because you move closer, but because the nature (focal and speed) of the lens is different.

All in all, I see some good reasons to use medium format lenses on smaller formats, and it's not because of some disputable formula.
I know that some people see it in a negative way, saying that the larger circle of coverage can cause inter reflections (especially in adapted objectives), and because some lenses are actually a tad less sharp than their 35mm equivalents.
Coverage comes at a price, optically speaking. On top of that, the design had to be good enough at lower enlargements, allowing for some compromises.
In reality, in some cases the use of medium format optics on smaller formats allows to have access, for relatively cheap, to a kind of rendition that is nowhere to be found in what the market offers at present times.
Let's also not forget that medium format lenses were designed as "pro" optics, with first tier performance.
If you want the "Sonnar character", is there any other choice in that focal range other than your 180mm for Pentacon Six?
Btw, using such big chunks of glass wouldn't be so cheap nowadays.
Same with Ernostar designs.
I could continue... but I guess I have made the point.
Medium format lenses have a place. It is up to individual choices and preferences if it would work, according to our needs and tastes, or not.

01-10-2019, 03:56 PM - 2 Likes   #122
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Posting with new soft focus lens, Pentax 67 120mm f 3.5 soft

I have just received a very nice copy of Pentax 67 120mm f 3.5 soft focus. It has decreasing degrees of soft focus effect as you move from f 3.5 to f 8.0, and then becomes a normally focussing lens at f 11.0, f 16.0, and f 22.0.

Here are a few landscapes with softness set at about f 5.6.

KIT: 645z with (adapted) Pentax 67 120mm f 3.5 soft.
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5 Days Ago - 1 Like   #123
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New (to me) soft focus lens

Here is one that just came to me a week or so ago, and I am really loving it. It is the Mamiya 145mm C f 4.0 SF. This lens is more complex than the Pentax lenses in that degree of softness is adjusted in two different ways: (1) by a 5-step softness ring at the front of the lens, which adjusts two internal lens elements in four softdness steps and one non-softness setting; and (2) by the selected aperture which adjusts softness within each of the four steps. This is a medium format lens, but cannot be used on Pentax medium format cameras owing to inconsistent registry differences. It can be used very well on the K-1, however. Mamiya-Pentax K mount adapters are readily available on eBay.This lens is a real delight in part because of the very well engineered and constructed all-metal body, ease of operation, and excellent image quality including the non softness setting. As a non-SF lens, it is super sharp, and can double as a street or even as birder lens on the K-3 where kit has lots of reach. Downsidses of the lens are: (1) size and weight may be too much for some folks, (2) minimum focal distance is maybe 4-5 feet, and (3) it is manual focus only as are most other SF lenses,.

Here are several test shots. I have thrown in some with both sharp and SF settings for the same/similar photos.
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