This is a 6x4.5 lens from Pentax for their Pentax 645 cameras, covering the focal lengths between 80mm to 160mm - which on a Fujifilm GFX would be equivalent to a 60-125mm ƒ 4.5 zoom lens. In other words; it begins as a little longer normal lens - all the way to telephoto.

Why this lens ?

Because it had a fantastic price ($100), covers the Fujifilm GFX sensor, and looks to be in very fine condition. The end price for me was 1600 SEK / 142 Euro. Not bad for a mediumformat lens, wouldn't you say ? Hopefully it performs well (after stopping down a bit**).

Pentax 6x7 version of this lens; too bulky

Also; the equivalent in the Pentax 6x7 line-up, the 67 SMC 90-180 mm ƒ5.6 zoom - is a lot bigger, heavier and bulkier (and nowadays sold without lens hood !) And it is a LOT more pricey. Often ending up around 5500 SEK or 510 € in total (with tax & import)

The Pentax 6x7 zooms have gone up in price a bit, and there are not as many available as there use to be.

Since I do have my Pentax 6x7 lens line-up covered with fixed lenses - which I mostly use with the Fotodiox VERTEX adapter, in order to make true digital 6x7 fullframe images. So, I don't really need a 6x7 based 90-180mm zoom.

Instead

I thought the Pentax 645 zoom might do it. Plus this is a FA version, which means autofocus on my film based Pentax 645N camera (whenever I use it with film, i mean) - so AF is a bonus. I never used AF on the Pentax 645 camera, because none of my Pentax 645 lenses have any AF. I use the A-versions, which are older, with manual focus.

The 645 Pentax FA 80-160mm zoom can be neat (flexible) for photo studio works - as well acting like a walk-around lens that is more telephoto oriented. Under the condition that I got a good lens. Sometimes lenses can be decentered, which lowers there optical performance, when not all lens elements are aligned. For example, because the previous owner dropped it on the floor. Or became decentered during assembly at the factory.

The Pentax 645 FA lenses are of later date, around 1997 - but most of the exhibit the same optical formula like their older, manual Pentax 645 A siblings from the early 80s. Only the lens coating might be newer in the FA-versions.

Into the Pentax 645 lens system

Since I just bought the Pentax 120mm macro for future film negative scanning with the Fujifilm GFX camera - I needed to buy an adapter. That naturally opens up for me to adapt any Pentax 645 lens in the future, too. It is not my main focus, though - because any Pentax 6x7 lens, which i got plenty of - can be adapted to any Pentax 645 camera. Therefore i didn't buy Pentax 645 lenses. I think i have only two which i used with the Pentax 645N camera; the Pentax A 150mm ƒ3.5 lens (portrait), and the 645 Pentax A 45mm ƒ2.8 lens (moderate wide angle).

Well, now I'll have 4 lenses instead.

It really wasn't a necessary lens for me to buy that 80-160mm zoom. I bought it on a "whim", so to speak. Yet, I did do a lot of research about it, simply because I was astonished how affordable the zoom is (in relation to the much more expensive 6x7 zoom version).

The manual 645 Pentax A 80-160mm version, can be had for as low as $60 (i have seen one good one for that price, e.g. without fungus, haze or mold). So, I wanted to know, what's about that zoom; if it is any good or is it cheap because it isn't valued as a good lens.

What do I know about the 645 Pentax FA 80-160mm ƒ4.5 lens ?

It flares, if you don't use the lens hood.

It has a so-so in sharpness at wide open aperture and can show haloation (bluish and/or purple around high contrast details). Post sharpening can be used of course, giving finer details a great boost. Once you stop the aperture down, it is considered to be a pretty sharp lens. Some users seem to own a lemon - while others consider the zoom to be as damn sharp lens. It appears to me, that it is critical that the lens elements must be centered, in order to perform as it was intended to.

Given that the zoom is a 645 lens, it COVERS the entire Fujifilm GFX sensor... there will be no dark corners.

Thanks god.

**) Mediumformat lenses in general

from the film era - almost always need to be stopped down for good optical performance. It is and has been very typical that mediumformat lenses perform they best when stopped down to ƒ8 - ƒ11 where they often peak. At wide open aperture, they are usually a bit soft, show chromatic aberration, and other optical "errors". That doesn't mean you can't use them. I often use them wide open, just for the flair or atmosphere / rendering of the scene. No problem.

but as a landscape photographer for example, he and she like sharp images - and that's where you stop down to middle apertures, in order to get most out of the mediumformat lenses. Whether it is film or used on a digital camera. Naturally, the film era lenses are not in the same league like the digital counterparts when it comes to micro sharpness.

But these older lenses tend to render images in a more "organic" way. Not so clinical. Small optical errors like fringing / chromatic aberrations, can often be fixed in post.