I tried to find images I took with the old manual Pentax 645 A 150mm ƒ3.5 lens - only finding two generic photos which didn't say much. Albeit I have had this lens since 2016 i believe for portraits (of Sal) with the analog Pentax 645N camera... Still, I didn't really use it with the Fujifilm GFX 50s II camera, I realize.

Well, I know why.

Because when I made portraits of Sal and myself, I used the larger Pentax 67 SMC 150/2.8 lens instead (among others. And that one is RAZOR sharp, especially when stopped down 1-2 stops - it will show off even the slightest hairs between skin cells in the face *LOL*

For unknown reasons, the tiny lightweight Pentax 645 A 150/3.5 never saw any usage. So, let's look at it a bit closer.

Current situation:

I suspect that my current double-adapter "solution" disables the cameras Image stabilization (IS).

Also; it prevents me from using ƒ3.5 - and seems to be only going to something like ƒ4.5 or ƒ4... (Only when i demount the lens, put it back to ƒ 3.5 - then the aperture stays open. So, i had to re-do the whole session).

Yet, i didn't see any difference in the background blur... how odd. They all look the same

One thing is for sure, the "double adapter" does not register manual dialed in focal length of 150 mm. Which means, IS (Image Stabilization) never worked on my Pentax 645 zooms, either. No wonder, it felt iffy to set focus manually - because the image though the viewfinder was shaking alike crazy (especially at 300 mm !!) and spoiled the whole telephoto experience... Now I know.

I will keep an eye on that.

Or better said

i skip this "double adapter" combination entirely - because with the new Fringer P645-GFX adapter arriving in a couple of weeks, it will enable IS while dialing in correct aperture value will be done on the GFX camera body instead). EXIF and everything will be registered too, and I don't have to add that later in a special EXIF app.

No more fiddling

Wide open aperture ƒ3.5 quality

It shows soft details due to soft micro contrast - albeit you can discern fine details. Once you sharpen the image ever so slightly, you'll see that sharpness is there at ƒ3.5

In an overall photo of 51 MP - the image looks sharp with a pleasant overall softness. For being an old era 80s film lens - the performance on digital sensor is admirable. (Remember, this is at wide open ƒ3.5 aperture - not stopped down yet !).

Fringing

Contrast with typical film-era made lenses, showing a slight glow of green and red in sharper outlines. Not really that disturbing, because you can easily correct that in Photoshop. What i mean is, that it is one of lenses where it is easier corrected. The "green/red bleeding" in outlines isn't that excessive). In high contrast situations, there can be purple fringing when you use wide open aperture ƒ3.5

Background Blur

Is gorgeous: gentle, soft and pleasant. (That's why people like this lens in combination with the analog Pentax 645 cameras, because the character is perfect for portraits). Plus the price is extremely affordable (for the manual "A" lens)

Without exaggerated contrast, it exhibits mild sharpness with beautiful background character. A perfect combination for pleasant portraits.

So yes. I will test this lens further. Since it is so small and light - i think it makes it a great "on-the-fly" lens, when going out and about - without the bulk and heavier lenses.

Vignetting

At wide open aperture ƒ3.5 there is pronounced vignetting visible, albeit of soft character. It starts to disappear at ƒ5.6

Example One

Example Two ƒ3.5

Example Three ƒ3.5

Admirable performance

The wide open aperture sharpness is admirably good - for a film lens from the 80s. I had expected worse.

Today's digital image tools

Given the digital tools we have today, lack sharpness - is not an issue. Because the original RAW files already show plenty of details at ƒ 3.5. From there, it only gets better - as you can see that the finest details do come forth with a light AI sharpening applied.

This is, why older lenses do sometimes make sense in a digital world of 2026. We have the tools now, to spice things up (as long it isn't exaggerated, in my opinion - because if you do it too much . it just looks tacky).

Organic look (overall photos)

I also like the "organic" feeling in images with this lens - the way it renders a motive. It is therefore more of the the opposite to the clinically, razor sharp, pretty much perfect Fujinon GF 110/2 lens.

Fringing / CA and Vignetting can be corrected relatively easily with the Pentax 150/3.5 lens.

Overall, I am very pleased with this light - and gosh so small - 150mm lens when used with the Fujifilm GFX. Giving me an interesting portrait alternative, when I wish to go light and small. (Walk around)

When mounted on the Fujifilm GFX - this lens has a perspective equivalent of a 120 mm ƒ 2.5 portrait lens on fullframe cameras.

At eBay

the prices start at the lowest level at around $85 (no tax nor shipping included). Mainly concentrated at a level of around $160-210, albeit European sellers seem to hover at 260-300€ and upwards instead (as those sellers are usually photo stores rather then private people).

The EU price is a bit over the top, in my opinion.