It is like the say at the Pentax forum... The Pentax 6x7 SMC 300 mm f 4 lens is one which really has a lot of chromatic aberration. Plenty of it. Both wide open as well stopped down.

It can be corrected digitally, to a large degree. And the sharpness at wide open aperture ƒ 4 i take care of with Topaz Sharpen AI or Photo AI - so that isn't any problem. At ƒ 11 the sharpness is good.


No problems in Black & White

When you use this lens in Black & White - then chromatic aberration is really not a problem. Given it's very low price (starting 50 Euro), it is a steal. On the other hand, it isn't an easy lens when mounted on a big mirror flappy Pentax 6x7 camera - because the lens has no tripod mount. This makes it rather challenging to get really sharp / to avoid blur from vibrations.

But - I like it together with the 6x6 Vertex adapter. I mean, i can do things with this lens - it is good enough. And with digital tools it can be made better - so I am not regretting this lens. In fact, I have never used it on the Pentax 6x7. It looks brand new, since i bought it for a low price back in 2018 - but never used it.

It is a the first time.


For my demands it is perfect

Given that my main "Scene" is just my Diary here, and the final images are only something like 2300 pixels wide here... A lens doesn't need to be stellar in order to look good here.

However, this Pentax 6x7 SMC 300 mm f 4 deserves to used much more, in order to get the hang of it - its strengths and weaknesses.

The Pentax SMC as well Takumar 300 mm f 4 have a minimum focus distance of 5 meter (!). The optical formula is the same between the three versions Pentax has come out with (The ED version not included). The later ED/IF version has a minimum focus distance just 200 cm.

After all, these are all 6x7 medium format lenses - with an image circle of at least 70 mm


There is another 300 mm lens

There is another 300 mm lens, the SMC Pentax-M* 67 300mm ƒ4 ED [IF]  - which is quite a notch up, because its optical design features 9 elements in 9 groups and has extra low dispersion elements (ED) in the optical design. As well Internal Focusing (IF = it doesn't extend when focused), and a tripod foot.

The price is actually reasonable on the second hand market as of 2023 - starting at around 500 Euro. But since I am not a heavy 300 mm user on a medium format camera - i doubt i need a better 300 mm lens.

I am already happy that it works with the Vertex adapter and Canon EOS R - where vibrations is so not a problem with this lens.


If I would buy the 300/4*ED IF version ?

then the older one would just collecting dust. So, i don't buy that lens, because 300 mm is just something i use very rarely with a Pentax 6x7, or with the Vertex adapter. Therefore the simpler version is totally fine for what I do.

Only if I often do serious work, e.g in nature with this type of lens - then i may consider it in the future. But i doubt that. I have excellent super telephoto lenses from Olympus, Canon and Sigma for such work, getting way further. (After all a 300 mm lens on a Pentax 6x7, is equivalent to only something like 140-150 mm on fullframe).

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