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Olympus Pen-F 250mm f5
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PostPosted: Thu Mar 16, 2023 5:53 pm    Post subject: Olympus Pen-F 250mm f5 Reply with quote
I am looking at an Olympus Pen-F 250mm f/5 on eBay. This is a half frame lens (for which I do have an adapter). It is my understanding that the 250mm is not very common. It is also somewhat heavy at 800 grams.

Anybody have any experience with this one? I own two PEN-F lenses and they are very nice, except a bit questionable on the radioactivity side of things (both make the meter beep but read normal after a full measuring cycle; weird). I have read that quite a few of these PEN lenses have some degree of radioactivity.

Anyway, curious if anyone has an opinion on the optical characteristics of this 250mm.

Regards, C.


PostPosted: Thu Mar 16, 2023 8:22 pm    Post subject: Reply with quote
Well, the (new to me - why didn't I look here sooner?) diagram from the Ponder and Best information booklet certainly is interesting - has to be another dense-flint 'apochromat'. For I don't know any other reason for the front group to look like that.



1.42x crop factor would make it 355mm (f7.1) equivalent.


PostPosted: Thu Mar 16, 2023 10:07 pm    Post subject: Reply with quote
I am sorry, "dense flint apochromat".... can you please explain?

Regards, C.


PostPosted: Thu Mar 16, 2023 11:44 pm    Post subject: Reply with quote
The Pen F lenses are indeed excellent, but I doubt the 250mm was an apochromatic lens, it's too old to have made much use of Thorium, Lanthanum etc.


PostPosted: Fri Mar 17, 2023 12:07 am    Post subject: Reply with quote
connloyalist wrote:
I am sorry, "dense flint apochromat".... can you please explain?

Regards, C.


Sorry - I should remember that's not quite common knowledge yet.. Very Happy

It is a type of optical design found in long (300mm+) focal length lenses that's quite distinct in it's deeply curved front triplet. This is used to apochromatically correct CA without notably low dispersion glass.

It is still recognizable even allowing for design variations.
I would like to say there is more to it, but there are only a few considerations and a few elements here (with the rear two serving to flatten the field). Once you put chromatic aberration to one side or settle for an average amount of it, we know what design can be used to achieve this speed - a simple doublet up front with a 1-2 element rear field flattener, or even a 4 element ernostar, all with less extreme curvature. As we have seen countless times before.

It is only CA that is this problematic to avoid at this aperture + focal length, often noted as requiring special treatment from growing in proportion to focal length. Which is hard to say about other aberrations.

For explanation (and discussion after this post of other lenses that count) see here


PostPosted: Fri Mar 17, 2023 12:17 am    Post subject: Reply with quote
I know that the most commonluy seen design for an apochromatic lens back in the 50s-60s was the dialyte - 4 air spaced elements. Most apo process lenses from this period are dialiytes, the rest are tessars, they were superceded by plasmats mostly. No exotic glasses involed, but the maximum apertures were of the order f9, f10, f11.


PostPosted: Fri Mar 17, 2023 7:10 am    Post subject: Reply with quote
eggplant wrote:
connloyalist wrote:
I am sorry, "dense flint apochromat".... can you please explain?

Regards, C.


Sorry - I should remember that's not quite common knowledge yet.. Very Happy

It is a type of optical design found in long (300mm+) focal length lenses that's quite distinct in it's deeply curved front triplet. This is used to apochromatically correct CA without notably low dispersion glass.

It is still recognizable even allowing for design variations.
I would like to say there is more to it, but there are only a few considerations and a few elements here (with the rear two serving to flatten the field). Once you put chromatic aberration to one side or settle for an average amount of it, we know what design can be used to achieve this speed - a simple doublet up front with a 1-2 element rear field flattener, or even a 4 element ernostar, all with less extreme curvature. As we have seen countless times before.

It is only CA that is this problematic to avoid at this aperture + focal length, often noted as requiring special treatment from growing in proportion to focal length. Which is hard to say about other aberrations.

For explanation (and discussion after this post of other lenses that count) see here


Aha, thank you. Interesting. It seems to me that in the 1960's when these PEN-F lenses were made Olympus may have had the technology available to make these cost effectively? Would the fact that this is a half-frame lens make the manufacturing process easier?

Regards, C.
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