Aetna Rokunar 300mm f5.6

Scheimpflug · Expire: 2011-11-18

I'm starting to think that perhaps this lens is NOT a direct copy of the Adaptamatic Auto Tamron... or any of the Tamron 300mm f5.6's for that matter. I've been comparing the versions, and mine just doesn't match up. Confused

So here's mine, the Aetna Rokunar 300mm f5.6:

.. and now let's look at the Tamrons. First is the Auto Tamron, with the Adaptamatic mount, model 670Au:

http://www.adaptall-2.com/lenses/670Au.html
(edit: now http://www.adaptall-2.org/lenses/670Au.html)

followed by the early (transitional?) Adaptall version (posted on the forum here by member dab63, but not listed on adaptall-2.com):

http://forum.mflenses.com/silver-tamron-300mm-f-5-6-adapt-a-matic-or-adaptall-t23757.html

followed by the Adaptall version, model CT-300:

http://www.tamron.co.jp/data/old-lens/ct300.htm

followed by the Adaptall-2 SP version, model 54B:

http://www.adaptall-2.com/lenses/54B.html
(edit: now http://www.adaptall-2.org/lenses/54B.html)

Comparisons:

The Aetna has the most visual similarity to the Auto Tamron.
The presence of a tripod collar on the Aetna matches it with the Auto Tamron and the early Adaptall.
The Aetna's focus/DOF "tree" is a diagonal fan-out style, matching the Adaptall version of the Tamron, but not the Auto Tamron or the early Adaptall.
The Aetna has 62mm filter threads match the Auto Tamron and the early Adaptall, but not the Adaptall or Adaptall-2 SP models (58mm).
The Aetna's focus grip moves away from the mount when focusing, which matches everything except the Adaptall-2 SP.
The Aetna's close focus distance is around 1.5m, and the lowest marking on the focus ring is 1.7m. The minimum focus for the Auto Tamron is 2.5m, and remains 2.5m for the Adaptall version. The only Tamron with a closer close focus is the Adaptall-2 SP at 1.4m.
The only Tamron to get consistent good reviews for optical quality is the Adaptall-2 SP.
The Adaptamatic has 4 elements in 2 groups, the Adaptall has 4 elements in 4 groups, and the Adaptall-2 SP has 6 elements in 5 groups. Looking into my Aetna through the mount side under a bright light with the lens cap on the front, I can see 5 reflections and a possible tiny tiny sixth.

... So what do I have? Question

Is this perhaps not a standard Tamron lens, but maybe a "clean-up" batch to make use of parts left over from other lens designs? Question

ManualFocus-G · Expire: 2014-11-24

Interesting. Please note though, there were at least two versions of the Auto Tamron (Adaptamatic). Mine looked very similar to yours with the same focusing barrel.

luisalegria · Expire: 2018-01-18

That Aetna looks like the Adaptamatic version indeed, and I would be surprised if it had a different optical layout, all the other important bits like the focusing helical and aperture mechanism are in exactly the same places as with the Adaptamatic. This all would be different with different glass. The differences vs the Adaptamatic are purely cosmetic. The Adaptall-style DOF scale is a case in point.

I bet this lens was yet another transitional type dating from the early 1970's, when the Adaptalls were coming in, made up possibly from existing bits but certainly from existing Adaptamatic tooling.

There were many undocumented variants it seems, especially those fixed mount types made for third parties. I even have lenses labelled by Taisei (Tamron) that have absolutely no relation to the "known" types.

As for performance - I have absolutely no complaints against my Adaptamatic, its one of those lenses that manages to almost focus itself.

Scheimpflug · Expire: 2011-11-18

Luis - what do you think about the large difference in the minimum focus distance? That is pretty much the only piece I can't explain as a cosmetic change...

luisalegria · Expire: 2018-01-18

I can't explain it either. I can only speculate. Possibly the helical in the basic Adaptamatic design of this lens has some additional travel available that is limited by a stop - not an unusual situation. For whatever reason - competitive feature bid against a rival maker ? - this one made for Aetna was given closer focus capability, maybe as simply as moving the stop and permitting some more rotation on the helical.

Whatever the explanation, the sum of all the features says "Tamron Adaptamatic" to me.

visualopsins · Expire: 2025-04-11

My copy, M42.

Scheimpflug · Expire: 2011-11-18

Thanks, visualopsins! That makes two... up until now, I had only know of mine, and I hadn't seen any like it on ebay or anywhere else. Wink

There are some slight differences, such as the chrome trim around the grip on mine, and the fact that mine says "AETNA ROKUNAR" while yours says "AUTO ROKUNAR"... but otherwise they appear to be identical! And now, I know what kind of knob to look for for the tripod collar set-screw. Cool

It is interesting how different the serial numbers are... 296xxx vs 693xxx.

Timmy2wheels · Joined: 22 Mar 2011 Posts: 3 Location: London

I am SO pleased I found this thread! I have been trying to identify the lens I bought off eBay about a year ago. The closest I have got until now is thinking it's a 670Au but it doesn't look quite like any of the 3 variants I have seen. It does, however, look exactly like the Auto Rokunar here, but it is branded Auto Tamron and has a Nikon mount (well, it was sold to me as Nikon mount and it certainly does fit). I was also thrown by the fact it came with a rear cap which says 'For Pentax K' and an Adaptall-2 front cap. So, perhaps this is one of the unknown variants. I will post pictures soon.

Can I use this with teleconverters? And if so, what would people recommend?

Scheimpflug · Expire: 2011-11-18

Glad the information was helpful! Please do post a photo of your lens if you can.

I can't say for sure how well this lens does with teleconverters... I only have two, a 3x Soligor, and a 2x macro focusing Vivitar, neither of which would really be good matches for this lens... I tried the Vivitar when I did those test shots last year, but I remember that I didn't have enough light for it...

Timmy2wheels · Joined: 22 Mar 2011 Posts: 3 Location: London

Here are some pictures of my Auto Tamron 300mm f/5.6. If this is a straight-up Adapt-A-Matic model 670Au I would be pleased, though the focus barrel doesn't look like the model on the Adaptall-2 website.

luisalegria · Expire: 2018-01-18

Hi Timmy,

It looks like one of the many undocumented fixed mount variants of many Tamron lenses.

I would say this is most likely a 670au all the way back to the mount, which seems to be fixed, not Adaptamatic.

Adaptamatics themselves were made with two styles of focus grips - earlier ones were ribbed metal, later ones were rubber.

Timmy2wheels · Joined: 22 Mar 2011 Posts: 3 Location: London

luisalegria · Expire: 2018-01-18

I guess any older Nikon-mount TC will work.

The newer AI/AIS TC's may not work as this isn't an AI mount. But you never know, you would have to try them to be certain. I have one of these that seems to work with some old lenses.

Scheimpflug · Expire: 2011-11-18

sandysuwandi · Posted: Fri Feb 22, 2013 8:12 pm Post subject:

I just deal a AETNA ROKUNAR 300mm 5.5 M42 Lens in Ebay for U$D50
Just curios about this lens ability...

I hope it will not disapoint me when arrive...

mo · Expire: 2016-07-30

Welcome Sandy,Please post up some images when the lens arrives. Very Happy

sandysuwandi · Posted: Sat Feb 23, 2013 5:14 am Post subject:

visualopsins · Expire: 2025-04-11

sandysuwandi · Posted: Sat Feb 23, 2013 10:54 am Post subject: