8" Dallmeyer Pentac f/2.9 - Any Users?

[Dan Fromm]

Randy, when I had a small pile of lenses with radiation browning I set them to bask under a 20 w BLB compact fluorescent bulb. Put them in a box lined with aluminum foil, bulb in a reflector on top of the box, turned the lenses once a week whether the needed it or not. Total clearing took a couple of months.

IKEA sells an LED work light JANSJÖ. I've read that these little beasties emit enough UV to clear lenses with radiation browning. I have one, its useful, but I'm not sure its useful for that application.

[Tin Can]

Thanks Dan, I am going to try a 80 watt UV LED that I have meant to buy anyway to try for Alt Prints.

Maybe overkill...

https://www.amazon.com/gp/product/B0...1TZHMM5V&psc=1

[Jody_S]

I have a 1920s Dallmeyer Pentac 8"/2.9 sunken-mount from a Marion variable-slit 4x5 reflex camera. No yellowing elements. I understand that during wartime, the UK made loads of these with different glasses because the original Jena glass was not available. I can't comment on the Air Ministry lenses, I've never had one, but mine is indeed beautiful wide open. It's not for sale.

[robertraymer]

I have been using an 8" Pentac for quite a while and it is one of my personal favorite close in portrait lenses for 4x5. Mine usually lives on either my speed graphic, or more often on my Graflex RB. Even wide open it has better than expected sharpness, beautiful falloff, and a bit of glow to it. Do be careful shooting into a light source though because it does tend to flare quite a bit of not shielded from the light. DM me if you want examples.

As for other information, you already have what the LVM says. The 8" pentac, as well as the 10 and 12 inch versions, were made to be used as aerial reconnaissance lenses (usually mounted on spitfires and the like, to my understanding) with a design that was required to be sharp in the center wide open, a necessity for their job. Given that they were designed for 5x5 it is no surprise to me that I have never had an issue with sharpness being less than expected. Being wartime, a number of factors including the need to spread production over a number of factories in different physical locations so as not to disrupt supply too much if one was bombed, availability of various metals, and availability of glass, lead to the "Dallmeyer" design being made by a number of companies, in both aluminum and brass barrels, and with differing qualities of glass. Dallmeyer marked lenses are the least common, as are brass barrels (aluminum was lighter and lighter is more desirable in a plane), but are said to be higher quality. My copy was made by NOC (National Optical Company) which I believe was owned by TTH, who had a long history of quality optics, and as I mentioned is quite good, though I do not have a Dallmeyer marked lens to compare it to.

To my thinking it was not that other makers, NOC or otherwise, did not make good lenses or that quality control suffered due to the war that causes problems with some of these lenses. I don't think that the AIR ministry would have spent money on these very important lenses if the quality was not there. Rather I think that the hard service life that surviving copies endured often in combat and at high altitudes and less than ideal conditions, combined with the fact that they are all over 70 years old has far more to do with any defects than does lineage. I was lucky to find one in very good condition, but many likely have issues that are not immediately noticeable on inspection.

[EdSawyer]

I have had probably at least 8 200mm pentacs, and never seen one with any browning like an AE will have.

[Tin Can]

Found my Pentac F8 f2.9 and it looks better to my eye than the last time I looked, 7 years ago. Cleaned the elements, they were oil coated. No brown.

And I finally noticed the front OD element has a tiny screw on the OD smack dab in the thread locking the thread.

Before I remove that screw and try SF, i will shoot as is. This is the brass version with a screw hole in the rear threads perhaps to secure a filter.

183886 on rear element A 'D' by the screwhole

14A/3385 with arrow for rear direction on front OD

N2 VV.183886 Smooth operating aperture

1612 grams with fixed attached flange. Perhaps OE wood box, been it that box decades.


Pentac F2.9 by TIN CAN COLLEGE, on Flickr

J.P., the Vade Mecum -- buy one! -- says that pre-war the Pentac was made up to 12", post-war to 10". It also says that some pre-war examples have variable softness, attained by changing the elements' separation.

Cheers,

Dan

[diversey]

This is the lens I am looking for my Graflex Series D 4x5!

Found my Pentac F8 f2.9 and it looks better to my eye than the last time I looked, 7 years ago. Cleaned the elements, they were oil coated. No brown.

And I finally noticed the front OD element has a tiny screw on the OD smack dab in the thread locking the thread.

Before I remove that screw and try SF, i will shoot as is. This is the brass version with a screw hole in the rear threads perhaps to secure a filter.

183886 on rear element A 'D' by the screwhole

14A/3385 with arrow for rear direction on front OD

N2 VV.183886 Smooth operating aperture

1612 grams with fixed attached flange. Perhaps OE wood box, been it that box decades.


Pentac F2.9 by TIN CAN COLLEGE, on Flickr

[Tin Can]

I am going to try it out my Speed with both the Pentac and an Aero Ektar as I have the mounting ring coming.

Now that Aero Liberator https://johnminnicks.com/ is very well known I imagine availability will vary.

Have you read this page? https://lommen9.home.xs4all.nl/

This is the lens I am looking for my Graflex Series D 4x5!

[diversey]

Yes, I did. I sold my Ektar Aero, now I am looking for another one. Never sell your gears!

Have you read this page? https://lommen9.home.xs4all.nl/[/QUOTE]

[Tin Can]

Good luck!

Yes, I did. I sold my Ektar Aero, now I am looking for another one. Mercer sell your gears!

Have you read this page? https://lommen9.home.xs4all.nl/

[/QUOTE]