8" Dallmeyer Pentac f/2.9 - Any Users?

[J. P. Mose]

I want a data dump on the subject lens. I have read this lens is fantastic wide open on 4x5 or 5x7. However, it is hard to find information about it. Are there any users out there? Does anyone know the history? Was quality control of this lens fairly consistant? Thanks for any information.

JP Mose

[Dan Fromm]

J.P., the Vade Mecum advises caution in buying WW-II era 8" Pentacs. They say that the lenses were made for the military in several factories, that QC was poor, and that many were beat up in use. Note that the WW-II RAF Pentacs weren't coated. And yes, the Vade Mecum says that Pentacs can be used wide open.

FWIW, I have a few other lenses -- no Pentacs -- that the Vade Mecum says are usable wide open. I doubt they mean "is very sharp" or "fantastic" when they say "usable." If you got "fantastic" from a vendor on eBay, well, some of them are conservative, others write honest hyperbole, and a few just lie. As for 5x7, well, Pentac is another way of spelling heliar so it isn't obvious that coverage is much larger than 200 mm.

Good luck, please tell us how yours shoots after you've got it,

Dan

[John Kasaian]

J.P.,

It is my understanding that this was a british aerial lens for a 5x5 camera. Most, if not all were marked AM and the picture of an arrow for Air Ministry (I just had an intrigueing thought---if it covers 5x7 and lens cone were available, I wonder how it would work on my Keystone F8?)

The performance of aerial lenses are quite good wide open or close to being wide open as fast shutter speeds and rather heavy yellow or red filtration are SOP on most "sorties. "

I've heard of pentacs being used on Speed Graphics but I've had no personal experience with the lens. Perhaps an inquiry posted on www.graflex.org will flush out someone with hands on experience( OTOH, if Winston Churchill were goiong to risk the lives of a Mosquito cameraship and its crew, its quite likely they weren't going to skimp on the quality of the optics!)

It would also be interesting to find out if these lenses are "hot" like the US made aero-ektars of the same vintage.

[J. P. Mose]

The phrase fantastic was used loosely. Jeff Kays at Lens & Repro praises the lens for the "glow"..."fingerprint"..."look" etc. that this lens yields wide open. I have heard others say the same thing. I thought it would be fun to try on by Super D Graflex. I also have a Press Graflex 57 but this lens may not work on it (at least not at infinity). I did get it off Ebay and haven't received it yet. The s/n is 214627....and yes it is stamped with AM. Does anyone have a chart on Dallmeyer serial numbers?

[Jason Greenberg Motamedi]

JP,

I have been using a Pentac for a few years, and have been pretty happy with the results. I had mine mounted into a Compound 5 shutter by SK Grimes, and have used it primarily for 4x5. While it produces an image circle large enough to cover 5x7, only about 160mm is reasonably sharp. Even stopped down to f/16 sharp coverage is only about 180mm. At portrait distances I have used it for 5x7.

As mentioned, they have a great "bokeh" (fingerprint?), and open wide there is a slight bit of flare, or maybe spherical aberration which causes the "glow" in the highlights. They are not exactly razor sharp open wide compared to a f2.8 Xenotar, but they make great portrait lenses and have the speed when you need it. If you would like I can post my resolution tests comparing a Xenotar, Pentac and Aero-Ektar.

As mentioned, most of Pentacs were produced for the British Air Ministry (AM) during WWII, and many are in poor condition. Since these are uncoated, flare can be a major problem. Coated versions are quite rare: I watched a late model coated version of the Pentac on eBay last week, which sold for a very high sum. The only other coated version I have seen was at Lens and Repro.

As for serial numbers, the AM Pentacs did not, as far as I know, follow Dallmeyer's numbers, so unless you can get into the records of the Ministry, I doubt you will find much out. Besides, if we are to believe the Vade Mecum (and I see no reason not to), many of the AM Pentacs were actually made by subcontractors, and not necessarily Dallmeyer. Some AM Pentacs have a "JHD" stamped on them in white ink. I assume that these were the ones actually made by Dallmeyer. The lens I had mounted by Grimes was one of these, and its quality, in the barrel, balsam separation, and resolution, seem to be higher than the non-JHD lenses I compared it to. Of course, your milage may vary.

Let me know if you have any specific questions...

best regards,

[J. P. Mose]

Jason,

I would like to see your data on the three named lenses. Mine is indeed a Dallmeyer, as it is written on the front lens ring. However, it also has the military stamp. I did bid on the coated Pentac last week but gave up at around $700. Quite frankly, the non coated version is what made it famous and I will be fine with it. Now, if I could just get a f/2.5 Cooke!

Thanks,

JP

[Jason Greenberg Motamedi]

<p align="left">JP,

<p align="left">Here are my results from a resolution test of four fast lenses.
As you can see, the Xenotar clearly shines above the others, however its price
also reflects this.

<p align="left">Testing was done using Charles Sleicher's resolution chart, with
a Canham wooden field camera, on 4x5 Kodak Ektachrome EPY transparency film,
with indirect light in my cramped living room, and read using a microscope at
100x. Exposures, metered at ASA 125, were usually: f/2.8@1/8 second, f/4@1/4
second, et cetera.



Naturally, these lenses were not made to photograph flat objects at close distances,
so these results should be taken with a lot of salt. However, my "real
world" use of these lenses in the field and studio support the results
of this test.

<table width="99%" border="2" cellpadding="6" cellspacing="0" bordercolor="#000000">
<tr>
<td width="25%"><div align="center">Regarding the Dallmeyer f/2.5 Series X Speedic you mentioned,
I experimented with a 7.5" version, and was shocked at how poor it was.
Very low contrast, poor resolution. I quickly returned mine to the seller. Of
course, your milage may vary...

&nbsp;

[Jason Greenberg Motamedi]

Sorry, I meant Cooke, not Dallmeyer, Speedic...

[J. P. Mose]

Jason,

Thanks for the information. Quite interesting! Do you know anything about the 10" Pentac? I was talking with Jeff Kays (Lens & Repro) earlier today and he mentioned it. I didn't have time to go into detail with him.

JP

[Dan Fromm]

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