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View Full Version : 8" Dallmeyer Pentac f/2.9 - Any Users?



J. P. Mose
12-Oct-2004, 10:58
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
12-Oct-2004, 11:47
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
12-Oct-2004, 11:54
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
12-Oct-2004, 12:42
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
12-Oct-2004, 18:31
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
13-Oct-2004, 07:44
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
13-Oct-2004, 08:22
<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
13-Oct-2004, 09:14
Sorry, I meant Cooke, not Dallmeyer, Speedic...

J. P. Mose
13-Oct-2004, 14:44
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
13-Oct-2004, 15:35
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

Jason Greenberg Motamedi
13-Oct-2004, 16:50
I have been looking for a 10" or 12" Pentac for more than three years, and have yet to find one, or even hear of one. Apparently they were made, but must be pretty rare. On the other hand, a 12" f/2.9 lens would be huge. I have a 13.5" f/3.5 Eastman Anastigmat which weighs 12 lbs; the 12" pentac would be larger!

I also recommend getting the Vade Mecum. It is full of holes and inconsistencies, but it is by far the best source on lenses we have.

Řyvind Dahle
14-Oct-2004, 03:07
"Brown discoloration due to radiation damage from Thorium glass cuts out at least a stop of light, effectively making the lens f/3.5"

At this link: http://www.largeformatphotography.info/lfforum/topic/249393.html

it was stated:

"Incidentally, I read on usenet that at least some of the colour centers in some of the radioactive lenses can be bleached by leaving the elements exposed to sunlight. If you are using these lenses and want to get close to their original performance, this might be worth a try.

--Struan Gray, 2002-03-26 06:19:57 "

So try the sun or UV-light! Please report back any change

Řyvind:D

Struan Gray
15-Oct-2004, 14:24
Řyvind: several people have reported success in bleaching their browned Aero-Ektars. There is yet another active Aero-Ektar thread on photo.net's LF forum right now, in which Micheal Briggs summarises a whole bunch of previous threads, and provides links to them.

www.photo.net/bboard/q-and-a-fetch-msg?msg_id=009mU2

Jason Greenberg Motamedi
16-Oct-2004, 09:17
Řyvind,

I got rid of my 7" Aero-Ektar some time back, so I can't try the sun treatment and retest.

I did bleach an earlier model of 9x9 Aero-Ektar, a 352mm f/3.5. After three weeks in the sun it lost most of its tea colored strain, but retained a distinct and strong yellow color. For aerial photography this yellow color would be an advantage, working kind of like like a UV filter, but for my purposes--using a blue sensitive alternative process--the color cast was a huge disadvantage.

David A. Goldfarb
16-Oct-2004, 11:03
Just to add another fast 5x7" lens to the list, I just received a Schneider 21cm/f:3.5 Xenar in barrel. The serial number dates it at 1925-28, but it looks like it's had an aftermarket coating added, and there's a sticker from Burke and James, who used to perform that service. It seems to be a standard tessar type.

Just holding it up and seeing what kind of image it projects on the wall, it looks pretty sharp in the center wide open, dropping off visibly in sharpness toward the edges of the image. I'll make a lensboard for it and try it out on my 5x7" Press Graflex, and will report back.

Dan Fromm
16-Oct-2004, 13:07
Jason, you might want to set your monster out to bask some more.

I have three tessar-type TTH process lenses that seem, pending a visit to Michael Briggs' geiger counter, to have radioactive rear cells. I'm not sure which element. All three arrived with yellowed rear cells, one so yellow that shots on EPP with it had a distinct yellow cast. After a month under a 20w BLB tube, all were clear. Shots on EPP with the bad 'un now show proper colors.

Cheers,

Dan

Jason Greenberg Motamedi
17-Oct-2004, 10:47
Thanks Dan, I will try using the black light bulbs and see what happens. Maybe, while I am at it, I should dig out my fuzzy "black light" posters from the 70s, to fully appreciate the effect.

Cole Seaborn
15-Dec-2004, 12:21
I read this entire thread with interest as I was doing some research on a Dallmeyer Pentac 8 inch f/2.9 (coated), that recently surfaced in my inventory. It was very helpful to read your comments, as I had no idea as to it's history, or value, prior to coming across this site. I have listed it on ebay, and will gladly email a link to anyone who cares to contact me