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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.

Øyvind 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

Øyvind:D

Struan Gray
15-Oct-2004, 14:24
Øyvind: 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
Øyvind,

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

markcornelison
3-Jun-2019, 07:08
I bought one on a nice Speed Graphic that the seller had refurbed. Images have a razor thing DOF, but great backgrounds. 192034

Tin Can
3-Jun-2019, 16:55
I have one, and wonder how powerful a UV lamp can I use to fix the brown?

I never used it as it looks so bad...

But it was the first lens I tried to use for LF and I had no idea how to get it into focus.

My camera didn't close up enough...

Dan Fromm
3-Jun-2019, 17:11
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
3-Jun-2019, 17:24
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/B07PR9RFC1/ref=ox_sc_saved_title_5?smid=A3QGPT1TZHMM5V&psc=1

Jody_S
3-Jun-2019, 18:43
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
3-Jun-2019, 18:57
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
3-Jun-2019, 21:40
I have had probably at least 8 200mm pentacs, and never seen one with any browning like an AE will have.

Tin Can
16-Dec-2019, 12:06
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.


https://live.staticflickr.com/65535/49229308686_7c3d71ab76_b.jpg (https://flic.kr/p/2i1e5mf)Pentac F2.9 (https://flic.kr/p/2i1e5mf) by TIN CAN COLLEGE (https://www.flickr.com/photos/tincancollege/), 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
16-Dec-2019, 13:09
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.


https://live.staticflickr.com/65535/49229308686_7c3d71ab76_b.jpg (https://flic.kr/p/2i1e5mf)Pentac F2.9 (https://flic.kr/p/2i1e5mf) by TIN CAN COLLEGE (https://www.flickr.com/photos/tincancollege/), on Flickr

Tin Can
16-Dec-2019, 13:33
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
16-Dec-2019, 16:36
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
16-Dec-2019, 16:39
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]

Jason Greenberg Motamedi
16-Dec-2019, 20:53
Randy, these are pretty soft (flare actually) open wide, so try yours before trying to dial in any additional softness. Its a nice look, I think. As mentioned above, these never had radioactive glass. I have owned at least a dozen of the 8" versions (ranging from pre-war Dallmeyer, NOC, and coated post war issues) and and sorted through a box of about 30 of the 10" versions, and have never seen any sign of tan glass. Someone is confusing these with other aerial lenses. They are for the most part, fine lenses, but there are some lemons, so test!

Tin Can
16-Dec-2019, 23:29
Of course

The price was right on this stuff

I can’t lose

EdSawyer
17-Dec-2019, 07:19
" a box of about 30 of the 10" versions"

there must be a story behind that... the 10" ones are a lot less common (and larger!)

Jason Greenberg Motamedi
17-Dec-2019, 08:08
Dallmeyer made a run of coated 10" Pentac lenses for NATO in the 1960s. A friend purchased the remainders about 10 years ago. It was a pretty amazing purchase (all gone now I think), but unfortunately all but one or two of the lenses had a very stubborn fog between elements that was impossible to remove short of repolishing. John at Focal Point looked at one I sent him, and said it was likely due to paint off gassing over the years.

The 10" versions are perfect for all of your Home Portrait Graflex cameras (two unicorns in one!).

EdSawyer
19-Dec-2019, 07:16
Thanks for the backstory!