I bought an Air Ministry Dallmeyer Pentac 8 inch aerial reconnaisance lens about ten years ago from a flea market stall in London’s Spitalfields antique market. At the time I was doing a lot of people shoots and had fancied the look of a Kodak Aero Ektar…but was put off by the radioactive thorium in the glass and the price! Eight inch Air Ministry Pentacs are the British Wartime equivalent of the American Aero Ektar and used to hang out the bottom of Spitfire wings on reconnaisance missions. There’s quite a lot of information out there about Aero Ektars, but less about these lenses which perform very similarly. I thought I’d share everything I’ve learned about these fun lenses through research and through using.

At 8 inches or 203mm, the lens is a little longer than an Aero Ektar (which runs to 7 inches or 178mm). The Pentac has a maximum aperture of f2.9 compared to the Ektar’s f2.5. A little maths will tell you that the aperture opening is effectively identical on both…71mm on the Ektar and 70mm on the Pentac.

Unlike the Aero Ektar, the glass on the Pentac is not readioactive and not subject to thorium yellowing. The front element is usually uncoated as on the Ektar.

They are easy to dismantle for cleaning. Remove a single screw on the front barrel of the lens and you can unscrew both the front and rear element groups. I needed to do this when I first got the lens to remove dust. Since then I’ve not needed to touch it. The Dallmeyer Pentac has 21 aperture blades, producing an incredibly round circle of confusion when wide open. This compares to the Aero Ektar’s 16 blades.

Some Air Ministry Pentacs were made by Dallmeyer, and some by other factories. Even the Dallmeyer ones are rarely branded, although they will often have a JHD stamp next to the Air Ministry mark and crown. Mine has the remnants of the JHD mark in the typical oval stamp, although it’s largely rubbed away. All the lenses, regardless of maker, seem to be marked 14A/780 which must have been the Air Ministry part number rather than a serial number.

I’ve also read online (and thus unverified) that the Dallmeyer-made lenses have a detachable mounting flange where as those from other makers have an integrated flange. Mine has a detachable one, although I don’t use it as I have it mounted in a JoLo Speed Graphic Aero Ektar lens board (which works fine once a little plumbers tape is wrapped around the threads to compensate for the slightly different mount size).

The front filter thread is just shy of 77mm. I guess it’s some sort of imperial thread as the UK didn’t adopt metric measurements or standards until the 1960s–and even then, reluctantly.

I’ve made a filter mount out of the end of a cardboard posting tube painted with blackboard paint with an 80mm to 77mm reducing ring glued on the end. It means I can use all the filters and the lens hood from my Mamiya RZ67, which uses a standard 77mm on all its system lens. The Mamiya lens hood from my 110mm lens works fine and doesn’t result in any vignetting.

The Pentac is a fairly incredible performer. Wide open, depth of field is insanely shallow (just like the Aero Ektar), but focusing is easy and precise on the chosen point. At f2.9 only about 1mm will be sharp with the rest of the image melting into creamy swirls and bubbles (obviously depending on background). As a result, even straight on and with no tilt/shift manipulations, it creates a slight ‘toy town’ effect when opened up.

At smaller apertures it is very sharp. By f8 (still a wide aperture for a large format lens), it’s incredibly sharp already. On infinity focus at f2.9 it creates a fairly sharp image with decent depth of field.

These lenses do produce fairly low contrast images. I find myself needing to print at Grade 3.5 or 4 in the darkroom. I’m going to search out a 77mm yellow filter to improve mine (painful given they cost more than I paid for the lens, but at least I can use it for the Mamiya). This won’t be an issue at all if you are a hybrid shooter and scan your negatives.

Coverage is ample for 5×4 (with rise and tilt shift if desired) and the lens is also easily able to cover 5×7. I’ve even seen people use these lens for 8×10, but can’t verify how succesful that is.

The Pentac has a minimum focus distance of just 55cm when the rails are fully extended on the Speed Graphic (by which point it needs about a stop and a half of exposure compensation to account for the bellows draw).

One thing that is worth mentioning, and this is not unique to the this lens, but applies to all barrel lenses used with the focal plance shutter: you can’t use an electronic flash. Althoug there is a flash port on the flocal plane shutter of a Graflex Pacemaker Speed Graphic, it has a built in delay to account fot flash bulbs…that means the flash will fire before the shuuter actually opens!

Other than that, the only really downside is the weight. Despite being made largely of aluminium and designed as an aircraft part, it’s still a beast and not the sort of thing you want to cary around all day (I did, but won’t be again!).

If you can still find one of these lens then I’d highly recommend them. Performance wise they are extremely capable. It’s never going to become your daily lens because they are just not really practical outside of a studio environment due to the size and weight. But for an occasional special effects lens, they are great fun and, even today, still a lot cheaper than an Aero Ektar.