Some not particularly scientific testing .
You may have heard of Kodak's legendary "Aero Ektar" - a lens made for reconnaissance cameras in WW2 and available in several sizes. The most popular is the 7in f/2.5 as it covers 5"x4" and combines super sharpness and a very fast aperture. Sometimes found grafted onto Speed Graphic or similar large format press cameras it was a useful tool for news photographers and there were plenty around in the 'fifties and 'sixties as military surplus. There are (rarer) 10" and a 12" versions too.
Despite my (ahem) extensive collection I've so far managed not to buy one of these, so when a friend mentioned he'd got one and never used it (not a photographer, he bought it in a charity shop as a curiosity) I said "bring it over"
So I've currently got four aero lenses here: The Aero Ektar 7in f/2.5, A Berthiot 520mm "Objectif Special Aviation" 520mm f/6.3 a Ross Xpres 20in f/6.3 and the monster Dallmeyer 36in f'6.3, so in true Top Gear style I decided to do a back to back test.
Left: Ross Xpres, Rear: Dallmeyer, Right, Berthiot, Front: Kodak Aero Ektar.
Horrible Ektar
Part of the deal with Robin was to do a wet-plate portrait using his own lens. However, when all was set up with the lens on the camera something was seriously amiss. It wouldn't focus!
Now on a plate camera the focus adjustment is not part of the lens. You move the camera's lens board back and forth until it's sharp. So when the best I could manage was a soft, mushy mess it was obvious something was wrong.
The rear element group was easy to unscrew - often a sign someone has been dismantling things. It turned out that two of the lens elements had been put back in the wrong way around. I've come across this before. It's very easy to get confused or not notice that a lens element isn't symmetrical but it makes a big difference! Luckily i found the diagram online and put things right.
The Aero Ektar came with its original flange for fitting to a K24 reconnaissance camera and as luck would have it I've got one of those ;-)
Designed to take 5.5in film in long rolls, they were carried by aircraft either pointing straight down or obliquely. Three bolts and it was installed.
The cameras is unusual in having a thick sheet of glass in front of the negative. This has registration marks etched into it which print onto each frame, which is interesting. I think differently marked glasses, with grid lines or other things could be easily swapped out as need be.
It's an unwieldy thing: very heavy with a huge 24V motor drive, winding mechanism and cassette for the film, not to mention the great big lens. There's also no tripod bush
(it must have been clamped into the aircraft but I've no idea how) and the cassette has no darkslide so the whole thing has to be loaded and unloaded in the darkroom. The cassette is awkward to latch but like most military hardware all that heavily-built stuff needs wrestling until it suddenly clicks into place beautifully.
As I don't have any 150 foot rolls of 5.5in film around I temporarily disabled the single-speed 1/450 sec shutter so I could use paper negative. The lens is prefocused on infinity but I partially unscrewed it from its mounting and stopped it all the way down to f/16.
The spots are from the glass plate. I wiped it as clean as I could but it may well have fungus on it. I do like the registration marks and arrow though!
I knew the Ektar covered 5"x5" - it even says so on the lens surround but how big of an image circle does it have? The way to test this was to mount it on my 12"x15" Chapman plate camera and see.
As expected, the image circle isn't huge. around 8in so anything larger than whole plate isn't going to work. The whole point is that fast aperture (at least two and a half stops faster than most other lenses of this size) so here's a test at f/2.5:
It is nice. with good bokeh without the distortion you get from old Petzval portrait lenses. - Personally I love those but this is a different look. My main reservation is that small image circle. I like a bit more room...
An Older Wartime Lens
Next I went to the Berthiot. This is a lovely thing, bought with the Chapman camera and one I use a lot. I know the coverage is easily more than 12"x15" but without making a mount to fit it to the 20"X24" I don't know how big. It's f/6.3 which again is fast for such a large lens and it's surprisingly light. Most of the body is aluminium.
I can't find much information on it but it seems this dates from the First World War
This is from the same viewpoint as the Aero Ektar.
Next is the Ross Xpres 20in f/6.3. I picked this up at an autojumble a while back and it's very similar to the Berthiot, with the same focal length and aperture. It's MUCH heavier though as the barrel is brass, rather than aluminium. A bit more contrast and edge sharpness (it's a mor recent design) It's a lovely thing but it's not significantly different from my Berthiot I'll be selling it on.
Lastly the monster! This is a 36in f/6.3 made by Dallmeyer for the UK Air Ministry in WW2. There's a geared quadrant on the aperture ring so it can be adjusted remotely (probably by a motor?) which is cool.
It weighs over 8kg, which means mounting it on a camera is difficult - Generally the camera has to be mounted onto the lens! It's a true telephoto design in that at infinity the distance from lens mount to film is less than the 36in focal length so the camera can be smaller. My 20x24" camera would need a major modification to its lens board to make this fit (one day...) so it was actually more practical to make a dedicated camera for it. As I've recorded in another post I made a sliding-box design for it which takes a 10"x8" back and holders so it's sort of practical!
This is from the same viewpoint but as it's only 10x8" it's cropped compared with the ones on 12x15". - I've been told it covers a much bigger image circle so that modification to the 20x24" camera might have to be done!
Note: Everything was shot on a horrible murky day through a not-very-clean window.
And if you're wondering about the dinosaur - that's Gertie!
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