SOM Berthiot 4.5/90 enlarger lens: is it APO?

[alex ph]

Got this enlarger lens and tested it on Sony Nex in these completely unsunny days. I wonder if there is a special word for such perfectly grey and dull daylight, as it is in his period. May we call it sole light, as opposed to sun light?

First I was moderately impressed with the lens' performance. At least, its sharpness looked on par with some other enlarger lenses I tested, with even sharpness across the field starting from WO. Then I played with PP tweaks.

One thing impressed me in particular. The colours were really those of the real world. When I was applying auto-contrast or was just pushing colours and constrast pretty far, the colour hue did not change. And this goes in the opposite direction with many lenses I tried. When I normally push the rulers, pretty soon some colour artefacts get visible: CA, colour cast, or colours just mutate. Not in this case. I wonder if this is an empirical confirmation of the lens' APO character.

The lens looks like a pretty young iteration of the Som Berthiot family, without any "series" or even "Flor" indication on the beauty ring. I found zero information about it in the net.

Here are several samples with colours tweaked, as I wished to pull them out of the sole light.


#1


#2


#3


#4


#5



And here is an example of an estonishingly natural colour reproductions under artificial light:

#6 With some minor tweaks, with glow around neon light edges, but with no visible CA


#7 A 100% unprocessed crop, handheld (I presume the sharpness at shorter exposures is even better)


Does it speak in favour of the APO correction of the lens? What is your experience in this field?

[danfromm]

Interesting. Is it engraved "Flor"? If so, it is most likely a tessar type. Count reflections to check.

Shouldn't be an apochromat. Berthiot made apochromatic process lenses badged Apographe, none faster than f/9 and continued Hermagis line of apochromatic (I think) process triplets badged "T.P.H."

[alex ph]

Thank you for the info, Dan. As I mentioned, this lens does not have "Flor" engraving. Just Som Berthiot 4.5 F=90, with modern painted letters. Here is its image I found in the net. My current light is poor, so I use this one. Unfortunately no further info is given.



I wonder what kind of glass properties are implied to preserve the colours even well pushed. Otherwise that gives an allusion of Zeiss T* coating effect, does not it?

[iangreenhalgh1]

I might not be correct, but my understanding is that a lens that is apochromatically corrected for close distances may not be apochromatically corrected for long distances.

I have a Rodenstock apo process lens that definitely isn't apo at distance, but I have a Wollensak apo process lens that is apo at distance.

[alex ph]

Most interesting, Ian. Not being a tech guy and looking through pop articles about colour correction like this one, I got an idea that once corrected is corrected forever, I mean for any distance. Do you have by chance a link or an illustration of how the correction works or not at different distances?

[alex ph]

Some more test shots to better see both in-focus (corners) and bokeh rendering

#1 At f4.5


#2 At f5.6


#3 At f8


#4 100% unprocessed crop at f4.5 (sorry for the dim light)


#5 100% unprocessed crop at f8

[alex ph]

In difficult light conditions, with minor PP tweaks

#1


#2

[kds315*]

[kymarto]

From the close up it certainly doesn't look anything like apochromatic to me. I have an Apo EL Nikkor and the Voigtlaender Apo-Lanthar, and this lens is, excuse me, very mediorce at best, with a pretty hefty dose of spherical aberration. Nor does it look like an early lens at all. SOM was founded in the early years of the 20th century. From the monocoating, the construction and the lettering, rather this looks like quite a late lens, probably from the 1950s-60s. I've found an example of a SOM enlarging lens, 105mm f4.5, that is not labeled Flor, than appears more recent than the 105mm f4.5 Flors. Perhaps at the end they dropped the name. On the other side of the coin, it does appear to be a rare lens, FWIW

[alex ph]

Thank you Klaus and Kymarto. I will do some more shots with a better light, to exclude handshake at long exposures, especially with such a slow lens.

As I noted in the initial post, the lens looks younger (more recent) than many better documented versions of Som Berthiot. It has a conventional M39 used in enlargers, it's curious why there is no info about it in the net.

[alex ph]

A couple more samples taken with this lens

#1


#2

[alex ph]

Now some shots and tests with better light. First a couple of separate images.

In some aspects it makes me think of Ross Resolux 4/11cm which is sharper while having a similar good bit of pop-up and general colour fidelity.

Here is Som Berthiot focused on far, mid and close range portions of the image.

#1


#2


#3

[alex ph]

Bokeh test with a more contrasty light and a larger distance between in-focus and OOF objects than above. I meand the first set with dull light.

All images are processed in the same way: exposure is slightly pushed up, contrast and saturation are tweaked to compensate the wash out efect caused by the exposure compensation.

#1 At F4.5


#2 At f5.6


#3 At f8


I think the difference in colour rendition is defined by in-camera auto WB settings.

[alex ph]

Corner performance with APS-C sensor

#1 Full image at f4.5, light PP


#2 A 100% crop from the previous at f4.5, unprocessed


#3 A 100% crop from the previous at f8, unprocessed


#4 Just to be clear what the item is, broken spectacles found on the road

[alex ph]

Flare resistance of the lens is pretty good, in spite of the coating which deos not seem to be multi.

#1 Sun in the frame edge, unprocessed except resizing


#2 Direct shot of the sun, unprocessed except resizing

[alex ph]

To finish with it, a couple of simple BW conversions.

#1


#2

[alex ph]

Now the lens' properties get more clear. It has CA in counterlight. They are not hard and coloured red like those produced by Rollei Planar HFT and CZJ Pancolar MC, not magenta like Tokina and some others give.

#1 Test shot


#2 A 100% unprocessed crop


#3 A 100% unprocessed crop from another part of the shot