Arca-Swiss 6x9 and 45mm/47mm lenses

[Massimo Squillace]

I recently upgraded to an Arca-Swiss 6x9 F-Classic, partly in order to be able to use shorter lenses.

I already have an APO-Grandagon 55mm with proper Rodenstock center filter (seldom used), and since the general consensus seems to indicate you need the center filter with shorter lenses I am leaning towards the 45mm APO-Grandagon, which requires the same filter.

On the other side, the more expensive 47mm Super Angulon XL has a greater image circle and a longer flangeback distance according to published specs, but will it accept the same center filter?

Moreover I think there is an inconsistency in the Arca-Swiss catalog: in the second to last page you can find a table of required lensboards for the currently available wideangle lenses, and while the flangeback distance of the 45mm is 55.5mm vs. the 59.1mm of the Schneider 47mm XL the latter requires a 7mm recessed lensboard while a flat one should be enough for the APO-G ... can anyone explain why?

[Steven Dusk]

You will need the recessed board for both of these lenses to get any useful movements (not to mention a bag bellows). You could of course go really wide with the 35mm instead which also uses the same centre filter...

Steven

[Emmanuel BIGLER]

Massimo. Congratulations for the Arca 6x9. For short focal lengths : the answer is that both the apo-grandagon 45 and the Schneider 47 have a certain amount of retrofocus design, i.e the distance between the rear lens element and the film is slightly longer than expected for a quasi-symmetrical lens. The flange to focal distance is 55.5mm for the apo-grandagon 45, and 52.2 for the Schneider SA-47. So the apo-grandagon can in theory be mounted on a flat Arca Swiss panel, there is no inconsistency in the Arca Swiss catalogue. The back clearance for the 47 Schneider is 'shorter' by 3mm although its focal length is longer by 2mm. But I agree with Steven that you'll be more comfortable with a recessed board for both lenses.

Those mechanical data are well documented on the manufacturers web sites.
And do not hesitate to ask any other question about the Arca Swiss 6x9, I have one and live just nearby the place where they are manufactured.

[Massimo Squillace]

Emmanuel,

the flangeback distance you mention is for the 'old' Schneider 47mm, the non-XL version. The catalog refers to the XL, whose flangeback is 59.1mm, hence the inconsistency (if I am not missing anything, that is).

Armin,

do you use the lenses on an Arca-Swiss, and if so, are they mounted on flat or recessed lensboards and do you use the wideangle bellows? It is my understanding that to use the same center filter different lenses must obey the same cos^4 or cos^3 light falloff rule ... is this the case for the 45mm APO-G and the 47mm XL?

Thanks to all who answered so far!

[Emmanuel BIGLER]

Massimo : if the back focal distance for the new SA 47XL is 59mm, it means that you can use it
on a flat lensboard like the 45 Rodenstock.
I use the 55 on a flat lensboard without centre filter. But I do 6x9 only.

I agree with Armin that you could use the same filter on a 45 or a SA47XL. The compensation does not appear to me as critical as proper focusing is.

And since, Massimo, you seem to like mathematical models for light fall-off very much ;-);-), we could add that the cos^4 theta law is not very applicable to extreme wide angle lenses, because the designers
let some pupillar distorsion appear to partially compensate for the ligh fall-off. The exit pupil seems to rotate when you look at then lenn from the back, in the corners of the fields. Also the lenses being slightly retrofocus, the angle theta
should be measured from the centre of the exit pupil, so the focal length again is not 100% significant in the light fall-off effect.

As fas as bellows are concerned, I would recommend the wide angle leather bellows 35-75. I can focus and tilt a little the apo grandagon 55 with the 75-150 universal 6x9 bellows, but eventually I got the smaller leather bellows in order to allow full movements without any possible damage to the bellows.

As a summary : a flat 110x110 board and a smaller 35-75 leather bellows will give you all you need for a SA47XL or a 45 Rodenstock used on the Arca Swiss 6x9.