Using Fujinon A 300 as a convertible lens

[pau3]

I have just realized that my Fujinon A 300 is capable of creating an image with the front cell removed. It seems to be a 600mm lens, roughly speaking. I imagine that, in this configuration, the quality of the image is not “good enough” (where I don’t know what “good enough” means). I should add that my standards of “enough goodness” are quite low, since I’m only interested in contact printing: no enlarging at all. My question is: has somebody test this particular lens with the front cell removed? I will do the test myself, but I was wondering if someone already did it.

Pau

[Pere Casals]

Hola Pau,

Not with this particular lens, but I've experimented a bit with that.

Convertible lenses like old 1960s Symmars or the Cooke Triple Convertible have their cells individually corrected, then with some limitations the front or the rear cell can be used alone with still very acceptable results.

"Non convertible" lenses (like the Fujinon A) are only corrected when the full lens is assembled, in those designs the rear cell and front cell are designed to make one compensate the defects of the other, in that case the intercell spacing may be an adjustment factor, some designs (Sironars, for example) use shims to adjust the intercell spacing to optimize each particular unit: the defects in the front lens "spread" more depending on the intercell spacing, so distance is adjusted to make the rear cell perfectly compensate the "defects" in the front cell, allowing for a refined optimization. Fujinons do not use shims in the front cell for that, but anyway the cells are not individually corrected.

So half a Fujinon A will form an image, but you cannot expect pictorial quality, of course it all depends on print size and personal standards. Just unscreew the front or rear cell and you will see with a magnifier in the ground glass the quality you have, is this case the ground glass will tell the truth because the image is worse than what GG graininess allows to see.

A remarkable choice to have a good 600 is the Symmar convertible 360, that is 620/12 converted, and in shutter. Even for 8x10 we only take the center of the image circle that it is quite good, with only 2 groups in the cell the absence of multicoating is less a problem, often still it requires a compendium shade because the illumination circle is insanely big and it will illuminate a lot the bellows inside.

An even cheaper choice is the Symmar 300 convertible to 500mm, from time to time there are opportunities to but the cells alone, around 150€ with shipping:



If you want I would lend you my Symmar 360/5.6 - 620/12 so you would see how it works. (just PM)


Salutacions !

[pau3]

Pere,

thanks for your offer and comments. I do own a symmar convertible. My question is about the actual performance of the rear group of the fujinon A 300. I am wondering if someone has already performed the experiment and is willing to share the results.

Pau

[ic-racer]

I have exposed film with the rear element only of the 300mm 5.6 Fujinon W lens and the results are pretty bad. I never printed any of the negatives so I have nothing to show.

[Pere Casals]

Pau, let me add that you can inspect the ground glass with a magnifier having the same power than the enlargement you plan, if you are to enlarge x4 then use a x4 magnifier and you'll see how the print is to be at reading distance, but I would not expect much.

[pau3]

I have exposed film with the rear element only of the 300mm 5.6 Fujinon W lens and the results are pretty bad. I never printed any of the negatives so I have nothing to show.

I’m beggining to think that the results I’ll get will be worse than I thought after looking at the ground glass. However, before doing the test myself, I was wondering what kind of aberrations are not corrected for the rear group and how that could affect the image. The diagram of fujinon a lenses seems to be so symmetrical! (I know l’m being naïve - ignorant is probably a more acurate word - ). I think that fujinon W lenses are not so symmetrical. Anyway, I’ll do a quick test tomorrow.

Pau

[Jac@stafford.net]

There is the satisfying outcome of going outside with the lens and trying it in real life. In the end you will likely have spent less time than waiting for abstract opinions from the 'net which remain impressionistic, words, opinions not evidenced upon film.

[pau3]

There is the satisfying outcome of going outside with the lens and trying it in real life. In the end you will likely have spent less time than waiting for abstract opinions from the 'net which remain impressionistic, words, opinions not evidenced upon film.

I completely agree. However, I’ll try to make a slightly scientific test and I’ll shoot the same images with the rear cell of a convertible symmar 300. Probably not the best contender, though.

[Pere Casals]

For 4x5", the 500mm conversion is as good as the 300mm full lens across all the format range, for 8x10 the conversion needs to be stopped (I guess f/22 is enough) to have good performance in the corners.

The conversion may have focus shift, so if focusing wide open at f/12 and later stopping the lens to shot then focus should be checked again at the shooting aperture.