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Lenses Suitable for a Bolex RX5


danny bartle

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The Rex-5 is a reflex camera that had several lenses designed for its specific needs. For focal lengths of 50mm and less, you should use a Kern lens marked with "RX."

Lenses for the Bolex H.16 Reflex

 

The re-designing of the turret head necessitated the introduction of special lenses up to 50mm. Lenses are produced by Kern and Angenieux for the reflex camera. Kern lenses for the reflex models can be identified by the letters RX or DV inside the lens mount. Lenses produced with the reflex fitting appear below. Above 50mm, the normal range of Kern or other lenses can be used.

 

      ~A.J. Surgenor, "Bolex Guide"

You'll find the following prime lenses suitable for your Rex-5, (marked with "RX"), as: Switar 16mm (f1.8), Switar 16mm (f1.4), Pizar 25mm (f1.5), Switar 50mm (f.1.4), Pizar 50mm (f1.8), Angenieux R22 10mm (f1.8), and Angenieux S42 25mm (f1.4). I'd recommend the Kern Vario-Switar zoom lenses, of which the 100 POE provides a focal range from 16mm to 100mm and has the option of automatic exposure. If you are converting your camera to Super-16, you may experience vignetting below 25mm.

 

For your non-reflex lenses, no, don't use them on your reflex camera.

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I'm currently having my REX-5 converted for S16 by Les Bosher, I've been reliably informed that the POE 16 - 100 should cover S16 through out the entire zoom range (there is often confusion between these and the newer lenses which have more trouble with S16) I will post the results once I have them.

Olly

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I've seen a Nikon Zoom on a Bolex before so I guess they can work, don't know if they cover S16 though but they may well do! I think the S16 conversion is around £850 including Tax. www.bolex.co.uk is a good resource for info, you can e-mail Andrew Alden from that site, he's a really nice guy. Les Bosher seems to be about the most respected camera engineer on the planet, I'll let you know how it went.....

Olly

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Hello all,

 

Finally found a RX5 & very keen to use it. I have 2 lenses, one is a 25mm Switar f1.5 (non RX) & the other is an Elgeet 13mm. Are these lenses ok to use on the RX5?

I've used 25mm 1.4 "non-RX" with rear focus set for Reflex prism on a Rex.

 

Not as good as the later 26mm RX, but OK. Undercorrected for spherical aberration induced by the prism I suspect. But it worked. I don't know if this f 1.5 you have is similar or not.

 

But, it must be set up for this.

 

I don't know anything about that Elgeet. Probably not.

 

-Sam

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  • 9 months later...

It is not so simple. The prism introduces spherical aberration which no "setting up" can undo. However, this effect is negligible past about f/2. The prism can also introduce astigmatism if the lens' exit pupil is not a healthy distance, like 30 mm away from it. With astigmatism, the image corners will be unsharp even with considerably more stopping down. Thus for successful use of a non-RX lens on a RX camera verify by eye that the exit pupil (which is the apparent location of the iris when seen through the rear elements) is deep in the lens. Notice that these considerations have nothing to do with focal length. The old RX-rules about less than 50 mm and greater than 50 mm were wrong.

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Yes, the 25 mm f/1.4 C-mount Switar is more or less astigmatism free on a C-mount camera but the prism (functioning just like a 9.5 mm thick glass pane) introduces severe astigmatism when the exit pupil is close. For this particular lens the exit pupil is about even with the flange. RX lenses solve this problem in one of two ways: the RX lens can have exactly the right amount of astigmatism of the opposite sign; or the RX lens can be astigmatic and have its exit pupil far from the image plane. I believe the 25 mm f/1.4 RX Switar worked the first way and the 26 mm f/1.1 RX Switar worked the second way.

Incidentally, the very concept of seting the backfocus of a C-mount lens for an RX camera is a confusion. If the C-mount lens is compatible, as many are, the rear focus should be the standard C-mount 0.690". If the C-mount is incompatible, as many are, you can only fudge a little and reduce the aberrational error by resetting the backfocus. It is worth doing with a zoom lens, but with a prime that will be focused by eye, if the reflex focusing works then the fudging will be accomplished there. And you guessed it, there is also a problem with the reflex focusing on the Bolex RX. The path to the film is 9.5 mm of glass while the path to the the groiundglass is 19 mm. This problem affects focusing with every kind of lens.

I wrote two articles on RX compatibility. A 1976 one is found at:

http://www.city-net.com/~fodder/bolex/truth.html

A 1987 one seems to be missing at:

http://erictheise.com/films/library/Dennis...n-RX-C-Rule.pdf

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For what it's worth, I borrowed a Schneider 10mm C-mount lens and used it on my Bolex EBM, converted to Super16 by CamerasPro (highly recommended). Obviously it's not an RX lens, so I tested before use, and have now shot plenty of footage with it (using a C-mount adapter), with NO backfocus problems. Sharp as a tack. There is a VERY SLIGHT amount of vignetting in the top right corner on the Super16 frame, but it's hardly a concern.

 

Recently I've been looking into using a 25mm prime because the 100POE zoom i have doesn't focus any closer than 5' and I'd like to get closer sometimes. I've borrowed a non-RX Switar 25mm from the same friend and have to admit I won't use it on anything important until I've tested it first. But I've been told the wider the lens the worse the effect of it being non-RX. And since I had no problem with the 10mm, I'm optimistic about this 25mm. If anyone has some actual experience with this lens, rather than just the same stuff Bolex officially says, I'd love to hear...

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Guest Ian Marks

Xandy, the 10mm Schneider you borrowed, was it the silver and black one with the bigger (55mm filter thread) front element?

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Guest Ian Marks
Yes, that accurately describes it. Why?

 

I have the same lens - purchased off of Ebay with the understanding that it would cover Super-16 - and coincidentally I just got a pair of dirt-cheap Rx4's. It's encouraging to hear that this lens worked well for you on a reflex Bolex without any special adjustments.

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