Bolex H8 Reflex lens question

[BAC]

I recently purchased a Bolex H8 Relex and just got my first roll of film back. The results were great, I'm very happy with it. I currently have the SOM Berthiot Pan Cinor 40 RX lens. I was looking at lenses on the Bolex Collector web site and they have the lenses listed either for H8 or H16. Am I only able to use the lenses specifically made for the H8 or will the H-16 lenses work with it as well?

The reason I ask is while looking at the Super 8 man web site he has a Bolex H8 Reflex with a 150mm Macro-Yvar f3.3 lens which is listed as an H-16 lens on the Bolex Collector web site. Can I use any C mount lens or will I have problems? It would greatly increase my options if I could use any C mount lens.

I understand Super 8 Man is on this forum, your input would be much appreciated. You did a great writeup on the H8 Reflex. That helped inspire me to get that camera and I love it.

[richard p. t.]

I just purchased an RX4 H8 myself. You can use any Bolex RX lens - including those designed for the H16 reflex. You just can't use the RX lenses designed for the h8 on an H16 I suspect (you would get vignetting).
richard

[bolextech]

There are two main issues in using H16RX lenses on a H8RX due to
1) the different flange focal distances.
2) the different thicknesses of the beamsplitter prism.

Issue #1: a H16RX lens used on a H8RX camera will always focus past infinity.
Some lenses, such as the 100mm macro were sold in a recollimated version for the H8RX and marked as such. This particular lens can also easily be recollimated to the H8RX.

The problem is with the shorter focal length lenses. Take the 10mm as an example. You will never get a 10mm H16RX lens to focus properly on a H8RX. To get the proper collimation, shimming between the body and lens is necessary. Usually this shim is over 1mm thick, so the lens will no longer be properly threaded into the turret all the way. The best solution is to have the turret permanently modified with one of the openings depth increased to compensate the flange focal distance. This is something I have done for a number of H8RX users.

Issue #2: What makes H16RX and H8RX lenses different than regular lenses? The beamplitter in the camera is an integral part of the lens formula.
A beamsplitter prism always introduces spherical aberration.
The RX lenses are designed with negative spherical aberration to compensate for this.
The H16RX beamsplitter is roughly 9mm thick. The H8RX is about 6mm thick.
Hence, the correction is slightly different on H16RX and on H8RX lenses.
This adds another element to the detriment of optical performance.
Fortunately in the case of spherical aberration, this issue can be improved substantially by stopping down the lens.

To fully understand the issues with the Bolex beamsplitter prism, I recommend reading the excellent analysis by Dennis Couzin avaialble at:
http://sites.google.com/site/cinetechinfo/
Download RXrule_76-78.pdf
or here
http://www.city-net.com/~fodder/bolex/truth.html

Cheers,
Jean-Louis

[super8man]

Glad you got a nice Bolex. It's a keeper for sure.

As for the 150mm, I believe mine is stamped with both H8-H16RX...but I may be mistaken. I'll dig it out and see.

Looks the other questions got covered way better than I could even try to provide. Good stuff.

Cheers,
Mike

[BAC]

Thanks for the replies. Some of that information is way over my head but it sounds like I should stick with the lenses that are designed for the H-8 Reflex if I want to get the best results.

[richard p. t.]

Well, I turned out to be quite wrong on that one!
I didn't realise Bolex made a different beam splitter for the H8 ...
I bow to your far greater bolex knowledge Jean-louis. Thanks for being part of the discussion.
richard