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Edwin Feliu

Which C-mount lens best for a Bolex H16?

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Look for lenses marked RX, which were designed to negate the aberrations introduced by the 9mm thick piece of glass that is the viewfinder prism in a reflex Bolex. It sits right behind the lens.

 

Kern Switars are very good, Macro-Switars even better, but they can be seriously pricey these days. Avoid the ones made for the H8 RX.

 

Yvars were a more budget range from Kern, with slower f stops than Switars, but still quite ok. I personally don't like the Berthiot Lytars, they tend to be rather low con compared to Kerns, and not as well made, but they should be cheap. Schneider made some RX C mount lenses for reflex Bolexes that were also rather good, and may be cheaper than Switars.

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Dom, thanks for the thorough response. I'm new to cinematography, so it's much appreciated. One last thing: Would a Kodak Cine Ektar be a contender?

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As Dom explains, you have that complication with the Reflex H cameras. The error introduced by the double prism, however, is negligible with focal lengths longer than 50 mm and or iris stops beyond f/3.3 (direction f/4 and smaller).

 

RX lenses were made by Kern, Schneider, Berthiot, Angénieux, and Steinheil. http://www.cinematography.com/index.php?showtopic=75200&do=findComment&comment=482791

 

Ciné Ektar are of various quality. The one-inch Ektar II is a very fine lens. Much sought also and very expensive still today is the two-inch f/1.6. If you want to shoot existing light, my recommendation is to switch to an standard camera model. The older and later S designated models don’t have a prism between lens and film but, with serial number below 100,400, longer threads in the turret and a wider shutter opening of 190 degrees. All standard Paillard-Bolex H except the very early ones have a focusing prism built in on which you can set a lens quite accurately. There are several aids to that, a 2.5 times magnifying doublet screwed into the camera body right above the focusing prism together with a black eyecup, the Eye-Level Focus that gives 6 times magnification or custom-made microscopes. With such a device you can see the frame magnified 10 or 15 times.

 

I mentioned the longer mount threads because there are lenses that have a long thread bush. This allows one to underlay shim washers which in turn opens the macro field adjacent to a lens’ shortest distance. An old Wollensak one-inch Cine Raptar I have can be screwed out the camera mount thread up to 2,75 mm and still hold firmly. At that additional pullout the plane in focus is about ten inches from the film, a 9:1 size ratio (object image nine times smaller on film). The old Switar 25-1.4 take up to 2 mm of shim. After that come the tubes.

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I regret starting this thread without getting my facts straight. I don't know whether my Bolex H16 is reflex or not: how does one tell?

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Reflex means the viewfinder lets you see through the lens that is being used to film.

 

Unscrew the middle lens (which is the one that provides an image to the film) and check if there is a piece of glass behind it. If there is, it's a reflex Bolex.

 

Non-reflex Bolexes viewed through the top lens, but filmed through the middle one, so you could rotate the turret around to focus the lens through the top mount position before moving it back down for filming. A door mounted viewfinder that viewed from the side could then be used to get a sense of framing while filming.

 

Do some more research on your camera, there are some good resources online, like the Bolex collector Website and the archives here. Andrew Alden's Bolex Bible is a good book to own.

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The early H-16 Reflex models have that designation engraved in the front top. All turret H-16 Reflex cameras have two shiny high lines on the right hand side of the black front plate.

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Simon and Dom, thank you so much. I've shot film most of my life but am new to cinematography. Thanks for clearing that up. As defined above, mine is a non-reflex. Man, I'm having so much fun! This is a wonderful forum.

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Would you mind telling the camera serial number? You can suppress the two last figures like 34,7XX but by the thousands one can tell the year of manufacture. From there the thread length is known. Accordingly recommendations may be given.

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Ciné Ektar are of various quality. The one-inch Ektar II is a very fine lens. Much sought also and very expensive still today is the two-inch f/1.6.

 

I sometimes read this sort of lens designation , i.e "a one-inch lens" or a "two-inch" lens , in older film literature, but I have to admit I don't understand exactly what the scale of "one-inch" , "two-inch" , etc. refers to ... For example , I have Cine Ektar lenses on my Kodak K100 that are designated with focal length in mm: 15mm , 25mm, and 63mm ... so what is the equivalent focal length of a "one-inch lens" in relation to the focal length given in mm ? Is there a chart you can refer me to that shows the equivalent mm focal length of one-inch , two-inch, three-inch , etc. lenses ? (I'm not sure how high up the scale it goes ... are there four-inch, five-inch, six-inch , or higher Cine lenses ? )

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Posted (edited)

Or I'm an idiot and it's just as simple as a straight conversion from inches to millimeters ?

 

Therefore a 1-inch lens is 25mm , a 2-inch lens is 50mm , etc

Edited by David T. Nethery

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It's a straight conversion of 25mm per inch. Focal lengths are often not exactly what is written on the barrel anyway, but an approximation.

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As a general and historic background information, the classic set of focal lengths for 16-mm. filming has been one inch or 25 mm as normal, a 3/5 wide angle (between 0.7" and 15 mm :huh:), and a three-times normal tele which would be three inches or 75 mm.

 

Zeiss offered a 180 mm Sonnar to the Movikon 16. Retrofocal wide-angle constructions were not available before WWII.

 

The rest is personal taste. At f/8 almost all images look alike whether they came from a triplet or a ten-elements lens.

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More about using Non-RX designated C-Mount lenses on a Bolex RX camera:

 

In this article: http://bolexh16user.net/H16Lenses.htm , it states that if the non-RX lens focal length is below 50mm , then to be safe it needs to be stopped down to f/3.3 or more to avoid focus problems :

"the rule of thumb is if you are shooting with a Non RX lens of 50mm focal length or less on a Bolex Reflex camera of which you've not had chance to do some proper testing with before being used on a shoot stop down the lens to at least f 3.3 or next highest."

 

 

But also says:

 

"There will be lots of lenses below 50mm in focal length out there that despite not being made by Bolex nor badged as H16 RX and that were never designed with any foreknowledge of being used in a Bolex Reflex camera with a prism in the light path will nevertheless produce no spherical aberrations with use. Only testing a lens fully open will find out."

 

What I'm wondering is if anyone has ever put together a list of non-RX lenses below 50mm in focal length that have been tested with a Bolex RX camera and showed no spherical aberrations ? This would be useful information to have , to know which regular (non-RX) C-Mount lenses are likely to produce good results when used with a Bolex RX camera. Lens tests would still be advisable I'm sure , but it would help to narrow down the available options to non-RX lenses that are known to work well with a RX camera.

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Everybody makes mistakes. Here I stop trusting the authorship because of spherical aberrations. The double-prism glass pane introduces a prismatic error, nothing spherical. I doubt the existence of lenses that crack the glass pane (optically). We have consistent dysfocus, smaller at f = 40 mm or 35 mm, but shorter focal lengths err out and wide angles don’t go at all unless stopped down to f/4.

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Simon, I appreciate all your input (and Dom's) . It's helpful in sorting through all the various information I find on the internet that may or may not be correct .

 

In one of your earlier posts you had mentioned :

 

"Ciné Ektar are of various quality. The one-inch Ektar II is a very fine lens. Much sought also and very expensive still today is the two-inch f/1.6 ."

 

Is the one-inch Ektar II lens you are referring to this one (attached photo) . It's marked Cine Ektar 25mm f:1.9 . I've used this one before with my Cine Kodak K100 , but not on the Bolex RX4 . Would it work ok as long as I am at f/4 or higher ?

 

https://tinyurl.com/CineEktar-25mm

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Perhaps some of my experience may be useful to you - though I've been shooting Super 16 (on a Bolex Rx5). I have two lenses on it, a Switar 16mm Rx and a Nikkor 50mm on a C mount adapter. Both lenses are great but I actually really like the look I get with the Nikkor. Beautiful, with subtle rendering of colours. I kept it stopped down a bit, plus also being 50mm there weren't any problems. A very good and low-cost lens set, as I already had the Nikkor. The Switar only cost me about $250 AUD.

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What I'm wondering is if anyone has ever put together a list of non-RX lenses below 50mm in focal length that have been tested with a Bolex RX camera and showed no spherical aberrations ? This would be useful information to have , to know which regular (non-RX) C-Mount lenses are likely to produce good results when used with a Bolex RX camera. Lens tests would still be advisable I'm sure , but it would help to narrow down the available options to non-RX lenses that are known to work well with a RX camera.

 

In my testing of RX vs non-RX lenses I came to the conclusion that the exit pupil depth is a better gauge of whether a lens is affected by the Bolex prism (or any glass block in the light path), rather than the focal length. The deeper the exit pupil, the less aberrations that are introduced. To check the exit pupil depth, simply look into the rear of a lens and see how far below the rear element the iris seems to be. Longer focal lengths tend to have naturally deeper exit pupils, which is why Bolex simplified things by just using focal length as a guide, but it's not always a direct correlation. The 10mm Switar for example has a deeper exit pupil than the 25mm Switar, so a non-RX 10mm Switar will actually work better than a non-RX 25mm on a reflex Bolex. See my blog post at:

http://cinetinker.blogspot.com/2014/12/rx-vs-non-rx-lenses.html?_sm_au_=iVV5jqw1fvcRwn4V

 

More modern telecentric designs will similarly be less affected.

 

So I don't have a list of lenses, but this is a pretty easy way of identifying lenses that should work better at large apertures.

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Everybody makes mistakes. Here I stop trusting the authorship because of spherical aberrations. The double-prism glass pane introduces a prismatic error, nothing spherical. I doubt the existence of lenses that crack the glass pane (optically). We have consistent dysfocus, smaller at f = 40 mm or 35 mm, but shorter focal lengths err out and wide angles don’t go at all unless stopped down to f/4.

 

There are only seven types of true abberation that a lens exhibits, so when descibing what the Bolex prism introduces we need to use the terms that descibe such aberrations. Prismatic error is not an aberration (and seems to be more related to non-parallel surfaces of a prism). From what I understand of it, a parallel glass block in the light path of a lens introduces a variety of aberrations, including astigmatism and coma, but the most prominent is spherical aberration.

 

There were a series of interesting articles by Roger Cicala of Lens Rentals on the effects of different filter stack (OLPF) thicknesses which are pertinent to this discussion, since a filter stack is essentially the same as the Bolex prism - a parallel block of glass in the light path. I think there was even the beginnings of a database of lens exit pupil depth.

See:

https://www.lensrentals.com/blog/2014/06/the-glass-in-the-path-sensor-stacks-and-adapted-lenses/

and:

https://www.lensrentals.com/blog/2014/06/sensor-stack-thickness-when-does-it-matter/

and:

https://www.lensrentals.com/blog/2014/07/sensor-stack-thickness-part-iii-the-summary/

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So I don't have a list of lenses, but this is a pretty easy way of identifying lenses that should work better at large apertures.

 

Thanks, Dom. Between what you've posted here on the forum, and your blog here: https://cinetinker.blogspot.com/2014/12/rx-vs-non-rx-lenses.html (and the earlier work by Dennis Couzin you referenced from here: https://sites.google.com/site/cinetechinfo/ ) I think I'm finally starting to see the light at the end of the tunnel (or the light at the end of the exit pupil depth, as it were) .

 

Even though Dennis published his findings in 1976 , and he published further information about what he calls the "RX/C Rule" in 1987, it seems to me that this information about how certain C-mount lenses may be used on Bolex Reflex cameras (and vice versa) is still not widely known or understood. It also surprises me that over the years that no one has compiled a list of normal C-Mount lenses that are known to work well on a Bolex RX camera, according to Couzin's "RX/C Rule" :

 

"A C-mount lens works well on a RX camera or RX-mount lens works well on a C-mount camera , if and only if:

 

(1.) The lens is slower than about f/2 or f/2.8 , or stopped down this far ;

 

AND

 

(2.) The lens has a deep set exit pupil, about 1.5” inches or farther into its screw mount."

 

Although I must admit that accurately estimating the depth of the exit pupil is still a little bit mysterious to me, even though Dennis Couzin says “The exit pupil mentioned in clause (2) is not mysterious . It is the appearance of the aperture from which the image forming rays all come . The exit pupil test can be easily applied by eye. View the lens from the rear. Close the iris a few stops . Estimate how deep into the lens the iris appears to be. A finger held along side the lens may help this estimation.”

 

.

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For anyone coming across this topic in the future , here's a page from the 'Bolex Reporter' magazine, Vol. 14 , No. 2 from 1964 , giving the official company line on lenses suitable for Bolex cameras.

50234202_10214868829289175_4785627512401

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