Basic Question About Lenses

[Norseman]

Sorry if this question is pretty simple to most of you. I recently obtained a couple of Kern-Paillard lenses (no instructions included) for my Bolex C8 and B8 cameras. On the 36mm telephoto lens, there is the exposure ring, and then there is another ring on it. I am "assuming" this is a focusing ring, with stops at 1 3/4, 2, 2 1/4, 2 1/2, 3, 3 1/2, 4, 5, 7, 10, 15, 30, 200. Measured in feet I believe. On these cameras, the viewfinder eyepiece and the lens are not connected to each other, so focusing is a guessing game. Are you suppose to estimate the distance in feet from your camera to the subject you are filming. and set the ring to that distance? Why are there so many settings for close up shots (1 to 3 feet away), and such a big jump from 30 feet to 200 feet? Excuse my ignorance please, but as you can see, I'm a bit confused here, as I've never used a lens like this before. Thanks for your help.

[Lunar07]

Sorry if this question is pretty simple to most of you. I recently obtained a couple of Kern-Paillard lenses (no instructions included) for my Bolex C8 and B8 cameras. On the 36mm telephoto lens, there is the exposure ring, and then there is another ring on it. I am "assuming" this is a focusing ring, with stops at 1 3/4, 2, 2 1/4, 2 1/2, 3, 3 1/2, 4, 5, 7, 10, 15, 30, 200. Measured in feet I believe. On these cameras, the viewfinder eyepiece and the lens are not connected to each other, so focusing is a guessing game. Are you suppose to estimate the distance in feet from your camera to the subject you are filming. and set the ring to that distance?

Yes! As long as you have a good idea, you are fine. Also, do not forget that you get a depth of field that increases as the aperture goes down.

Why are there so many settings for close up shots (1 to 3 feet away), and such a big jump from 30 feet to 200 feet? Excuse my ignorance please, but as you can see, I'm a bit confused here, as I've never used a lens like this before. Thanks for your help.

You can use the C8/B8/D8 cameras with an accessory attachment that is a parallax correction for close up photography (attachments come in two pairs - one for 1' and 2' and one for 20cm and 50cm.) This allows you to see what the lens is seeing at these close quarters. If you measure the distance corectly, you can use it for shooting at these close distances. Distance jump means that focusing at such distances is not as distance critical as for closer objects. There is another Bolex attachment that allows you to see what the lens sees at all distances.
Also, do not forget that the H-8 accepts D-mount lenses like the one you are using for the C8 and B8. The H-8 allows for via the lens focusing. Along with the critical focus rack (another Bolex acessory) you can focus the H-8 then switch the lens to the film gate position while keeping the lens directed at what you are shooting.

[clivetobin]

Are you suppose to estimate the distance in feet from your camera to the subject you are filming. and set the ring to that distance? Why are there so many settings for close up shots (1 to 3 feet away), and such a big jump from 30 feet to 200 feet? .

Yes. Actually you estimate from the subject, to the film plane mark on the side of the camera which is a circle with a vertical line through it. (This is true for nearly all cameras except amateur Polaroid, which measure from the front of the lens.)

At close distances the magnification is greater so the focus becomes more critical. At 200 feet it might as well be at infinity as the magnification is less, so the markings are closer together on the dial.

There should be depth of field marks next to the focus ring, to show what range of distance will be in acceptable focus for a given F number setting. The smaller the aperture (the larger the F number) the more leeway you have in focus error.

[Norseman]

On this lens (Kern-Paillard 36mm telephoto), there is a series of orange dots in a wide V pattern, that appear and disappear when the exposure ring is turned. The dots are all there at setting 22, and are all gone at setting 2.8. Do these dots have any meaning?

[discs of tron]

yes. they are the old fashioned version of a depth-of field preview. the aperture (f stop) you set determines the depth of field. the orange dots will line up with one of the distances on the focus ring. the smaller your aperture (f22 being the smallest,) the deeper your depth of field. the orange dots illustrate (semi-accurately) what ranges will be in focus. at f22 with a 36mm lens, you pretty much get infinite d.o.f.

[tlatosmd]

I guess this is as much a conventient thread as any other for my question.

What, exactly, constitutes a c-mount?

I intend to put my PROSKAR anamorphic lens on eBay again. I've done so before some time ago but ended up with a non-paying buyer. However, I've got some questions about whether it was c-mount and I couldn't reply to that because I had absolutely no idea.

I asked people back then (couldn't even find anything revealing on wikipedia or elsewhere on the net) and they told me it's a c-mount 'if it looks like a c'. However, I doubt that, also because you people seem to talk about a-mounts, b-mounts, d-mounts, etc.-mounts all the time. From a post a while back, I figure it might have to do with thread diameter.

[clivetobin]

What, exactly, constitutes a c-mount?

C Mount is a standard thread for mounting taking lenses on a camera body, not for accessory lenses that go in front such as anamorphics. Anyone asking if an accessory lens is C Mount has no understanding of the subject.

C Mount is defined further as 1" thread diameter, 32 threads per inch, and .690" from the lens seat to the film plane. It is used mostly for 16mm cameras. CS Mount is used on some video lenses and it is the same except that the lens seat to CCD plane is about 5mm less, or about 12.5mm which is .492".

I have misplaced my reference material but I think I recall that D Mount is 5/8" thread diameter, 32 threads per inch, and .484" from lens seat to film plane. It is used mostly on 8mm cameras. Bolex L8 cameras used the same thread but the focus distance was different.

Bolex H-16RX lenses are the same as C mount except they are computed to allow for a glass reflexing prism. They will focus on other 16mm C Mount cameras but the resolution or color fringing may not be optimum. The actual physical distance is greater owing to the thickness and refractive index of the prism.

Bolex H-8RX lenses are deceiving as they have the same threads as C Mount, however the lens to 8mm film focus distance is much less, I don't recall the figure. These lenses cannot be used on 16mm cameras except for extreme closeups and will not focus to normal subject distances much less to infinity. Despite what unscrupulous or ignorant Ebay sellers say about them.

[Lunar07]

C Mount is defined further as 1" thread diameter, 32 threads per inch, and .690" from the lens seat to the film plane.

In metric - the lens seat to film plane is 17.52mm

I have misplaced my reference material but I think I recall that D Mount is 5/8" thread diameter, 32 threads per inch, and .484" from lens seat to film plane. It is used mostly on 8mm cameras. Bolex L8 cameras used the same thread but the focus distance was different.

This is correct - in metric the distance is 12.29mm. Except for the L8 as you mention in which case the distance is the much shorter 0.3075" (7.8mm).

Bolex H-8RX lenses are deceiving as they have the same threads as C Mount, however the lens to 8mm film focus distance is much less, I don't recall the figure.

Can you find out what this distance is? Once I had a modified H-8 Rex turret. It was modified in such a way as to create a recessed C mount for 'regular' C mount lenses. This suggests the distance for the C mount lenses made for the H-8 Rex is greater than 17.52mm. I just could not find this modiffied turret. I'd like to use a 25mm C mount prime lens on my H-8 Rex DS-8 but I do not think there were 25mm prime lenses made for the H-8 Rex.

[Lunar07]

On this lens (Kern-Paillard 36mm telephoto), there is a series of orange dots in a wide V pattern, that appear and disappear when the exposure ring is turned. The dots are all there at setting 22, and are all gone at setting 2.8. Do these dots have any meaning?

Just to add - This model of lenses with the pattern you mention are refered to as Visi-Focus lenses.
Also, if you do some research and find out what is the hyperfocal distance of a lens you'll be in good shape. When a lens is set to the hyperfocal distance it will focus everything from half this distance to infinity.

[Rob]

This is correct - in metric the distance is 12.29mm. Except for the L8 as you mention in which case the distance is the much shorter 0.3075" (7.8mm).

This must mean that L8 lenses are not usable on any other Bolex camera, any other camera at all in fact. Are these lenses marked accordingly?

Rob

[Lunar07]

This is correct - in metric the distance is 12.29mm. Except for the L8 as you mention in which case the distance is the much shorter 0.3075" (7.8mm).

This must mean that L8 lenses are not usable on any other Bolex camera, any other camera at all in fact. Are these lenses marked accordingly?

Rob

Some of them are marked with L8 at the bottom of the lens. I do not know if all of them are. But you are right - there is always a risk of someone selling an older Kern D mount lens which was made for the L8 without knowing about it if it is not marked for the L8.

[tlatosmd]

C Mount is a standard thread for mounting taking lenses on a camera body, not for accessory lenses that go in front such as anamorphics. Anyone asking if an accessory lens is C Mount has no understanding of the subject.

C Mount is defined further as 1" thread diameter, 32 threads per inch, and .690" from the lens seat to the film plane. It is used mostly for 16mm cameras. CS Mount is used on some video lenses and it is the same except that the lens seat to CCD plane is about 5mm less, or about 12.5mm which is .492".

My anamorphic lens has a thread that is 4cm in diameter, about 1 1/2 (one and a half) inches, so I suppose it falls into that C-mount category of 'further as 1'' thread diameter'. However, I doubt it is attached on another lens.

[Lunar07]

C Mount is a standard thread for mounting taking lenses on a camera body, not for accessory lenses that go in front such as anamorphics. Anyone asking if an accessory lens is C Mount has no understanding of the subject.

C Mount is defined further as 1" thread diameter, 32 threads per inch, and .690" from the lens seat to the film plane. It is used mostly for 16mm cameras. CS Mount is used on some video lenses and it is the same except that the lens seat to CCD plane is about 5mm less, or about 12.5mm which is .492".

My anamorphic lens has a thread that is 4cm in diameter, about 1 1/2 (one and a half) inches, so I suppose it falls into that C-mount category of 'further as 1'' thread diameter'. However, I doubt it is attached on another lens.

Maybe I got you wrong here. But "C Mount is defined further as 1" thread diameter" means that 'additionally C mount is defined as a 1" thread diameter." The anamorphic lens that you have has a rear thread of 40mm so of course it is not a C mount lens. This anamorphic is attached or screwed in front of another lens that does not have to essentially be a C mount lens. For example, you can attach this anamorphic in front of a projector lens, a D mount lens, a C mount lens or an SLR lens.

[clivetobin]

Can you find out what this distance is? Once I had a modified H-8 Rex

I vaguely recall that the H8RX flange to film plane through the prism is the same *physical* distance as that of a regular C mount lens. But owing to the prism the *optical* distance is less. I don't know exactly how much less, seems to me it was about .1 to .2 inches or 2.5 to 5 mm, too little a difference to be able to use a short extension tube but too much to be able to use a shim washer. I used to know until we last moved across state but now I can't find anything. So we are all at the mercy of my increasing senility.