Jump to content
Matt Rosen

Bolex focus problems

Recommended Posts

I recently shot a short film on an H16 reflex. It was my first time shooting on celluloid, so I asked advice from a more experienced friend of mine. He advised to not trust my own eyes, but to measure distance from the back of the lens to the subject's eyes. If it looked out of focus in the eyepiece (which had no diopter), I should ignore my instinct and trust the measurement.

 

I followed his directions, but the footage came back extremely out of focus (just as it looked in the eyepiece).

 

The camera had a Switar 25mm lens at f-1.4, a Cine-tel 51mm at f-3.5, and a 4-inch Tele Megor at f-4.

 

 

I realize that the camera and lenses are likely in poor repair, but was there anything I could've done to prevent these problems under those circumstances?

Share this post


Link to post
Share on other sites

I recently shot a short film on an H16 reflex. It was my first time shooting on celluloid, so I asked advice from a more experienced friend of mine. He advised to not trust my own eyes, but to measure distance from the back of the lens to the subject's eyes. If it looked out of focus in the eyepiece (which had no diopter), I should ignore my instinct and trust the measurement.

 

I followed his directions, but the footage came back extremely out of focus (just as it looked in the eyepiece).

 

The camera had a Switar 25mm lens at f-1.4, a Cine-tel 51mm at f-3.5, and a 4-inch Tele Megor at f-4.

 

 

I realize that the camera and lenses are likely in poor repair, but was there anything I could've done to prevent these problems under those circumstances?

If its a reflex camera you should get what you see through the viewer. So long as the lens is adjusted to the bolex...

Edited by Patrick Clement

Share this post


Link to post
Share on other sites

Hi Matt,

 

The rotating turret is sometimes confusing to first time Bolex users. The lens closest to the viewfinder is not the lens being used, it's the lens farthest to the left as you are facing the viewfinder. Use the metal turret lever to rotate and change lenses.

 

If it's a reflex it should have a diopter, here's a picture that you can see the diopter adjust right after the eyepiece (the big lens is in the taking position in this particular photo by the way):

 

th_bolex-h16-reflex.jpg

 

Always adjust the diopter to your eyesight. Rotate the diopter until you can see grain on the groundglass, then lock the diopter. If you are having problems adjusting the diopter rotate the lens turret so that there isn't a lens on the taking position, point it at a bright light, or both.

 

Hope this helps!

Share this post


Link to post
Share on other sites
If its a reflex camera you should get what you see through the viewer. So long as the lens is adjusted to the bolex...

 

What do you mean by adjusted to the bolex? Are these adjustments I can make, or is it just a question of whether the lens fits the camera?

 

Obviously on a camera with a diopter I should adjust it to my eyesight, but otherwise is there anyway I can check to see if it's accurate?

Share this post


Link to post
Share on other sites
Hi Matt,

 

The rotating turret is sometimes confusing to first time Bolex users. The lens closest to the viewfinder is not the lens being used, it's the lens farthest to the left as you are facing the viewfinder. Use the metal turret lever to rotate and change lenses.

 

If it's a reflex it should have a diopter, here's a picture that you can see the diopter adjust right after the eyepiece (the big lens is in the taking position in this particular photo by the way):

 

th_bolex-h16-reflex.jpg

 

Always adjust the diopter to your eyesight. Rotate the diopter until you can see grain on the groundglass, then lock the diopter. If you are having problems adjusting the diopter rotate the lens turret so that there isn't a lens on the taking position, point it at a bright light, or both.

 

Hope this helps!

 

Unfortunately, that Bolex is better equipped than the one I was using. As you can see, there is no diopter on this one:

 

Bolex1_by_pykoslave42.jpg

 

Bolex2_by_pykoslave42.jpg

Share this post


Link to post
Share on other sites

Hi Matt,

judging by the viewfinder in your picture, your camera looks like a Rex1 with its 6x magnification viewfinder.

Here is a page on the Rex1: http://www.bolexcollector.com/cameras/h16reflex.html

According to this page, even the Rex1 has a diopter adjustment. I haven't used a Rex1 for a long time, but I believe this to indeed be the case. Is it simply a matter of rotating the plastic eye piece in or out? I have a feeling that is so. Take the rubber eye cup off the plastic eye piece and see if you can gently rotate the plastic eye piece. If so, it would be better to set it with the rubber eye cup in place if that is what you are using. But see if you can loosen it first.

 

As for lenses, its all quite simple. If you have a reflex bolex (and you do) then the c-mount lenses you use need to have 'RX' written on them. In point of fact this is only important with the wider angle lenses (say below 25 ... but I am sure there is an official figure on that) and even then, only important if you are more open than say f5.6. Assuming there is no problem with your lens mount (like the turret is very loose) then this won't be your problem.

 

As for not trusting your eye, well if the diopter isn't set right, then the ground glass won't be in focus. But its not nearly as catastrophic as diopter setting on a super 8 camera, precisely because there is a ground glass. With a camera with a ground glass, even if the diopter is off, it is possible to pull the focus with your eye so that the ground glass is clear. The ground glass is exactly the same distance from the lens as the film plane, so if an image is in focus on the ground glass, its in focus on the film (ok unless your lenses need colimiting, but lets assume they haven't been played with). So yes, with a camera with a ground glass, even when the diopter is not set exactly to your eye, you can still trust your eye as your eye is a powerful organ and will aim for the ground glass regardless - it will just be more work for your eye. So as long as you can see the grain in the ground glass, you can trust your eye.

 

As for distance markings, these are always correct provided no one has taken the front element off the lens. If so, then the lens needs to be colimited before it can be trusted again. But it seems you were told that you measure from the rear of the lens. That is not so. You measure from the film plane (ie where the film is inside the camera - the point where the lens is focusing). I think you will find etched on the side of the bolex there is a little circle with a line through it. This is the film plane mark and it is to here that you need to measure. Now if you are talking about subjects several meters away, it won't make much difference if you measure from here exactly or not ... but the closer your subject is, the more important it is to measure from the film plane mark. Personally I think this is where you went wrong.

 

I hope that helps,

richard

Share this post


Link to post
Share on other sites

What do you mean by adjusted to the bolex? Are these adjustments I can make, or is it just a question of whether the lens fits the camera?

 

Hi, my knowledge of bolex cameras is very limited, so i may be waffling a little here...

 

I think the above posters means that a lens must be adjusted/collimated to the camera to obtain best results. When i purchased my r16 a few years ago, i alway obtained soft images when the lens was wide open, thus the lens was not properly adjusted to the camera body. A specialist dealer/service agent with the correct equipment can only make the adjustments.

 

Is your bolex a 'reflex' model?. If so, you MUST ( i may stand corrected here ) use switar/schneider lenses with the marking RX on them, any old c=mount lens will not give one sharp focus, i beleive the 75mm f2.8 yvar 'AR' is an exception. If your lenses are just plan c-mounts with the AR marking, these will only work on non-reflex H16.

 

 

hope thats of some help

 

Andy

Edited by andy oliver

Share this post


Link to post
Share on other sites

If the diopter wasn't in focus for your eye then it will always be out of focus - you cant have an out of focus diopter 'trick' an out of focus lens into making a image appear in focus once a ground glass has been introduced - its actually two unrelated optical systems...

 

'RX' adjusted/collimated or not a reflex lens will project onto the film what you see focused on the ground glass, so if what you see is in focus then its should be on film. *Unless* the distance from the GG to the lens has been moved to be further or closer than the distance to the film plane - quite hard to do actually and not an intermittent fault.

 

Dont measure from 'the back of the lens' - measure from the film plane, a circle with a line through it on the 'control side' of your Bolex. Yes it is near the back of the lens, but not exactly - especially important with macro/close up shots

 

Your friend probably worked with cameras that lacked a ground glass and had a pure optical path viewfinding system not relevant to Bolexes

 

You can use any lens you want btw ;) just that any lens under about 25mm that isn't marked RX or otherwise to indicate the reflex collimation will cause less than perfect results - have a read:

 

http://www.apecity.com/manuals/bolex_lense...6mm_cameras.pdf

 

http://www.apecity.com/manuals/bolex_lense...6mm_cameras.pdf

 

http://www.apecity.com/manuals/bolex_lense...6mm_cameras.pdf

 

http://www.apecity.com/manuals/bolex_lense...6mm_cameras.pdf

 

http://www.apecity.com/manuals/bolex_lense...6mm_cameras.pdf

 

http://www.apecity.com/manuals/bolex_lense...6mm_cameras.pdf

 

http://www.apecity.com/manuals/bolex_lense...6mm_cameras.pdf

 

http://www.apecity.com/manuals/bolex_lense...6mm_cameras.pdf

 

http://www.apecity.com/manuals/bolex_lense...6mm_cameras.pdf

 

http://www.apecity.com/manuals/bolex_lense...6mm_cameras.pdf

 

http://www.apecity.com/manuals/bolex_lense...6mm_cameras.pdf

 

http://www.apecity.com/manuals/bolex_lense...6mm_cameras.pdf

Share this post


Link to post
Share on other sites

Thanks to everyone for your help. I'm pretty sure I know what went wrong.

 

A big part of it was bad information. I was told to trust my measurements over my eye, but the discrepency between the two meant that there was clearly something wrong.

 

The camera does indeed have a diopter, and it was focussed all along. My ignorance of that made me unconfident and more willing to trust the lenses, which I am almost positive need to be colimited.

 

Measuring from the lens instead of the film plane and using lenses not designed for the reflex might've contributed in some small ways to the problem, but I don't think they were the main cause.

 

I've learned a ton from this thread and am eternally grateful for everyone's help. Thanks.

Share this post


Link to post
Share on other sites
If the diopter wasn't in focus for your eye then it will always be out of focus - you cant have an out of focus diopter 'trick' an out of focus lens into making a image appear in focus once a ground glass has been introduced - its actually two unrelated optical systems...

 

This is indeed correct. When using a camera with a ground glass focusing screen, unless the distance or other optical components have been damaged or altered, anything in focus on the ground glass will be in focus on the film. Even if the eyepiece diopter is set wrong, this remains the case. And if the diopter is set wrong on such a camera, your eye is powerful enough to pull focus onto the ground glass anyway.

 

 

'RX' adjusted/collimated or not a reflex lens will project onto the film what you see focused on the ground glass, so if what you see is in focus then its should be on film. *Unless* the distance from the GG to the lens has been moved to be further or closer than the distance to the film plane - quite hard to do actually and not an intermittent fault.

 

Quite right, I mentioned collimatry with relation to the RX issue, but of course its nothing to do with that. Slip of the brain. Its a back focus issue. The RX lenses focus a different distance from the rear of their c-mount lens to other c-mount lenses simply because the bolex reflex system incorporates a prism to split in coming light to the viewfinder. This prism requires the different focus distance.

Share this post


Link to post
Share on other sites

This is just a wild guess....I only know because I know someone who did it with a Bolex.

 

Are the measurements on the lens Metric or US? Were you using the same for the distance?

 

Our school has both, so you always have to make sure you know what lens you have.

Edited by Adam Orton

Share this post


Link to post
Share on other sites
Is your bolex a 'reflex' model?. If so, you MUST ( i may stand corrected here ) use switar/schneider lenses with the marking RX on them, any old c=mount lens will not give one sharp focus, i beleive the 75mm f2.8 yvar 'AR' is an exception. If your lenses are just plan c-mounts with the AR marking, these will only work on non-reflex H16.

 

Hi Andy,

 

that's not quite true. Since wide angle lenses have a very shallow depth of focus these lenses will be out of focus if non-RX lenses are used wide open. Stopping them down to at least f4 will get rid of the problem, usually. With longer focal lenses (>50mm) you won't have any problem. In fact lenses longer than 50mm were never produced in RX or non-RX versions. The 75mm Yvar you mention is called AR for Anti-Reflection, which just indicates it is MC coated. BTW, the whole thing works the other way round as well, when using RX lens es on a non-reflex Bolex (or any other C-mount 16mm camera) be sure to stop them down a couple of stops from wide open. And test before you shoot any critical stuff!

 

Regards, Dave

Share this post


Link to post
Share on other sites

[Are the measurements on the lens Metric or US? Were you using the same for the distance?]

 

They would not be US. They would be Imperial/International.

Share this post


Link to post
Share on other sites
Guest Glenn Brady
In fact lenses longer than 50mm were never produced in RX or non-RX versions.

 

This is not strictly correct. Bolex offered 75mm f/2.8 Yvar H8 RX, 100mm f/2.8 Macro-Yvar H8 RX, and 150mm f/3.8 Macro-Yvar H8 RX lenses. They're shown in the factory catalogs of the period. I own a 75mm f/2.8 Yvar lens that's so engraved.

Share this post


Link to post
Share on other sites
[Are the measurements on the lens Metric or US? Were you using the same for the distance?]

 

They would not be US. They would be Imperial/International.

 

FYI, you quote someone by simply pushing the 'quote' button, as I've done.

 

And Imperial is also referred to as US customary units.

 

Anyway, if you aren't aware of what measurement you are using to focus, this can really screw up your footage, obviously. It's a simple mess-up but is easy to do if you're constantly switching between lenses.

Share this post


Link to post
Share on other sites

Thanks Adam, that was something that never even crossed my mind. I double-checked just now though, and they're all in feet.

 

How do I go about getting the lenses colimited? I just did a test where I looked at my roommate through the balanced 25mm at 7' away, and in order to get him in focus, I needed to set the lens to 200'. That was as wide as the focus would go. It's a wide angle lens that can't shoot wide angles. The other lenses aren't that bad, but I still want to get this fixed as soon as possible.

 

Any recommendations in the New York area?

Share this post


Link to post
Share on other sites
This is not strictly correct. Bolex offered 75mm f/2.8 Yvar H8 RX, 100mm f/2.8 Macro-Yvar H8 RX, and 150mm f/3.8 Macro-Yvar H8 RX lenses. They're shown in the factory catalogs of the period. I own a 75mm f/2.8 Yvar lens that's so engraved.

 

Hi Glenn,

 

interesting. My Bolex literature (e.g. Andrew Alden's Bolex Bible) doesn't mention that, but it's about the H16 only. Maybe they didn't offer that line of lenses for other formats that 8mm?

 

Regards, Dave

Share this post


Link to post
Share on other sites
I just did a test where I looked at my roommate through the balanced 25mm at 7' away, and in order to get him in focus, I needed to set the lens to 200'. That was as wide as the focus would go. It's a wide angle lens that can't shoot wide angles. The other lenses aren't that bad, but I still want to get this fixed as soon as possible.

 

Hi Matt,

 

be careful! 25mm may be a wide angle in 35mm still and slightly wide in 35mm cine but in 16mm it's a rather long lens. The normal lens in 16mm is considered to be the 12mm if you follow the rule of format diagonal to determine the normal focal length!

 

Cheers, Dave

Share this post


Link to post
Share on other sites
Guest Glenn Brady
Maybe they didn't offer that line of lenses for other formats that 8mm?

 

Yes, that's correct. Lenses shown in the same catalog for the H16 RX aren't marked RX for focal lengths beyond 50mm as you indicate.

Share this post


Link to post
Share on other sites
Yes, that's correct. Lenses shown in the same catalog for the H16 RX aren't marked RX for focal lengths beyond 50mm as you indicate.

 

Hm, now that's kinda curious. Marketing maybe? Or would there indeed be a difference with depth of focus and those focal lengths in 8mm?

 

Cheers, Dave

Share this post


Link to post
Share on other sites
Guest Glenn Brady
Hm, now that's kinda curious. Marketing maybe? Or would there indeed be a difference with depth of focus and those focal lengths in 8mm?

 

The optical flange focus distance is different between the H8 RX and H16 RX (15.305mm versus 20.76mm), so I believe a regular long focus C-mount lens works properly on the H16 RX but not on the H8 RX.

Share this post


Link to post
Share on other sites
The optical flange focus distance is different between the H8 RX and H16 RX (15.305mm versus 20.76mm), so I believe a regular long focus C-mount lens works properly on the H16 RX but not on the H8 RX.

 

Hm, that is not really logical. A normal non RX C mount has a FFD of 17.52mm, so much closer to 15.3 than 20.76.

 

Cheers, Dave

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.



  • Visual Products



    Tai Audio



    FJS International



    Wooden Camera



    Rig Wheels Passport



    Serious Gear



    Abel Cine



    Glidecam



    The Original Slider



    G-Force Grips



    Gamma Ray Digital Inc



    Media Blackout - Custom Cables and AKS



    Ritter Battery



    Broadcast Solutions Inc



    Paralinx LLC



    Just Cinema Gear



    Metropolis Post



    New Pro Video - New and Used Equipment



    CineLab


    Cinematography Books and Gear
×
×
  • Create New...