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Eclair NPR Test...footage out of focus


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#1 Brian Rose

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Posted 17 September 2013 - 11:17 AM

Guys and Gals I could use your help: I just got my test footage back from my Eclair NPR S16 I picked up not long ago. And a funny thing happened. All my night shots (of a city skyline, using 400 ASA stock) were uniformly out of focus. I can't figure out why since I checked measurements both by lens markings, and by eye. I mean i'm looking through the viewfinder as I film, and everything was sharp to my eye. How can it be, that the image would be properly focused in my viewfinder, but come out soft on the actual film? A misalignment with the prism beamsplitter inside perhaps? I was using 35mm primes with a c-mount adapter, if that information is helpful. 

 

My daylight footage is better, and I've got stuff shot with the same lenses and mounts that came out quite crisp and lovely, but I'm wondering if this because I was stopped down and had greater depth of field to counteract focus issue?  When I shot a focus/framing chart it came out quite sharp (albeit slight off center which further suggests a prism misalignment of some sort).  The night footage of course was wide open and had less tolerance for misadjustment.  

 

Any advice would be deeply appreciated!

BR


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#2 Adrian Sierkowski

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Posted 17 September 2013 - 11:24 AM

If it's on all lenses, I would assume Flange depth is out.

 

The lenses in daylight, stopped down more probably wouldn't shot that as much. I'd get camera flage depth checked.


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#3 Brian Rose

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Posted 17 September 2013 - 11:45 AM

If it's on all lenses, I would assume Flange depth is out.

 

The lenses in daylight, stopped down more probably wouldn't shot that as much. I'd get camera flage depth checked.

 

I haven't had time yet to organize my footage, but I kept careful notes of what lens and mount or adapter was used in each shot.  And it does on initial appraisal seem to be isolated to the 35mm primes I mounted via a c-mount adapter.  

 

But if indeed it's the flange depth, then wouldn't that have been plain in the viewfinder? That's what bothers me, how it could be ostensibly sharp in the viewfinder, yet a blurry mess on the actual film, especially when I was looking through the viewfinder during the shot, and I even adjust focus while the camera is running to suit my eye, but to little effect on the film.  

 

That freaks me out, that my viewfinder could be unreliable.


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#4 Stephen Williams

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Posted 17 September 2013 - 12:02 PM

The viewfinder may not be set to the same depth as the film, when the film is running.......


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#5 Brian Rose

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Posted 17 September 2013 - 12:18 PM

Let me ask you all this, if this is a sound plan:

 

Going off of Bernie O'Doherty's advice, using a bit of semi-transparent material over the gate, I first ensure back focus is achieved through the gate.  Then I check the prism alignment and fix if need be.

 

I mean, if it's sharp looking through the gate, and then sharp through the viewfinder, and my measurement markings are correct...I should be set as far as focus is concerned, am I right?


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#6 Stephen Williams

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Posted 17 September 2013 - 02:25 PM

Let me ask you all this, if this is a sound plan:

 

Going off of Bernie O'Doherty's advice, using a bit of semi-transparent material over the gate, I first ensure back focus is achieved through the gate.  Then I check the prism alignment and fix if need be.

 

I mean, if it's sharp looking through the gate, and then sharp through the viewfinder, and my measurement markings are correct...I should be set as far as focus is concerned, am I right?

 

 

 

Up to a point, better to check when the film is moving.......As thats where you have the problem.


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#7 Brian Rose

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Posted 17 September 2013 - 03:43 PM

 

Up to a point, better to check when the film is moving.......As thats where you have the problem.

 

Luckily the film itself is steady, and there are plenty of moments when the footage is sharp...owing to stopping down and greater depth of field.  I just need to isolate the problem I think by ensuring the image at the gate is in focus, and the prism corresponds to the image itself.


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#8 Dom Jaeger

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Posted 17 September 2013 - 09:08 PM

Hi Brian,

 

if this is an important project and you've just picked up a film camera off ebay or something you need to have the camera, lenses and adapters checked over by a technician. Trying to adjust things by yourself is simply not how to do it if you care about the image quality, or want to feel confident about the gear holding up over the course of shooting your project. 

 

There are a few factors that can lead to soft images. As you've mentioned, stopping down increases your depth of field, but it also reduces aberrations in the lens itself, which leads to sharper looking pictures. Some lenses perform better than others wide open, but virtually all lenses will sharpen up stopped down a couple of stops. As well as this, with wider focal lengths (combined with larger apertures) the back-focus distance becomes more critical, a tiny error in this distance and everything will be soft.

 

There are 3 factors at play in the focus adjustment of a reflex film camera:

 

The lens itself should be calibrated for correct infinity back-focus, so that you can rely on the distance scale and infinity can be reached. With zooms it's even more important, so that focus is maintained through the zoom range.

 

The camera flange depth needs to be set to factory specifications, matching the infinity back-focus of the lenses (or sometimes a very tiny bit shorter, to allow for the film to float as it runs through the gate, and the light to penetrate into the film emulsion layers). This is usually done with a depth gauge accurate to at least one hundredth of a mm (less than half a thousandth of an inch). It can be checked on an autocollimator with film running through.

 

The ground glass needs to be set at a depth that exactly matches the infinity back-focus distance of the lenses (or the nominal camera flange depth), so that the viewfinder image matches what is recorded on the film. This distance is not physically measureable since it bounces off a mirror (or sometimes a prism), so it needs specialised equipment like an autocollimator which measures it optically to properly check and adjust the setting. You can try and do it by eye, but it's very difficult to get exactly right.

 

Other aspects, like the viewfinder framelines matching the gate are determined by the groundglass/prism assembly being correctly positioned in the 2 axis perpendicular to the depth. 

 

I would strongly recommend that you send the camera and lenses to an experienced tech to get at least these basic settings checked. And since adapters can also introduce variations, they should be checked as well.

 


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#9 Brian Rose

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Posted 17 September 2013 - 09:41 PM

Okay, I think I've solved my problem.  I'm pretty sure it was a combination of three things: the camera's ground glass was not aligned properly, and my viewfinder was not perfectly focused...I have it set to my prescription so I won't have to wear my eye glasses while looking through the VF, and it was a bit off, exacerbated no doubt thanks to the ground glass.  And lastly, I think the c-mount adapter I'm using for some of my primes doesn't have a suitable focal flange depth, which was throwing things off.

 

I could use your help to check me though.  So I have realigned everything, and now with my camera pointed at a focus chart precisely 4 feet away, with my zoom lens in place in the CA-1 mount, when I set the focus to 4 feet, it is dead on, sharp focus, both in the view finder, and in the gate when I use a DIY focus screen.  And the focus holds when I pull back as wide as the lens will go.  

 

And given my tests have shown the pull down movement works wonderfully, the image is rock steady without ghosting, runs smooth and very quiet, does it sound to you all like I've solved the problem?  Do you think i've caught everything, and can hazard tests again?

 

BR 


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#10 David Mullen ASC

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Posted 17 September 2013 - 10:16 PM

One issue with the NPR is that pin you pull out to flip the front plate between the C-mount and the CA-mount -- it creates another point where the back-focus can be off other than the mounts themselves.  Often before I shot, I would pull that pin, pull that plate forward, and then push it back in hard and lock it down again to make sure it was seated firmly.

 

If all of the back focus is correct and the film itself is soft, then perhaps the mag and pressure plate is not seating correctly, though you would think then that pulldown claw wouldn't be able to engage.


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#11 Brian Rose

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Posted 17 September 2013 - 10:36 PM

One issue with the NPR is that pin you pull out to flip the front plate between the C-mount and the CA-mount -- it creates another point where the back-focus can be off other than the mounts themselves.  Often before I shot, I would pull that pin, pull that plate forward, and then push it back in hard and lock it down again to make sure it was seated firmly.

 

If all of the back focus is correct and the film itself is soft, then perhaps the mag and pressure plate is not seating correctly, though you would think then that pulldown claw wouldn't be able to engage.

 

Point well made David.  That turret is tricky, and too always take care to make sure it is firm and locked.  Ideally I'll take the lenses off, rotate the turret, and then mount again just to be safe.

 

I'm pretty sure I've caught the problem now...several things really that I've now sorted out.  I just did a bunch of back focus tests, at 4, 5 6, and 7 feet aimed at a focus chart.  I set the focus purely by eye, using a semi-transparent screen in the place of the film in the gate, and with the aid of a magnifier, I set the focus, and verify the viewfinder is sharp.  And every time, when I've finished, the lens marking reads....4 feet, 5 feet, 6 and 7!  It's dead on.  :)


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