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Lens Problem?


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#1 Ward Crockett

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Posted 29 September 2006 - 08:15 PM

This issue requires some introduction---
My producer and I recently bought a Bolex EBM (converted to S16) with a Vario-Switar 100 POE. We shot some scenes in a TV studio on black and white reversal. A few weeks later, we shot two reels of test footage on reversal--we processed one as reversal and cross-processed the other---we did this to see how cross-processed footage compares to straight reversal processing. These two test reels were recans.

We had all of the film mentioned above processed and transferred to DV in two separate labs. The footage we shot in the television studio came out fine. The test footage (both reels) came out with a strange ghosting effect (not sure if ghosting is the right term). You can see the images here: Bolex Test Images

The weird effect is on the right side of the man---his ear seems to pop out, the lettering on his shirt pops off, etc.

The ghosting isn't as pronounced in indoor shots, though it is present. Strangely, it seems to vary. In the last two images (two consecutive frames), the magnitude of the effect is different. Notice the effect on the right side of the man's thumb---it's worse in the first image.

The effect shows up at different frame rates, from 10 to 50. The effect did not change during frame rate changes (we switched from 24 to 50 while rolling).

Since we shot the test footage, I've looked thru the reflex viewfinder on an outdoor subject in comparable sunlight conditions and have not seen the ghosting. I've stopped it down to see if the effect appears at smaller apertures but have not seen the effect. Seems like I'd see this effect in the viewfinder if it were a lens problem, but from what I've heard, there are some lens problems that won't be noticeable in the viewfinder (true?).

Again, the other footage we processed and transferred at a different lab looks fine. We did shoot the footage a few weeks apart, so there's the possibility that the lens was damaged during that time---unlikely, though, since it was sitting in its cut-foam flight case all that time.

I do know that I didn't have the filter holder in place when I shot the test footage (don't remember if it was in place for the television studio footage). Bolex says you must have the filter holder in place whether you're using a filter or not (to prevent light infiltration). I don't see how that could cause this particular effect, but I'm pretty new to this.

I've been unable to find any examples of this problem anywhere. We showed the transferred footage to a local lab and the tech was convinced it was a lens problem. We're going to go back and have them take a look at the original film on their viewer to see if the problem is on the film.

Meanwhile, I'm wondering if any of you have ideas on what this is. Sorry about the massive post--I wanted to provide as much detail as I could. Happy to provide more. Thanks for your help!

-Ward Crockett
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#2 Nathan Milford

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Posted 29 September 2006 - 08:23 PM

Your link sends you to a page that says:

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This Interactive Web Site Management System requires that you login to active the dymanic components of the site. An authentication window should have opened if you have popup windows enabled for this site. If not, you can Click Here to login.


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#3 Bernie O'Doherty

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Posted 29 September 2006 - 10:05 PM

This issue requires some introduction---
My producer and I recently bought a Bolex EBM (converted to S16) with a Vario-Switar 100 POE. We shot some scenes in a TV studio on black and white reversal. A few weeks later, we shot two reels of test footage on reversal--we processed one as reversal and cross-processed the other---we did this to see how cross-processed footage compares to straight reversal processing. These two test reels were recans.

We had all of the film mentioned above processed and transferred to DV in two separate labs. The footage we shot in the television studio came out fine. The test footage (both reels) came out with a strange ghosting effect (not sure if ghosting is the right term). You can see the images here: Bolex Test Images

The weird effect is on the right side of the man---his ear seems to pop out, the lettering on his shirt pops off, etc.

The ghosting isn't as pronounced in indoor shots, though it is present. Strangely, it seems to vary. In the last two images (two consecutive frames), the magnitude of the effect is different. Notice the effect on the right side of the man's thumb---it's worse in the first image.

The effect shows up at different frame rates, from 10 to 50. The effect did not change during frame rate changes (we switched from 24 to 50 while rolling).

Since we shot the test footage, I've looked thru the reflex viewfinder on an outdoor subject in comparable sunlight conditions and have not seen the ghosting. I've stopped it down to see if the effect appears at smaller apertures but have not seen the effect. Seems like I'd see this effect in the viewfinder if it were a lens problem, but from what I've heard, there are some lens problems that won't be noticeable in the viewfinder (true?).

Again, the other footage we processed and transferred at a different lab looks fine. We did shoot the footage a few weeks apart, so there's the possibility that the lens was damaged during that time---unlikely, though, since it was sitting in its cut-foam flight case all that time.

I do know that I didn't have the filter holder in place when I shot the test footage (don't remember if it was in place for the television studio footage). Bolex says you must have the filter holder in place whether you're using a filter or not (to prevent light infiltration). I don't see how that could cause this particular effect, but I'm pretty new to this.

I've been unable to find any examples of this problem anywhere. We showed the transferred footage to a local lab and the tech was convinced it was a lens problem. We're going to go back and have them take a look at the original film on their viewer to see if the problem is on the film.

Meanwhile, I'm wondering if any of you have ideas on what this is. Sorry about the massive post--I wanted to provide as much detail as I could. Happy to provide more. Thanks for your help!

-Ward Crockett

Hi Ward,
Couldn't see the film clip. Anyway, it seems the problem is either in the timing of the movement, or perhaps registration was partially lost. Doesn't seem like a lens problem to me. If one test or the other footage was fine, then the lens is good, and the registration was good in the studio. If the lens was off, all your footage would be bad.
Take the camera to a good tech for a check-out,

Cheers,

Bernie
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#4 Ward Crockett

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Posted 30 September 2006 - 12:03 AM

Hi Ward,
Couldn't see the film clip. Anyway, it seems the problem is either in the timing of the movement, or perhaps registration was partially lost. Doesn't seem like a lens problem to me. If one test or the other footage was fine, then the lens is good, and the registration was good in the studio. If the lens was off, all your footage would be bad.
Take the camera to a good tech for a check-out,

Cheers,

Bernie


Sorry about the link, everyone--I'll try to fix that up so you can check out the pics.

And thanks Bernie. Yeah, I'm leaning away from a lens problem as well. The other thought I had was the telecine or film chain transfer---I'll have to find out what kind of transfer the lab did. Can this kind of issue occur if some element of the transfer is misaligned? I don't know enough about video transfer to know if this could occur.

Thanks!
-Ward
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#5 Ward Crockett

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Posted 30 September 2006 - 12:15 AM

Attached is a still from the messed up footage. I'll try to get that web page working correctly.
-Ward

Attached Images

  • camera_test_3.jpg

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#6 Peter Tripodi

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Posted 30 September 2006 - 02:49 AM

Weird, the aberration is horizontal. Every registration problem I?ve had (in my limited experience) has been vertical.

Could the beam splitter be loose, perhaps the little door in front of the gate it sits in was not seated? Odd as they?re made to snap closed.

Weird.

Please let us Bolexers know if you find the source of the problem.

Good luck
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Opal

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CineTape

The Slider

Paralinx LLC

Gamma Ray Digital Inc

Metropolis Post

Wooden Camera

Rig Wheels Passport

Broadcast Solutions Inc

Technodolly