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Old March 8th, 2009, 06:52 PM   #1
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Is there an increase in latitude when using a DoF adapter?

Someone told me there's an increase in latitude when using a DoF adapter.

Is that true?
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Old March 8th, 2009, 07:05 PM   #2
 
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no
no
and no
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Old March 8th, 2009, 11:47 PM   #3
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There is an "apparent" beneficial effect in the reduction of classic video harshness but in realworld terms the answer has to be no. I imagine a polariser and good UV filter might be a good thing to have where you are if you intend to use a DOF adaptor. Groundglass flare across relatively dark objects which would appear normal in less extreme lighting conditions might be reduced with these filters.
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Old March 9th, 2009, 06:44 AM   #4
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I thought there might be some internal reflections/diffraction that could have added a low level of fog. Not enough to be seen, but sufficient to raise the toe of the overall sensitometry curve. A bit like flashing the neg in film-land - you can't see the flash, but it brings out a little shadow detail. Useful where you can't put light in shadows, or to get a particular 'look'. Sadly all that's history now it's gone DI. But no-one's noticed anything? Oh well. Always worth asking.

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Old March 9th, 2009, 08:41 AM   #5
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I think because of the inherent light loss that comes with using an adaptor. This means you'll have to operate your camera at a wider aperture, thus giving you the look of more latitude.

If the look of a wide latitude is what your after, wider aperture = the look of more latitude. (but you probably already knew that) :)
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Old March 9th, 2009, 08:49 AM   #6
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It's not an issue. I just remember reading it somewhere and always meant to ask.
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Old March 9th, 2009, 10:44 AM   #7
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Don't give up too soon.

That is more or less the "apparent" effect I mentioned. It seems similar to the effect of pre-fogging film or filming a subject in low light through passing smoke. To be truthful, I have never attempted to provoke, examine or measure it.

I was prompted to this observation by the effect of a light leak onto the groundglass of a home-made AGUS35 and even suggested on this forum, the application of a low level of broad light across the groundglass but I did not pursue this any furthur beyond shining a little LED onto the disk which was too localised in its effect.

My imagining also leaned in the direction of using coloured filters as a additive form of colour adjustment as an effect.

I have heard that ARRI developed an optical filter to reproduce the prefogging effect.
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Old March 9th, 2009, 01:06 PM   #8
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It was called the Varicon and was invented by Freddie Francis as a development from his lightflex which he'd used extensively and to great effect on Dune, and Glory. I've used it myself (I borrowed his) and it's a great tool for lifting the shadows a tad, and coloring them slightly. Something you couldn't do in film post until recently. Your idea is exactly like one that crossed my mind - snap! You need the LED on a calibrated potentiometer, and with a filter slot.

The varicon fitted into the camera's mattbox filter slots - the pic below shows it upside down! There was a slot below the strip light that accepted a gel holder. It used to get hot, and it was difficult to maintain the effect's continuity between shots - I learned to keep plenty of notes and to rigorously stick to the same stop during a scene. Some very very nice stuff though - adding a hint of green to shadows (though the blacks would stay black) or lifting a dark corner. But of course you can do most of this now in post...

It's why, when I read about it, I wasn't surprised to hear how a dof adapter might increase latitude. I'm surprised it doesn't. :-)

http://www.movie-college.de/filmschu.../Varicon2b.jpg

The Arri Varicon & Panavision?s PanaFlasher
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Old March 9th, 2009, 02:07 PM   #9
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I am a bit vague and uneducated on this but I think you will find that whilst there is this "apparent" effect, because the groundglass adaptors generally hit a wall at f5.6 before they introduce artifacts, that the effective dynamic range may become less.

P+S Technik may deal with the theory in their internal resource library.
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Old March 9th, 2009, 06:00 PM   #10
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"groundglass adaptors generally hit a wall at f5.6"

Never used one. What do you mean?
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Old March 9th, 2009, 06:36 PM   #11
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1. The dynamic range of the camera is not affected, obviously.

2. Without any empirical evidence, but based on my experience with shooting a bit of adapter footage, I always had the feeling that the way the image is projected on to the ground glass there an image created that is easier to capture both the highlights and shadow detail..
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Old March 9th, 2009, 06:37 PM   #12
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That's true with vibrating ground glass 35mm adaptors (Letus Extreme, Red Rock M1, etc...)
But with the spinning ground glass adaptors you're not subject to those limitations. You can set the f-stop to what ever you want and the shutter speed to what ever you want, without fear of negative effects.

Examples of spinning ground glass 35mm adaptors are:
Letus Ultimate (what I have)
P+S Techinque (I think that's what they use...I don't have any experience with them)
Red Rock M2 (new model)
SGBlade (I think that's what it's called)
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Old March 9th, 2009, 07:39 PM   #13
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maybe this is the only way to get more latitude?

contrast filters

specially the "ultra contrast filter" that doesn't add glow on the highlights it "uses ambient light to add brightness at the shadows" i guess kinda like exposing a little light to the groundglass

but if it depends on ambient light if that ambient changes (lets say you move the camera to a darker area, or change the shot to a darker area, or a cloud happen to darken your area) the shadows may change?
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Old March 9th, 2009, 09:57 PM   #14
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The f5.6 aperture setting is more or less an accepted limit that P+S Technik established with the Mini35-300 which has a spinning groundglass.


It is a sensible boundary which is perhaps a little conservative but assures consistent results with most lenses.

Some lenses, usually the longer ones will perform to a groundglass at higher apertures. Some ultra-wides like the Peleng 8mm and Nikon 14mm f2.8 fcome down to about f3.5. for consistent results.

I have used high apertures and hight shutter speeds with gain up just to see what happens with a CD-R sized groundglass disk. My recall is 1/2500th sec or thereabouts. You can get an image, an acceptable image.

There are artifacts, more subtle than with short throw groundglass movements but they are there. Whilst you don't necessarily get flicker or a vortex with a good groundglass finish the colour and tone rendition seems to be slightly muddy by comparison.

This link is to a test with 1/2500th sec shutter with no added gain. You will observe the colour rendering leaves some to be desired.

http://exposureroom.com/members/DARA...1c77b9aef5ee4/

On subject of "prefogging", my recall of how I lit the groundglass screen is a bit defective. I remember the little glass round thing and a wire, but forgot it was not a LED but a Toslink cable which I lit at the other end and shoved in through a drilled hole in the adaptor casing and moved about.

You can shove bits of coloured lighting gel in between your light source and the "eye" of the Toslink cable.

The visual effect in deep shade, brought up texture in the bark of a tree trunk out of an overall brown-grey.

Basic laziness prevailed and I did not pursue it furthur. However a fourth new drillhole in an already modded Letus Extreme can't hurt, especially with a SI2K attached. I imagine a piece of diffuser material to spread the pinpoint of light from the outputting cable eye might do the trick.

Lighting the spinning groundglass through the edge doesn't work at home-build quality levels as the flicker is too bad. Lighting from the back seemed to be best. My test was far from precise, moving the cable around from outside through the small hole.

Last edited by Bob Hart; March 9th, 2009 at 11:37 PM. Reason: added URL
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Old March 10th, 2009, 06:16 AM   #15
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I still think your idea will work though Bob. And possibly very well, such as at night. But you may have a big problem with avoiding a hot spot. Not sure a bit of diffusion will be enough.

I did some tests a few years back with stills using a gray scale to try to calibrate the effect of flashing on film and, if I get the time, I'll scan and post them up. Check out Dune. Interesting film.

Also (and you probably already know) you should choose your LED carefully. The common ones have terrible spectral distribution with spikes and such like. They also change color as they warm up and as they age. But there are a few, notably those developed for cinematography softlights, that deliver. If you visit the 'candlepower' forum you'll find a whole bunch of guys who know more about LEDs than can be considered really healthy (and while you're there you can vote for your favorite flashlight!). You will not believe how many subscribers that forum has!


Biel, I think the problem with a low contrast filter is really the lack of any control. It is set at what it is, and as you say trying to arrange the correct amount of ambient light is not ideal. I think there's also a risk of losing your blacks.

Last edited by Karel Bata; March 11th, 2009 at 06:06 AM.
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