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Filtration with a wide-angle lens

filter matte box 9mm field of view wide angle lens arriflex

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#1 Bill DiPietra

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Posted 29 December 2014 - 05:29 PM

Hi everyone.  I'm trying to get some shots with a 9mm Cooke lens I have for my Arri S/B, I'd like to put some filtration in front of it.  The problem is that, due to the wide field of view, I'm still getting the interior of the matte box on the edges of the picture frame.

 

I'm trying to figure out how to rig something but I thought I'd put my query up here since I know others have run into and dealt with this before.

 

Thanks in advance for any help.


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#2 Gregg MacPherson

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Posted 29 December 2014 - 08:01 PM

Hey Bill,
Putting it in terms of what is inadverdently "matting" the image, (the inside edge of the box or the filter frame). You need to get closer to that, or make it bigger, or wider if it's a square box and you are seeing the sides.

If you have a base you can put some light weight rods on then you can find a matte box that will clear that lens. I have a cheap Proaim MB-900 (an Arri/Chrosziel clone) which takes two 4x4/4x5.65, one 4x4 and a 138mm round in the rubber bellows at the rear. Quite a stack, but if I put a Zeiss 8mm just behind the 4x4 it just clears the sides.

You may end up with a diferent MB for hand held if you're trying to keep the weight down, and just accept less options for that.

Common sense I know. You may get some ideas on solutions particular to that camera, which would be really usefull.

EDIT: Some MB are designed to enable wider lenses.

Edited by Gregg MacPherson, 29 December 2014 - 08:04 PM.

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#3 Miguel Angel

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Posted 29 December 2014 - 09:29 PM

These kind of things (attaching filters in front of the lenses) are very common in a shooting environment and the best approach is usually the simplest one. 

 

If your lens can be covered completely by a 4.5 x 6 or a 4 x4 filter, take the mattebox off and stick the filter to the front of the lens by using gaffer tape. 

 

1) Cut a long piece of gaffer tape.

2) Roll it in the long way so you end up with the gaffer tape being sticky on both sides.

3) Carefully place the gaffer tape around the front part of your lens (not inside the lens but around)

4) Put the filter on the lens and make sure that it sticks to the gaffer tape tightly. 

5) Surround the filter with gaffer tape by attaching gaffer tape to the lens so the gaffer tape holds the filter in a more secure way. 

 

Check it and shoot! 

 

I will post some photos tomorrow as I don't have gaffer tape with me right now. 

Sadly I am not able to find a picture of what I am talking about on the Internet but I hope you see the process! :)

 

It can be done with a 6x6 filter but you need to be more careful when operating. 

 

Have a good day. 

 

:)


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#4 Bill DiPietra

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Posted 29 December 2014 - 09:41 PM

These kind of things (attaching filters in front of the lenses) are very common in a shooting environment and the best approach is usually the simplest one. 

 

If your lens can be covered completely by a 4.5 x 6 or a 4 x4 filter, take the mattebox off and stick the filter to the front of the lens by using gaffer tape.

 

Thanks but I had that thought and tried it earlier today.  Seemed good in theory, but in practice not so much.  I plan to give it another try since I was rushing, today.

 

Gregg, my filters are 2x2 so I will see what I can rig. 

 

Thanks for the suggestions, guys.


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#5 Dennis Couzin

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Posted 30 December 2014 - 08:59 AM

There is an optical reason not to use filters in front of wide angle lenses.  The light from the wide parts of the scene traverse the filter at an angle, changing its color.  (For a filter behind the wide angle lens, the light leaving the lens toward the frame corner generally makes a much smaller angle.)

 

A 9 mm lens on the 16 mm format isn't very wide, so you can probably get away with it.  Here's what happens. The light rays from the corners of the scene reach the filter at 35°, measured from the normal.  They bend at the glass and then pass through the filter at a 22° angle.  This means the density of the filter is increased by 8% (for those rays from the corner of the scene).  If it's an ND 1.0 filter, it becomes an ND 1.08 filter for the corners.  Moreover, the effect is wavelength-by-wavelength, so if it's a #85 filter, it is about a third of the way from #85 to #85B (plus a tad of ND) for the corners.

 

The front filter effect becomes more serious with "really wide-angle" lenses like the Angenieux 5.9 mm, causing density to increase by 14% for the corner, or the Century 3.5 mm, causing density to increase by 22% for the corner.  Then the reflections at the filter must also be considered.


Edited by Dennis Couzin, 30 December 2014 - 09:04 AM.

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#6 Bill DiPietra

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Posted 30 December 2014 - 07:10 PM

There is an optical reason not to use filters in front of wide angle lenses.  The light from the wide parts of the scene traverse the filter at an angle, changing its color.  (For a filter behind the wide angle lens, the light leaving the lens toward the frame corner generally makes a much smaller angle.)

 

A 9 mm lens on the 16 mm format isn't very wide, so you can probably get away with it.  Here's what happens. The light rays from the corners of the scene reach the filter at 35°, measured from the normal.  They bend at the glass and then pass through the filter at a 22° angle.  This means the density of the filter is increased by 8% (for those rays from the corner of the scene).  If it's an ND 1.0 filter, it becomes an ND 1.08 filter for the corners.  Moreover, the effect is wavelength-by-wavelength, so if it's a #85 filter, it is about a third of the way from #85 to #85B (plus a tad of ND) for the corners.

 

The front filter effect becomes more serious with "really wide-angle" lenses like the Angenieux 5.9 mm, causing density to increase by 14% for the corner, or the Century 3.5 mm, causing density to increase by 22% for the corner.  Then the reflections at the filter must also be considered.

 

Wow, I didn't know anything about this,  Thanks for all that info, Dennis! 


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#7 Gregg MacPherson

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Posted 31 December 2014 - 07:24 PM

 

Hi everyone.  I'm trying to get some shots with a 9mm Cooke lens I have for my Arri S/B, I'd like to put some filtration in front of it.  The problem is that, due to the wide field of view, I'm still getting the interior of the matte box on the edges of the picture frame.


Sticking a filter with tape onto the front of a lens is an ok solution (Miguel) if you are caught out, unprepared, but if you own the lens, camera, MB, maybe a more general solution is useful.

The notes from Dennis are very interesting to us both, but for the 9mm, they are probably not that relevent.

It is a problem that the 2x2 is quite small when you come to adapt to lenses that commonly take a 4x4 or 4x5.65. Who knows what you will need. Maybe 4x4 would be a better size to own (cost vs usefulness). The only problem I see is that your Arri is a completely front heavy unit, so adding crap to the front of that will be no fun when you hand holding.

I'll try again asking about your new project. When one leaves the cinema, what will one feel or think about (what would you wish us to feel, or think)
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#8 Bill DiPietra

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Posted 31 December 2014 - 07:50 PM

 It is a problem that the 2x2 is quite small when you come to adapt to lenses that commonly take a 4x4 or 4x5.65. Who knows what you will need.

 

Hey Gregg!  Take a look at the tutorial I posted on the solution I found to this issue (http://www.cinematog...topic=65955&hl=).

 

Happy New Year!


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