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Cutting glass filters


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#1 Dave Barak

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Posted 22 February 2014 - 01:01 PM

Hello everyone,

 

I'm new here, so please forgive me if I've posted this in the wrong forum. If so, let me know and I'll repost in a different one.

 

Anyway, has anyone here ever tried cutting glass filters down to a smaller size? I've got some 6x6 filters that are getting a bit ugly around the edges, and I'd like to cut them down to 4x4 if that's practical. Any thoughts?

 

Dave


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#2 Gregg MacPherson

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Posted 22 February 2014 - 03:51 PM

I've had that done.  I think they were Tiffen.  I got lucky and found a local glass cutter who had done it before,  but I got the feeling that any good glass cutter guy could do it.  Maybe give him a junk one to practice on. 

 

A description of what was done if that helps.  I prepared the filters by applying some sticky paper that was 1.5mm clear of the cut line.  Then if he placed a straight edge at the paper edge his cutter would scratch at a 1.5mm offset  (need to check the width of the cutter used).  He scratched both sides,  cracked the glass,  then bent it slightly so he could cut the filter film with a razor blade.  Then he square ground the cut edge just a little and beveled the edges and corners.  It took about 20 minutes for 5 or 6 filters.

 

The paper also protected the finished filter.  But a careful guy may not need that.  Filters that are easy to see through you could just draw the cut line on the glass. 

 

In case anyone in New Zealand wants to know.  The glass cutter was Neil at Sauvarins Kingsland branch here in Auckland.

 

Cheers,

Gregg


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#3 Dave Barak

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Posted 22 February 2014 - 05:07 PM

Hi Gregg,

 

Thanks for the great reply. It's good to know I'm not off my rocker.  ; ) I've got some glass shops in mind, so I'll see what they have to say.

 

Dave


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#4 John Salim

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Posted 23 February 2014 - 07:38 AM

One thing to mention is most glass filters are actually of a 'glass-filter-glass' sandwich construction, so a simple glass cutter wouldn't work without messing up one side ( or both ).

 

John S :mellow:


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#5 Gregg MacPherson

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Posted 23 February 2014 - 02:46 PM

The Tiffens I had cut were the normal sandwich construction as you describe,  with what looks like a plastic filter in the centre.  As I describe above (perhaps not well enough),  a simple cutter did work.  Both sides were scratched first, then,  doing my best to remember,  he stressed (cracked) first one side then the other.  I'm trying to remember how he stressed the glass.  Was it with the pliers,  or just by bending? 


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#6 Dave Barak

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Posted 23 February 2014 - 05:26 PM

I know what with some pro glass cutting, they use padded pliers (probably just guaze or something) to snap the glass apart.


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#7 Gregg MacPherson

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Posted 23 February 2014 - 06:55 PM

I had to cut some glass for the wooden house I built myself,  and I have a pair of pliers here on my desk still.  They differ from normal utility pliers in that they are shaped so that the tips of the pliers are what is contacting the 3 or 4mm thick glass.  So the loads are placed close to the scratch line.  No padding on those.

 

Though I had cut a little glass myself,  I suspected that cutting filters might require a depth of knowledge I did not have.  I was right about that (I think) and pleasantly surprised that the pro cutter guy charged only $20 cash for 5 or 6 filters.  He had cut some before though.  And most glass cutters will have a wet disk so they can dress the edges the way you want.

 

Maybe I was just jucky to find a guy who had done it before.  No padding on his pliers also.  They gripped just on the outside of the line,  not on the finished filter.

 

 


Edited by Gregg MacPherson, 23 February 2014 - 06:58 PM.

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#8 Dave Barak

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Posted 23 February 2014 - 07:27 PM

Well that's some good news, the price and ability to dress the edges. I'm feeling a bit more confident now about having this done. I'll make a few calls and see what can be done. Thanks everyone!


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#9 Gregg MacPherson

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Posted 23 February 2014 - 07:46 PM

I would try and find someone who has done it before, even if you have to do it in LA.  Good luck.

 

Maybe sometime later the stress from the cutting process will cause some delamination....Who knows.


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#10 Tom Turley

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Posted 07 September 2014 - 02:35 PM

Does anyone know who in London would be best to ask about getting a 6x6" cut down to 4x4"?


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#11 David E Elkins

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Posted 17 February 2015 - 07:37 PM

Check The Filter Gallery in NY.  They specialize in cutting down filters.

 

http://www.filtergallery.com/


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#12 Dennis Couzin

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Posted 18 February 2015 - 02:01 AM

One thing to mention is most glass filters are actually of a 'glass-filter-glass' sandwich construction, ..

 

I don't know of any current manufacturer of filters except for Tiffen using that construction. 

It makes sense when a spectral curve is achievable with dyes in gelatin (or plastic or whatever Tiffen packs in there), but not achievable with in colored glass.  Which filters are those?  On the other hand some spectral curves are only achievable in glass.  Which filters are those?

 

Solid glass filters are far superior optically.  For one thing, Tiffen filters lack anti-reflection coating.  Tiffen offers this gibberish justification:

 

Q: Do multi-coated filters offer a benefit over Tiffen non-coated filters? A: Only to the extent that they emit about 1/10th of an f:stop more light, which is almost immeasurable. Coated filters do cut down lens flare. This can also be done just by using a lens shade. Furthermore, many multi-coated filters on the market are not coated 8-12 times as found in lenses, but usually about two times, and sometimes not even on both sides of the filter! Properly coated lenses minimize or eliminate lens flare with or without coated filters.

 

They concede that coated filters can cut down lens flare but reply that the lens shade can also do it.  This misses the point that coated filter + lens shade assures lower flare than uncoated filter + lens shade.  Their final sentence commits the same fallacy. Work it out. The uncoated Tiffen filters have about 4.2% reflectance on both sides.  These two reflectors can exceed the total of all the reflective surfaces within a complex lens.  Lens flare and glosts is caused by one surface somewhere in the lens reflecting the light back toward the scene and then another surface forward of that surface sending it back toward the film.  The Tiffen front surface can play the second part, and the Tiffen rear surface can play either the first or second part in a flare contributing scenario.  With a high quality lens having 10 air-to-glass surfaces, all multicoated to have 0.4% reflectance, adding the Tiffen filter will multiply the lens flare 8×.  With a cheapo lens having 6 air-to-glass surfaces, all MgF2 coated to have 2% reflectance, adding the Tiffen filter will multiply the lens flare 3×.  This quick analysis has ignored diffuse reflections within the lens assembly. 

 

Here is one independent tester who, whether they realized it or not, failed the Tiffen filter on account of its being uncoated: http://www.lenstip.c...en_72mm_UV.html

 

Uncoated filters suit macho film crews who can wipe 'em on their sleeves.

 

In general, thicker optical glass can be ground and polished flatter than thinner optical glass.  So unless the Tiffen filters are twice as thick (and heavy) as competitor's filters, or ground and polished with special effort, they are of inferior optical surface quality to the competitors.  This can be measured with an interferometer. Someone should.

 

Tiffen's uncoated, sandwich type filters have a cult following, especially by US cinematographers.  Why?


Edited by Dennis Couzin, 18 February 2015 - 02:03 AM.

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#13 Gregg MacPherson

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Posted 18 February 2015 - 02:47 AM

 

I don't know of any current manufacturer of filters except for Tiffen using that construction. 

 

I have some Schneider NDs that look laminated.  It is a little hard to be certain as they have a a layer of sealant on the edge.  I don'y know when they were manufactured.  Perhaps Schneider make them differently now.


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#14 Dennis Couzin

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Posted 18 February 2015 - 08:21 AM

Gregg, today Schneider sells the B+W line of solid glass filters.  I don't know if they bought B+W or just partner with them.

 

Your mention of sealant around the edge could be relevant to the discussion.  If a laminated filter has edge-seal, then there had better be sealant reapplied after cutting the filter down.


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#15 Gregg MacPherson

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Posted 18 February 2015 - 03:06 PM

If anyone knows what the edge sealant is could they please tell us.  It looks like epoxy but it may be specialized.  My guess was that as a sealant it was to reduce delamination.  But I think it is pigmented black (hard to tell for sure),  one assumes to stop some stray light.  The sealant may also be there to hide imperfect edge grinding.  The areas on the edge that are ground vs unground will treat the stray light differently and the black sealant may help fix that.


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#16 Dennis Couzin

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Posted 18 February 2015 - 05:56 PM

I just now removed a Tiffen 812 filter from its housing.  No edge seal on the sandwich.  Not even black paint (but it's a flare bomb anyhow). 

Lack of seal indicates that the Tiffen colorant, whatever it is, is non-hygroscopic.  It could itself be an optical epoxy that has been dyed (but with that construction color uniformity would be hard to conrol).

 

Kodak used to sandwich some of their gelatin filters between glasses.  Gelatin is extremely hygroscopic.  As I recall, Kodak made the glasses a bit larger than the gelatin in order to have a margin with the (non-hygroscopic) cement.  One wouldn't dare to cut those filters.


Edited by Dennis Couzin, 18 February 2015 - 05:58 PM.

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