From: Bill Collins (photo@intrex.net)
Date: 08/23/02-06:23:31 AM Z
I bought a 4x5 field camera that had a plastic "ground glass". It turned out to be a fresnel (without any ground glass), so I replaced it with real ground glass, but I did notice that it had numerous scratches from the previous owner. I suppose you could have plastic treated with an anti-scratch coating (like is used on eyeglasses), but that sounds expensive.
Bill
---------- Original Message ----------------------------------
From: Clay Harmon <wcharmon@wt.net>
Reply-to: alt-photo-process-l@sask.usask.ca
Date: Fri, 23 Aug 2002 06:38:14 -0500
>John:
>
>Uh, I can actually speak from experience here, instead of theorizing: I own
>a 14x17 camera with a p-95 plexi ground 'glass'. I was convinced by the
>maker that it was a lighter, safer and more robust alternative. I believe
>all that to be true. What is not discussed is that as a focusing screen, it
>bites.
>
>The plastic has such a fine etched surface that it creates the mother of all
>hot spots. Image composition is excruciatingly difficult, as it is
>impossible to see the whole image from a single point of view. With my
>glasses on the end of my nose, I can look at any given 3" circle on the
>focusing screen with my nose pressed against it. I have come to the
>conclusion that the only solution is to either purchase an enormous fresnel
>to slap on the thing, or change it out for a traditional ground glass.
>
>Another subsidiary defect is that it will flex under the pressure of a loupe
>- which could potentially cause focusing errors. This is avoidable, but a
>defect nonetheless in my mind.
>
>Of course, you can't put your knee through it, no matter how much you'd like
>to do so after wrestling with the damn thing.
>
>Clay
>
>
>
>on 8/23/02 3:12 AM, John Cremati at johnjohnc@core.com wrote:
>
>>>
>>>> N1861@aol.com <N1861@aol.com> wrote:
>>>>
>>>> Has anyone made a ground glass from acrylic or polycarbonate sheet,
>>>> as a
>>>> lighter weight alternative to glass?
>>>>
>> John Cremati wrote:
>>
>> My concern would be the warpage of the polycarbonate sheet on a larger view
>> camera as well as cleaning.....I have etched decorative designs into
>> Plexiglas on many occasions as commercial artwork.. I have noticed several
>> things about it.. I would think the huge advantage is that is very light
>> weight , resists breakage, and my guess would be that once etched it
>> should produce a great image as the etching seems to be extremely fine
>> grained ...
>> 1) After removing the protective cover wrapping the plastic seems to have
>> a static electrical charge that attracts dust. This is very obvious after
>> sandblasting, during which electrical fields may even become visible on the
>> Plexiglas.. I usually have to flood wash the plastic when thru etching and
>> this seems to neutralize the static electricity...
>> 2) the plastic will warp or expand dramatically with temperature
>> change..It may be wise to mount in a floating frame...
>> 3) Plexiglas may become yellow with age.. a better grade of polycarbonate
>> may be in order and should be researched..
>> 4) The Plastic scratches very easily ...Special cleaners are used to
>> minimize this as well a keep the plastic from yellowing.. These cleaners may
>> get into the pores of the etched surface and may cause streaking, staining
>> or a blotting appearance...This happens so much that on my decorative work
>> I always use a separate plastic cover plate over the etched surface to
>> protect it sandwiching the engraving......
>> 5)During the sandblast process the plastic requires several passes as it
>> does not sandblast easily .. This may be the reason for such a fine grained
>> appearance when finished..The plastic probably resists the sand blast action
>> and only allows for minimal penetration into the plastic surface.......
>> Happy Trails,
>> John Cremati
>>
>>
>>
>>>
>>> No, but I don't see any reason why not. Most interchangeable focusing
>> screens
>>> for 35mm & MF SLRs are made of some sort of plastic.
>>>
>>> Wayne Harridge
>>
>>>
>>
>>
>
>
This archive was generated by hypermail 2.1.5 : 09/19/02-11:02:50 AM Z CST