[rollei_list] Re: Rolleiflex F ground glass

  • From: CarlosMFreaza <cmfreaza@xxxxxxxxx>
  • To: rollei_list@xxxxxxxxxxxxx
  • Date: Thu, 1 Apr 2010 12:50:35 -0300

OK Elias, according I understood the process and I'm not sure my
interpretation is 100% correct, the copper "Master" plate surface was
prepared with millions of  microelements -microlenses ?- to break or
to split the light, these microelements  were caused by impacting  a
needle or needles on the surface, the needle changed the impact
angles, this way the surface was flat at the centre becoming steeper
to the edges, it's the cause for the apparent "warped" middle you
noticed in the screen. At this point the explanation says that the
changes of angle for the needle impact were made by "traditional" or
"conventional" means, because there were no computers at the time,  I
don't know about those conventional means, but it's clear that
computers are used in the process today. This "Master" copper plate
structure was finished making impressions by a heat process and
afterward using an injection machine to spatter granule.
One of the advantages regarding a "pure" Fresnel lens is to judge
sharpness with a magnifying glass without the disturbing Fresnel lens
grooves.

Carlos


2010/4/1 Elias_Roustom <elroustom@xxxxxxxxx>:
> What a handy reference you have there Carlso, and thank you for the effort
> you put into sharing it.
>
> I've noticed on the plain grid screen that the middle is a bit warped  - and
> aides in focusing sometimes.
> It makes me wonder if the liquid plastic was pumped into the mold from the
> center.
>
> I also wonder if the new screens we're able to buy today from third party
> manufacturers are made the same way.
>
>
> On Apr 1, 2010, at 5:22 AM, CarlosMFreaza wrote:
>
>> Yes John, he explains that in order to be able to manufacture the
>> plastic focusing screen, it was necessary a copper "Master" like for
>> vinyl records, this is the example used in the book.
>>
>> Carlos
>>
>>
>>
>> 2010/4/1 John Wild <jwild@xxxxxxxxxxxxxxxxxxxxxx>:
>>>
>>> Is the same basic principle as the production of vinyl records - using a
>>> copper plate master?
>>>
>>> John
>>>
>>>
>>> On 01/04/2010 04:00, "CarlosMFreaza" <cmfreaza@xxxxxxxxx> wrote:
>>>
>>> ....... there is a detailed explanation about the process to manufacture
>>>>
>>>> the screens, but German technical terminology is not clear to me,
>>>> anyway I understood they worked on a copper plate taken as "Master".
>>>> These screens were standard for Rollei TLR cameras with
>>>> interchangeable focusing screen from 1958 and it's interesting to note
>>>> that the factory had special kits to replace the older models ground
>>>> glass with the new screens.
>>>>
>>>
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