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Re: [OM] IMG: My Ross Lens Project

Subject: Re: [OM] IMG: My Ross Lens Project
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Tue, 04 Jan 2011 08:33:04 -0500
Thanks.  I got the focal length correct at 200mm but must have mentally 
substituted 8" for the aperture.  f/16 as max aperture makes it even 
clearer why it performs well as regards common optical abberations. 
Even at wide open it's also well into diffraction territory for a 35mm 
size image.

Chuck Norcutt

On 1/3/2011 9:37 PM, Jim Nichols wrote:
> Hi Chuck,
>
> I should like to correct your statement about my Ross lens, though your
> approach would appear to be correct.  My lens has a maximum apperture of
> f/16, 1/2-inch dia for an 8-in FL.  This permits the use of the wheel-type
> Waterhouse stop mechanism, with openings corresponding to f/16 through f/64.
> It seems there was some sort of aperture-mechanism patent at that time that
> led to the continuation of the Waterhouse stop approach.
>
> The next generation of lens was probably classed as the "rapid rectilinear",
> and, with apertures up to f/6.8, the openings were too large to be used with
> a wheel.  Somehow the patent squabble was overcome, and the modern internal
> iris mechanism was used.
>
> Jim Nichols
> Tullahoma, TN USA
> ----- Original Message -----
> From: "Chuck Norcutt"<chucknorcutt@xxxxxxxxxxxxxxxx>
> To: "Olympus Camera Discussion"<olympus@xxxxxxxxxxxxxxxxx>
> Sent: Monday, January 03, 2011 6:42 PM
> Subject: Re: [OM] IMG: My Ross Lens Project
>
>
>>  From this<http://en.wikipedia.org/wiki/Ross_%28optics%29>  it appears
>> that Ross was fairly well along in lens design for the time.  I suspect
>> that the good performance shown by Jim's lens is due to long focal
>> length (200mm), moderate max aperture (f/8) and especially much smaller
>> image format than the lens was designed for.  I tried looking up the
>> history of apochromats but couldn't find when the first was designed.
>> Actually, the trick was not the design effort but having glass of
>> suitable index of refraction.
>>
>> Chuck Norcutt
>>
>>
>> On 1/3/2011 2:48 PM, Jim Nichols wrote:
>>> Jan,
>>>
>>> In reviewing all of the images, I found one that I liked in color.  It is
>>> linked below:
>>> http://gallery.leica-users.org/v/OldNick/Mocking+Bird.jpg.html
>>>
>>> I have not searched it critically, but the colors and bokeh look pretty
>>> good
>>> for a 19th Century design.
>>>
>>> Jim Nichols
>>> Tullahoma, TN USA
>>> ----- Original Message -----
>>> From: "Jan Steinman"<Jan@xxxxxxxxxxxxxx>
>>> To:<olympus@xxxxxxxxxxxxxxxxx>
>>> Sent: Monday, January 03, 2011 12:44 PM
>>> Subject: Re: [OM] IMG: My Ross Lens Project
>>>
>>>
>>>>> From: "Jim Nichols"<jhnichols@xxxxxxxxxxxxx>
>>>>>
>>>>> The best example is shown below, showing battle flags at a local
>>>>> Confederate Cemetery.  This was made at ISO 200, 1/400 at f/16, RAW,
>>>>> converted to B&W using a PhotoPlugins converter.
>>>>> http://gallery.leica-users.org/v/OldNick/Flags+BW.jpg.html
>>>>
>>>> That looks promising, but I'm wondering about colour, and why you chose
>>>> to
>>>> convert to B&W.
>>>>
>>>> Old lenses that predate colour film (certainly 1890) are generally not
>>>> corrected for colour.
>>>>
>>>> On the colour images, do you see any evidence of fringing or CA? It
>>>> would
>>>> probably be most prevalent in the corners, where spectral dispersion
>>>> would
>>>> be expected to be greatest.
>>>>
>>>> ----------------
>>>> Every now and then go away, have a little relaxation, for when you come
>>>> back to your work your judgment will be surer. Go some distance away
>>>> because then the work appears smaller and more of it can be taken in at
>>>> a
>>>> glance and a lack of harmony and proportion is more readily seen. --
>>>> Leonardo da Vinci
>>>> :::: Jan Steinman, EcoReality Co-op ::::
>>>>
>>>> --
>>>> _________________________________________________________________
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>>>> Archives: http://lists.thomasclausen.net/mailman/private/olympus/
>>>> Themed Olympus Photo Exhibition: http://www.tope.nl/
>>>>
>>>>
>>>
>>>
>> --
>> _________________________________________________________________
>> Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
>> Archives: http://lists.thomasclausen.net/mailman/private/olympus/
>> Themed Olympus Photo Exhibition: http://www.tope.nl/
>>
>>
>
>
-- 
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