[rollei_list] Re: Rollei B&W filters blog
- From: CarlosMFreaza <cmfreaza@xxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Fri, 29 Jul 2011 15:18:02 -0300
Most regular good lenses are color corrected to bring some main light
wavelengths -two or three- to a common focus, the wavelengths out of
this correction don't coincide, they are the secondary spectra that
causes minor color faults which are negligible in normal photography
(color or B&W). Infra-red and UV rays are well beyond the regular lens
color correction and then it's necessary to bring the IR rays to focus
with this lenses for dedicated IR photography, it's the reason for the
special mark in the lens barrel focusing ring for IR photography.
Rollei TLR cameras infra-red filters made from 1951 have a special
treatment including a dedicated filter glass polishing that bring IR
rays to focus and then you can focus with the viewfinder as always.
There are some very expensive lenses with color correction even for IR
and UV rays, they needn't focus compensation for IR photography, a
sample is the CZ Sonnar Superachromat 250mm/f5.6 for the Rolleiflex
SL66, it is used for scientific work mainly.-
Carlos
2011/7/29 hari ho <hariho@xxxxxxxxxxxxxxx>:
> Just so I understand it better, how does the Rollei TLR infra-red filter
> compensate for the IR focus shift?
>
>
>
>
> On 29/07/2011, at 9:07 PM, CarlosMFreaza wrote:
>
>> Taking as reference the opaque Hoya R72 IR filter that allows to pass
>> dark red and infrared above 720nm, the Rollei Infra-red filter allows
>> to pass dark red and infrared rays above 700nm, it would be a R70
>> filter, close to the Hoya and then you can take your films exposures
>> with this Hoya R72 as basis, f.e.Aura rate at 1/1.5 ISO, Aperture
>> f/16, 1 - 8 seconds exposure (suggested in the Freestyle website).
>> Rollei TLR infra-red filters have the advantage they already are
>> compensated for the focus shift in IR photography, I forgot to mention
>> it in my blog.-
>>
>> Carlos
>>
>> 2011/7/29 hari ho <hariho@xxxxxxxxxxxxxxx>:
>>>
>>> Thank you for the information Carlos. I have a Rollei RIII Infrarot
>>> filter
>>> (extremely dark red, much darker than R25) that I'll be using with Efke
>>> IR820 and Efke IR820 Aura film. I do know that exposure and filter
>>> compensation for this is very much trial and error. However, does anyone
>>> have data or experience as to where I should begin in terms of bracketing
>>> my
>>> exposures? Thanks.
>>>
>>> Hari
>>>
>>>
>>> On 29/07/2011, at 1:28 PM, CarlosMFreaza wrote:
>>>
>>>> I have uploaded to one of my blogs some Rollei B&W filters tables,
>>>> Rollei Red and Orange filters instructions in several languages, a
>>>> photograph with filters samples and some comments, the images are
>>>> thumbnails and it's necessary to click on them:
>>>>
>>>> http://dobleobjetivo.blogspot.com/2011/07/rollei-b-filters.html
>>>>
>>>> Carlos
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