[Leica] IMGs: Finding the "right lens/film/sensor/camera" combination:

[Dante Stella]

For infrared, most lenses should respond to close focusing the lens such that the barrel is extended 1/200 of the focal length.

Put the lens at infinity. Measure the whole length with a caliper. Focus closer to extend the lens (so 1/4mm for a 50mm lens). You can place your IR mark where infinity is.

This will not work with IF lenses.

Dante

> On Sep 10, 2015, at 6:56 PM, Jim Nichols <jhnichols at lighttube.net> wrote:
> 
> Ken,
> Thanks.  I reviewed the list.
> 
> Jim Nichols
> Tullahoma, TN USA
> 
>> On 9/10/2015 5:47 PM, Ken Carney wrote:
>> Jim,
>> 
>> If a lens is vulnerable to a hot spot, it gets worse as the lens is stopped down.  Kolari (http://kolarivision.com/articles/lens-hotspot-list/) says that your Fuji 27mm is only useable at 2.8, which is probably OK anyway since you'll need all the light you can get.  Based on my experience with other Fuji lenses, I'm confident that auto focus will be fine.  With your Leica lens, you can just magnify and focus through the EVF.
>> 
>> Ken
>> 
>>> On 9/10/2015 4:20 PM, Jim Nichols wrote:
>>> In my mind, the "hot spots" have no direct connection to focusing, unless, in their effort to get the total image focused in one plane, they have created the hot spot much as one does with a simple magnifying glass.  It could be an unexpected result of their pursuit of perfection.  But, I could be totally off-base here.
>>> 
>>> Jim Nichols
>>> Tullahoma, TN USA
>>> 
>>>> On 9/10/2015 4:04 PM, George Lottermoser wrote:
>>>>> On Sep 10, 2015, at 3:53 PM, Jim Nichols wrote:
>>>>> 
>>>>> What I have read this afternoon indicates that the latest Leica lenses are focus-corrected to such high wavelengths that, for all intents and purposes, no further correction is required.  Having no intention of making such an investment any time soon, I did not spend a lot of time following this back to its source.
>>>>> 
>>>>> Another slant on this was that Leica removed the IR index because it confused their customers, and that it is really only valid at infinity, anyway.  And, with zoom lenses, there are multiple correction settings depending on where the lens is in the zoom range.
>>>>> 
>>>>> Most folks seem to feel that some experimenting is necessary to find the most useful setting for the type of photography intended to be carried out.
>>>> Interesting.
>>>> 
>>>> Though my experience with the 093 IR filter from B+W
>>>> contradicts the claim;
>>>> at least for the 28 Summicron, 50 Summilux Asp, and 35 Summilux Asph.
>>>> Perhaps these are no longer considered the "latest Leica lenses."
>>>> Even if they did focus correctly;
>>>> they still all produce the significant hot spots;
>>>> and ever more prominently as you stop down.
>>>> 
>>>> And yes the proof is, as always, in the YMMV pudding.
>>>> 
>>>> Regards,
>>>> George Lottermoser
>>>> 
>>>> http://www.imagist.com
>>>> http://www.imagist.com/blog
>>>> http://www.linkedin.com/in/imagist
>>>> 
>>>> 
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