Chuck,
Please forgive a mental lapse; I'm a very senior citizen. ;~)
Jim Nichols
Tullahoma, TN USA
----- Original Message -----
From: "Chuck Norcutt" <chucknorcutt@xxxxxxxxxxxxxxxx>
To: "Olympus Camera Discussion" <olympus@xxxxxxxxxxxxxxxxx>
Sent: Sunday, June 24, 2012 8:48 PM
Subject: Re: [OM] IMG: More Skippers
> Diffraction, not refraction. Anyhow I think the answer is yes but I
> don't have specs on the exposure increase for your lens when fully
> extended.
>
> Refraction is the bending of light caused by slowing down or speeding up
> as the light beam enters a material of different refractive index. As
> light passes from air to glass it slows down and its path is bent.
> Diffraction is the bending of light as it passes around an obstruction
> such as the edges of the lens cell retaining the glass or the edges of
> the diaphragm blades.
>
> Chuck Norcutt
>
> On 6/24/2012 12:52 PM, Jim Nichols wrote:
>> Does that mean I have to expose at f/5.6 to avoid refraction problems
>> when
>> fully extended?
>>
>> Jim Nichols
>> Tullahoma, TN USA
>> ----- Original Message -----
>> From: "Chuck Norcutt" <chucknorcutt@xxxxxxxxxxxxxxxx>
>> To: "Olympus Camera Discussion" <olympus@xxxxxxxxxxxxxxxxx>
>> Sent: Sunday, June 24, 2012 9:05 AM
>> Subject: Re: [OM] IMG: More Skippers
>>
>>
>>> The equation accounts for it perfectly... it's just that you have to
>>> compute the effective focal ratio. Not hard actually if you refer to
>>> your macro lens's exposure table. If it says to increase the exposure
>>> by a factor of two at a given extension then the effective f-stop is one
>>> stop smaller than indicated. If it's reading f/8 then it's actually
>>> f/11.
>>>
>>> Chuck Norcutt
>>>
>>>
>>> On 6/24/2012 12:16 AM, Jim Nichols wrote:
>>>> Thanks, Chuck. You expressed it in a nutshell, which I appreciate.
>>>>
>>>> Probably the best image I ever made with this camera/lens combination,
>>>> at
>>>> least the one that gathered the most compliments ( and contained no
>>>> senoritas) was a shot of a red Canadian Beech Staggerwing cranking up.
>>>> It
>>>> was shot at f/10, so I suspect that f/8-f/9 is about right for the
>>>> upper
>>>> limit. The link to that image is given below:
>>>>
>>>> http://gallery.leica-users.org/v/OldNick/Staggerwing+Cranking+NI.jpg.html
>>>>
>>>> Just to ponder a bit, a macro lens extends quite a bit on closeups,
>>>> effectively increasing the f-number. How does your equation account
>>>> for
>>>> that?
>>>
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>>>
>>
>>
>
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