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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