You might be remembering two aspects.
Stephen, Ken, etc brought up how a longer focal length has to be used to
have the same image framing with a larger image size. From
<http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm>
"As sensor size increases, the depth of field will decrease for a given
aperture (when filling the frame with a subject of the same size and
distance). This is because larger sensors require one to get closer to
their subject, or to use a longer focal length in order to fill the frame
with that subject. This means that one has to use progressively smaller
aperture sizes in order to maintain the same depth of field on larger
sensors."
It has also been brought up how often a fast lens set at say f1.2 doesn't
have one stop more light than at f1.4. Many/most lenses provide more even
lighting at higher aperture number settings ... light fall off in the
corners is often greater at wider apertures.
But an f no. is just focal length divided by aperture. If both focal length
and aperture are unchanged (the same lens), a larger sensor will just cover
a wider image with typically more fall off in the corners.
Jeff Keller
-----Original Message-----
From: Andrew Fildes [mailto:afildes@xxxxxxxxxxxxx]
Subject: Re: [OM] 0.95
Well, not exactly plenty, but it is a 25mm so it's better than something
like a Noctilux.
Now I have a question. There has been some discussion here in the past.
I'm of the understanding that a f0.95 lens is a true f0.95 regardless of
sensor size - after all, if I put a medium format f2.8 lens on a 35mm body,
it's still f2.8 AFAIK.
But there is a persistent theory that a 0.95 on an FT sensor is really
equivalent to a true f1.7 or some such. I really don't understand the
thinking behind this claim.
Anyone care to opine on this and help me make sense of it before I make some
claims in print.?
Andrew Fildes
afildes@xxxxxxxxxxxxx
On 17/11/2010, at 10:32 PM, Wayne Harridge wrote:
> Hmmm, f1.0 and still plenty of DOF.
>
> ...Wayne
>
>>
>> Voigt 25mm arrived today - and as luck would have it I had a model
>> handy.
>> Hard work to get focus right but it's rather good.
>> This image is completely unretouched (usual warnings - if nudity
>> offends, don't go there) -
>> http://www.pbase.com/image/130383184
>> The images from the 5D2 look positvely harsh in comparison.
>> I may be in love (er, with the lens).
>> Andrew Fildes
>> afildes@xxxxxxxxxxxxx
>>
>
>
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