Lense, f-stop, focal point... DOF....
 

"Jonathan Wilson" wrote in message
...
Ok, so with a given focal point... lense mm, and F-stop, you can just
about work out a DOF "in focus...."

The main difference, from experience, is that a PAS has a large DOF
and a "common" dSLR as a smaller DOF[My personal experience] (and if I
used it 35mm has less dof, and medium format even less and Large
Format a DOF so small its bordering on the bizzare!)

So knowing what I know about the basic theory about the above....

Is it posible to have a lense that "gathers" enough light to equate to
say F1.8, but reduces that to a focal plane and film size that equates
to an f11?

I know the maths is off based on numbers... but what I am thinking of
is a large DOF but a low f-number....

You can cheat in some cases, if the stuff you want to be in focus is roughly
in the same plane in space. Look up Scheimpflug in Google. With a Canon
dSLR, you can buy a TSE lens that allows you to do that. They're slow
(f/3.5) lenses, though. And not cheap.

David J. Littleboy
Tokyo, Japan

Lense, f-stop, focal point... DOF....
 

Ok, so with a given focal point... lense mm, and F-stop, you can just
about work out a DOF "in focus...."

The main difference, from experience, is that a PAS has a large DOF
and a "common" dSLR as a smaller DOF[My personal experience] (and if I
used it 35mm has less dof, and medium format even less and Large
Format a DOF so small its bordering on the bizzare!)

So knowing what I know about the basic theory about the above....

Is it posible to have a lense that "gathers" enough light to equate to
say F1.8, but reduces that to a focal plane and film size that equates
to an f11?

I know the maths is off based on numbers... but what I am thinking of
is a large DOF but a low f-number....

The apature is a variable based on the mm, but what if the lense takes
all the available light, but puts the apature at a different point
along the lense?

Say you wanted a photo, and you wanted to have everything from 1 foot
to 12 foot to be in focus, with a PAS you could have that at f2... but
a dSLR at f2 the "infocus" shrinks to 5cm, is it posible to create a
lense that has enough "light" input to equate to f2, but somehow
manages to have a DOF as a f11 but the available exposure "light" as
the original f2?

Would a huge physical (circum) lense allow enough light in, so that
when it hit the the film plane it was "bright" but the 'physical'
apature was so far back in the physical "lenght" that it had a greater
DOF/different f-stop, than the reality.

One thing I miss from my old PAS, is the low f-no, but large DOF
compared with my dSLR. I have to shoot ISO1600 to get the same
"light" as my old PAS at 400/800, but I have to make sure the focus
point is "spot on" where as the old PAS could be out by quite a big
margin,

I'm not sure if anyone will understand what i'm getting at, but hey,
lol

In simple terms... is it posible to "gather lots of light" but have a
large f-no... creating a big DOF with a large f-stop number....
Physically if not mathmatially.

We have "light enhancing" opticals, such as the "night scopes" used by
the army... can that be applied to standard cameras, or is that
something totaly different.

If i've not described this corectly then I will try, depending on the
responses given.

Jon

--
Jonathan Wilson.
www.somethingerotic.com

Lense, f-stop, focal point... DOF....
 

On Thu, 15 Jul 2004 03:06:11 GMT, Jonathan Wilson
wrote:
Just had a fiddle....

If I shoot in Jpeg, at "small" then I can get 4 quick shots, and 1
shot every 1/2 second roughly.....

In "raw" I have 4 quick shots, then 1 after 1/2 second, then 1 every
1-5 seconds.....

The timings are not exact... just perceptual.

I normally shoot raw, so was supprised at the jpeg difference.


--
Jonathan Wilson.
www.somethingerotic.com