Optimum lens aperture for Sigma 8mm

[Dayve]

Hi all,
I'm using a Canon 1ds (Mk1) with a sigma 8mm 3.5 EX DG to shoot my
panos. I've seen some spectacular panos, where the sharpness and image
quality really stand out. I'm not sure if I'm getting that from my set-
up. I wondered if there was an optimum aperture, as I'm using f22 for
everything at the moment. Any ideas / suggestions would be very
welcome.

Cheers,
Dayve

[perspixe]

f22 is not optimum aperture. I am not very used to very wide angle
lenses but generally as you close your aperture, you get more dof but
also more diffraction and that is not good for resolution.
that has to do with the digital format and the circle of confusion.
There are a lot of articles on that subject on the web.
f8 to f11 would be much better (use a ND filter if that's too open for
you), you should spend time making tests at different apertures with
your own setup to find out what is best.
Again this is something I can definitely confirm with my lenses,
telephoto ones, but I do not own something as wide as 8mm so I cannot
be sure really.

Greg

[Misho Ristov]

from my experience
f13 max on a DX sensor
f16 on full-frame

m.

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[Robert C. Fisher]

I found that the optimum aperture for my Sigma 8mm was f8. I shot a
bunch of test images to figure out what worked best. With the 8mm I
shoot mostly at f8 but sometimes f11 but nothing over that or big bad
diffraction takes over and the images look worse. Also for best DOF I
set my focus at a squeak under infinity for most things and in tight
spaces I would try a few test shots to figure out what worked best.

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Cheers
Robert C. Fisher
VR Photography / Cinematography
rcf...@pacbell.net

[Robert Eather]

f22 is definitely not optimum - typically about the center of the f-stop range of a lens is optimum,  Lower f-stop numbers increase optical lens aberrations, and high increase diffraction effects.  I would recommend f5.6 - f8 as optimum.

Robert

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[Dayve]

Thanks guys,

I have this with other lenses, so I'm not surprised to learn it with
the Sigma. I'll run some tests from f5.6 to f16 to cover the range. I
expect that, with such a lens, the dof would be adequate for room
shots and landscapes?

cheers,
Dayve

On Apr 14, 4:08 pm, Robert Eather <keocons...@gmail.com> wrote:
> f22 is definitely not optimum - typically about the center of the f-stop
> range of a lens is optimum,  Lower f-stop numbers increase optical lens
> aberrations, and high increase diffraction effects.  I would recommend f5.6
> - f8 as optimum.
>
> Robert
>
> On Thu, Apr 14, 2011 at 10:46 AM, Dayve

> <enquir...@photographybyward.co.uk>wrote:

>
>
>
>
>
> > Hi all,
> > I'm using a Canon 1ds (Mk1) with a sigma 8mm 3.5 EX DG to shoot my
> > panos. I've seen some spectacular panos, where the sharpness and image
> > quality really stand out. I'm not sure if I'm getting that from my set-
> > up. I wondered if there was an optimum aperture, as I'm using f22 for
> > everything at the moment. Any ideas / suggestions would be very
> > welcome.
>
> > Cheers,
> > Dayve
>
> > --
> > You received this message because you are subscribed to the Google Groups
> > "PTGui" group.
> > To post to this group, send email to pt...@googlegroups.com
> > To unsubscribe from this group, send email to
> > ptgui+un...@googlegroups.com
> > Please do not add attachments to your posts; instead you may upload files
> > at
> >http://groups.google.com/group/ptgui/files

> > For more options, visit this group athttp://groups.google.com/group/ptgui

>
> --
> Robert Eather
> Keo Consultants
> 27 Irving St.
> Brookline  MA  02445
> 617 734 7305
> --------------------------
> 126 Longwood Ave. APT 3
> Brookline  MA  02446

> 617 277 3251- Hide quoted text -
>
> - Show quoted text -

[Dayve]

I've run a test on my Sigma 8mm and have uploaded the results. I used
a subject with a high amount of depth. I set the lens to a point well
before infinity and shot a series from maximum aperture to f22. I then
chose the first image that retained acceptable sharpness throughout
(f8) and compared this with both f11 and f22. I think that, in this
subject, f11 had the slight edge over f8 in terms of maintaining
subject sharpness, while f22 is definitely suffering from diffraction.
It's difficult to see a great difference from these crops of the full
fisheye though. By the way, I've applied 25 sharpening in Lightroom as
I normall do, but no other adjustments.

http://www.photographybyward.co.uk/sigma-test/f8-f22%20comparison.jpg

Worth doing the test and many thanks for your advice.
Dayve

> > - Show quoted text -- Hide quoted text -

[mcz...@gmail.com]

I have also found that F8 also gives excellent results on a Cannon 450D

[Roger D. Williams]

F/22 is probably too small. Interference degrades sharpness at that
level. This Sigma is at its sharpest between F/5.6 and F/8 in my own
experience.

Roger W.

--
Work: www.adex-japan.com

[DennisS]

After shooting a series of test shots when I first got the lens, on my
D300, F5.6 gives the best results. I once did a panorama where the
ground was in sharp focus as well as an airplane flying overhead at
20,000+ feet (just a guess on the altitude). You also need to find
the optimum focus setting. I use 1m. Do a series of test shots for
yourself.

[Dayve Ward (Photography by Ward)]

I've just been refreshing my theory regarding diffraction. Diffraction
certainly becomes more apparent with smaller apertures. On a very good lens,
where aberrations have been reduced to a minimum, the only significant loss
in quality comes from diffraction (the lens is said to be diffraction
limited). It would transpire from this that the Sigma 8mm f3.8 EX DG must be
diffraction limited to a significant degree. I have another lens (a 120mm
Rodenstock f5.6 apo macro digital) which I use for jewellery photography. I
noticed that, although it physically stops down to f64, it's at it's best at
f5.6 / f8. For such close up work, I often have to resort to focus stacking
to get a high dof and the highest sharpness from this lens.

I also refreshed myself on the hyperfocal distance, and the Sigma has a
useful scale to set this distance. Setting a focus of about 1 foot (0.3m) at
f8 should render everything sharp from about 0.7 feet (0.25m) to infinity
according the the lenses scale.

Dayve

--

[Roger D. Williams]

On Fri, 15 Apr 2011 16:49:00 +0900, Dayve Ward (Photography by Ward)
<enqu...@photographybyward.co.uk> wrote:

> I've just been refreshing my theory regarding diffraction. Diffraction
> certainly becomes more apparent with smaller apertures. On a very good
> lens, where aberrations have been reduced to a minimum, the only
> significant loss in quality comes from diffraction (the lens is said to
> be diffraction limited). It would transpire from this that the Sigma 8mm
> f3.8 EX DG must be diffraction limited to a significant degree. I have
> another lens (a 120mm Rodenstock f5.6 apo macro digital) which I use for
> jewellery photography. I noticed that, although it physically stops down
> to f64, it's at it's best at f5.6 / f8. For such close up work, I often
> have to resort to focus stacking to get a high dof and the highest
> sharpness from this lens.
>
> I also refreshed myself on the hyperfocal distance, and the Sigma has a
> useful scale to set this distance. Setting a focus of about 1 foot
> (0.3m) at f8 should render everything sharp from about 0.7 feet (0.25m)
> to infinity according the the lenses scale.

Theory is important, of course, but do not trust the scale on the lens.
In my experience it is simply not true that setting it at 0.3m and F/8
will give you everything sharp from 0.25m to infinity. Of course you
definition of "sharp" may be different from mine, but there is no
substitute for actual experiment. My own preferred setting is much nearer
the infinity mark.

[Dayve Ward (Photography by Ward)]

You're quite right Roger. No substitute for practical testing (using theory
as a starting point).

Dayve

Roger W.

--
Work: www.adex-japan.com

--

[Erik Krause]

Am 15.04.2011 09:49, schrieb Dayve Ward (Photography by Ward):
> I also refreshed myself on the hyperfocal distance, and the Sigma has a
> useful scale to set this distance. Setting a focus of about 1 foot (0.3m) at
> f8 should render everything sharp from about 0.7 feet (0.25m) to infinity
> according the the lenses scale.

DoF of a fisheye lens might be quite strange:
http://michel.thoby.free.fr/Fisheyes_Focus/Focus_mapping.html

Furthermore DoF must be calculated differently for images that are
zoomable to pixel level. Classical DoF calculation assumes prints as a
basis. See
http://wiki.panotools.org/DOF#Considerations_for_zoomable_panoramas

--
Erik Krause
http://www.erik-krause.de