Is there a resolution limitation to ultra-wide lenses?

[teru]

I have a question about my Sigma 10-20mm f/4-5.6 EX DC HSM.

 

<P>On several occassions, I've tried to shoot cityscape photos with my Sigma @ 10mm with the intent of cropping

them in PP to get a panoramic effect. However, I've noticed that all my shots come out with terrible focus everytime.

See sample:

 

<P><IMG SRC="http://images2.fotop.net/albums2/teruphoto/Temp/Sigma_8835.jpg">

 

<P>100% crop:

 

<P><IMG SRC="http://images2.fotop.net/albums2/teruphoto/Temp/Sigma_8835_crop.jpg">

 

<P>Is this a problem with the lens or an issue with ultra-wides in general? Do they have problems resolving the

details of small points of light?

 

<P>My Sigma should be OK because it's taken sharp 10mm shots before:

 

<P><IMG SRC="http://images2.fotop.net/albums2/teruphoto/Architecture/HKCEC_3358.jpg">

 

<P>and even did well inside a cave:

 

<P><IMG SRC="http://images2.fotop.net/albums2/teruphoto/Okinawa/087_Okinawa_7293.jpg">

 

<P>Any ideas?

[shuo_zhao]

Teru, what were your camera's settings when you took the shot?

[rainer_t]

Teru, from the exif data of your first picture, i get:

 

Focus-Mode: manual

 

Focus-Position 0.79m

 

Hyperfocal-Distance 0.62m

 

Depth of Field: 0.35m - inf

 

This is a very good example of how bad hyperfocal focussing can be at times. Besides that, you picture shows absolutely nothing of interes in the near field ... why didn't you focus on infinity? The image quality would have been heaps better. For me ... (sorry, no offence meant) ... this is a user error.

[teru]

Hmm, that's right. But let me look through my files for a sample @ infinity (I used manual focus on several shots). I'll upload another photo when I get home.

[ronald_moravec1]

Hyper focal rarely works for me as there is only one plane of true focus. The rest is a compromise.

 

A lens will not change unless you drop it.

[obakesan]

Teru

<P>

in addition to the other points above also be aware that many modern zoom lenses do not focus at infinity when

you feel the focus ring hit the 'stop'. Sometimes even the focus marker is 'off'. However if you are stopping

down a wee bit (say f5.6) then it should not be so critical.

<P>

Your AF should work well on those city lights, perhaps AF then click it off

<hr width=50>

<P>

Rainer, do the Nikons report focused distance properly when the camera is set to manual? If so, nice feature

<P>

:-)

[mike dixon]

Rainier makes a very good point about your focus setting. Another important factor in reducing the ultimate resolution of distant objects is atmospheric haze and humidity. Particulates and water in the air, even on a clear-looking day, reduce the "sharpness" of distant objects.

[rainer_t]

-- "do the Nikons report focused distance properly when the camera is set to manual?"

 

I don't know ... I just used exiftool to dump out available information. But this should be easy to verify ... just two shots with MF (one at infinity, one at minimum focus distance) ... and both dumped with exiftool. All I can say ... Canons do have the distance info even with MF ... but only if the lens is capable of sending it of course.

[obakesan]

Rainer

 

dratt ... I have canon but none of my lenses are new enough (expensive enough ;-) to report distance information.

[teru]

<P>From an earlier shoot. 10mm focal length, manual focus, distance = 6.31m (which is my Sigma's equivalent of near infinity, because as Chris pointed out, it's best not to 'hit the stop')

 

<P><img src="http://images4.fotop.net/albums2/teruphoto/Temp/DSC_7943c.jpg">

 

<P>The weather wasn't bad, because I got this photo using my 24-70mm

 

<P><IMG SRC="http://images4.fotop.net/albums2/teruphoto/Cityscape/Victoria_Harbor_7935.jpg">

[teru]

BTW, the 10mm sample above is a 100% crop from the original, much wider photo.

[Ed_Ingold]

Thank you for posting these enormous images. It makes me regret settling for DSL when I could have a fiber optic link to my house :-)

 

The lens is probably performing within the limits of your digital format. You are fooling yourself to think resolution will hold with such drastic cropping. It wouldn't work with film either. Instead of wasting so much vertical space, you should choose a lens that gives the vertical framing you want then stitch two or three images together. I've done that with medium format, and you can see the shade pulls in condominium windows.

[teru]

Sorry if this is a stupid question, but do I have any way to change the hyperfocal distance chosen by my camera/lens? Looking at many of my 10mm shots, I've found that regardless of the auto/manual focus distance, the hyperfocal distance is very often 0.62m. With my other lenses, the hyperfocal distance is usually a more appropriate value.

[Ed_Ingold]

"do I have any way to change the hyperfocal distance chosen by my camera/lens? "

 

The hyperfocal distance is a function of the focal length and aperture. In general, you are best to focus at infinity if the background contains important detail, thun use a small aperture and hope for the best in the foreground.

[obakesan]

Teru

<P>

try reading <B><A HREF="http://en.wikipedia.org/wiki/Hyperfocal_distance" target="_blank">this</A></B> page

<P>

also, if you have a palm OS handheld (I see that there are other handhelds supported), download an application called VadeMecum (<A HREF="http://www.bobwheeler.com/photo/Software/software.html" target="_blank"><B>here</B></A>)

as it has excellent calculations for depth of field allowing you to choose your film format (sensor size) and desired

circle of confusion (more or less the smallest point that can be differentiable)

<P>

Lastly, some of us are on slower dsl connections, and big images (like bigger than 800 pixels wide) will take time to load. So please take that into consideration when linking to big images

[teru]

Actually, I already have an ok idea on hyperfocal distances. It's just that all of my previous exif viewers didn't provide hyperfocal distance info, so it wasn't until I switched to exiftool that I noticed that many of my Sigma 10-20mm shots shot at 10mm have a setting of 0.62m. This seems to be a problem since often times the object of my focus is near or at infinity.

[bill_tuthill]

Do other Sigma 10-20 lenses focus further than .79 meters at 10mm?

I'm wondering if this is a design flaw or a poor lens sample.

A quick Google search turns up many posts where photographers

sent their 10-20 back to Sigma for successful infinity adjustment.