Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
04-02-2010, 09:42 PM   #1
Inactive Account




Join Date: Apr 2010
Location: Singapore
Photos: Gallery
Posts: 31
I'm having a funny problem with aperture. It's not working as it shold be

I'm using pentax kx 18-55mm kit lens.

I read that high f-stop gives good focus on far n near object. And i see on the net people use f9 and above when shooting buildings, landscapes and far objects.

So i tried experimenting on my own.

but the sharpest image i get is when i use f5.6. not f3.5 nor f9+.


F9+ is making the buildings n trees blur. And i also don't how come F5.6 is sharper than f3.5.

Av Mode 17mm:
Cropped

f3.5


f5.6


f9


04-02-2010, 10:00 PM   #2
Inactive Account




Join Date: Aug 2008
Location: Michigan, USA
Photos: Gallery | Albums
Posts: 7,484
Many lenses are not "sharp" wide open, especially kit zooms. Stopped down one or two stops (f5.6) generally improves that dramatically (on some lenses more than others). At f9+ your shutter speed may be too slow to get a good shot. If you really want to experiment with it, get 3 like objects (like AA batteries, I know you have some of those) and line them up about a foot or so apart on a table. Focus on the middle one from various distances and at various apertures. You will discover 2 things. First, the closer you are to the objects especially wide open, the more blurred the outer objects will be. Second, the further away you are, the more in focus they will be, even at the same apertures.

Without worrying too much about the physics of it, You've just learned the useful application of Depth Of Field (DOF).

Now take it one step further and adjust your ISO so you can get a faster shutter speed if need be. The Antishake is a nice tool but that's all it is, and it's a fallible one at that.



04-02-2010, 10:06 PM   #3
Veteran Member




Join Date: Apr 2009
Location: NJ, USA
Photos: Albums
Posts: 1,270
The lower the aperture (larger f-stop number), the slower the shutter is at the same exposure. It is possible that f/9 is causing the shutter to be slow enough that either camera shake or a light breeze disturbing the foliage is causing things to be less "sharp".

Could you post the EXIF for your images?
04-02-2010, 10:11 PM   #4
Administrator
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 43,136
See here: https://www.pentaxforums.com/forums/photography-articles/62522-exposure-shutt...rture-iso.html

Keep in mind that the higher aperture will require a slower shutter speed, so your images might have been subjected to added shaking/motion blur.


Adam
PentaxForums.com Webmaster (Site Usage Guide | Site Help | My Photography)



PentaxForums.com's high server and development costs are user-supported. You can help cover those costs by donating. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

04-02-2010, 10:56 PM   #5
Pentaxian




Join Date: Mar 2009
Location: Perth Australia
Photos: Albums
Posts: 1,511
lens resolution and focus are different things also...

all lenses have an optimal f stop where they get the best resolution, this is also a factor at play here.
04-02-2010, 11:20 PM   #6
Veteran Member
mickeyobe's Avatar

Join Date: Dec 2006
Location: Toronto, Ontario, Canada
Posts: 1,759
From looking at your pictures I would conclude that you focused on the foreground.

For landscapes you might try setting your lens on manual and set the distance on infinity "∞".
I think everything in your photo is far enough away to be considered at infinity - even the foreground palm trees.

It also appears that you may not be hold your camera steadily enough. Keep your arms down at your sides.

Mickey
04-02-2010, 11:35 PM   #7
Inactive Account




Join Date: Apr 2010
Location: Singapore
Photos: Gallery
Posts: 31
Original Poster
Hi guys, thanks for all yr help

here are 3 more shot

I used a tripod
IS off
AE spot & AF spot
Focus on the white honda civic.

what I see is now the f3.5 is the sharpest among all.
I already know low f-stop give bokeh while high f-stop bring everything in focus.

now i learned that low f-stop also give better sharpness than high f-stop despite high f-stop bring backgrd n foregrd in focus.
for these shot, the car is very far away.. And, i have no close foregrd object so i think no need to use high f-stop. its impossible to make bokeh on the car unless i use super zoom lens. tt's why using low f-stop that bring best sharpness is the best for distant object.

must correct me if i m wrong!! please

cheers

f10

F5.6


F3.5
04-03-2010, 09:19 AM   #8
New Member




Join Date: Apr 2010
Posts: 6
Maybe my eyes are not so good but to me all 3 pictures are not sharp. The picture taken at f3.5 has higher contrast but the sharpness is not better than the other two.

04-03-2010, 09:28 AM   #9
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
Your basic problem is a basic misunderstanding of the topic of Depth of Field, so I'd suggest googling that term to get a better understanding of how aperture actually affects focus. it has nothing to do with how sharp the in--focus areas are, but with how *much* is in focus, and that is also affected by *where* you are focusing.

In the case of the car samples, nothing looks particular sharp to me, but I'd say you are seeing the effects of slight difference in focus and perhaps some camera shake (did you use the two-second timer on the tripod? how sturdy of a tripod?). because no way if f/3.5 going to be sharper than f/5.6 on that lens.
04-03-2010, 10:30 AM   #10
Veteran Member




Join Date: Dec 2009
Location: Deep Forest
Posts: 630
suggest turn off autofocus; focus manually at widest aperture (lowest f/#), then stop down to take photo.
04-03-2010, 10:34 AM   #11
Veteran Member
mickeyobe's Avatar

Join Date: Dec 2006
Location: Toronto, Ontario, Canada
Posts: 1,759
None of the three pictures is truly sharp.
Regarding f stops. Think of them as fractions.
eg 1/3.5, 1/5.6, 1/10. Therefore, 1/3.5 is larger then 1/5.6 which is larger than 1/10.

You spot focused on the white Honda Civic. Depending upon where you put the spot, that car is almost featureless and lacks adjacent contrasting areas which autofocus needs to obtain its focus.

Why don't you try manual focus and set the lens at infinity as I suggested earlier and see what happens?
Focus with the lens at its maximum aperture which I presume is f3.5 and gradually stop down to minimum aperture (f10 ?) being sure not to alter the focus.

I think you are causing yourself needless aggravation. You have a good camera and a good lens and they will perform to your expectations when properly understood and correctly used.

Now let's see your next batch of photos taken in cooperation with your equipment. Forget about bokeh.

Mickey
04-03-2010, 06:45 PM   #12
Veteran Member
tokyoso's Avatar

Join Date: Jan 2010
Location: Tokyo
Photos: Albums
Posts: 723
QuoteOriginally posted by learnphotography Quote
I'm using pentax kx 18-55mm kit lens.

I read that high f-stop gives good focus on far n near object. And i see on the net people use f9 and above when shooting buildings, landscapes and far objects.

So i tried experimenting on my own.

but the sharpest image i get is when i use f5.6. not f3.5 nor f9+.


F9+ is making the buildings n trees blur. And i also don't how come F5.6 is sharper than f3.5.

Av Mode 17mm:
Cropped

f3.5


f5.6


f9
i think like mickeyobe said flip your camera to MF and turn the focus ring all the way to infinity. set the camera on a table or lay on the ground outdoors when it's sunny. point it to somewhere far like you did there. set to Av mode , 2 sec timer and press the shutter.

try this with different focal lengths and fstops... etc. sounds like fun..
04-03-2010, 08:17 PM   #13
Inactive Account




Join Date: Apr 2010
Location: Singapore
Photos: Gallery
Posts: 31
Original Poster
Hello thanks for all the comments,

here are another experiment as suggested my mickeyobe

AV mode
infinity focus at widest aperture (check with live view at 10x and the FAT tree is focused at infinity)
On a tripod
IS turned off
2 sec timer
mirror locked up

f13

f5.6

f3.5


I cannot see any noticeable difference. Only that the f3.5 sample shows a tad more contrast.

I'm focusing the fat tree in my lens hyperfocal zone i guess.
04-03-2010, 09:00 PM   #14
Veteran Member
tokyoso's Avatar

Join Date: Jan 2010
Location: Tokyo
Photos: Albums
Posts: 723
i see that the exif data is stripped, but try focusing on the FAT building instead. my k-x kit has always focused to infinity with the focus ring all the way turned, AF or MF... but some lenses may vary.
04-04-2010, 06:19 AM   #15
Veteran Member
Laurentiu Cristofor's Avatar

Join Date: Nov 2009
Location: WA
Photos: Albums
Posts: 3,044
Since you have the K-x that has Live View, you may want to use that for focusing - use the info button to zoom in and adjust focus (you can move the zoomed in area around with the arrows).

Ignore the trees, whose foliage might move, and focus on the building.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
buildings, camera, dslr, f3.5, f5.6, photography
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Vivitar 85-205mm 2.8/f aperture not working Minoltaguy Pentax SLR Lens Discussion 0 03-29-2010 09:33 PM
K20D Problem: Manual and Menu not working anamnezis Pentax DSLR Discussion 5 01-05-2010 02:48 PM
K200d and weird non working aperture. zelovoc Pentax DSLR Discussion 3 12-13-2009 02:38 AM
aperture problem with 50 1.7 kent Pentax SLR Lens Discussion 9 11-01-2009 05:11 AM
SEARS 80-200mm aperture not working michalko99 Pentax SLR Lens Discussion 1 08-24-2009 09:44 AM



All times are GMT -7. The time now is 07:12 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top