Forgot Password
Pentax Camera Forums Home

Show Printable Version Search this Thread
09-14-2010, 07:51 PM   #1
Inactive Account

Join Date: Jan 2009
Location: Lafayette, LA
Posts: 10
Help with aperture

I am confused. I took the picture below at F/7.1 which I thought meant that the whole picture would be in focus. I can't even tell what IS in focus, but to me this looks more like a F/2.0 photo. I am new to this so excuse if my terminology is wrong or if I am totally backwards in my thinking, but I would really appreciate any help to clarify this for me. Thanks so much!
Taken with 18-55mm II kit lens at 47.5mm, ISO 400, f/7.1, 1/25 sec

Attached Images
09-14-2010, 08:14 PM   #2
Veteran Member
KxBlaze's Avatar

Join Date: Feb 2010
Location: California
Photos: Gallery
Posts: 1,594
You focal length has to do with DOF too. The more you zoom in the less DOF you will have. Try taking that same pic but at 25mm or less and with 7.1 the entire pic should be in focus.

As for the pic not being in focus that is probably due to the 1/25 shutter speed. That is pretty slow and a little hard to hand hold.

So try the pic at 1/50 or faster and 20mm or less.
09-14-2010, 08:42 PM   #3
Loyal Site Supporter
imtheguy's Avatar

Join Date: Mar 2009
Location: Virginia Beach
Photos: Gallery | Albums
Posts: 2,950
It also looks like you were very close which greatly impacts the DOF. If that shot was 24" away, the DOF for 50mm at f8 is only 4.7cm, less than 2 inches. If you have never done so, play with the online calculator linked below to get a feel for the relationships.

Depth of Field: Optical: Glossary: Learn: Digital Photography Review
09-14-2010, 08:52 PM   #4
Inactive Account

Join Date: Jan 2009
Location: Lafayette, LA
Posts: 10
Original Poster
Thanks so much for the information. Yes, I was very close to the subject but did not understand that it would make that much of a difference if the aperture was that high. I will check out that link also, thank you for that!

09-14-2010, 10:22 PM   #5
Inactive Account

Join Date: Aug 2008
Location: Michigan, USA
Photos: Gallery | Albums
Posts: 7,484
I was just going to say, I think you are too close to whatever you're taking a picture of. The closer you are, the more shallow your DOF, regardless of the lens itself. Here is a shot at f11 (with a macro lens).

The lens front is about 2 inches from the flowers.

Same lens and situation at f32

Same lens, f6.3

Peeper version

Completely different from your particular situation but I hope it demonstrates the point of Aperture vs Distance.

09-15-2010, 08:29 AM   #6
Inactive Account

Join Date: Jan 2009
Location: Lafayette, LA
Posts: 10
Original Poster
Thanks so much for the examples Jeff, beautiful photos! Seeing the different pictures with the info really helps! Thanks again.
09-16-2010, 06:46 PM   #7
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
f/7.1 is not particularly high. Closeup/macro photography is often done at f/16 or more.

  • 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!
camera, focus, help, pentax help, photography, picture
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Similar Threads
Thread Thread Starter Forum Replies Last Post
Aperture 3 mongo General Talk 1 02-09-2010 07:42 PM
Constant Aperture vs Variable Aperture Netsoft Pentax SLR Lens Discussion 13 01-11-2010 07:29 AM
Use of Aperture-Ring 43mm/1.9 -> no aperture data Deimo Pentax SLR Lens Discussion 7 06-24-2009 03:25 PM
FA 50/1.4 aperture voltigore Pentax SLR Lens Discussion 9 03-29-2008 10:49 AM
I don't get it (aperture) Cloudy Wizzard General Talk 23 10-15-2007 09:31 AM

All times are GMT -7. The time now is 11:33 AM. | See also:, 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?
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]