Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
04-19-2015, 02:40 PM   #1
Site Supporter
reh321's Avatar

Join Date: Nov 2014
Location: South Bend, IN, USA
Photos: Gallery | Albums
Posts: 2,724
Proper aperture

Today I became aware of the following article:
Chromatic Aberration - What is it and How to Avoid it

I was very interested in this because my pictures of birds in the snow last winter using adapted zoom lenses showed visible CA. Recently I did get a new Sigma 70-300mm lens, hoping that its coatings would reduce my problem - but without having bright white snow in the background, no pictures I could take right now would test for that condition.

Anyway, beyond that, the article recommends "Stop down your aperture". My understanding is that diffraction starts becoming an issue for the Q family quite early. Other than tedious testing, is there any information available about picking an aperture that will balance out losses from more diffraction and gains from less CA?

04-19-2015, 03:31 PM   #2
Administrator
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 40,957
QuoteOriginally posted by reh321 Quote
Today I became aware of the following article:
Chromatic Aberration - What is it and How to Avoid it

I was very interested in this because my pictures of birds in the snow last winter using adapted zoom lenses showed visible CA. Recently I did get a new Sigma 70-300mm lens, hoping that its coatings would reduce my problem - but without having bright white snow in the background, no pictures I could take right now would test for that condition.

Anyway, beyond that, the article recommends "Stop down your aperture". My understanding is that diffraction starts becoming an issue for the Q family quite early. Other than tedious testing, is there any information available about picking an aperture that will balance out losses from more diffraction and gains from less CA?
It's definitely tough with the Q- since its sensor looks at a very small portion of the frame at a relatively high resolution, it has a tendency to make minor axial aberrations more visible. Your best bet would be to shoot at F4 to F5.6, generally speaking. Using a modern prime should also help. The good news is that since you're only using the very center of the frame, distortion and lateral CA aren't a concern.

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:

04-20-2015, 10:43 AM - 2 Likes   #3
Forum Member




Join Date: Sep 2014
Posts: 69
The Q tries to resolve 4000/6.08/2 lp/mm = 329, whereas the Q7 tries to resolve 4000/7.6/2 = 263. The resolvable lp/mm are 400 at f4, ~280 at f5.6, 200 at f8, so you need not worry about diffraction on a Q at f4 and on a Q7 at f5.6.
04-20-2015, 11:19 AM   #4
Site Supporter
reh321's Avatar

Join Date: Nov 2014
Location: South Bend, IN, USA
Photos: Gallery | Albums
Posts: 2,724
Original Poster
QuoteOriginally posted by Antonio Marques Quote
The Q tries to resolve 4000/6.08/2 lp/mm = 329, whereas the Q7 tries to resolve 4000/7.6/2 = 263. The resolvable lp/mm are 400 at f4, ~280 at f5.6, 200 at f8, so you need not worry about diffraction on a Q at f4 and on a Q7 at f5.6.
Thank you! That at least gives me a starting point for future testing.

BTW - where did you get all this info from??

04-21-2015, 02:48 AM   #5
Forum Member




Join Date: Sep 2014
Posts: 69
I've decided that the Q's sensor is 6.08 (x4.56), since the other figures don't make sense. The Q7's is known to be 7.6 (x5.7).

For the diffraction values, I really don't know if they're independent of every other factor, but I'm following a table that is inverse of aperture:
(Notice that the numbers for integer apertures are exact, whereas the others are rounded. It's what we do anyway for f numbers, which are really multiples of the square root of 2.)

f1 1600
f1.4 1100
f2 800
f2.8 560
f4 400
f5.6 280
f8 200
f11 140
f16 100
f22 70
f32 50

Last edited by Antonio Marques; 04-21-2015 at 02:57 AM.
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!
aperture, article, ca aperture, camera, diffraction, mirrorless, pentax q, pentax q10, pentax q7, pictures, q-s1, q10, q7, snow
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Raindrops...until I get a proper lens EllenJ Macro Photography 11 05-20-2014 06:17 AM
First proper go with Lightzone Tsuken Digital Processing, Software, and Printing 5 04-15-2014 03:36 PM
Proper film storage LFLee Pentax Medium Format 5 03-19-2014 04:04 PM
Proper way to store backup hard drives? barondla Digital Processing, Software, and Printing 3 08-22-2013 07:03 AM
Proper Lens Hood Tonytee Pentax Camera and Field Accessories 2 05-17-2013 02:32 AM



All times are GMT -7. The time now is 07:46 PM. | See also: NikonForums.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