Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
02-10-2024, 08:58 AM   #1
New Member




Join Date: Jan 2024
Photos: Gallery
Posts: 18
Possible Optical Axis Problem of DFA 24-70

Hi Everyone,

I think I found some evidence of a potential optical axis problem on the pentax DFA 24-70 after I accidentally kicked the tripod, and the lens is dropped inside the snow on the ground (see this post: Problem with lens - Page 2 - PentaxForums.com). I think the tripod was at about 1.5m of height and the lens dropped to the snow-covered ground. I would like to discuss it here, since I am not an expert in lenses.
This is one image I took at night with a tripod that is at f3.5 and 2min of exposure. Picture one is zoomed in the center, and picture two is zoomed in the right side of the image. As I can see, the right side is clearly not in focus, but the middle is in focus. There's another image I took where every other place is not in focus except the right side of the image(see picture five, which is a focus stacked picture of the two pictures). It is clear that picture five's image is more in focus than picture two.
Therefore, I concluded that there may be an optical axis problem with this lens.
Another piece of evidence is here: images six and seven are zoomed in from one image, where six is from the left and seven is from the right. It's clear that six is a focused image and seven is not.
Can anybody help if they agree/disagree with my concerns? I would appreciate any help.

Jerry*

Attached Images
             
02-10-2024, 09:38 AM   #2
Loyal Site Supporter
Loyal Site Supporter
UncleVanya's Avatar

Join Date: Jul 2014
Photos: Gallery | Albums
Posts: 27,792
This method is the best way to quantify the problem:

How to check how decentered your lens is - phillipreeve.net
02-10-2024, 10:11 AM   #3
Loyal Site Supporter
Loyal Site Supporter




Join Date: Jul 2021
Location: Zuiderkempen - Grote Netewoud - Belgium
Photos: Gallery | Albums
Posts: 1,285
I find it difficult to judge as subject distance differs significantly between left, center and right side, and the far to infinity distance area seems not so sharp either and I think it is due to atmospheric disturbances accumulating with increasing distance.....as the right side is also at larger distance this atmospheric condition might play a role. All in the assumption that your other settings allowed depth of field to cover a range like 20m to infinity and hence infinity sharpness would be guaranteed, but infinity looks hazy or foggy....so my suspected atmospheric condition...


Note that the pine forest in background (left to right going behind yellow left and center rocks) isnít soo sharp, and it looks a bit that the right hand side of red rock's are at same far distance as forest. But I admit judging distance on a picture is tricky....
02-11-2024, 09:17 PM   #4
Site Supporter
Site Supporter




Join Date: Aug 2016
Location: Leura NSW
Posts: 466
A quick test would be to take 2 pictures. One with camera upright and then one with the camera upside down from the same point without activating the AF between shots. Softness should shift sides if there's anything wrong.

02-14-2024, 02:51 AM   #5
New Member




Join Date: Jan 2024
Photos: Gallery
Posts: 18
Original Poster
I tested today. It looks that there are some decentering zoomed at 70mm of this lens. I use the method to take the same image in different corners and then crop it. Did not change any settings/focus. The images are taken: 1 at bottom left corner 2 at top right corner. It's clear that the first image is more sharp.
Attached Images
   
02-14-2024, 06:15 AM   #6
Loyal Site Supporter
Loyal Site Supporter
UncleVanya's Avatar

Join Date: Jul 2014
Photos: Gallery | Albums
Posts: 27,792
QuoteOriginally posted by ziywang50 Quote
I tested today. It looks that there are some decentering zoomed at 70mm of this lens. I use the method to take the same image in different corners and then crop it. Did not change any settings/focus. The images are taken: 1 at bottom left corner 2 at top right corner. It's clear that the first image is more sharp.
Thatís a lot easier to see and compare. The next question is, does this matter to you. If it does, look for another copy of the lens.
02-14-2024, 02:29 PM   #7
New Member




Join Date: Jan 2024
Photos: Gallery
Posts: 18
Original Poster
QuoteOriginally posted by UncleVanya Quote
Thatís a lot easier to see and compare. The next question is, does this matter to you. If it does, look for another copy of the lens.
Probably not for right now, since it still produces good quality images if it's not close to the edges.

02-14-2024, 08:31 PM   #8
New Member




Join Date: Jan 2024
Photos: Gallery
Posts: 18
Original Poster
Note sure about it now... I am lost. I did another test for samyang 135mm and I still get the upper right is a little not sharp... hard to tell.
I also tested on the 50mm, and for that one it's pretty hard to tell difference from left and right.
The 3rd is from upper right, the 1st is from lower left.
Not sure about it now...
Attached Images
       
5 Days Ago   #9
New Member




Join Date: Jan 2024
Photos: Gallery
Posts: 18
Original Poster
Just did one more test with another scene. It turns out that unfortunately it's the problem of the 24-70 lens. It is unable to get an image of both left and right sides in focus even at f/4.
I tested one shot with this lens and another shot with the same lens shooting upside-down. The upper and lower sharpness when shooting vertically is clearly not the same.
It's my first time getting a lens at this price.
There's also a problem with the zoom lock that I can't lock my zoom except at 24mm.
I may try to send it to precision for repairing in several months, if I can afford this. However, it's probably not worth it since the base price is about $500...

Last edited by ziywang50; 5 Days Ago at 05:05 PM.
5 Days Ago   #10
New Member




Join Date: Jan 2024
Photos: Gallery
Posts: 18
Original Poster
70mm left/right performances
Did not change any settings, including focus, for this test.
Attached Images
   

Last edited by ziywang50; 5 Days Ago at 07:48 PM.
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!
axis, camera, dfa, focus, ground, image, lens, pentax help, photography, picture, seven, tripod, troubleshooting
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Does a DFA 150-450 fit in a Pelican 1510 or 1535 along the short axis with trekpack? Shivaess Pentax Camera and Field Accessories 5 04-27-2021 07:52 AM
Dilemma: Portrait Shooting between DFA 24-70 or DFA 70-200 Gerard_Dirks Pentax SLR Lens Discussion 22 10-05-2017 04:34 PM
Help me understand: Flexible Tilt-Type LCD monitor - any angle along the optical axis Gray Pentax K-1 & K-1 II 31 02-21-2016 11:22 PM



All times are GMT -7. The time now is 09:47 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