Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
04-28-2008, 07:08 PM   #1
Forum Member




Join Date: Dec 2007
Location: Rockford, IL
Posts: 52
DA-series vs A-series lens .. does it make a diference on a dSLR?

Ok...
I had posted a thread earlier today about some strange focusing issues I've been having...
https://www.pentaxforums.com/forums/pentax-dslr-discussion/26191-backfocus-frontfocus-k10d.html

I got an interesting test to determine weather my K10d back/front focusing. I somewhat loosely followed the instructions on this test and found out that my camera was Front Focusing by some degree. Knowing that May have not achieved 100% accuracy in the parameters of my test, I decided to simplify the procedure but taking a picture of the barcodes of TWO separate boxes, one of them being in front by the estimated distance ( about and 1.0-1.5") my previous test had indicated that the camera was front focusing. Sure enough though I focused on the BACK box, the front box was dead sharp, while the back one was slightly blury.

Damn! I was running in my mind about all that I now needed to do to get the camera serviced ... when I decided to test another lens.

Originally, I was using a 50mm prime f2.0 A-Series lens ( it's the only fast prime and its shallow DOF really alloead to see any BF/FF issues with the camera) At the same time I remember that a friend had told me that manual camera lenses aren't all that kosher with digital SLRs . I had dismissed that idea since she shoots with a Nikon and i really wasn't sure if it was brand thing) I decided to run BOTH tests again with my 18-55/ f3.5-5.6 kit DA-Series kit lens. I've never had any focus problems with this lens' AF, that I could notice...but then again , even at f 3.5 I just cant get that shallow of a DOF with that lens to accurately run the test.

OK, so the question is... do non DA lenses cause BF/FF issues in an of themselves, or if I found out that my camera was FF'ing with an A-series lens then it's doing the same with all lenses?

04-28-2008, 08:43 PM   #2
Veteran Member




Join Date: Mar 2008
Location: CT / NY
Photos: Gallery
Posts: 822
Something is not clear: how are you focusing the SMC-A lens? I actually have the same lens and I could hear the BEEP or just follow the focusing screen. I do not follow the BEEP.


I ask this, because from what I read about DSLR and AF (in general, not only Pentax) is that the problem is only with the AF... having this is mind I am not sure how you are having focusing problems with a manual lens.... unless you are counting on the BEEP.


Does that makes sense??
04-28-2008, 09:26 PM   #3
Forum Member




Join Date: Dec 2007
Location: Rockford, IL
Posts: 52
Original Poster
BBear,
The beep/ focus indicator "work" as plan.. I hear the beep ...shortly after (tho sometimes it takes some hunting when I am usining my manual lens) the green hexagon focus indactor goes on, and the picture snaps ( using the technique called "focus trapping") This using A-series lens, which is a lens I used to use with my K1000. However what is happening with this lens is that I get some front focusing. That is even though it says I am focused on somethingam actually focused about 1-2" in front. Essentially if I am using very shallow DOF I am totally off.

I guess I am following the beep because it's kinda hard to tell through the lenss if I am focused or not. I missed the split prism screen my old k1000 had.

My AF lenses either work fine or if they are not working then I can barely tell because the widest apperture I get in any of them is f3.5/4.5( at 50mm) so by this point i have such a deep DOF is difficult to test for back or front focusing.

I want to know if it's fomething with the actual K10d body that i have to have serviced or if digitals dont like the old manual lenses ( even though they "work" with each other)

Name:  IMGP2020.jpg
Views: 2568
Size:  36.4 KB

Name:  IMGP2017.jpg
Views: 2402
Size:  37.2 KB

Hopefully these samples will make clear what I mean. I could not take similar samples with my DA lenses because off their DEEP DOF. In other words at that distance between the boxes, they are BOTH sharp.

Last edited by dresden_phoenix; 04-28-2008 at 10:01 PM.
04-28-2008, 11:54 PM   #4
Banned




Join Date: Oct 2007
Location: Savannah, U.S./Baguio City, P.H.
Posts: 5,979
sorry to get off topic but how did your k1000 have a split prism focusing screen?

04-29-2008, 06:58 AM   #5
Veteran Member
jeffkrol's Avatar

Join Date: Sep 2006
Location: Wisconsin USA
Photos: Gallery
Posts: 8,435
QuoteOriginally posted by dresden_phoenix Quote

Attachment 11486

Attachment 11487

Hopefully these samples will make clear what I mean. I could not take similar samples with my DA lenses because off their DEEP DOF. In other words at that distance between the boxes, they are BOTH sharp.
If that is one shot, you are pretty close to centering both boxes and if you are using the center AF point you could be getting the wrong choice (AF point and brackets are not totally coinciding on many bodies).
Pretty sure the AF module is also larger than the spot....
So it could have just locked on the right one...
DOF is 12mm if you are accurate in your distance to the box, drops to 3mm by the time you get to a foot...
Not saying you don't have ff/ issue, just some thoughts.Online Depth of Field Calculator

Last edited by jeffkrol; 04-29-2008 at 07:09 AM.
04-29-2008, 07:51 AM   #6
Forum Member




Join Date: Dec 2007
Location: Rockford, IL
Posts: 52
Original Poster
Jeff,
I am using centerpoint AF. What do you mean by "AF point and brackets are not totally coinciding on many bodies"? I did the test several times last night. there was one ocassion with this lens that the photo came out as expected. Which weirded me out. You may have something there... but I dont understand the term "AF point and brackets"

I know (or at least think) that the other lenses i own dont show this because of their deeper DOF, which is why I cant test them this way and thus be able to know if this is a matter of the camera body or incompatibility of the lens to the camera.
04-29-2008, 07:52 AM   #7
Forum Member




Join Date: Dec 2007
Location: Rockford, IL
Posts: 52
Original Poster
And sorry, I meant microprism focusing screen, not split prism. Anyway, in the K1000 days that was very helpful .
04-29-2008, 07:54 AM   #8
Veteran Member




Join Date: Mar 2008
Location: CT / NY
Photos: Gallery
Posts: 822
Dresden

I think he is saying that the zoning you see in the focusing screen does not necessarily matches the focusing electronics in the camera.

for instance, if you are trying to do center AF, you'd normally center the subject right at the center of the focusing screen... he is saying that the circuitry could be offset. That what I understood from his statement.

04-29-2008, 07:56 AM   #9
Veteran Member




Join Date: Mar 2008
Location: CT / NY
Photos: Gallery
Posts: 822
QuoteOriginally posted by dresden_phoenix Quote
And sorry, I meant microprism focusing screen, not split prism. Anyway, in the K1000 days that was very helpful .

I think you already know you can easily change the focusing screen in the K10D. Pentax made it so easy as if they already knew people using older lenses would prefer the old style split screen.
04-29-2008, 09:12 AM   #10
Forum Member




Join Date: Dec 2007
Location: Rockford, IL
Posts: 52
Original Poster
Bbear,

Wouldnt that offcet of AF point sbe considered a defect in the camera tho?

The way I am reading what you are saying is that: though the camera "red square", the center-focus point indicator was in the middle of the box on the left, the actual AF point was on the box on the right. in other words, the camera focuses correctly, but it indicates where it's focusing wrong.
04-29-2008, 10:11 AM   #11
Veteran Member




Join Date: Mar 2008
Location: CT / NY
Photos: Gallery
Posts: 822
Assuming we are in the same page as jeffkrol, then it'd be a question of how much off the electronics from the brackets. If you read the Nikon AF Test Guide, it explains how the AF works and all.


But I still dont see how you are getting focus errors in manual mode.


another thing i just realized: you are using the A lens with AF-S mode... have u tried to use it under MANUAL FOCUS mode in the camera?


Later
04-29-2008, 11:37 AM   #12
Veteran Member
jeffkrol's Avatar

Join Date: Sep 2006
Location: Wisconsin USA
Photos: Gallery
Posts: 8,435
QuoteOriginally posted by dresden_phoenix Quote
Bbear,

Wouldnt that offcet of AF point sbe considered a defect in the camera tho?

The way I am reading what you are saying is that: though the camera "red square", the center-focus point indicator was in the middle of the box on the left, the actual AF point was on the box on the right. in other words, the camera focuses correctly, but it indicates where it's focusing wrong.
Defect is in the eye of the beholder. Actually I believe the AF module covers a greater area then the little box shows. also it can be slightly offset left or right up or down.
There are ways to check this:
Re: i think the AF area sucks: Pentax SLR Talk Forum: Digital Photography Review
the black dot test - again: Pentax SLR Talk Forum: Digital Photography Review
04-29-2008, 12:23 PM   #13
Forum Member




Join Date: Dec 2007
Location: Rockford, IL
Posts: 52
Original Poster
I am inclined to believe you are right, jeff. Alas, no simple fix for that. MAybe now that I know this I can compensate better. I will run some more tests tonight.
05-01-2008, 10:31 PM   #14
Forum Member




Join Date: Dec 2007
Location: Rockford, IL
Posts: 52
Original Poster
Jeffkrol,
you were right.

For the longest time I was thinking that where the red box lit up that was EXACTLY the point where the camera was focused on. With new mindset I took the same photos again, using center focus, this time taking into account that the focus would be the "point" of HIGHEST CONTRAST between the "( + )" rather than where the red box popped up. I haven't tested long distances. BUT for the 1-12' range it was DEAD ON 100% of the time, with BOTH my DSC-A series and DA-series lenses. Also Manually focusing or using AF-S mode worked equally well.

Some subjects were harder than others, of course. But I know that it's because some subject's point of highest contrast are harder to find than another's. Also... MIND THE SHADOWS!!!

It now also stands to reason why it's HARDER "hit focus" using wider lenses.. simply ... there is more STUFF between the "( + )" area thus more possibility to confuse the camera... but really not that much of a problem in MF.

THANK YOU ALL for all your help in helping me understand my camera and making it seem a bit more predictable.
05-02-2008, 04:57 AM   #15
Banned




Join Date: Oct 2007
Location: Savannah, U.S./Baguio City, P.H.
Posts: 5,979
QuoteOriginally posted by BBear Quote
I think you already know you can easily change the focusing screen in the K10D. Pentax made it so easy as if they already knew people using older lenses would prefer the old style split screen.
he was talking about the K1000 not the K10D.
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!
a-series, camera, dslr, front, issues, kit, lens, lenses, photography, test
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Cokin P Series, Z-Pro Series and quality filters max11 Pentax Camera and Field Accessories 2 06-08-2009 04:00 PM
At Combo's request Pentax will make a limited white series K-m+kit lens RaduA Pentax News and Rumors 9 12-25-2008 05:14 AM
Bogen 190 series and 055 series - advice needed geauxpez Pentax Camera and Field Accessories 9 12-16-2008 01:34 PM
Can I use K and M lenses on my PENTAX DSLR (K-series, *istD-series)? Ole Pentax DSLR and Camera Articles 7 12-11-2006 11:29 AM



All times are GMT -7. The time now is 09:39 AM. | 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