Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
12-19-2008, 09:55 AM   #1
Senior Member




Join Date: Dec 2008
Location: Quebec
Photos: Gallery | Albums
Posts: 210
Why focus varies from one lens to another

Hello fellow Pentaxians,

Although the title is pretty explicit, let me explain my question. I own a few Pentax lens. A few days ago, I decided to test focus using Yvon Bourque's chart. To my surprise, all my lens are spot on, except one. My very much appreciated DA35 has a 3mm FF problem. So my question to all the experts on this forum: Could anyone explain to me how come all my lenses are spot on and one suffers from FF? Should I return my DA35 to Pentax?

Thanks for your advices.

Sylvain

12-19-2008, 11:43 AM   #2
Veteran Member
Torphoto's Avatar

Join Date: Mar 2008
Location: Trinidad W.I.
Photos: Gallery
Posts: 620
It's called sample variation, when they test the lens what ever rig they use can be a few mm off from the next one or the one they were using before. 3mm FF is minor as long as the lens does what it should and isn't FF'ing shots out of focus, try adjusting it in the firmware if you can.
12-19-2008, 11:45 AM   #3
Veteran Member
nostatic's Avatar

Join Date: Feb 2008
Location: socal
Photos: Gallery
Posts: 1,576
If you don't shoot pictures of focus charts, odds are your problem will be solved
12-19-2008, 11:46 AM   #4
Veteran Member
farfisa's Avatar

Join Date: Nov 2008
Location: Toronto, Canada
Photos: Gallery
Posts: 1,274
QuoteOriginally posted by SylBer Quote
Hello fellow Pentaxians,

Although the title is pretty explicit, let me explain my question. I own a few Pentax lens. A few days ago, I decided to test focus using Yvon Bourque's chart. To my surprise, all my lens are spot on, except one. My very much appreciated DA35 has a 3mm FF problem. So my question to all the experts on this forum: Could anyone explain to me how come all my lenses are spot on and one suffers from FF? Should I return my DA35 to Pentax?

Thanks for your advices.

Sylvain
Did you use Yvon's separate Macro chart for the DA35?

12-19-2008, 12:01 PM   #5
Veteran Member
Miserere's Avatar

Join Date: Sep 2007
Location: Boston
Photos: Gallery
Posts: 1,994
QuoteOriginally posted by nostatic Quote
If you don't shoot pictures of focus charts, odds are your problem will be solved
While this is normally the case, this is a macro lens, and front-focusing can be a huge problem at macro distances.
12-19-2008, 12:25 PM   #6
Veteran Member
Buddha Jones's Avatar

Join Date: Sep 2006
Location: Charlotte, NC
Photos: Gallery
Posts: 2,591
QuoteQuote:
QuoteOriginally posted by nostatic Quote
If you don't shoot pictures of focus charts, odds are your problem will be solved
QuoteOriginally posted by Miserere Quote
While this is normally the case, this is a macro lens, and front-focusing can be a huge problem at macro distances.
An attempt at humor foiled by logic.
12-19-2008, 01:39 PM   #7
Senior Member




Join Date: Dec 2008
Location: Quebec
Photos: Gallery | Albums
Posts: 210
Original Poster
Yes, I did use the appropriate chart. As far as macro is concerned, I can always focus manually. My point was, if all my other lens are correct, this probably means my K10D is not affected by the BF/FF problems reported on different forums. Is it possible for Pentax to fix this lens problem? If you were me, would you send it back?

Thanks guys.
12-19-2008, 02:06 PM   #8
Veteran Member
nostatic's Avatar

Join Date: Feb 2008
Location: socal
Photos: Gallery
Posts: 1,576
QuoteOriginally posted by Buddha Jones Quote
An attempt at humor foiled by logic.
bah humbug!

12-19-2008, 02:29 PM   #9
Senior Moderator
Loyal Site Supporter
Parallax's Avatar

Join Date: Apr 2008
Location: South Dakota
Photos: Gallery
Posts: 15,103
QuoteOriginally posted by Buddha Jones Quote
An attempt at humor foiled by logic.
Made me laugh.
01-09-2009, 05:43 AM   #10
Pentaxian
Class A's Avatar

Join Date: Aug 2008
Location: Wellington, New Zealand
Posts: 8,934
QuoteOriginally posted by Torphoto Quote
It's called sample variation, when they test the lens what ever rig they use can be a few mm off from the next one or the one they were using before.
The body does the AF, not the lens. If the body works well with a number of lenses, how can one lens be off?
Even if the lens is odd in some respect, the feedback loop in the AF mechanisms should keep adjusting until the subject is in focus.

Apparently, individual lenses can throw off the AF system, but as to why exactly is one of the great lens mysteries to me.
01-09-2009, 09:12 AM   #11
Veteran Member
gkopeliadis's Avatar

Join Date: Mar 2008
Location: ATHENS, GREECE
Posts: 311
QuoteOriginally posted by nostatic Quote
If you don't shoot pictures of focus charts, odds are your problem will be solved
concealed ... not solved at all
01-09-2009, 10:00 AM   #12
Igilligan
Guest




QuoteOriginally posted by nostatic Quote
If you don't shoot pictures of focus charts, odds are your problem will be solved

Well that may be true, unless you shoot faces... then the beautiful eye you think is in focus become a blur and the tip of the nose is so sharp it bleeds...

That is what I am getting with a couple of my lenses on the K20... and you know I love shootin' those close in face shots..

Humor and logic gets tossed when I am standing on the ledge wanting to jump... haha hehe
01-09-2009, 11:46 AM   #13
Loyal Site Supporter
Canada_Rockies's Avatar

Join Date: Nov 2007
Location: Sparwood, BC, Canada
Photos: Gallery | Albums
Posts: 9,134
QuoteOriginally posted by Class A Quote
The body does the AF, not the lens. If the body works well with a number of lenses, how can one lens be off?
Even if the lens is odd in some respect, the feedback loop in the AF mechanisms should keep adjusting until the subject is in focus.

Apparently, individual lenses can throw off the AF system, but as to why exactly is one of the great lens mysteries to me.
Lighting can throw it off as well. It seems, from some of my reading, that tungsten lighting does not focus the same as daylight. I suspect that colour temperature will affect focus somewhat. Lenses [used to] have focusing marks for infrared for just this problem, but at a greater difference in frequency, of course. I suspect that tungsten would require a technical correction to the focus, and the detector might be thrown off.
01-09-2009, 12:20 PM   #14
Veteran Member
alohadave's Avatar

Join Date: Jan 2008
Location: Quincy, MA
Photos: Gallery | Albums
Posts: 2,024
QuoteOriginally posted by Igilligan Quote
Well that may be true, unless you shoot faces... then the beautiful eye you think is in focus become a blur and the tip of the nose is so sharp it bleeds...

That is what I am getting with a couple of my lenses on the K20... and you know I love shootin' those close in face shots..

Humor and logic gets tossed when I am standing on the ledge wanting to jump... haha hehe

Last time I checked, the tip of my nose is a lot further from my eye than 3mm.
01-09-2009, 12:52 PM   #15
Igilligan
Guest




Think angled profile....

Not every face shot has to be straight on...

and my nose is a LOT more than 3mm, but I am turning and its getting closer...........
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!
da35, ff, focus, k-mount, lens, pentax, pentax lens, question, slr lens, spot
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Can a manual-focus lens have back focus problems? PocketPixels Pentax DSLR Discussion 33 02-13-2011 05:37 AM
Suggestion How about adding Focus Throw to lens details in the Lens database? brecklundin Site Suggestions and Help 2 12-08-2009 05:49 PM
Front focus/ back focus on Manual lens. Possible? WangJianWei Troubleshooting and Beginner Help 6 04-20-2009 07:50 PM
Colour varies between applications nobbsie Digital Processing, Software, and Printing 0 09-23-2008 04:05 AM



All times are GMT -7. The time now is 09:25 AM. | 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