Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
03-23-2011, 05:04 AM   #1
New Member




Join Date: Mar 2011
Location: Denmark
Posts: 6
Is it just me? - FF problem

I received my k-r camera a month ago (replacement for my k-x which were stolen) and have been very satisfied with the images so far.

The strange thing is that I am not experiencing any FF problems in any of my images taken in artificial light or tungsten light. Actually I wasn’t aware about the problem before I read about it in this forum a few days ago.

If the problem is caused by a software bug which can be eliminated trough a firmware update, then it should be found on all k-r cameras!

So is it just me who is not critical enough then I examine my images og is there anybody else who have a k-r camera which do not suffer from heavy FF problems?

03-23-2011, 05:12 AM   #2
Veteran Member
Verglace's Avatar

Join Date: Mar 2011
Posts: 468
This is interesting, if it is a physical problem then maybe that is why there is no firmware update available. Can you check your setting menu->c->3->21 AF Fine Adjustment check what settings that is set to?
03-23-2011, 05:28 AM   #3
New Member




Join Date: Mar 2011
Location: Denmark
Posts: 6
Original Poster
AF ajustment is set to 0.

I have not made any dedicated focus tests with test sheets, it is only my impression based the family photos I have taken so far with the kit lens and a Tamron 18 - 200.
03-23-2011, 05:48 AM   #4
Inactive Account




Join Date: Sep 2008
Location: Gold Coast, Qld
Photos: Gallery
Posts: 95
I appear to have no problems either with any lens. My AF adjustment is on 1. I think most of my settings are on 1 as I have never touched them.
I have done the focus chart tests after I got worried by all the bad publicity and mine is fine. No adjustment needed. I even got a local Pro that I know, who uses Canon gear to check it out for me to make sure I was looking at it right and he agreed - no FF on mine.
If an update comes out to FIX this problem, what are the odds of it screwing up my camera ?

03-23-2011, 06:19 AM - 1 Like   #5
Veteran Member
jolepp's Avatar

Join Date: Oct 2010
Location: Finland
Photos: Albums
Posts: 3,196
Some related musings (or thinking aloud ) ...

One aspect of BF/FF problems is that the (copy of the) lens used affects it: the very existence of lens (copy) specific compensation settings of the fancier DLSRs are proof enough of this IMO. The underlying reason is shrouded in mystery though (or at least I have not seen a convincing explanation ... probably a combination of a multitude of factors with a complex interaction which would make the explanation too hairy to be convincing ). The root cause (or one of them at least ) of BF/FF is different wavelengths of light having different refractive indexes (or propagation speed in mediums other than vacuum such as the optical glass); this is why/how a glass prism produces a spectrum of light visible to the naked eye. Lens makers put in much effort to compensate by clever use of materials with different refractive indexes and this is where things start to get seriously complicated . That is, the good job that is apparenty done in getting rid of chromatic aberrations in the visible spectrum might come back to bite us here (?).

BF/FF stated in another way is that the focused image the AF sensor "sees" is different than what the image sensor "sees". A number of factors is at play, among them different spectral sensitivity of the AF sensor light detectors to the image sensor light detectors, the AF sensor "seeing" only a strip of the image (or a narrow section of the scene), physical mismatch of the AF/image sensor planes, and mechanical limits to the precision/repeatability adjusting the focus mechanism (as in a bit of simple mechanical play and inertia affecting things).

I suppose the firmaware / AF algorithm can compensate the effects of essentially physical imperfections to some degree, most likely at the cost of AF speed. Say, a simple, fast algorithm might do just fine when everything happens to be in the middle of its respective tolerance, whereas some other combinations might be overcome by tweaking the algorithm to compensate which is likely to require more data being collected as in allowing for longer integration times and more readings of the AF sensor while adjusting the focus mechanism. An outright bug (say, register/variable overflow) in the AF algorithm implementation can throw things out of whack, but it can also be about the algorithm being in need of improvement / tweaking: with this in mind the line between a physical / software defect becomes blurred.

Image sensors having gotten ever more less noisy has pushed the practical use of AF into lower levels of light where this is difficult to do / new, also, the ready ability to pixel peep also means the ability to see focus errors much more clearly.

Last edited by jolepp; 03-23-2011 at 06:31 AM.
03-23-2011, 06:37 AM   #6
Veteran Member
Verglace's Avatar

Join Date: Mar 2011
Posts: 468
Hrmm, thats interesting. Come to think of It i've been using the kit lens in all tungsten light situations so far. My 35mm prime should arrive tomorrow, I will test it on that, and also on the Tamron. If it's just the kit lens, it's a good excuse to buy that 18-135mm lens!
03-23-2011, 12:54 PM   #7
Veteran Member
awo425's Avatar

Join Date: Jan 2008
Location: NYC, USA
Posts: 481
Try it with a prime or F2.8 lens, you will see a difference
03-23-2011, 04:18 PM   #8
Senior Member




Join Date: Sep 2006
Location: Vienna, Austria
Photos: Gallery
Posts: 112
The K-r's unhealthy FF is well documented

You'll find hundreds and thousands postings about this issue. That is the reason why I returned my K-r. As a starting point:
K-r FF patch on the way from Pentex: Pentax SLR Talk Forum: Digital Photography Review

03-24-2011, 04:52 AM   #9
Senior Member




Join Date: Mar 2010
Posts: 230
Sorry for a stupid question but has anyone tried using Auto AF (5 or 11) points instead of a fixed selected AF point when testing for Tungsten FF?
03-24-2011, 06:13 AM   #10
Veteran Member
jolepp's Avatar

Join Date: Oct 2010
Location: Finland
Photos: Albums
Posts: 3,196
I suppose there are two issues (at least ) with testing 5/11 point modes:

1) A test target with which FF/BF will be readily visible is iffy to come by

2) In 5/11 point mode results depend on happenstance; there is a fair change that what you'd like is in focus but also that it is not. Knowing the algorithm used would help, but AFAIK it is not documented anywhere (having to figure out what/why it might do in a particular scene might defeat the purpose of automation though )

I suppose using all the points for a flat target might give better results if there was a "majority vote" between the sensors or somesuch, but then most of the scenes are not like that which makes testing somewhat pointless, not that the results might not be interesting and potentially useful while figuring out the mystery that (Pentax) AF would appear to be.

With the K-5 1.03 FW this mystery would seem to be of less practical consequence, but I suppose the potential of discovering your AF lens collection has ceased to work in an optimal fashion with a new body is still there. Sending everything in for adjustment and potentially having to pay for that does not sound like an appealing proposition to me in case someone wonders about that: I'd rather have something that works out of the box(es), also I'd like to the key proposition of interchangeable lenses to hold.
04-01-2011, 08:25 AM   #11
Site Supporter




Join Date: Oct 2009
Location: Michigan
Photos: Gallery
Posts: 87
I have had my K-r for three weeks shooting in all kinds of light with no focus problems at all. I have used several lenses, including Sigma 50-500 EX DG, Pentax 55-300, Pentax 80-320, Pentax 16-45, Pentax 35-70 F 3.5-4.5, and pentax 50-135. Have yet to try my others. The other day I got some really good shots with the 50-500 hand held. Absolutely no auto focus issues. I almost always use the view finder. I change my focus points to best serve what I am photographing. My dial settings I use, 70% of the time are aperture priority mode, 20% manual mode, and 10% others. I bought this camera as a low light backup to my K20, but I find myself using the K-r more than I thought I would. Bottom line? Much better camera than it is sometimes getting credit for.
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!
camera, ff, images, k-r, kr, light, pentax k-r
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Is this a front focusing camera problem or lens problem? Lens tests Metalwizards Pentax K-r 15 03-06-2011 01:24 AM
K-5 battery problem? camera problem? user problem? imtheguy Pentax K-5 39 11-03-2010 06:02 PM
Anyone have this problem? dankuno Pentax DSLR Discussion 9 12-10-2009 08:00 AM
Need help with problem dankuno Troubleshooting and Beginner Help 11 08-17-2009 02:09 AM
Card read problem K20d. Have you had this problem? rsi1986 Pentax DSLR Discussion 8 12-27-2008 05:25 AM



All times are GMT -7. The time now is 07:41 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