Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
10-31-2010, 10:57 AM   #16
Veteran Member




Join Date: May 2009
Location: Twin Cities, MN
Posts: 2,869
QuoteOriginally posted by JohnBee Quote
Wow that's somewhat disappointing...
I was really hoping to use live-view AF to overcome slower lenses with my AF TC rather then conventional AF, but now I'm not sure its going to work at all...

Also can you explain the difference between Phase and contrast AF?
John, I think you are going to be happy. I went to national camera and managed to find a quantaray 2x tc with af. The metered scene for testing (using my 55-300 at 100mm) is 1/15th f5.6 and iso6400. Center point phase detect the camera won't even bother. Liveview finds proper focus in under 3 seconds - slow yes (on a relatively slow lens af-wise) but it is getting it right.

One other note, this is based on resetting to minimum focus on each attempt. It is occasionally not finding focus, but the tc is pretty aged as well (in other words this is probably about the worst lens/tc combo that will do af). Also, if the focus is reasonably close it is quite a bit faster.

I am not going to promise any video test, but those are my impressions after about 20 minutes of indoor testing.


Last edited by pxpaulx; 10-31-2010 at 11:04 AM.
10-31-2010, 06:10 PM   #17
Veteran Member




Join Date: Jun 2009
Photos: Albums
Posts: 1,679
I have a question about the AF. I know the focus points are either cross or a "bar" (vertical) type AF point. My question is I haven't found info on the sensitivity of each AF point and how many cross type there are. I ask because I am curious what influence the sensitivity of the points will have for the two distinct AF modes, especially in Live View. Also would mapping the actual location of each AF point on your given body help to improve issues which your particular body has help out to get better and more consistent results?

I am loathe to spend time mapping an AF point's actually position vs. where the small box says it is in general. But if AF accuracy is really important for your uses I could see the time as being well spent as every body will have variations as to the true position of the points. And I can't help but wonder if that could be a factor here when the different AF modes does not deliver as hoped?
10-31-2010, 06:18 PM   #18
Forum Member




Join Date: Sep 2010
Location: Sofia,Bulgaria.
Posts: 56
За мен също е интересно каква е чувствителността на АФ точките на К-5?
10-31-2010, 06:26 PM   #19
Veteran Member




Join Date: Jun 2009
Photos: Albums
Posts: 1,679
QuoteOriginally posted by pefoto01 Quote
За мен също е интересно каква е чувствителността на АФ точките на К-5?
Just in case you haven't read a lot about how AF points work in general and how they can be pretty far from where the viewfinder indicates, here is a page that while it doesn't use Pentax as the body, it offers a nice explanation of AF points and how they really work.

Andre's Blog • Cross type AF points in EOS 7D

10-31-2010, 06:35 PM   #20
Veteran Member




Join Date: May 2009
Location: Twin Cities, MN
Posts: 2,869
QuoteOriginally posted by brecklundin Quote
I have a question about the AF. I know the focus points are either cross or a "bar" (vertical) type AF point. My question is I haven't found info on the sensitivity of each AF point and how many cross type there are. I ask because I am curious what influence the sensitivity of the points will have for the two distinct AF modes, especially in Live View. Also would mapping the actual location of each AF point on your given body help to improve issues which your particular body has help out to get better and more consistent results?

I am loathe to spend time mapping an AF point's actually position vs. where the small box says it is in general. But if AF accuracy is really important for your uses I could see the time as being well spent as every body will have variations as to the true position of the points. And I can't help but wonder if that could be a factor here when the different AF modes does not deliver as hoped?
If you will go back and read the wiki regarding phase and contrast af I linked to, you'll note that contrast detect af is conducted using contrast within the scene as shown on the sensor itself during liveview. In other words it does not have anything to do with the phase detect autofocus array. With the contrast detect, you are able to select any point on the liveview scene (the square shown in the video can be moved all over the scene, with the exception of the far edges - a border area about the size of the square itself).
10-31-2010, 06:43 PM   #21
Veteran Member




Join Date: Jun 2009
Photos: Albums
Posts: 1,679
QuoteOriginally posted by pxpaulx Quote
If you will go back and read the wiki regarding phase and contrast af I linked to, you'll note that contrast detect af is conducted using contrast within the scene as shown on the sensor itself during liveview. In other words it does not have anything to do with the phase detect autofocus array. With the contrast detect, you are able to select any point on the liveview scene (the square shown in the video can be moved all over the scene, with the exception of the far edges - a border area about the size of the square itself).
ahhhh...OK, I get it now, for all intents and purposes the AF points (the sensor array might be the correct term but some might not make the connection to the set of AF elements being an array of info gathering sites in the camera) don't exist when using Live View "contrast AF mode". I kinda just glossed over the info in the Wiki link so thanks for the patience to explain it again.
10-31-2010, 07:14 PM   #22
Veteran Member




Join Date: May 2009
Location: Twin Cities, MN
Posts: 2,869
Glad I could help! It makes sense once you give it a read over...but I still have a hard time explaining the difference myself! I am not a technological expert on the subject at all, but they are definitely two different beasts. From what I have found so far, the K5 is a very big step up in terms of contrast detect AF over its predecessor. Basically for the first time it is delving into the realm of being a viable alternative. Each of the systems have their own strengths and weaknesses (i.e. the brief teleconverter testing I noted above).
10-31-2010, 08:37 PM   #23
Veteran Member




Join Date: Jun 2009
Photos: Albums
Posts: 1,679
After reading the Wiki summary I see why it can be difficult to express the differences in words for the layperson. But the info on the page also is written in a fashion that allowed me to understand the real differences and once I got that part the rest makes total sense.

I have often wondered why camera makers have abandon the laser assisted contrast AF as some of the early-ish Sony digitals (can't call them PnS's really) used. The DSC-F707 and DSC-F717 had that feature and seemed to do a super job even in total darkness. My backup is an old Sony DSC-S70 which also can focus pretty much in total darkness but it supposedly uses a sonar AF assist, still it does a good job in essentially no light.

And that exhausts my knowledge of how AF works...but thanks to your info I have a much improved understanding of the current tech used in the DSLR's.

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!
af, camera, dslr, k-5, k-5 ii, k-5 iis, k5, liveview, pentax k-5, video
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
K-x LiveView: Is there a way to keep the mirror up? RolloR Pentax DSLR Discussion 2 06-06-2010 09:23 AM
KX Liveview Question Ira Pentax DSLR Discussion 4 02-17-2010 11:21 AM
K7 not focusing on LiveView onairda Pentax DSLR Discussion 9 09-03-2009 10:53 PM
K-7 Liveview report ManuH Pentax DSLR Discussion 2 07-08-2009 09:57 AM
LiveView for Macro? TimB Photographic Technique 8 10-31-2008 02:17 PM



All times are GMT -7. The time now is 09:07 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