Originally posted by kp0c I'm gonna guess you have ruled out the motion blur possibility. 50mm at 1.2 is an insanely shallow depth of field for relatively close subject. Any movement on your part after focus confirmation and before the picture will make the picture blurry. Have you tried with a tripod, just to make so test?
Also, your K-x has live view, so you could try using the magnified view to focus and take the picture, just to see what sort of result your get.
It could well be that the Tungsten lighting messes up your camera's focus calculation, but at 1.2 - 1.4, the margin of error is so small that "user error" cannot be ruled out entirely.
Good luck!
Thank you for posting a reply
The recommended shutter speed I got was 1/125 at iso 800 so I guess i didnt require a tripod. Plus the SR in pentax bodies is good upto 1/15 shutter speed (atleast for me when I hold the camera as still as possible)
K-x live view with magnification is difficult to use handheld plus the live view image is a downscaled version of the sensor's actual resolution and creates false edges which look sharp but when clicked the image appears a bit soft
Its possible the white balancing under tungsten lighting might screw up the camera's focus. will look into it and change white balance and see if it affects focus confirmation
---------- Post added 09-18-14 at 12:35 PM ----------
Originally posted by jatrax The k-x will have three separate focusing systems:
1) The viewfinder AF which also controls the AF confirm light, which uses PDAF
2) The LCD focusing which is independent of the viewfinder system completely and uses CDAF
3) The manual focusing system that shows an image on the focusing screen and allows you to adjust the focus until it looks correct
Changing the focusing screen may improve manual focus as it is rendered on the focusing screen, it has nothing to do with the AF confirm light or either AF system. In some cases, depending on the screen, it may actually make the view darker though most screens do not change things much. I used an after market focusing screen in my k-x for years.
Part of the problem is that you are perhaps relying on the AF confirm light which is not accurate below perhaps f/4. The AF light will come on if the focus is good enough for f/4 but if you are at f/1.4 the depth of focus is much smaller so what is in focus may not be what you intended. I have had some success using the 'edge' of the AF confirm light, meaning that near to far edge or far to near edge may result in consistent focus, whereas the center of the confirm range may no. This will vary depending on lens of course.
Thank you for posting a reply
Its interesting to know the af system is designed for f4 but I must mention when I use the da 50mm f1.8 the af works fine and I have managed to get sharp results in relatively low light conditions
so changing a focusing screen as far as focus confirmation is concerned wont have much of a benefit, thanks for pointing that out.
Can you please explain a bit more about the edge method?
---------- Post added 09-18-14 at 12:42 PM ----------
Originally posted by micromacro I can say about K200D only. If you take pictures in twilight or so, focus confirmation may work properly, but you may not see where exactly it focuses. And even bright object seems bright enough, still, you can not see clearly. I've been tricked that way, even with magnifying viewfinder eyepiece.
Or with wide open it's shallow DOF. Or even you think your speed is fast enough, it's not, even with shake reduction.
Anyway, for K200 in twilight with manual focus lens tripod must have, imo, since ISO higher than 400 number usually is not good idea for that camera.
Thank you for posting a reply
I have a k200d body and apart from higher megapixel and better af it more or less shares same features as the k100d
anyway same problem while trying to shoot in low light
I have tried shooting with a tripod and its same under f1.2 (incase u assumed the focusing was affected due to shallow depth of field and handheld shake)
---------- Post added 09-18-14 at 12:50 PM ----------
Originally posted by stevebrot The title of this thread holds the key. Focus confirm uses the AF system to indicate point of focus and unfortunately there are limits to the focus sensitivity (ability to detect an out-of-focus condition) for the PDAF sensors. The PDAF sensors on your cameras have the same sensitivity at f/5.6 as with your fastest lenses.
What that translates into is a high probability of missed focus when shooting at wider apertures.
As noted above, you have a couple of options for fine focus with faster lenses:
- Magnified live view using focus peaking (newest bodies only)
- Viewfinder magnifier using the stock focus screen. Some users on this site have reported good success with traditional manual focus by simply magnifying the viewfinder image.
- Switching to an aftermarket focus screen having greater focus sensitivity and/or focus aids (split-image or microprism)
In regards to the stock focus screen...It is nice and bright, but unfortunately has focus sensitivity that is not much better than the PDAF system. Estimates indicate a limit of about f/4. A high sensitivity matte field (e.g. Canon-derived S-type screen) or a split-image viewfinder aide will provide sensitivity adequate for your M 50/1.2.*
An aftermarket screen was my choice several years ago when I could not get acceptable results from any of my faster lenses. I have not regretted that choice, though there were trade-offs. Potential issues include loss of spot metering (split-image types), other metering issues, and calibration (shim) problems. Often, the stock screen calibration requires no changes. If adjustment to the shims is needed, it can be tedious.
Good luck.
Steve
* The most popular screens on this site are the Type-S from focusingscreen.com, the KatzEye screen, and products from various eBay vendors.
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Its quite possible due to the focus sensitivity on the pdaf sensor towards f5.6 might be reason why fast primes might not be focusing accurately
The stock screen which comes along with the camera bodies have microprisms which ensure to a certain extent even narrow aperture lenses appear bright in thye viewfinder and when you mount a fast prime the viewfinder displays dof of lens at an aperture of f3.5 or something close to that. I could see this when the bokeh of the f1.2 appears very different when seen thru the viewfinder and when actually clicked
I have tried a cheap chinese viewfinder magnifier attachment but hasnt solved my problem
was planning on going for a split prism screen or the more expensive katzeye but there is still the issue of the viewfinder view still been small for aps-c bodies as compared to film camera bodies which had larger pentaprisms and viewfinder and made manual focusing a breeze
---------- Post added 09-18-14 at 12:51 PM ----------
Originally posted by rawr The Pentax O-ME53 1.2X magnifying eyepiece (or similar magnifying eyepieces like the nice
Tenpa 1.36X, and others) are indeed viable options. I'd even consider them option 1, due to their ease of installation and use.
Thank you for posting a reply
will look into this item certainly
---------- Post added 09-18-14 at 12:55 PM ----------
Originally posted by ScooterMaxi Jim The universal 1.3x magnifier system also is very good - quality multi-coatings -
1 3X Magnifier View Finder Eyecup for Canon Nikon Pentax Olympus Sony DSLR | eBay.
Some of the newer cameras (K5ii/s and K3) have advanced AF precision that is pretty good for f/2-2.8. The older cameras such as the ones you have listed require your talents to focus correctly manually.
Changing focus screens might help in low light, but has a trade-off in normal light - and might degrade exposure consistency. Its a bit of a crap shoot and can be rather expensive.
thank you for posting a reply
i am considering trying out that one and hope and hope its not the same as the chinese one i bought sometime back
not planning on going for the new models as money is limited
u r right it takes talent and skill to get precise focus using manual lenses on older pentax aps-c bodies
i have considered changing focusing screen with a split prism screen but the viewfinder is still small and I think I will have trouble viewing if the prism display in the viewfinder has fully turned into sharp focus as compared to older film bodies with split prisms which were easy to view at
---------- Post added 09-18-14 at 12:59 PM ----------
Originally posted by Just1MoreDave It is pretty easy to exceed the Ev limits of the AF sensors. The K100DS AF only works down to Ev 0. At its base ISO of 200, that's 0.5 sec at f1.4, a bit of a risk for handheld shots but I might try it. The other cameras go to Ev -1. That might be the problem.
I prefer the k100d's sensor (ccd) compared to the new cmos sensors on pentax bodies. One thing is the good highlight recovery and 'film like' output you get on the k100d's sensor while the new cmos sensors give out a more digital like look to the pic. Ofcourse under high isos the cmos sensors have a major edge but I rarely go above iso 800 so not an issue for me
i think its very hard to get a sharp non blurry pic at 0.5 second with the k100d. The least I have managed to go is 1/15 (after many tries).