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02-09-2011, 08:23 PM - 1 Like   #1
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Focus correct with Live view, but not through the viewfinder?

I'm shooting a 35mm LTD macro.

I've been starting to wonder why I keep ending up with blurry pictures of people when I have center focus on, I focus directly on their face(usually on an eye) and end up with bad results. I thought it was me screwing up somehow.
Playing around with it in other ways, it seems to give me great shots still really close up, when I zoom it it's still crisp, but at longer distances it just sucks.
I've been able to recover somewhat with sharpening, but it still isn't good.
I noticed that if I use Live View, I get a consistently good focus.

Is this a sign that I should use one of the focus adjustment charts?

It is spoiling some otherwise really good shots.




This one came out ok after a lot of sharpening and fiddling around, but I focused on her right eye, and it's clearly not focused there.

most of the others are way worse, like this, consistently.



Is this just me aiming badly, or could this be an actual issue with the camera? It seems to me that is it too consistent, I have it set to always center focus, but I'm frequently getting the background in focus when I aim at people's faces.
Set to full auto focus I tend to get slightly better results, but still not what I'd call crisp by any stretch of the imagination, except for very close up shots.

02-09-2011, 08:44 PM   #2
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I don't know if this helps, but I had a similar problem with a DSLR. It shot fine with any of my zoom lenses, but as soon as I put on my 50mm lens the focus would always be slighty out. Out of frustration I called the manufacturer and they asked me to send it in. They recalibrated the camera and no more problems. The amazing thing was they did it without the lens, all they wanted me to send was the body.

No explanation how they did it, but there you are.
02-09-2011, 08:55 PM   #3
gtl
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Are you using a KR or a K5?

https://www.pentaxforums.com/forums/pentax-k-5-forum/128562-relevant-news-re-...-light-33.html
02-09-2011, 09:27 PM   #4
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Unfortunately you stripped the EXIF data out of the pics, but I suspect the cause of your blurry images.

Are you shooting on green auto or Av? It sure looks like it because to me the problem looks like the shutter speed is far too slow. In the first pic nothing is sharp, likely camera shake from too slow shutter. In the second everything is sharp except subjects head, likely subject movement caused by again, too slow shutter speed.

This is a know "feature" of the Pentax cameras, when they decide to use the flash in auto mode, instead of choosing something sensible like 1/100 or so, it seems to pick 1/20 or so which makes getting a sharp image almost impossible. In Av mode the camera will set shutter based on ambient, again resulting in too slow shutter speed.

The solution is "easy", never use flash (when intended to be the key light as opposed to fill) in auto or Av mode, only in "Tv" mode or much better, in full manual mode. That's pretty well the only time I use manual mode, I find it pretty essential for good flash exposure. I also invested in an external flash, makes a huge difference and allows me to take pictures with a flash that don't look like I used the flash at all.


Last edited by twitch; 02-09-2011 at 09:43 PM.
02-10-2011, 02:01 AM   #5
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Hi,
The first picture looks really out of focus, the second one looks bit mixed - face looks blurred because of motion, but focus is more on background (lamps and Santa look more sharp). I have the same AF inconstancy with DA 35 Ltd in low light (I shoot K-x) with both FF and BF on static subjects. It happens more for further distance, and sometimes remains after refocus. I think it is more because of camera as in a daylight everything is fine, and in low light defocus varies. IMHO every camera and lens combination has some AF issues under low light, but shooting with FA 50 at f 2.8 in low light I get more constant and better results. Now I use it mainly with external flash, in M set at f 5.6 - 8.0, and prefer rise ISO for distance. After one year and about 10.000 shots with DA 35ltd I find it as terrific daylight lens, but not so for low light. Yes, you can adjust focus manually, but I still find it very difficult because of short throw for further distance and a bit dim K-x viewfinder.

A.
02-10-2011, 02:07 AM   #6
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Seriously, this is by far most likely a shutter speed issue until proven otherwise.
02-10-2011, 03:30 AM   #7
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Since your camera has live view this is, I think, the best way to check whether you need a focus adjustment.

AF microadjustment for the 1Ds mark III, 1D Mk3, 5D Mk2, 7D
02-10-2011, 03:52 AM   #8
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some articles regarding sharpness and factors that can have an impact

LensRentals.com - "This lens is soft" and other FACTS
Focus Fallibility: Lens Test Fallacies - SLRgear.com!

02-10-2011, 04:04 AM   #9
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you`ve probably got frontocus/backfocus problem, I discovered this with my K-x when I got the 35/2,8 ltd too, now I have it set to -60 mikrometers due to previous backfocus issue and it works with all lenses I have to date
another helpful link (hopefully) RiceHigh's Pentax Blog: K-x Debug Mode Tutorial - AF Adjustment
02-10-2011, 03:18 PM   #10
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The diopter wouldn't do that would it?
The first one, I can't tell. Nothing appears to be focused.
The second shot is sharp...except for the subject. Maybe motion blur but it looks more like it's far sited.
02-11-2011, 07:50 AM   #11
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That's an interesting point, does the Diopter affect the focusing mechanisms in the camera?(mine is set to the farthest right setting, as I am pretty nearsighted)

I don't think it's motion blur, it's too consistent throughout ALL of my photographs of people, even synched 180/flash is showing the same issues, the wall behind will be in focus, the subject is clearly out of focus.

Does live view use AF sensors, or contrast focusing? It is perfectly in focus, which is making me suspect something might be wrong with the AF sensor itself. Happens in daylight, artificial light, everywhere.


I'm always shooting manual mode, center focus, center meter, except if I'm busy at the same time, then I tend to shoot P mode, and control my aperture, let shutter speed do what it needs to to adjust. I've tried it shooting at walls to, focus point is always behind where I aimed.

I'm shooting a K7 with 35mm LTD Macro.
I WAS getting razor sharp images before, even down to 1/15 handheld.
I use the AF button separately from the shutter button, so I can get SR started before focusing by half pressing it, allowing me to shoot as soon as I get a lock.

I've tested it over and over, and my focus is never actually on the point I focus on.

Last edited by JGB; 02-11-2011 at 07:56 AM.
02-11-2011, 08:48 AM   #12
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QuoteOriginally posted by JGB Quote
Does live view use AF sensors, or contrast focusing? It is perfectly in focus, which is making me suspect something might be wrong with the AF sensor itself. Happens in daylight, artificial light, everywhere.

I'm shooting a K7 with 35mm LTD Macro.
I WAS getting razor sharp images before, even down to 1/15 handheld.
I use the AF button separately from the shutter button, so I can get SR started before focusing by half pressing it, allowing me to shoot as soon as I get a lock.
First question answered:
- LifeView uses the contrast information taken off the sensor.
- "Normal" AF uses a special set of 11 AF sensors placed in the light path between mirror and the oculair (eye piece).
That's why LifeView is normally spot on, while the AF sensor may need AF adjustment.

For the rest:
I have a K-7 and done AF tuning with my lenses more than a year ago.
Suddenly, last december, I had the problem that all my photo's where back focussed (I do not use LV a lot on my K-7).
I had to redo the micro adjustment and where all lenses needed an offset of approximatly -5 before, they were on average +5 now...
There has been one more post of somebody with a K-7 that suffered from the same effect.

My advise is: use the AF methode showed in one of the replies before this one and adjust your AF for this lens.
Please check if the problem is consistent with all lenses, calibrate them all.

Cheers, Bert

Last edited by bymy141; 02-11-2011 at 10:05 AM.
02-11-2011, 09:11 AM   #13
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Let's clear some things up

QuoteOriginally posted by JGB Quote
That's an interesting point, does the Diopter affect the focusing mechanisms in the camera?(mine is set to the farthest right setting, as I am pretty nearsighted)
The diopter setting has no effect on the phase AF system. The light is actually split when it enters the lens, some goes to the viewfinder, and hence your eye, some goes to the phase AF sensors. What you choose to do with the light entering your eye (i.e. adjusting the diopter setting) will have no effect on the light going to the phase AF system since the light has been split before that.

Notice I say phase AF system. I make the distinction because there are actually two AF systems in your k-7 camera. The one you claim to have trouble with is phase AF. The one that you claim is working well for you is contrast AF. The contrast AF is only in use during live view, and is using the image on the sensor to actually focus the lens. Note that the mirror is engaged during contrast AF so nothing is visible through the viewfinder. Contrast AF has also proven much less likely to front or back focus since the system uses the image on the sensor itself to aquire the point of greatest contrast (which conveniently occurs at sharpest focus). The phase AF actually needs to be calibrated carefully to focus the lens such that the light will focus itself on the image sensor once the shutter has been released. However, the camera can consistently front or backfocus in this mode if the length of the light path is NOT what the camera expects. We are talking precision thousandths of a inch here... any offset from the manufacturers spec will result in poor focusing.

Thankfully, you yourself can dial this offset into the camera. I would suggest taking the time to run some simple tests in daylight to determine whether a misfocus exists, and whether it is front or back (it will typically be consistent). Once you have that sorted, just enter the offset into the camera, power off and on, then try again. Rinse and repeat until focus is acceptable to you.

Search the forum for good resources on how to properly calibrate the k-7.
Once you've read up come back here and I can help you try to fix AF problems you have with the camera, but first I must caution you that many, many things can cause focus problems, the most common being user error. From the photos you posted, it is difficult to make a global statement about your camera. Just take a tripod, and hour of your time, pay careful attention and run some proper calibration tests to see what it going on.


Well, bymy141 beat me to it... never noticed. I'll keep the post here since I took ten minutes to actually type it!

Last edited by firefly; 02-11-2011 at 09:16 AM. Reason: ummmm... felt like it.
02-11-2011, 10:20 AM   #14
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QuoteOriginally posted by firefly Quote
Well, bymy141 beat me to it... never noticed. I'll keep the post here since I took ten minutes to actually type it!
Sorry... you took a lot more effort to explain...

- Bert
02-12-2011, 08:25 PM   #15
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On the first picture, nothing is in focus. It's possible your camera focused on the plane where the hair comes down the shoulder (about the sharpest thing in the image), but even that's not that sharp which makes me think motion blur.

On the second picture, it looks pretty severely backfocused.

Both pictures look like they were taken indoors in dim lighting, which is pretty challenging for any AF (or even MF) attempt. There's a limit to how good the AF can get when it's dark. Test pictures in daylight might be more helpful.

Also, the viewfinder AF points are not always very precise. This is a limitation of all dSLRs. You can try to find the exact AF sensor location by using a pencil tip and testing different parts of the focus point indicators to see where it really is.
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