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04-26-2009, 09:26 AM   #1
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I've got the BF !

I'v had a go at focus testing my K10D, mainly due to having bad eyes at either distance or close up, and wear bi-foculs to correct this. But i'm not convinced, even with wearing good glasses and having the diopter adjustment that i was focusing properly. I dont trust my own eyes.

So the test :
All taken @ ISO 280 / Centre Weighted
Focus point was on number 7 of the ruler, well as acurately as i could get the 7 inside the centre of the big circle.
No refocusing between shots to keep conistency

Tripod and remote cable - SMC-A 50mm - shot from widest f1.7 to f22, though i havent included any shots after f9.5 because the DOF gets quite deep and gets progressively harder to determine the exact focus point. So i have uploaded only shots from f1.7 - f9.5 inclusive.

Not really for test purposes , i set EV bracket for -1 / 0 / +1 , and what has me confused is the very first shot, ( f1.7 ) i checked the EXIF and EV bracket read 0 / +1 / +1 ...from then on, all shots in the EXIF read as they were supposed to I.E. -1 / 0 / +1 which is how i set it. That is, until f22 where the EXIF read -1 / -1 / 0 which is the complete reverse of the f1.7 shots. Weird ?

Would appreciate any comments

f1.7

f2

f2.4

f2.8

f3.5

f4

f4.5

f5.6

f6.7

f8

f9.5



Last edited by Squier; 04-26-2009 at 09:35 AM.
04-26-2009, 09:31 AM   #2
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bad link...
04-26-2009, 09:56 AM   #3
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I've posted direct now - do they show ?
04-26-2009, 10:19 AM   #4
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QuoteOriginally posted by Squier Quote
I'v had a go at focus testing my K10D, mainly due to having bad eyes at either distance or close up, and wear bi-foculs to correct this. But i'm not convinced, even with wearing good glasses and having the diopter adjustment that i was focusing properly. I dont trust my own eyes.

So the test :
All taken @ ISO 280 / Centre Weighted
Focus point was on number 7 of the ruler, well as acurately as i could get the 7 inside the centre of the big circle.
No refocusing between shots to keep conistency

Tripod and remote cable - SMC-A 50mm - shot from widest f1.7 to f22, though i havent included any shots after f9.5 because the DOF gets quite deep and gets progressively harder to determine the exact focus point. So i have uploaded only shots from f1.7 - f9.5 inclusive.

Not really for test purposes , i set EV bracket for -1 / 0 / +1 , and what has me confused is the very first shot, ( f1.7 ) i checked the EXIF and EV bracket read 0 / +1 / +1 ...from then on, all shots in the EXIF read as they were supposed to I.E. -1 / 0 / +1 which is how i set it. That is, until f22 where the EXIF read -1 / -1 / 0 which is the complete reverse of the f1.7 shots. Weird ?

Would appreciate any comments
[B]
f1.7
[snip]
  • Only need to check the widest aperature...It's ~5/6 less images to check. (You could delete all the images in your OP, except the f/1.7 image.)
  • Use a gray card to set the exposure instead of EB'ing. It's 2/3 of images to check.
  • Use your lowest ISO setting. It's a sharpness test.
  • Not clear if you are using MF or AF for your test. Test both, they may be doing different things, they are different mechanisms.
  • Do the test on all your lenses to make sure it's a problem with the body, not the lens.


04-26-2009, 10:23 AM   #5
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that really does not look like a focus test chart it looks like a ruler... how do you know your camera isn't focusing on some point other than the 7?

a proper focus test chart is designed to give only one point of focus and eliminate such a variable.

you can find one to print out with a quick google search.

also make sure everything is nice and square when you do the test, this ruler is not lined up properly making the measurements on it useless to you.
04-26-2009, 10:25 AM   #6
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OK guys - i'll try that . I was using MF
04-26-2009, 10:59 AM   #7
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QuoteOriginally posted by WerTicus Quote
that really does not look like a focus test chart it looks like a ruler... how do you know your camera isn't focusing on some point other than the 7?

a proper focus test chart is designed to give only one point of focus and eliminate such a variable.

you can find one to print out with a quick google search.

also make sure everything is nice and square when you do the test, this ruler is not lined up properly making the measurements on it useless to you.
If you are using AF (or using MF with AF-confirmation) then you need an isolated point. The AF sensor is relatively large (about the size of the "( )" marks in the viewfinder, so anything inside those brackets (such as the multiple ruler markings) could be the focus point.

However, a ruler is OK with MF to check for relative FF/BF.
04-26-2009, 11:10 AM   #8
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Hi Dave - I was using MF only , not using AF to confirm focus. I used the scroll wheels front and back to change F stop and shutter speed.

I focused just once for the first shot,. I then didnt touch it again

04-26-2009, 11:16 AM   #9
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Would anyone recommend this as a chart ?

Camera Focus Test Chart
04-26-2009, 01:02 PM   #10
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Manual focus?

I do the majority of my shooting with MF lenses and had problems attaining consistent sharp focus despite years of experience using the same lenses on 35mm film SLRs. The cause? (Drum roll...)
The Stock Pentax Focus Screen
The stock screen is optimized for brightness and due to a number of reasons (would take many paragraphs to explain...even if I were smart enough to do so...) the apparent DOF in the viewfinder is never less than if the same lens were stopped down to about f/4. As a result, your eye sees sharp even when the real focus point is forward/back of that point.

Need proof? Using the camera's DOF preview feature, compare the screen brightness/DOF at both f/1.4 and f/4.

For critical manual focus with fast lenses, it is almost essential to use an aftermarket focus screen, preferably with a split-image or microprism focus aid. I replaced the stock focus screen on my K10D with a Katz Eye screen about 5 months ago and have not had any issues since. While the Katz Eye is pricey, there are less expensive options available from various eBay merchants and from FocusingScreen.com.

Steve

(No relation to any vendors of any screens...just a satisfied user...)
04-26-2009, 01:17 PM   #11
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Steve - i would never of thought about the screen till you mentioned it, and of course i have read all the threads here about the Katz / Jinfinance / Focusing.com but myself i was really thinking of an *iST D/DS screen rather than any of the split image types. These have been mentioned as being real good compared to the K10 screen

What made you go for the Katz rather than trying the *iST screen - did you specifically want a split image as opposed to just wanting a better screen ?
04-26-2009, 03:01 PM   #12
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It is correct that a ruler is not a good. well, ruler of focus adjustment, but all that aside; if the camera did in fact focus on the 7, and the 7 is blurred but things in front of the 7 are in focus, then wouldn't that be a FF problem, not BF as the thread title suggests?
04-26-2009, 03:23 PM   #13
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I've been advised by more knowledgeable folk that this has not been the best way to test, this could now be academic, but i'll carry on

We can apparently disregard all but the first max wide open shot ( f1.7 )

If you look at the that first shot, the crispest point is the number 9, with more in focus behind the 9 than there is in front of the 9. This i would expect, but i was focusing on the number 7. There is no in-focus point ahead of the 7.

So isnt the camera back focusing on the 9 instead ?

As has been said, not the best test - knocked it up fast at home, but since i was manually focusing, i wasnt being over ridden by any AF hunting around for a different focus spot
04-26-2009, 04:44 PM   #14
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The problem with MF with wide aperture lenses is that the viewfinder lies to you abut how much of the scene is in focus - it is incapable of rendering DOF as narrow as what will actually be in focus in the picture. When you focuses manually, you should hav noticed that not *just* the "7" was in focus, but a certain region in front and beind it as well. But the viewfinder was lying - only part of that region is really in focu. That's just life with the stock focusing screen. You need toleanr to visualize the entire focus zone and see how to place the "7" correctly *within* that zone, rather than simply stopping when the "7" is in focus, so that the "7" doesn't end up being part of the focus zone that isn't *really* in focus.

I takes a while to get the hang of, but the ruler is actually a good practice tool. Focus wherever you want, but manke a mental note of the furthest and closest lines that appear to be in focus in the viewfinder, then take the picture and see which of those lines are *actually* in focus. It will probably only around half as many. Then use that information to get better at focusing.

BTW, you have to use a tropod in tests like this - your head normally moves at least as much as the centimeter or two that focus appears to be off. If you were hand-holding, you most likely leaned forward slightly after focusing but before snapping.

But it *is* possible that your focus screen is misaligned, which would cause errors that cannot be accounted for by these explanations. It's extremely rare, I find - the vast majority of people who initially discover what they think are focus problems are actually being tripped up by this behavior of focus screens. So I wouldn't try repositioning the screen until you've really tried hard to perform the expeirments I've suggested, and only if you find that the area of sharpest focus in the picture was *not* within the focus zone in the viewfinder. That would be a real problem. But merely finding that some things that looked in focus in the viewfinder aren't in the picture - that is unfortunately normal at large apertures with shallow DOF when using the stock focus screen.

Last edited by Marc Sabatella; 04-26-2009 at 04:49 PM.
04-26-2009, 05:56 PM   #15
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"BTW, you have to use a tripod in tests like this - your head normally moves at least as much as the centimeter or two that focus appears to be off. If you were hand-holding, you most likely leaned forward slightly after focusing but before snapping."

-------------------------------------------------------------------

Thanks for the reply Marc, but i take it you didnt read my first post too well, ( happens on forums a lot ) other wise you would have seen that i used a tripod and a remote cable

I will try other lenses too, as advised, and just use the widest ap of the lenses, also as advised, and see how may lenses come up the same as the one above.

I was already planning to change the screen before i discovered this focus problem, if indeed there really is a problem. I dont shoot at max wide very much, so it may not be an issue, but i will admit i dont like the look of it
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