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01-18-2022, 05:52 PM   #1
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Focus issues: solutions?

Hi Pentaxians,

I'm trying to figure out how to get around my Pentax DSLRs' inability to focus sharply.

My D100 Super autofocuses on a given object, but if I zoom in, it isn't very sharp.

My K50 (which recently suffered from the iris control failure issue) has been used solely with my film prime lenses, as I was so frustrated with its inability to autofocus reliably with its zoom lens.

I installed a split-prism focusing screen, to help me manually focus the film prime lenses, but although it appears to be correctly calibrated, again when I play back images, very often the image isn't in focus, especially when using my 28mm wide angle lens (which equates to a 42mm lens).

The end result is that I have to take several photos in order to get the lens set in focus. Fine for buildings/ panoramas / inanimate objects, but virtually useless for taking photos of my children!

I'm getting to the point of despair!

Do I have to consider a different rival brand of camera?!?

This would be difficult, as all my flash guns are Pentax specific, as are my lenses.

The current range of new Pentax DSLRs seems to be pretty limited.

It's either rob a bank and buy a K1, or spend several hundred bucks and get a K700. But even then, how do I know they'll be any better at auto focusing?

I like using prime lenses, but if I got a new DSLR prime, it wouldn't have any manual focus calibrations and wouldn't have any manual iris control, so it would have to rely on auto iris and mostly auto focus.

How do I know a new K700 wouldn't suffer the same iris control failure my K50 suffered after a few years?
Then, any DSLR prime lens would be effectively unusable.

On the subject of auto focus, I know if I fit one of my flash guns to the hot shoe, then the camera uses the flash gun's auto focus beam instead of its built-in beam, and as the flash gun's beam is better, then the camera can focus better when using the flash gun.

Can I use the flash gun auto focus beam without using the flash itself? Maybe focus, then switch to manual focus and switch off the flash gun, then take the photo with available light..?

All seems a bit of a malarky just to get the damn camera to focus!

What are people's methods for getting reliably auto focus with a Pentax DSLR?

Are the likes of the new K700 far better at auto focus than my old K100D Super / Kx / K50?

I know that the K1 is full frame, so my film lenses should give better clarity, assisting in focus, but as they are purely manual focus, I'd have to install a split-prism focus screen.

Any advice would be greatly appreciated.

Thank you.
Regards - D

01-18-2022, 06:02 PM - 2 Likes   #2
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some photo examples, with EXIF data intact, would help us diagnose your issues...
01-18-2022, 07:18 PM   #3
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QuoteOriginally posted by DafTekno Quote
Hi Pentaxians,

I'm trying to figure out how to get around my Pentax DSLRs' inability to focus sharply.

My D100 Super autofocuses on a given object, but if I zoom in, it isn't very sharp.

My K50 (which recently suffered from the iris control failure issue) has been used solely with my film prime lenses, as I was so frustrated with its inability to autofocus reliably with its zoom lens.

I installed a split-prism focusing screen, to help me manually focus the film prime lenses, but although it appears to be correctly calibrated, again when I play back images, very often the image isn't in focus, especially when using my 28mm wide angle lens (which equates to a 42mm lens).

The end result is that I have to take several photos in order to get the lens set in focus. Fine for buildings/ panoramas / inanimate objects, but virtually useless for taking photos of my children!

I'm getting to the point of despair!

Do I have to consider a different rival brand of camera?!?

This would be difficult, as all my flash guns are Pentax specific, as are my lenses.

The current range of new Pentax DSLRs seems to be pretty limited.

It's either rob a bank and buy a K1, or spend several hundred bucks and get a K700. But even then, how do I know they'll be any better at auto focusing?

I like using prime lenses, but if I got a new DSLR prime, it wouldn't have any manual focus calibrations and wouldn't have any manual iris control, so it would have to rely on auto iris and mostly auto focus.

How do I know a new K700 wouldn't suffer the same iris control failure my K50 suffered after a few years?
Then, any DSLR prime lens would be effectively unusable.

On the subject of auto focus, I know if I fit one of my flash guns to the hot shoe, then the camera uses the flash gun's auto focus beam instead of its built-in beam, and as the flash gun's beam is better, then the camera can focus better when using the flash gun.

Can I use the flash gun auto focus beam without using the flash itself? Maybe focus, then switch to manual focus and switch off the flash gun, then take the photo with available light..?

All seems a bit of a malarky just to get the damn camera to focus!

What are people's methods for getting reliably auto focus with a Pentax DSLR?

Are the likes of the new K700 far better at auto focus than my old K100D Super / Kx / K50?

I know that the K1 is full frame, so my film lenses should give better clarity, assisting in focus, but as they are purely manual focus, I'd have to install a split-prism focus screen.

Any advice would be greatly appreciated.

Thank you.
Regards - D
I doubt the problem is one of a specific brand of camera. I'd suggest posting some photos and with a bit of luck members may be able to help you narrow down where the problems are that are preventing you from obtaining sharply focused images.

I guess you're meaning a K70? There will certainly be some improvement in image quality going from a K100D to that. Likewise, a K-1ii which is a superb camera. The new K-3iii is getting good reviews for autofocus capability on moving subjects.
01-18-2022, 07:18 PM   #4
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-The new camera you're talking about is K70, not K700. It's a very capable camera for the money, and I've never heard of anyone having consistent autofocus issues that couldn't be resolved. It is possible you'll have aperture block issues with that camera (others might have more info on the likelihood of that happening).
None of the rest of the cameras I'll mention commonly suffer from that problem.

-K1 is significantly more expensive (if you get one for under US$1000 used right now, you've done very well, and you would pay US$1800 for a new K1ii, which replaced K1 but is largely the same camera), but it's very nice (it's full frame as you noted, as well as various other advanced features). You may well not need that much camera at this stage, although I can't say that for sure.
It too will autofocus capably, although still not as fast as more modern cameras from some competitors or the (US$2000) K3iii, Pentax's newest camera and it's best autofocus performer ever (a significant upgrade for the brand, which has long lagged somewhat behind the competition if AF speed)

-Another possibility would be to get a used high end crop camera from several years back, like maybe the K3ii (probably comprable price to a new K70). It will absolutely be more capable at AF than your K100D Super, and probably be more durable than a new K70 (definitely the aperture block) since it was top of the line when released. Remember, your K100D Super is 15 years old at this point, any newer Pentax will have improved autofocus over that model.

-Here's a comparison of some of these models. There are links there to the staff and user reviews for each camera as well, which should have plenty of info.

-All that said, it's possible that your current camera can focus okay with different techniques or settings, or possibly if there is an issue with the camera or lens that we can help diagnose and maybe correct. As pepperberry farm mentioned, posting some shots with exif data would be the next step to getting to the bottom of that.

A few more notes:

-Newer cameras will allow zooming in for manual focusing with the back screen in live view (your K50 might, I'm not sure), and have focus peaking which is very nice in most situations. They also can use the AF system to give focus confirmation (a little square lights up where the picture is in focus) through the viewfinder. So a split prism isn't necessary to use MF lenses, although you still may end up wanting to go that way (I have) if you continue using MF lenses.
Live view (not using the viewfinder) is always the most accurate way to manual focus, even with a split prism installed.

-Some modern lenses do have electronic aperture, but not all. There are still lenses from Pentax with the aperture ring.

------


I hope any of that might be helpful to you, there was a lot to respond to in your post and I didn't get to all of it.


Last edited by wadge22; 01-19-2022 at 03:25 AM.
01-18-2022, 07:48 PM   #5
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QuoteOriginally posted by DafTekno Quote
I installed a split-prism focusing screen, to help me manually focus the film prime lenses, but although it appears to be correctly calibrated, again when I play back images, very often the image isn't in focus, especially when using my 28mm wide angle lens (which equates to a 42mm lens).
I've been reading on replacing focusing screens (and I ordered one, which I am awaiting in the mail). I kept reading about shims and how it was trial and error re needing new shims and such so that the new focus screen works properly (maybe the new one is thinner/thicker that the OEM...)

Could this be something OP has to deal with?
01-18-2022, 07:51 PM   #6
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Maybe try setting up the camera on a tripod, focus and then use a remote or self timer to trigger the shutter. Make sure SR is off. You might have an involuntary movement when you press the shutter button which the camera can't cope with.
01-18-2022, 08:01 PM   #7
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If your split prism screen shots are off then your screen isn’t perfectly calibrated (shimmed) or the technique is flawed.

The k-50 can be repaired (diy) cheaply. As can the k-70 but it can seem like an overwhelming bit of work depending on the comfort level with complex machinery and electronics. Good tutorials exist.

The trick with manual focus is live view focus peaking or magnified view. But in my honest opinion fast lenses can still be tough on any dslr to get critical focus with my eyes.

01-18-2022, 08:48 PM   #8
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I would make sure to use fast enough shutter speed and try auto focus on Live view.
or
Use Live view to maximize the view to 100% and manual focus. You pretty much have to pre-focus and wait for this one + use fast enough shutter speed.

I have been using the 2 methods with good success in dark alley at night (K3 classic), but people won't walk as fast as kids running.
01-18-2022, 10:05 PM   #9
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QuoteOriginally posted by DafTekno Quote
Hi Pentaxians,

I'm trying to figure out how to get around my Pentax DSLRs' inability to focus sharply.

My D100 Super autofocuses on a given object, but if I zoom in, it isn't very sharp.
6.1 mega pixels and very old focusing system. Compared to similar era cameras from Nikon and Canon I don’t think it lags behind much at all.

QuoteOriginally posted by DafTekno Quote
My K50 (which recently suffered from the iris control failure issue) has been used solely with my film prime lenses, as I was so frustrated with its inability to autofocus reliably with its zoom lens.
Which lens? Did you try more than one? Did you fine tune the autofocus for that lens? All DSLR’s suffer from having focusing systems that are separate from the sensor. The optical length of the path to the focus points is intended to be the same as the optical length to the sensor. But as resolution increased over time the accuracy of the two distances matching has gone down dramatically. In addition, The tolerance of lens mount is also to blame as the sensor based approach means accurate focus can be shorter or longer Than theoretical.

QuoteOriginally posted by DafTekno Quote
I installed a split-prism focusing screen, to help me manually focus the film prime lenses, but although it appears to be correctly calibrated, again when I play back images, very often the image isn't in focus, especially when using my 28mm wide angle lens (which equates to a 42mm lens).
This suggests either it isn’t calibrated correctly or your
Misinterpreting low density of pixels for lack of focus.

QuoteOriginally posted by DafTekno Quote
The end result is that I have to take several photos in order to get the lens set in focus. Fine for buildings/ panoramas / inanimate objects, but virtually useless for taking photos of my children!
As another user suggested, post images so we can see EXIF.

QuoteOriginally posted by DafTekno Quote
I'm getting to the point of despair!

Do I have to consider a different rival brand of camera?!?
No—-but maybe if you are fed up?

QuoteOriginally posted by DafTekno Quote
This would be difficult, as all my flash guns are Pentax specific, as are my lenses.

The current range of new Pentax DSLRs seems to be pretty limited.

It's either rob a bank and buy a K1, or spend several hundred bucks and get a K700. But even then, how do I know they'll be any better at auto focusing?
Need to know what lens.

QuoteOriginally posted by DafTekno Quote
I like using prime lenses, but if I got a new DSLR prime, it wouldn't have any manual focus calibrations and wouldn't have any manual iris control, so it would have to rely on auto iris and mostly auto focus.
I’m baffled. I can’t decipher what you are saying above me

QuoteOriginally posted by DafTekno Quote
How do I know a new K700 wouldn't suffer the same iris control failure my K50 suffered after a few years?
Then, any DSLR prime lens would be effectively unusable.
Except Kaf4 lenses.

QuoteOriginally posted by DafTekno Quote
On the subject of auto focus, I know if I fit one of my flash guns to the hot shoe, then the camera uses the flash gun's auto focus beam instead of its built-in beam, and as the flash gun's beam is better, then the camera can focus better when using the flash gun.
This is only when the light is too weak for the focusing system to see the subject well. The flash gun focus beam is just brighter and only is usable in poor light to actually improve focus results - but it doesn’t actually improve focus much unless light is very dim.

QuoteOriginally posted by DafTekno Quote
Can I use the flash gun auto focus beam without using the flash itself? Maybe focus, then switch to manual focus and switch off the flash gun, then take the photo with available light..?
Not that I know of.

QuoteOriginally posted by DafTekno Quote
All seems a bit of a malarky just to get the damn camera to focus!

What are people's methods for getting reliably auto focus with a Pentax DSLR?
Plenty of people will tell you they have the magic bullet. Testing with an experienced user to help guide you is an option you might want to explore.

QuoteOriginally posted by DafTekno Quote
Are the likes of the new K700 far better at auto focus than my old K100D Super / Kx / K50?
not sure. My impression is that there’s some improvement.

Post example shots with EXIF. Show a few successes and failures.
01-18-2022, 11:38 PM   #10
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QuoteOriginally posted by DafTekno Quote
It's either rob a bank and buy a K1, or spend several hundred bucks and get a K700. But even then, how do I know they'll be any better at auto focusing?
Yes, you could get a Pentax K70. The K70 has the pixel shift function that gives better focused images when zoomed in at 200%. You can also use Topaz Sharpen AI software ; Topaz Sharpen AI has a mode to improve the focus of images, you can try it for free and see how the focus of your images is improved.
01-19-2022, 12:19 AM   #11
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OK - my take:
As above - need an example picture to see the problem.

You said you had a Split-prism focusing screen - so you are not using the original Pentax AF (autofocus) matte screens? The AF might be affected by this if the screens are not Pentax brand and not designed for an auto focus camera.

How 'Zoomed In' are you when looking at pictures? Nothing looks perfect at 100% pixel peeping but will print out just fine.

Does the auto focus problem exist only indoors? I get this idea as the camera works with the red light from the flash unit.
Tungsten lights and flourescent lights aren't anywhere near to matching daylight wavelengths. In particular earlier AF cameras will not handle indoor lighting well and the solution is to stop down a bit to hedge your bets on the focal range. You have to test autofocus outdoors in daylight because that's the lighting the camera is designed for. The K-3 was the first Pentax that seems to perform OK with indoor light focusing.

Anyway, post some examples to give everyone a shot at diagnosing.
01-19-2022, 12:35 AM - 2 Likes   #12
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QuoteOriginally posted by calsan Quote
You said you had a Split-prism focusing screen - so you are not using the original Pentax AF (autofocus) matte screens? The AF might be affected by this if the screens are not Pentax brand and not designed for an auto focus camera.
the matte screen does not sit in front of the AF sensor it is located on a different path from the lens. The matte screen can however mess with the metering of the camera
01-19-2022, 01:06 AM - 1 Like   #13
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Oh right - thanks Ian!
01-19-2022, 04:28 AM - 1 Like   #14
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Too many potential problem points in this inital post. Problems should be narrowed down by focusing on one point at a time, or else the solution won't be sharp.
01-19-2022, 06:57 AM   #15
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Personally, I'd do away with any after-market focussing screen, re-install the original and check the focussing using the "Green Hexagon" focus confirmation indicator in the viewfinder.
I use this feature regularly on all my bodies and find it totally reliable, if a little non-intuitive, being at the bottom of the viewfinder, but you get used to it
All this guff about "film primes" and "digital primes" is totally irrelevant … newer lenses may be measurably better than older lenses on the optical bench, very few would notice any difference on an A4 or smaller print!
Reliable auto-focus on a Pentax DSLR? … fit an auto-focus lens! No issues, no problems, they just work!
The available range of Pentax APS-C DSLRs is perfectly adequate … there's a very good one and a significantly superior one … would you want anything less than "very good"?
The a/f on the newer cameras is better in low light than the older cameras.
The K-3iii, and the KP, to a lesser extent, seem to be able to cope with lower-contrast subjects than the K-70 and earlier, in my experience, but that's a very subjective issue, no two shots in the "real world" are ever "identical" and I rarely have two bodies with me and ready to use, let alone fitted with the same lens.
Can't help with the flash-gun questions … a) because I don't have a problem in the first place and b) because I don't have a P-TTL Pentax gun.

Last edited by kypfer; 01-19-2022 at 07:06 AM.
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