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09-27-2021, 07:36 AM - 1 Like   #16
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QuoteOriginally posted by 35mmfilmfan Quote
Many thanks for this suggestion - I look forward to trying it. BTW, how long after drinking the wine does it take for your eyes to return to their own preferred 'zone of sharpness' ?
For optimum results I suggest using an unopened bottle. Then once calibration is complete, grab the corkscrew.

09-27-2021, 12:57 PM - 1 Like   #17
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If you only every use slower lenses (> f2.8) and ultra wide to normal focal range, then calibrating your lenses is not essential.

However, as others have already pointed out, its still a worth while process as it can also help identify any specific issues with a "new" lens.

Obviously with faster lenses it becomes pretty important (even if you shoot mostly manual focus as the focus confirm can be very helpful for those quick shots).
09-27-2021, 08:45 PM   #18
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QuoteOriginally posted by kiwi_jono Quote

However, as others have already pointed out, its still a worth while process as it can also help identify any specific issues with a "new" lens.
Sure, you'd regret it if you try to sell such a thing later unfixed to someone else.
09-28-2021, 03:41 PM   #19
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QuoteOriginally posted by 35mmfilmfan Quote
Many thanks for this suggestion - I look forward to trying it. BTW, how long after drinking the wine does it take for your eyes to return to their own preferred 'zone of sharpness' ?
LMAO !!! lol! (that's a good one comment that really made my day! )

09-28-2021, 03:43 PM   #20
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QuoteOriginally posted by kiwi_jono Quote
If you only every use slower lenses (> f2.8) and ultra wide to normal focal range, then calibrating your lenses is not essential.

However, as others have already pointed out, its still a worth while process as it can also help identify any specific issues with a "new" lens.

Obviously with faster lenses it becomes pretty important (even if you shoot mostly manual focus as the focus confirm can be very helpful for those quick shots).
I would add that this would also be worthwile onlong focal lenses... DoF contracts with long FLs.. even at f5.6
09-29-2021, 01:18 AM   #21
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Can anyone explain this to me. I had thought that all digital cameras use some property of the actual image (often contrast) to detect best focus. How could there be an offset required in such a situation?
09-29-2021, 04:36 AM - 1 Like   #22
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QuoteOriginally posted by mikeavison Quote
Can anyone explain this to me. I had thought that all digital cameras use some property of the actual image (often contrast) to detect best focus. How could there be an offset required in such a situation?
What is discussed here is AF when using the viewfinder on a DSLR..... PDAF (Phase Detect). While using the viewfinder, the mirror is down, the shutter is closed and the sensor that captures the image is not being exposed to light. AF is done on an AF sensor that sits in the mirror box. Slight manufacturing tolerances can have an affect.

What you are describing is CDAF (contrast detect), which is done on the recording sensor itself. All mirrorless designs use this , as do Pentax DSLR cameras when in LV (live View) mode. Here the mirror is up, the first shutter curtain is open and the recording sensor is receiving light. The image, for framing is displayed on the rear lcd screen.

Any autofocus fine adjustment is not required in CDAF, and indeed there is no provision for it.

09-29-2021, 09:55 PM - 1 Like   #23
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QuoteOriginally posted by pschlute Quote
but now my quick and dirty method is to use a wine bottle that has clear lettering running a long way around the label. With an uncalibrated lens the BF is clearly evident, and I just adjust it until it is gone.
I like it- dealing with real-world subjects that present this kind of field of detailed set of distances to clearly show what adjustment is needed, if any. I generally use a similar setup, but this is a good specific suggestion.
09-30-2021, 02:36 AM - 1 Like   #24
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QuoteOriginally posted by pschlute Quote
What is discussed here is AF when using the viewfinder on a DSLR..... PDAF (Phase Detect). While using the viewfinder, the mirror is down, the shutter is closed and the sensor that captures the image is not being exposed to light. AF is done on an AF sensor that sits in the mirror box. Slight manufacturing tolerances can have an affect.

What you are describing is CDAF (contrast detect), which is done on the recording sensor itself. All mirrorless designs use this , as do Pentax DSLR cameras when in LV (live View) mode. Here the mirror is up, the first shutter curtain is open and the recording sensor is receiving light. The image, for framing is displayed on the rear lcd screen.

Any autofocus fine adjustment is not required in CDAF, and indeed there is no provision for it.
PSchlute thanks for the reminder. Pretty stupid of me I should have thought of that, since similar thinking is required with film cameras if you wanted a leaf shutter and interchangeable lenses - you can't have TTL viewing (unless you want to go through a slow process of opening the lens, viewing, closing the lens, taking a picture with mirror synced to the lens). I guess this may be one reason why rangefinder cameras and TLRs have enduring appeal. You get the lower latency, quieter operation and (relevant with vintage cameras) longer reliability of a leaf shutter compared with a blind shutter. But I digress horribly - sorry.
09-30-2021, 09:21 AM - 1 Like   #25
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QuoteOriginally posted by psoo Quote
I normally use Pentax lenses on my K50 and K70 and note from the user manuals that it is possible to apply "Fine Adjustments" to my cameras to get even sharper images. I have never bothered to use the complicated procedures to correct for front and back focussing since my images seem quite satisfactory for my type of photography. The fine adjustment procedure on the Pentaxes seems straight forward but II want to ask if any of you experienced Pentaxians bother to fine adjust the focus on your cameras. Is it worth the trouble for a "general photographer" like me? Of course I could give it a try but any comments would be welcome.
If you tend to use slow zooms, and shoot mostly outside with the lens stopped down, you may find you don't need to. Depth of field may mask focus errors sufficiently.
If you tend to shoot faster primes, and also tend to shoot at wider apertures, I think taking the time to dial in the AF is pretty important, as under those shooting conditions, it's fairly likely that AF accuracy can be improved to show a noticeable increase in image sharpness.

Both my D FA* 50/1.4 and 85/1.4 required enough AF bias that had I left the adjustment alone, I may as well have been using Coke bottle zooms. Certainly the $4k I spent on those two lenses would have been wasted by about $3.5k
09-30-2021, 10:01 AM - 1 Like   #26
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QuoteOriginally posted by pschlute Quote
For optimum results I suggest using an unopened bottle. Then once calibration is complete, grab the corkscrew.
I agree. If you opened the bottle beforehand you probably wouldn't be able to see straight enough to do the fine adjustment.
09-30-2021, 11:45 AM   #27
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I don't use a lot of modern lenses because their images look too sterile in my opinion (I know this might be worth a new thread to discuss this, but I'm not trying to derail the thread). I've noticed older lenses don't need any calibration. If I'm spending a lot of money on high-end lenses I believe I shouldn't have to adjust them. So far this has been true and I've never needed to make an adjustment to a lens. I like the look and character in the images produced by older lenses so I rarely buy a modern lens.
09-30-2021, 11:49 AM   #28
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QuoteOriginally posted by builttospill Quote
If I'm spending a lot of money on high-end lenses I believe I shouldn't have to adjust them.
It is the camera that has the issue usually, not the lens. But in my experience it is the two combined.

But interested as to why you think that modern lenses can in any way be less accurate at focussing than an old lens ?
09-30-2021, 03:47 PM   #29
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QuoteOriginally posted by pschlute Quote
It is the camera that has the issue usually, not the lens. But in my experience it is the two combined.

But interested as to why you think that modern lenses can in any way be less accurate at focussing than an old lens ?
Yes, it's factory tolerances from cameras and lenses combined which create the issue.

Older lenses were built with less automation. Of course this can be both good and bad for production quality. I would expect high-end lenses, both modern and older ones, to have tighter tolerances during construction and assembly. Why do MIJ FA Limited lenses command a higher selling price than AIV Limited lenses? Unfortunately without knowing the QC and tolerances set, does assembling them by hand in Japan make them better than assembling them by hand in Vietnam? Some say there are no differences and there may not be, but I think lowering the costs of production can ultimately lower quality control.
10-01-2021, 01:23 PM   #30
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I think the majority of the Pentaxians who responded to my post must be pros or advanced photographers who demand the very best from their lenses and cameras. Most photographers like myself are satisfied with the quality of their shots without wanting to carry out the complex procedures of fine focusing using charts, tape measures and bottle surfaces to do the necessary adjustments. Jatrax said above that to fine tune his lenses it takes at least half an hour to to fine tune. In the K50 manual the fine tuning procedure seems to be a quick one that one can used. However, the manual states that one should "Be sure to use fine adjustment only when necessary. Care should be taken as adjusting the auto focus may make it difficult to capture images with the appropriate focus" whatever that means. I did attempt to follow the quick Pentax procedure. with my K50 and a Pentax 18-135 mm lens and saw no sharpening of the image, but maybe I didn't carry out the procedure correctly. In any case, the warning given in the manual was enough to discourage me from fiddling with fine adjustment. I think I'll forget this adjustment since, as I said above, I'm basically happy with the sharpness of my lenses for the type of general photography that I do. Nevertheless, the advice given by the responders was an eye opener and I now believe that fine adjustment is not for the faint hearted, like me. Thanks for all your comments.
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