[richardstringer]

I'm having focus problems with my new Tamron 17-50mm lens, it's not focusing where I select the auto-focus point to be. Can you guys please help? I selected auto-focus and selected spot focus set to the centre, I focused on the number '6' and adjusted the 'AF Fine Adjustment' in the Pentax K30 settings, which photo looks to your eyes, to have the sharpest number '6'?

Photo 1 -10


Photo 2 +10


Photo 3 0


Photo 4 +5


Photo 5 -6


The numbers - and + are the setting on AF Fine Adjustment. As far as I can see -10 is the closest to the number '6' being sharpest, but still it seems it's not brilliant. Do you think I might have a bad copy because surely no lens needs the massive -10 of fine adjustment does it?

[scratchpaddy]

surely no lens needs the massive -10 of fine adjustment does it?

I'd say it's only a problem if it's outside of your camera's adjustment range, which does happen, especially on certain Tamron and Sigma lenses. -10 looks the best to me, so you should use it.

[richardstringer]

Thanks matey, I wasn't 100% sure that -10 was the best because for one thing I thought to myself "surely a lens's focus can't need THAT much adjustement can it?" and also because I don't 100% trust my eyes, my eyes water a lot (hayfever) which makes it hard.

[lytrytyr]

Richard, I'd recommend CDAF in live view for critical focussing,
at least when you're not in a hurry.

[thornburg]

Just to back it up, I agree that the first shot, (-10) has the sharpest 6.

[richardstringer]

What's CDAF? I only really use live view to view the histogram. Would it be a good idea to contact Tamron about this? Or is fine adjustment being WAY off and out the camera's settings range a normal thing?

Thanks thornburg, now i'm getting somewhere, I got the lens yesterday and took loads of pictures, then I got home, looked at them all and was gutted that not one was remotely in focus. I felt very down having taken like 30 or 40 pictures.

[K57XR]

What's CDAF?.

Contrast Detection Auto Focus.
Autofocus - Wikipedia, the free encyclopedia

[richardstringer]

How do I set it to contrast detection auto focus?

[scratchpaddy]

Contrast Detect AutoFocus (CDAF) is what the camera always uses in live view. It's actually taking the image from the sensor and adjusting the focus until the contrast is greatest at your chosen focal point. It's pretty much the same way we perceive focus in a picture, so it's almost guaranteed to be perfectly accurate.

Outside live view, the camera uses phase-detect autofocus (PDAF), which is faster, but it involves beam splitters, microlenses, and sensors separate from the actual image sensor, so it's prone to some inaccuracies.

[pacerr]

There are advantages to CDAF -- if and when using live view is appropriate. One minor reason I have for using the DSLR vs. P&S is to use the VF and avoid unsupported, hand-held shooting with the LCD screen.

You didn't mention the manner of supporting the camera for consistency for those shots. Tripod, beanbag, hand-held? I'd hesitate to comment without that info.

H2

[lytrytyr]

There are advantages to CDAF -- if and when using live view is appropriate. One minor reason I have for using the DSLR vs. P&S is to use the VF and avoid unsupported, hand-held shooting with the LCD screen.

Quite apart from the accuracy of Contrast-Detection Auto Focus in live view
(after which you can usually switch to eye-level viewing anyway),
I often find live view on modern DSLRs very useful
for framing shots at awkward angles
where you can't get your head behind the camera.

Way better than the waist-level finder on the LX back in the film days.

[richardstringer]

How do I zoom in to focus more acurately when I enable live view?

[scratchpaddy]

How do I zoom in to focus more acurately when I enable live view?

Hit the "Info" button. Note that this won't affect autofocus performance. It's only a visual aid for manual focusing.

[Wildbunch]

My copy of this lens gave me similar focus problems, I could more or less fix it through AF fine adjustment but that only works at a certain focal lenght, it made the issue bigger at other focal lenghts. Adjustment somewhere around 35mm didn't help. I even gave the lens in repairs and it came back saying it performs within factory tolerance. Disappointed, I put it in the corner of my cupboard and it stayed there for two years.

Now I use it on my new K-01 (CDAF) and focus is spot on all the time.

[richardstringer]

I hope I don't get anymore problems, if this is the kind of problems you have everytime you use a different lens the what's the point un having more than one lens really. I can't be bothered to keep adjusting the AF fine adjustment for each lens.