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09-20-2013, 12:02 PM   #1
Roger Walter
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Zoom lens with Pentax k-r camera

This is probably a really stupid question but this is Beginners Corner. I have purchased a Pentax 18-135 lens to use with my k-r, which came with an 18-50 lens. I am not sure if I should have my camera set on auto focus or manual focus to use the new lens, which is a varifocal and not a parfocal. Set on AF the shutter will not operate once the lens is zoomed unless I also move the focus ring. Set on MF the viewfinder shows a red square after each zoom and allowed the shutter to operate at all times. the pictures shot using MF appear to be in better focus than those using AF, which sometimes requires fine tuning with the focus ring.

Can some kind soul explain to this simpleton how he should be using the new lens. My preference would be not to have to focus at all, which is how the 18-50 lens operates.

Thanks

Roger

09-20-2013, 12:28 PM   #2
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Did you buy the DA 18-135mm new or used?
Because it should work exactly as your DA 18-55mm. That its not parfocal only means that you need to focus after you zoom. Zooming changes its focus.
Make sure the lens contacts are clean.
But remember that if you use AF, you can't just twist the focus ring. That breaks the focus mechanism. You need to switch the AF/MF switch up to MF. Also, there are many threads about AF fine adjustment and on using focus charts, so feel free to search for them and find more details.
Other than that, AF should work normally.
09-20-2013, 12:45 PM   #3
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QuoteOriginally posted by Na Horuk Quote
But remember that if you use AF, you can't just twist the focus ring. That breaks the focus mechanism. You need to switch the AF/MF switch up to MF.
The DA 18-135 has quickshift, so this rule does not apply.
However, I would try to avoid correcting manually at the same time the AF is also doing it.
09-20-2013, 01:11 PM   #4
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QuoteOriginally posted by Roger Walter Quote
This is probably a really stupid question but this is Beginners Corner. I have purchased a Pentax 18-135 lens to use with my k-r, which came with an 18-50 lens. I am not sure if I should have my camera set on auto focus or manual focus to use the new lens, which is a varifocal and not a parfocal. Set on AF the shutter will not operate once the lens is zoomed unless I also move the focus ring. Set on MF the viewfinder shows a red square after each zoom and allowed the shutter to operate at all times. the pictures shot using MF appear to be in better focus than those using AF, which sometimes requires fine tuning with the focus ring.

Can some kind soul explain to this simpleton how he should be using the new lens. My preference would be not to have to focus at all, which is how the 18-50 lens operates.

Thanks

Roger
If you're in AF.S and the image isn't in focus, the shutter won't fire. If there's a custom setting that allows you to set the AF to release priority, then it will. Otherwise, just switch to MF or re-focus after zooming in.


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09-20-2013, 03:53 PM   #5
Roger Walter
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Zoom lens with k-r camera

Thank you everyone for your prompt responses.

I bought the 18-135 lens new. It seems that I should set the camera to AF but then I could not touch the focus ring. Or I could set the camera to MF and do the whole thing manually. I shall certainly check the other threads on AF fine adjustment. Or maybe I should leave it on AF then adjust the fine tuning until it lets me take a shot - then I would know it's in focus. Obviously this question was not as stupid as I thought it was. Does anyone know what the red squares in the viewfinder signify when I am in MF mode and zooming? Do they mean that I am then in focus?

I love this k-r camera, which my wife bought me to stop me from using my beloved Olympus OM1 and having to keep getting the films developed, but I can't help feeling that life was a lot simpler then.

Thanks again

Roger
09-20-2013, 04:37 PM   #6
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AF-C vs AF-S

Quick shift can be a handy feature, some people may us it differently but I like to use it when the autofocus mode is set to AF-C and the shutter is set to release when you push the button. I use this when I am shooting sports, mainly hockey. With a lot of different targets and the glass or net between you and the target the autofocus system is easily confused but when this happens just adjust the autofocus until it is close and then let the camera start tracking again. As long as the shutter is half pressed the camera will try to track targets for you, make sure the correct red dot indicater is active when you push the button the rest of the way.

Alternatively when I have the camera on AF-S I prefer to use focus priority, the camera will not take a picture until it has achieved focus lock. Once the camera has achieved focus lock you can then adjust the quick shift to change the point that is in focus.

There is a lot to learn, just read the manual and play with the different settings to figure out what you like.
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