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10-20-2010, 12:13 PM   #1
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do i have the right lens?

a while back i purshased an sf1 on ebay and it's a sight to behold. i then purchased a quantaray 28-90 mm auto focus lens because i didn't have any of those.it's brand new and when i installed it on the camera it won't auto focus. it'will manual focus just fine. because of the age of the camera do i have to get aparticular lens? i've checked my settings and their right on.( i was able to get a manual). according to the box it works on all of the other auto focus film cameras.
what am i doing wrong?

10-20-2010, 01:01 PM   #2
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Just to be clear, you're saying you have the focus mode switch on the camera body set to either AF Single or AF Servo?
10-21-2010, 05:09 AM   #3
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yes that is there. when you engage those modes the lens responds but not by auto focusing. on the manual mode the focus ring turns freely like it should. when you engage either af single or af servo the focus rings is engaged but will not respond on it's own. every other picture i've seen of these they have the "f" series lens. and i am wondering if that"s not where i screwed up.
10-21-2010, 06:50 AM   #4
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QuoteOriginally posted by newpentaxman Quote
a while back i purshased an sf1 on ebay and it's a sight to behold. i then purchased a quantaray 28-90 mm auto focus lens because i didn't have any of those.it's brand new and when i installed it on the camera it won't auto focus. it'will manual focus just fine. because of the age of the camera do i have to get aparticular lens? i've checked my settings and their right on.( i was able to get a manual). according to the box it works on all of the other auto focus film cameras.
what am i doing wrong?
Just to be clear, and I don't mean to be insulting, but are you sure that the lens is designed for Pentax cameras? Quantaray certainly made a 28-90mm AF zoom for Pentax. I have one. But they also made identical lenses for other mounts, such as Nikon and Canon.

A Nikon-mount lens will fit on a Pentax camera, but none of the electrical or mechanical connections will work. This could explain why your lens won't autofocus.

Any k-mount AF lens should work on an SF1, except for the newest SDM (in lens focus motor) lenses.

BTW, the SF1 is a nice camera. I've got one. In fact, that's the camera I use my Quantaray 28-90mm zoom on. The camera is built like a tank.

Check out the photos of Pentax lens mounts in the Beginner's forum:

https://www.pentaxforums.com/forums/pentax-beginners-corner-q/87608-photos-lens-mounts.html

Scroll down to the KAF mount lens. Note the AF drive screw at about four o'clock in that photo. It looks like a flat-blade screw head. The rest of the screws, that actually hold the lens together, are Phillips screws. Does yours have one of these? With the lens off the camera, turn the focus ring. The drive screw should turn as you turn the focus ring. If it doesn't something is broken inside the lens.


Last edited by noblepa; 10-21-2010 at 06:56 AM.
10-21-2010, 07:37 PM   #5
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Well, the most obvious answer is the AF on the camera is broke which is why they sold it. See if you can get another AF Pentax lens to try and if that doesn't work you know you likely have a broken camera and should stick to MF lenses (not a bad thing!)
10-22-2010, 05:39 AM   #6
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that was my wonder also.was the af not working on this. i'm waiting for my second lens to arrive.should be able to tell after. i was kind of hoping the auto focus would work.
10-22-2010, 05:50 AM   #7
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a couple of comments and many things to check.

It could be that much of the issue has to do with receiving focus data from the lens to the camera. this is transmitted over the last pin in the mount, i.e. furthest away from the lens release pin. It could be dirty. AF will not work with this contact missing.

Since the selection of AF and MF seems to imply the focusing drive is engaging, I think we can exclude issues of this being other than a K mount.

So the issue then is, either the body has an issue or the lens has an issue. To determine which, you need another AF lens. If it works on the camera, then it is the lens, if not it may be the body.

ALsso look to see if there is any AF switch on the lens itself,
10-22-2010, 05:22 PM   #8
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I can attest for another reason. I can mount my Sigma 70-300 F4-5.6 (non APO version), on my SF-1N and it won't autofocus. It'll meter and operate the aperture, however. If I stick the lens on my PZ-1p, it'll work perfectly. Mind you, I can stick my FA 28-70 F4 on my SF-1N and it'll work properly too, so it's not that the lens isn't letting enough light through to the focusing sensor.

10-23-2010, 07:10 AM   #9
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i was wondering if it was only going to operate correctly with an "fa" type lens. that's what i was trying to figure out.
10-23-2010, 08:25 PM   #10
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I have both an SF1 and the Quantaray 28-90mm AF zoom. I never realized that I had never tried the two together.

I just did. Guess what. Mine won't autofocus on the SF1 either. The lens autofocuses just fine on a ZX-60, which is what I bought the lens for, so its not a bad lens. The SF1 autofocuses perfectly with a Pentax F 28-80 zoom that I have, so there's nothing wrong with the camera, either.

I think that maybe Lowell is on the right track. I wasn't able to match up the contacts on the lens with those on the camera, to verify his theory.

On the SF1, there are seven evenly spaced contacts in an arc from the six o'clock to the eight o'clock position. 0000000.

On the lens, there are five. 0_0_000. The _ indicates a space or missing contact. It appears that the pins on each end line up.

I tried both AF-S and AF-C. Neither would cause the lens to AF. With the camera in either AF mode, the focus ring on the lens would not turn, indicating that the screw drive on the lens had locked into the drive socket on the camera.
10-24-2010, 05:30 AM   #11
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enough said.so i do have to get different lens or lenses.i have a 70-300 mm quantaray lens
which should be here this week i got really good deals on them.it looks a lot like the 28-90mm.i'll try it and i'll probably have to sell it as well. i have been missing with lenses here lately between misinformation and ignorance on my part. i just assumed they were all the same here. so it has to be the "f" lens i'll wager. thanks all.
10-27-2010, 07:13 PM   #12
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the quantaray 70-300 arrived today and it matches the 28-90, physically in every way except it's larger of course.i locked it on to the sf1 and it worked beautifully.without a hitch! alright within the next few days an mz50 is going to arrive and i'll test the 28-90 on it. if it works,guess whats getting sold? yes the mz50 which i got cheaply just for this purpose. and let me tell you...compared to the sf1....well there is no comparison. i have one that doesn't work that someone gave me and in my opinion it's not pentax's greatest contribution to us.
cheap is the word that comes to mind. anyways thanks to all for your help.
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