Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
07-02-2012, 02:49 PM   #1
Pentaxian
Kozlok's Avatar

Join Date: Jun 2012
Location: Albuquerque
Photos: Gallery
Posts: 1,759
Manual Lens Problems

I have a KX, and have acquired a trio of manual prime lenses. I read about green button metering, and 2 of the lenses work great, perfect every time. The third lens doesn't meter properly at all, and when I change the green button mode to optical preview, when I press it, nothing at all happens. No noise, no darkening of the viewfinder, nothing. The aperture setting doesn't seem to matter, it does nothing when I press the green button. The aperture ring operates the blades correctly, and the lever arm that controls the blades seems to work just fine.

That being said, when I press the shutter release, the aperture snaps down to however I set the aperture ring. The blades move a little sluggishly, but not that bad.

The lens is a Rexatar Auto MC 1:2.8 135mm, the mount appears to be a standard K mount as far as I can tell. Even though the name says "Auto", there is no auto on the aperture ring.

Don't laugh, as it cost all of $18, and it looks like it might be sharper than my DAL50-200 (I know that's not saying much).

Thanks in advance!

07-02-2012, 03:08 PM   #2
Senior Member




Join Date: Mar 2011
Posts: 119
QuoteOriginally posted by Kozlok Quote
The lens is a Rexatar Auto MC 1:2.8 135mm, the mount appears to be a standard K mount as far as I can tell. Even though the name says "Auto", there is no auto on the aperture ring.
There are two kinds of "auto".
1) On the right camera (read: film camera), the old kind of auto will automatically calculate the shutter speed when you change the aperture setting on the aperture ring.
2) The new kind is the "A" setting on the aperture ring. This is the only useful kind to us these days.
07-02-2012, 03:30 PM   #3
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,397
Can you show a photo of the lens mount. It almost sounds like it is an M42 lens with a flanged K mount
07-02-2012, 03:31 PM   #4
Veteran Member
lammie200's Avatar

Join Date: Jun 2011
Location: San Francisco
Photos: Albums
Posts: 1,028
One of my previous replies when the subject came up before:

"Auto" for lenses can mean 1 of 3 things. It can mean 1) autofocus, 2) auto aperture or an "A" lens (you can set the aperture from the camera without rotating the aperture ring by having it in the "A" position), or 3) auto as in the aperture will stay wide open and automatically change to the aperture that the aperture ring is set to once the shutter is released. Some lenses have all three of these features. Some have none. Most modern lenses (from the 70's onward) will at least have the last one.

For example, Let's say that you have an 85mm f1.4 lens that you want use as manual focus. You also want to set the aperture manually. Let's also say that it only has the third feature described above. You want to set the aperture at f8 so you rotate the aperture ring accordingly. Now you look through the viewfinder and everything looks nice and bright. That is because you are looking through the lens as if it were set to f1.4. When you press the shutter the camera will allow the aperture to close to f8.

BTW, "M" lenses are still useful provided you meter using the green button for your shot. The metering will be based on the setting that you set the aperture ring to. "A" lenses are similar except that the camera will let you set the aperture if you have the aperture ring on the "A" setting. Since you are setting the aperture in the camera with an "A" lens, the camera meters automatically. With "M" lenses the camera doesn't know what aperture the lens is set at because there is no electronic communication between the lens and the camera. Hence, you need to use the green button to stop down meter.

I don't know why you are having an issue with that one lens, but as someone else posted, there may be an issue with the mount.

Hope that helps.


Last edited by lammie200; 07-02-2012 at 03:49 PM.
07-02-2012, 06:53 PM   #5
Pentaxian




Join Date: Nov 2011
Photos: Gallery | Albums
Posts: 3,705
QuoteOriginally posted by lammie200 Quote
With "M" lenses the camera doesn't know what aperture the lens is set at because there is no electronic communication between the lens and the camera. Hence, you need to use the green button to stop down meter.
To clarify that for the K-x:

If you have "Enable Aperture ring" set in the menu,
and with your green button doing optical preview as posted,
you can press the Av button on the top of the camera
to get it to set whatever shutter speed
is appropriate for the aperture you have set with the aperture ring,
with "M," "K," or similar third-party lenses
and the M mode selected on the mode dial.

Press firmly on the buttons, and make sure your battery level is good.
You might have an issue with the green button,
but using the Av button should avoid that kind of problem.
07-02-2012, 08:09 PM   #6
Pentaxian
Kozlok's Avatar

Join Date: Jun 2012
Location: Albuquerque
Photos: Gallery
Posts: 1,759
Original Poster
OK, here are some pictures of the mount. To be clear, I am using green button metering just fine on 2 different MF lenses. Just this one doesn't meter properly when I press the green button. It basically meters for wide open. The green button also doesn't change the aperture when I use the green button in DOF preview mode, either. The other lenses also work fine in DOF preview mode. My question is, what would cause a lens to not respond to the green button?






07-02-2012, 08:21 PM   #7
Veteran Member
lammie200's Avatar

Join Date: Jun 2011
Location: San Francisco
Photos: Albums
Posts: 1,028
QuoteOriginally posted by Kozlok Quote
...My question is, what would cause a lens to not respond to the green button?
I don't know for sure, but there have been posts about mounts that are painted or powdercoated that won't allow the camera mount contacts to short out. I believe that even though that camera can't read any info from the lens in terms aperture setting, it still needs to pass current between the camera mount contact points. It might not be passing current, thus behaving as if there is no lens attached at all. The reason that it shoots wide open is because of my first post and the description of the third type of "auto" lens. Do the other two lenses have bare metal mounts?

Last edited by lammie200; 07-02-2012 at 08:29 PM.
07-02-2012, 08:23 PM   #8
Pentaxian
Kozlok's Avatar

Join Date: Jun 2012
Location: Albuquerque
Photos: Gallery
Posts: 1,759
Original Poster
There are no electrical contacts of any kind

07-02-2012, 08:28 PM   #9
Veteran Member
lammie200's Avatar

Join Date: Jun 2011
Location: San Francisco
Photos: Albums
Posts: 1,028
QuoteOriginally posted by Kozlok Quote
There are no electrical contacts of any kind
You don't need electrical contacts. Are the other two mounts bare metal or painted like the one in the photos?
07-02-2012, 08:30 PM   #10
Pentaxian
Kozlok's Avatar

Join Date: Jun 2012
Location: Albuquerque
Photos: Gallery
Posts: 1,759
Original Poster
They are both bare metal, look like aluminum
07-02-2012, 08:39 PM   #11
Veteran Member
crewl1's Avatar

Join Date: Jul 2010
Location: Los Angeles, CA
Photos: Gallery | Albums
Posts: 9,796
The black paint is not allowing your k-x to short the appropriate pins on its mount.
You can either remove the paint around where the camera mount contacs would mate up, or use a n aluminum foil trick some have luck with.
On my iPhone or I'd search it for you.
07-02-2012, 08:41 PM   #12
Veteran Member
lammie200's Avatar

Join Date: Jun 2011
Location: San Francisco
Photos: Albums
Posts: 1,028
OK. So your problem might be the black paint on the lens mount for the 135. Because I don't claim to be an expert, your best bet is to do a little searching on this site and see if you can find some threads that describe this problem. I have heard of people putting a strip of tin foil on the lens mount where the pins on the camera mount hits it. Either that or sanding off the paint on the lens mount. But I don't want to tell you something wrong. You really should try a search.

Edit: See post #21 in this thread.

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/49422-removing...e-value-2.html

Your lens probably isn't worth much. You might get better results by sanding off the paint. I would tape over the glass first to keep dust from getting inside if you do. Good luck.

Last edited by lammie200; 07-02-2012 at 08:50 PM.
07-02-2012, 08:57 PM   #13
Pentaxian
Kozlok's Avatar

Join Date: Jun 2012
Location: Albuquerque
Photos: Gallery
Posts: 1,759
Original Poster
To test Lammie's theory, I wedged a little aluminum foil in the mount. Meters perfectly now. I'll get some emery paper and polish off the paint. This lens was an $18 investment, so I'm willing to live with it being reduced in value to $16 or $17! Thanks a million Lammie!
07-02-2012, 09:05 PM   #14
Veteran Member
lammie200's Avatar

Join Date: Jun 2011
Location: San Francisco
Photos: Albums
Posts: 1,028
QuoteOriginally posted by Kozlok Quote
To test Lammie's theory, I wedged a little aluminum foil in the mount. Meters perfectly now. I'll get some emery paper and polish off the paint. This lens was an $18 investment, so I'm willing to live with it being reduced in value to $16 or $17! Thanks a million Lammie!
Sure thing. Do want my address to send me the million? I assume we are talking dollars because I don't need a million of anything else.
07-02-2012, 09:51 PM - 1 Like   #15
Pentaxian
Kozlok's Avatar

Join Date: Jun 2012
Location: Albuquerque
Photos: Gallery
Posts: 1,759
Original Poster
Final update. A quick once over with a Dremel tool and some emery cloth stripped the paint over the contact. Works like a charm now. Might even be a semi-sharp lens.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
aperture, auto, blades, button, k-mount, lens, lenses, mount, pentax lens, press, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Can a manual-focus lens have back focus problems? PocketPixels Pentax DSLR Discussion 33 02-13-2011 05:37 AM
Problems using K110d and manual lenses sglasco Pentax DSLR Discussion 3 08-31-2010 02:14 AM
would a manual lens experience front/back focus problems? blu3ness Troubleshooting and Beginner Help 8 11-04-2009 11:14 AM
HELP! manual lens problems with K10d jster91 Pentax SLR Lens Discussion 13 04-14-2008 03:41 PM
Manual Lens Problems on the K10D Kemal Pentax DSLR Discussion 11 02-23-2007 02:57 PM



All times are GMT -7. The time now is 06:45 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top