Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
07-30-2013, 05:12 AM   #1
Junior Member




Join Date: Jul 2013
Posts: 35
Pentax M 28 / 2.8

Hello,

today I got a cheap Pentax M 28 / 2.8. I got it cheap, because the aperture blades are closing a bit slowly. I took the risk to buy it because I think it can be repaired. I once repaired an old Tokina RMC 28 / 2.8, which was not that difficult. Does somebody know, if the Pentax M is similar to the Tokina with respect to dismantling the front and rear lens elements in order to clean the aperture blades?

Thanks,

Jim

07-30-2013, 05:28 AM   #2
Site Supporter




Join Date: Jan 2010
Location: Michigan
Photos: Gallery
Posts: 2,070
I have one (7162082) with same problem. It works better when warmed up so it is probably a dry lubricant problem. Aperture blades are visible and they are dry and clean.
Can you take off the mount first, to see if there is a pivot in there you may be able to put a drop of solvent on?
I will be interested to follow your progress, however i use a Vivitar 28/2 mostly.
07-30-2013, 06:57 AM   #3
Giveaway winner!
MysteryOnion's Avatar

Join Date: Dec 2007
Location: beantown
Photos: Albums
Posts: 885
JimKnopf, quick test also if you have a chance... Gently and while the lens is set to infinity, tap the front against a not too hard surface... a book, or sheet of cardboard. Then check to see if any change in blade action. My M28/2.8 seemed the same slow blade problem and dry lube didn't solve. When I took the lens apart is when I found that the set screw broke loose and allowed the front portion of the aperture assembly to press down too tight on the blades in the lower cup portion. Since servicing the lens and re-set and thread-locking the screws, no issues since.
07-30-2013, 08:15 AM   #4
Junior Member




Join Date: Jul 2013
Posts: 35
Original Poster
@wombat2go: I'll keep you posted ...

@MysteryOnion: What helped with my Tokina was to really get out the lens elements and then putting some acetone on the aperture blades. Basically this would be the first thing that I would try. However, before opening up the whole thing, I would still need to try the lens out more thoroughly, as I need to analyze under which conditions I get overexposed images.


Last edited by JimKnopf; 07-30-2013 at 08:54 AM.
07-30-2013, 08:19 AM   #5
Veteran Member




Join Date: Feb 2010
Location: Kokubunji, Tokyo
Photos: Gallery
Posts: 458
DO NOT APPLY ANY LUBRICANT!!

The aperture blades are meant to be run dry. Acetone will certainly clean the blades of oil but it should not be applied in situ. The aperture assembly should be taken apart and then cleaned. Acetone has a nasty habit of attacking any plastic parts, paint, etc.

I have no experience with the Tokina lens, so I can't help you there. However, the M28/2.8 is fairly easy to take apart and it's more or less the same procedure as disassembling the M50/1.4 or similar. There are plenty of articles on this forum and the web on how to do it.
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, blades, pentax, pentax help, tokina
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Pentax M 28/2.8 Schmidlapper Lens Sample Photo Archive 10 06-23-2013 06:33 PM
For Sale - Sold: Pentax-M 50/1.4, Pentax-A 28/2.8, Tamron 70-300 jlandecker Sold Items 10 04-16-2013 05:13 AM



All times are GMT -7. The time now is 05:10 AM. | See also: NikonForums.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