Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
01-28-2009, 11:13 AM   #1
Veteran Member




Join Date: Feb 2008
Location: Lachine, Quebec, Canada
Photos: Gallery | Albums
Posts: 453
Infinity focus problem- M 50mm f/1.7

Hey all-

I have a great little Pentax-M 50mm f/1.7 that I adore, but I seem to be having infinity focus issues with it when wide open. I can't seem to get good focus at infinity, and sometimes a slight tweak "back" on the focus rings helps, but oftentimes not. I can't really get decent focus until stopped down to ~f/8, and I'm wondering if anyone knows of a site that details how to adjust infinity focus on these lenses?

I don't know of anybody in the area (greater Montreal) that does this type of repair work. I've had the lens for 1 1/2 years, mostly shooting indoors where I don't seem to have this problem. Was just doing a bit of snowy day shooting, and wanted to shoot wide open due to the dim lighting.

I did notice that the front bezel ring that has all the lens info was loose- I tightened this up the best I could by hand, but I really don't want to start messing around tightening it further with tools, etc, since these front bezel rings don't have any pierced holes for a spanner, etc.

Thanks!

01-28-2009, 11:59 AM   #2
Pentaxian
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 4,859
QuoteOriginally posted by virgilr Quote
Hey all-

I have a great little Pentax-M 50mm f/1.7 that I adore, but I seem to be having infinity focus issues with it when wide open. I can't seem to get good focus at infinity, and sometimes a slight tweak "back" on the focus rings helps, but oftentimes not. I can't really get decent focus until stopped down to ~f/8, and I'm wondering if anyone knows of a site that details how to adjust infinity focus on these lenses?

I don't know of anybody in the area (greater Montreal) that does this type of repair work. I've had the lens for 1 1/2 years, mostly shooting indoors where I don't seem to have this problem. Was just doing a bit of snowy day shooting, and wanted to shoot wide open due to the dim lighting.

I did notice that the front bezel ring that has all the lens info was loose- I tightened this up the best I could by hand, but I really don't want to start messing around tightening it further with tools, etc, since these front bezel rings don't have any pierced holes for a spanner, etc.

Thanks!
Maybe some bad news here, but you can easily fix the lens yourself if you can get that ring loose again. If you can, you'll see six small screws. You'll need a Phillips #00 screwdriver for these, and you'll only remove the three that hold on the filter ring, not the three under the filter ring. (Small arcs are cut into the filter ring for the screws underneath, which hold the front lens group in place.) Lift off the filter ring.

Now you'll see an aluminum groove deeper inside the lens, just inside the focus ring. Three more screws are in the groove. Mount the camera on a tripod, point the lens at a distant view and focus the lens to the infinity setting. Loosen the three screws but don't remove them. When they're loose enough, you can rotate the focus ring without changing the actual lens focus. Move the focus ring a bit, let's say to 15 meters. Tighten one screw and look through the viewfinder. See if you can focus on a distant object now. If not, you'll need to repeat the previous steps. If the lens focuses "to infinity and beyond", you can focus on the distant object, loosen the screws, set the focus ring to point at infinity and tighten all the screws.

Possibly helpful hints: the bezel ring is designed to be removed with a rubber friction tool. Anything that fits it without touching the front element will help. Clean the filter threads with a toothbrush so grit doesn't jam the ring. There may be two slots 180 apart, one above the PT in "OPT." and the other between M and 1 in "PENTAX-M 1:1.7". Sometimes a small flat screwdriver will work in these slots, sometimes it won't fit. These lenses were made for a long time and parts varied slightly, so the slots might not be there. You'll probably find one or two loose screws when you make adjustments; that allowed focus to shift. An old film camera viewfinder is larger and might make focus adjustment easier.

I happen to have one of these apart in front of me right now. Let me know if you need photos.
01-29-2009, 03:09 PM   #3
Veteran Member




Join Date: Feb 2008
Location: Lachine, Quebec, Canada
Photos: Gallery | Albums
Posts: 453
Original Poster
Wow! Thank you SO much- I'll tackle this tomorrow. I'll try my best to loosen the ring- I ruined another f/1.4 trying to get the darned thing off, to the tune of 60 bucks- but I'm willing to try this with your tips and get this little puppy in focus!
01-30-2009, 08:21 AM   #4
Veteran Member




Join Date: Feb 2008
Location: Lachine, Quebec, Canada
Photos: Gallery | Albums
Posts: 453
Original Poster
Dave-

Again, thank you tremendously! I did the procedure as you outlined it- yes, infinity was off by ~2 degrees on the focus ring. The screws on initial loosening seemed nice and tight, though.

Anyways, This helped a ton- I think I may have a so-so copy, though, because I had to shoot at f/4 on a cloudy snowy winter day to be able to actually test focus properly.

Wide open- reaaaally soft. Not much wide open night shooting outdoors with this 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!
50mm, bezel, f/1.7, focus, front, infinity, infinity focus, k-mount, lens, pentax lens, rings, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
DA 15mm infinity focus lock problem stillshunter Pentax SLR Lens Discussion 3 08-06-2010 08:03 PM
Samyang 800mm + T2 -> Pentax infinity focus problem k7bb Troubleshooting and Beginner Help 24 06-29-2010 10:37 AM
K7: Focus problem at infinity (Vivitar Series 1 70-210 F3.5) peter.antonius Pentax SLR Lens Discussion 3 05-27-2010 02:34 PM
Vivitar Series 1 105mm macro infinity focus problem mjkwee Pentax SLR Lens Discussion 1 05-12-2010 01:31 PM
Help - Infinity focus problem with DA* 50-135mm 2.8 chickentender Pentax SLR Lens Discussion 9 08-06-2009 10:20 PM



All times are GMT -7. The time now is 07:36 PM. | 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