Go Back   Steve's Digicams Forums > Digital SLR and Interchangeable Lens Cameras > Sony Alpha dSLR / Konica Minolta dSLR, Sony SLT

Reply
 
Thread Tools Search this Thread
Old May 28, 2010, 10:17 PM   #1
Junior Member
 
Join Date: May 2010
Posts: 5
Default lenses with metal mounts...

Hello all,

As a new owner of a 230A one of the first lenses I sought out was a Maxxum 50mm f1.7, and after watching eBay for a few days I got a nice clean, almost like new, lens for $30 shipped.

It came today and the first thing I noticed was that when mounting it to the A230 body I could feel the metal lugs on the lens chewing up the plastic lugs on the body. Closer inspection of the lens revealed that the leading edges of the bayonet lugs were very well machined--to the pin that they were almost chisel-like when mating with the body's plastic flange.

So, I use a small "swiss" file to "break" and bevel the inside leading edges of the lens' mounting lugs which made engagement with the body smooth and no longer an obvious exercise in wearing out the body's mount.

Just thought I'd share, as I have not doubt that there was damage being done and debris being generated by simply mounting this metal backplate lens on the body's plastic receiver...
cliffyk is offline   Reply With Quote
Sponsored Links
Old May 29, 2010, 7:26 AM   #2
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,572
Default

I am almost certain that your fears are unfounded. The lens mount on the A230 is capable of holding much heavier lenses than the Minolta 50/1.7, and it is extremely unlikely that any load bearing part of the A230's mount is made entirely out of plastic, or that the lens mount would have been sharp enough to score the camera mount and generate particulate matter that could negatively affect the camera.

If anything, I think it's more likely that the lens or its mount were damaged, and that's why it was being sold.
__________________
  • The lens is the thing.
  • 'Full Frame' is the new 'Medium Format'.
  • "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.

Last edited by TCav; May 29, 2010 at 7:28 AM.
TCav is offline   Reply With Quote
Old May 29, 2010, 7:38 AM   #3
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

I don't think any of the load bearing parts of it are plastic from what I can tell comparing the images to the mount on my A700 (although there is a darker section inside that's a more flexible metal).

I've never heard anyone mentioning what you're saying about one either. You sometimes hear complaints about the plastic lens mounts on the cheaper lenses (but, I've never heard anyone claim that the camera mount was that way, and I think I'd have read something like that by now -- or noticed it when I've tried one in the past). Here's an A230 image showing the mount. AFAIK, the inside flange section is a flexible metal, not plastic. What do you mean by "I could feel the metal lugs on the lens chewing up the plastic lugs on the body"?

Touch the part you're talking about, tap it, etc. I think you'll find it's metal versus plastic, unless you're talking about something directly underneath the part where the lugs are on the inside of the camera mount that the lens is touching (versus the load bearing portion of the mount the lens locks into when mounting one).
Attached Images
 
JimC is offline   Reply With Quote
Old May 29, 2010, 11:21 AM   #4
Junior Member
 
Join Date: May 2010
Posts: 5
Default

If you examine the body's bayonet mounting lugs (indicated by the green arrows below) you will see that they are indeed made of made of plastic--it is these lugs that bear the load of the lens' mass, and other loads applied separately to the body and lens.



Also you will observe that the inner leading edge of each lug is an unprotected plastic surface; and that there is a metal (it appears to be stainless steel) wave spring that offers wear protection to the central portion of the bearing surface. The wear protection functionality however is likely an artifact of the spring's primary purpose of providing a snug fit of the lens and body.

As I said in my first post, prior to breaking the leading edges of the lens' lugs you could feel the scraping taking place while affixing the lens. And in just the 2 or 3 times I mounted the the unmodified metal mount lens there were created visible scratches in the plastic leading end of the inner bearing surface of body's lugs, and also on the inner surface of the wave spring.

None of this is of course relevant to using the plastic mount lenses...
cliffyk is offline   Reply With Quote
Old May 29, 2010, 11:35 AM   #5
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

I don't have an A230 here to take a closer look. But, with the Sony and Minolta A Mount cameras I do have, if you look closely at the lugs on a lens, the lens lugs lines up under the metal tabs on the mount when you insert one so that the the load bearing portion of the mount is metal. So, I suspect that any plastic you're seeing is just for buffer purposes between the metal surfaces, with the metal mount supporting the lens load.

I'll take another look at an A230 as soon as I get a chance. But, I'd think that if any of the load bearing surface was plastic, we'd have seen a lot of complaints about it by now (and I frequent a number of forums where these models are discussed).
JimC is offline   Reply With Quote
Old May 29, 2010, 12:47 PM   #6
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,572
Default

I suspect that what you're dealing with is a damaged lens, and the lens barrel touches the camera body before the mount is fully inserted, so you must exert more force than usual to turn and lock the lens in place. It is this misalignment of the lens' mount with its barrel, that causes this extra friction. What you've done may have decreased the friction, but I still think the problem is with the lens. I suggest you put it through its paces to make sure it operates correctly in all other respects.
__________________
  • The lens is the thing.
  • 'Full Frame' is the new 'Medium Format'.
  • "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.
TCav is offline   Reply With Quote
Old May 29, 2010, 4:37 PM   #7
Junior Member
 
Join Date: May 2010
Posts: 5
Default

Sheesh...

I realise I am a newbie here, but please accept that I am not new to the repair of cameras and other photographic equipment--having been doing that, and gun and electronic test equipment repair for over 40 years. Now trying to be retired I provide laboratory instrument data interface system design work for a number of clients, and although arthritis has affected my hands to some extent I can still do all but the most delicate assembly and disassembly.

That out of the way, I really haven't made any of this up; nor do I view it as any premier shortcoming of the Alpha series' design. Many modern plastics out-perform metals and are entirely acceptable choices for many applications.

It remains however that when mounting an older metal flange lens on the new body the chrome plated sharp right-angle profile of the leading edge of the lens' mounting lugs can, and do, scrape up the inner bearing surfaces of the body's lens mount receiver lugs.

Here is an exploded view of the lens mount (this is from the A300 service manual, but the entire series uses the same design╣):



The plastic ring with the projecting bayonet lugs is sandwiched, along with the metal ring with the stamped wave springs, between the outer metal ring and the mirror box--held in place by six screws. Using the metal outer ring allows it to be somewhat thinner in section, and adds an impression of a high quality mount.

Here's a closeup of the stamped ring with the finger springs.



When assembled the fingers protect only the central portion of the mounting lugs bearing surface. The specified E-85 grease is a medium bodied PTFE lubricant.

-------------------------------------------------
╣ - This is from the A100 service manual, the drawing has lesser detail howbeit the sameness of the component parts is obvious--their dimensions are of course identical. Part (1)-5 is the plastic ring.

cliffyk is offline   Reply With Quote
Old May 29, 2010, 6:28 PM   #8
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,572
Default

I understand and appreciate your knowledge and skills, not to mention your determination.

The Minolta 50mm f/1.7 is a very popular lens. It was one of the first lenses Minolta manufactured for their new autofocus Maxxum film SLRs in '85, and was in production (with the occasional cosmetic change) right up until Sony discontinued it when they bought all of Konica Minolta's camera business in '06. There are lots of them changing hands on the used market. Between 10 and 15 get sold each week on eBay alone.

Yours is the first one I've ever heard about that had this problem.

In addition to the one I had which did not do what you describe, I also had two of the early Sigma lenses for the Minolta Maxxum cameras. Those lenses were notorious for their tight fit, and when using them, it never occured to me that they may be causing some damage to my camera.

I really think the problem you describe is unique to the lens you have, and that you should check it for damage.
__________________
  • The lens is the thing.
  • 'Full Frame' is the new 'Medium Format'.
  • "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.
TCav is offline   Reply With Quote
Old May 29, 2010, 7:30 PM   #9
Junior Member
 
Join Date: May 2010
Posts: 5
Default

Silly me--I apologise for bothering you with this...

Last edited by cliffyk; May 29, 2010 at 7:34 PM.
cliffyk is offline   Reply With Quote
Old Jun 2, 2010, 2:47 PM   #10
Senior Member
 
bernabeu's Avatar
 
Join Date: Jan 2005
Posts: 990
Default

cliffyk,

thank you for the excellent 'write-up' .. will keep my head up
bernabeu is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 11:34 PM.