Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
11-22-2020, 06:44 AM   #1
Site Supporter
Site Supporter




Join Date: Sep 2014
Photos: Gallery
Posts: 90
Pentax A 645 300mm f 4 doesn't change the diaphragm opening

I just received this lens which I bought on eBay and I figured that moving an aperture ring in manual mode doesn't change the aperture opening. I'm not familiar with medium format Pentax lenses but on Pentax A lenses the aperture ring actually changes the opening wether the lens attached to a camera or not. Is it different in case of 645 A lenses? I wouldn't ask such question if I could check father, but I haven't got the "645 to K mount" adapter yet. Did I buy a lemon?

11-22-2020, 07:26 AM   #2
Loyal Site Supporter
Loyal Site Supporter




Join Date: Feb 2018
Posts: 361
This sounds normal, not a lemon..
Normally the aperture stays open at the widest setting. You need as much light as possible to see your subject.
There is a small tab that moves in a slot on the back of the lens that will stop the lens down to the manually set aperture.

Set the aperture to say F/8. Then on the back, you can very very gently move the tab with your fingernail and the aperture blades will close.
It will spring back.
Then try the smallest aperture eg f/22

If the lens is in A mode, then push the round button down on the aperture ring, and turn to the manual setting you want.
11-22-2020, 08:16 AM   #3
Site Supporter
Site Supporter




Join Date: Sep 2014
Photos: Gallery
Posts: 90
Original Poster
Thanks. The matter is ,that the diaphragm remains fully open even been set to manual. Any A lens for 35mm Pentax camera allows to change the aperture manually out in the air, and without touching the lever on the mounting surface of the lens IF the lens aperture ring is set on any given aperture value. That lever on the back of the lens is getting pushed by the camera corresponding lever when the aperture ring of the lens is set on "A" (automatic). The lens I got doesn't change the diaphragm opening even if the ring is set to manual (not "A"). But it's possible, that if the lens is attached to the camera, that little aperture control lever is getting cocked by the camera lever all the time thus allowing manual aperture setting.
11-22-2020, 08:27 AM   #4
Site Supporter
Site Supporter
Pål Jensen's Avatar

Join Date: Dec 2007
Location: Norway
Photos: Albums
Posts: 3,783
QuoteOriginally posted by hatsofe Quote
Thanks. The matter is ,that the diaphragm remains fully open even been set to manual. Any A lens for 35mm Pentax camera allows to change the aperture manually out in the air, and without touching the lever on the mounting surface of the lens IF the lens aperture ring is set on any given aperture value. That lever on the back of the lens is getting pushed by the camera corresponding lever when the aperture ring of the lens is set on "A" (automatic). The lens I got doesn't change the diaphragm opening even if the ring is set to manual (not "A"). But it's possible, that if the lens is attached to the camera, that little aperture control lever is getting cocked by the camera lever all the time thus allowing manual aperture setting.
It is normal for 645 lenses. It works the opposite way to K-mount lenses. The aperture remain open regardless when off camera.You can make the lens stop down by actuating the lever on the lens mount as the professor have already suggested.

11-22-2020, 08:44 AM   #5
Site Supporter
Site Supporter




Join Date: Sep 2014
Photos: Gallery
Posts: 90
Original Poster
QuoteOriginally posted by Pål Jensen Quote
It is normal for 645 lenses. It works the opposite way to K-mount lenses. The aperture remain open regardless when off camera.You can make the lens stop down by actuating the lever on the lens mount as the professor have already suggested.
I see. It's a relief. Thank you!
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!
645d, 645z, aperture, camera, change, change the diaphragm, lens, lenses, medium format, pentax
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Pentax S series and auto diaphragm kaihc Troubleshooting and Beginner Help 2 05-09-2020 10:45 AM
K-70 and pentax DA 18 - 135 mm diaphragm problem SADCritical Troubleshooting and Beginner Help 7 04-29-2020 07:11 PM
Pentax Aperture/Diaphragm Control Block Failures SharkyCA Troubleshooting and Beginner Help 29 10-10-2019 03:35 PM
Sports Opening Day at the" K " - K 3 + D FA* 70-200mm F2.8 or DA* 300mm F4 aslyfox Post Your Photos! 11 04-02-2019 08:14 PM
K-30 doesn't control diaphragm anymore! SunValley Troubleshooting and Beginner Help 4 12-23-2014 01:50 PM



All times are GMT -7. The time now is 02:44 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