Forgot Password
Pentax Camera Forums Home

Show Printable Version Search this Thread
02-26-2007, 04:27 PM   #1
Senior Member

Join Date: Oct 2006
Location: Chicago
Posts: 136
Screwmount lens

I did some searching and I am still a little cloudy about something.

I picked up a 400mm screwmount lens that I intend on using on my k100d.

The part I don't understand is the correct sequence to set the lens up.

Say I want to shoot at f/8.

I would assume that I would set the the aperture to f/8, press the AE/L button to find the correct shutter speed and snap the picture.

However I have read that with a manual K-mount lens the camera would stop down, meter and set the shutter speed. Obviously the screwmount lens cannot be stepped down via the body so I would need to do that myself.

To my understanding "stopping down" means to move to a smaller aperture (higher number)

Why in the world would I want to do that? Or am I misunderstanding something? If I do stop down, what do I stop down to?

Another interesting tidbit is that the lens has 2 aperture rings. One operates normally and the other will rotate freely between the largest setting (f/5.6) and the number set with the normal ring. Any particular reason for this?

Sorry if this is a total n00b question.

02-26-2007, 04:33 PM   #2
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 43,032
To stop down, set the diaphragm clutch from auto to manual, and then select the desired aperture.

"Stopping down" simply refers to the closing of the aperture diaphragm. When using an automatic lens, you set the aperture via the aperture ring (or internally through the camera) and a lever on the camera "stops down" the lens to the desired aperture when you take the picture. You have to stop screwmount lenses down manually because they lack the coupler that K-mount lenses otherwise have.

Edit: it looks like you have a very old takumar with two silver aperture rings. It doesn't have the diaphragm clutch, but I'm pretty sure that one ring stops the lens down while the other is just used as a guide for the other.

Adam Webmaster (Site Usage Guide | Site Help | My Photography)'s high server and development costs are user-supported. You can help cover those costs by donating. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

02-26-2007, 05:01 PM   #3
Inactive Account
roy's Avatar

Join Date: Sep 2006
Location: D/FW area, Tx.
Photos: Gallery
Posts: 1,712
that's a preset lense. what you do is set the ap you want to take at and focus wide open. just before you trip the shutter you spin the actual ap ring down. the preset ring will stop the other ring at the preset ap. you do all of this in Av mode. you do not need to press the AE-L button as the cam is measuring the actual light that the lens is passing..
02-26-2007, 06:24 PM   #4
Senior Member

Join Date: Oct 2006
Location: Chicago
Posts: 136
Original Poster
So what you guys are saying is that I should focus the camera when the aperture is at its lowest numerical number and "stopping down" is just setting the aperture to the desired size for the picture?

I am still waiting on my K-mount adapter to arrive so I can test everything out.

Thanks for clearing this up guys. I must say that that second ring will make this whole stopping down thing super easy since you won't need to double check that you put the ring back into the correct position.

02-26-2007, 06:30 PM   #5
Inactive Account
roy's Avatar

Join Date: Sep 2006
Location: D/FW area, Tx.
Photos: Gallery
Posts: 1,712
that's exactly what the 2nd ap ring is for.. i wish my 500 had it, altho i'm getting good at hitting the ap i want..

  • 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, f/8, k-mount, lens, pentax lens, screwmount, shutter, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale - Sold: Vivitar M42 28mm f/2.5 Screwmount Lens (Worldwide) woof Sold Items 2 09-13-2010 05:03 PM
For Sale - Sold: Spiratone 24mm f/2.5 Pluracoat M42/Screwmount (CONUS) Green Chile Sold Items 5 04-09-2010 08:50 AM
For Sale - Sold: [Worldwide] Takumar 500mm f4.5 lens in M42 Screwmount ChipB Sold Items 3 02-17-2010 08:26 PM
For Sale - Sold: 200mm f/3.3 M42 Screwmount Lens - Free, Just Pay Shipping! wallyb Sold Items 6 02-02-2010 07:36 PM

All times are GMT -7. The time now is 10:40 AM. | See also:, 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?
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]