Forgot Password
Pentax Camera Forums Home

Show Printable Version Search this Thread
08-02-2017, 04:07 PM - 1 Like   #1
RoxnDox's Avatar

Join Date: May 2007
Location: Gig Harbor, Washington, USA, Terra
Photos: Gallery | Albums
Posts: 3,742
figuring f-stop with green button exposure on K-50

Getting ready for the upcoming eclipse, I've been doing some preparations and practice sessions, and a question arises as I try to record the successful settings.

Normally I am using modern lenses that communicate with the camera, so I haven't really had to use the infamous green button exposure setting. But this time, I have added a new wrinkle. In between the K-50 and my trusty 70-300 Promaster, I put in an old (pre-1983, came with the wife and her ME Super...) Zykkor brand 2x TC, which is totally manual. It gives me a good enough reach, of course, but... Figuring the exposure has me a bit puzzled. Yes, I am using a solar filter, one of the inexpensive cardboard and mylar ones from B&H.

First, the lens: If I take it off the 'A' setting and put it at f/11, that will mechanically set the internal mechanism to the right opening size and leave it there, yes? It does when looking thru the lens off-camera at any rate.

Second, the green button: When I press it (Manual mode, with ISO 100, 1/500s), the shutter speed was reset to 0.5s, and the sun came out reasonably well exposed. No information on what the f-stop is though.

I've read a lot of green-button questions here over the years (tho not recently), and it boils down to 'shooting with the lens stopped down' as I recall. So that would be f/32 for that lens -
--- does a 2x TC take it two stops to f/16? Or am I completely confused?
--- with a manual TC in there, howintheHelsinki does it do that?

this image was also done with almost the same setup, just a different celestial body so no filter

08-02-2017, 04:25 PM   #2
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 48,873
The f stop is whatever you set on the lens without a TC, 1 stop less with a 1.4x, or 2 stops less with a 2x TC.

So F11 would become F16 at 1.4x or F22 at 2x.

Adam Webmaster (Site Usage Guide | Site Help | My Photography) server and development costs are user-supported. You can help cover these 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:

08-02-2017, 04:35 PM   #3
RoxnDox's Avatar

Join Date: May 2007
Location: Gig Harbor, Washington, USA, Terra
Photos: Gallery | Albums
Posts: 3,742
Original Poster
Thanks, Adam... Confusion, it ought to be my middle name. <sigh> I'll keep practicing

  • 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!
2x, button, button exposure, exposure, f-stop, filter, k-50, lens, photography, tc
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Similar Threads
Thread Thread Starter Forum Replies Last Post
Figuring out macro with the Q7 NoRules Pentax Q 3 02-10-2017 02:50 PM
Fast normal, struggling with figuring out what would be optimal for ~$500 rrstuff Pentax SLR Lens Discussion 22 09-03-2016 06:57 PM
Help needed figuring out D FA 28-105 Paul the Sunman Pentax SLR Lens Discussion 102 07-30-2016 02:41 AM
Stop Down Metering With The Green Button: Wrong Exposure Recomendations Obs Troubleshooting and Beginner Help 55 03-27-2015 09:39 AM
Green Button Stop-Down Metering Acting Differently woefulwabbit Pentax DSLR Discussion 22 03-29-2011 09:56 PM

All times are GMT -7. The time now is 10:03 PM. | 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]