Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
12-20-2018, 01:18 PM   #1
New Member




Join Date: Oct 2018
Posts: 13
Problem with zoom

So, I got a Pentax Kp about a month ago, didn't notice until now (maybe I changed something without knowing), the thing is that aperture changes when I zoom in whith a 18-135 lens. It gets higher when I zoom in, anyone could help me? I can't set a lower aperture, once the camera sets the aperture in one determined number I can't set it lower.
I shoot in manual.

12-20-2018, 01:42 PM - 2 Likes   #2
amateur dirt farmer
Loyal Site Supporter
pepperberry farm's Avatar

Join Date: Dec 2014
Location: probably out in a field somewhere...
Photos: Gallery | Albums
Posts: 41,257
the DA18-135 is a variable-aperture zoom...

if you are shooting wide-open, the aperture is going to change as you run through the focal-length range...
12-20-2018, 01:46 PM - 1 Like   #3
Moderator
Loyal Site Supporter
Loyal Site Supporter
pschlute's Avatar

Join Date: Mar 2007
Location: Surrey, UK
Photos: Gallery
Posts: 8,115
Yep, the clue is in the name : Pentax 18-135mm f/3.5-5.6
12-20-2018, 01:50 PM - 1 Like   #4
Loyal Site Supporter
Loyal Site Supporter
MossyRocks's Avatar

Join Date: Nov 2017
Location: Minnesota
Photos: Gallery | Albums
Posts: 2,978
Unless you have a fixed maximum aperture zoom this is expected. On your lens (I assume this is the one) the maximum aperture is f/3.5 which is likely at 18mm. As you zoom the length of the lens increases while the aperture opening remains the same making the total aperture value greater up to a value of f/5.6 at 135mm.

There are some zooms that have a fixed max aperture either because the opening varies as they zoom, or they are an internal zoom like this lens.

If you are zoomed to 135mm and the aperture won't open up to f/5.6 then I would be concerned. If it only opens up to f/5.6 at 135mm then everything is normal and this is expected behavior.

12-20-2018, 02:24 PM - 3 Likes   #5
Pentaxian
reh321's Avatar

Join Date: Nov 2014
Location: South Bend, IN, USA
Photos: Gallery | Albums
Posts: 23,128
QuoteOriginally posted by MossyRocks Quote
Unless you have a fixed maximum aperture zoom this is expected. On your lens (I assume this is the one) the maximum aperture is f/3.5 which is likely at 18mm. As you zoom the length of the lens increases while the aperture opening remains the same making the total aperture value greater up to a value of f/5.6 at 135mm.

There are some zooms that have a fixed max aperture either because the opening varies as they zoom, or they are an internal zoom like this lens.

If you are zoomed to 135mm and the aperture won't open up to f/5.6 then I would be concerned. If it only opens up to f/5.6 at 135mm then everything is normal and this is expected behavior.
I checked with my 18-135 mounted on my KP {below are approximate values}

At 18mm, it is a f/3.5-16 lens

At roughly 24mm, it becomes a f/4.0-16 lens

At roughly 35mm, it becomes a f/4.5 -16 lens

At roughly 75mm, it becomes a f/5.6-16 lens
12-20-2018, 03:48 PM   #6
Pentaxian




Join Date: May 2013
Location: Hertfordshire, England
Posts: 845
You will also observe that the minimum aperture changes from f/40 at 135mm to f/22 at 18mm.

If you set the aperture to any value from f/5.6 to f/22 inclusive, it will not change during zooming.

Philip
12-20-2018, 03:56 PM - 1 Like   #7
Otis Memorial Pentaxian
Otis FanOtis FanOtis FanOtis FanOtis FanOtis Fan
Loyal Site Supporter
clackers's Avatar

Join Date: Jul 2013
Location: Melbourne
Photos: Albums
Posts: 16,394
QuoteOriginally posted by Agi Quote
So, I got a Pentax Kp about a month ago, didn't notice until now (maybe I changed something without knowing), the thing is that aperture changes when I zoom in whith a 18-135 lens. It gets higher when I zoom in, anyone could help me? I can't set a lower aperture, once the camera sets the aperture in one determined number I can't set it lower.
I shoot in manual.
Lenses like the DA*16-50 and DA*50-135 don't change aperture as you zoom, Agi, it's why you pay more for them.

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!
aperture, camera, pentax help, photography, troubleshooting
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
K2 Shutter problem - is it a common problem? johnha Film SLRs and Compact Film Cameras 13 12-13-2020 04:44 PM
Battery problem or Charger Problem? troika Troubleshooting and Beginner Help 10 10-01-2018 09:59 AM
1 premium WR zoom VS. cheap WR zoom-premium zoom combo mythguy9 Pentax SLR Lens Discussion 19 11-27-2013 08:51 AM
K-5 battery problem? camera problem? user problem? imtheguy Pentax K-5 & K-5 II 39 11-03-2010 06:02 PM
Zoom, Zoom, Zoom racinsince55 Pentax SLR Lens Discussion 11 03-31-2008 07:10 PM



All times are GMT -7. The time now is 11:31 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