Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
09-29-2018, 04:38 AM   #1
Forum Member




Join Date: Jun 2015
Posts: 87
K3 and legacy (non-conductiv) lenses

Hi all,

just got me a new K3, and the first lens I had to try was the 50mm f1.7. However I noticed some odd behavior.

Previously I owned a K30, and for manual lenses, I usually covered the Lens where the contacts would be with some tape. The reason behind this is I could set the aperture to, let's say 4 and adjust exposure compensation by +3.5 (from 1.7-4) and bob's your uncle, no stop down metering (green button) necessary.

However, the K3 does not seem to stop-down the aperture and instead always takes the shot fully open, why is that and is it possibly to change this?

Cheers!

09-29-2018, 05:02 AM   #2
New Member




Join Date: Jun 2018
Posts: 16
Did you set "Use Aperture Ring" in the menu selections?
09-29-2018, 05:05 AM   #3
Forum Member




Join Date: Jun 2015
Posts: 87
Original Poster
Yes, also using Av Mode. In M, stop-down works with the green button, but it's a huge loss of comfort having to press the green button before every shot.
09-29-2018, 06:07 AM - 1 Like   #4
Site Supporter
Site Supporter




Join Date: Nov 2012
Location: North Wales
Photos: Gallery | Albums
Posts: 1,834
I don
QuoteOriginally posted by manufocus Quote
, I usually covered the Lens where the contacts would be with some tape. The reason behind this is I could set the aperture to, let's say 4 and adjust exposure compensation by +3.5 (from 1.7-4) and bob's your uncle, no stop down metering (green button) necessary.
I don't understand this. With a K mount lens, "K" or "M" series, a pentax dslr simply doesn't stop down at all in Av mode. This is because the "crippled" KAF mount doesn't have the second mechanical aperture connection that the film cameras have, this comunicates the f-stop set. Moving the aperture ring of a K/M lens on a dslr to a larger F number while in Av mode does nothing, the iris is held open by the camera. The only hack that can be done is to not fully mount the lens. In this case the lens aperture lever doesn't connect with the camera aperture actuator and so the iris does stop down. However you have to careful of your lens falling off!

Av mode works with M42 lenses because there is no connection between the camera and the iris, you have stop down aperture priority.

09-29-2018, 07:56 AM   #5
Forum Member




Join Date: Jun 2015
Posts: 87
Original Poster
QuoteOriginally posted by marcusBMG Quote
I don

I don't understand this. With a K mount lens, "K" or "M" series, a pentax dslr simply doesn't stop down at all in Av mode. This is because the "crippled" KAF mount doesn't have the second mechanical aperture connection that the film cameras have, this comunicates the f-stop set. Moving the aperture ring of a K/M lens on a dslr to a larger F number while in Av mode does nothing, the iris is held open by the camera. The only hack that can be done is to not fully mount the lens. In this case the lens aperture lever doesn't connect with the camera aperture actuator and so the iris does stop down. However you have to careful of your lens falling off!

Av mode works with M42 lenses because there is no connection between the camera and the iris, you have stop down aperture priority.
With the K30, if there was no electrical connection to the lensmount, the camera would try to stop down the lens as much as set in by the aperture ring. So normally the aperture is held open, but on pressing the shutter, the camera would stop down the lens to whatever the aperture ring was set to.
Now the interesting part is, the K30 would adjust exposure automatically for widest aperture (e.g. f1.7) by itself. Now if I set the aperture ring to f4, the K30 would still measure at f1.7 and stop down the lens (as far as it would go) to f4 prior to taking the shot. This results in a picture that is overexposed by exactly 2.5 steps (slight error in previous post).
Now these 2.5 steps can be set by using the cameras exposure compensation, thus eliminating the need for the green button.
This in turn means that you have to adjust EV comp. with changing the aperture, however this is much less trouble than the classic stop-down metering.

For simplification ev-steps for M 50mm f1.7:
1.7 -> +0
2.0 -> +0.5
2.8 -> +1.5
4 -> 2.5
09-29-2018, 08:18 AM   #6
Pentaxian
Not a Number's Avatar

Join Date: Mar 2012
Location: Venice, CA
Posts: 5,615
What version of the firmware is on the K-30? I've long suspected the behavior changes at some point in time reflected by the firmware version. Models released after this point in time (such as the K-3) have this change starting from v1.0.
09-29-2018, 08:24 AM   #7
Forum Member




Join Date: Jun 2015
Posts: 87
Original Poster
Firmware 1.05, maybe 1.06 (latest).
09-29-2018, 09:01 AM   #8
Loyal Site Supporter
Loyal Site Supporter
pschlute's Avatar

Join Date: Mar 2007
Location: Surrey, UK
Photos: Gallery
Posts: 2,475
My understanding is that all Pentax DSLR cameras would not stop down a manual lens in Av mode. *istDS; K10D; K1 all need to be in M mode for the lens to be stopped down when taking the picture. In Av mode it will always be exposed wide open.

never used a K30 though, maybe it was different.

---------- Post added 09-29-18 at 05:07 PM ----------

QuoteOriginally posted by manufocus Quote
Now the interesting part is, the K30 would adjust exposure automatically for widest aperture (e.g. f1.7) by itself. Now if I set the aperture ring to f4, the K30 would still measure at f1.7 and stop down the lens (as far as it would go) to f4 prior to taking the shot. This results in a picture that is overexposed by exactly 2.5 steps
if that behaviour was true you would be getting an underexposed image, not an overexposed one.

Pentax cameras of that era all had a general failing when using Manual exposure mode with stop-down metering. This was due to the design of the focus screen. It manifested itself with manual lenses by a gradual overexposed meter reading as you stopped the lens down in Manual mode. Perhaps this is what you were thinking of ?


Last edited by pschlute; 09-29-2018 at 09:13 AM.
09-29-2018, 09:22 AM   #9
Otis Memorial Pentaxian
Loyal Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 31,402
QuoteOriginally posted by manufocus Quote
However, the K3 does not seem to stop-down the aperture and instead always takes the shot fully open, why is that and is it possibly to change this?
Your K-30 behaves the same way, though you may not have noticed it as such. Non-A K-mount lenses in modes other than M shoot wide open. There is no work around short of surgical conversion of the aperture mechanism to full-manual.

That out of the way, rules for the K-3 for lenses lacking the "A contacts" are a little different than those for the K-30 (generally, in a good way):
  • It is not necessary to short-out contacts for catch-in-focus with M42 lenses
  • Stop-down metering for K-mount lenses still requires M mode
  • K-mount lenses (and accessories) with non-conductive bases will not stop down (always wide open), regardless of mode. I believe this is the only case where shorting contacts or otherwise creating a conductive surface is needed.
  • Green button in M mode works for both M42 and K-mount. The same is true for EV scale stop-down metering using the optical DOF preview in M mode.
  • Auto-ISO is disallowed in M mode, rather than resulting in a silent fail-over to TAv mode as with the K-30. This is a huge improvement.
I believe these are the important points (going from memory regarding how the K-30 works).


Steve
09-29-2018, 09:24 AM   #10
Forum Member




Join Date: Jun 2015
Posts: 87
Original Poster
QuoteOriginally posted by pschlute Quote
My understanding is that all Pentax DSLR cameras would not stop down a manual lens in Av mode. *istDS; K10D; K1 all need to be in M mode for the lens to be stopped down when taking the picture. In Av mode it will always be exposed wide open.

never used a K30 though, maybe it was different.

---------- Post added 09-29-18 at 05:07 PM ----------



if that behaviour was true you would be getting an underexposed image, not an overexposed one.

Pentax cameras of that era all had a general failing when using Manual exposure mode with stop-down metering. This was due to the design of the focus screen. It manifested itself with manual lenses by a gradual overexposed meter reading as you stopped the lens down in Manual mode. Perhaps this is what you were thinking of ?
Ah yes underexposed. I don't have the camera anymore, so it's a bit confusing.

No, this was no error, the difference is just that the K30 would stop down the lens in Av mode as opposed to the K3 which does not stop down the lens (or at least I can't get it to stop down in Av mode). This is quite a bit disappointing :-/ M-Lenses were just so easy to use with the K30...
09-29-2018, 09:50 AM   #11
Loyal Site Supporter
Loyal Site Supporter
pschlute's Avatar

Join Date: Mar 2007
Location: Surrey, UK
Photos: Gallery
Posts: 2,475
QuoteOriginally posted by manufocus Quote
This is quite a bit disappointing :-/ M-Lenses were just so easy to use with the K30
I am not disbelieving you, but how can you be sure it stopped the lens down in Av mode ?
09-29-2018, 09:52 AM   #12
Otis Memorial Pentaxian
Loyal Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 31,402
QuoteOriginally posted by manufocus Quote
No, this was no error, the difference is just that the K30 would stop down the lens in Av mode as opposed to the K3 which does not stop down the lens (or at least I can't get it to stop down in Av mode). This is quite a bit disappointing :-/ M-Lenses were just so easy to use with the K30...
You must have had a very special K-30. No Pentax dSLR in proper working condition will stop-down in other than M-mode unless the "A" contact is detected.*


Steve

* May be spoofed with a wad of foil, but not recommended.
09-29-2018, 10:07 AM   #13
Otis Memorial Pentaxian
Loyal Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 31,402
QuoteOriginally posted by manufocus Quote
This is quite a bit disappointing :-/ M-Lenses were just so easy to use with the K30...
QuoteOriginally posted by stevebrot Quote
No Pentax dSLR in proper working condition will stop-down in other than M-mode unless the "A" contact is detected.
I did a look-back on the OP's posting history. Their K-30 had the aperture controller issue (post from about a year ago), which may be part of the confusion. FWIW, the OP's first post to this site indicates strange behavior of the K-30 at that time (June, 2015)* as well as providing some background for this current post.

Pentax Manual Lens ignored aperture in Av mode (green button) - PentaxForums.com

All that aside, the K-3 behaves how it behaves and how it behaves in regards to lenses where it cannot control the aperture is consistent with other Pentax dSLRs.


Steve

* Apparently able to stop down in Av mode using EC to bias shutter speed for selected aperture.

Last edited by stevebrot; 09-29-2018 at 10:12 AM. Reason: completeness
09-29-2018, 10:09 AM   #14
Forum Member




Join Date: Jun 2015
Posts: 87
Original Poster
QuoteOriginally posted by pschlute Quote
I am not disbelieving you, but how can you be sure it stopped the lens down in Av mode ?
Just looking at the Lens when taking a photo, I could see the aperture closing. Also, correctly exposed pictures when using the EV compensation. I'm sure I have some pictures with ev +2 or something and correct exposure if absolute proof is needed ;-)

QuoteOriginally posted by stevebrot Quote
You must have had a very special K-30. No Pentax dSLR in proper working condition will stop-down in other than M-mode unless the "A" contact is detected.*


Steve

* May be spoofed with a wad of foil, but not recommended.
Dammit! I knew it a was a magical bond between me and my K30! Maybe the K3 is just shy?? But kidding aside, the Av-Stopdown works only with a non-conducting base. I discovered this by accident using a Porst-Lens and not being able to get the green button working. With a regular M-Lens, stop down does also not work in Av Mode. So this is why I cover the contacts with a bit of tape to trick the camera.
09-29-2018, 10:21 AM   #15
Otis Memorial Pentaxian
Loyal Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 31,402
QuoteOriginally posted by manufocus Quote
But kidding aside, the Av-Stopdown works only with a non-conducting base.
OK...lacking a K-30 to confirm, I take this at face value. Sorry that your K-3 does not work that way.


Steve
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, av, dslr, f1.7, f4, k-3, k3, k3 and legacy, k30, lens, lenses, mode, pentax dslr cameras, pentax k-3, picture
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Non-K, Non-42 Adaptable Lenses jawats Pentax SLR Lens Discussion 15 05-15-2018 07:29 AM
Using manual legacy Pentax zoom KA lenses and shake reduction with K1 GaryT Pentax K-1 6 09-25-2017 11:21 AM
K3 and legacy lenses rayhf1485 Pentax K-3 19 05-06-2017 12:00 PM
DA-L and non * / non ltd lenses to be DC ? formercanuck Pentax SLR Lens Discussion 10 01-09-2015 06:56 PM
People Sigma 70-200mm (non DG, non macro, non HSM) Just12hvFun Post Your Photos! 7 04-17-2010 10:49 PM



All times are GMT -7. The time now is 04:52 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