Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
05-31-2011, 01:47 PM   #1
Veteran Member




Join Date: Apr 2011
Location: Texas
Photos: Gallery | Albums
Posts: 528
Why did pentax do away with auto aperture with introduction of K mount?

.. I mean, they had auto aperture with the M42 lenses.. Why weren't the Pentax-M and Pentax K auto aperture capable as well?

05-31-2011, 01:52 PM   #2
Veteran Member
dgaies's Avatar

Join Date: Oct 2009
Location: Maryland / Washington DC
Posts: 3,917
QuoteOriginally posted by geekette Quote
.. I mean, they had auto aperture with the M42 lenses.. Why weren't the Pentax-M and Pentax K auto aperture capable as well?
I could be wrong, but I think they are so long as you use them on a non-crippled mount.
05-31-2011, 02:00 PM   #3
Moderator
Site Supporter
Blue's Avatar

Join Date: Jun 2008
Location: Florida Hill Country
Photos: Gallery | Albums
Posts: 17,213
QuoteOriginally posted by geekette Quote
.. I mean, they had auto aperture with the M42 lenses.. Why weren't the Pentax-M and Pentax K auto aperture capable as well?
The M and k were auto aperture. They worked via the lever rather than the pin used on the m42. In fact, they work with open aperture metering on pentax k-mount bodies. The meaning of A on A series lens has a different meaning in that it allows for bodies to set the aperture when in shutter priority or program mode, and of course require an A series body to take advantage of this.

Features and Operation of the Ka Mount


http://kmp.bdimitrov.de/technology/K-mount/K.html

Last edited by Blue; 05-31-2011 at 02:08 PM.
05-31-2011, 02:05 PM   #4
Inactive Account




Join Date: Mar 2011
Photos: Gallery | Albums
Posts: 302
I'm under the impression that "Auto" on M42 lenses dealt with being able to see what you were looking at to frame an object without the darkening of a closed aperture, then the camera actually closing the aperture when you took the shot. If that's what "Auto" indeed did mean on M42 mounting, I believe K mount lenses are by definition, "Auto".

Someone chime in to correct me if I'm wrong.

05-31-2011, 02:10 PM   #5
Moderator
Site Supporter
Blue's Avatar

Join Date: Jun 2008
Location: Florida Hill Country
Photos: Gallery | Albums
Posts: 17,213
QuoteOriginally posted by icywindow Quote
I'm under the impression that "Auto" on M42 lenses dealt with being able to see what you were looking at to frame an object without the darkening of a closed aperture, then the camera actually closing the aperture when you took the shot. If that's what "Auto" indeed did mean on M42 mounting, I believe K mount lenses are by definition, "Auto".

Someone chime in to correct me if I'm wrong.
That is basically accurate. None of the pre-spotmatic bodies could do open aperture metering and in fact, only the Elecro Spotmatic, ES, ESII and Spotmatic F could do open aperture metering if they were used with a compatible lens.
05-31-2011, 02:53 PM   #6
Veteran Member




Join Date: Aug 2009
Location: New England
Photos: Albums
Posts: 691
QuoteOriginally posted by geekette Quote
.. I mean, they had auto aperture with the M42 lenses.. Why weren't the Pentax-M and Pentax K auto aperture capable as well?
M42 auto aperture and KA-mount auto aperture are different things. K-mount lenses like the M and K series actually work just like auto M42 auto lenses with regards to aperture (as I understand things). For detail on how KA-mount works (and differs from all previous mounts), Bojidar Dimitrov has a good summary in his "Features and Operation of the KA Mount".

Incidentally I noticed that he didn't refer to an auto mode for KA-mount lenses (just an 'A' setting) on that page, so I went and checked the Pentax Super Program manual and they do call it an Auto setting, i.e. from page 3: "Rotate the aperture ring on your 'A' series lens to the Auto position (indexed in green), while depressing the aperture auto lock button."

I can understand how such similar terminology could be confusing, but as you can see, KA-mount adds a significant amount of additional functionality that is not present in the older K-mount or M42 auto mount.
05-31-2011, 03:16 PM   #7
Veteran Member




Join Date: Apr 2011
Location: Texas
Photos: Gallery | Albums
Posts: 528
Original Poster
Ok I understand, auto in the sense that you can look through the lens wide open while at a higher f stop setting.. the camera automatically closes up the iris, snaps it and opens it back up.

Thanks for clearing that up for me.

So the "AUTO" on my M42 Tokina 400mm lens (switchable between A and M) means it has capability to automatically have supported camera close up the iris when snapping and opening it back to wide open. My K-X doesn't support this AUTO since it can't control the pin so I guess I am limited to: manual M42 lenses, switchable, or if I get an AUTO only lens, I have to keep that pin pressed in somehow.

So in the old days, all SLR's were dim through the viewfinder the higher the f-stop. Hey if they could get by doing that then, so can I with m42 lens on my K-X I guess

Last edited by geekette; 05-31-2011 at 03:28 PM.
05-31-2011, 03:30 PM   #8
Veteran Member




Join Date: Apr 2011
Location: Texas
Photos: Gallery | Albums
Posts: 528
Original Poster
One thing I notice though, when I use a manual M42 on my K-X in Av mode, it underexposes for some reason. I don't understand since it should be able to meter accurately since it's all through the lens.

05-31-2011, 03:35 PM   #9
Pentaxian




Join Date: Feb 2009
Location: Alameda, CA
Posts: 3,198
QuoteOriginally posted by geekette Quote
...when I use a manual M42 on my K-X in Av mode, it underexposes for some reason.
The metering problem with manual lenses (pK and M42) of Pentax K-series DSLRs is well-known.

Depending on the lens, it can be over- or underexposure.

You have to learn the metering character of each lens and compensate accordingly.

Read this recent thread on the topic.

Last edited by SOldBear; 05-31-2011 at 03:42 PM.
05-31-2011, 03:40 PM   #10
Site Supporter
Site Supporter
boriscleto's Avatar

Join Date: Dec 2009
Location: Liverpool, NY
Photos: Gallery
Posts: 12,894
QuoteOriginally posted by SOldBear Quote
The metering problem with manual lenses (pK and M42) of Pentax K-series DSLRs is well-known.

Depending on the lens, it can be over- or underexposure.

You have to learn the metering character of each lens and compensate accordingly.
Or use it in M mode and use the AV+- button.
05-31-2011, 04:51 PM   #11
Veteran Member
mtansley's Avatar

Join Date: Oct 2008
Location: Ajax, Ontario, Canada
Photos: Gallery
Posts: 1,139
QuoteOriginally posted by geekette Quote
So in the old days, all SLR's were dim through the viewfinder the higher the f-stop. Hey if they could get by doing that then, so can I with m42 lens on my K-X I guess
Actually, I have a 400mm Lentar M42 lens and it has two aperture dials, one has click stops and right behind it is another one that is smooth running. You'd set your aperture on the click stop one and you could still open the aperture wide for focusing by turning the other dial fully open, once you'd focused you just had to remember to turn the smooth dial back to where it would stop, at that point the aperture would be back to where you'd set it for exposure.

If that makes sense!!
05-31-2011, 05:00 PM   #12
Moderator
Site Supporter
Blue's Avatar

Join Date: Jun 2008
Location: Florida Hill Country
Photos: Gallery | Albums
Posts: 17,213
QuoteOriginally posted by mtansley Quote
Actually, I have a 400mm Lentar M42 lens and it has two aperture dials, one has click stops and right behind it is another one that is smooth running. You'd set your aperture on the click stop one and you could still open the aperture wide for focusing by turning the other dial fully open, once you'd focused you just had to remember to turn the smooth dial back to where it would stop, at that point the aperture would be back to where you'd set it for exposure.

If that makes sense!!
That type of aperture diaphragm is referred to as a pre-set diaphragm, hence preset lens.
05-31-2011, 05:04 PM   #13
Veteran Member
mtansley's Avatar

Join Date: Oct 2008
Location: Ajax, Ontario, Canada
Photos: Gallery
Posts: 1,139
QuoteOriginally posted by Blue Quote
That type of aperture diaphragm is referred to as a pre-set diaphragm, hence preset lens.
Now that I didn't know.

I imagine they date from quite a few years ago.

I haven't a clue how old my lens is. The IQ isn't great so I imagine that brand was probably quite a cheap brand.
05-31-2011, 05:18 PM   #14
Veteran Member
RioRico's Avatar

Join Date: Jun 2008
Location: Limbo, California
Posts: 11,264
QuoteOriginally posted by mtansley Quote
Actually, I have a 400mm Lentar M42 lens and it has two aperture dials, one has click stops and right behind it is another one that is smooth running.
This type of aperture is called a PRESET. Pentax made a few presets, as did others. Many presets also have many aperture blades, for smooth bokeh, and these are what I lust after now. My two-ring presets are:

Mir-1 37/2.8 (M42, only 8 iris blades)
Macro-Takumar 50/4 (1:1, M42, 8 blades)
Jupiter-9 85/2 (M39, 15 iris blades)
Opticam 135/2.8 (T2, 10 iris blades)
Hanimar Preset 135/3.5 (M42, 13 blades)
Jupiter-11 135/4 (M39, 11 iris blades)
Tele-Takumar 200/5.6 (M42, 10 blades)

I have sold exactly one preset, because of too much PF. Knowing what I do now, I should have kept it:

Sunset Telephoto 135/2.8 (M42, 8 iris blades)

As for exposure variance: some non-A-type manual lenses meter erratically on my K20D, and some don't. It's a crap-shoot. And some meter erratically due to Operator Error, ie I focked up and let the meter-select switch slide between positions. Oops.
05-31-2011, 06:15 PM   #15
Veteran Member




Join Date: Apr 2011
Location: Texas
Photos: Gallery | Albums
Posts: 528
Original Poster
QuoteOriginally posted by boriscleto Quote
Or use it in M mode and use the AV+- button.
With m42 lens, in manual mode, the +/- button doesn't meter. If a Pentax-M or Pentax K lens is in it and I press the +/- it does stop down metering fine. I cannot get the camera to meter through the m42 lens in manual mode at all. So I make a guess and snap and look at histo.. it's wasteful but the best I can do atm.
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, auto, auto aperture, k-mount, pentax, pentax lens, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale - Sold: [Worldwide] Pentax 2x Auto Takumar Teleconverter KA-mount wallyb Sold Items 2 02-15-2010 08:12 PM
For Sale - Sold: CPC 70-210mm f/4 KA-mount auto-aperture lens, Pentax SMC-A copy, Worldwide shi wallyb Sold Items 15 10-21-2009 03:16 PM
For Sale - Sold: CPC 80-200mm f/4 Constant-aperture Auto KA-mount Zoom Lens, Only $20 wallyb Sold Items 4 09-10-2009 07:00 PM
For Sale - Sold: Pentacon 200mm f/4 Prime, auto/manual aperture, M42 mount, excellent condition wallyb Sold Items 7 07-15-2009 09:53 PM
A photographic introduction (auto related) Cmanuel Post Your Photos! 17 12-31-2007 07:29 AM



All times are GMT -7. The time now is 03:47 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