Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
03-06-2009, 08:53 PM   #1
Junior Member
ldpercy's Avatar

Join Date: Sep 2008
Location: Sydney
Photos: Gallery
Posts: 29
Auto ISO with Manual Lenses?

Hi all, quick query:

* K20D
* Fully manual lens - no A setting (K 200 f2.5 if it matters)

Can I manually set my aperture and shutter speed and have the camera automatically calculate and set the ISO (using the green button or similar)?

Cheers,
Percy.

03-07-2009, 02:10 PM   #2
Site Supporter
pschlute's Avatar

Join Date: Mar 2007
Location: Surrey, UK
Photos: Gallery
Posts: 715
I use the K10, and the answer for me is no. You should check your manual, but I suspect it is the same with the K20.


You have to use stop-down metering with this lens. If the result does not give you the shutter speed you want (and you dont want to alter the aperture), you will have to adjust the shutter speed/ISO yourself the same number of stops.
03-07-2009, 07:49 PM   #3
Junior Member
ldpercy's Avatar

Join Date: Sep 2008
Location: Sydney
Photos: Gallery
Posts: 29
Original Poster
Cheers, was kind of coming to the same conclusion myself.

'Tis a mighty shame though because the TAv mode on the k20d would seem to be a perfect candidate for this kind of operation.
Pushing the green button isn't a problem, just seems silly that we don't get the option of making the sensitivity the free variable.
I expect this functionality could be added in the firmware too - i don't see any reason why it would be a hardware limitation.

Is there any way that we can request features/upgrades like this from Pentax?
03-07-2009, 08:03 PM   #4
Senior Member




Join Date: Jan 2008
Location: Barrie, ON
Photos: Gallery
Posts: 174
It is a hardware limitation because the lens doesn't tell the camera what aperture it is set at. Without it, the camera cannot find the correct exposure. It would be very nice if you could select the aperture like with SR. it would be very time consuming if you wanted to switch the aperture on the fly but we can dream...

03-07-2009, 09:11 PM   #5
Veteran Member
Mike Cash's Avatar

Join Date: Jan 2007
Location: Japan
Photos: Gallery
Posts: 6,952
You can use auto ISO in Av mode with M42 lenses. The only problem is that you can't select your shutter speed. The camera will (usually) attempt to set an ISO to give you a shutter speed which equal to or faster than 1 over the focal length (1/f). Fine enough for still life, but not really useful for moving subjects.
03-07-2009, 09:21 PM   #6
Veteran Member
RioRico's Avatar

Join Date: Jun 2008
Location: Limbo, California
Posts: 11,264
Nope. That's one of the challenges of non-A shooting on the K20D. The best you can do is:

* set ISO so you're comfortable with the noise level
* dial up M-mode; set the aperture on the lens
* hit the Green button to calculate the shutter

If I don't like the shutter calculation, I change the aperture. If I still don't like it, I grumble and change the ISO, or sigh and change the EV, or wince and change the lighting. Or I cheat, whip out the Sony DSC-V1, set it to NightShot, and hope.

EDIT: Note that not all non-A lenses are created equal. With Pentax-M-compatibles, in M-mode the Green button briefly stops down and measures the exposure, then opens up again; the lens stops down when you hit the shutter. Lots of 'foreign' glass depends on aperture presets; with those, M-mode keeps your ISO setting, and Av mode sets the shutter and ISO to whatever it wants. I think I have that right...

Last edited by RioRico; 03-07-2009 at 10:08 PM.
03-07-2009, 09:44 PM   #7
Junior Member
ldpercy's Avatar

Join Date: Sep 2008
Location: Sydney
Photos: Gallery
Posts: 29
Original Poster
QuoteOriginally posted by ghost Quote
It is a hardware limitation because the lens doesn't tell the camera what aperture it is set at. Without it, the camera cannot find the correct exposure. It would be very nice if you could select the aperture like with SR. it would be very time consuming if you wanted to switch the aperture on the fly but we can dream...
That's what the green button on the K20D is for - on the K100D you can press the AE-L button to much the same effect: it stops down the aperture temporarily to take an exposure reading. The camera then has enough information to calculate the correct shutter speed (given the ISO). By corollary the camera should be able to calculate the needed ISO given a shutter speed.


Thanks all for the replies, I was hoping that the K20D would be a little bit cleverer/more flexible in this regard, but I'll get over it

Last edited by ldpercy; 03-07-2009 at 10:06 PM.
03-09-2009, 06:15 PM   #8
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,314
Its a shame that pentax didn't take my suggestion to enter max and min apature, and calculate the movement needed on the apature activation lever to control exposure like an A series lens,

Oh well

03-10-2009, 01:24 AM   #9
Veteran Member




Join Date: Jul 2008
Location: Var, South of France
Photos: Albums
Posts: 1,071
Lowell: the problem with this proposal is that the lever doesn't necessary move the aperture in a predictable relation.

ldpercy: only solution I found was to drill a second locking hole into the lens, in order to lock it partway in the mount, before the lens aperture lever comes into contact with the camera actuator... The lens then behaves as a m42, allowing Av with auto-iso (but with a dark viewfinder if you"re using a small aperture)...

And you can still lock the lens with the original locking hole and use it as a PK-m lens...
03-10-2009, 03:04 AM   #10
Junior Member
ldpercy's Avatar

Join Date: Sep 2008
Location: Sydney
Photos: Gallery
Posts: 29
Original Poster
Re: the aperture activation lever - virgilr has a similar sounding idea posted in the 'next generation' thread that's also floating about.
Technically it sounds feasible - it wouldn't be perfect of course but it could be done.

If I was feeling cynical I might think that Pentax are deliberately hobbling the use of their older lenses to a degree to keep the market up for their newer glass - certainly that would be their prerogative if it were the case (they are a business after all) but I'm reminded of Hanlon's Razor - they just might not have the time/resources for supporting legacy systems.

Incidentally are these kinds of requests effectively the same as calling for the un-crippling of the K-mount, or is that something different?

Last edited by ldpercy; 03-10-2009 at 03:24 AM.
03-10-2009, 03:28 AM   #11
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,314
QuoteOriginally posted by dlacouture Quote
Lowell: the problem with this proposal is that the lever doesn't necessary move the aperture in a predictable relation.

ldpercy: only solution I found was to drill a second locking hole into the lens, in order to lock it partway in the mount, before the lens aperture lever comes into contact with the camera actuator... The lens then behaves as a m42, allowing Av with auto-iso (but with a dark viewfinder if you"re using a small aperture)...

And you can still lock the lens with the original locking hole and use it as a PK-m lens...
i believe actually the lever does move in a predictable manner, just not the same as A lenses. Someone reported (I think on the mark rogers site) that the diameter is linear with movement, where A lenses it is the area that is linear with movement, making control at small stops easier, but lets just leave it at pentax would not make abny concessions with respect to manual lenses
03-10-2009, 04:24 AM   #12
Veteran Member




Join Date: Jul 2008
Location: Var, South of France
Photos: Albums
Posts: 1,071
From my limited meddling with non-A lenses, I'd be inclined to believe that pentax and takumar lenses *maybe* behave this way, but I'm quite sure 3rd-party lenses are not necessarily diameter-linear... After all, they were designed for several mounts, with different aperture control...

For instance, my Porst 55/1.2 is in fact approximatively area-related...
I guess no one can really explain why they removed the coupling, while at the same time touting the backward compatibility...
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!
auto iso, camera, dslr, iso, photography
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Auto ISO in manual mode yusuf Pentax DSLR Discussion 37 03-10-2012 05:44 PM
[Auto-ISO] so, is the K5 and Kr brave enough to use max iso? Reportage Pentax K-5 13 10-24-2010 03:30 PM
Do I need manual lenses for ISO-controlled video? ronald Video and Pentax HDSLRs 5 05-18-2010 09:45 PM
Auto-Focus Lenses on Manual Bodies pdx138 Pentax Film SLR Discussion 7 08-22-2009 06:47 PM
K10D and AUTO ISO with manual lenses kevbirder Pentax DSLR Discussion 10 11-15-2008 10:03 PM



All times are GMT -7. The time now is 07:34 AM. | See also: NikonForums.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