Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
05-03-2012, 05:58 AM   #31
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,400
QuoteOriginally posted by minahasa Quote
Lowell, that's exactly my point. If those "A" lenses are just AF lenses without AF function, and metering with those (although with added ease of use) just added another thing to worry because we know that it will go meter by itself but there's no guarantee it will meter correct, then why not do it all by our self? The convenience -ease of use- we get from "A" lenses is, for me, not really enough to justify the added price and for faster-action events I rather grab an all-automatic lens instead.
I think you miss the real point here.

I have attached the performance of different cameras using green button metering I trust this will help explain the issue



what you can see is that for example the A50/1.2 (data from another user) shows the metering performance with green button both in and out of the A position

If the camera Knows the aperture range of the lens it does open aperture metering and calculates the aperture for the selected one through the body, and then stops the lens down accordingly. As you can see, in the A position, the exposure line is almost perfectly flat across the entire range, but out of the A position the same lens on the same camera meters rather badly because there are non linearities in the metering that are corrected in software but only if the maximum aperture is known.

I would rather trust the camera, relitive to metering and corrections, than to remember this curve, and have to compensate for it 100% of the time. You can also see, even in A mode the aperture control is not perfect, but the error at F1.2 is about 1/6 of a stop (not too bad) and at minimum aperture about 1/2 stop, otherwise it is pretty good.

05-03-2012, 06:26 AM   #32
Site Supporter




Join Date: Jan 2010
Location: Michigan
Photos: Gallery
Posts: 2,180
Lowell, Can you explain further about metering "out of A position"

As I know it you then have to be in M mode, and use the stop down button , whereby the lens is actually stopped down to the aperture on the ring and the camera meters the real light.
Are you saying there are errors there?
05-03-2012, 06:46 AM   #33
Pentaxian
audiobomber's Avatar

Join Date: May 2008
Location: Sudbury, Ontario
Photos: Albums
Posts: 6,684
QuoteOriginally posted by jimr-pdx Quote
Does not the EXIF data misrepresent with A lenses when taken off A? No effect on images, but lousy for feedback later.. and a crummy conversation starter when the first question someone asks me is for exposure data . When I take my Sigma macro off the A setting, every image records max aperture.
That's odd. When I take my auto lenses off A position, aperture says F--- , exactly as though I have a manual lens mounted.
05-03-2012, 07:03 AM   #34
Veteran Member
joe.penn's Avatar

Join Date: Mar 2011
Location: Maryland (Right Outside Washington DC)
Photos: Gallery | Albums
Posts: 2,902
QuoteOriginally posted by wombat2go Quote
As I know it you then have to be in M mode, and use the stop down button , whereby the lens is actually stopped down to the aperture on the ring and the camera meters the real light.
Yes, that is how it works in "Hyper Manual Mode" with one EXCEPTION - if you are in "Hyper Manual Mode" with a live "A" contact and you green button meter the lens will not stop down and just use the data [as set by the body] for the metering.

05-03-2012, 07:06 AM   #35
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,400
QuoteOriginally posted by wombat2go Quote
Lowell, Can you explain further about metering "out of A position"

As I know it you then have to be in M mode, and use the stop down button , whereby the lens is actually stopped down to the aperture on the ring and the camera meters the real light.
Are you saying there are errors there?
That is exactly what I am saying. each camera I own, *istD, K10D, K7D and K5 D have their own behavior when metering using the green button, and manual aperture lenses. Except for the really flat line, each curve represents a lens on one of the cameras / with one of the focusing screens tested, in manual mode doing stopped down metering.

The *istD, and K5D have very similar errors as a function of aperture, but they are within +/- 1/2 stop of nominal exposure across the entire aperture range of the lens, and really can be lived with.

the K10D is a disaster, with under exposure by as much as a stop below F2.8 and over exposure by about 2 stops at F11. there is no way of knowing exactly the source of the error, other than part of this is related to the focusing screen and its reflective behavior, I suspect (and this is my own thinking, with no other proof) due to the scattering of light off the focusing screen due to light that hits at other than a right angle. As you stop down, light becomes more and more normal to the focusing screen.

the K7 is better but can still drift by -1/2 +1 stop, or about 1/2 the drift of the K10D.

as for taking a lens out of A, this removes the connection between the 3rd pin from the lens locking pin to the lens mount, which is needed to tell the camera that there is an A lens mounted. In this case, the A lens behaves just like a K lens, and you can see the change in exposure accuracy by physically stopping down and reading the light, as opposed to reading the light wide open, and compensating for the known error vs maximum aperture, and calculating the correct shutter speed to match the aperture.

Just look at the difference for the A50/1.2 in the A position and out of it.

The history of this issue, began with some anecdotal comments about erratic metering on the K10D, and almost at the same time, questions about exposure errors due to the use of a teleconverter. I did some testing using my sigma 70-200/2.8EX and both 1.4x and 2X TCs. what I noticed was that I needed about .7 stops with a 1.4x and 1.3 stops with a 2x. Then I went and did some other testing, determining that for normal contrast settings, from about 25 greyscale to 225 grey scale in the histogram, each stop is linear and has about a 40-45 greyscale value. Then I did the plot for my K50/1.4 and it all became apparent.

If you consider adding a 1.4x TC, my 70-200/2.8 becomes an F4 lens If you look at how a K10D meters at F2.8 and F4, there is a difference in greyscale reading of about 40 which is 1 stop. The TC feeds the aperture directly through to the camera without modification, hence it is putting the wrong correction , if you add a 2x, there is even more error, because the camera still thinks there is an F2.8 lens attached but it is actually an F5.6

This is how it all came about historically many years ago.

Last edited by Lowell Goudge; 05-03-2012 at 07:17 AM.
05-03-2012, 07:17 AM   #36
Site Supporter




Join Date: Jan 2010
Location: Michigan
Photos: Gallery
Posts: 2,180
Thanks Lowell, I now recall going thru this before and replicating your graph on my ist ds and then forgot all about the error issue because I only use ist ds ands my errors were less than your graph.
For Audio and Joe, here is exif data for the "M" and "AV" modes of the ist ds

Here is exif data for the ist ds with the SMC Pentax-A 1:2.0 50 mm in M Mode with the Aperture ring off the A setting
**See how it reports the Actual Aperture as 0.1, and it got the min/max correct.

[prXXXX@localhost tests]$ exiftool -a -u -g1 imgp5379.jpg | grep Aperture
Picture Mode : Manual, Off-Auto-Aperture; 1/2 EV steps
Picture Mode 2 : Manual, Off-Auto-Aperture
Aperture Ring Use : Prohibited
AE Aperture : 0.1
AE Max Aperture : 2.0
AE Max Aperture 2 : 2.0
AE Min Aperture : 23
Auto Aperture : Off
Min Aperture : 22
Nominal Max Aperture : 1.0
Nominal Min Aperture : 6


Here is exif data for the ist ds with the SMC Pentax-A 1:2.0 50 mm in Av Mode with the Aperture ring At the A setting
**It got it all correctly
[prXXX@localhost tests]$ exiftool -a -u -g1 imgp5380.jpg | grep Aperture
Exposure Program : Aperture-priority AE
Picture Mode : Aperture Priority; 1/2 EV steps
Picture Mode 2 : Aperture Priority
Aperture Ring Use : Prohibited
AE Aperture : 6.7
AE Max Aperture : 2.0
AE Max Aperture 2 : 2.0
AE Min Aperture : 23
Auto Aperture : On
Min Aperture : 22
Nominal Max Aperture : 1.0
Nominal Min Aperture : 6
Aperture : 6.7
05-03-2012, 07:53 AM   #37
Veteran Member
magkelly's Avatar

Join Date: May 2010
Photos: Gallery
Posts: 5,905
If I want an AF lens I'll use a more modern digital lens. The "A" switch on most of my old lenses never gets used much. I shoot either in full manual (more often than not) or in a program mode if I am shooting from the hip and just need to aim and fire. If my eyes are crappy then I shoot more with AF. If I'm having a good day and my eyes aren't seemingly burning their way out of my head and don't feel like they are filled with grit then I'll happily spend all my time "fiddling" with my MF lenses. I'm a Tak freak. If I am going to shoot MF, take that time, then why wouldn't I want to do it all?

If I have to shoot fast I'm not reaching for the oldest lenses in my kit anyway. I'm reaching for a digital lens with AF. On the other hand if I want to take my time and make absolutely sure all my images come out totally sharp I'm going to shoot with a Takumar most likely and certainly I'll take my time. I don't try to shoot fast moving objects with old lenses very often. With my eyes that's pretty much wasted effort. About the only one of my older primes that can keep up a bit, work fast in low light is an "A" series 50 for what it's worth. It takes time but that's a really great lens. Someday I'd love to have an AF prime lens worthy of replacing that one but to do that I'd be spending way too much, alas...
05-03-2012, 08:32 AM   #38
Veteran Member




Join Date: Jan 2011
Location: Minahasa, North Celebes (Sulawesi)
Photos: Albums
Posts: 585
Original Poster
Lowell, I really appreciate all the efforts showed by you and other friends in this thread to explain technically, but this is getting exactly toward the reason I posted this thread: I find "A" lenses to be more complicated to handle (and to think of) than full manuals. Probably this has something to do with how I take pictures. I set the aperture-speed-iso-wb. I take the first shot (thank God for digital imaging ). From that 'test' shot I will know what to set next. With time, I have gotten used to this and getting better, and I seems to be able to sense and calculate everything right -less test shots needed, probably like Sunny 16. Perhaps this is just too Jurassic, a waste of technology, but it works for me.

I'm not saying that Auto Aperture technology is totally unreliable and a waste, I merely saying that it's making me uneasy. All-manual lenses make myself able to determine everything to my like and getting the result in my liking.

05-03-2012, 09:04 AM   #39
Site Supporter




Join Date: Feb 2012
Photos: Gallery
Posts: 91
What's everyones favorite auto mode setting for a A lens, in my case it's on a K20.

Now what about in less than ideal light, subject in the shadows, strong back light, ect. In those cases I either go to manual or bump up the AE comp.
05-03-2012, 09:08 AM   #40
Veteran Member




Join Date: Oct 2010
Location: Taiwan
Photos: Gallery | Albums
Posts: 1,075
I'm like several here and shoot in M mode almost all of the time. If the light is not changing then why adjust exposure? I'm also using bracketing frequently so it doesn't matter if I'm dead on for exposure. But there are times that shooting in Av is useful and I like having the option. But most of my recent purchases have been K/M lenses with a new lens sprinkled in.
05-03-2012, 05:00 PM   #41
Site Supporter
jimr-pdx's Avatar

Join Date: May 2010
Location: 1hr north of PDX
Photos: Gallery | Albums
Posts: 3,550
QuoteOriginally posted by audiobomber Quote
That's odd. When I take my auto lenses off A position, aperture says F--- , exactly as though I have a manual lens mounted.
I'll check that again. While cross-testing the Tamron 90 and Sigma 50 macros I shot using the aperture dial, and in both cases I thought I read f/2.8 at three settings. I shall look over my "notes" though, user errer is not uncommon here but perhaps these being modern AF lenses changes how they act compared to true SMC-A designs of old.
05-03-2012, 06:27 PM   #42
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,400
QuoteOriginally posted by minahasa Quote
Lowell, I really appreciate all the efforts showed by you and other friends in this thread to explain technically, but this is getting exactly toward the reason I posted this thread: I find "A" lenses to be more complicated to handle (and to think of) than full manuals. Probably this has something to do with how I take pictures. I set the aperture-speed-iso-wb. I take the first shot (thank God for digital imaging ). From that 'test' shot I will know what to set next. With time, I have gotten used to this and getting better, and I seems to be able to sense and calculate everything right -less test shots needed, probably like Sunny 16. Perhaps this is just too Jurassic, a waste of technology, but it works for me.

I'm not saying that Auto Aperture technology is totally unreliable and a waste, I merely saying that it's making me uneasy. All-manual lenses make myself able to determine everything to my like and getting the result in my liking.
What I dont get is why you thing auto aperture is more complicated or confusing, when it meters much better than a K lens, therefore eliminating the test shots for exposure. To me you've got it wrong, unless you have a problem transitioning from lens to lens and therefore want the same thought process for all lenses.
05-03-2012, 06:51 PM   #43
Veteran Member
joe.penn's Avatar

Join Date: Mar 2011
Location: Maryland (Right Outside Washington DC)
Photos: Gallery | Albums
Posts: 2,902
QuoteOriginally posted by Mike C Quote
What's everyones favorite auto mode setting for a A lens, in my case it's on a K20.

Now what about in less than ideal light, subject in the shadows, strong back light, ect. In those cases I either go to manual or bump up the AE comp.
- Aperture Value ("AV")
- Aperture Value ("AV")
- Aperture Value ("AV") with "EV" comp if no sky is framed in scene
- Aperture Value ("AV") with "EV" comp if no sky is framed in scene

For Reference: If a sky in framed in the scene, I use a negative "EV" comp and use fill flash/hss to overcome backlighting or shadow issues...
05-03-2012, 06:56 PM   #44
Veteran Member




Join Date: Jan 2011
Location: Minahasa, North Celebes (Sulawesi)
Photos: Albums
Posts: 585
Original Poster
QuoteOriginally posted by Lowell Goudge Quote
What I dont get is why you thing auto aperture is more complicated or confusing, when it meters much better than a K lens, therefore eliminating the test shots for exposure. To me you've got it wrong, unless you have a problem transitioning from lens to lens and therefore want the same thought process for all lenses.
A lenses can meter more easier and probably better, yes, but many times it gives me not what I want. It's not like that the metering is incorrect, no. It's the capability to 'think' seems different than mine that bothers me, giving me not what I want. Yes I can fiddle around to find settings that suits me, but then I prefer overriding to full-manual for better controls. Probably you are correct, I have a problem. My solution is going full-manual and learning each lens' character for better results. That's why although I have tried many lenses, I kept only several -one for every usable FL- and mostly primes and have constant aperture.
05-03-2012, 07:40 PM   #45
Veteran Member
creampuff's Avatar

Join Date: May 2007
Location: Singapore
Photos: Gallery
Posts: 3,955
I can see no advantage or reason to use an A lens off the A setting. Lenses with the PKA mount provide superior functionality over previous non-A series lenses (K & M series).

No limitation of exposure metering modes, more accurate exposure metering, more exposure modes including Hyper Manual are just some of the obvious advantages. With an A-lens, because exposure settings are controlled by the camera body, exposure control is far quicker as exposure information is visible in the viewfinder and LCD as well as faster exposure compensation input. And with EXIF information readily available with an A lens, it is a lot easier to sort, categorize, archive and search for images when cataloging digital images.

My only conclusion is OP is probably still grappling to handle a multi-function camera in the digital age. Those still determining exposure and using their DSLRs the way they used to with their 35mm film cameras, time to get a refresher and unlearn the old ways.

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!
advantage, function, k-mount, lenses, love, pentax lens, series, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Don't say Pentax "Q" in French ... "Q" = "cul" = "A--" Jean Poitiers Pentax Q 52 11-10-2013 06:25 AM
Abstract Andy Warhol watch out--"Food for Thought" charliezap Post Your Photos! 10 01-31-2012 12:06 PM
When was the last time you heard "That's a Pentax? Thought they went out of business" m8o General Talk 31 01-06-2011 07:23 AM
65 "thought lost or destroyed" Ansel Adams negatives found MRRiley Photographic Technique 18 07-30-2010 03:45 PM
What does "auto" mean on older manual focus lenses? jonhock Pentax SLR Lens Discussion 18 12-03-2009 11:32 AM



All times are GMT -7. The time now is 03:27 AM. | 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