Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
11-09-2011, 12:35 PM   #16
Loyal Site Supporter
eddie1960's Avatar

Join Date: Aug 2010
Location: Toronto
Photos: Gallery | Albums
Posts: 12,271
QuoteOriginally posted by bjake Quote
Find the A lens to be much more accurate.When using M lens I just go to manual and guess the exposure which I seem to be able to do as well as the camera and much faster.This probably comes from using a Spotmatic for 30 or so years a lot of the time with no battery installed.
Jake
I have Sunny 16 imprinted on my brain from manual film cameras

11-09-2011, 03:34 PM   #17
Site Supporter
Spodeworld's Avatar

Join Date: Aug 2011
Location: New Joisey
Photos: Gallery | Albums
Posts: 1,240
Original Poster
I guess I'll get to find out..going to get the 50mm1.7 and the 28mm2.8, but A.

I just got a cheap split screen focus screen a day ago, and while it seems useful, it starts to black out at f4. (As an aside, use of the split screen highlights that AF isn't always perfectly on.) Perhaps the A will help since the aperture will stay open fully until the actual shot is taken keeping it bright all except for the instant of shooting, versus the M, where you focus, stop down at which point you run the risk of it blacking out, meter and then shoot. Of course, if you shoot wider than f4, that advantage is lost.
11-09-2011, 04:15 PM   #18
Veteran Member
RioRico's Avatar

Join Date: Jun 2008
Location: Limbo, California
Posts: 11,264
I've been shooting an A-type Toyo 28/2.8 the last few days. Sometimes it meters fine;sometimes it meters high, and I dial-down the EV. Similar results with the M28/2.8 and M42 Makinon 28/2.8. The modded Nikon-mount Vivitar-Komine 28/2 CFWA and Adaptall (M-type) Tamron BBAR 28/2.5 show little variance. So, it all depends on the lens...

QuoteOriginally posted by Spodeworld Quote
Perhaps the A will help since the aperture will stay open fully until the actual shot is taken keeping it bright all except for the instant of shooting, versus the M, where you focus, stop down at which point you run the risk of it blacking out, meter and then shoot.
With an M-type lens in M mode, compose the shot wide-open, hit the Green button to meter, then shoot. No need (or ability!) for stop-down composing; the iris stays wide open until you hit the Green button.

Using M-types on my K20D, I often set the mode dial to TAv which is right next to M. For wide open shooting, I'm set -- it defaults to Av mode. For stop-down shooting, I just quick-twist it to M and hit the Green button. It's almost automagic that way.
11-09-2011, 06:42 PM   #19
Site Supporter
Spodeworld's Avatar

Join Date: Aug 2011
Location: New Joisey
Photos: Gallery | Albums
Posts: 1,240
Original Poster
I've basically been using M42s and have hardly touched my 2 M-type lenses and didn't realize that there was no stop-down metering! I thought they behaved like the M42s! Well, you learn something new every day.

Let me see if I got what you are saying: you use TAv for when you want to shoot wide open for the automatic metering, and M for when you want to stop down?

Is the reason you use TAv instead of Av is for its proximity to M for a quick change?

QuoteOriginally posted by RioRico Quote
With an M-type lens in M mode, compose the shot wide-open, hit the Green button to meter, then shoot. No need (or ability!) for stop-down composing; the iris stays wide open until you hit the Green button.

Using M-types on my K20D, I often set the mode dial to TAv which is right next to M. For wide open shooting, I'm set -- it defaults to Av mode. For stop-down shooting, I just quick-twist it to M and hit the Green button. It's almost automagic that way.


11-09-2011, 09:40 PM   #20
Veteran Member
sterretje's Avatar

Join Date: Dec 2008
Location: Roodepoort, South Africa
Photos: Gallery | Albums
Posts: 3,534
QuoteOriginally posted by Spodeworld Quote
I just got a cheap split screen focus screen a day ago, and while it seems useful, it starts to black out at f4. (As an aside, use of the split screen highlights that AF isn't always perfectly on.)
That is not necessarily true unless your images look better when focusing using the split prism. Else you need to shim your focusing screen.
11-10-2011, 02:04 AM   #21
Veteran Member
Philoslothical's Avatar

Join Date: May 2011
Posts: 1,723
I think part of the confusion around this issue is a result of people thinking that Av mode is suitable for manual aperture lenses. It is not, it's quite inaccurate, and gets worse as you stop down the lens. The Pentax site itself warns about this and recommends using M mode with the green button.

This is a non-issue with A series lenses. Av mode meters properly with them, provided that the aperture ring on the lens is set to A. You can use A series lenses in M mode with the green button, if you want to set the aperture on the lens, but there's no need to do this under normal conditions. Reliable Av mode metering is the main advantage of using an A series lens.
11-10-2011, 03:15 AM   #22
Veteran Member
RioRico's Avatar

Join Date: Jun 2008
Location: Limbo, California
Posts: 11,264
QuoteOriginally posted by Spodeworld Quote
I've basically been using M42s and have hardly touched my 2 M-type lenses and didn't realize that there was no stop-down metering! I thought they behaved like the M42s! Well, you learn something new every day.
M-type lenses will stop-down for metering and exposures in M mode and only in M mode. Anywhere else, they're wide-open.

QuoteQuote:
Let me see if I got what you are saying: you use TAv for when you want to shoot wide open for the automatic metering, and M for when you want to stop down?
If I put onto the camera any lens that doesn't have the aperture contacts (which only A-type and AF lenses have) then when the dial is set to any Auto mode (Av, Sv, Tv, TAv, Green) the camera defaults to Av mode. Try it: put an M-type lens on the camera, then switch between the Auto modes. The Info screen will tell you that you're in Av.

Let's say I'm wandering around beautiful historic Santa Fe NM in the morning with my beloved K50/1.2 mounted and set to f/8. I see some moody floral shots in a partly-shaded courtyard so I set the dial to TAv (the camera defaults to Av) and shoot wide-open. Back on the street, I see a quaint adobe home surrounded by a succulent garden so I quick-switch to M, hit the Green button, and shoot. Easy-peasy.

QuoteQuote:
Is the reason you use TAv instead of Av is for its proximity to M for a quick change?
Exactly right!
11-10-2011, 07:33 AM   #23
Site Supporter
Spodeworld's Avatar

Join Date: Aug 2011
Location: New Joisey
Photos: Gallery | Albums
Posts: 1,240
Original Poster
Very useful advice in that comment!

QuoteOriginally posted by RioRico Quote
Let's say I'm wandering around beautiful historic Santa Fe NM in the morning with my beloved K50/1.2 mounted and set to f/8. I see some moody floral shots in a partly-shaded courtyard so I set the dial to TAv (the camera defaults to Av) and shoot wide-open. Back on the street, I see a quaint adobe home surrounded by a succulent garden so I quick-switch to M, hit the Green button, and shoot. Easy-peasy.


11-10-2011, 01:15 PM   #24
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,400
I think the issue has not been fully answered or explained, so here goes. I note the OP uses a K20D which is very relevant to this whole issue.

First of all, as many have pointed out, SMC-M lenses (basic K mount lenses) do not have aperture coding contacts, so the camera simply does not know the maximum and minimum apertures. SMC-A lenses (KA mount lenses) provide the maximum and minimum aperture information to the camera via 5 contacts (or insulated positions) on the lens mount., The 6th contact on the KA mount (If all pins are present) tells the camera whether the lens is in the A position or not.

I have posted the chart below many many times in the past. WHat it shows is how each of my cameras at the time metered in manual with my K50/1.4. I also have tested the K10D with both the *istD LL-60 screen, and with a split image screen, because I have come to the conclusion that the metering inconsistancies with the K10D and K20D specifically are the stock focusing screen.



The curve was generated by taking for each camera/focusing screen combination, a series of photographs of a uniformly lit surface uniform surface(the block wall at the back of my house, or a paved road, or concrete pathway) at each aperture detent, and then pressing the green button to "meter". It should be noted that each 40-50 greyscale is one stop (I say 40-50 because it depends on the contrast setting, i used low contrast, which gives a greyscale of 40 per stop, when in the middle of the histogram)

You can see that the greyscale value changes as a function of aperture (manual mode green button metering) and that the camera is not picking the correct shutter speed as a function of aperture. It is only really correct between F4-5.6 (i.e. the aperture range of the kit lens)

My theory is that with KA lenses of apertures different than F4-5.6, the camera has a "fudge factor" to correct the metering, using basically an exposure compensation that negates the curve above, relitive to a greyscale of 110-120 which is "correct" metering.

This is how the cameras meter.

Secondly, and this has been pointed out, some screw mounts, when put on some cameras have a predominant offset, due to the fact that the camera thinks no lens is attached (pin 7 not shorted to lens mount) This is easily compensatred for when using M42 lenses in Av mode.

K mount lenses in Av mode only expose at maximum aperture because the camera does not know the maximum aperture value, and will suffer all the errors of the chart at maximum aperture. i.e. under or over expose
11-10-2011, 01:56 PM   #25
Pentaxian
Jonathan Mac's Avatar

Join Date: Apr 2009
Location: Madrid, Spain
Posts: 4,361
For my A50 f/1.7 I will usually set EV compensation to +0.7. On my M50 lenses (and other Ms) Iīll use the green button to meter, then adjust the shutter speed down by around 2/3 of a stop and shoot. Itīs effectively the same adjustment and the results come out the same. At ISO 100 (where I usually have it set) the results have plenty of margin for adjustment in PP.
11-10-2011, 02:01 PM   #26
Pentaxian
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 4,864
The 16-segment metering is OK but with A lenses on a K-7 or K-5, you get 77 segment metering. That is so good, I actually pay attention to it. But I'm used to seeing metering as a suggestion, not an absolute.
11-10-2011, 11:07 PM   #27
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
It matters what camera you are using, and which focus screen you are using. See a number of other threads on metering with "M" lenses - there are issues with the K10D and K20D most specifically, with the stock focus screen. Also be aware that with M lenses, pattern metering isn't available - it's center weighted by default. So that often catches people by surprise.

Anyhow, I've tested my K200D with a number of M lenses, checking exposure at each aperture, and it's totally consistent - within a half stop every time. But others have done the same with the K10D/K20D and found exposure discrepancies as they stopped down.
11-11-2011, 04:17 AM   #28
Site Supporter
Mychael's Avatar

Join Date: Oct 2011
Location: Melbourne,Victoria,Australia
Photos: Albums
Posts: 215
As I'm getting my K5 tomorrow and will be using a mixture of K & KA lenses can you dumb it down a bit more for me to just get started. I'm sure it will more clear when I actually have the camera in my hands.
So lets say I'm useing a 'm' lens, I'll set the camera mode to manual, set the menu to allow use of aperture ring, then what? Say I want to keep the iso down to 100 as a constant, do I then turn the aperture ring to the setting I want and leave it there, then press then green button, then what? does it tell me a shutter speed I need to set to get a correct exposure or have I got this all wrong.

Then take same scenario only with an KA lens, set the aperture ring to 'A' the camera to AV (will Tv also work), then what?

Sorry if my questions are basic 101 but I just want a few parameters to get me started.

Thanks.
11-11-2011, 06:49 AM   #29
Site Supporter
Spodeworld's Avatar

Join Date: Aug 2011
Location: New Joisey
Photos: Gallery | Albums
Posts: 1,240
Original Poster
@Mychael - When you press the green button in Manual, it will actually set the shutter speed for you (you can change it). Coming from a Nikon, the functionality surprised me.

Have a look here at the sticky threads at the top. That is how I got my start learning how to use these lenses
Pentax Beginner's Corner Q&A - PentaxForums.com

Steve
11-11-2011, 06:57 AM   #30
Site Supporter
Spodeworld's Avatar

Join Date: Aug 2011
Location: New Joisey
Photos: Gallery | Albums
Posts: 1,240
Original Poster
I've used a few m lenses, both M42 and K mount, and yes on the K20D the metering is usually off by a stop or so. The reason for the post was because I was curious if the A lenses tended to be more accurate. I'm getting the sense that the A is probably more accurate (I would hope so), which was my main concern, but there are other advantages that were brought up: compared to M, more metering modes, more functional exposure modes, recording of exposure data. There may be others.

QuoteOriginally posted by Marc Sabatella Quote
It matters what camera you are using, and which focus screen you are using. See a number of other threads on metering with "M" lenses - there are issues with the K10D and K20D most specifically, with the stock focus screen. Also be aware that with M lenses, pattern metering isn't available - it's center weighted by default. So that often catches people by surprise.

Anyhow, I've tested my K200D with a number of M lenses, checking exposure at each aperture, and it's totally consistent - within a half stop every time. But others have done the same with the K10D/K20D and found exposure discrepancies as they stopped down.

Last edited by Spodeworld; 11-11-2011 at 07:33 AM.
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!
camera, pentax help, photography, smc pentax, vs
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale - Sold: Pentax SMC-M 28mm F2.8 and Pentax SMC-A 50mm F1.7 (non func A setting) (US) pxpaulx Sold Items 5 07-23-2010 10:38 PM
For Sale - Sold: SMC Pentax-F 35-70mm F3.5-4.5;SMC Pentax-A 50mm F2;SMC Pentax-DA L 18-55mm F3. TATA Sold Items 14 06-17-2010 04:05 PM



All times are GMT -7. The time now is 02:03 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