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10-07-2009, 12:06 PM   #1
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Metering with Manual lenses..

I am looking to get a 50m-58mm manual focus lens...M42 most likely, or a M39 with a PK adapter....

I can't really find much in my K20 Manual on this..other than using Av with "A" lenses...and I guess M with pre-set lenses.

BUT, What about "M" lenses? Is there a way to use stop-down metering with the "M" PK lenses from Pentax and other makers? I have heard that the even though I will the aperture ring on, let's say f/8, the meter reads wide open SO, I would think that all "M" and other lenses need be used in Stop/Down viewing mode for meter readings?

Pre-sets...Read at the working aperture, after focusing wide open. Right? And does the meter read better (less EC) with Pre-sets over "M" type lenses?

10-07-2009, 12:09 PM   #2
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if the lens you are using has manual aperture control that stops down independant of whether you are taking a photo or not (such as an M42 lens)

then you can shoot in AV mode

if its a lens that has a TAB sticking out, you are pretty much set on having to use step down metering, which is nothing more than pressing the green button.

you would step down meter at the aperture that you are going to shoot at, not "wide open", unless you want to shoot wide open...

really, its not that hard, just buy the lens and go at it...
10-07-2009, 12:23 PM   #3
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If you enable aperture ring and set the camera in manual, you can make use of the green button for the camera to perform stop down metering. The "sticky's" on how to shoot with a manual lens and use of the green button in the beginner's forum will explain this in more detail.
10-07-2009, 01:00 PM   #4
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QuoteOriginally posted by libbyh Quote
If you enable aperture ring and set the camera in manual, you can make use of the green button for the camera to perform stop down metering. The "sticky's" on how to shoot with a manual lens and use of the green button in the beginner's forum will explain this in more detail.
Well, on my "A" lens, set on anything but "A", the green button goes to "Auto ISO" and exposes properly. But it meters WideOpen and knows what f/stop I picked ("A" mode Lenses have that one contact). Every exposure at different f/stops were fine, but, it was not "StopDown" metering, though. I guess the "M" lenses are as an "A" lens "OFF" the "A" mark. Maybe a "M" lens will meter in true "StopDown" mode, since it has no contact for the f/stop
Don't have one, so I can't check it out.

BTW, thanks for the link...Should have looked there 1st

10-07-2009, 01:02 PM   #5
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QuoteOriginally posted by Gooshin Quote
if the lens you are using has manual aperture control that stops down independant of whether you are taking a photo or not (such as an M42 lens) then you can shoot in AV mode
I didn't know that about M42 lenses. Does the adapter affect this in any way? I suppose the viewfinder gets darker as one stops down. (Perhaps focus first wide open, then set the aperture as needed ..)

How far off is the exposure metering with M42 lenses? Some over-exposure seems to be the norm with stopped-down metering with M and K lenses, at least with K10d or k20d. From what I've read and been told, it seems to vary from lens to lens too. I've had better luck with my M lens by following sunny-16, 1/ISO method -- far less over-exposed pics.
10-07-2009, 01:07 PM   #6
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QuoteOriginally posted by wasim_altaf Quote
I didn't know that about M42 lenses. Does the adapter affect this in any way? I suppose the viewfinder gets darker as one stops down. (Perhaps focus first wide open, then set the aperture as needed ..)

How far off is the exposure metering with M42 lenses? Some over-exposure seems to be the norm with stopped-down metering with M and K lenses, at least with K10d or k20d. From what I've read and been told, it seems to vary from lens to lens too. I've had better luck with my M lens by following sunny-16, 1/ISO method -- far less over-exposed pics.
1. its not the adapter, its the fact that M42 lenses do not have the flat rectangular pin that regulates the aperture in all K-Mount (and similar) lenses.. the camera has no impact on the aperture of such lenses.

as you change the aperture, the screen indeed gets darker. Av mode is an on the fly metering algorithm, so its perfect for use with M42 lenses.

as for exposure accuracy, in my experience each lens works differently and requires some time to get accustomed to, but usually on my K20D +0.7 or +1.0 is needed.

however on my FILM camera i had no such problems and shot at 0 EV at all times.
10-07-2009, 02:03 PM   #7
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QuoteOriginally posted by libbyh Quote
If you enable aperture ring and set the camera in manual, you can make use of the green button for the camera to perform stop down metering. The "sticky's" on how to shoot with a manual lens and use of the green button in the beginner's forum will explain this in more detail.
Right - see the sticky threads in the Beginner's Q&A forum. But short answer is that a button will make any Pentax camera momentarily stop down, mete,r and set shutter speed for you; on all models but the K2000/K-m, DOF preview can be used to stop down and get a "live" metering reading for as long as you like.
10-07-2009, 02:10 PM   #8
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QuoteOriginally posted by wasim_altaf Quote
I didn't know that about M42 lenses. Does the adapter affect this in any way? I suppose the viewfinder gets darker as one stops down. (Perhaps focus first wide open, then set the aperture as needed ..)

How far off is the exposure metering with M42 lenses? Some over-exposure seems to be the norm with stopped-down metering with M and K lenses, at least with K10d or k20d. From what I've read and been told, it seems to vary from lens to lens too. I've had better luck with my M lens by following sunny-16, 1/ISO method -- far less over-exposed pics.
I believe it is Lowell G who said that metering problems with stop-down lenses are greatly reduced if you use a focusing screen from a *ist.

I haven't made that switch as I'm using a Jinfinance split screen with my k100d & have few enough metering problems that I prefer the gain in focusing ability to the modest loss in meter precision I experience (if the appropriate pins on the camera's mount are shorted....the DATA pin for sure.)

Dave in Iowa

10-07-2009, 05:50 PM   #9
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QuoteOriginally posted by newarts Quote
I believe it is Lowell G who said that metering problems with stop-down lenses are greatly reduced if you use a focusing screen from a *ist.

I haven't made that switch as I'm using a Jinfinance split screen with my k100d & have few enough metering problems that I prefer the gain in focusing ability to the modest loss in meter precision I experience (if the appropriate pins on the camera's mount are shorted....the DATA pin for sure.)

Dave in Iowa
Lowell was one person who influenced me to install the LL60 screen to correct the metering in my K10D. I can vouch that it is in fact, useful.
10-08-2009, 09:58 AM   #10
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having seen my name here prompts me to respond. I was going to let this post go, because I seem to be writing the same thing every time with respect to metering on K10D and K20D.

a very long time ago (at least it seems so now) I posted the following.

https://www.pentaxforums.com/forums/241716-post69.html

I think the post is self explanatory but please excuse the title as there was a little verbal jousting taking place at the time.

the issue is, as far as I can establish with my "crude" test method, of using the camera's metering on a uniformly lit surface (usually a paved road, sidewalk or block wall), I compare the grey scale value of the central 10% of the screen (i do this in PSP X2), that the screen type dominates the metering issue.

with previous tests I have established that for neutral contrast one stop is about 45 greyscale, (as long as you are between 25 and 230).

I test all my lenses on each body with this test to see how they meter, but I am terribly behind in testing with my K7. I need to do it as well.

I did this because the K10D was much more inconsistant than my *istD, and this was a way to determine the impact of the focusing screen since the *istD and K10D/K20D share the same screen.

Last edited by Lowell Goudge; 10-08-2009 at 10:35 AM.
10-08-2009, 10:01 AM   #11
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QuoteOriginally posted by newarts Quote
I believe it is Lowell G who said that metering problems with stop-down lenses are greatly reduced if you use a focusing screen from a *ist.

I haven't made that switch as I'm using a Jinfinance split screen with my k100d & have few enough metering problems that I prefer the gain in focusing ability to the modest loss in meter precision I experience (if the appropriate pins on the camera's mount are shorted....the DATA pin for sure.)

Dave in Iowa
I have the same setup in my K10D for the same reason, Now that I know the issue and the general trend of the error, it is relitively easy to work out,

What is not as easy is using an aftermarket TC (like sigma's) which does not correct aperture for the TC. this causes an error and you need to set exposure compensation for that case. But at least with a KA/KAF mount TC the error is constant because you meter wide open.
01-03-2010, 05:45 PM   #12
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If you will permit me to ask a related question in this thread...

I have been practicing with a new K-x and 50mm "M" lenses in M mode. Just today I was using an F1.4 lens at about F4 - I composed my shot, hit the Av +/- button (not green) to get an auto picked shutter speed, then took the pic. I then decided to get shallower DOF so I opened up to 1.4 and did the same thing... and heard a SLOW "Ca - Clunk!" Looked at the screen and saw pure white... what? Apparently when I opened up to 1.4 the camera picked ONE THIRD of a second (0.3"). Did I do something wrong? Closed down a bit the shutter was at 1/4000th, so when I opened up more, shouldn't it have maxxed out at 1/6000th? Instead for some reason it goes to a slow shutter speed instead of the fastest. It did this repeatedly... Anyone know why?

I tried a quick search and was reading this thread and thought I would ask - thanks.
01-03-2010, 06:04 PM   #13
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QuoteOriginally posted by Optical Illusion Quote
If you will permit me to ask a related question in this thread...

I have been practicing with a new K-x and 50mm "M" lenses in M mode. Just today I was using an F1.4 lens at about F4 - I composed my shot, hit the Av +/- button (not green) to get an auto picked shutter speed, then took the pic. I then decided to get shallower DOF so I opened up to 1.4 and did the same thing... and heard a SLOW "Ca - Clunk!" Looked at the screen and saw pure white... what? Apparently when I opened up to 1.4 the camera picked ONE THIRD of a second (0.3"). Did I do something wrong? Closed down a bit the shutter was at 1/4000th, so when I opened up more, shouldn't it have maxxed out at 1/6000th? Instead for some reason it goes to a slow shutter speed instead of the fastest. It did this repeatedly... Anyone know why?

I tried a quick search and was reading this thread and thought I would ask - thanks.
The scene was too bright for the lens at f/1.4 and the ISO used. There is a problem with the K-x where it will vastly overexpose an image that is too bright for the current settings, instead of using the 1/6000th shutter speed. I don't know why.

But there is an easy way around it, just use a lower ISO or a smaller aperture, in bright scenes.
01-03-2010, 06:13 PM   #14
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Thanks for that... So that is a known issue? I was already at the lowest ISO (200)... My main question is why would it pick 0.3 seconds as a shutter speed in this scenario?

You are correct that going to a smaller aperture would fix it, but I wanted the 1.4 shallow DOF in this case - I guess this is where a neutral density filter would come into play! But I still think it's a bug in how the K-x operates...
01-03-2010, 06:29 PM   #15
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QuoteOriginally posted by Optical Illusion Quote
Thanks for that... So that is a known issue? I was already at the lowest ISO (200)... My main question is why would it pick 0.3 seconds as a shutter speed in this scenario?
I would like to know the answer to this too Sorry I can't be of more help about it. But it's a known issue in that I know about it, . But I haven't seen it talked about anywhere, I just brush it off as one of the quirks of my favorite camera.
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