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12-03-2008, 09:52 PM   #1
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Takumar Question // Exposure & Aperture

Just received a Super Takumar 135 f/2.5


Two questions after some playing time:


1) does it matter how I set the aperture ring? I mean, it only seems to change the aperture if I leave it in AUTO (MAN. appearing).

2) Interestingly, exposure seems to be good for any aperture BUT f/2.5! It is absolutely underexposing...

I dont have pictures to show, but I can provide shutter values for comparison:


SPOT Metering:
f/2.5 > it gives me 1/180 (totally dark)
f/4.0 > it gives me 1/6 (right exposure)


MATRIX Metering
f/2.5 > 1/60
f/4.0 > 1/10



Weird weird weird..... Any ideas?

12-03-2008, 11:39 PM   #2
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From my short experience with a 50 1.4 Super Tak, "MAN" appearing means the lens will work in manual mode (for aperture).

As for exposure I cannot say anything yet since I still do not have that M42 to K-mount adapter from ebay.
12-03-2008, 11:40 PM   #3
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QuoteOriginally posted by BBear Quote
Just received a Super Takumar 135 f/2.5


Two questions after some playing time:


1) does it matter how I set the aperture ring? I mean, it only seems to change the aperture if I leave it in AUTO (MAN. appearing).

2) Interestingly, exposure seems to be good for any aperture BUT f/2.5! It is absolutely underexposing...

I dont have pictures to show, but I can provide shutter values for comparison:


SPOT Metering:
f/2.5 > it gives me 1/180 (totally dark)
f/4.0 > it gives me 1/6 (right exposure)


MATRIX Metering
f/2.5 > 1/60
f/4.0 > 1/10



Weird weird weird..... Any ideas?
If "Man" is visible, than the switch is in the manual position. That is where it should be unless you are using a m-42 body.

As for the metering issues...Welcome to the wonderful world of manual metering on the K10D. The owner's manual indicates that metering is unreliable using non-A mount lenses and it is not kidding. For the most part there is significant underexposure at wider apertures (wider than f/4). Some lenses also have over/underexposure at the narrow end as well. My Jupiter-9, for example will underexpose a full 2-3 stops at f/2, but is fine at f/4-f/16. The cause is poorly understood and has been the topic of a ton of discussion. It seems to be related to how the meter voltages are processed and/or certain dynamics of the focus screen.

Here is the drill for your Tak:
  • Shoot in AV mode with the lens set to manual aperture
  • Forget about matrix metering. The camera will default to center-weighted with non-A lenses. (Spot still works though)
  • Focus wide open and stop down to the desired aperture.
  • Take a shot and chimp the histogram
  • If needed, adjust the exposure compensation to shift the curve and try again

Enjoy!

Steve

(Has far too much experience with this matter...see sig...)

Last edited by stevebrot; 12-04-2008 at 12:04 AM.
12-03-2008, 11:43 PM   #4
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I just got a Super Takumar 55mm f/1.8 and it seems underexposes a bit wide open but setting a +.05 on the exposure takes care of it since they work best in AV mode. My other takumar, the SMC 135mm f/3.5 seems to expose right at all apertures so I'm not sure what it could be...I do have a katz eye in my k10d but that shouldn't affect anything but spot metering.

12-03-2008, 11:58 PM   #5
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QuoteOriginally posted by sharko Quote
I just got a Super Takumar 55mm f/1.8 and it seems underexposes a bit wide open but setting a +.05 on the exposure takes care of it since they work best in AV mode. My other takumar, the SMC 135mm f/3.5 seems to expose right at all apertures so I'm not sure what it could be...I do have a katz eye in my k10d but that shouldn't affect anything but spot metering.
There are some reports that the Katzeye screen provides a partial cure. Since you are only seeing a half stop bias wide open, I am tempted to believe that the claims are true. My Rikenon 50/1.7 requires +1.5 exposure compensation wide open. Ditto for my Pentax-M 50/1.7.

Steve

BTW...Lowell Goudge swears that the older *istD screens also provide a cure.
12-04-2008, 12:23 AM   #6
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What stevebrot says is all good and better said than I can do. All I'll add is stick with it and you will get better. I have empathy for you because I remember my early attempts at metering lenses before the As and I sure did get frustrated.

You can also use the "Sunny f/16 Anchor Point." There is a great explanation of it and how to use only your brain to expose correctly here Ultimate Exposure Computer

Best of luck to you!
12-04-2008, 02:17 AM   #7
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Well, this problem is linked to the focus screen...

The standard focus screen is not made to be used with m42 lenses, but with PK-A lenses where the metering is always done wide open and the aperture is controlled from the body.

Switching to a LL60 screen does solve the problem (altough it imposes a constant 1/3Ev comp).

At least, I don't have metering problems anymore with my three m42 lenses and my PK-M f/1.2 lens...

The whole story : k10 split-screen, lf80 & ll60 exposure accuracy
12-04-2008, 04:18 AM   #8
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Another fine thread. Thanks to BBear, Stevebrot, and all who contributed. This is the sort of considerate, mutual support that gives this site its useful and welcome character...

12-04-2008, 07:46 AM   #9
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Original Poster
QuoteOriginally posted by stevebrot Quote
If "Man" is visible, than the switch is in the manual position.
Thanks for the clarification!



QuoteOriginally posted by stevebrot Quote
As for the metering issues...Welcome to the wonderful world of manual metering on the K10D. The owner's manual indicates that metering is unreliable using non-A mount lenses and it is not kidding.
Yeah... right on! They do know their products!

(Un)fortunately, it seems like I only have the underexposure when wide-open, stopped down it seems to be fine!
12-04-2008, 07:47 AM   #10
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QuoteOriginally posted by dlacouture Quote
Well, this problem is linked to the focus screen...

hmm... in my particular case, I do have the ebay focus screen... just for the record!
12-04-2008, 08:05 AM   #11
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QuoteOriginally posted by stevebrot Quote
There are some reports that the Katzeye screen provides a partial cure. Since you are only seeing a half stop bias wide open, I am tempted to believe that the claims are true. My Rikenon 50/1.7 requires +1.5 exposure compensation wide open. Ditto for my Pentax-M 50/1.7.

Steve

BTW...Lowell Goudge swears that the older *istD screens also provide a cure.
Steve

Thanks for the reference, but I will swear to nothing, I will however repeat my observation with data.

Just to clarify, I have attached a link to the graph I posted showing the K10D and *istD (each with their factory screen) metering using a K 50mm F1.4,

There is an additional line showing the K10D metering using the *istD screen.

What this shows is that I can replicate the *istD metering on a K10D by using the *istD screen.

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

Note, I believe my copy (perhaps all) of the K50mm F1.4 have a slight error in apature setting as you stop down. This is shown by the slightly increasing grey scale value on the chart.

For the OP, welcome to the wonderful wacky world of K10D metering
12-04-2008, 08:54 AM   #12
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BBear, I've tried the chinese split-screen, and it behaves exactly like the original screen, meaning that you'll have underexposure between f/1.2 and f/4, then f/4-5.6 seems ok, then F/5.6 and above suffer from overexposure.
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