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10-29-2008, 03:45 AM   #16
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Hello OrenMc,

Well, this is a direct consequence of the focus screen behavior I talked about in this thread: k10 & split-screen, lf80 & ll60 exposure accuracy.

And fitting a LL60 *ist screen does solves this problem... Or at least produce a constant underexposure, with whatever lens you use (my k10 is now set with a permanent +2/3Ev, and this works quite well with all my lenses, them being FA, DA, m42 or PK...).

Regarding the "fudge factor", I simply believe there is none...
Everybody says that pentax voluntarily underexposed to preserve highlights...
I simply think they designed a new focus screen to be brighter, tried it with the lenses they had at the time (FA50 f1/4 being the fastest, with kit lenses going down to f/5.6 on the other side of the spectrum), and noted a slight underexposure that could be passed as "Highlights conservatism" (and a direct consequence of a brighter focus screen, btw)...

Don't forget that metering with A lenses is done wide open, then shutter speeds for smaller apertures are mathematically determined, thus always linear (from f/1.4 to f/2, you halve the shutter speed). And from f/1.4 to f/4, the K10's factory screen underexpose (more or less, depending upon the actual aperture), so it's not a great deal and won't lead to severe customer complaints or reviewer bashings (on the contrary!).

I guess they never went to the trouble of checking the metering system accuracy with stop-down or PK lenses (or even PKA lenses in non-A position), apart from adding the options and validating that the green button does actually stop-down the lens and then meters.
Checking that obtained values were actually linear was out of the validating process, I think.

That's how they could have missed that f/8-f/16 shots are severely overexposed...

And that's also why the *ist LL60 screen does a much better job, even with DA & FA lenses : it is actually quite linear from f/1.4 to f/16, but a little bit darker, as it's a direct descendant of the MZ series and surely was checked more accurately for manual lenses.

Without having one, I'm pretty sure that all those f/2.8 limited or * lenses can cope with a +1 Ev comp without blowing the highlights...


Last edited by dlacouture; 10-29-2008 at 03:58 AM.
10-29-2008, 05:39 AM   #17
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dlacouture, thank you very much.

I did read you post earlier because I am thinking of going with a split screen to aid with the focusing of my manual lenes. I just got the O-M53 eyecup last night and haven't had much of a chance to test it. I did put it on and tried it for a bit and can't see much difference but I don't want to jump the gun on my conclusion. A lot of folks really like it as it does help them.

I am not very good at charts but from what I can tell, I will be dealing with exposure problems with the split screen also. And the LL-60 which seems to at least give a fairly constant exposure but doesn't help with the focusing issue.

Bottom line though, after a bit more use I think I will be able to know what to expect and adjust accordingly. I will give the eyecup a week or so of use before I decide on the split screen. It seems the one you purchased at jinfinace is a bargain and works fine.

One more thing though. ( do things have to be so complicated ) I see you have the 45 degree screen. I heard that some folks like the horizontal. Whats the big difference? Is it just a matter of taste?
Opinions, opinions.

Last edited by OrenMc; 10-29-2008 at 07:01 AM.
10-29-2008, 06:12 AM   #18
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Oren, concerning the me53, just use it for a while then take it off... The difference will be obvious!

And yes, I have the same problem :
- Split-screen is great for focus, but produces bad exposure
- LL60 is linear, but doesn't really help with MF...

I'll perhaps bit the bullet and buy a KatzEye focus screen, but as its metering impact is still unknown to me (KatzEye told me they tried it with PKA lenses only), I'll wait for the Euro to come back to an acceptable level (1.60$ would be just great!).

As for diagonal vs horizontal, I personally prefer diagonal, as it will work in a similar way in both V/H orientations, whereas you'll have to change your behavior with a horizontal split.

Portrait-wise, I found that an horizontal split is not so great in landscape position, as you'll have nothing vertical in a face to focus upon (at least nothing in the same focus plan as the eyes)...
But it works well in portrait orientation, as you can then have the split riding right across the subject's eye and eyelashes. Diagonal split is a little less "obvious" in this orientation, but has the advantage of remaining diagonal in both orientations.
10-29-2008, 09:30 AM   #19
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QuoteOriginally posted by georgweb Quote

Shortcut the cameras' bayonet contacts (all of them is a good starting point) via tin foil or 'blanking' the lens' back at the contact points. Bojidar Dimitrov has a table on his pages that explain exactly the settings. This usually helps metering.
I searched Dimitrov's site and could not find anything about shorting contacts, though I seen comments about doing this before. I am curious as to what this would accomplish. The reason is that I have lenses with both conducting and non-conducting base flanges and both types have inaccurate metering.

Do you have the link?

Steve


Last edited by stevebrot; 10-29-2008 at 12:18 PM.
10-29-2008, 11:36 AM   #20
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QuoteOriginally posted by OrenMc Quote
I just got the O-M53 eyecup last night and haven't had much of a chance to test it. I did put it on and tried it for a bit and can't see much difference but I don't want to jump the gun on my conclusion. A lot of folks really like it as it does help them.
I find it makes a noticeable difference in low light. Outdoors, I prefer having it off, as I have glasses, and the fact that I cannot see the whole frame with the O-ME53 bugs me more than an small difference in size.
10-29-2008, 07:46 PM   #21
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QuoteOriginally posted by OrenMc Quote
For the Voigtlander I quess I also can't shoot wide open at 1.4 either? Same conditions.
Got to be able to shoot wide open for the blurred back ground ( bokeh ) with these lenses.
Different light?
Why does it underexpose in such bright conditions?
I can't see the image you posted (blocked) nor gather from the text if it's really over-exposed (is it too light or too dark?) but even at 100iso you are going to have problems on a sunny day.

the Sunny-16 'rule' says that exposure will be 1/iso @ f16 on a clear sunny day. If you convert that you get

f16 - 1/100sec
f11 - 1/200
f8 - 1/400
f5.6 - 1/800
f4 - 1/1600
f2.8 - 1/3200
f2 - 1/6400
f1.4 - 1/12800

Any lens brighter than f2.8 is going to be a problem. So the advice about a ND filter or choosing less sunny days is all you can do if you want to shoot that f1.4 on a sunny day.

Nige.
10-30-2008, 05:07 AM   #22
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Thanks,
One of these days all this will all come natural I hope. I completely forgot about the Sunny-16 rule. I think I could use an ND filter anyway for other things such as waterfalls.
Good thing is, my Tak 1.8 and the Nok 1.4 are both 58mm fliter thread.
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