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10-15-2008, 06:25 AM   #31
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QuoteOriginally posted by bentax Quote
RE: what a difference blocking the viewfinder makes!

Humour me.

Put camera on tripod, in S.AF mode.
Put eye to viewfinder.
Focus on a subject that doesnt have much contrast, but still focuses fine.
Take eye/body away from viewfinder.
Attempt focus again.
Doesnt lock focus?
Why is that? Anyone have an explanation?
The camera doesn't need you looking through it to be able to focus?
Seriously, the AF sensor is located low in the mirror box. There is a pellicle portion on the reflex mirror that allows some light to pass through to a sub mirror which reflects light down to the AF sensor.
The metering sensor is in the optical path of the viewfinder, pretty much as far away from the AF sensor as it can be, and still be in the same camera.

10-15-2008, 06:40 AM   #32
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Mmh...you have just invented the wheel.

Seriously, I'm surprised this is a news to so many. I learned this already as a kid in the youth section of my local camera club. Sort of next after they told me not to open the camera without returning the film, or why a lens shade is good to have, or that I can shoot on longer exposure times if I hold the camera and my arms close to my body.

And this is why almost all SLRs, also Pentax, comes with a piece of plastic that fits over the viewfinder. It's meant to be in your camera bag, not back home in the camera box in the back of your closet. And it is why even many camera neck straps has a small pocket for that view finder cover, so that you will always have it available. And it is one reason to why an eye cup is a good idea to use.
10-15-2008, 06:45 AM   #33
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QuoteOriginally posted by Douglas_of_Sweden Quote
Mmh...you have just invented the wheel.

Seriously, I'm surprised this is a news to so many. I learned this already as a kid in the youth section of my local camera club. Sort of next after they told me not to open the camera without returning the film, or why a lens shade is good to have, or that I can shoot on longer exposure times if I hold the camera and my arms close to my body.

And this is why almost all SLRs, also Pentax, comes with a piece of plastic that fits over the viewfinder. It's meant to be in your camera bag, not back home in the camera box in the back of your closet. And it is why even many camera neck straps has a small pocket for that view finder cover, so that you will always have it available. And it is one reason to why an eye cup is a good idea to use.
i knew it had an effect, but the reason for my post is how BIG of an effect.

my original assumptions were that the difference was so negligebale that some ev comp would offset it.

also keep in mind that many of us here were never "taught" things and the forums are as close to a "club" as any us will have.
10-15-2008, 06:51 AM   #34
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I remember reading something about it in the K10D manual, and that's where I first knew about such an issue. Never really paid much attention to it though. I've dug it up, on page 80 of the K10D manual:

Exposure may be affected if light enters the viewfinder. Attach the provided ME viewfinder cap or use the AE lock function (p.162). (Ignore the light entering the viewfinder when the exposure mode is set to M)

10-15-2008, 07:19 AM   #35
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That viewfinder cap is all well and good if you're shooting from a nice solid tripod, but tricky when using a beanbag to do macro shots - when the slightest nudge can send the shot out of alignment or focus. Not very convenient either, but still useful, and I'm glad it's not an optional extra.

A viewfinder shutter would be a very nice feature on a future model.
My Canon A-1 and T90 both have them, but they're no Pentax DSLR...
10-15-2008, 07:34 AM   #36
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So what about LV metering?

OK, during LiveView the viewfinder is blocked (mirror is up) and so no effect. But during AF meter operates and if not to push AE-L (but when?- because AF resets even AE-L...) then exposure goes...
Best and happy shooting and discovering, JR
10-15-2008, 08:38 AM   #37
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Well, this has certainly been an interesting thread... As one of those longtime users, it was still news to me (but makes perfect sense once explained). Guess I'll get in the habit of using the AE-L button on the tripod!

Jim
10-15-2008, 08:55 AM   #38
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I almost never use a tripod. It's a good thing to remember, though.

10-15-2008, 09:48 AM   #39
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The Pentax model that resolved the issue elegantly was the LX. Its exposure values were read off the film surface during the exposure.
10-15-2008, 01:59 PM   #40
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LX, That the Ticket.

QuoteOriginally posted by Canada_Rockies Quote
The Pentax model that resolved the issue elegantly was the LX. Its exposure values were read off the film surface during the exposure.
Exactly what I was thinking while reading this whole thread! I guess that they are putting the autofocus sensor in that spot now... Sure would be nice to get back to the metering abilities of a 28 year old camera...

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10-15-2008, 02:10 PM   #41
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I have a piece of duct tape which I just stuff on the viewfinder to cover it with tripod work. The little black plastic crap which came with the camera is a joke to use. Far too much hassle.
10-15-2008, 05:19 PM   #42
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QuoteOriginally posted by Gooshin Quote
i knew it had an effect, but the reason for my post is how BIG of an effect.

my original assumptions were that the difference was so negligebale that some ev comp would offset it.

also keep in mind that many of us here were never "taught" things and the forums are as close to a "club" as any us will have.
You know, when I opened this thread I was convinced you were confused about this, but I realized you're right.

When metering with modern lenses you're always wide open. So say you're shooting a DA 35.. it'll meter everything at f/2.0 so the amount of light coming in via the viewfinder will be very little comparatively.

But say I'd find an equivalent M42 lens, and stop it down to f/8 -- the light hitting the meter from the lens will be 4 stops less, or 1/16th. Suddenly the small amount of light coming in from the viewfinder might make a BIG difference; because the ratio of lens:viewfinder light has changed from say 100:1 to 6:1.

So no wonder a lot of people go "oh, I knew that already" because they've shot with older gear and had to deal with this in the past. But anybody who's been using more current stuff will probably think you've been smoking crack.
10-16-2008, 03:14 AM   #43
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I learned about this in 1982 when I took the radical step of actually reading the manual that came with my Canon AE-1. Granted, reading manuals was a far less daunting task back in those days.
10-16-2008, 04:00 AM   #44
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QuoteOriginally posted by Maffer Quote
The little black plastic crap which came with the camera is a joke to use. Far too much hassle.
I keep the little plastic cap with me in my bag but I have to agree that getting the eye piece back on is very inconvenient. I don't understand why the cap wasn't designed to cover the eyepiece.

Anyhow, perhaps this viewfinder exposure irritation can also explain why some measurebators find the exposure to be erratic. If some bright light is randomly blocked / not blocked during test shots, this could influence measurement results.

I cannot really relate to the common "underexposure" complaint. In pattern metering mode I often get slightly blown out highlights I have to correct for manually. Perhaps "underexposure" only relates to an assumed 18% gray value but the way digital overexposure looks, I think it should basically only occur if the user really wants it and compensates the exposure accordingly. In any event, one of the reasons that detracted me from the Nikon D40 and convinced me regarding the K100D was that I much prefer an underexposed image to one that is even slightly overexposed.

Last edited by Class A; 10-16-2008 at 04:03 AM. Reason: typo
10-16-2008, 04:01 AM   #45
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I did a bit of testing on this when i got my K10D:

Misc Tests

This is a 14 minute exposure (at 1600 iso) with the lens cap on, in a medium lit room:



(I was really testing the high iso at long exposures, to see how that performed, but found this ...)

Last edited by tcdk; 10-16-2008 at 04:17 AM.
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