[TomGarn]

We got that additional cap for our viewfinders - to stop any strange light entering through the backdoor. I never used it till today for experimental reasons only, nor did I ever think about it. In days of film we were aware not to let the sun shine in there, cause it might brighten up the celluloid - or even burn it ? More understandable not to let the main lenses watch the sun directly

In dark areas with high ISO something might sneak in from that rear opening, when you don't cover the viewfinder with your eye by looking through it ... for example when you do long period stargazing or you have show-lighting from behind and you are continously filming the speaker in a steady and unshaded position - camera left alone on the tripod.

I tried to simulate that tonight and from some angles. The floorlamp really did some ugly and strong reflections on the screen. Anyone of you have had observations in a natural environment, or in special jobs ? And do you use the cover when doing videography sometimes to prevent those unwanted effects ?

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Last edited by TomGarn; 10-15-2014 at 03:58 AM.

[Steve.Ledger]

We got that additional cap for our viewfinders

You did?
I never saw one for the *istDS, K-7 or K-50.. ?

[TomGarn]

with K10D and K-7 ... and K-5 too I think ...

[Steve.Ledger]

Nope, nothing like that with my K-7.
Blu-tack works anyway

[rburgoss]

The eyepiece blind is used to avoid erroneous exposure in auto exposure mode (Av / Tv / P) mode on any camera capable of such mode, when ambient light can enter viewfinder, thus throwing reading off. Usually this happens when tripod is used, auto or program mode is used and the photographer clears the eyepiece during exposure, such as when shooting with self timer.

During actual exposure, no matter how much light gets into viewfinder, it will not affect exposure, because such light will be blocked by the mirror itself.

BTW, viewfinder blinds are supplied by Pentax with every auto capable camera since (1975) with the K2 (and K2DMD), ME and ME Super. Not sure about the Spotmatic era, but if any was capable of auto exposure, it was most likely to be supplied with an eyepiece blind.

The old advice about not pointing a camera (not the lens!) towards the sun, its easy to understand: You may burn a hole on the focusing screen or the shutter curtain! Remember: you are projecting the sun's image on a single tiny spot, just like when burning ants with a magnifying glass under the sun! This advice has nothing to do with the lens. In fact, no lens damage is at risk.

[fgaudet]

During actual exposure, no matter how much light gets into viewfinder, it will not affect exposure, because such light will be blocked by the mirror itself.

The mirror has a fairly large translucent part (used for AF) smack down the middle and even though it gets covered by the secondary mirror, it may let light bleed through during exposure. Not much of a problem on short exposure but 5 seconds + will show a washed out part with odd reflection about 2/3 of the way down the picture. It's not so bad on the K-7, it's noticeable on the K-5 but it's very bad on the K-3.

They don't supply the viewfinder cover just for the fun of it.

[TomGarn]

From small parts of lightfingers ... to quite big illuminations ... I easily managed to produce this effect.
Today - in the dark Blues-Club - I closed this gap for the first time - to prevent the spotlights to disturb
my film-making, even though it might occur only very rarely ...

[rburgoss]

The mirror has a fairly large translucent part (used for AF) smack down the middle and even though it gets covered by the secondary mirror, it may let light bleed through during exposure. Not much of a problem on short exposure but 5 seconds + will show a washed out part with odd reflection about 2/3 of the way down the picture. It's not so bad on the K-7, it's noticeable on the K-5 but it's very bad on the K-3.

They don't supply the viewfinder cover just for the fun of it.

Hmmm... that is interesting. Never heard about viewfinder light affecting actual image (reflections, flare, etc.). What I find interesting, is that seems that cameras without AA filters on sensors, are more prone to this happening. I know as a fact that sensors are quite "reflective" when compared to film, and sometimes, extraneous flares show on long exposures with legacy optics, that can be traced to reflections of bounced back light from sensor to back of lens and back to sensor, like from a bare metal ring or something shiny around the back on the lens.

In my case, I would try to pinpoint the source of such flares. It could be the body or it could be certain lenses only. Heck, it may be traced to certain filter attached to certain lens. Of course, it could be traced to light leakage entering the viewfinder, but in this case, I would trust Pentax is aware of such condition and advice using the VF blind on owners manual. Ever since the digital era started, I've seen more ghosts than during a Ouija Board marathon in Salem, Massachusetts.

About the eyepice blind, of course there is a reason to supply it. Here is the reference frm the K20D manual, which is about the same as with any other camera capable of auto exposure and has a self timer.

[asp1880]

I digged out that cap for the first time ever a month ago. I used a monopod and a shutter release cord to lift the camera up over a crowd to illustrate a mass of people with a wideangle. Good thing I practiced at home first, because the shots (in P or Tv mode I believe), came out 2-3 stops too dark without the little cap.
In that case the viewfinder points up into the bright sky and the meter is seriously disturbed - probably the worst case scenario.


It's a fun way to shoot a crowd by the way. Fisheye works great there.


Regards,
--Anders.

[Steve.Ledger]

I wonder why this cover was was not included with my *istDS, K-7 or my current K-50?? There were all bought new from Genuine Australian suppliers.
I just checked the K-50 box again. Nope, nothing. Looking in the manual confirms it's not included in the parts.

[stevebrot]

with K10D and K-7 ... and K-5 too I think ...

and K-3 and K-50* and also with the Super Program.

Edit: The K-5 manual includes the ME viewfinder cap on the packing list.


Steve

* I could have sworn that one was there when I helped my friend unbox her K-50, but as Steve points out above, it is not in the list in the manual.

---------- Post added 10-16-14 at 08:36 PM ----------

During actual exposure, no matter how much light gets into viewfinder, it will not affect exposure, because such light will be blocked by the mirror itself.

Never heard about viewfinder light affecting actual image (reflections, flare, etc.).

Me neither, though I was well-aware of the issues related to auto-exposure systems. It was not until I read about it here and actually did a test* that I became aware. I might also note that on a recent night shot with a local camera club, several of the more experienced members counseled the others to avoid lighting their viewfinders or lens mounts during long exposures.

Here is the reference frm the K20D manual, which is about the same as with any other camera capable of auto exposure and has a self timer.

In regards to metering, the self-timer is not the issue so much as simply having the eye away from the viewfinder. As Steve noted, a thumb or a bit of gaffer's tape is a good substitute for the blind.


Steve


* A strong light from behind the camera such as a reflection, setting sun, flash, or car headlamps may be enough. It is a problem with time exposures or with high ISO. The points of leakage are around the edges of the mirror and through the mirror itself (the entire surface is partially silvered).

[rburgoss]

and K-3 and K-50* and also with the Super Program.


Steve

* I could have sworn that one was there when I helped my friend unbox her K-50, but as Steve points out above, it is not in the list in the manual.

This is getting more interesting now. I know my K2dmd, ME Super, PZ10, PZ20, PZ1P, *istD and my K20D, were all bought new and all had their own VF blind. The K1000 and MX were NOT supplied with it.

I know also as a fact, that if camera measures light as reflected from the film plane, there is no need for a vf blind because any actual (going on) auto exposure, will be adjusted if the light changes during exposure. Olympus OM systems were promoted as the only OTF (off the film) meter around the late 70's. Don't know if other camera makers or even Pentax did their own OTF metering.

In real world shooting, I must confess I never used one even I've had plenty of chances or situations where "it was needed". But I've found easier to switch to manual rather than go through eyecup removal, blind in, blind out to recompose, in again (repeat as necessary), then remove for the rest of the day anf reinstall eyecup.... Its easier to swtch to manual, aim, compose, press green button and you are all set!

Anyway, I still believe the only purpose (as forseen by Pentax) to supply the thingie, is to prevent stray light from causing bad exposures on AUTO while using tripod and/or self timer, as described in the K20D manual.

[baro-nite]

Don't know if other camera makers or even Pentax did their own OTF metering.

Pentax LX - Pentax Manual Focus Film SLRs - Pentax Camera Reviews and Specifications

[Clavius]

If you do some long exposures that little cap becomes VERY important. The OVF then really is one big fat light-leak... Another point for the mirrorless cameras...

[rburgoss]

Pentax LX - Pentax Manual Focus Film SLRs - Pentax Camera Reviews and Specifications

That is correct. Last night I kept thinking about the LX. Yes, this body had OTF light metering and I believe it was the only one from Pentax to ever feature this gimmick.

I duuno, but with today's digital systems, I guess the image sensor can also serve as light meter during actual exposure, thus having an even more accurate "real time" "OTS" (Of The Sensor) metering. In fact, some cameras may already have this feature, but like "space shuttle launches"... few eyebrows get lifted...