[Reportage]

opinions please?

[boesgaard]

Both.

A lens with a large aperture will let in more light.

If you have a f2.8 lens, you can easily see the difference by stopping it down, and use the DOF-preview-button.


I suppose the penta-prism or penta-mirror will have some effect as well.

[asdf]

opinions please?

When you zoom in with the kit lens to 55, the aperture wide open is f/5.6, which means the viewfinder is 2^4 = 16 times dimmer than with FA 50 f/1.4.

[manteiv]

When you zoom in with the kit lens to 55, the aperture wide open is f/5.6, which means the viewfinder is 2^4 = 16 times dimmer than with FA 50 f/1.4.

is-it 2^4 or 4^2 ?

in this case both are the same, 16 times less light

does it mean every stop on the aperture ring is double/half the light of the previous stop? so from F1.4 to 5.6 to go through F1.8, 2.8, 4, 5.6 resulting in 4 steps which is 2^4=16 or 4^2 I am confused, please someone correct or confirms my understanding (as I understand, the amount is a square relationship every step)

[asdf]

is-it 2^4 or 4^2 ?

in this case both are the same, 16 times less light

does it mean every stop on the aperture ring is double/half the light of the previous stop? so from F1.4 to 5.6 to go through F1.8, 2.8, 4, 5.6 resulting in 4 steps which is 2^4=16 or 4^2 I am confused, please someone correct or confirms my understanding (as I understand, the amount is a square relationship every step)

F-number - Wikipedia, the free encyclopedia

[Cideway]

The brightness of a VF depends on

1. Lens aperture (bigger aperture more light, smaller aperture less light)
2. Mirror (the silvering of the mirror and with AF systems how much light is split off to the AF sensor)
3. Focus screen (the cut, coating and transmisive quality of the screen)
4. Prism housing (Penta-prism or mirror, the quality of the coatings, the quality of the glass and the size. How much light is taken off for metering)
5. Eye piece optics (the quality of the coatings, the quality of the glass and the size)

[Marc Sabatella]

Each f-stop doubles the amount of light, not squares it.

As for the difference viewfinder brightness, though, it isn't directly proprotional to this, since the focus screen eats a fair amount of light. There's not as much difference in viewfinder brightness at focusing apertures wider than f/2.8 as there is from there to f/5.6, it seems to me.

[stevebrot]

Each f-stop doubles the amount of light, not squares it.

As for the difference viewfinder brightness, though, it isn't directly proprotional to this, since the focus screen eats a fair amount of light. There's not as much difference in viewfinder brightness at focusing apertures wider than f/2.8 as there is from there to f/5.6, it seems to me.

Marc is correct regarding the tendency of some screens to "eat" light. The stock screen on my K10D shows NO brightness difference from f/3.5 to f/1.7 (my fastest lens). On the other hand, my Katz Eye shows definite differences in brightness between stops. The same is true for DOF and is the cause of manual focus imprecision with the stock screen.

Steve

[Lowell Goudge]

there will be many factors that impact the brightness of the view finder.

In my view, these are, in order

- maximum aperture of the lens, since nothing has as much control on the total amount of light hitting the focusing screen
- the magnification ratio of the finder, and hence the size. higher magnification means a bigger finder, but this spreads the light (which is limited) over a larger area, reducing the intensity at any given point
- the surface of the focusing screen. As seen on the K10 and K20 the focusing screen is brighter than the same size screen on the *istD due to the finish on the screen. Katz Eye also have different coarings that impact finder brightness
- penta prism vs penta mirror with prism's being brighter.

no matter what you do, the biggest impact you can have on the brightness is the lens. just compare an F1.4 lens to the typical F5.6 kit lens and you can appreciate how bright even a poorly designed (i.e. all the wrong points on the 2nd through 4th points list) can be

edit note, in re-reading some of the posts, I agree the mirror should be added to this because some mirrors are not 100% reflective and I seem to recall some makers taking a percentage of light through the mirror, I forget now what they did with this (i.e. metering or AF)

[asdf]

Marc is correct regarding the tendency of some screens to "eat" light. The stock screen on my K10D shows NO brightness difference from f/3.5 to f/1.7 (my fastest lens). On the other hand, my Katz Eye shows definite differences in brightness between stops. The same is true for DOF and is the cause of manual focus imprecision with the stock screen.

Steve

The eye's aperture ranges from around f/2 to f/8--your pupil/aperture adjusts depending on the light entering your eye. So your perception of what's going on isn't all too relevant.

[Marc Sabatella]

Now that's interesting - hadn't considered that possibility. But still, it doesn't seem that would render our perceptions irrelevant - it would just provide an alternate explanation for those perceptions. But it's our *perception* of how bright the viewfinder is that matters. If we can't perceive an improvement in brightness, then there's no advantage in having it. At leas,t not that I can see. Unless perhaps it does turn out that empirical tests show people do better with a brighter viewfinder even if they can't see the difference.

[Blue]

The eye's aperture ranges from around f/2 to f/8--your pupil/aperture adjusts depending on the light entering your eye. So your perception of what's going on isn't all too relevant.

Actually, your optic nerve and eye is having to adjust for that change in lighting. It isn't exactly linear either. You have to have a certain amount of light to see while on the other hand you can have too much light and need sun glasses. If the viewfinder is too dark to see how to focus, it matters! Hence, it may night matter in an optimum range. Its pushing the extremes that it matters. That's why we have 50mm f1.2 lenses.

[asdf]

Now that's interesting - hadn't considered that possibility. But still, it doesn't seem that would render our perceptions irrelevant - it would just provide an alternate explanation for those perceptions. But it's our *perception* of how bright the viewfinder is that matters. If we can't perceive an improvement in brightness, then there's no advantage in having it. At leas,t not that I can see. Unless perhaps it does turn out that empirical tests show people do better with a brighter viewfinder even if they can't see the difference.

Actually, your optic nerve and eye is having to adjust for that change in lighting. It isn't exactly linear either. You have to have a certain amount of light to see while on the other hand you can have too much light and need sun glasses. If the viewfinder is too dark to see how to focus, it matters!

Of course, it's relevant and it matters. I try to be careful with my words: I said "isn't all too relevant" not "is utterly irrelevant".

[Lowell Goudge]

I think the concept of the eye adjusting may have something to do with not seeing the entire impact of brightness on a sunny day, but what about at night, when the eye is "wide open".

you will certainly see the differences then.