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05-01-2011, 07:16 AM   #16
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QuoteOriginally posted by dlacouture Quote
If you take the factory screen and chart its behavior in stop-down mode, you'll see that it underexposes from f/1.4 to f/4, then overexposes from f/5.6 to f/22 (roughly, it can depend on the lens used)...

This means that the metering sensor sees to much light between f/1.4-4, and not enough under f/5.6, thus proving that the Pentax screens darken faster once below f/5.6 than a linear screen such as the EE-S...

This points to an optimization with lenses faster than f/5.6, which is consistent with the very name of the Pentax screens (labeled "Bright matte" IIRC).

EDIT:
I've just thought about an easy test to check exposure against a reliable reference, and used LV... Using a defocused target (to lessen the differences due to the higher accuracy of LV against small highlights), I get identical values between LV and the EE-S screen on the whole aperture range (M mode, Aperture ring manually set)!

So, for me, it's really the ultimate screen :
- accurate DoF
- linear response to stop-down metering
- accurate metering compared to LV
- blank!
Thanks, dlacouture for your practical experience. The theory without practice mean nothing.
But I have a question about your conclusion. Is the linearity of the exposure with the old lenses kept also with the DA/FA lenses? If the response of the original focus screen is nonlinear about the constant line (with under and over-exposure in camera response), than the metering response can apply a transfer function to align the total response from the lens to the correct exposure. Is this a correct affirmation from your practice?
If your optimization with the ee-S screen is great with the good old manual lenses but is not so with the DA/FA lenses, it remains to use 2 specialized cameras. Is this a useful conclusion (maybe expansive, but there are many of us who upgrade the camera) ?

05-01-2011, 08:35 AM   #17
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Minäkin olen kuvannut yli puoli vuosisataa. Olen kokemyksesta oppinyt, että välineet optiikat mukaanlukien eivät kestä ikuisesti. Siksi uusin kalustoa säänöllisin väliajoin. Vanhat romut joutavat lasten leikkeihin. Jää aikaa itse kuvaamiselle, kun ei tee turhaa työtä kaikenmailman kokeiluilla.
05-01-2011, 09:30 AM   #18
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QuoteOriginally posted by dlacouture Quote
Well, there is a definite center on the EE-S, you can see concentric "circles" on the fresnel face. But simply laying your screen on the EE-S and centering it is good enough, I think...

As for the Dremel, yep, should be faster, but you'll have to securely fasten it in place so you won't rip and scratch it...

Frankly, I think a good saw with very fine teeth and a protective screen (maybe a Nintendo DS protective screen, those working with static forces) are sufficient for the job...

I went the hurried route and did not protect the screen, and it ended with only a really small scratch (say, a dot) invisible at working apertures (and I'm not even sure it's not some saw dust gunk)...

Well, shoot (about there being a center). That definitely makes it more tedious. I had thought about needing to protect the surface, but the protective screen is a great idea. I had only thought of tape, and I knew I didn't want to do that.
05-01-2011, 12:17 PM   #19
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Paunel, I don't really understand your point... With DA/FA lenses, the metering is always done wide open, so if there is an impact, it will be a general offset, applying on the whole aperture range.

Let's say this screen is slightly darker than the stock screen at f/1.4 (say, by 0.5Ev). Your FA50/1.4 will then overexpose by 0.5Ev on its whole aperture range, because the metering is done wide open only!
I'll compare with the stock screen during the week, but seeing that I get identical values between LV and standard metering, I'm pretty sure they are equivalent, with maybe a slight brightness advantage for the stock screen with lenses around f/2.8, it being optimized for such apertures (but then producing a slight underexposure with these lenses)...

Could someone try the LV vs metering sensor test with their stock screen?

05-01-2011, 12:22 PM   #20
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QuoteOriginally posted by DogLover Quote
Well, shoot (about there being a center). That definitely makes it more tedious. I had thought about needing to protect the surface, but the protective screen is a great idea. I had only thought of tape, and I knew I didn't want to do that.
Several people before who have cut down their own screens have used scotch tape as a protector and it worked great. The nice thing about scotch tape, by the way, is that you can pencil in the lines to cut.
05-01-2011, 12:35 PM   #21
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QuoteOriginally posted by macTak Quote
Several people before who have cut down their own screens have used scotch tape as a protector and it worked great. The nice thing about scotch tape, by the way, is that you can pencil in the lines to cut.
Really? I would be afraid the tape would leave some residue. I did want to mark my trim lines, though, no matter what I use. I thought I might use an exacto knife to trace the stock screen dimensions on the one being cut down. I guess some type of fine marker or something would be safer.
05-02-2011, 04:38 AM - 1 Like   #22
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dlacouture,

Congratulations. Since I switched from Canon, I have been looking for someone to do this because I have used the Canon type S focusing screens for many years. Now that I am using the K5 with the stock screen, I understand the major differences. I am still using a K 135f2.5 lens which I modified for my previous Canon 5D and its aperture lever had been removed. So, when I now use it on my K5, and stop it down pass f5.6, the screen is not only dark but has a funny hazy look which never happened on my former 5D with the Ee-s focusing screen. The Canon type S focusing screen will remain totally transparent in dark situation or even when you stop down the lens pass f5.6. The other fantastic benefit of using this type S screen is the ability to tell whether your AF lens focuses correctly because, if it's in focus, you can actually see it even for lenses at f1.4.
05-02-2011, 04:50 AM   #23
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QuoteOriginally posted by DogLover Quote
I think I see a great little side business for you of buying and modifying these screens for Pentax use. If you can work out stricter methods so as to avoid scratching them, you're all set. I'd definitely be interested.
Well, problem is that here in France, the screen alone cost 32€... I'll let you do the math to see how much it'll cost you in the end, but I think you'd be better buying two EE-S screens and give it a try...
But for Europeans, yeah, it's a good idea!

05-02-2011, 05:27 AM - 2 Likes   #24
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QuoteOriginally posted by dlacouture Quote
Well, problem is that here in France, the screen alone cost 32€... I'll let you do the math to see how much it'll cost you in the end, but I think you'd be better buying two EE-S screens and give it a try...
But for Europeans, yeah, it's a good idea!
I have written to focusingscreen.com to ask whether they can produce a K5 screen with the Canon type S focusing screen and hopefully they can. They are using this particular screen for other cameras and they should be able to do it for K5, I hope.
05-02-2011, 05:47 AM   #25
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QuoteOriginally posted by Anthony Lee Quote
I have written to focusingscreen.com to ask whether they can produce a K5 screen with the Canon type S focusing screen and hopefully they can. They are using this particular screen for other cameras and they should be able to do it for K5, I hope.
Thank you.
I was looking at their site yesterday but ended up bying the orginal Canon EE-S screen. Cant wait to get it in my K-5. My Katzeye is killing me
05-02-2011, 10:05 AM   #26
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QuoteOriginally posted by dlacouture Quote
Paunel, I don't really understand your point... With DA/FA lenses, the metering is always done wide open, so if there is an impact, it will be a general offset, applying on the whole aperture range.
I rephrase: is the exposure for manual lenses OK? Is the exposure for DA/FA lenses OK? OK means a good hystogram of the shot.
Because changing the focus screen means changing (more or less) the light for metering and exposure. If there is a change ( not necessarily a constant offset because the different Fresnel lens effect can be nonlinear) in the practical case for a DA/FA what is this change, 1/3EV to 1EV or more? Thank you for the patience
05-02-2011, 11:46 AM   #27
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Well, I've not made comparative tests yet between the stock screen and the EE-S...

All I've made is tests between metering through the screen and LiveView, lens in A position...
All I can say is the following:
- for my Samyang 85/1.4, metering is nearly identical...
- for my FA 50/1.4, metering is nearly identical...
- For my tamron 28-75/2.8, metering is nearly identical...
- For my tamron 70-200/2.8, metering is nearly identical...
- For my Chinon 45/2.8 (PK-m), metering is nearly identical...
(I say "nearly" because there were some rare metering discrepancies depending on the scene, about 0.5Ev, which does not surprise me)

Now, with the DA18-55 (only DA I got), LiveView gives me slower speeds. At 18mm (f/3.5), I have about 0.5Ev difference, and at 55mm (f/5.6), it goes up to 1 or 1.5Ev...
Which I find frankly interesting, as this is enough proof for me that from f/3.5 on, the Canon is in fact brighter than the stock screen, thus underexposing the scene compared to Liveview (I'm supposing that with the stock screen, metering values would be nearly identical)...

For me, this means that the Canon is, in the worst cases (fast lenses), as bright as the stock screen!!!
I'll validate this as soon as I can get hold of my old K7 and compare both viewfinders...
05-03-2011, 04:24 AM   #28
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I've thought about another test, and compared exposure with my FA50 and my 18-55 set at 50mm... They are identical using viewfinder metering (which is good news!!), but different with Liveview...

So either the camera cooks the LV metering value depending on the lens used, or the DA 18-55 really gets different metering results given its DA construction (which presumably uses parallel rays to avoid excessive vignetting)...
05-03-2011, 07:04 AM - 1 Like   #29
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QuoteOriginally posted by Anthony Lee Quote
I have written to focusingscreen.com to ask whether they can produce a K5 screen with the Canon type S focusing screen and hopefully they can. They are using this particular screen for other cameras and they should be able to do it for K5, I hope.
Thanks Anthony, let us know what he says.

I've got an EC-A screen right now, and while it's better than the stock screen for accuracy, my composition has suffered since I'm always focusing in the center microprism.

The S type screen looks perfect, better DOF than stock or EC-A, minimal effects to metering (including spot), and no focus aids that make composition less intuitive.

Questions to the OP, you mentioned concentric circles on the screen, are these at all visible in the VF? Also, does not having a center area defined in the VF cause you any trouble with determining where the spot meter and AF confirmation point are located?

Thanks for starting this thread!
05-03-2011, 07:54 AM   #30
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The concentric circles are nearly invisible in the viewfinder... Sometimes, when stopped down to f/11-16 and looking for them, I can see them, but otherwise I'd swear it's a pure ground glass and nothing else.

I've really only noticed them while handling the screen to determine which way was up. Light played on the circles the same way it plays on a CD, so...

Regarding AF location and Spot meter, well, I was used to the ME-60 blank screen for my K5 (an unmarked screen)... But anyway, the selected AF point lights up during half-press, so it's easy to check from time to time where the AF sensor is.
In AF Auto mode, you can have a problem as you don't know which point will be used. But approximate locations are easy to determine, in relation to the bottom LCD information:
- leftmost AF point is above the AF point selection icon.
- second column is above aperture's "F"
- center column is between AF confirmation hexagon and Ev bar
- Third column is between Ev bar and "ISO Auto RAW" text
- Rightmost AF point is above ISO speed.

And for the spot meter, well, I'd use the center AF point as a rough guide...
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