[Quicksand]

Can you tell me, please, if the dimensions of the K7 screen are the same with those of the k5 screen and the k20? I have only the dimension of the k20/gx20 screen and I cut a nikon k3 focus screen for it. It seems all the 3 screens are the same dimensions, only the location of the handle is different. And the thickness of the k3 screen is not equal with the K20 screen which leads to the need of shim(s). Witch are the thickness of the K7 and K5 focus screens? Thanks!

The width/length dimensions are not the same. The screen dimensions for the K-5 and K-7 are the same (and the screens are interchangeable), but they are different and slightly larger than the screen for the K20D/GX20.

I didn't measure, but when I received my K-5 I took out its screen and compared it to the stock K20D screen I had removed previously from my old camera. It was pretty obviously different.

And as you noted, the little handle tab is on the opposite side, which also prevents the screen from fitting unless you cut it off (since there's an opening in the screen frame only where the tab is expected to be).

I can't say about the thickness -- I didn't check that, since I already concluded based on observation that the other dimensions were problematic.

[giofi]

Probably here. She did mention that her English wasn't the best, Not being a pedant, I just presumed that when she said add on, she meant an aftermarket screen....

Yes, what I should have written easy, not easier. What I meant is that she said that focusing is not easy, which I definetely agree with.





Does it matter?

Well yes, if you see her profile, she also has a K10D, so maybe (I can't be sure) she is not a novice, and some of the comments where about learning her basics first. I just find that sometimes we are quick on making conclusions and rather than answering the OP question we start giving lessons.....

[dlacouture]

And the thickness of the k3 screen is not equal with the K20 screen which leads to the need of shim(s). Witch are the thickness of the K7 and K5 focus screens? Thanks!

Thickness has no impact... The important part of a focus screen (the ground glass) is located upside, so is resting against the Pentaprism housing, and if your previous screen was properly located (there are shims between the screen and the pentaprism), then changing for a different screen thickness won't have any impact.

[Paunel]

Thanks, Quicksand!
But I must say mr. dlacouture, the thickness is important. The optic "way" from the mirror reflexion till the upside matte screen focus surface must be kept to the same value as before changing the screen. This way has 2 components: one in the air (d1) and one in the plastic glass of the screen (d2). Optic way is d1+ n*d2 where n is the optic index of the refractive screen (about 1.5 for perspex). If the new screen has a major thickness than the old one, the new (d1) must be decreased to preserve the sum. That means need for shim of the difference: old (d1)-new(d1). But if the new screen is thinner than the old one, it must be positioned upper (closer to the pentaprism) and if there are no shims to be removed (with the needed correction) is no chance to obtain a good focus. This explain the different results on the forum regarding the change of the focus screen.
For exemple the old screen thickness is 1.3mm and the new one is 1.5mm. The optic difference is (1.5-1.3)*1.5[refractive index]=0.2*1.5=0.3mm. You must compensate adding shim(s) of total thickness of 0.3mm.
The downside surface of the screen is a Fresnel lens (a plane lens) and if the focus length is different changing the screen then is a change in the resulted exposure because more or less light is distributed on the exposure sensor in the front of the pentaprism. The Katzeye screen with optic coating (like the lens coating) is more luminous and the result is an underexposure that must be compensated in camera. But if exist also the effect of different focus of the Fresnel lens the compensation can be in every sense (over or under). This must be tested, I only give you a simple theory implied in this process.
And, to prevent various "observations" here, I must say I'm licensed in physics.

---

Last edited by Paunel; 04-29-2011 at 09:48 AM.

[dlacouture]

You are of course right, and I never thought about it this way...

[dexmus]

Thanks, Quicksand!
But I must say mr. dlacouture, the thickness is important. The optic "way" from the mirror reflexion till the upside matte screen focus surface must be kept to the same value as before changing the screen. This way has 2 components: one in the air (d1) and one in the plastic glass of the screen (d2). Optic way is d1+ n*d2 where n is the optic index of the refractive screen (about 1.5 for perspex). If the new screen has a major thickness than the old one, the new (d1) must be decreased to preserve the sum. That means need for shim of the difference: old (d1)-new(d1). But if the new screen is thinner than the old one, it must be positioned upper (closer to the pentaprism) and if there are no shims to be removed (with the needed correction) is no chance to obtain a good focus. This explain the different results on the forum regarding the change of the focus screen.
For exemple the old screen thickness is 1.3mm and the new one is 1.5mm. The optic difference is (1.5-1.3)*1.5[refractive index]=0.2*1.5=0.3mm. You must compensate adding shim(s) of total thickness of 0.3mm.
The downside surface of the screen is a Fresnel lens (a plane lens) and if the focus length is different changing the screen then is a change in the resulted exposure because more or less light is distributed on the exposure sensor in the front of the pentaprism. The Katzeye screen with optic coating (like the lens coating) is more luminous and the result is an underexposure that must be compensated in camera. But if exist also the effect of different focus of the Fresnel lens the compensation can be in every sense (over or under). This must be tested, I only give you a simple theory implied in this process.
And, to prevent various "observations" here, I must say I'm licensed in physics.

This, Sir, is one of the best explanations I can imagine - describing optical path without the aid of any diagram. Very well put. I take it that you are licensed in teaching as well.


cheers,

Abhi

[Anthony Lee]

Thanks, Quicksand!
But I must say mr. dlacouture, the thickness is important. The optic "way" from the mirror reflexion till the upside matte screen focus surface must be kept to the same value as before changing the screen. This way has 2 components: one in the air (d1) and one in the plastic glass of the screen (d2). Optic way is d1+ n*d2 where n is the optic index of the refractive screen (about 1.5 for perspex). If the new screen has a major thickness than the old one, the new (d1) must be decreased to preserve the sum. That means need for shim of the difference: old (d1)-new(d1). But if the new screen is thinner than the old one, it must be positioned upper (closer to the pentaprism) and if there are no shims to be removed (with the needed correction) is no chance to obtain a good focus. This explain the different results on the forum regarding the change of the focus screen.
For exemple the old screen thickness is 1.3mm and the new one is 1.5mm. The optic difference is (1.5-1.3)*1.5[refractive index]=0.2*1.5=0.3mm. You must compensate adding shim(s) of total thickness of 0.3mm.
The downside surface of the screen is a Fresnel lens (a plane lens) and if the focus length is different changing the screen then is a change in the resulted exposure because more or less light is distributed on the exposure sensor in the front of the pentaprism. The Katzeye screen with optic coating (like the lens coating) is more luminous and the result is an underexposure that must be compensated in camera. But if exist also the effect of different focus of the Fresnel lens the compensation can be in every sense (over or under). This must be tested, I only give you a simple theory implied in this process.
And, to prevent various "observations" here, I must say I'm licensed in physics.

I like the last part of your explanation about metering with a non-Pentax focusing screen, and I agree that there will be some metering interference. For this, I have decided not to change my focusing screen unless there is an alternative from Pentax plus a firmware upgrage to include a custom function to compensate for this new screen to maintain metering accuracy, just like what Canon does with their type S focusing screens for most of their 40/50/60D, 5D, 5D2. Members here should join in one loud voice to influence Pentax to come out with a manual focusing screen and I am sure it will be very popular. What's the use of all the legacy lenses if one cannot get to use them to their optimum. I switched from Canon (40D & 5D) because I like to use old Pentax lenses on both my Canon cameras and I am now finding that the same lenses are actually more difficult to use on a Pentax body because of the lack of a proper focusing screen.

[Paunel]

I like the last part of your explanation about metering with a non-Pentax focusing screen, and I agree that there will be some metering interference. For this, I have decided not to change my focusing screen unless there is an alternative from Pentax plus a firmware upgrage to include a custom function to compensate for this new screen to maintain metering accuracy, just like what Canon does with their type S focusing screens for most of their 40/50/60D, 5D, 5D2. Members here should join in one loud voice to influence Pentax to come out with a manual focusing screen and I am sure it will be very popular. What's the use of all the legacy lenses if one cannot get to use them to their optimum. I switched from Canon (40D & 5D) because I like to use old Pentax lenses on both my Canon cameras and I am now finding that the same lenses are actually more difficult to use on a Pentax body because of the lack of a proper focusing screen.

I completely agree with you, but I think Pentax need to sell the new lenses and create a disadvantage for the great old lenses. This is proved by the fact that in the menus does not exist the possibility to "ground" the "A pin" and to specify the maximum aperture of the lens (like in Nikon D200 or Fuji S5). The apparent motivation: "the old lenses for 35mm diffuse light or has a large angle of incident light on senzor and for this you must use the green button bla, bla..." contradict the mode of using Pentax FA lenses (all for film cameras and with great results on DSLR). Pentax was a great listener for the need of the photographer once, but now the politics has changed from the new master and this appear as a pressure to the Internal Quality Assurance as you observed with the K5 "problems".
It remains us only the possibility of adjusting such things in "Minitechniqus" mode, only for the skilled persons...

[dlacouture]

Have a look to my thread about using a Canon S screen in my K5... That's heaven on m42 land for ya!

And you can always add a little bit of conductive matter on the A pin, this will enable P-TTL on all legacy lenses (but you will still have to use the old "partial mount" trick with PK-m lenses)...

[DogLover]

I like the last part of your explanation about metering with a non-Pentax focusing screen, and I agree that there will be some metering interference. For this, I have decided not to change my focusing screen unless there is an alternative from Pentax plus a firmware upgrage to include a custom function to compensate for this new screen to maintain metering accuracy, just like what Canon does with their type S focusing screens for most of their 40/50/60D, 5D, 5D2. Members here should join in one loud voice to influence Pentax to come out with a manual focusing screen and I am sure it will be very popular. What's the use of all the legacy lenses if one cannot get to use them to their optimum. I switched from Canon (40D & 5D) because I like to use old Pentax lenses on both my Canon cameras and I am now finding that the same lenses are actually more difficult to use on a Pentax body because of the lack of a proper focusing screen.

The Katzeye brand of screen's effect on spot metering (with K7 or K5) is so minimal that I can't imagine that being a problem, especially if you shoot raw in which case it's not even worth thinking about. The benefits of that screen far outweigh that one tiny negative. In fact, it's so minimal that I don't even think of it as being a negative. You are unnecessarily denying yourself an excellent solution for what is, IMO, a silly reason. Now, the Katzeye will not help you discern extremely shallow depths-of-field like the Canon s-screens apparently will, but you didn't mention that as being your problem.

[Anthony Lee]

The Katzeye brand of screen's effect on spot metering (with K7 or K5) is so minimal that I can't imagine that being a problem, especially if you shoot raw in which case it's not even worth thinking about. The benefits of that screen far outweigh that one tiny negative. In fact, it's so minimal that I don't even think of it as being a negative. You are unnecessarily denying yourself an excellent solution for what is, IMO, a silly reason. Now, the Katzeye will not help you discern extremely shallow depths-of-field like the Canon s-screens apparently will, but you didn't mention that as being your problem.

I had tried to use a split focusing screen on my Canon 40D /5D and I gave up on that and prefered the Canon type S in terms of focusing speed. With my 5D I had 15 manual focus lenses and one AF lens and my main subject was my 2 year old grandson. I had been using split screen all my life since the late '60s and I still have an MX now with split screen and I understand how cumbersome it is to use split screen screen. So my reason is far from silly as I have tried both and I know which is better as a standard screen for both manual and AF lenses on a DSLR.

[DogLover]

I had tried to use a split focusing screen on my Canon 40D /5D and I gave up on that and prefered the Canon type S in terms of focusing speed. With my 5D I had 15 manual focus lenses and one AF lens and my main subject was my 2 year old grandson. I had been using split screen all my life since the late '60s and I still have an MX now with split screen and I understand how cumbersome it is to use split screen screen. So my reason is far from silly as I have tried both and I know which is better as a standard screen for both manual and AF lenses on a DSLR.

Dude, read your post again. You said the reason you weren't going to change screens is because of the effect on metering. Then read my response.

[Skymist]

I purchased the FSB focusing screen for K-5 from focusingscreen.com for $59. Installation went well.

Careful tests with a Pentax F/1.9 43mm Limited lens showed consistent front-focusing behavior. The screen came with two shims. I installed them and retested. The FF continued. I couldn't say for certain if the shims improved it or not.

Their FSB screen is definitely thinner than the K-5 screen. I assume that had something to do with it.

I spent quite a bit of time working with it. The texture area combined with the split center button is a good mix for helping with a variety of focus situations. My main concern was with low light, fast lens focusing. After practicing with it I saw that one could learn to compensate for the error - always defocusing an amount. But I didn't like that as a solution.

So I uninstalled it, and put the original K-5 screen back. It works fairly well and practice seems to improve results with it as much as with the other, and at least it gives accurate results. Best focus is best focus.

I'm not sure what the problem is. I wonder if I am being overly demanding of focus precision. Anyone else have a suggestion?

[dlacouture]

You have to remove the factory-supplied metal shim (you can see it resting against the pentaprism when the screen is hinged down).

There is a little lock, quite identical to the one locking the screen into place, that holds it.

[Skymist]

You have to remove the factory-supplied metal shim (you can see it resting against the pentaprism when the screen is hinged down).

There is a little lock, quite identical to the one locking the screen into place, that holds it.

Thanks! I hadn't noticed the metal shim. Now it is close to correct focus. However, the two shims supplied were not quite adequate. I may try to shim it out a tiny bit further to see if I can get more accurate results. As it is, though, it is usable.