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Focus screens for manual lenses
#11
[quote name='genotypewriter' date='20 June 2010 - 12:43 PM' timestamp='1277030607' post='624']

There are rare times when either the sensor or the focusing screen is not shimmed equally/correctly. These will cause differences in focus between the captured image (sensor) and what's on the VF. And I've heard that misalignment (i.e. focus on one side, etc.) can also be caused by incorrect shimming. I don't think there are multiple shims for the focusing screen, so it has to be your sensor mount then (if there is such a problem at all). Just thinking out loud...



GTW

[/quote]

There actually are multiple shims for the focusing screen, in several thicknesses, for each camera body. Shims can be bought in sets of different thicknesses, so that the correct distances of focusing screen to lens can be set. This is not aprocedure for th efaint of heart, however, and is probably best left to a Canon Service Center for most of us.



HTH, kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....
#12
[quote name='wim' date='20 June 2010 - 12:51 PM' timestamp='1277034701' post='625']

There actually are multiple shims for the focusing screen, in several thicknesses, for each camera body. Shims can be bought in sets of different thicknesses, so that the correct distances of focusing screen to lens can be set. This is not aprocedure for th efaint of heart, however, and is probably best left to a Canon Service Center for most of us.



HTH, kind regards, Wim

[/quote]



It could also be my eye. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/rolleyes.gif' class='bbc_emoticon' alt='Big Grin' />



I do tend to have problems with blurriness towards the edges of the viewing area when focussing on off-centre subjects. I checked again today, and in the centre the S screen is fine, but towards the edges it gets more difficult to really nail the focus.
#13
[quote name='Pinhole' date='20 June 2010 - 10:41 PM' timestamp='1277066511' post='628']

It could also be my eye. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/rolleyes.gif' class='bbc_emoticon' alt='Big Grin' />



I do tend to have problems with blurriness towards the edges of the viewing area when focussing on off-centre subjects. I checked again today, and in the centre the S screen is fine, but towards the edges it gets more difficult to really nail the focus.

[/quote]

Well, it does get harder. Faster lenses do generally have some light fall-off towards the edges and corners, after all.



However, I find i do not really have any problems with the 5D II and Eg-S. I did find it a little harder with the 5D Classic and EE-S for unclear reasons.



Kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....
#14
[quote name='wim' date='20 June 2010 - 09:51 PM' timestamp='1277034701' post='625']

There actually are multiple shims for the focusing screen, in several thicknesses, for each camera body. Shims can be bought in sets of different thicknesses, so that the correct distances of focusing screen to lens can be set. This is not aprocedure for th efaint of heart, however, and is probably best left to a Canon Service Center for most of us.



HTH, kind regards, Wim

[/quote]



Hi Wim,



Yes, you're right. I actually meant to say multiple shims for each corner (like there is on the sensor mount?).



I got this IR modded 50D and VF is completely off. The AF works fine for most lenses (partly thanks to micro-adjust) but I want to shim the focusing screen properly to make it consistent with the sensor. I know this is a big can of worms because different lenses focus IR different points so there's no one right place to pick. But I have the 200 f/2 which needs no correction for IR (it's the most APO lens out of all the [url="http://forum.photozone.de/index.php?/user/10892-genotypewriter/page__tab__aboutme"]ones I've used[/url]) and I want to be able to MF through the VF on that because the AF "correction" done to ensure proper IR focusing for my other lenses is so heavy that not even full microadjust is enough to get the 200 to AF.



I know there are multiple shims in there but I've been too chicken to meddle around in case I break something. I've already changed the focusing screen to the S type but that's all. Any ideas on how to pull those shims out? (I might actually need to add instead of remove... can't remember the error).



Thanks...
#15
Hi Geno,

[quote name='genotypewriter' date='22 June 2010 - 05:49 AM' timestamp='1277178571' post='648']

Hi Wim,



Yes, you're right. I actually meant to say multiple shims for each corner (like there is on the sensor mount?)./quote]

Ah, ok. No I don't think those are available. You'd have to construct those yourself I am afraid.

quote]I got this IR modded 50D and VF is completely off. The AF works fine for most lenses (partly thanks to micro-adjust) but I want to shim the focusing screen properly to make it consistent with the sensor. I know this is a big can of worms because different lenses focus IR different points so there's no one right place to pick. But I have the 200 f/2 which needs no correction for IR (it's the most APO lens out of all the [url="http://forum.photozone.de/index.php?/user/10892-genotypewriter/page__tab__aboutme"]ones I've used[/url]) and I want to be able to MF through the VF on that because the AF "correction" done to ensure proper IR focusing for my other lenses is so heavy that not even full microadjust is enough to get the 200 to AF.



I know there are multiple shims in there but I've been too chicken to meddle around in case I break something. I've already changed the focusing screen to the S type but that's all. Any ideas on how to pull those shims out? (I might actually need to add instead of remove... can't remember the error).



Thanks...

[/quote]

I would think you would get backfocus errors (longer wavelength and hence focuspoint). So probably removing shims to lengthen the pathway to the focusing screen, which might be difficult, because it could well be there aren't enough shims to take away. Considering the differences between lenses, a can of worms is indeed an apt description.



However, what you could do in order to get a good visual idea, is to adjust the diopter setting. However, this would again be different for each lens, so a lot of work to figure out...



Another option would be a thinner focusing screen, but then you have the problem on how to make sure it will still be clamped in properly, plus that you need different thicknesses for different lenses...



In short, I think the simplest and easiest way likely is to figure out the different diopter settings on the VF for each lens, and do MF with the -S type screen <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='Big Grin' />.



Kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....
#16
[quote name='wim' date='22 June 2010 - 08:52 PM' timestamp='1277203964' post='650']

I would think you would get backfocus errors (longer wavelength and hence focuspoint). So probably removing shims to lengthen the pathway to the focusing screen, which might be difficult, because it could well be there aren't enough shims to take away. Considering the differences between lenses, a can of worms is indeed an apt description.

[/quote]



One thing I didn't mention before was the differences introduced by the thickness of the IR filter that replaced the original IR cut filter. The original filter was a multi-layered one that also had the two AA filters and the sensor cleaning layer. The IR filter that was put on is most probably thinner, because it's a specially made on-sensor filter (rather than a glass filter cut to size).



The good news is that I don't need the VF to work for all the lenses. Just my 200 because the rest can AF without a problem. All that needs to be done is make the focusing screen distance consistent with the sensor distance.



[quote name='wim' date='22 June 2010 - 08:52 PM' timestamp='1277203964' post='650']

In short, I think the simplest and easiest way likely is to figure out the different diopter settings on the VF for each lens, and do MF with the -S type screen <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='Big Grin' />.

[/quote]



I'm not sure how diopter adjustments can help lens focus... the lens image is already made on the focusing screen and any diopter adjustments will only affect how the eye focuses on the focusing screen, right?



GTW
#17
[quote name='genotypewriter' date='19 June 2010 - 04:34 AM' timestamp='1276950870' post='609']

Interesting... how does this compare to the EG-S for off-center focusing?

[/quote]



Much depends on the body you are using and the screen model. For example I use the brightscreen p222 in both my Ds and D Canon 1 series cameras and the screen is excellent for off centre focusing with both models of cameras, but obviously the same screen in the H sensor camera has a larger portion of the viewable area covered by the fresnel. I have katz-eye too for the c sensor bodies, and the Canon S for the IIn and the B also for the the Ds and D bodies, but I always use just the brightscreen now.

I would add that the screens are great for autofocus only people too since I believe the fresnel helps visualize the relationship between objects in the image.



To answer you question though, if you are focusing on fast moving subjects with a telephoto that has a large aperture, the S screen is better for that specific application, but not manual focusing in a still life setting as the brightscreen matte portion is also very good.
#18
[quote name='genotypewriter' date='23 June 2010 - 04:36 AM' timestamp='1277260566' post='658']

One thing I didn't mention before was the differences introduced by the thickness of the IR filter that replaced the original IR cut filter. The original filter was a multi-layered one that also had the two AA filters and the sensor cleaning layer. The IR filter that was put on is most probably thinner, because it's a specially made on-sensor filter (rather than a glass filter cut to size).



The good news is that I don't need the VF to work for all the lenses. Just my 200 because the rest can AF without a problem. All that needs to be done is make the focusing screen distance consistent with the sensor distance.







I'm not sure how diopter adjustments can help lens focus... the lens image is already made on the focusing screen and any diopter adjustments will only affect how the eye focuses on the focusing screen, right?



GTW

[/quote]

That last remark was for accurate MF, not for AF <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='Big Grin' />. The differences between correct MF for each lens could be mitigated by different diopter settings for each lens. That's all I ment here. A theoretical more than a practical exercise <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='Big Grin' />.



Kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....
  


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