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Archive 2005 · 20D Split/Micro Prism Focusing Screen available!
  
 
Roy Pertchik
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p.2 #1 · p.2 #1 · 20D Split/Micro Prism Focusing Screen available!


After learning here on FM about the pitfalls of focus and recompose, I still use the technique, but i am careful about it. If I have a shallow DOF, then I kbnow it's best to avoid it. So, if I stay concious of DOF and make an effort to focus on something that's at the proper distance, then I think I am using the technique safely. I wouldn't shoot a portrait with my 85 1.8 wide open and try to recompose hand held from the eyes to a fat belly, for example, but with my 17-40 at f/8.. no problem. Now, it may seem that if I have enough DOF to cover focus and recompose, then why do I have to check the AF? Well, sometimes when AF fails, it fails big time. It's just a stupid computer after all, and I'd like to know when it's screwing up. Since it now seems I can have a focusing circle for whenever it is useful, I'm going to jump on it.


Apr 05, 2005 at 04:17 AM
nutek
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p.2 #2 · p.2 #2 · 20D Split/Micro Prism Focusing Screen available!


I don't understand. So let's say you are shooting a portrait with your 17-40 at f8 and your aim is to have everything sharp, especially the eyes. So:

1) You use your prism to focus manually on the eyes of the subject.
2) Then you recompose to have a suitable composition, e.g. now the eyes are near the top of the frame, while the belly is covered by the prism now.
3) You check your focus again (using the prism) on the belly now (??)

At f8 on a relatively-wide lens (17mm~=28mm on your 20D), there *might be* sufficient depth of field to cover your subject to be in sharp focus from head to toe. So what part of the body are you wanting to check focus again? The belly or the eyes?

- Wenyao

RoyPertchi wrote:
After learning here on FM about the pitfalls of focus and recompose, I still use the technique, but i am careful about it. If I have a shallow DOF, then I kbnow it's best to avoid it. So, if I stay concious of DOF and make an effort to focus on something that's at the proper distance, then I think I am using the technique safely. I wouldn't shoot a portrait with my 85 1.8 wide open and try to recompose hand held from the eyes to a fat belly, for example, but with my 17-40 at f/8.. no problem.
...Show more



Apr 05, 2005 at 04:30 AM
Roy Pertchik
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p.2 #3 · p.2 #3 · 20D Split/Micro Prism Focusing Screen available!


Nuyek, you are raising very good points. The fact that the prism is only in the center is a big limit on the usefuess. Still, for whatever it's worth, whenever it's useful, I think it would be nice to use it to at least confirm somewhat that the focus is what i think it is.

In our portrait example, if I had the focusing circle, one thing I would try is to AF on the eyes with the center point, and check that the prism looked good, then I could look at the belly and see if it was good too...the MF prism is now working like a DOF checker, I knew it would come in handy!

Anyway, as you hinted, at f/8 a 17mm on my 1.6 camera (28mm equivelent) focused at 10' has a DoF from 6' to 40' (according to Don Flemings DoFmaster for palm pilot). I don't think focus and recompose is a problem under these circumstances. I could focus on the eyes, and then sneeze, dance a jig, and then point the camera at the belly and still have DoF cover. I also don't think AF should be too tough here either, but sometimes the camera thinks it's tough! If I got a little hinky about the camera's focus for some reason, like low light, or if the subjects eyes are in profile against a plaid background, and maybe my AF sensor is not exactly ligned up with the little red box in the viewfinder (they're not necessarily dead on, you know) well, then I could just look at the prism area and be reassured the plaid didn't distract the AF.

Now, if it were my 85 at 1.8, the DoF would be from 9'-8" to 10'-2", a 4" spread. That would be tougher to focus and recompose. So I'd try it with an off center AF point on the eyes, and I'd look at the prism on the belly, or maybe the arm, and try to find something else that is in focus when the camera says the eyes are in focus, and then I would think if it's reasonable that these two points are in the same plane, and again I'd have a pretty good confirmation that things are ok.

For my really slow set up shots, right now I put C.Fn 4 on 1, which means focus is on the * button. Then I go about my business setting things up, taking exposures and test shots as often as I like, and I do a final focus at the last minute. Sometimes I have to put something into the scene at a point where I want to center the DoF and that happens to hit an AF point as well... the other day I put a ketchup bottle there, focused, and took it away. But I had no visual confirmation! I had no way to know for sure that the camera got it right until I broke the set, packed, took a train home, and down loaded to the PC. It would have been nice to look at that ketchup bottle with a focusing prism.




Apr 05, 2005 at 05:26 AM
nutek
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p.2 #4 · p.2 #4 · 20D Split/Micro Prism Focusing Screen available!


In the 17mm (28mm) portrait example, since the depth of field is large enough to cover any user movement/error, then everything is fine.

However, what I would like to point out is that this technique of using depth of field to cover focus errors isn't applicable/transferrable to high magnification or telephoto shots. It is but an inferior (sorry!) technique left over from the era of MF-days when autofocus wasn't available. [On the contrary, this technique is excellent for landscapes though - that is why many landscape photogs don't even use AF.]

In the AF-era, I would say it is simpler just to compose your picture, select the focussing point that covers the eyes (or whatever part of the body you want sharp), focus, then fire. This would work for most kinds of situation - wide-angle, telephoto, macro, etc, and works not only in portraits, but wildlife as well, when you may not be able to find another plane of focus that is the same as the eyes easily.

If you are using FLR and then checking focus accuracy on the belly instead of the eyes, then you're introducing another dimension of error into the situation - i.e. your ability to distinguish whether the belly is in the same focus plane as the eyes. So why not just reduce the amount of errors that can be made, and just focus on the eyes using AF instead? After all, the technology is there for you to use.

As you rightly pointed out, the AF system does sometimes get confused by things like plaid backgrounds, and yes, a focussing prism would be useful to help determine AF accuracy, but if and only if your subject is center-framed. In other cases, I would perform focus bracketing around the autofocused point instead - this is where USM lenses and CF4-1/3 really shine.



Apr 05, 2005 at 06:09 AM
Roy Pertchik
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p.2 #5 · p.2 #5 · 20D Split/Micro Prism Focusing Screen available!


Very well said :-) I would say, however, that the center focus prism is still better than completely useless for off center focus points, if only because it's a measuring device that can give you some information.


Apr 05, 2005 at 12:27 PM
tmessenger
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p.2 #6 · p.2 #6 · 20D Split/Micro Prism Focusing Screen available!


I find the mat finish on the contax screen I'm using is much better for off center focusing then the canon oem screen, it just shows a lot more contrast but it is dark in low light, trade offs.

tm



Apr 05, 2005 at 05:57 PM
Greg Feldman
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p.2 #7 · p.2 #7 · 20D Split/Micro Prism Focusing Screen available!


I really want one of these for my 300D. Fact is, autofocus is far from infallible, and I can still focus better than any autofocus camera if I have the tools to do it. Frankly, autofocus is far and away the least important new feature of modern cameras in the last 20 years--for me.

Is there a Web page with more specifics about getting and using these screens for a 300D?



Apr 05, 2005 at 06:19 PM
goering
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p.2 #8 · p.2 #8 · 20D Split/Micro Prism Focusing Screen available!


Nutek, there are some situations when this may be useful eg I was contemplating using a 2X entender on a 400/5.6 lens and I will be deprived of AF.

The resultant, very dim f11 would be a pain to MF without a split focusing screen. I know I should not be attempting this, but when you cannot afford a longer lens and you need the reach ...



Apr 05, 2005 at 06:28 PM
m3rocket
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p.2 #9 · p.2 #9 · 20D Split/Micro Prism Focusing Screen available!


Update--the post got deleted! DPR is such a farce--I guess the self-appointed police got to that post. Can we get Rachael to post and comment here instead? I sent her an inquiry last night, but have yet to get a reply.


Apr 05, 2005 at 07:17 PM
BRR5
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p.2 #10 · p.2 #10 · 20D Split/Micro Prism Focusing Screen available!


Hope this makes things clear as mud

Rachael Katz's response-

Installation is not terribly difficult, but it does require care. Instructions for the 20D are not available, as Canon never officially released a replacement screen. But, someone wrote instructions for the 300D which are available here (http://groups.yahoo.com/group/canondigicamhacking/files/). The basic instructions are the same as the 300D and the pictures in the posted instructions give a good idea of what's involved. There are only really two points that are slightly different: 1. if the shim is removed or dislodged, it has to be inserted a certain way. The top edge (furthest from the mirror) has to be put in first and then the other edge tipped down into place. 2. Because of the 2nd screen with the composition marks, it seems to be more difficult to get the installation dust free. Keep the environment very clean and use the air puffer liberally at each step. Beyond these two points, it's pretty much the same as the 300D. If you don't feel confident installing it, your local camera shop should be able do it for less than $50.

If you have any other questions, please donít hesitate to let me know.
Take care,
Rachael Katz

Katz Engineering Services

(916) 361 - 2143 Office

[email protected]



Apr 05, 2005 at 07:32 PM
 

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Nori
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p.2 #11 · p.2 #11 · 20D Split/Micro Prism Focusing Screen available!


Hi All,

I have been using Beattie Intenscreen for Nikon FA / FE / FE2 / FM2 Cameras - Matte with Horizontal Split Image.

Any Beattie screen for Nikon FA/FE/FE2 camera that works with D30/D60 should also work with 20D. I filed the screen to fit the D60 myself and AF works as it should and manual focus is much easier.

The advantages of using a Beattie screen is that the viewfinder is brighter by atleast a stop. MF is much easier with TS-E and MP-E lenses and you can actually see the effect of the tilt in the viewfinder. Which I could never see using the dark viewfinder which comes with the D60. Exposure compensation is required when using lenses f/4 and higher.

Here is a link to the product on b&h website.

http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=4473&is=REG

I have tried the contax focusing screen, but I did not like it. Using the contax screen only the split image area was brighter than the original D60's focusing screen. The rest of the screen was much darker than what I had with the D60.

If you are a bit handy in doing things you can fix the beattie screen yourself. There is also a beattie plain matte screen in used section of B&H

Plain Matte


Hope that helps

Nori



Apr 05, 2005 at 07:52 PM
Roy Pertchik
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p.2 #12 · p.2 #12 · 20D Split/Micro Prism Focusing Screen available!


I just ordered a screen from Rachael. I took the extra bright Hi-lux finish which she has to send out. All together, it's supposed to be here in about 2 weeks. I'll keep y'all posted :-)




Apr 06, 2005 at 01:17 AM
m3rocket
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p.2 #13 · p.2 #13 · 20D Split/Micro Prism Focusing Screen available!


Thanx for the update Roy! Do you know whether it's a Nikon, Contax, or some other screen that Rachael is "refitting?" Will the Hi-Lux finish affect exposure? She hasn't responded to my email inquiry last night.

Nori--I have a Beattie on my A2E; the additional brightness is addictive, but I lost the AF points. If Roy's transplant is successful, I'll be next in line since this mod evidently retains the focusing points on the 20D.



Apr 06, 2005 at 01:38 AM
Roy Pertchik
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p.2 #14 · p.2 #14 · 20D Split/Micro Prism Focusing Screen available!


Her mailbox is apparently swamped! I kidded her about it and she said yes, it is. But I guess I got in the que a little early ( I inquired within about an hour of seeing the post here last night), so we've e-maild a cople of plys in the past several hours. She is very, very professional and chrystal clear about everything involved.
I don't know what she uses for blanks, I didn't think to ask that. The exposure is not affected. Focussing is not affected. I asked her about any AF points misbehaving, display problems, etc. My understanding is that every thing keeps ticking as per normal.



Apr 06, 2005 at 01:57 AM
radamo
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p.2 #15 · p.2 #15 · 20D Split/Micro Prism Focusing Screen available!


RoyPertchi wrote:
...My understanding is that every thing keeps ticking as per normal.



Roy,
This does sound really interesting. Please keep us posted as to how you do.
Thanks,
RA



Apr 06, 2005 at 02:33 AM
Roy Pertchik
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p.2 #16 · p.2 #16 · 20D Split/Micro Prism Focusing Screen available!


RoyPertchi wrote:
My understanding is that every thing keeps ticking as per normal.


I actually forgot, somewhere I read that she found that partial metering mode might be off somewhat, but EC would make it ok, once you knew how much. Other than that (which I never use anyway) every thing keeps ticking as pwer normal, AFAIK.



Apr 06, 2005 at 02:44 AM
Grouse
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p.2 #17 · p.2 #17 · 20D Split/Micro Prism Focusing Screen available!


her response to my email


Hi Aaron,

Installation is not terribly difficult, but it does require care.
Instructions for the 20D are not available, as Canon never officially
released a replacement screen. But, someone wrote instructions for the 300D
which are available at
http://groups.yahoo.com/group/canondigicamhacking/files/How%20To%20Remove%20
the%20Canon%20Digital%20Rebel%20Focusing%20Screen.pdf. The basic
instructions are the same as the 300D and the pictures in the posted
instructions give a good idea of what's involved. There are only really two
points that are slightly different: 1. if the shim is removed or dislodged,
it has to be inserted a certain way. The top edge (furthest from the
mirror) has to be put in first and then the other edge tipped down into
place. 2. Because of the 2nd screen with the composition marks, it seems to
be more difficult to get the installation dust free. Keep the environment
very clean and use the air puffer liberally at each step. Beyond these two
points, it's pretty much the same as the 300D. If you don't feel confident
installing it, your local camera shop should be able do it for less than
$50.

The benefit is that you will be able to do very accurate manual focusing.
This is especially helpful and almost a necessity if you are using and
adapter to use manual lenses, such as older Contax, Zeiss, Nikkor, or
Pentax. Through the viewfinder, you will see the same view seen in older
film SLR's - a center circle which is split horizontally. When the image is
out of focus, the top part of the image in the circle is shifted left or
right relative to the bottom half. In other words, vertical lines or edges
are broken as they pass over the split line. When you achieve proper focus,
the top and bottom images will align, assuring dead on focus on the object
that YOU pick, not the camera's computer.

Thanks for your interest, and if you have any other questions, please don't
hesitate to let me know.

Take care,
Rachael Katz



Apr 06, 2005 at 02:46 AM
dobro
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p.2 #18 · p.2 #18 · 20D Split/Micro Prism Focusing Screen available!


goering wrote:
I was contemplating using a 2X entender on a 400/5.6 lens and I will be deprived of AF.

The resultant, very dim f11 would be a pain to MF without a split focusing screen.

Unfortunately, this won't work. The split-image will black-out and become unusable around f/5.6 or 6.3 or so. The matte finish surrounding the split image may be better for manual focusing than the stock screen however.

Lee





Apr 06, 2005 at 05:00 AM
discreet
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p.2 #19 · p.2 #19 · 20D Split/Micro Prism Focusing Screen available!


I like to add a few more points the MF case.

Sometimes, the AF of certain cameras are not accurate enough if you want to shoot the low DOF portrait shots. As i am using a Drebel, only my center AF point is accurate enough to focus accurately on the eyes of the person. Sometime I will use my 85/1.8 at f2 because i want that shallow DOF to make the eyes pop out and choosing a non center AF point is not very practical at times as it refuses to lock focus.

What i usually do for this kind of shot, is to set the tripod up and use the center AF point to focus on just the eyes. I will shot a bit wider and crop later to get the composition i desire. Not very efficient in using the entire 6 meg crop i have, but if it is going to get me the focus i desire at low DOF. that is what i have to do.

So in this case MF will work. I dont really trust the center AF point at times and sometimes i wish i had a center split prism where i can really see whether it is in focus or not.


But for normal day to day shooting...i find it quite irrevelant to MF as it like pissing in the wind. Yes, some people can do it but more often than not, you end up pissing on yourself. i rather forgo the MF and focus on composition and learning how to maximise the AF of my camera.


nutek wrote:
I don't understand. So let's say you are shooting a portrait with your 17-40 at f8 and your aim is to have everything sharp, especially the eyes. So:

1) You use your prism to focus manually on the eyes of the subject.
2) Then you recompose to have a suitable composition, e.g. now the eyes are near the top of the frame, while the belly is covered by the prism now.
3) You check your focus again (using the prism) on the belly now (??)

At f8 on a relatively-wide lens (17mm~=28mm on your 20D), there *might be* sufficient depth of field
...Show more



Apr 06, 2005 at 07:40 AM
nottageek
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p.2 #20 · p.2 #20 · 20D Split/Micro Prism Focusing Screen available!


I'm taking notes of names in this thread. Then I'll cross-check them against people in the Buy & Sell forum who are selling bodies....

"Canon 300D LNIB!!
(Well, apart from the gaffer tape where the viewfinder should be. I couldn't adjust the shim, I got the matte and the stock screen mixed up, I didn't use my puffer liberally enough, then at 5.6 it blacked out and I panicked) p.s. if you find my tweezers in there, send them back to me please..."



Apr 06, 2005 at 11:54 AM
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