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Focusing with Haoda split screen

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kenw said:
... he asks you to ask the questions by email or on his
yahoo group if you'd like more answers. I believe this is on
account of past threads being removed here as violating selling a
product posting clauses.
Click to expand...
Possibly.

There are other possibilities. (Note- your profile lists no e-address.)
 
I just know who and how produced this chip. Not a lot of chips are made at the time. You can see that on a posted link only 8 are available for sale.
 
Hi, Larry,
Larry H. Smith said:
Please critique the following discussion:

Screen position is critical, as Doug has explained above.

Manufacturing tolerances(Canon's) are such that the camera/screen
pairing may produce a "fit" anywhere between two extremes,
..camera/screen "too tight", ...camera/screen "too loose".

"Anywhere between" becomes the issue.

Thus, a range of shim-sizes, to be used to fit the PARTICULAR
screen and PARTICULAR body being discussed.
Click to expand...
Just to get things in teh peoper perspective, note that in camera manufacture, the position of teh focsuing screen is not matched to that of the sensor. The position of the sensor is adjusted (it as itas own set of shim screws) to attain (so far as possible) its standard design location (focal plane 44.00 mm behind teh face of teh mount flange.

Theh teh screen is adjusted so its focal plane is 44.00 mm behind the face of teh mount flange (via the reflex mirror, of course).
Larry H. Smith said:
Assume(momentarily) that the Haoda screen has a manufacturing
tolerance of zero. Unless its thickness exactly matches that of the
Canon screen being re-placed, using the original shim will NOT
"match" the camera/screen fit of the original factory assembly.
Click to expand...
Haoda sys that in his"original" desigg, it is intended that teh thkcness would be that of the OEM screen plus the shim thincknedss he believd at the time was universal.
Larry H. Smith said:
If Haoda has a "manufacturing tolerance" greater-than-zero, which
is certainly the case, the Haoda screen would need its own
"matched to this PARTICULAR body" shim, ...or there will be a
mis-match.
Click to expand...
Indeed.
Larry H. Smith said:
When both screen and shim, IN COMBINATION, must match a particular
body, to a design-point fit,...then shim must be custom-fitted to
screen.

Instruction from Haoda to "just use the original shim" can easily
be incorrect., if screen thickness is different from original Canon
screen.
Click to expand...
Of course. The same would be true if we bought a new screen from Canon, or from Rachael Katz. The same is potentially true when Canon replaces the screen at a depot.

Best regards,

Doug

Visit The Pumpkin, a library of my technical articles on photography, optics, and other topics:

http://doug.kerr.home.att.net/pumpkin

'Make everything as simple as possible, but no simpler.'
 
Hi, Arjen,
Arjen van Andel said:
Arjen van Andel said:
If Haoda has a "manufacturing tolerance" greater-than-zero, which
is certainly the case, the Haoda screen would need its own
"matched to this PARTICULAR body" shim, ...or there will be a
mis-match.
Click to expand...
Haoda's screen has a thickness of zero, just like the Canon screen.
The thickness does't matter very much since you only 'see' the
matted part and that is resting against the shim.
Click to expand...
In fact, the "ground glass" plane is on the bottom surface of the screen plate.

The top surface carries the Fresnel "field lens".

Best regards,

Doug
 
. . on the OEM focsuing screen, the top surface does not rest against the shim anyway - there is a relief around the edge, and that sets against the shim. The actual top surface is a little higher.

The KatzEye replacement screens follow this design.

Here is the OEM screen:



The annotations pertain to the text in my paper on replacing the focsuing screen in an EOS 20D,, which incidentally is available here:

http://doug.kerr.home.att.net/pumpkin/index.htm#ReplaceScreen

Best regards,

Doug
 
Doug Kerr said:
Doug Kerr said:
If Haoda has a "manufacturing tolerance" greater-than-zero, which
is certainly the case, the Haoda screen would need its own
"matched to this PARTICULAR body" shim, ...or there will be a
mis-match.
Click to expand...
Indeed.
Doug Kerr said:
When both screen and shim, IN COMBINATION, must match a particular
body, to a design-point fit,...then shim must be custom-fitted to
screen.

Instruction from Haoda to "just use the original shim" can easily
be incorrect., if screen thickness is different from original Canon
screen.
Click to expand...
Of course. The same would be true if we bought a new screen from
Canon, or from Rachael Katz. The same is potentially true when
Canon replaces the screen at a depot.
Click to expand...
...the new Canon (or any brand)screen is subject to the same-type/different-degree variation as the original, and Average Joe Public would be left to hope that the original shim was appropriate to the new screen.

Is this the bottom line:...Send the camera/screen to Canon, ...hope they have/will-install the correct shim(s), to assure optimum focus?

Or is there a way to do this stuff at home, with care, and be SURE one has obtained optimum results? To me, the whole point of this exercise is to get focus-capability that is as good as possible. Otherwise, why bother?!

Thanks Doug, and other contributors. ;-)

Larry
 
I think people have already posted in this form their results with "do it your self" salvaged screens using razor blades and sand paper. If you aren't comfortable making the necessary adjustments (should they even be necessary) then send it to someone and pay them to do it. That’s the beauty of paying someone to do it. If you screw it up yourself you don’t have anyone to yell at. In worst case, you put your factory original back in and kindly ask to return the screen that didn’t work for you or ask for the one that uses a spacer. Or you go out and buy a box of shim stock and make your own shims and experiment until you wring every last little drop of focus accuracy out of it.
 
Doug Kerr said:
Doug Kerr said:
Doug Kerr said:
kenw said:
Haoda has found that the vast majority of cameras all have the identical shim installed
Click to expand...
The secondary AF mirror, however,
Click to expand...
does have an adjustable cammed mirror stop for trimming the
distance to the AF sensor.
Click to expand...
It's actually for trimming the position of teh spot that each of
the AF detectors regards. It also changes the distnce to the AF
sensors, but not consistently for all of them, and I don't think it
is intended to do that dury as well as its other purpose. (People
of course keep doing that; I assume they have no idea where in the
frame their AF detector end up regarding.)
Click to expand...
Hi Doug,

I've been a bit curious about this because I can't find a repair manual for any of these cameras. Obviously adjusting the cam does alter the position of the focus sensors relative to the imager in addition to just changing the distance. But I'm not certain that canon intends to line them up that close or use this adjustment for that. The reasons for my thinking are:

1. As it arrived from the factory my XT backfocused just a smidgen (within a DOF though). The AF sensor appears to be about twice as big as the box and was not centered, rather the AF sensor is aligned with the bottom of the box and rises to about twice the height of the box. It is aligned in the horizontal direction. This mirror would do nothing to align in the horizontal, only the vertical so why would they put it in just for viewfinder alignment? Canon clearly didn't use it to align mine.

2. I made adjustments using the cam screw and altered the focus quite easily. The relative position of the sensors didn't change noticably at all from where the were originally. While the angle of the mirror does change the more dramatic change appears to be in distance. This is I think because very small angle changes alter the distance drammatically realtive to the very shallow depth of focus. Just running some quick numbers and trig seems to show this.

3. This post http://www.fredmiranda.com/forum/topic/241524 implies that canon makes no effort to carefully align the AF sensors relative to the AF boxes in the viewfinder.

So I really do think the mirror cam screw is for autofocus adjust and nothing else. Any thoughts or contradictory info?

I am still bothered by the fact that it seems that this should effect the top and bottom AF sensors differently than the centerline ones, but this may not be that significant. The sensors are not that far apart in the vertical and how significant the error between the top and bottom sensors is would be a function of the baseline of the two sensors compared to their distance from the mirror hinge. This error may be tolerable, but I haven't sat down with pencil and paper and tried to prove it.
--
Ken W
Rebel XT, DSC-S85, and a whole lot of 35mm and 4x5 sitting in the closet...
 
Hi, K,
kenw said:
Hi Doug,

I've been a bit curious about this because I can't find a repair
manual for any of these cameras.
Click to expand...
I donl't have such either.
kenw said:
Obviously adjusting the cam does
alter the position of the focus sensors relative to the imager in
addition to just changing the distance. But I'm not certain that
canon intends to line them up that close or use this adjustment for
that. The reasons for my thinking are:

1. As it arrived from the factory my XT backfocused just a smidgen
(within a DOF though). The AF sensor appears to be about twice as
big as the box and was not centered, rather the AF sensor is
aligned with the bottom of the box and rises to about twice the
height of the box. It is aligned in the horizontal direction.
This mirror would do nothing to align in the horizontal, only the
vertical so why would they put it in just for viewfinder alignment?
Click to expand...
Well, since the mirror pivots, the resting position is critical for vertcial registration of the aiming point of the AF detectors, so it certainly needs an adjustment. There is no correspndoing reason that the horizontal registration would be substantially off.
kenw said:
Canon clearly didn't use it to align mine.
Click to expand...
Evidently.
kenw said:
2. I made adjustments using the cam screw and altered the focus
quite easily. The relative position of the sensors didn't change
noticably at all from where the were originally. While the angle
of the mirror does change the more dramatic change appears to be in
distance. This is I think because very small angle changes alter
the distance drammatically realtive to the very shallow depth of
focus. Just running some quick numbers and trig seems to show this.
Click to expand...
Could well be.
kenw said:
3. This post http://www.fredmiranda.com/forum/topic/241524 implies
that canon makes no effort to carefully align the AF sensors
relative to the AF boxes in the viewfinder.
Click to expand...
I'm sure we have no idea what Canon's factory tolerances are on that matter.
kenw said:
So I really do think the mirror cam screw is for autofocus adjust
and nothing else. Any thoughts or contradictory info?
Click to expand...
No, I think it is just to adjust the registration of the AF points. There is no need to adjust the distance to the AF detectors - any discrepancy is readily taken care of by table settings in the firmware.

uIt is not as if the two images are compared "side by side" as we do visually in the split image prism system. Ther, the correct distance is critical.

But in fact, the detectors for the two "sides" of each AF detector aren't even adjacent - that simplifies both the optical design and the chip layout.. The positions of the images on the two sensors are compared by autocorrelation technque, and any bias needed to adjust for the precise distance to the AF detector array in a particular camera can readily be applied arithmetically.
kenw said:
I am still bothered by the fact that it seems that this should
effect the top and bottom AF sensors differently than the
centerline ones, but this may not be that significant.
Click to expand...
That's why it would not be a good way to adjust the distances to the AF sensors, if such were in fact necessary.
kenw said:
The sensors
are not that far apart in the vertical and how significant the
error between the top and bottom sensors is would be a function of
the baseline of the two sensors compared to their distance from the
mirror hinge. This error may be tolerable, but I haven't sat down
with pencil and paper and tried to prove it.
Click to expand...
Me neither.

Best regards,

Doug
 
Doug Kerr said:
In fact, the "ground glass" plane is on the bottom surface of the
screen plate.

The top surface carries the Fresnel "field lens".
Click to expand...
Ok, but how would the image of the grounded plane line up with the Fresnel? And where is the split located? Also at the top, in the same plane the Fresnel is in?

Arjen.
 
Ah, good point Doug. AF adjust could just be done in firmware.

Thanks for your thoughts.
--
Ken W
Rebel XT, DSC-S85, and a whole lot of 35mm and 4x5 sitting in the closet...
 
Hi, Arjen,
Arjen van Andel said:
Arjen van Andel said:
In fact, the "ground glass" plane is on the bottom surface of the
screen plate.

The top surface carries the Fresnel "field lens".
Click to expand...
Ok, but how would the image of the grounded plane line up with the
Fresnel?
Click to expand...
"Line up" in what way?

The Fresnel field lens is just "downstream" of the image in the pipeline. Its purpose is to concentrate the light emitted, diffusely, from any spot on the ground glass so that a greater fraction of it actually heads toward the eyepiece lens (through the pentaprism, of course), thus improving finder image brightness. This is discussed in my article referenced below.
Arjen van Andel said:
And where is the split located? Also at the top, in the
same plane the Fresnel is in?
Click to expand...
The split prism is at the focal plane, at the bottom of the plate. Usually, each prism entends equal distances above and below the focal plane - that is, half of each prism projects beydnd the genera llower surface of the plate (is "proud of it", as our British machinist friends would say).

This is required if the image line is to pass unbroken across the split in the case where the image is actually formed at the focal plane (the situation for "correct focus", assuming of course that the distance to the focsuing screen is proper).

A lot of this is discussed in my tutorial article, "Principle of the Split Image Focusing Aid and the Phase Comparison Autofocus Detector in Single Lens Reflex Cameras", available here:

http://doug.kerr.home.att.net/pumpkin/index.htm#SplitPrism

Best regards,

Doug
 
Larry H. Smith said:
I do not wish to appear disrespectfully antagonistic, ...but OTOH,
I don't wish to be disrespectfully brushed-off, either.

Giving me directions to other addresses for answers to questions
asked in THIS forum,...doesn't inform other members HERE.
Click to expand...
In case anyone is interested, I received several e-replies from Haoda Fu.

My concerns included some questions re. business/politics, and so the discussion, which was both private and inappropriate to this forum, will not be repeated here.

Haoda's replies were courteous and indicated an understanding of my reasons for questioning, ...he took no apparent offense to my inquiry, and repeatedly expressed appreciation for my interest.

Best wishes,

Larry
 
This is a portion of an exchange with Haoda Fu, and is posted here in hopes of prompting "ideal screen" comment from other members:

My past use of film SLR's makes me demanding of good manual-focus capability, so I will be considering all the available screens, including yours, when I get my rig.

I will be following screen developments with interest while I wait. (With the film cameras, my favorite was a screen with a split center, surrounded by a micro-prism "collar", similar to the screens in cameras such as the 1960-'70s Minolta SRT 101 cameras. Using one of these, with a fast lens (58mm/1.2, for example,) is a real pleasure. Any good used-camera shop will have one of these for you to look at if you are interested.

One suggestion I can make, to non-English speaking manufacturers, is this: Have a person who is VERY good with the English language, and who thinks like a "teacher", write the installation/use instructions which accompany your product, for the English-speaking markets. The instructions need to be clear and complete, or the presentation will appear "amateurish", especially to Americans, for whom "a manual written in English by someone from China or Japan" is usually taken to mean a nearly un-decipherible one. ;-)

You should also have a very good interpreter read correspondence that you receive from English-speakers, so their feedback is fully understood, ...because sometimes fine-points are being addressed, and a crude language-skill level will increase the likely-hood of misunderstanding or missing some points. IMO, Westerners are more "direct" than people from your countries, and often, like I do, expect a plain and clear answer to the exact question asked. People from Eastern countries often seem to believe that "some talk" is the same thing as "the answer". We don't think so. ;-)

Of course my Chinese/Japanese language-skills are non-existent, ...but that is beside the point - I am not trying to write a manual for a product I wish to sell to those countries.

I believe this is important, if you wish to make a "professional" impression.The thinking goes like this: If they can't figure out how to write a decent manual, ...how good can their PRODUCT be? The world knows that there are some excellent engineers, etc., from your countries, ...but we also know that not ALL of them are geniuses. :-)

The feedback you are getting from the forums should help you understand what buyers will need to know.

One last suggestion:

If you can engrave/print/whatever, a 4:5 aspect-ratio "Crop" frame on your screen, this will be something that a great many photographers have asked for, ...enabling them to effectively frame their images for the common-and-popular 8X10 and 16X20(inch) print sizes. When you are unsure of exactly how much to include for an 8X10 image, you have to include "extra" stuff in the frame, to be sure you have enough.

When you throw away the "extra", in printing, you are wasting some of the pixels(resolution) captured by your fancy (and expensive) camera. Boo!

("Fixing" this would only require two thin lines, equi-distant from the long-ends of the frame, placed so as to create the "5" ratio which matches the "4" of the short-side.) This also has the advantage of using the sharper center of the lens, rather than the more "edge" resolution which you get if you start the "4X5 guesstimate" at one of the ends, when framing for the shot. . There are photographers who try to put such lines on their existing screens, something which would be much more easily done by the manufacturer of the screen.

This 'frame" will be a consideration for me, when I buy a screen.

HTH,

Larry
 
Good points, of course, but if you run a company that way you need to either double the price (business would go away) or triple the sale (not so easy). There are alternatives that cost up four times as much, and I'm sure they both have a little higher quality and perhaps even a manual in english german and urdu.

The power is with the customer. For my cheap camera I chose the cheaper Haoda screen, and found it worked well. Had it not worked well, I would only have lost the equivalent of a round of beer (yes, I have many a friend)...
 
What a pain in the ass. Lighten up already Larry.

This thread is giving me a huge headache. And I don't even own a Haoda screen.
 
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