Brightscreen P235D in the
Canon 5D
Checking this diagonal center-split and microprisms
for focus function and exposure compatibility.
1. I was immediately dismayed to install the screen
to the 5D and find the focusing features off-center.
2. Measuring this in my CAD program shows that the focusing features
are shifted about 0.63mm left:
Despite spotless lenses, this picture shows heavy crud in the external
eyepiece of the camera.
3. This is what the screen looks like in use:
Focus Tests
4. I took a whole series of images to test focus,
but the only critical focusing was found wide open aperture with
the fast 85mm f/1.2L mkII lens.
Split-screen focusing was wildy out of focus until adding the Brightscreen
adjusting shim. Here is the test scene:
Manual focus was done very carefully, taking 30 seconds to one minute
to make my best effort.
Focus test series #1 (85mm f/1.2)
(4) Manual focus with center split
(5) Manual focus with "AF-confirm" (6)
AF
 
Focus test series #2, backside of can (85mm f/1.2) 100%
Crops
(7) Manual focus with center split
(8) Manual focus with "AF-confirm" (9)
AF
  
When using AF-confirm, the light blinks once the object resolves
to high contrast. This can be done approaching focus from either
the near or far side. Further investigation could show that one
is more successful than the other (hypothesis that approaching from
near side is more sensitive).
Conclusion: What we see here is that
Autofocus is the most reliable.
Exposure Tests
Exposure tests were done both indoors with fixed
room lighting for consistency, and outdoors during an overcast day.
At first review, both indoor and outdoor lighted results are identical.
No discernable change in available light was observed during the
outdoor exposure tests. For these spot metering tests, the spot
is left in the viewfinder center.
Canon OEM baseline with a slow lens: 100-400mm @
100mm f/4.5 using Ee-A screen, custom function
00:Ee-A
[ ] Center Weighted Average
[(o)] Evaluative Metering
[( )] Partial Metering
[ o ] Spot Metering
   
100-400mm @ 100mm f/4.5 using Brightscreen
P235D screen, custom function 00:Ee-A
[ ] Center Weighted Average
[(o)] Evaluative Metering
[( )] Partial Metering
[ o ] Spot Metering
   
The Canon Ee-S screen is darker at smaller apertures than the stock
Ee-S screen, so let's see if changing the camera custom function
helps:
100-400mm @ 100mm f/4.5 using Brightscreen P235D
screen, custom function 00:Ee-S
[ ] Center Weighted Average
[(o)] Evaluative Metering
[( )] Partial Metering
[ o ] Spot Metering
   
Let's try the same thing with a fast lens:
Canon OEM baseline: 85mm f/1.2 using Ee-A screen,
custom function 00:Ee-A
[ ] Center Weighted Average
[(o)] Evaluative Metering
[( )] Partial Metering
[ o ] Spot Metering
   
85mm f/1.2 using Brightscreen P235D , custom function
00:Ee-A
[ ] Center Weighted Average
[(o)] Evaluative Metering
[( )] Partial Metering
[ o ] Spot Metering
   
85mm f/16 using Brightscreen P235D
, custom function 00:Ee-A
[ ] Center Weighted Average
[(o)] Evaluative Metering
[( )] Partial Metering
[ o ] Spot Metering
  
Now changing custom function 00: 85mm f/1.2 using Brightscreen
P235D , custom function 00:Ee-S
[ ] Center Weighted Average
[(o)] Evaluative Metering
[( )] Partial Metering
[ o ] Spot Metering
   
85mm f/16 using Brightscreen P235D
, custom function 00:Ee-S
[ ] Center Weighted Average
[(o)] Evaluative Metering
[( )] Partial Metering
[ o ] Spot Metering
   
Conclusions
1. Although I really wanted a manual focusing
aid, this Brightscreen P235D is not compatible with slower lenses.
I did not test for medium speed lenses, such as f/2.8. Reports
are that the microprisms are not compatible with shift lenses.
2. Giving up all but CWA metering is not an attractive compromise.
3. Using Autofocus is more reliable when available. Using
manual focus confirm light is the next preference due to speed and
accuracy.
4. Because the split was off-center and because Brightscreen
does not provide any exposure compensation information and although
this product is rather expensive, this is incomplete.
I returned mine. I'll be happy with focus-confirm
with my MF lenses because it works reasonably well and fast.
Links
Cleaning
the 5D Viewfinder
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