Hello all!
For those not willing to go on the other pentax forum, I'll repeat here a post I've made there...
I recently acquired a chinese 45° split-screen for my manual lenses (bought at JinFinance on ebay)...
First thing : focus is accurate... They changed their design, and the screen no longer needs shims to be at the proper place. A slight raise can be felt around the screen, so I guess it's been altered to include this ridge. Anyway, installation is really easy.
Now, about the use:
- Split prisms seem simply huge in the viewfinder! It's a real treat to focus, easier than on FF split-screens...
- Brightness has not really changed...
- Only thing that bother me : the AF red square is really distracting... I tried to disable it, but then it won't even show which focus point you select on a FA lens... Bad thinking, Pentax!
Now, having met the standard exposure problems with the original screen, I then tried to chart exposure with this split screen.
Experiment : display a Gretag chart on my laptop, in a dark room, frame to include (and crop if needed) only the screen, use the viewfinder cover, and shoot away at all apertures...
Hardware :
- k10 with split-screen
- Lenses:
- FA 50 f/1.4 in non-A position
- Porst 55 f/1.2 (PK, M + GreenButton)
- Apollo 135mm f/1.8 (m42, Av mode & M+GB)
- SMC Tak 200mm f/4 (m42, Av mode & M+GB)
This is a reference of what the K10 considered as a "correct" exposure with the FA lens, meaning that it's what you'll always have by controling the aperture on the body... (for information, it's underexposed to my taste, and can cope with +1ev without clipping, as with the original screen).
The chart below show the exposure of each lens compared to the reference exposure (0EV).
As you can see, all the lenses follow the same behavior:
- approximatively "correct" exposures between f/1.4 & f/2.5 and at f/22
- general (and massive!) overexposure between f/2.5 and f/22
Once compensated for proper exposure (+1ev), you end up with:
- approximatively "correct" exposures at f/1, f/4 and f/16
- general underexposure between f/1 and f/4
- general (including a massive +1 1/2Ev!) overexposure between f/4 and f/16
- general underexposure above f/22
These measures follow quite exactly what I found at the time with the original Lx-80 family screen, but with a slight +1/3ev exposure compared to it.
And this is what I experienced on the field, with both the original screen AND this split screen.
My brother (having a K10, the original screen, a new LL-60 screen, the FA 50 f/1.4 and a nice collection of manual lenses) repeated these tests with the original screen and the LL-60.
Our conclusions:
- original screen (and by extension all Lx-80 screens) and the split screen behave exactly the same way, with a slight, constant overexposure (around +1/3ev) for the split screen.
- Split screen had no impact (apart for the +1/3Ev overexposure) on slower lenses...
- LL60 really handles exposure in a better way (I'll post results later today) :
+ quite constant exposure between f/3.5 and f/11 (around +1/3ev from 3.5 to 11)
+ slight underexposure above f/3.5 and below f/11
I guess Pentax will soon run out of LL60s!!!
If only they made a Lx-60 split screen!!!