Split-image vs microprism screen

[AgX]

hmm I didn't know you can't focus on clear screens. Good to know.

Strictly speaking you cannot focus on a clear screen!

As the eye has the ability to focus on the aerial image wherever it is located, and that is not necessarily in the camera plane of focus, you must have a reference.
And that can be a crosshairs mark on that clear screen.

 

[Gerald C Koch]

Gerald -- I don't think it's the focal length that is critica, but the size of the largest aperture setting. It is the case that most normal 35mm-format lens are f/2 or f/1.8, 1.7, 1.4 etc. A 35mm-format 200mm telephoto lenses are more likely to be f/3.5, f/2.8 if you're lucky. In my experience in the latter cases that part of the split image may darken; if I use my 135mm f/2.5 or 200mm f/3 lenses, no darkening.

To the general topic: I have both microprism and split-image cameras, and greatly prefer split-image. It was only recently, when I got a Konica Auto Reflex (the full-frame/half-frame camera), that I found a camera with a microprism central spot that I liked. Other factors come into play, though. About 12 years ago I attended a wedding, bringing my Contax 167MT with 28-85 Zeiss zoom, and tried to take some flash pictures of people dancing in the evening. Impossible to focus in the low light -- just couldn't tell with any accuracy where the lens was focusing (what a split-image). This drove me quickly toward much greater use of rangefinder cameras which, with my 65-year-old eyes, provided much more assurance as to final focus.

You're right. The lenses that I have had difficulty with are smaller aperture. Funny you remember the focal lengths but not the each max aperture.

I too am a member of the presbyopian congregation.

 

[RichardJack]

This is a matter of taste and application. With fast f1.2 & 1.4 lenses I prefer a split image, high f-stops don't work well with splits (or micro prisms). I like and use the clear collar area that surrounds the split or micro prism most of the time.
A more important issue here is your vision. I have been near sighted most of my life and hate using glasses with a camera. When ever I bought a new camera I bought the proper eyepiece correction lens (usually a -1 or -2 for me). That helped more than the type of screen I was using. Newer cameras have built in diopter adjustments.
Rick

 

[RichardJack]

Clear screens....
Depends. Minolta made clear screens for their XK model that you could focus with, I owned them. They were models C1, C2, & C3 for different focal lengths. I have a Nikon type H screen with a clear center, but it has cross made of two parallel lines. It's for astrophotography.
Beattie screens are the way to go if you need more light, provided you can find one made for your camera.

 

[wiltw]

Beattie screens are the way to go if you need more light, provided you can find one made for your camera.

...and assuming that your camera does not have TTL metering sensors in the pentaprism where the brighter Beattie screens throw off the metering.

 

[Slixtiesix]

It depends on the subject. For landscape and architecture, I definitely prefer split-image. For portraiture and close-up photography, I also like the plain screen. For my taste, the Rollei High-D-Screen is the best overall screen because it is a plain (and very bright) screen with a very small and non-distracting split-image at the center. The Hasselblad Acute Matte D comes second. I have the one with the microprism and split-image. The split-image is convenient but I do not like the microprism. With very fast lenses I also like the plain crosshair-screen for portraiture.

 

[Dan Daniel]

Maybe it's been mentioned and I missed it- the problem i have with split image screens is that you need to reframe all the time. The odds of the proper focus point bring in the center of the screen is pretty small.

In many cases this reframing is no big deal. But if you are at close distances without much depth of field- common for portraits- reframing can involve enough camera movement to lose the proper focus point.

 

[Leigh B]

One advantage of a split-image is that it tells you whether you're turning the lens in the right direction.

If the lines converge, you're doing it right. If they diverge, go the other way.

- Leigh

 

[wiltw]

One advantage of a split-image is that it tells you whether you're turning the lens in the right direction.

If the lines converge, you're doing it right. If they diverge, go the other way.

- Leigh

I get the same 'advantage' seen in the magnitude of the 'shimmer' seen thru microprism.

 

[thuggins]

I think that what your FIRST SLR had will have a lot to do with individual preference.

While there are certainly different strokes for different folks and some folks may have a preference for priority, this is not the case with me and I doubt that most would prefer a system they struggled with just because it was the first one they used. My first SLR, which I used for many years, was a Pen FT which has a relatively large microprism spot. The matte area is much easier to focus on, and if anything the microprism just serves a confirmation of what the matte area has already shown you. I just ran a couple of hundred frames thru the FT over Xmas and still found myself focusing the same way. And although the FT will always be my first love and I always thrill to see that string of 75 or so beautiful jewels on a strip of slide film, I constantly thought how clunky and awkward she seemed compared to her far more sophisticated big brothers.

One issue that has not been addressed explicitely so far is speed.

It may be that one focusing means yields most precision, but takes a long time to probe, whereas another means may yield a good result in in a second or so.
Just a thought.

This is an excellent point. Many have pointed out (here and elsewhere) that with the split prism you can snap the focus in quickly as long as you have a sharp edge to work with. With both matte and microprism you have to "hunt", going back and forth thru the focus until you settle on the "not out of focus" position.

You can't focus on a clear screen. But if you take the clear screen and add a
+ or other reference to the center. You can focus on the aerial image. Don't they do that
in astronomy?

Without getting into subtleties of semantics you can focus on a clear screen, you just can't get a Depth of Field indication. Olympus made clear focus screens for astrophotography and I can attest first hand that these are absolutely crucial for such work. You cannot focus a celestial object with a matte screen because the "grain" associated with the matte competes with the true focus of the image. Put another way, astrophotography requires getting a razor sharp image in focus and a matte screen is by nature always a bit soft.

 

[Maris]

In theory a split image prism focussing screen should deliver greater accuracy than a plain ground glass. Split image focussing depends on the superior vernier sensitivity of the eye, when things line up or they don't, rather than the vague "best contrast" criterion of a plain ground glass. A split image prism is in effect a rangefinder with the baseline of that rangefinder defined by the width of the aperture of the image forming lens. That's why at small apertures, effectively short rangefinder baselines, the split image system doesn't work so well.

Split image "blackout" at small apertures depends on the steepness of the opposing prisms. The steeper the prisms the greater the focus sensitivity and the necessity for a fast lens if blackout is to be avoided. Split image prisms can be made with shallow wedges to avoid black-out even at small apertures but then focus sensitivity is much reduced. Camera makers have to decide what compromise they will adopt.

A microprism spot is an array of multiple tiny split image prisms. The focussing information it presents is a mix of "vernier" and "best contrast" criteria; a popular compromise.

 

[AgX]

Sometimes screens are designed for a certain range of lenses.
In the best case all, the lens, the split-screen and the micro-prisms are designed for that very range.

 

[wiltw]

Without getting into subtleties of semantics you can focus on a clear screen, you just can't get a Depth of Field indication. Olympus made clear focus screens for astrophotography and I can attest first hand that these are absolutely crucial for such work. You cannot focus a celestial object with a matte screen because the "grain" associated with the matte competes with the true focus of the image. Put another way, astrophotography requires getting a razor sharp image in focus and a matte screen is by nature always a bit soft.

I am somewhat befuddled about the clear screens for astrophotography...with the subject matter out at Infinity distance (even the moon, as close as it is), why is there a need to 'focus' per se?!

JK, I know there is a need to focus the eyepiece when you are looking thru a terrestrial telescope at a passing ship, but one would think that a celestial scope could avoid that task.

 

[Sirius Glass]

I find that microprisms are faster to focus than split image, but I still prefer ground glass for the Hasselblad.

 

[RichardJack]

I am somewhat befuddled about the clear screens for astrophotography...with the subject matter out at Infinity distance (even the moon, as close as it is), why is there a need to 'focus' per se?!

Simple answer: Astronomical telescopes do not have infinity stops. Also different wavelengths focus at different image planes, with film we had to calculate, digital makes life easier being able to use trail and error or focusing in live view. A clear screen just made it easier being able to see what you were aiming at (I still managed to screw up the focus 50% of the time with film).
http://www.pbase.com/rick_jack/astrophotography