old lens on new camera ?

Funny.
I just tried, and had no problem using trap focus with an Olympus Zuiko on a K-5

I have three focus screens.
One split prism, one microprism and the original plain one that came with the camera.
For low light the split prism is virtually useless, the microprism is a bit better, but I get the best results by using the plain one.
For daylight stuff where you have any straight lines the split screen is great. You can focus quicker with a manual lens using it, than you can with af on a lens with a little bit of throw length
For portraits I find the microprism to be the one to go to. Using the split prism puts more strain on my eyes then needed for that stuff.


@Algernon
How can you possibly get misfocus with LV and zooming?
Isn't LV just an EVF in the sense of WYSIWYG?

Like all things LV has a DOF and the aperture changes depending
on the light level. Most of the time I have about +/- 20mm or
40mm total DOF and by definition (of DOF) it will look in
focus anywhere within that DOF. It was the same using enlargers
until someone invented grain magnifiers.

The Green Hexagon/Beep also has a DOF and will be in focus at
a different point if you turn the lens from INF or from MIN
FOCUS. Then you have the problem of no micro adjustment to the
focus on the lens.

Last time I looked at split image finders I looked at the
corner of a box and it showed 3 corners (couldn't see the
4th) in focus even though there was about 75mm difference....
so they are quite crude and are also independent of the
camera electronics, so lenses may need to be mechanically
tweaked.

It seems to me there's a problem with the language Algi. The things you describe don't have a depth of field. Lenses have a depth of field.

If you are saying that there's some leeway and error in the point that focusing devices select, then in the case of these being measured by either the human eye or an electronic system I'm sure you'd be right.

The electronic system is probably more accurate because it doesn't compensate and doesn't get tired.

Anything optical has a DOF even your eyes Look at an
object on the horizon with one eye and then hold a finger an
inch in front of your eye and it won't be in focus. Your eyes
have a greater DOF during the day than at night.

It really is very basic optics.... any lens can only focus
on one point/distance.... all other points are OOF.

Your camera particularly film cameras had a lever called
a DOF lever..... What do you think that did?
What can you see when you press it down?

Why doesn't AF work properly with lenses of
f/8 f/11 aperture?

It's very easy to check any of these focusing
methods. Just focus on something a meter away
and then move the camera (or object) 20mm at
a time and see if it still looks in focus.

Last time I tried on a small rack LV looked in
focus over a range of about 150mm.... Ouch!


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The lens of the eye causes the DOF. Putting your finger up causes a reduced aperture to give an increased DOF. Bright light also closes down the eye, just like a camera lens. The retina does not have a DOF, it's the lens.

AF doesn't work properly with small apertures because there's not enough light to make it reliable, just like our eyes.

OK you say you focus by looking at the screen. I presume that
if you were using a preset 85mm f/1.4 lens you would open it
up to wide open to focus, but would be quite happy to frame
the picture at say f/8..... Why don't you also focus at f/8
Could it be that the DOF is too great at f/8 to focus properly?

People even change their screens for the Canon Ee-s screen
because you can't see the DOF with the standard Pentax
screen with a f/1.2 - f/1.4 lens.... This is similar to
the problem with LV... It all looks in focus.

Canon_Screens
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The flat area of the graph at the bottom of this page shows quite
clearly that there are several positions of the camera where
electronically the camera looks in focus due to DOF. It
covers about 4 rail positions.

The article also explains why non of the methods are reliable.

http://www.slrgear.com/articles/focus/focus.htm

I did ask blob if he could come back in 20 years....

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Partly that reduced DOF at wider apertures makes the image snap in and out better and partly because a very dark image, such as when stopped down, is too dark for the eye to judge anything.

You've moved the argument back to the lens with this, whereas you started suggesting it was something else, or so it seemed.

I think most things have been covered above, however, here's one more vote for 'old lenses are great'

SnoozeMoose - I was talking about using an olympus DSLR body - I was hoping, and sounds like it is the case, that this issue will go away with the Pentax Body.

On the Focus/DoF issue, I think that you need to go back to the circle (sphere) of confusion (or do we have enough confusion?) and accept that there isn't an absolute point of focus in the real world.
I also think that the cameras mechanism for detecting focus - looking for sharp contrasts - is always going to be better at large apertures. At small apertures you have two issues, the amount of light reaching the sensor is reduced and the depth of acceptable focus is so great that the camer cannot detect the centre of the focal zone.

Well put blob

I'll be continuing my personal tests with the Green Hex/Beep so far
all I've established is that the trap-focus is useless at f/2.8.
Unless you somehow take an average of two positions.. one
moving forward the other moving backward. But at least I know
how to accurately set up the micro-focus adjustment for the
lenses and determine if a lenses wide open performance is
good enough for the electronic focus detection circuitry.

I suppose I could easily establish what aperture I would have
to stop down to for trap-focus to fall within the DOF at various
distances, but that won't be ideal.

I won't post any further findings or test shots here....
seems that to the average Pentax user the main criteria
is buying lenses not actually using them properly
What's wrong with a watch that doesn't work it's dead
right twice day!

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@Algi
I also enjoy getting to know my lenses rather intimately.

To really test the focus with the k-5 and all my lenses, is something I have not managed yet. Probably because of lack of knowledge on how to do it correctly.
My goal is to learn how to focus all my lenses in every situation, and find a better and quicker way to manually focus at f1.4.

I like your analogy about watches though, but in another direction.
Most people that buy high end watches, doesn't know jack shit about them, other than it might be a luxury brand.
I am not so sure if they really want to know that their £10.000 watch actually use a quartz movement worth £5.

How would putting a finger up in the near feild cause a reduce eye aperture? I would have thought the brain would only close the aperture down with brighter light, while it would refocus the eye's lens when changing object distance.

[quote]

It reduces aperture like a Waterhouse stop would, in the case of the finger by obscuring half of the field of the lens. As I'm short sighted I can actually do this and see the effect. Look at a distant landscape and place the finger near the eye and along the edge distant objects will become less blurred.

I can confirm John's statement.

I used to wear glasses for reading and these were often perched on the end of my nose. Teletext on TV was difficult to read but by lifting my head so the frame of the specs was just in sight the letters on the screen above it would become clear.