Focusing Screens

There's been some mention of focusing screens for thye 50mm f1.2 lens, but rather than divert other threads I've opened this one instead.

It has been suggested that it's difficult to focus the 50mm f1.2 lens accurately, but unfortunately (or fortunately) I can't judge this as I don't have any difficulty focusing any lens. What I can say is the manual focusing is inherently inaccurate. Experiments have revealed (see Photo Technique in the 1970s)that generally people will focus any lens at quite different positions every time. Probably the way the eye adapts very quickly accounts for part of this, and for some a lack of acuity.

There are, however, and have been, various manual focus screens and although they may or may not be usable with DSLRs with adaption, there are some that may be helpful.

SC-26 is extra bright for use with telephoto lenses. SA-23/SA-26?SA-3 feature sharper microprism angles for easier focusing of lenses from f2.8 to f1.2. There are also lots of other options for those specialising in macro, super-telephoto, astronomy, architecture and so on.

The only suitable screen I know of is made by Canon
It's FF and has to be cut down for Pentax. There is an online
retailer who sells them cut down.

This is just the details of the screen:

http://www.digitalrev.com/product/canon-ee-s-focusing-screen/MzI1NQ_A_A

Some reviews: link

31 pages on the US Forum: link

Really? You also claim you've never had to adjust the AF fine tune parameter for any of your lenses on any of your Pentax Cameras.

I've had to adjust the AF fine tuning for most of my lenses on every modern Pentax Cam I've owned K10D,K20D and three K-5s

Onto the 50mm/1.2, I'm the one who mentioned the problem with trying to focus at g/1.2 becuase of the extremely narrow DOF. It's not a suggestion, it's claim based upon factual experience.

You don't own a 50/1.2 so how can you claim to not have difficulty focussing any lens? Have you owned a 50/1.2 in the past? if so did you have a view finder that was able to resolve the narrow DOFs you get at f/1.2


Anyway the (partial)solutions to focussing at such narrow DOFs are either Live View ( magnified where necessary ) or get the Canon EE-S focussing screen which needs to be cut down to fit Pentax DSLRS

Yup that's the one I was thinking of. Well done Algernon!

No need to get excited about it, we are just trying to be helpful.

The information about Pentax screens is accurate, and if we think for a moment it would be bizarre indeed if Pentax (or anyone else) made a lens but not a screen to assist in its use.

However, the screens are from the manual focus era, plus some are from the Z series, and may need adaptation.

In the wider sense, this is not too unusual. For example, Zeiss made a special pink-hued screen for thei 18mm lens for use in the Contarex.

These things are not essential, but they do help.

As rgeards the question of lens adjustments, the instructions do stress only do this if absolutely necessary and with my Pentax lenses and bodies I have not so far found it to be. My images are as crisp as anyone else's.

I suppose adjustment is more likely in other makes of lens used on a Pentax body, but even so I would hope that most of them were correctly set up. What concerns me is setting newbies off on a path that isn't needed and could get them into all sorts of trouble. Other marques often don't even offer the option, although incresingly on the higher priced bodies they do.

Actually Smeggy I've never had to adjust the AF for any of my lenses either, my 16-50 back focuses slightly on my K10D but not to the extent that it's ever been a problem.

As soon as I get the chance I'll see how the Pentax f/1.2
focuses using Live View at 25X focal length.

Are you more than one person? And I'm not excited about it all

Why would anyone adjust AF fine adjustment if it wasn't necessary?



In my experience there's no less of a chance of pentax lenses needed AF adjustment.

How do you know it isn't needed? I would advise anyone to check the accuracy of the AF indicator on their cam and lenses, if they haven't done so already. Then any lenses that need tweaking then it can be done.

"All sorts of trouble" That's just plain absurd. There' no trouble to get into. It's just another parameter in the menu which is easily changed to the correct value of the wrong value is entered. Sometimes the correct value is zero sometimes it isn't.

But at least you've checked your lenses and found that they didn't need adjustment

Just had a quick look.

LV seems to show DOF for all apertures from f/1.2

The small 3" LCD isn't good enough for focusing even at 10X
plus a 5X magnifier When I'm in focus at 1.25M at f/1.2
according to LV I can move forward about 60mm and backwards
about 30mm before I see the LV image going OOF. The DOF is
only mm's at f/1.2 so LV isn't accurate enough for focusing.

Focusing through the optical VF is quite difficult, partly
because it's focusing at around f/2.6

LV is accurate enough when magnified though. The problem for hand held shots is that returning to 1x mag to compose the shot means you can easily move the camera the few millimetres to throw it OOF.

Much hassle really.

My 50/1.2 is way outside the +/-10 AF confirmation fine tuning window too.

A tripod is probably our best accessory if fine focusing is tricky.

Of course, sometimes the subject wavers about as well, so then it only helps to a limited degree. An example of this would be flowers waving in the breeze.

If I were to be shooting at open aperture then certainly sveral shots would be helpful is ensuring that at least one was spot on.

We rarely see shots at f1.2, so it would be interesting to see some where the extra wide aperture enhanced the image. The SMC Pentax 50mm f1.2 is especialy good for night shots, rendering point light sources as proper points and not smears.

I'm beginning to find your agressive and constantly whingeing tone tiresome but, hey, that's just my honest opinion.

I resized the Canon Ees screen and wacked on a Tenpa magnifier.
My K50/1.2 is now easy to focus accurately wide open.
Pete

Pete, did you need to use shims with the Ees focusing screen?
Thanks