How do you focus with an old SLR?

[hoakin1981]

http://www.pentaxforums.com/forums/...screens-se-amp-sg-pentax_mx_focus_screens.jpg


I have a Pentax MX. I am no expert but I have read that this little baby has one of the biggest viewfinders there is and it certainly looks that way. In any case, I am a sucker for razor sharp images regardless of whether I always nail such lever of accuracy.

So, since I have decided to venture in MF/analog photography from now on and my MX will be my main workhorse I would appreciate some info. on how to effectively focus, fast and accurate.

I have the top left focusing screen on the above image. So far I focus using the center area but what happens if my subject is elsewhere on the frame? Focusing on it and moving the camera to recompose is risky since the slightest change in distance will mess up the focus. I have tried focusing by looking at the subject directly but I cant be sure if this method achieves good results.

Any tips???

Many thanks in advance.

 

[dmb]

Focusing on it and moving the camera to recompose is

the answer.

 

[Ian Grant]

Focus on the part of the image that you feel is most important to be sharp and in focus, that may not always be the centre.

Ian

 

[Nuff]

I use MX as well, initially I will compose using split prism. Easy and fast. Recompose and adjust focus to make sure the subject pops into focus, the MX focusing is pretty good at it and you should be able to see clearly what is and isn't in focus.

 

[AgX]

So far I focus using the center area but what happens if my subject is elsewhere on the frame? Focusing on it and moving the camera to recompose is risky since the slightest change in distance will mess up the focus.

To be true I never thought of this...


However the longer the focal length, the more shallow the depth-of-focus, but also the smaller the angle of view and thus the angle you can swing the camera for composing.
The shorter the focal length the more swing it allows but the larger the DOF will be too.


Why not not make a test target to focus on:

1. focus on it by means of the focusing aid in the center and expose

2. focus on it by means of the focusing aid in the center, swing the camera and expose

3. focus on it at the edge by means of the plain ground glass and expose


Check at prints which method yields they sharpest target. At least with the latter method do several attempts.

 

[Xmas]

Don't worry unless you have a /0.95 lens and are wide open and close in
Your head will pivot on the neck bones and keep the sharpest plane distance sensibly constant.
If you are using slow film and can hold the camera steady then you will see the lens performance 'slide' off axis at wide apertures.
Use /5.6 - /11 for critical work and heavy tripod.
lock the mirror up if you have the option.

 

[AgX]

Your head will pivot on the neck bones and keep the sharpest plane distance sensibly constant.

You did not understand the issue.


The plane of focus is rectangular to the optical axis. Like a tangent to a circle with the radius of focal distance.
Even if you swing the camera not on your cervical vertebra but on a swing head with the axis going through the film plane, the plane of focus will swing off from any object when re-composing.

 

[David Brown]

OMG. Many of us used manual focus cameras for decades before auto focus came along and many of us still do. It ain't rocket science. Just use the camera for a while and you will figure it out.

 

[Xmas]

ok bad English on my part for sensibly read 'sufficiently approximate'

Yes I understand the rest of the geometry but there is an 'old SLR' in the title and the lens on my Varex IIa is not wonderful off axis eg for flatness of field and the film may not be flat either.

I know Leica have floating elements in their wides and normals and have altered all their tolerances and that can be a problem even with film but don't think that applies here.

 

[gone]

"So far I focus using the center area but what happens if my subject is elsewhere on the frame? Focusing on it and moving the camera to recompose is risky since the slightest change in distance will mess up the focus".

No, there will be no change in focus unless you're shooting very closeup w/ a very fast lens. Otherwise that's exactly how it works. You're WAY over thinking this. The center area is where you attain sharp focus w/ that screen. Find the area you wish to focus on, attain focus, then recompose.

 

[AgX]

OMG. Many of us used manual focus cameras for decades before auto focus came along and many of us still do. It ain't rocket science. Just use the camera for a while and you will figure it out.

But I find it an interesting question nevertheless.

 

[nsurit]

You don't say what your usual subject matter is however the depth of field scales on many old lenses provide an effective way to focus. When I had not celebrate so many birthdays the mat screeen was my favored focusing screen. These days the split image screen has replaced it. As others have said, give the camera a good workout and figure out what works for you. Whatever it is you will probably like it at least as well as you like Mr. Automatic focus. Bill Barber

 

[elekm]

In theory, you should focus and then slide your camera left, right, up or down to recompose.

If you are shooting at a smaller aperture, the depth of field should compensate for focusing errors if you merely want to pivot the camera left or right.

If you are shooting wide open at a close distance, I would slide the camera laterally or vertically. Also, use the camera's viewing screen to ensure that things are still in focus.

And as others have said, use your camera a lot and get a feel for how it operates.

I think the Olympus OM (single digits) have brighter focusing screens, followed by the Pentax.

The Yashica/Kyocera Contax has one of the brightest screens, I think.

 

[removed account4]

i don't focus at all, its easier that way

 

[nsurit]

I think the Olympus OM (single digits) have brighter focusing screens, followed by the Pentax.


Yes and I didn't mention that the OM cameras are what I use. The 2 series screen for the OM cameras are really nice and bright. Beattie also made screens for many different cameras that are probably worth more than the cameras for which they were made in many cases. Bill Barber

 

[omaha]

OMG. Many of us used manual focus cameras for decades before auto focus came along and many of us still do. It ain't rocket science. Just use the camera for a while and you will figure it out.

My thought exactly.

35 years ago, I shot football games at night in crap light with a Pentax body and a Vivitar zoom lens. Everything 100% manual. Managed to get a few "keepers" along the way (or at least the paper's photo editor thought so...)

AF is a wonderful thing, but you'd be amazed how well you can do without it with a bit of practice.

FWIW, re-learning how to really look for focus was probably my biggest initial hurdle when returning to film, so I get where the OP is coming from.

 

[analoguey]

Hmm, so if I want to take a portrait with the subject not dead center, shouldnt it just work with regular focusing but checking for focus based on the subject's location, in camera/vf, than focusing for the center and then moving camera to recompose? :-/
I have usually done that.

Sent from Tap-a-talk

 

[winger]

The only time I use focus / recompose is when I'm using autofocus or a camera with the focus indicator. With my older cameras, I put the subject where I want it and focus - with a matte screen, it doesn't need to be in the middle to see if it's right. And, yes, there's a little overthinking about the focus being off by moving that much. Experience is a great teacher in this respect.
And the late Herbert Keppler used to love the Pentax viewfinders, IIRC.

 

[AgX]

Hmm, so if I want to take a portrait with the subject not dead center, shouldnt it just work with regular focusing but checking for focus based on the subject's location, in camera/vf, than focusing for the center and then moving camera to recompose? :-/

But a focusing on groundglass is less simple/precise than using a splitscreen focusing aid. So one has to weigh this disadvantage against the focus shift when swinging the camera for recomposing.
As indicated by others this all is very academic.

 

[Chan Tran]

I simply focus on the ground glass. I don't use the split image. In fact on cameras that I can change focusing screen I install one without the split image. That's way it's the fastest. No focus and recompose but rather compose and focus at the same time.

 

[randyB]

OMG. Many of us used manual focus cameras for decades before auto focus came along and many of us still do. It ain't rocket science. Just use the camera for a while and you will figure it out.

Ditto what David says.

Just use the camera, experiment, play, have fun with it. You will learn from any mistakes made.

 

[pbromaghin]

What's auto focus?

 

[Lee Rust]

In my experience, even the most elaborate digitally controlled autofocus systems make a focussing error just about as often as I would with manual focus. Additionally, with an autofocus camera, quite often I must take extra steps to let the camera know where my subject is, sometimes to the point of actually having to 'trick' the camera into focussing where I would like. With manual focus no tricks are needed.

For a century and a half, photographers focussed with rangefinders, ground glass, zones or depth of field scales. The mechanisms and procedures were simple and, more often than not, the focus was fine. Then along came autofocus. Now, more often than not, the focus is fine.

I'm amazed how elaborate the modern multipoint autofocus systems have become, even to the point of facial or eyeball recognition, but what have we really gained? What have we lost, besides lenses with focus rings?

Granted, I am not an professional action photographer shooting 8 frames per second through a telephoto lens at a football game, just an amateur taking photos of the neighborhood. I've always thought focussing a camera was kind of fun.

 

[Pioneer]

My two favorite viewfinders belong to the Pentax SV and LX. After that comes the SRT101. I use the microprism focus screen on all of them. Of course the SV and the SRT101 both came with the microprism and I installed the SA23 screen in my LX.

On a tripod, with the mirror locked up, the LX and SRT101 are stunningly accurate even when I focus close up with fast 50s. And the focus is very fast with the microprism screen, even using glasses. In fact, I was very disappointed with the autofocus performance on my K200D (my very first digital) and I returned it because my images did not even come close to what I was getting from those two cameras. I later learned that this could be adjusted but at the time I didn't realize it. I am not certain why but I do find that film cameras seem to be a little more forgiving of small focus errors than digital cameras.

As for focusing off center and then recomposing, I have never noticed a problem with this unless I am very close and wide open with very fast glass. Even then I can usually focus with the edges of my microprism center so the shift is not very big. If I do think that there may be a slight problem I shoot several frames, some at the same aperture and some at narrower apertures. By doing this I have never been in a situation where I didn't have a sharp picture to work with. There are times when bracketing is your friend and it isn't always just for exposure factors.

 

[MattKing]

As for focusing off center and then recomposing, I have never noticed a problem with this unless I am very close and wide open with very fast glass. Even then I can usually focus with the edges of my microprism center so the shift is not very big. If I do think that there may be a slight problem I shoot several frames, some at the same aperture and some at narrower apertures. By doing this I have never been in a situation where I didn't have a sharp picture to work with. There are times when bracketing is your friend and it isn't always just for exposure factors.

+1

What concerns me most, though is that the OP refers to a Pentax MX as an "old SLR".