Lock exposure, focus and refocus

[sean_reid]

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Locking exposure and setting focus don't need to be done at the same time with the M8. So, here's what I would suggest.

 

1. Place the object, within the subject, that you want to be in sharpest focus so that it is overlapped by by the RF patch. Set focus.

 

2. Reframe to include the part of the subject that you want to use for metering, half press the shutter to lock AE.

 

3. Return to your original framing and make your picture.

 

This whole idea that focus and exposure lock need to be set at the same time is just a convention from automatic cameras.

 

Cheers,

 

Sean

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[Perspectics]

Locking exposure and setting focus don't need to be done at the same time with the M8. So, here's what I would suggest.

 

1. Place the object, within the subject, that you want to be in sharpest focus so that it is overlapped by by the RF patch. Set focus.

 

2. Reframe to include the part of the subject that you want to use for metering, half press the shutter to lock AE.

 

3. Return to your original framing and make your picture.

 

This whole idea that focus and exposure lock need to be set at the same time is just a convention from automatic cameras.

 

Cheers,

 

Sean

 

Thanks Sean - this means that the former hints from several forum members to "move sidewards" or move "on a parrallel line" when refocussing is simply wrong. I am greatly relieved. Thanks again.

[j. borger]

Thanks Sean - this means that the former hints from several forum members to "move sidewards" or move "on a parrallel line" when refocussing is simply wrong. I am greatly relieved. Thanks again.

No they were not wrong ....... look at the drawing provided !!!

It all depend on the actual scene and f-stop used how critical this is however!

[hankg]

Anyone who has used a view camera will be familiar with the plane of focus and shifts in the plane of focus. Look at this illustration when you rotate the camera the plane of focus rotates with it. The green arrow indicates where you are focused after turning the camera to the right -it's behind the point you intended to focus on.

 

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[Perspectics]

Isn't the "plane of focus" rather a "radius of focus"? Or are you trying to include the distance between RF and lenses ewhen rotating the camera?

[hankg]

Ed, I am with you.

 

Simple question to Hank: Which of the lines is the focus line for a shot like this?

 

IMHO line A is the line along which you will find all object in focus.

 

If its line B then... hm, I'll go home and sleep it over until I understand... please educate me, I'm about to become confused.

 

You put in the plane of focus but left out the film plane.

 

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[jaapv]

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Anyone who has used a view camera will be familiar with the plane of focus and shifts in the plane of focus. Look at this illustration when you rotate the camera the plane of focus rotates with it. The green arrow indicates where you are focused after turning the camera to the right -it's behind the point you intended to focus on.

 

[ATTACH]55577[/ATTACH]

 

Both views on this subject are correct. If one shifts the position of the subject parallel between the plane of focus and the film/sensor the distance stays indeed the same(the green arrow)However, if one keeps the subject in the centre of the rangefinder, where the patch is, the movement becomes radial and the distance changes.(the red arrow falls short)

[sean_reid]

Thanks Sean - this means that the former hints from several forum members to "move sidewards" or move "on a parrallel line" when refocussing is simply wrong. I am greatly relieved. Thanks again.

 

They aren't wrong, per se, it just needn't be so complicated. Focus where you need to, reframe temporarily for metering and then return to your original framing. The object in sharpest focus needn't stay exactly in the middle of the frame but moving it to one side or another (within the frame) isn't usually to going to make a lot of difference to your focus. Of course if you're working close up at F/1.4, you'll need to be more careful.

 

Sometime we over-think things.

 

Cheers,

 

Sean

[ChrisC]

Hmmmm - Two schools of thought here. Those who think that the field of focus is described as an arc, and those who understand it to be a plane which renders the focused object out of optimum focus when the camera is rotated to recompose the image. Hmmmmm.

 

With respect to the other part of the original question, i.e. exposure locking; I tried for some time to get comfortable with AE on the M8, and have totally abandoned it in favour of manual metering.

 

For how I shoot, M8 AE is too much like hard work, and unreliable unless using the meter/hold exposure/recompose method; which I have always disliked. I now manually meter with consideration for the M8's heavily centre-weighted tendency. If I expect a bright element to end up anywhere in my image [maybe in the corner], with a pre-selected aperture I make sure that the bright subject is fairly central when metering for my shutter speed, and then my settings are good to go. It's old school, but a hell of a sight easier for me than using AE.

 

................ Chris

[Shootist]

Well from any given point to another point at the same distance is a arc (radius). Otherwise it is a triangle and as we all know the hypotenuse of a right triangle is longer.

[hankg]

They aren't wrong, per se, it just needn't be so complicated. Focus where you need to, reframe temporarily for metering and then return to your original framing. The object in sharpest focus needn't stay exactly in the middle of the frame but moving it to one side or another (within the frame) isn't usually to going to make a lot of difference to your focus. Of course if you're working close up at F/1.4, you'll need to be more careful.

 

Sometime we over-think things.

 

 

If you are shooting close in and wide open and focus on an object which you want to keep in sharp focus but reframe it so it is at the edge of your frame you would be advised to get in the habit of shifting sideways rather then turning to reframe. It is a slight movement either way and easily learned. All those additional thousands of dollars to get that last additional tenth of performance in a lens is quickly lost with a slight misfocus.

[larry]

Well, so much for the "decisive moment." :-)

 

Larry

[stunsworth]

The field of focus is meant to be a plane as far as I'm aware.

 

The problems described by the focus recompose tecnique are largely theoretical in my experience - i.e. it isn't something I worry about.

[hankg]

You can see this in practice for yourself. Mount the M8 with a 70 or 50 set at f1.4 on a macro focusing rail so it moves left to right. Mark 2 targets on a sheet of paper -one on center and one at the edge. Focus on center target at closest focusing distance -take photograph 1. Move the camera on the rail paralell to the paper and place the center mark at edge of frame and edge mark in center. -take photograph 2. Return the camera to center position and instead of moving camera sideways turn camera to reframe. -take photograph 3.

 

The DOF will be shallow enough to see the difference in methods. You will note that the edge and center marks on photograph 1 are in dead focus because they are on the same plane (unless your lens has severe spherical aberration).

 

You could also set a set of objects in a semi-circle and you will note that the objects at the edge closer to the plane of focus are out of focus even though they are the same distance from the center of the lens as the object in the center.

 

So if you need practical proof it is easy enough to get running these little tests.

[hankg]

Well, so much for the "decisive moment." :-)

 

Larry

 

If you get in the habit of working a certain way. It's not sometyhing you think about while shooting -like learning to focus with a rangefinder. If you are worrying about resolution and planes of focus while shooting sell your M8 and get yourself an 8x10 view camera.

[Jamie Roberts]

Hank--

 

I agree with you, but I'd like to know something I'm fuzzy on myself. Don't your calculations assume a flat focal field?

 

One thing I've read completely diverging opinions on is how many modern lenses really have a flat focal field. Some people say most modern lenses are designed this way but others say it's actually quite rare due to focal shifts and field distortions.

 

And I also agree with Sean; under wide angle distance shooting conditions at f3.2 or 4 you're not likely to see a difference at regular-ish print sizes, wouldn't you agree?

[sean_reid]

All those additional thousands of dollars to get that last additional tenth of performance in a lens is quickly lost with a slight misfocus.

 

Hi Hank,

 

That tenth is lost almost all the time unless one is using a tripod (which I don't normally do with the M8). One can see a difference in resolution with a lens rotation so slight that it doesn't move the focusing patch. Misfocus (to slight degrees) is the rule, rather than the exception, for most pictures and, most often, it just doesn't matter. Now, close up and wide open is, as I said above, a different story.

 

Very often, chasing resolution, per se, is a red herring. It usually won't make or break a picture.

 

Cheers,

 

Sean

[hankg]

Hank--

 

I agree with you, but I'd like to know something I'm fuzzy on myself. Don't your calculations assume a flat focal field?

 

One thing I've read completely diverging opinions on is how many modern lenses really have a flat focal field. Some people say most modern lenses are designed this way but others say it's actually quite rare due to focal shifts and field distortions.

 

And I also agree with Sean; under wide angle distance shooting conditions at f3.2 or 4 you're not likely to see a difference at regular-ish print sizes, wouldn't you agree?

 

In a perfect world your focus field is flat and your sensor plane is flat in the real world not so much:) Enlarging and process lenses have very flat focus fields but it's not as high a priority for lenses intended for shooting 3D objects. Film is not at all flat but digital sensors are very flat.

 

It is a common modern convention with wide angles to have a subject at the edge of the frame and a prominent background for context -if you are stopped down it doesn't matter much how you reframe but if you are shooting wide open as some like to do with the fast Leica lenses for selective focus it can be an issue. It's not any harder to reframe one way or another so I use the sideways movement as a habit.

 

Again anyone who wants a real world proof set up the shot shown below. Point the camera at object 'A' -focus and shoot. Which object at the edge of the frame will be in focus? -the red object or the green object? See for yourself if don't believe me.

 

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[hankg]

Hi Hank,

 

That tenth is lost almost all the time unless one is using a tripod (which I don't normally do with the M8). One can see a difference in resolution with a lens rotation so slight that it doesn't move the focusing patch. Misfocus (to slight degrees) is the rule, rather than the exception, for most pictures and, most often, it just doesn't matter. Now, close up and wide open is, as I said above, a different story.

 

Very often, chasing resolution, per se, is a red herring. It usually won't make or break a picture.

 

Cheers,

 

Sean

 

I agree completely still we do our best to get the thing we want in focus in focus. So if all other things are equal and when possible I'll keep shutter speed at 500 or above, shift sideways, keep my lens and finder calibrated. But when shooting it's not something I think about.

[hankg]

One last example to try and make this clear. If you shoot a brick wall straight on wide open -are the bricks at the edges of your photograph in focus?

 

If your lens focused on a radius instead of a plane only the center of your image would be in focus and as you moved away from the center in all directions you would get progressively more out of focus. But that doesn't happen. With some lenses you do lose some resolution at the edges because the lens is not focusing perfectly flat but that is considered a lens fault and it is kept to a minimum with most modern lenses.