A Question About Manual Focusing

JamieB · Jun 2, 2017

Hi everyone

A quick question about manually focusing my SLR cameras. This might sound odd but MF is new to me, generally speaking, and I just want to clarify something. When looking through the viewfinder of my camera, there are a couple of circles and then a central square, to aid focusing. If I put the square over the subject I want in focus then I can better see that I am focusing. Naturally. But what if the subject is not in the centre of the frame? Well, once I have focused I could recompose the shot but I am guessing I will not get the same results especially at wider apertures because the shift in position might or will change the focus plain (?) So, can I ignore the little square in the centre and concentrate my eye on whatever part of the scene I want in focus, and focus that way? I know this is an analogue forum but the same applies to DSLRs, I assume. There is one or more focus points. Can I ignore them and just concentrate my eye anywhere I want on the screen and focus until where I am looking at is as sharp as possible?
I hope that's clearly explained!

ac12 · Jun 2, 2017

If the squares you are referring to are the AF sensors, ignore them for manual focusing.
I focus in the center then recompose, at least that is how I did it with my 35mm cameras. The focusing aids (split image or microprism) were/are in the center.
But if you feel that the focus is different when you recompose, by all means focus with the subject in the final screen position.

JamieB · Jun 2, 2017

ac12 said:
If the squares you are referring to are the AF sensors, ignore them for manual focusing.
I focus in the center then recompose, at least that is how I did it with my 35mm cameras. The focusing aids (split image or microprism) were/are in the center.
But if you feel that the focus is different when you recompose, by all means focus with the subject in the final screen position.

Perfect. Thanks a lot.

shutterfinger · Jun 2, 2017

When in manual focus mode of any camera you can eye focus any part of the focusing screen/viewfinder/groundglass and the resulting image should match what you set when composing, if it doesn't there is likely something wrong with the camera or its electronics/controls are lying to you.

Leigh B · Jun 2, 2017

Many ground glass screens have a focus aid in the center, i.e. a split image or similar.
If such exists, use it regardless of how the overall image fits your envisioned composition.

Focus on the important area of the subject, then recompose as desired and shoot.
The focus will not shift when you move the camera (as long as you don't move the ring on the lens).

- Leigh

Sirius Glass · Jun 2, 2017

Leigh B said:
Many ground glass screens have a focus aid in the center, i.e. a split image or similar.
If such exists, use it regardless of how the overall image fits your envisioned composition.

Focus on the important area of the subject, then recompose as desired and shoot.
The focus will not shift when you move the camera (as long as you don't move the ring on the lens).

- Leigh

+1

wiltw · Jun 2, 2017

Leigh B said:
Many ground glass screens have a focus aid in the center, i.e. a split image or similar.
If such exists, use it regardless of how the overall image fits your envisioned composition.

Focus on the important area of the subject, then recompose as desired and shoot.
The focus will not shift when you move the camera (as long as you don't move the ring on the lens).

- Leigh

Above reply discounts the reality...recompose error DOES occur when you alter the subject position within the frame. But the amount of recompose error matters, for the angular change and for the shooting aperture used...if the angle is small, even if the aperture is large, DOF will compensate suffiently. But if the angular change is about 15-20 degrees (almost half the of 50mm FL frame) and shooting aperture is large, the focus error can be visible in spite of DOF. The yellow cells indicate when DOF is inadequate to mask the focus error caused by recompose.

AF cameras have the disadvantage of half of the light diverted down to the AF sensor, so the focus screen is deliberately made brighter by making it less coarse than in a manual focus film camera...less precise for visualizing focus accuracy. Focus away from any focus aid in the center makes focus effort less accurate; so between focus recompose error and focus screen imprecision, you're screwed.

Luckless · Jun 2, 2017

Focus-and-recompose is a very useful tool to use, but do keep in mind relative distances and narrow depths of field: It is entirely possible to focus on a given point, then change the angle of your camera such that the plane of sharp focus is now in front or behind the thing you had just focused on.

Don Craig · Jun 2, 2017

An SLR should have a delpth-of-field preview button, how about using that?

wiltw · Jun 3, 2017

Don Craig said:
An SLR should have a delpth-of-field preview button, how about using that?

I frankly have NEVER used DOF Preview on any 135 format camera...after all, DOF tables assume poor human vision, which is unable to see with 20/20 visual acuity that your optometrist tries to achieve when correcting your vision, and it assumes you are looking at 8x10 print from about 12" away...so how accurate do you think DOF preview is when you look at a dinky focus screen which is typically viewed smaller magnification than the true frame area and magnification, so less than 24mm x 36mm?! If it is a useless tool for evaluating DOF in your photo, how good is it for determining 'in focus' within the true DOF zone?!

Don't take my word for it, assess that for yourself with a simple test...
At 50mm FL focused at 60", at f/8 the 20/20 vision DOF zone extends from 52" to 70.7"...look in your viewfinder with the DOF Preview and try to determine if YOUR viewfinder shows

that something at 50" or at 73" looks 'out of focus' and outside the DOF zone
while something at 54" or at 60" looks to be 'in focus' and inside the DOF zone

and determine for your own eyes and your camera's focus screen how well or how poorly you can assess 'in focus' vs. 'out of focus'! Just remember, you have to be able to reliably determine 'in focus' vs. 'out of focus' status if you are to be depending upon it to save your bacon after focus recompose focus shift, and do that while viewing a darkened screen!

ic-racer · Jun 3, 2017

On 35mm I use DOF preview all the time. Unless you shoot wide open all the time, who does not want to see what the image will look like at shooting aperture?? I guess some people enjoy the surprise factor of film photography.

Chan Tran · Jun 3, 2017

First of all I hope that we're talking about SLR (or DSLR for that matter) and not rangefinder.
40 years ago when I was shopping for my first camera I decided that I wanted a SLR and not a rangefinder. The primary reason is that with the rangefinder I could only focus at the center of the frame and recompose while with a SLR I can focus anywhere in the frame. While as someone pointed out focus and recompose does introduce some error and although the error is small at normal distance doing the focus and recompose slows me down so I hate it. So when I got my camera the first thing I bought was a focusing screen that doesn't have any of the focusing aid like split image or microprism.

Agulliver · Jun 3, 2017

I certainly use DOF preview from time to time on my Praktica SLRs....but my vision is somewhat better than 20/20 so this might help? DOF preview helps me know what the background and foreground will look like in the final photograph. Experience gives me a fair idea but it only takes a second to check.

I second the advice to focus on the subject you need to be in focus, then recompose if necessary. In 99% of cases you won't need to do any focus adjustments upon recomposing the shot.

Most cameras have a ground glass with some sort of fine focus assist in the centre.

shutterfinger · Jun 3, 2017

I too switch to a plain focus screen asap. I have gotten more focusing errors using the microprism than without it.

Sirius Glass · Jun 3, 2017

wiltw said:
I frankly have NEVER used DOF Preview on any 135 format camera...after all, DOF tables assume poor human vision, which is unable to see with 20/20 visual acuity that your optometrist tries to achieve when correcting your vision, and it assumes you are looking at 8x10 print from about 12" away...so how accurate do you think DOF preview is when you look at a dinky focus screen which is typically viewed smaller magnification than the true frame area and magnification, so less than 24mm x 36mm?! If it is a useless tool for evaluating DOF in your photo, how good is it for determining 'in focus' within the true DOF zone?!

Don't take my word for it, assess that for yourself with a simple test...
At 50mm FL focused at 60", at f/8 the 20/20 vision DOF zone extends from 52" to 70.7"...look in your viewfinder with the DOF Preview and try to determine if YOUR viewfinder shows

that something at 50" or at 73" looks 'out of focus' and outside the DOF zone

while something at 54" or at 60" looks to be 'in focus' and inside the DOF zone

and determine for your own eyes and your camera's focus screen how well or how poorly you can assess 'in focus' vs. 'out of focus'! Just remember, you have to be able to reliably determine 'in focus' vs. 'out of focus' status if you are to be depending upon it to save your bacon after focus recompose focus shift, and do that while viewing a darkened screen!

I use the depth of field button on my slr cameras when I need to regardless of format. It tells me what the depth of field will be. There are no assumptions about poor vision nor about 12", the optics tells the story. It is one of many advantages of slr cameras over rangefinder and tlr cameras. My 35mm slr cameras were chosen in part by the apparent image size and the ability to discern details that other brands or model could not show. Of course there is no problem discerning details in the Hasselblad; perhaps you should try a Hasselblad with a 45° prism for yourself.

wiltw · Jun 3, 2017

I stand very strongly behind my challenge...TRY IT to test your ability to determine 'in focus' vs. 'out of focus' distances in the viewfinder !!!

I just took a Topcon Super D with 58mm f/1.4 lens and set targets precisely at 55" (-5" outside DOF at f/8), 57" (-2" inside DOF at f/8), 60" (perfect focus), 63" (+2", inside DOF at f/8), and 65" (+5", outside DOF at f/8). Targets were VCR boxes with large and small text on the cover, to judge readability.

According to the Cambridge Color DOF calculator, set to Advanced mode, with 20/20 vision selected for visual acuity of the observer,

at 60" focus, 58mm f/1.4 has DOF zone extending from 59.6" to 60.4"
at 60" focus, 58mm f/8 has DOF zone extending from 57.8" to 62.3"

focused carefully at the target at 60", I tried to assess the two targets in front of it, then the two targets behind it. The target pairs were set up so that one of them should start at f/1.4 as 'out of focus' but sharpen up at f/8 to 'in focus', while the other target remains 'out of focus' regardless of aperture.

I could not judge that one was 'in focus' while the other was 'out of focus' when DOF Preview was stopped down to f/8! The image does not suddenly sharpen up to make the 'in focus' target readable while the 'out of focus' target is not readable. It is too subjective to render that judgement of one status vs. the other!!!
Can YOU? especially if you are using a more recent SLR with viewfinder status information which forces the focusing screen to be viewed at only 0.87X, rather than at 0.93X or 1.0X!

mdarnton · Jun 3, 2017

I used the instant feedback my DSLR gives to teach me how to focus my film SLR. When you make mistakes on a DSLR, you know right away. By learning what works for me that way, I can transfer that to the film cameras. I recommend you start experimenting and see what works, rather than ask.

I thought that everyone knew that depth of focus is an illusion, depending on print size, viewing distance, everything else. When I shoot, for me there is only one point of focus, and either I hit it. . . or I don't. How something looks in a print is interesting, but don't confuse it with "all in focus because I used a small aperture", because it is not.

Sirius Glass · Jun 3, 2017

Sirius Glass said:
I use the depth of field button on my slr cameras when I need to regardless of format. It tells me what the depth of field will be. There are no assumptions about poor vision nor about 12", the optics tells the story. It is one of many advantages of slr cameras over rangefinder and tlr cameras. My 35mm slr cameras were chosen in part by the apparent image size and the ability to discern details that other brands or model could not show. Of course there is no problem discerning details in the Hasselblad; perhaps you should try a Hasselblad with a 45° prism for yourself.

I check the depth of field at the aperture which I will use for the photograph. That is the real optical depth of field and does not depend on printing or slide projection. It is not useful to check the depth of field for an aperture that is smaller than you are going to use, unless you like looking at a dim screen.

wiltw · Jun 25, 2017

Sirius Glass said:
I check the depth of field at the aperture which I will use for the photograph. That is the real optical depth of field and does not depend on printing or slide projection. It is not useful to check the depth of field for an aperture that is smaller than you are going to use, unless you like looking at a dim screen.

But your PERCEPTION of the DOF zone as seen in the viewfinder is indeed going to be different when the final print is 16x20 rather than only 8x10, when the viewer does not stand back a proportionally larger (4x farther) distance when viewing the larger print!

film_man · Jun 25, 2017

Two things.

If you are using an AF camera, then just ignore the AF sensors. You can use any part of the screen to focus and you'll get just as good a result.

If you are using a manual camera then, if you have screen with a split-image, microprism or anything else that you're supposed to use to focus in the centre of the screen then...
- either use it and recompose
- or get rid of that screen for a plain matte one and focus wherever you want

Personally I want as clear a view as I can so just go for a plain screen. I especially dislike split-image screens.

Sirius Glass · Jun 25, 2017

Sirius Glass said:
I check the depth of field at the aperture which I will use for the photograph. That is the real optical depth of field and does not depend on printing or slide projection. It is not useful to check the depth of field for an aperture that is smaller than you are going to use, unless you like looking at a dim screen.

wiltw said:
But your PERCEPTION of the DOF zone as seen in the viewfinder is indeed going to be different when the final print is 16x20 rather than only 8x10, when the viewer does not stand back a proportionally larger (4x farther) distance when viewing the larger print!

No, a sharp negative is a sharp negative. If something is not sharp in the negative, one cannot add sharpness after the fact. Good enlarger lenses will properly reproduce the negative.

wiltw · Jun 25, 2017

Sirius Glass said:
No, a sharp negative is a sharp negative. If something is not sharp in the negative, one cannot add sharpness after the fact. Good enlarger lenses will properly reproduce the negative.

Hang on a second...a negative is enlarged to make a print.
A perfectly focused point data is perfect point data, and focus blur circles -- whether those small enough to fool your brain, and those large enough to be perceived as blur -- are both magnified to make an enlargement. Few negatives capture ONLY the plane of focus (flat artwork) but most negative also capture things not at the plane of focus.

So enlarging a CofC blur circle from its on-film size of 0.02501mm to 8x10" print size (8.5x enlargement) vs. 16x20" print size (16.9x) results in blur circles of 0.2125mm or 0.4227mm on print...and decreased viewing distance of 16x20" print makes the 0.4mm more apparent as 'blurry' and not fool your eye and brain into thinking 'sharp'.

Sirius Glass · Jun 25, 2017

wiltw said:
Hang on a second...a negative is enlarged to make a print.
A perfectly focused point data is perfect point data, and focus blur circles -- whether those small enough to fool your brain, and those large enough to be perceived as blur -- are both magnified to make an enlargement. Few negatives capture ONLY the plane of focus (flat artwork) but most negative also capture things not at the plane of focus.

So enlarging a CofC blur circle from its on-film size of 0.02501mm to 8x10" print size (8.5x enlargement) vs. 16x20" print size (16.9x) results in blur circles of 0.2125mm or 0.4227mm on print...and decreased viewing distance of 16x20" print makes the 0.4mm more apparent as 'blurry' and not fool your eye and brain into thinking 'sharp'.

The blur circle does come into play but it is a small player because if the sharpness in not there the blur circle will not and cannot improve it. If the lens I am using is not good enough for an enlargement, I can change to another lens. I cannot change what is on the negative. I have not had a problem with a good composition at 8"x10" be unprintable at 16"x20" with negatives, however my avatar was shot with a digital camera at less than a quarter megapixel and there is nothing that can be done to print it larger much larger than the avatar. If the information is not there, nothing will bring it back. So given that one has chosen the depth of field, the print can be made without the blur circle changing the depth of field, the blur circle can only effect the details not change the depth of field. I can always find a better 50mm lens for 35mm film, I can always find a better 80mm lens for 120 film, I can always find a better 135mm to 150mm lens for a 4"x5" or I can even use a 80mm lens on a 35mm negative or a 50mm lens on a 120 negative. You are confusing apples with bowling pins. You do not even have the right shape for your comparison.

wiltw · Jun 25, 2017

Sirius Glass said:
The blur circle does come into play but it is a small player because if the sharpness in not there the blur circle will not and cannot improve it.

The 0.02501mm CofC size was established as the size of a blur circle ON FILM which would be the threshold of 'not blurry' vs. 'blurry' when the 24mm x 36mm image of 135 was enlarged by 8.6x to 0.2125mm size on 8x10" print viewed from 12" away, where the eye of the substandard vision viewer perceives that blur as 'sharp enough' and yet the viewer with 20/20 vision says 'blurry focus'.

That same blur circle, enlarged to 16x20 print is now 0.4227mm in absolute size...if you stood back at about 24" your eye (with substandard vision) would still see that blur circle as 'sharp enough', and the viewer with 20/20 vision still sees it as 'blurry focus'. If both of you move to 12", both of you detect that 0.4227mm blur circle as 'blurry focus' even though that identical point on the 8x10" print is 'in focus' to your eye. Same negative, different perceptions of 'blur' vs. 'sharp enough'.

The perceived DOF when the 16x20" print made with 50mm f/4 lens is focused at 30' is a DOF zone of 9.53' deep, viewed from 50cm.
That same print viewed from 25cm has a DOF zone of only 4.68'

Change an interchangeable focus screen to a finer one, to brighten the finder with a long tele lens, and the viewfinder has altered the in-viewfinder perception of 'in focus'...even though on the 8x10" print viewed at 12", you can perceive that point as 'not in focus', it looks sharp enough due to the finer focus screen...the viewfinder does not match the print perception, even though the print is 8x10"!

Theo Sulphate · Jun 25, 2017

JamieB said:
Hi everyone
...
When looking through the viewfinder of my camera, there are a couple of circles and then a central square, to aid focusing. If I put the square over the subject I want in focus then I can better see that I am focusing. Naturally. But what if the subject is not in the centre of the frame? Well, once I have focused I could recompose the shot but I am guessing I will not get the same results especially at wider apertures because the shift in position might or will change the focus plain (?)...

Most of the time you can focus within the clearer central area and then recompose because the distance from subject to film plane isn't changing that much when you recompose. The situation to be careful with is wide apertures and close distances because then the shift is likely significant. For example, if you're making a portrait and focus on the subject's eye, then recompose, it's likely the resulting image won't have the eye in focus. In cases like that, you'll want to do your final composing first and then (without recomposing) adjust the lens focus so that the eye is sharp wherever it happens to be be in the viewfinder.

A Question About Manual Focusing

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