Questions about autofocus

Ryanse · Dec 8, 2017

Hi everyone,

I've got a few questions, I'm hoping someone can set me straight.

I bought a Canon EOS 1000f body so I could use my 85mm f1.8. I was out shooting and I wanted to give the AF a try, but I remember the camera focusing just behind my subject, whereas I intended on focusing on the face of my subject. Anyway, I turned the AF and focused manually.

But now I've just gotten the roll back, and I can see that while it appeared that I was focused on the subjects, I was actually focused just behind the subject!

Does anyone have any idea of why this might be?
Is it an issue with using a newer lens on an older camera?

I've included an image where you can see how it's focused on the plants just behind the subject.

Thanks, and any help is very much appreciated!

Ryan.

pentaxuser · Dec 8, 2017

Which part of the pic do you think the correct focus is on?. If anything it looks like the lines in the coat's check pattern are close or on focus. The part behind is presumably the barbed-wire fence and the posts but these do not look to be in any sharper focus than the coat's pattern and are maybe less in focus.

I take it there is a signal in the viewfinder that indicates which area is in correct focus and this signal came on in the area you desired the correct focus to be? What aperture was this? It looks to be very large, giving a very small DoF of maybe a few inches only when things can become.problematical

pentaxuser

winger · Dec 8, 2017

Can you change the diopter setting for the viewfinder? If what you see isn't accurate to what happens on the film, then the viewfinder is where it's likely going wrong.

Sirius Glass · Dec 8, 2017

You have a thin depth of field. I think the AF is working correctly, use it.

Chan Tran · Dec 8, 2017

I think the grass at the lower right corner is the sharpest.

pentaxuser · Dec 8, 2017

We need the OP to answer a few questions about his aperture and what the autofocus system was showing. Otherwise we are again punching the air in terms of helping the OP. He needs to help us help him

pentaxuser

AgX · Dec 8, 2017

Chan Tran said:
I think the grass at the lower right corner is the sharpest.

Seemingly, as the OP already said, the plane of focus is short behind the girl.

AgX · Dec 8, 2017

winger said:
Can you change the diopter setting for the viewfinder? If what you see isn't accurate to what happens on the film, then the viewfinder is where it's likely going wrong.

I do not understand what a bad eyesight has to do with this issue. The autofocus just offers the chance to come up for bad eyesight. As long as the sight is good enough to see where the focus mark is directed at.

(writes a bad-sighted manual focusser...)

DWThomas · Dec 8, 2017

For sure bad eyesight uncorrected doesn't help, but with most SLRs, the user is observing an image on a ground glass screen. I would expect with bad eyesight what one sees would never be sharp, but I would think moving focus back and forth would still show an optimum at the right place. Now with some optical systems, one is looking at an aerial image; e.g., not projected onto anything, there, bad eyesight could be a problem. I admit I don't know, perhaps the split prism focus screens rely more on an aerial image.

Does this camera have an interchangeable focus screen? If so, maybe it's not seated correctly, or mayhaps the mirror stop, bumper, or whatever is out of wack or deteriorated. That could make the focus distance to the viewfinder different from the focus distance to the film.

One could place ground glass (or frosted cellophane tape) across the film plane and try to compare the viewfinder focus against the film plane focus. For 35mm you will definitely want a loupe of 8 or 10x to do this. Doing this one needs to be sure the ground glass is against whatever surface establishes the film position and isn't lifted by some guide rail.

(Just a few thoughts.)

MikeDahlke · Dec 8, 2017

I can tell you 100% that if you have bad eyesight and your using an AF camera without glasses/contacts the AF system is definitely going to pick a focus point that looks wrong to your eyes. Been using AF the last few days as I couldn’t wear my contacts...

winger · Dec 8, 2017

AgX said:
I do not understand what a bad eyesight has to do with this issue. The autofocus just offers the chance to come up for bad eyesight. As long as the sight is good enough to see where the focus mark is directed at.

(writes a bad-sighted manual focusser...)

"I bought a Canon EOS 1000f body so I could use my 85mm f1.8. I was out shooting and I wanted to give the AF a try, but I remember the camera focusing just behind my subject, whereas I intended on focusing on the face of my subject. Anyway, I turned the AF and focused manually.
But now I've just gotten the roll back, and I can see that while it appeared that I was focused on the subjects, I was actually focused just behind the subject!"

Because the OP wrote that what he thought was out of focus turned out to be in focus and vice versa. That can happen if the viewfinder is off a bit or if the focussing screen is off a bit as Dave mentioned.

Sirius Glass · Dec 8, 2017

The camera could be out of alignment. If so it is time for a CLA by a qualified repairman.

shutterfinger · Dec 8, 2017

Download a copy of the instruction manual here: https://www.manualagent.com/canon/eos-1000-f/users-manual
Butkus shows it to be the same as a EOS Rebel S.
Specs show a standard diopter adjusted to -1, focus screen is fixed.

Wide apertures have a very shallow depth of field.
You should have been using 1/90 to 1/125 shutter speed or faster at f5.6 to f8 to get the face in sharp focus.
Slower shutter speed will likely result in camera shake. Very minor camera shake will degrade overall sharpness which can be mistaken for poor focus.

AgX · Dec 9, 2017

The OP admitted, if I understand him right, that he misfocused manual focused exposures.
But nevertheless before that he stated:
"I was out shooting and I wanted to give the AF a try, but I remember the camera focusing just behind my subject, whereas I intended on focusing on the face of my subject."
I still do not understand how the latter is related either to bad eyesight or a misaligned screen.

cooltouch · Dec 9, 2017

I don't think eyesight, whether good or bad, had anything to do with the above photo. Nor did camera shake. It is plain to see that the nearest shrubbery in the bottom right of the photo is in focus. I think DaveT nailed the issue. I bought a Pentax LX a couple years ago that had a seriously misaligned mirror. Say the subject was six feet away -- the lens's focusing scale was saying it was ten feet away. Obviously something was out of whack, and it turned out to be the mirror's bump stops had deteriorated, causing the problem. I suspect the OP is having a similar problem. It might not be the mirror. The pentaprism may have gotten displaced, for example. He can confirm this by looking at the distance scale on the lens and comparing it to the actual distance from camera to subject.

Sirius Glass · Dec 9, 2017

Nothing weird here. The shrubbery, hands and face are within the depth of field.

Ryanse · Dec 9, 2017

I really appreciate everyone taking the time to help!

Some things I should have mentioned - the sun was very strong, so I shot at something along the lines of f11 at 1/250 with 200 speed film.

Looking through the viewfinder it was clear to me that the autofocus wasn't as it should be, and that when I manually focused, it appeared to be correct.

Following what u/cooltouch advised, I did a test and autofocused on something that was 7ft away, but the distance scale on the lens read over 7ft (maybe somewhere between 7.5ft - 8ft). Does this mean the mirror is the issue?

AgX · Dec 9, 2017

This whole discussion is fruitless.

We cannot even agree if the plane of focus is where it should be, or where it is.
Let alone how an autofocus error, if there was, could have happened.

Ryanse · Dec 9, 2017

AgX said:
This whole discussion is fruitless.

We cannot even agree if the plane of focus is where it should be, or where it is.
Let alone how an autofocus error, if there was, could have happened.

The plane of focus is about a meter behind the girl, whereas it was intended to be on the girl

AgX · Dec 9, 2017

I just realized that the respective camera is as digital one, although this forum is for analog cameras.
And I am not sure whether I can apply my knowledge on the working of the autofocus at such system.

Ryanse · Dec 9, 2017

AgX said:
I just realized that the respective camera is as digital one, although this forum is for analog cameras.
And I am not sure whether I can apply my knowledge on the working of the autofocus at such system.

Okay man, it's still a film camera, so I figured it'd be okay to post here?

Thanks for pitching in.

shutterfinger · Dec 9, 2017

Ryanse said:
I did a test and autofocused on something that was 7ft away, but the distance scale on the lens read over 7ft (maybe somewhere between 7.5ft - 8ft). Does this mean the mirror is the issue?

Take a look at post 126 (top of page 6) of this thread https://www.photrio.com/forum/threads/pentacon-six-biometar-80-focus-problem.153796/page-6
Set the camera up on a tripod, level the camera, place a good, fine detail target parallel to the film plane 10 to 15 feet away (3 to 4 meters) measuring from the film plane to the target. Some cameras have a film plane mark on the camera top, some do not. I don't think yours does so the rear of the LCD panel will be close enough for checking. Focus on the target and check the lens distance scale, it should be close to the measured distance. The scale is not perfect but should be near center of a single digit to the outer edge of that digit or at the gap between digits to have the width of the digits either side of center with a double digit distance.
Also you should evaluate the sharpness on the negative with a good loupe with the negative backlit. The scan used for this post may be soft and if the basic scan from the lab it is likely not reliable for anything more than overall composition and general exposure. A 50mm camera lens used in reverse makes a good loupe substitute.

How you release the shutter can cause camera movement as can your breathing cycle at 1/500 and slower shutter speeds.
Shutter release should be a smooth gentle push not a hard jab, breath should be half out and hold not inhale or exhale.

shutterfinger · Dec 9, 2017

AgX said:
I just realized that the respective camera is as digital one, although this forum is for analog cameras.

1000f = film camera; 1000D electronic sensor camera with logic system that records on electronic medium.

Ryanse · Dec 9, 2017

shutterfinger said:
Take a look at post 126 (top of page 6) of this thread https://www.photrio.com/forum/threads/pentacon-six-biometar-80-focus-problem.153796/page-6
Set the camera up on a tripod, level the camera, place a good, fine detail target parallel to the film plane 10 to 15 feet away (3 to 4 meters) measuring from the film plane to the target.

That's great, thank you!

AgX · Dec 9, 2017

shutterfinger said:
1000f = film camera; 1000D electronic sensor camera with logic system that records on electronic medium.

Yes, I googled for exactly "Canon EOS 1000f" but nevertheless got as result at top an excerpt of the Wikipedia article for the d-model... Blame me, blame Google...

Sorry! I stand corrected.

Questions about autofocus

Privacy & Transparency

Privacy & Transparency