Help With Focusing and Depth of Field

ditto1958

Well-Known Member
When I view my pictures critically, the most common problems I have are with focusing and depth of field.

As to focusing, I notice that too often my pictures come back with the subject slight out of focus, but objects just behind are in focus. Just the opposite of what I want.

I guess depth of field is related, but it seems that a mark of many professional photos is that the subject is in focus and the background is extremely blurry- thus causing the subject to stand out. I try to do this, but it is difficult to do. Is it necessary to have large aperture lenses to accomplish this more regularly?}
 

biofos

Active Member
>This sounds as though your imaging is slightly out. Could be a number of things. Incorrect screen, or screen not fitted or sitting in the frame p roperly. A slight imperfection in the pentaprism. Bad previous servicing. Touch of fungus in the lens. Lens needs servicing and re-calibrating. Po ssibly your eye sight might be a little off too - I suffer the same. Some days it's fine, others I'm well out - it can be a simple as not enough s leep! Not enough to warrant a dioptre but perhaps have your eyes checked out. As for DoF, accurate focus is essential to give the effect you desir e regardless of large aperture. Bone up on DoF and Hyperfocal Distance to fully appreciate what's going on in your lens when you expose wide open or stopped down. If you don't get the focus right initially any DoF you a chieve from the aperture/exposure can make it worse. Accurate SLR focusin g is not easy; especially as you get on in years. That's why many Pro's g o AF. And don't rely too much on the preview button. > > JF.
 

ditto1958

Well-Known Member
I don't think there is any equipment problem as I have done this with more than one camera. I can relate to your comments about eyesight, though. You know you are getting older when you pick up your first pair of bifocals!

I understand how to focus at hyperfocal distance to make use of maximum dof, e.g., in a landscape photo. What I would like to improve at is using minimum dof so that more of my shots have the subject in focus and the background out of focus. It seems as though that is hard to do-- especially outside on bright days.
 

biofos

Active Member
>Posted by Mark M. Ditter (Ditto1958) on Tuesday, March 22, 2005 - 4:50 am: > >I don't think there is any equipment problem as I have done this with >more than one camera. I can relate to your comments about eyesight, >though. You know you are getting older when you pick up your first >pair of bifocals! > > Yes indeed! This certainly points towards an eyesight issue; this is very difficult to redress. My suggestion is still to look at your equipment. Try a series 2 screen or a Beatie screen that will give you not only a brighter image but a clearer one. Though I hear what you say about getting it right on bright days - too much brightness for your eyes to cope with, not enough contrast for precise focus with your eye? Try different screens to find the one that best suits your eye and gives the most consistent results. You could ask your optician for some help; I know this sounds like over-kill but it's demoralising when carefully composed and exposed shots come out with that tad of unwanted blur. However, there are many that have had to abandon manual focus systems because of this problem, so it's worth spending some time trying to find a workaround.

>I understand how to focus at hyperfocal distance to make use of >maximum dof, e.g., in a landscape photo. What I would like to improve >at is using minimum dof so that more of my shots have the subject in >focus and the background out of focus. It seems as though that is hard >to do-- especially outside on bright days. > > That you know the intricacies of dof and hd suggests you have tried to use these to compensate. Of course everything changes with the light and the lens choice. You could experiment with fixed subject to film plane distance and dial the measured distance into your lens rather than using the ground glass. (A lens calibrated to your body by a good technician is essential.) A few shots either side of the measured distance will confirm if there is a mechanical fault. This is done at various apertures. Then you repeat this using your eye to focus and see if there is a consistent error that you can then use to compensate. I suspect the result will be so variable that compensation is unlikely; but it might be worth a try. Lens choice is also a factor. Fast lenses exacerbate this problem as there is more light in the finder for your eye to manage. And fast tele's - the ones that give the effect you want - are more difficult to focus precisely if your eyesight is slightly off. Wide angle lenses give more dof but this is going in the wrong direction. It is a major problem and I'm sorry I can't provide an easy answer.

JF.
 

gjames52

Well-Known Member
Mark wrote> understand how to focus at hyperfocal distance to make use of maximum dof, e.g., in a landscape photo. What I would like to improve at is using minimum dof so that more of my shots have the subject in focus and the background out of focus. It seems as though that is hard to do-- especially outside on bright
days.

Mark:

As you know bokeh (out of focus) background is controlled by lens design (telephoto for ex&le shortens the DoF, wide angle lenses increase DoF) easily observed by the DoF scales on the lenses. Also, opening the lens reduces the DoF and blurs the background. That is why basic recommendations in most manuals suggest opening F5.6 or F4 as for portraits, allowing for good subject focus and out of focus background.

My guess is that if you try slow speed film and open the aperture, perhaps starting at F5.6 then progressively to wide open, focusing on the same point and the same subject and then observe the differences on your images and you will find out how that lens performs. If the subject is still too bright to open up your lens, perhaps a lens filter can be used to reduce the amount exposure enough.

Just to be sure your glasses aren't causing your problem: focus on a subject and have a person with known good eyesight confirm your focus. Also, for precise focusing Olympus made the Verimagfinder, that has 1.2x and 2.5x magnification that will aid focusing.

I know a Nikon instructor that stated that he only shoots wide open.

Best Regards:

Gilbert
 
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