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02-03-2010, 11:03 PM   #1
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DOF question (moved from the manual lens thread)

I have a K-X and manual lens. I am following the tutorial provided within this thread. I am unsure what the problem is, but the only depth of field I am getting is not as shallow as I am intending. I have tried reading the manual and the only thing I am getting is frustrated. I am using a K 50/1.4 and have the camera set to allow using the aperture ring. I have the lens set at 1.4, yet I am not getting a shallow depth of field. I have tried relatively close shots with three bottles approximately 3-4 feet away from me and all within about 6-8" of one another. I am focusing on the first bottle, yet the last bottle still is relatively in focus.

Another shot I attempted a few times was a box approximately ten feet away. Everything as far as twelve feet behind the box is still not blurred out in a thin depth of field like I am intending.

I have a general understanding of depth of field and what creates a shallow depth of field as well as what creates a wider depth of field. However, in practice, I am unable to get the results that I know the lens is capable of.

Can anybody offer me some tips or suggestions for troubleshooting so that I can get the result I am looking to achieve?

02-03-2010, 11:13 PM   #2
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QuoteOriginally posted by jbush02s Quote
Can anybody offer me some tips or suggestions for troubleshooting so that I can get the result I am looking to achieve?
Not sure if this question really belongs in this thread. You would've been better off starting a new thread, but oh well.

Look inside the lens while you adjust the aperture ring (this is easier with lens off the camera). Is the aperture opening and closing properly as you turn that ring? Are the aperture blades opening up all the way at 1.4? You shouldn't even be able to see them anymore, they should just disappear into the lens barrel at 1.4.

If the aperture blades are opening all the way at f1.4, then there's nothing wrong with your lens. If not, then there's something wrong. A 50mm lens at f1.4 focusing just 4 feet away should give you only about 1" to 2" of depth of field, which is very little.
02-03-2010, 11:22 PM   #3
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I guess everyone has different ideas whether certain replies belong in new threads or within existing threads. I guess that is why the site has moderators. If they want it moved, it will be taken care of. It just seemed to be a logical place to put the question since it was the thread I was using as a reference.

I did double check to make sure the blades were opening all the way at 1.4 as you suggested. I agree that the DOF should not be what it is. I am sure I am just making a simple mistake somewhere within the setup of the camera. Thank you very much for your reply.
02-03-2010, 11:31 PM   #4
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QuoteOriginally posted by jbush02s Quote
I guess everyone has different ideas whether certain replies belong in new threads or within existing threads. I guess that is why the site has moderators. If they want it moved, it will be taken care of. It just seemed to be a logical place to put the question since it was the thread I was using as a reference.
Personally, I don't really care. The problem is that when you post a new question into an existing thread, the only people who will see it are those who are still subscribed to that thread (ie. like me). If you start a new thread, you'll get a lot more people looking at it who can help you.

QuoteOriginally posted by jbush02s Quote
I did double check to make sure the blades were opening all the way at 1.4 as you suggested. I agree that the DOF should not be what it is. I am sure I am just making a simple mistake somewhere within the setup of the camera. Thank you very much for your reply.
There's really nothing to configure in the camera that would affect depth of field. If you're using a lens with manual aperture control, then all the depth of field will be controlled by that and nothing else. I doubt you're doing anything wrong, I think maybe you're just expecting more than what you should get.

Here's a shot I just took of my keyboard from 3 feet away with my Super Takumar 50mm set to f1.4.

View Picture EXIF
Name:  GORE4627.JPG
Views: 261
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Notice the front and rear of the keyboard are out of focus, and only a couple rows of keys are really in focus. That's exactly the kind of result I'd expect, and that's exactly the kind of result you should be getting too, regardless of the camera's settings.

02-03-2010, 11:54 PM   #5
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QuoteOriginally posted by GoremanX Quote
Personally, I don't really care. The problem is that when you post a new question into an existing thread, the only people who will see it are those who are still subscribed to that thread (ie. like me). If you start a new thread, you'll get a lot more people looking at it who can help you.

Ah, OK. I figured that either way it would go to the top of the forum, but I guess if the forum posts move fast enough others would not read far enough down to find my question. I understand where you are coming from with that.

I did just shoot another shot (similar in focal range to the one you just shot and displayed) and I got shallow depth of field. I also set up a shot similar to the other (longer) shot I had done before. I think you are correct. My expectations are the problem, as opposed to my setup. If I was shooting a longer focal length, would my depth of field be reduced in that longer shot? For example, if I was shooting the shot with an 85mm lens with a large aperture (1.8 or so), would that blur the background on that longer shot more than with my 50mm, all other things being equal?
02-04-2010, 12:06 AM   #6
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I can also see, particularly with the longer shot, that my camera is focusing BEHIND what I am intending to focus on. I need to learn a little more about focusing and which settings to use because the camera sometimes is focusing behind the box and the box is somewhat blurry with the background in focus. I believe that is either a technique or setting problem. I think I need to look more into focusing points and the proper setup because, much like a computer, I am sure the camera is only doing what I am (perhaps unknowingly) telling it to do.

I appreciate your help. Your input has been helpful because it has given me the ability to focus (pun intended) in on the actual problem I am having.
02-04-2010, 12:29 AM   #7
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QuoteOriginally posted by jbush02s Quote
If I was shooting a longer focal length, would my depth of field be reduced in that longer shot? For example, if I was shooting the shot with an 85mm lens with a large aperture (1.8 or so), would that blur the background on that longer shot more than with my 50mm, all other things being equal?
Probably, but check it out for yourself:

Online Depth of Field Calculator

I find that calculator invaluable sometimes. A longer focal length will always give you shallower depth of field, all other factors being equal. But a longer focal length often means a smaller aperture, or being required to shoot from farther away, so it really depends on the situation.

QuoteOriginally posted by jbush02s Quote
I think I need to look more into focusing points and the proper setup because, much like a computer, I am sure the camera is only doing what I am (perhaps unknowingly) telling it to do.
Manual focusing takes practice, especially since there's no focus aid on the focusing screen. There are plenty of threads on this forum that show good practice techniques.

02-04-2010, 08:42 PM   #8
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I agree this belongs in its own thread, both to guarantee it gets seen, and to avoid diluting the thread on manual lenses.

As for where "the camera" focuse, this is a manual focus lens we are talking about, so it's *you* that does the focusing, of course. But it's an unfortunate fact that with large apertures, the viewfinders on modern DSLR's will show *too much* DOF. So it's normal for some thigns to look in focus in the viewfinder that won't be in the picture. The reverse should not be true, however.
02-04-2010, 10:37 PM   #9
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Goreman:

Thank you for the link. That does help to give me a better understanding of the spatial relationship of how depth of field will appear.

Marc:

Whether you agree with my semantics or not, the fact remains that my shots are turning out with some of the wrong objects in and out of focus and it is not detectable to my eye through the viewfinder. It is not something I can see until I have downloaded my photos.

It is pretty obvious who is doing the focusing with a manual focus lens. As you said, more appears in focus within the viewfinder than ends up in focus in the photo. Now, guessing whether the object in the foreground or the background is going to be as focused as it appears in the viewfinder can be another story altogether, particularly in the longer shot I was setting up. I will have to do some more research on the site to determine how to overcome this. Some shots seem more difficult to focus dead-on than others, in my experience.
02-05-2010, 02:55 AM   #10
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QuoteOriginally posted by jbush02s Quote
Whether you agree with my semantics or not, the fact remains that my shots are turning out with some of the wrong objects in and out of focus and it is not detectable to my eye through the viewfinder. It is not something I can see until I have downloaded my photos.
The camera can't selectively mess up your depth of field, that's physically impossible. Your depth of field is entirely based on distance from subject, focal length, aperture size and circle of confusion. The circle of confusion is permanently set by your camera sensor's size and position (in this case APS-C), which only leaves distance from subject, focal length and aperture size as the determining factors. This is all completely determined by your lens and the way it lets light through. There's no fancy digital way for cameras to make things in focus outside of your depth of field. Therefore, there's no way to adjust this with camera settings. The points of focus have nothing to do with it, the focusing system has nothing to do with it, and the options set in your camera will have no effect.

Your best bet is to practice with different arrangements until you're happy with the results. But to be honest, you're not likely to get a shallower depth of field than a 50mm lens at f1.4 from 4 feet away (unless you spend the money on a f1.2 lens).
02-05-2010, 09:38 AM   #11
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QuoteOriginally posted by jbush02s Quote
Whether you agree with my semantics or not, the fact remains that my shots are turning out with some of the wrong objects in and out of focus
I just wanted to make sure no one took your comments to mean there was a camera defect here.

QuoteQuote:
As you said, more appears in focus within the viewfinder than ends up in focus in the photo. Now, guessing whether the object in the foreground or the background is going to be as focused as it appears in the viewfinder can be another story altogether, particularly in the longer shot I was setting up. I will have to do some more research on the site to determine how to overcome this.
Mostly, it's just about practice. Learning to see the entire zone of apparently acceptable focus in the viewfinder (by watching what changes as you turn the ring), and positioning your subject so it is in the part of that zone that experimentation tells you will actually be in focus.
02-05-2010, 10:15 AM   #12
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This is from a Super-Tak 50/1.4 @ 1.4



and this one is a few stops down


Last edited by boriscleto; 02-10-2010 at 09:17 PM.
02-05-2010, 11:31 AM   #13
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I think what you are seeing is not an issue of the lens not being wide open or the DOF scale being wrong but you aren't getting the bokeh you desire. Boriscleto's first shot is a good example. Only the peak of the roof of the birdhouse is in sharp focus. While the DOF is quite narrow and the rest of the picture is out of focus, it isn't totally blurred out. Only one spot of the lower eaves and roof are blurred. This is the charactarstics of the particular lens. The distance of the lens to the objects, the distance of the different objects to each other and the lighting will all affect it. To really throw the foreground and background into a total blur, I prefer a longer lens.
02-05-2010, 07:36 PM   #14
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Every now and then I swing by Ned Bunnell's blog. Today, I see he has an item on Depth of Field, that is very similar to your question.

NED BUNNELL: Depth of Field Can Be Pencil Thin
02-06-2010, 12:46 AM   #15
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Thank you very much for all of your replies. I believe part of my problem was technique. When you have a narrow depth of field, there is less margin for error. Overall, I have been very satisfied with the results I have gotten, but the anomalies are what have thrown me off a bit from time-to-time. Part of my problem is that I am working on learning B & W darkroom technique, manual focus on dslr (definitely takes more technique than manual focus w/35mm), etc. etc. and I am not able to improve one area at a time.

Fortunately, I am getting better at all of the things I am working on, but my "aha" moments appear, sometimes seemingly out of nowhere, as randomly as the varied tasks I am approaching.
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