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Subject: "Where is the focus?" Previous topic | Next topic
grnzbra Silver Member Nikonian since 28th Sep 2011Tue 21-Aug-12 12:22 PM
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"Where is the focus?"


Springfield, US
          

In the picture here ( http://images.nikonians.org/galleries/showphoto.php/photo/388181/size/big/cat/22223 ), I used AF-S focused on the black line on the front round. I am not sure where sharp focus is. The distance was about 4 feet with 18-200mm lens set at 200mm. Where does the sharpest focus appear? I'm not sure. Looking at the rim at the bottom of the round on the right side of the second row, it appears to me that the focus is there.

Is there perhaps these there is too much reflection to make a determination?

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JosephK Silver Member Fellow Ribbon awarded for his excellent and frequent contributions and sharing his in-depth knowledge and experience with the community in the Nikonians spirit. Nikonian since 17th Apr 2006Tue 21-Aug-12 02:11 PM
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#1. "RE: Where is the focus?"
In response to Reply # 0


Seattle, WA, US
          

Looking at the rims of the cases and the folds in the bullets, I would say that the focus is at the front of rounds 2 and 3.

---------+---------+---------+---------+
Joseph K
Seattle, WA, USA

D700, D200, D70S, 24-70mm f/2.8, VR 70-200mm f/2.8 II, 50mm f/1.4 D,
17-55mm f/2.8 DX, 70-300mm f/4.5-5.6 VR, 18-70mm f/3.5-4.5 DX

  

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gkaiseril Gold Member Nikonian since 28th Oct 2005Tue 21-Aug-12 06:24 PM
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#2. "RE: Where is the focus?"
In response to Reply # 0


Chicago, US
          

With a small subject and being fairly close to the subject you will also have to deal with a limited Depth of Field, DOF.

George
My Nikonian Galleries

  

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grnzbra Silver Member Nikonian since 28th Sep 2011Thu 23-Aug-12 05:18 PM
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#3. "RE: Where is the focus?"
In response to Reply # 2


Springfield, US
          

>With a small subject and being fairly close to the subject
>you will also have to deal with a limited Depth of Field, DOF.
>

For my purposes, that's the idea. To me, this camera produces "soft" pictures, although, this past weekend they seemed to have sharpened up somewhat. What I am trying to do either prove that there's nothing wrong with the camera (by producing a picture in which the item that is supposed to be in focus is sharp) or that the focus is "off" because of a still subject which should be in focus isn't while something else is. So far, I've had no luck. I haven't been able to get a picture of a still subject in which any part of the picture was sharp. Even on test patterns that are supposed to show where the focus actually is, the whole thing seems soft when viewed full size. And I've tried to follow all the suggestions - solid tripod, weight hanging from center shaft of tripod, shutter speed equal to lens focul length.

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gkaiseril Gold Member Nikonian since 28th Oct 2005Thu 23-Aug-12 09:55 PM
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#4. "RE: Where is the focus?"
In response to Reply # 3


Chicago, US
          

You also need a very flat clearly printed and high contrast target. And this would be start of process for testing the AF system.

You shutter speed formula is for the FX or 35mm full frame camera. For a DX sensor, you need to adjust the focal length for the crop factor.

George
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grnzbra Silver Member Nikonian since 28th Sep 2011Thu 23-Aug-12 10:10 PM
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#5. "RE: Where is the focus?"
In response to Reply # 4
Thu 23-Aug-12 10:25 PM by grnzbra

Springfield, US
          

>You also need a very flat clearly printed and high contrast
>target. And this would be start of process for testing the AF
>system.
>
>You shutter speed formula is for the FX or 35mm full frame
>camera. For a DX sensor, you need to adjust the focal length
>for the crop factor.
>

Got one. While one can see approximately where the focus is, there is no point where the picture is crisp. It's soft everywhere. Yet when I take some pictures, it seems that I can sometimes see an area behind the point on which I focused that is sharper than the focus point. For example, in this picture ( http://images.nikonians.org/galleries/showphoto.php/photo/388775/size/big/cat/22196 ), the bug was the point of focus, but it is obvious that the point in focus is the on the flower, about an inch behind the bug. (I know, it's only 1/80th of a second, not 1/200 but I was taking pix of a yellow flower in the sun just before this and the shutter speed was 1/360)

OK. You lost me on the second part. From what I've been reading in forums relative to focus, shutter speed should equal or exceed the focal length. I set the focal length as high as it will go much of the time because I am shooting small things like flowers, or rather the small pollen stalks within the flowers. What is "crop factor" and how should it be related to focal length?

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Skyco Silver Member Nikonian since 12th Mar 2012Fri 24-Aug-12 01:40 PM
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#6. "RE: Where is the focus?"
In response to Reply # 5
Fri 24-Aug-12 03:46 PM by Skyco

Roanoke Island, US
          

I think that the real issue is that the 18-200 3.5-5.6 G DX is not a very sharp lens. My experience with that lens is that is not capable of the critical detail that you seem to be looking for.

I have been very disappointed with my 18-200 at 18 and 200mm, and especially macro at 200mm. The in-between focal lengths and distances can be ok especially at f/8. I read a post by a Nikonian team member a few months ago that the 18-200 NIKKOR lens was not as good optically as the 18-55 or 55-200 "kit lenses" so I tried some macro shots of a cone flower with the 18-55 and had fine detail in the flower that the 18-200 only had fuzzy edges with. I used manual and auto focus with both lenses on a D3100.

Try those same shots you had with the 18-55 "kit lens". The 18-55 focuses very close and will reveal detail in the photo that the 18-200 can't come close to.


I hope this helps.

Well Wishes,

Ken

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"Humans don't rise to the occasion. Instead, we fall to our level of training and experience". Archilochus, a Greek soldier and poet.
The best photo advice I ever received was at a John Shaw workshop. "... Practice your craft... ... Pixels are free...Practice... experiment with your camera".

  

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pjonesCET Gold Member Nikonian since 11th Jul 2011Fri 24-Aug-12 02:23 PM
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#7. "RE: Where is the focus?"
In response to Reply # 3
Sat 25-Aug-12 11:51 PM by pjonesCET

Martinsville, US
          

One issue I see is the bright light in the background.The camera is using that light to select camera speed or aperture. neither of what it should be doing. You never want the background light be brighter than the light in front. With one possibel exception

Your outside in bright sun light and the subject is standing in front of tree with lots of shade. In that case you need fill flash but it should never be bright than what you use in front. else you will always get these washed out pictures. I've tried and everytime the background was brighter than the foreground I always get pictures that look like this.

Phillip M Jones, CET
pjonescet@comcast.net
http://www.phillipmjones.net/

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pjonesCET Gold Member Nikonian since 11th Jul 2011Fri 24-Aug-12 02:37 PM
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#8. "RE: Where is the focus?"
In response to Reply # 5
Fri 24-Aug-12 02:42 PM by pjonesCET

Martinsville, US
          

In this picture you actually fouses on part of the flower to theft of the butterfly.

You need to change theFocus setup so that focus in this pattern

•-----•-----•
•-----------•
•-----*-----•
•-----------•
•-----•-----•

Hard to draw exactly (i needed to add dashes to space everything corect)
you need to set so that the center item is chosen

Here is an example using my camera:



Phillip M Jones, CET
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http://www.phillipmjones.net/

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gkaiseril Gold Member Nikonian since 28th Oct 2005Fri 24-Aug-12 03:00 PM
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#9. "RE: Where is the focus?"
In response to Reply # 5


Chicago, US
          

Maybe we need to step back to some very basic concepts.

A Prime lens is a fixed focal length lens and is optimized for sharp focus, corona aberration, and other lens properties.

A Zoom lens tries to cover a number of various focal lengths and has a sweet focal length for which the majority of lens properties are optimized and only acceptable at other focal lengths.

If you want to shoot Macro, it is best to use a prime lens designed for macro work. If you must use a zoom lens, then find the best focal length for that lens and use that length. So setting the focal length to the largest or smallest value may put your lens at the end of the reasonable results.

Focusing in a Macro mode is different than in the macro mode. In the Macro mode the lens focal length determines the magnification and the camera to object adjust the focus. That is why there are focus rails for serious macro shooters. You might want to switch to manual focus.

Another point to consider is that Macro images are magnified from the Macro image and camera shake, mirror slap, or any camera movement is magnified. So you either need a very good tripod and remove all sources of movement or have a very good VR lens and very good hand holding technique along with breath control.

If you look at the meta data for images shot with a prime lens you will see a tag for the "Effective focal length" as well as the "focal length". If you put a 50nn focal length lens on a D4 the values for these tags will be the same. If you put that same 50mm lens on your D5100, the focal length will be 50mm but the effective focal length will be 75mm. If you were to look through the viewfinder, you would see that the D5100 showed less of the scene than the D4 would show. And the amount less would be more than the 5% difference in the viewfinder. See "Field of View Values for Common Focal Lengths" And if you printed the captured images you would see that the D5100 only captured the 50% center section of the D4 image. The effective focal length is a means of comparing a 35mm size sensor to a different sized sensor for the users of 35mm film cameras. And since the original digital cameras had a sensor smaller than the 35mm cameras, it was referred to as the "crop factior".

George
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grnzbra Silver Member Nikonian since 28th Sep 2011Sat 25-Aug-12 01:11 AM
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#10. "RE: Where is the focus?"
In response to Reply # 6


Springfield, US
          

>I think that the real issue is that the 18-200 3.5-5.6 G DX
>is not a very sharp lens. My experience with that lens is
>that is not capable of the critical detail that you seem to be
>looking for.
>

Well that really sucks considering it's an eight hundred plus dollar lens.

>
>I have been very disappointed with my 18-200 at 18 and 200mm,
>and especially macro at 200mm. The in-between focal lengths
>and distances can be ok especially at f/8. I read a post by a
>Nikonian team member a few months ago that the 18-200 NIKKOR
>lens was not as good optically as the 18-55 or 55-200
>"kit lenses" so I tried some macro shots of a cone
>flower with the 18-55 and had fine detail in the flower that
>the 18-200 only had fuzzy edges with. I used manual and auto
>focus with both lenses on a D3100.
>
>Try those same shots you had with the 18-55 "kit
>lens". The 18-55 focuses very close and will reveal
>detail in the photo that the 18-200 can't come close to.
>
>
>I hope this helps.
>
>Well Wishes,
>
>Ken

Your right! This pic ( http://images.nikonians.org/galleries/showphoto.php/photo/388947/size/big/cat/22196 ) was taken with the 18-55 kit lens. I was focused on the tip of the blue plant and expected to see something an inch down from the top in focus. But that tip is really there.

But why? As I understand it, the light comes in the lens and most of it is reflected up to the eyepiece. The rest of it, since the mirror lets some of the light through, goes to anoter mirror behind the main mirro and at a 90 degree angle and is reflected down to the focusing sensor on the floor of the camera. When the picture if focused, the sensor tells the lens to stop focusing. If the distance the light travels between the back of the lens and the focusing sensor is not exactly the same as the distance it travels between the back of the lense and the imaging sensor, the focus will be wrong. If there is something wrong, how is changing the lens going to affect this. If the focus is right, how is a different lens going to mess it up? What does the lens have to do with any difference between these two distances?

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Skyco Silver Member Nikonian since 12th Mar 2012Sat 25-Aug-12 11:51 PM
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#11. "RE: Where is the focus?"
In response to Reply # 10


Roanoke Island, US
          

>But why? As I understand it, the light comes in the lens and
>most of it is reflected up to the eyepiece. The rest of it,
>since the mirror lets some of the light through, goes to
>anoter mirror behind the main mirro and at a 90 degree angle
>and is reflected down to the focusing sensor on the floor of
>the camera. When the picture if focused, the sensor tells the
>lens to stop focusing. If the distance the light travels
>between the back of the lens and the focusing sensor is not
>exactly the same as the distance it travels between the back
>of the lense and the imaging sensor, the focus will be wrong.
>If there is something wrong, how is changing the lens going to
>affect this. If the focus is right, how is a different lens
>going to mess it up? What does the lens have to do with any
>difference between these two distances?

I think that we are talking about two different things, image quality of the lens and Auto Focus.

IMAGE QUALITY: I think its the quality of the lens glass - placement of the lens elements I don't know - Like you said it sucks. We would expect more from an $800 lens. It doesn't affect the focus of the camera, its just that at some (maybe many) focal lengths and distances the 18-200 lens is not very sharp (your question "Where is the focus"). There are quite a few photos that I took with that lens which I have been very disappointed with and kept thinking it was me or the camera.

AUTO FOCUS and what may have pulled your camera's auto focus: Items of high contrast near your intended subject of focus can influence your camera's auto focus. In your first photo of the flower from your earlier post, I think what happened there was that the brighter light and difference in contrast pulled the focus to the flower pedals behind the part of the flower you intended to focus on.

Sometimes manual focus works better when there are items near your intended target that have greater contrast, or moving to get a darker background. Earlier this summer I was photographing day lilies and to get the front for most stamen and the others behind in focus, I had to use manual focus because the camera kept shifting focus to the stamens that were closer into the flower (more contrast) and I wanted to keep a wider aperture to keep the background out of focus.

Looking at that flower and the petals "in focus" in your earlier photo the 18-200 still did not produce a crisp fine image of the detail on those pedals. I am amazed at the detail that the 18-55 and 55-200 "kit lenses" show, and bummed that I spent $800 on a lens that I have been more often than not disappointed in.

Well Wishes,

Ken

Visit my Nikonians gallery.



http://www.flickr.com/photos/skyco_g/

"Humans don't rise to the occasion. Instead, we fall to our level of training and experience". Archilochus, a Greek soldier and poet.
The best photo advice I ever received was at a John Shaw workshop. "... Practice your craft... ... Pixels are free...Practice... experiment with your camera".

  

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Stonecherub Silver Member Nikonian since 03rd Jan 2011Sun 26-Aug-12 02:41 AM
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#12. "RE: Where is the focus?"
In response to Reply # 7


Tucson, US
          

Ditto on the 18-200 mm Nikkor coke-bottle. My lens is awful. I knew that there would be some compromises in a lens of that focal length range but I work in the desert and wanted to mate the lens to the body and never have to change it, particularly in the field.

I'm a geologist taking pictures of volcanoes. In some of my images, the distant mountains are so soft, I could fall on them without injury. I have been bitterly disappointed with this lens and it has colored my respect for Nikon.

I am going to get another lens when I can afford it.

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gkaiseril Gold Member Nikonian since 28th Oct 2005Sun 26-Aug-12 05:03 PM
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#13. "RE: Where is the focus?"
In response to Reply # 12


Chicago, US
          

Nikon publishes a lot of technical information about its products. It makes cameras and lenses for the entry and consumer markets as well as the professional markets.

As noted all zoom lenses are compromises and the more the difference between the focal lengths, the greater number of compromises are made.

There are also a number of outside factors that can affect the quality of an image.

George
My Nikonian Galleries

  

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grnzbra Silver Member Nikonian since 28th Sep 2011Sun 26-Aug-12 11:34 PM
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#14. "RE: Where is the focus?"
In response to Reply # 13


Springfield, US
          

Thank you everyone. Your suggestions have been extremely helpful. I've gone to using the 24-55 lens for macro work and have even started to get the hang of using the 18-200. I backed it off to somewhere below 135mm and pix of the bird feeder seem a lot sharper.

Oh, and one other thing if found today is that for macro, a tripod is a must. I shot a lot of pix and found that due to the almost nonexistant deapth of field, even at f/11, my body motion when in an awkward position can move the focused subject outside the deapth of field and blow a really good shot.

Again, thank you all.

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