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Circles of Confusion?
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Dec 4, 2011 16:14:25   #
Adirondack Hiker Loc: Southern Adirondacks
 
pdwoodswood wrote:
Paw Paw Bill wrote:
lesdmd wrote:
Hello Nikonian, would the CoC in this lens present at all apertures to a more or lesser degree as aperture is changed?


Am I the only person who is amazed at how few people read anything but the most immediate posting and/or choose to ignore all previous relevant information?
.


Agree, I know it is five pages, but read them all before posting. I know I do, and think it's the only proper way to post intelligently.


That is precisely why I directed my question directly to Nikonian regarding CoC vs Aperture as I believe as he does that the problem is not spherical abberation but a CoC problem in the lens. Additionally "it was decided"; who decided that as absolute fact? There are numerous posts that are not fact based but posted with current knowledge on board, the very fact that a person "hangs his post out" for critique is educational for all. If a person reads each post as factual then due to his lack of knowledge he becomes confused. Confusion is the first step in seeking the facts and thus learning[/quote]

One final time, CoC has ABSOLUTELY NOTHING TO DO WITH THE LENS, IT IS BASED ON THE SIZE OF THE DETECTOR. YOU CAN TAKE THE LENS OFF, AND THE CoC WILL BE THE SAME. Before using terms, know their meaning.

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Dec 4, 2011 17:09:34   #
Nikonian72 Loc: Chico CA
 
Adirondack Hiker wrote:
One final time, CoC has ABSOLUTELY NOTHING TO DO WITH THE LENS, IT IS BASED ON THE SIZE OF THE DETECTOR. YOU CAN TAKE THE LENS OFF, AND THE CoC WILL BE THE SAME. Before using terms, know their meaning.

A Circle of Confusion is formed on a camera sensor, by a lens. No lens = no CoC.

http://en.wikipedia.org/wiki/Circle_of_confusion
"A circle of confusion is an optical spot caused by a cone of light rays from a lens, not coming to a perfect focus when imaging (on a camera sensor) a point source. It is also known as disk of confusion, circle of indistinctness, blur circle, or blur spot."

"In photography, the circle of confusion (“CoC”) is used to determine the depth of field, the part of an image that is acceptably sharp. A standard value of CoC is often associated with each image format, but the most appropriate value depends on visual acuity, viewing conditions, and the amount of enlargement. Properly, this is the maximum permissible circle of confusion, the circle of confusion diameter limit, or the circle of confusion criterion, but is often informally called simply the circle of confusion."

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Dec 4, 2011 17:14:49   #
pdwoodswood Loc: Lewisville, NC
 
Adirondack Hiker wrote:
pdwoodswood wrote:
Paw Paw Bill wrote:
lesdmd wrote:
Hello Nikonian, would the CoC in this lens present at all apertures to a more or lesser degree as aperture is changed?


Am I the only person who is amazed at how few people read anything but the most immediate posting and/or choose to ignore all previous relevant information?
.


Agree, I know it is five pages, but read them all before posting. I know I do, and think it's the only proper way to post intelligently.


That is precisely why I directed my question directly to Nikonian regarding CoC vs Aperture as I believe as he does that the problem is not spherical abberation but a CoC problem in the lens. Additionally "it was decided"; who decided that as absolute fact? There are numerous posts that are not fact based but posted with current knowledge on board, the very fact that a person "hangs his post out" for critique is educational for all. If a person reads each post as factual then due to his lack of knowledge he becomes confused. Confusion is the first step in seeking the facts and thus learning
quote=pdwoodswood quote=Paw Paw Bill quote=lesd... (show quote)


One final time, CoC has ABSOLUTELY NOTHING TO DO WITH THE LENS, IT IS BASED ON THE SIZE OF THE DETECTOR. YOU CAN TAKE THE LENS OFF, AND THE CoC WILL BE THE SAME. Before using terms, know their meaning.[/quote]

bite me

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Dec 4, 2011 17:26:29   #
Nikonian72 Loc: Chico CA
 
pdwoodswood wrote:
bite me

'Nuf said!

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Dec 4, 2011 17:44:53   #
rayford2 Loc: New Bethlehem, PA
 
Doe wrote:
Adirondack Hiker wrote:
Doe wrote:
Also, in the last pic taken with my D5100, I noticed that the whites look blue. How can I fix that??????

I really appreciate any information or thoughts on these two problems.


Lets start with the last photo, then go to the first. The blue tint is because of an incorrect white balance, set too cold. This is why I never have any of my camera settings in AUTO. If you have Elements, it is an easy fix. Go to correct color cast and click on the shirt, it will turn white. I normally leave my white balance in CLOUDY, and since i shoot in RAW, can fine tune it.

Now the first photo. First off, the circle of confusion has to do with calculating the depth of field, not artifacts on an image. For example, the D5100 has a CoC of 0.02, non full frame Canons are typically 0.018 and a point and shoot about 0.005. The "circles" appear to be overposed patches of light. Because of the f/stop setting, the depth of field is very limited, and they are severely out of focus. If it was a lens problem, the circles would also be on the people, but they are not.

I find it amazing how often the first thing people say, especially beginners, when an image is bad "its the lens", when in fact 99.99% of the time it is pilot error. You spent a lot on the camera and lens, invest another $25 on some good manuals, Amazon has many used in great shape for little cost. Learn the relationship between f/stop and depth of field, the best ISO (normally 200 for your camera), most important how to read the histogram, and set the camera to "blinkies" to show the overexposed regions.
quote=Doe Also, in the last pic taken with my D51... (show quote)


I agree.....my lack of knowledge when it comes to knowing how to use the f/stop, exposures, etc could have caused the circles. The purchase of the D5100 was because I wanted to make taking shots for HDR photos a little easier and the purchase of the Tamron lens was to keep from having to change out my other two lenses so often. I do have several books that I am in the process of reading. The camera, I have had a very short time and had used my other two lenses on it and there have been no issues with little (donut) circles, and because I have limited knowledge about either of these items and no knowledge about all the different effects that can happen using cameras, I was afraid I had a broke $700 lens and I was still in the time frame that I could send it back, no questions asked.

Tamron techs said they had not seen this type of effect and said to send it to them. But I had purchased a third party warranty and figured it would be better to return it to the company I bought it from for them to send a new one. When I sent the same pictures to them, they were the ones telling me about the CoC.

My problem is.......if it's me, I want to keep the lens and learn how to prevent the CoC. But if it is that the lens is broken in some way, I need to send it back. The box it came in was somewhat smashed on one side and that concerned me before I even put it on the camera.

I don't know the answer because I don't have the knowledge that everyone else has.....but when I have a bunch of people divided on what the problem is.....how do I know what is the correct answer to the problem?
quote=Adirondack Hiker quote=Doe Also, in the la... (show quote)


Send the lens back to the Pro's at Tamron like they requested, along with the sample pic Nikonian72 recommended. If it's OK they'll send it back. If not they'll fix it and send it back. You have nothing to lose but a couple of bucks for postage and you'll have peace of mind.
...May the force be with you.

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Dec 8, 2011 14:38:32   #
ALYN Loc: Lebanon, Indiana
 
I would opine that you had your aperture :too open: Your depth of field is too shallow. This is great for portraits, but if you use a smaller aperture, your depth of field will be greater and the circles will disappear.
ALYN

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Dec 8, 2011 22:49:21   #
Doe Loc: N, Augusta, South Carolina
 
Turbo wrote:
I took the liberty to use Photoshop CS4 on the first pic and blurred the background while darkening the left side a bit.

There are other options but this was the easiest...


You did a fantastic job of correcting the problem.....THANK YOU!

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