Where is the dust on my sensor?

stormcrow

stormcrow

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Dale
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I've just been cleaning my sensor and in the process of doing so I again got a bit confused as to the actual position of the dust specs on my sensor.

I'm never sure if the image we see is just flipped vertically or if it is flipped vertically & horizontally.

In an effort for me to get this once and for all into my head I have hopefully created an easy to understand example.

The first image is what I would see on a photograph. There are 2 specs of dust A & B what I would like to know is when I am looking into my camera directly at the sensor where are these specs of dust is it image 1 or 2?

Thanks

dustposition.jpg
 
I've been looking into this again after long session of cleaning my sensor yesterday.
Why is it that I always get it 98% clean on my first go but then on my next go trying to get that other 2% I end up with it looking worse than when I started :)
I know I should just stop at 98% clean but the voice in my head says go on one more go should do it :lol:

This article says that the correct position of the dust would be Image 1
http://www.copperhillimages.com/index.php?pr=Tutorials5

Does anyone else have opinions as to which is correct image 1 or 2?
 
2
 
fracster said:
2
Click to expand...

That is what I initially thought but the copperhill tutorial says that the image is only flipped vertically so that would be the same as image 1 in my examples as image 2 is flipped vertically and horizontally.

fxcYz.jpg


"First, determine exactly where the speck(s) is located by using the "up/down" or "one vertical flip" alignment. This means that if your speck is in the upper left of your image, it is actually sitting on the lower left of your sensor AS YOU LOOK AT IT from the front of the camera. Similarly, if it's in the lower right of your image, it's actually sitting on the upper right of your sensor AS YOU LOOK AT IT. Upper center of the image, lower center of the sensor, etc., etc. One vertical flip"

I've ordered a Sensor loupe so that will hopefully help me locate the little bu**ers better.
 
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If you get yourself a sensor loupe it will take out all the guesswork.

Realspeed
 
Answer 2.

If you take a bare lens and focus an image on to a piece of paper, you'll see it is both upsidedown and reversed left to right.
 
HoppyUK said:
Answer 2.

If you take a bare lens and focus an image on to a piece of paper, you'll see it is both upsidedown and reversed left to right.
Click to expand...

I've just done that and it is most definatley number 2 that is correct, thanks for the idea.
So the Copperhill site is talking bo**ocks then, you would have thought they should have got something like that right.
 
Bet you find others with the Loupe you didnt get as well ;-)
 
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Definately 2. The lens does not know vertical from horizontal and behaves the same in both planes.
 
Ozei said:
See posts 3 & 6 here http://photography-on-the.net/forum/showthread.php?t=104968. Copperhill are correct.
Click to expand...

They're not, or at least the quote on POTN is wrong. Image #2 is correct. Do the check suggested above - a bare lens focusing an image on a sheet of paper - and it cannot be otherwise.

There's a lot of confusion about this on the web if you search, I think maybe because right becomes left when you imagine things from the back of the camera, and then look at it from the front. But just forget that and observe how the lens presents the image.
 
HoppyUK said:
They're not, or at least the quote on POTN is wrong. Image #2 is correct. Do the check suggested above - a bare lens focusing an image on a sheet of paper - and it cannot be otherwise.
Click to expand...

I would have to agree with HoppyUk, I did the test as he suggested and the projected image was flipped vertically and horizontally. So if you replace the white paper for the sensor the top right becomes bottom left on the sensor.
I didn't realise there were so many different opinions on this when I asked.
I must admit I thought there would have been more info on this on the web particularly from the people selling sensor cleaning gear.
 
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It's certainly a conundrum :thinking: but I've tried the lens & paper test and I still think Copperhill are correct - i.e. image 1 is the answer.

Here's what I did:
  • Sit in an upright position at a desk.
  • Point a steerable halogen desk lamp (like this one http://www.whsmith.co.uk/CatalogAndSearch/ProductDetails.aspx?productID=32920703) straight towards your face.
  • Place a sheet of paper in the vertical plane between your eyes and the desk lamp - clamp/support the paper in this position.
  • Hold a lens between the lamp and the paper and adjust position of the lens so that the image of the lamp is in focus on the paper - clamp/support the lens in this position.
  • You are now looking through the paper towards the lamp.

  • Draw a T with a felt pen on the top left corner of the lamp glass (top left as viewed from where you're sitting).
  • Look at the paper and the image of the T should be upside-down in the bottom right (viewed through the paper from where you're sitting) - i.e. the lens has flipped the image vertically and horizontally.
  • Now walk round and look at the other side of the paper (the side nearest the lamp) - the image of the T is still upside-down but it's now bottom left.
In this analogy the T is the dust bunny and the piece of paper is the camera's sensor. Looking at the sensor from the lens mount side, the dust bunny is upside-down bottom left - i.e. as per image 1.

NB. The whole exercise is much more fun if you've got a glamorous assistant to position the paper and lens. :lol:

NB2. I have had a few beers. :lol::lol:
 
PS. If you don't have a glamorous assistant, a small child-slave will suffice. :lol:
 
Ozei said:
It's certainly a conundrum :thinking: but I've tried the lens & paper test and I still think Copperhill are correct - i.e. image 1 is the answer.

Here's what I did:
  • Sit in an upright position at a desk.
  • Point a steerable halogen desk lamp (like this one http://www.whsmith.co.uk/CatalogAndSearch/ProductDetails.aspx?productID=32920703) straight towards your face.
  • Place a sheet of paper in the vertical plane between your eyes and the desk lamp - clamp/support the paper in this position.
  • Hold a lens between the lamp and the paper and adjust position of the lens so that the image of the lamp is in focus on the paper - clamp/support the lens in this position.
  • You are now looking through the paper towards the lamp.

  • Draw a T with a felt pen on the top left corner of the lamp glass (top left as viewed from where you're sitting).
  • Look at the paper and the image of the T should be upside-down in the bottom right (viewed through the paper from where you're sitting) - i.e. the lens has flipped the image vertically and horizontally.
  • Now walk round and look at the other side of the paper (the side nearest the lamp) - the image of the T is still upside-down but it's now bottom left.
In this analogy the T is the dust bunny and the piece of paper is the camera's sensor. Looking at the sensor from the lens mount side, the dust bunny is upside-down bottom left - i.e. as per image 1.

NB. The whole exercise is much more fun if you've got a glamorous assistant to position the paper and lens. :lol:

NB2. I have had a few beers. :lol::lol:
Click to expand...

I'm so sorry guys, I'm wrong :nuts: I've contradicted my own explanation, and it's taken a guy with beer goggles to point it out LOL

The correct answer to the question as posed by the OP is #1. A dust bunny appearing in the scene top left, is on the sensor bottom left, when "looking directly at the sensor in the camera" through the lens mount.

Many apologies :bonk:
 
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Bet this thread confuses the hell out of anyone wanting to know the location of dust on their sensor, :lol: I know I have gone through several answers up to now.

Finally thanks to the perseverence of Ozei and his assistant beer the penny is begining to drop. :) I've done the lens test again it seems so obvious now!!!!
Ok my final descision is the copperhill site is right so image 1 is correct.
Even if I change my mind again I'm not going to mention it :)

jOd2m.jpg

My Sensor loupe has just arrived and it works great (once I worked out not to use my reading glasses). Now I need some dust wish I hadn't cleaned the sensor now, I'm sure some will be along soon though.
 
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For the immage to be transposed up top to bottom but not left to right your lenses would have to be either a cylinder or a flattened cylinder. As they are spheroid they WILL exhibit the same behaviour left to right as they do top to bottom. How on earth can they not?

Answer two is correct.
 
Oggy said:
For the immage to be transposed up top to bottom but not left to right your lenses would have to be either a cylinder or a flattened cylinder. As they are spheroid they WILL exhibit the same behaviour left to right as they do top to bottom. How on earth can they not?

Answer two is correct.
Click to expand...

Read the question, consider the options, then apply your own explanation. The answer will be #1.
 
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