blue dot phenomenom

Started 8 months ago | Questions
twelvebellys
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blue dot phenomenom
8 months ago

Strange blue dots have appeared in some of my photo's whentaking shots at night , it seems to come from a certain type of exterior light , I 'n not sure if the light is a halogen light but my photo's seem ok with led and sodium lighting . what can I use to stop this happening .

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Nikon D5200 Olympus M.Zuiko Digital ED 12-50mm 1:3.5-6.3 EZ
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RaymondR
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Re: blue dot phenomenom
In reply to twelvebellys, 8 months ago

Post a specimen of the issue please.
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RaymondR

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steelhead3
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Re: blue dot phenomenom
In reply to RaymondR, 8 months ago

In Sony land, we call that Zeiss.

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twelvebellys
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Re: blue dot phenomenom
In reply to RaymondR, 8 months ago

It only happpens with a couple of lenses

theres a blue dot here  , I was just seeing which lenses work and which don;t

This is an old praktica b 35 - 70 lens mc coated its not great

They are more obvious with a 28mm carl zeiss jena , is this the lens. the dot moves with the lens

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twelvebellys
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Re: blue dot phenomenom
In reply to twelvebellys, 8 months ago

these are they the blue rings and dots

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AuroraProject08
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Re: blue dot phenomenom
In reply to twelvebellys, 8 months ago

Looks like lens flare to me. Odd that its only with certain types of lighting.

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Leonard Migliore
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Re: blue dot phenomenom
In reply to twelvebellys, 8 months ago

Do you have a UV filter on that lens? It looks like a reflection of a bright light off the sensor and then back from the flat filter surface.

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Leonard Migliore

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Mark Scott Abeln
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Re: blue dot phenomenom
In reply to twelvebellys, 8 months ago

I'd say that is lens flare, which is very common, but…

I've never seen flare quite like that — and especially that color. I suspect there are a number of factors contributing to this.

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twelvebellys
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Re: blue dot phenomenom
In reply to Leonard Migliore, 8 months ago

Leonard Migliore wrote:

Do you have a UV filter on that lens? It looks like a reflection of a bright light off the sensor and then back from the flat filter surface.

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Leonard Migliore

No  there are no filters employed on the lens I could  get a uv filter or lens hood for these lensesit seems to affect mostly my 28mm carl seiiss 35- 70 mm praktica zoom but not my 50mm m. zuiko and they are all multi coated lenses.

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Barrie Davis
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Re: blue dot phenomenom
In reply to twelvebellys, 8 months ago

twelvebellys wrote:

It only happpens with a couple of lenses

theres a blue dot here  , I was just seeing which lenses work and which don;t

This is an old praktica b 35 - 70 lens mc coated its not great

They are more obvious with a 28mm carl zeiss jena , is this the lens. the dot moves with the lens

It is only to be expected... you have light sources in frame, and a dark background for the flares
to show up against.

Modern lens coatings can make the flares less noticable.... even mask them completely.

If you are using a UV filter, take it off, as filters make light-source flares more likely, especially if the filter in question is UN-coated.

And use a lens hood.... (remember, to be efficient on APS crop the lens hood needs to be DEEPER than the one originally supplied for use with 35mm film.)

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sherwoodpete
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Re: blue dot phenomenom
In reply to Mark Scott Abeln, 8 months ago

Mark Scott Abeln wrote:

I'd say that is lens flare, which is very common, but…

I've never seen flare quite like that — and especially that color. I suspect there are a number of factors contributing to this.

I guess the colour is a result of anti-reflective coatings. All modern lenses have such coatings, which suppress most, but not all reflections. The light which is not suppressed gives rise to reflections of various colours when one looks at the lens.

In this case, since the light has a consistent blue colour, it probably has a common cause, which presumably is light reflected back from the surface of the sensor, or the filter immediately in front of the sensor. In order for that reflected light to be visible in the picture, it must then reflect back down to the sensor, from some elements of the lens (or in other cases, from an attached UV filter).

The reason why it is visible in these types of shots is the extremely high contrast ratio between the darker areas of the subject, the very bright light source. The same light path must be possible with all types of subject, but normally it would be so weak as to be negligible.

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twelvebellys
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Re: blue dot phenomenom
In reply to Barrie Davis, 8 months ago

Barrie Davis wrote:

twelvebellys wrote:

It only happpens with a couple of lenses

theres a blue dot here , I was just seeing which lenses work and which don;t

This is an old praktica b 35 - 70 lens mc coated its not great

They are more obvious with a 28mm carl zeiss jena , is this the lens. the dot moves with the lens

It is only to be expected... you have light sources in frame, and a dark background for the flares
to show up against.

Modern lens coatings can make the flares less noticable.... even mask them completely.

If you are using a UV filter, take it off, as filters make light-source flares more likely, especially if the filter in question is UN-coated.

And use a lens hood.... (remember, to be efficient on APS crop the lens hood needs to be DEEPER than the one originally supplied for use with 35mm film.)

-- hide signature --

Regards,
Baz
:
"Ahh... But the thing is, these guys were no ORDINARY time travellers!"

I was thinking of a lens hood so might be whats needed.

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sherwoodpete
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Re: blue dot phenomenom
In reply to twelvebellys, 8 months ago

twelvebellys wrote:

I was thinking of a lens hood so might be whats needed.

A lens hood can solve issues caused by light sources outside the picture area. If you include a light source in the picture itself, the lens hood cannot help (though it should not do any harm).

So, yes, use a lens hood, but don't expect it to be a complete solution when it is the choice of subject which is the actual cause.

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hotdog321
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Re: blue dot phenomenom
In reply to sherwoodpete, 8 months ago

A bit of education for anyone who is interested:

As others have said, this is lens flare. All lenses have this problem to some extent, though some display almost no flare due to superior manufacturing and exotic lens elements/coatings.

Zoom lenses are generally more prone to flare than fixed focal length lenses because they have many more optical elements inside the lens. Getting rid of any filters can help, too.

A lens hood will not help with photos where the hot spot is directly in the frame. But you should always use a lens hood, anyway. They minimize flare from sources just outside the frame, add contrast, and provide terrific impact protection. Quite the bang for the buck!

One last trick if you must have a hot light in the frame. Arrange the shot so the flare appears directly on top of the hot spot instead of a dark area of the picture.

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twelvebellys
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Re: blue dot phenomenom
In reply to hotdog321, 8 months ago

Thanks  thats helpful .:-)

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Carsten Pauer 2
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Re: blue dot phenomenom
In reply to twelvebellys, 8 months ago

what can I use to stop this happening .

Test some more Lenses with better Coatings...

Worst Case Scenario.

Regards: Carsten

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Dr JLW
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Re: blue dot phenomenom
In reply to hotdog321, 7 months ago

The explanation is correct but the terminology is a bit off.

Flare is scatter around a bright object.  Wheat we are seeing is a "ghost".  The strong source is being reflected from several surfaces but most likely the sensor.  The reflected light then reflects against from a surface concave towards the sensor plane and forms an image.

They show up in either sun images of lights at night as the others ahve stated.  Anti reflection coaiting typically limit the reflection to a few tenths of a percent but when you have a lamp about 10,000 times brighter than the background the ghosts come out and can be seen.

Before AR coatings avoiding ghosts was a major headache in lens design.  Correction, particuarly of spherical aberration strongly favors surfaces concave towards the sensor and light reflected from the sensor, typically a few percent, can be reflected again by one or more of these surfaces (as the sun image shows).  Once you have a source more than ten thousand time the background ghosts start to appera.

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