Need help solving mystery

[RadarContact]

I cannot for the life of me figure out what this large purple dot is in the center of this picture.

WINNIPEG Flickr - Photo Sharing

I took 3 photos in total and all 3 have the same purple dot. I wanted to take a perfect picture so I'm concerned this is an error on my part. There are no spots on the lens and other photos of different things turn out fine.

Thanks!

 

[tecboy]

Looks like a lens flare. Are you using an UV filter?

 

[RadarContact]

No lens filter.

 

[tecboy]

You are going to have to try different vantage point. It is usually normal depending on what kind of lenses. Have a lens hood that would sometimes helps.

 

[Light Guru]

I don't see any large purple dot in the center of the image.

 

[qleak]

It looks like it's either flare or something on the front of the lens to me.

 

[tecboy]

There is a fainted purple spot or looks like a smear. May have to adjust your monitor or calibrate.

 

[Derrel]

It is a pretty well-known optical issue, which is seen off and on. It used to be referred to as "the red dot problem" or "the red dot issue"; this is caused by the light that is passing through the exit pupil of the lens, causing an internal reflection/imaging off of the sensor. Some lenses suffer from this quite often. Nikon's 50/1.8 AF and AF-D, and Tamron's older 90mm AF-SP for example, but other lenses as well. On older cameras, like the Kodak 14n digital SLR, the red dot issue was a HUGE problem.

Lens designers have optimized the designs in a number of newer lenses released over the past decade or so, in an effort to minimize the occurrence of this issue. And no, I am not kidding you, this is a real issue. In this sample, it's subtle, but it *is* there.

 

[RadarContact]

Thank you so much for the explanation. I was wondering if you can tell if the photo below suffers from the same issue?

WINNIPEG Flickr - Photo Sharing

I noticed two purple-ish dots under the bridge.

Thanks,

 

[480sparky]

Lens flare.

 

[Derrel]

Thank you so much for the explanation. I was wondering if you can tell if the photo below suffers from the same issue?

WINNIPEG Flickr - Photo Sharing

I noticed two purple-ish dots under the bridge.

Thanks,

The two small purple areas under the bridge are just regular old lens flare; one of the main aspects of the red dot issue is that it is always right in the center of the image area...it's caused by the light exiting the exit pupil of a lens and causing a "hot spot" on the front of the AA-filter array, or on the central area of the sensor in cameras that do not have an anti-aliasing filter array. The red dot issue was a problem with a fair number of older, pre-digital lenses. After digital capture became almost the only way most people were using still photography lenses, there was a major effort to come up with new lens designs that were more "telecentric" (another,separate issue entirely), and which also were less prone to this type of a faint ghosting of the lens' exit pupil. Moving the positioning of the exit pupil a bit farther forward, farther toward the center of the lens, is one design response I've read about from Thom Hogan's site. Some lens makers, like Tamron as one example, introduced new specifications to acknowledge their new Di or Digitally Integrated lens design efforts, I think in large part because their 90mm AF-SP was one of the worst offenders...and also one of their most-successful single model lenses...I own an older 90 AF-SP, and it WILL give the red-dot problem on the Nikon D2x, especially when used in a darkish studio with a lot of light bouncing around.

The red dot issue is most visible when there are strong, bright light sources in the scene, and when what is called the field is mostly dark; night time shots are a perfect example of where it's super-easy to see the red dot issue. The red part of red dot issue was mostly on the Kodak 14n,where it was often a bright reddish-orange colored splotch; on that, specific camera was where this issue was REALLY a big, big deal.