blue patch in the middle of image frame

[fidelreblando]

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shooting details:
f9
iso 100
speed 125
nikon d90 - 50mm lens


hi digital photographers.
i am puzzled at this image i took at our studio, it has blue patch in the center of the frame.i am thinking its because of my lighting setup because if i turned off the backlight the blue patch disappears.another 50mm i attached also shows the same patch.but heres the thing, if used 18-135mm lens i get good image without the patch.

heres the image i took using 18-105mm lens @ same settings and lighting setup.


can anyone enlighten me where i am going wrong, in my lighting setup or the lens i am using.
thanks.

[Nelson Yu]

Someone correct me if I am wrong, but I think what you are experiencing if not lens flare it is called Lens COMA. The reason why when you use the 18-105mm the blue patch disappears is because of the shape of the lens' optical elements. Read more about Lens COMA, this could be the answer for your question.

[fidelreblando]

ok i will.thanks.
my image did not attached with the post, i uploaded it at flickr.ill try to upload using other image hosting site.

[fidelreblando]

(Not linked)

heres the link to the image i uploaded.
please do leave comments.

[fidelreblando]

the link still didnt work.sorry i havent use the site for a long time.
heres the link.

[Nelson Yu]

It looks like lens glare than Coma. Were you using a lens hood? If you are then, try to reposition your light, some of the lights are bouncing off the white wall and hitting the lens. See if this works.

[fidelreblando]

yes i do have lens hood.the patch disappears if i turn off the back light or use honey comb.what confuse me is if i use 18-105 or 18-135 i didnt get that blue patch in my picture.i had another experience with 50mm in a color background, sort of lens flare, a color patch in the hair of my subject, probably coming from the hair light.that patch also disappear when i use 18-105mm lens.
i am thinking the 50mm lens would not do for the lighting i am using.

[Nelson Yu]

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yes i do have lens hood.the patch disappears if i turn off the back light or use honey comb.what confuse me is if i use 18-105 or 18-135 i didnt get that blue patch in my picture.i had another experience with 50mm in a color background, sort of lens flare, a color patch in the hair of my subject, probably coming from the hair light.that patch also disappear when i use 18-105mm lens.
i am thinking the 50mm lens would not do for the lighting i am using.

Most likely, the reason why variable focal length don't get this blue patch is because of the shape and the number of elements inside the body of the lens. Primes have significantly less of elements because there is only one focal length. Since you have a white wall, some of those lights bounce and is hitting the lens thereby creating that glare. If it was a lens COMA, the shape would be like a keyhole. Lens flare will look like rings to circular patches.