50mm f1.8D question...

Horoscope Fish

Horoscope Fish

Senior Member
alfaholic said:
A friend asked me to shoot him while practising, so I brought my D7000 and 50mm f1.8D.

Here is just one of over 400 photos I made today:

Download BBA_7909.NEF from Sendspace.com - send big files the easy way

You can see some strange halo around my subject. Does anyone know what is this about?
Click to expand...
That's "chromatic aberration". It happens, typically, in areas of very strong contrast and some lenses are more prone to creating it than others. Good post-processing software can remove most, if not all, chromatic aberration, usually. The CA in that particular shot is going to be tough to remove because it's so diffuse. The CA that I've had to deal with has been sharper and more clearly defined which makes it easier for the software to detect and correct automatically.

....
 
4

480sparky

Senior Member
Looks more to me like there's moisture condensed on the front element of the lens.

Shooting wide-open doesn't give you the sharpest images either. You could easily bump your IOS up to 400 or 800 on a D7000 and get your aperture down to 4 or 5.6 and still have no noise issues.
 
A

aroy

Senior Member
There is definitely a halo around the white areas. I examined the image in View NX, and find that there are a lot of blow highlights. The CA may be due to excessive exposure.

I then opened the image in Capture NX-D and got rid of the purple fringe using colour aberration under lense correction, but the halo remained. That is due to electrons over flowing after the sensel well is full. The width of the halo gives a fair indication of the amount of over exposure.

Examining the image here are my thoughts
. exposure is F1.8, 1/4000, ISO 100. The exposure could be reduced by at least 3 stops - in this case F2.8 or F4.
. Matrix exposure was used, center weighed would give better exposure control, else when so much white is there try bracketing at -1, -2 and -3 EV to get the optimum exposure.
. The width of max brightness (on the sleeve of the arm holding racket) is approximately 10 pixels, about the same as the halo, which points to a massive over exposure.

With high DR of the current sensors, It is better to meter so that the brightest portions are not blown. Shadows are easily recovered, but blow highlights are BLOWN and lost.
 
Last edited:
Top