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Light fall-off because of the CCD?

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Tri-Elmar

Tri-Elmar

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I shot this photo of the sky with the kit lens at 50mm and f/16 (all photos exaggerated with Photoshop auto levels so it's easy to judge)



...and my reaction was that the kit lens had lots of light fall-off.

Then I shot the following photos with a 45/2.8 MF lens at f/2.8 f/5.6 f/11 and f/16









What we can see is:

1) There is the same light fall-off with this lens too. But this lens is a full frame MF lens and we should not be able to see any light fall-off at all, since the circle of the image of the lens is much bigger than the frame, am I wrong?

2) There is no difference from f/2.8 up to f/16 and I know that light fall-off is eliminated by stopping down a couple of f/stops.

So, is this result because of the CCD? Maybe it is because of the angle of the light falling at the down corners of the CCD? What is it anyway?

Please can you check with your camera and lens? Just shoot a clear sky at -say- f/8 and then use auto levels in Photoshop to see what is going on? Or if I am missing something can you please explain to me all these?
 
Yes, it probably is due to the CCD. Read Joe Wisniewski's page about digital lens design and you'll see that short focus lenses for 35mm cameras are not ideal for digital cameras:
http://swissarmyfork.com/digital_lens_faq.htm
Tri-Elmar said:
I shot this photo of the sky with the kit lens at 50mm and f/16
(all photos exaggerated with Photoshop auto levels so it's easy to
judge)



...and my reaction was that the kit lens had lots of light fall-off.
Then I shot the following photos with a 45/2.8 MF lens at f/2.8
f/5.6 f/11 and f/16









What we can see is:
1) There is the same light fall-off with this lens too. But this
lens is a full frame MF lens and we should not be able to see any
light fall-off at all, since the circle of the image of the lens is
much bigger than the frame, am I wrong?
2) There is no difference from f/2.8 up to f/16 and I know that
light fall-off is eliminated by stopping down a couple of f/stops.
So, is this result because of the CCD? Maybe it is because of the
angle of the light falling at the down corners of the CCD? What is
it anyway?

Please can you check with your camera and lens? Just shoot a clear
sky at -say- f/8 and then use auto levels in Photoshop to see what
is going on? Or if I am missing something can you please explain to
me all these?
Click to expand...
--
http://radio.weblogs.com/0101365/categories/photos/
 
Don't do autolevels. It tries to find the black point and the white point and will set the contrast so high as to find black in the corners enen though it may not be bad.

There is a scripture about having a mote in your eye. Do you know you have a big piece of dust on your CCD? We can see it, can you?

--
TANSTAAFL - There aint no such thing as a free lunch.
If it sounds too good to be true it just might be so.
D70 Owner
 
Do you also test your new car for leakage on the bottom of a swimming pool?

my honest advice: make pictures and be happy with the beautiful -visible!- results instead of hunting along the edge trying to force odd invisibilities being visible. Like me, you will enjoy your new camera.

Paules
 
We do make pictures, Paules.
( Please check: http://www.jordan.gr )

But this doesn't mean that we should ignore hardware problems when we notice them, isn't it?
paules said:
Do you also test your new car for leakage on the bottom of a
swimming pool?

my honest advice: make pictures and be happy with the beautiful
-visible!- results instead of hunting along the edge trying to
force odd invisibilities being visible. Like me, you will enjoy
your new camera.

Paules
Click to expand...
 
Actually, I have noticed vignetting on real life photos with the kit lens, in some cases quite strong (70 mm wide open). I didn't crank up the auto levels on purpose, it just so happened. Stopped down to 5.6 it's OK below 50 mm. At 50 - 70 mm, you have to stop down to f8 to get rid of it. Likely, it matters only on very even subjects.

See here

http://forums.dpreview.com/forums/read.asp?forum=1034&message=9617562

and here

http://forums.dpreview.com/forums/read.asp?forum=1034&message=9618730

In your test: the 45 mm is a Tessar based design, renowned for few elements, very good center sharpness and contrast, but prone to vignetting.

There's trade offs everywhere.

MBK
 
Slight vignetting is common to digital and non-digital SLR/lens combos, at least the ones in my range. The cool thing with the D70 is you can fix it with a click in Nikon Capture Editor.
mbk said:
Actually, I have noticed vignetting on real life photos with the
kit lens, in some cases quite strong (70 mm wide open). I didn't
crank up the auto levels on purpose, it just so happened. Stopped
down to 5.6 it's OK below 50 mm. At 50 - 70 mm, you have to stop
down to f8 to get rid of it. Likely, it matters only on very even
subjects.

See here

http://forums.dpreview.com/forums/read.asp?forum=1034&message=9617562

and here

http://forums.dpreview.com/forums/read.asp?forum=1034&message=9618730

In your test: the 45 mm is a Tessar based design, renowned for few
elements, very good center sharpness and contrast, but prone to
vignetting.

There's trade offs everywhere.

MBK
Click to expand...
--
still learning...
 
Can you please make a similar test with your lens as I don't have another lens available? It would be useful to see if there is any difference, so we will know if it is the lens or the CCD.
mbk said:
In your test: the 45 mm is a Tessar based design, renowned for few
elements, very good center sharpness and contrast, but prone to
vignetting.
Click to expand...
 
Sorry, I don't have the 45 mm.

My opinion on the 45 was derived from lens descriptions I have read, and because I have had a tessar based design on a film camera (Yashica T4, it has an excellent and tiny Zeiss Tessar lens). This was a popular "giant killer" P/S in the 90's. I got what I described-superb colors and contrast, very sharp, but easy vignetting.

The one I had was 35 mm; the standard Zeiss Tessar offer for Contax is/was a 45 mm, and the Nikon 45 looks like the spitting image of it. The Tessar has been around as a standard Zeiss design for something like 100 years (conjecture but not far off). It's one of these "elementary" designs. I am sure you can find info on Google on this configuration's characteristics.

MBK
Tri-Elmar said:
Tri-Elmar said:
In your test: the 45 mm is a Tessar based design, renowned for few
elements, very good center sharpness and contrast, but prone to
vignetting.
Click to expand...
Click to expand...
 
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