Light 'fanning' in night shots

[jtfan2004]

I use an Olympus 5050Z and was wondering if the 'fanning' of lights in night shots is normal. Sounds stupid, I know. It only happens if I close the aperture all the way down (f8.0 on the 5050Z). I like the effect, but do not get the same result when done with my 35mm without a filter.

[bobtrips]

I don't know what you mean by 'fanning'. Can you post an example? Maybe one from each medium?

[jtfan2004]

Here is one of my digital images that prompted me to ask:

http://www.pbase.com/image/24952264

I guess what I meant was the 'star light' type effect with streetlights. Unfortunately, I do not have a scanner at the moment, so I cannot post a 35mm example.

Thanks

[bobtrips]

Wow! I haven't seen that before. On the other hand I haven't shot any bright lights.

I have had some stars/rays from points of reflected sunlight in water shots. I don't remember getting similar effects with 35 mm film. My guess is that it might have something to do with the very small aperture (actual aperture, not aperture ratio/f-stop) that one has with small sensor digitals.

I know that there is some minimal opening that can be used in optics because below that size some type of distortion occurs. That doesn't help a lot, I know.

I emailed a link to a friend of mine who is much more knowledgeable and I suspect we both will get a bit of education in a day or so.

Until then ....

[bobtrips]

Here's a link to a 'star' shot that I took with my Oly C2100z.


http://www.trekearth.com/images/photos/ ... 779__d.jpg

[bobtrips]

OK, here's what I got back.

>Do you have any idea what caused this 'star' effect around the lights?
> http://www.pbase.com/image/24952264

Yup, that's fairly normal when you stick a lens at minimum aperture - the
number of points is related to the number of blades in the diaphragm.
Generally I've found that film tends to create pointed stars, digital
creates stars with divergent "points". I have a feeling that has something
to do with sensor blooming, but I'm not 100% certain!

Sorry I can't give a more exact answer...
---

My guess it that one could determine the number of blades in their shutter by counting the points on the stars. Four rays = four blades, a ray coming from each corner where the blades meet.

I think the number of blades also has something to do with even drop-off of focus as one goes from into to out-of focus in DOF situations. Seems like Leica puts lots of blades in their lenses.

[jtfan2004]

Cool. Thank you for the information.

And I liked that picture on your site... very nice!

Thanks again,
Mike