Lens starburst at fully open aperture

Dirty filter? Fog in the air?

to get a good starburst, you have to setup your lens down to f16 and lower!

Atis photo wrote:

1Dx4me wrote:

to get a good starburst, you have to setup your lens down to f16 and lower!

Hi,

my goal is to get rid of any starburst if possible. And I am wondering why does it appear with fully open aperture?

sorry, i misunderstood you, but as has been suggested, i am pretty sure it is the fog that comes in mind. a polarized filter should take care of that, IMO.

Atis photo wrote:

Hi,

what could be the reason for starburst effect at fully open aperture 0.5'' @ f4 (RF L24-105) ?

Is it the angle of the light bulb? Or my RF lens is somehow damaged?

I don't have that RF zoom, but other constant aperture zooms I do have achieve their constant aperture by stopping down the iris towards the wider end of the zoom. The nine bladed iris of your zoom would be consistent with the eighteen pointed starburst here.

See the Sunstar section of Ken Rockwell's review here (it's a long way down the review) https://www.kenrockwell.com/canon/eos-r/lenses/24-105mm.htm

Well, since fully open aperture is f/4 @105 mm it's diameter is 26.25 mm (or at least apparent diameter). This would make it f/0.9 @ 24 mm.

Atis photo wrote:

Sittatunga wrote:

I don't have that RF zoom, but other constant aperture zooms I do have achieve their constant aperture by stopping down the iris towards the wider end of the zoom.

WOW, that's a new one for me! That might be the issue! So in reality, at wider end of the zoom, the lens might be brighter than f4, say f3? And it is stopped down to f4 just so that it matches fixed aperture of f4?

This lens opens fully at the long end only, indeed. There is no conspiracy here. Take a look here. The off-corner mechanical vignetting is much stronger than what the physical diaphragm does. If you open the aperture somehow more, a large off-center part will get no extra light; you will get a hot spot in the central part only. In other words, the vignetting would be horrible.

And no, it is not a crippled 24/0.95 lens...

Atis photo wrote:

J A C S wrote:

Atis photo wrote:

Sittatunga wrote:

I don't have that RF zoom, but other constant aperture zooms I do have achieve their constant aperture by stopping down the iris towards the wider end of the zoom.

WOW, that's a new one for me! That might be the issue! So in reality, at wider end of the zoom, the lens might be brighter than f4, say f3? And it is stopped down to f4 just so that it matches fixed aperture of f4?

This lens opens fully at the long end only, indeed. There is no conspiracy here. Take a look here. The off-corner mechanical vignetting is much stronger than what the physical diaphragm does. If you open the aperture somehow more, a large off-center part will get no extra light; you will get a hot spot in the central part only. In other words, the vignetting would be horrible.

And no, it is not a crippled 24/0.95 lens...

Thank you! This answers all my questions! Love the https://www.photonstophotos.net/ and didn't know that they had these cool graphs!

As I shoot mainly night photos and strive to achieve starburst-free photos it is a bit disappointing that L series zoom lens does not provide that. Seems like RF24-105mm f4-7.1 is stm is more suited for me, BUT it is not weather sealed (and probably optically less sharp).

No constant aperture zoom of any quality will provide that at anything other than the long end of the zoom.  The STM lens might, and you can probably arrange the composition so that the dodgy corners are black anyway.  Night scenes generally look horrible if it's raining or dusty anyway.