Rainbows and other sky phenomena

Do you know if I could still have had a spiky sun at F/11 in daylight?

Depends on the mechanics of the lens, I suspect. You probably will still see them, but it will be more subtle. See here for an example of one of my images at f/11. Ultimately, it's a trade off... if you shoot at f/22 then your image will be softer, but you will increase diffraction spikes on bright point sources of light.

Sorry to hear about your lens. Sigma do offer a repair service, but it will probably cost close to £100 or so. See here.

Good idea about the useful links...  I may set up another sub forum called "Useful Stuff"... what do you think?

Good idea about the useful links…  I may set up another sub forum called “Useful Stuff”… what do you think?

Definitely!! 🙂

Thanks for the example - yeah my aim at the time was for spikes 🙂 But I will bear in mind for situations where I do not need that many spikes.

Non-astro related, here are pictures I tried to take, where I ended up having to use a high F number. I would have liked to be able to try more combinations (as I had suggested to Tej the other day :p) but in that situation it was more of a 'get it right first time if you get a chance'.
Do you think I could have got away with a lower F number? I was at the time not too sure what I was doing (and being distracted while being attacked by the Enemy).
Here F/27 with Flash:

Here, no good at all F5.4.

Sorry to hear about your lens. Sigma do offer a repair service, but it will probably cost close to £100 or so. See here.

Thanks for this! I had seen it and thought perhaps I would get a better deal if I went to a photography shop instead? £100 seems a bit much compared to getting a new lens...

Good idea about the useful links…  I may set up another sub forum called “Useful Stuff”… what do you think?

Could work - although it could get messy if we can't organise things? Or perhaps people can post the links there and then they can be reorganised into the Resources category once in a while?

I can't remember the name of this system now, where everyone can bookmark links into a common library and tag them. I will look it up let you know.

Could work – although it could get messy if we can’t organise things?

Moderators to the rescue?

Do you think I could have got away with a lower F number?

With macro photography, it's always difficult to use low f-numbers, as you want a decent depth of field, and all of your subject in focus. Nonetheless, I wouldn't go beyond f/11... the softness which results from going to f/27 does detract from the image. You should find everything pretty sharp at f/11.

Moderators to the rescue?

Yep, agree with that Andy! I think it can work. I'll set it up later and we'll see how it goes.

With macro photography, it’s always difficult to use low f-numbers, as you want a decent depth of field, and all of your subject in focus. Nonetheless, I wouldn’t go beyond f/11… the softness which results from going to f/27 does detract from the image. You should find everything pretty sharp at f/11.

I'll try again next time (perhaps not with the Enemy though). It was painful.

Yep, agree with that Andy! I think it can work. I’ll set it up later and we’ll see how it goes.

Great! So perhaps we suggest some rules, where the users provide some 'tags' with their links? For instance for my Milky Way link "Milky Way, Wide angle astrophoto, ETTR"

All done 😉

http://flamsteed.info/forums/forum/useful-stuff/

All done
http://flamsteed.info/forums/forum/useful-stuff/

Mike - Like Lucky Luke, creates threads faster than his shadow! (I've put my link as well)

[caption id="" align="alignnone" width="548"] Lucky Luke[/caption]

Saw this image on the Telegraph website this morning and had to share it here:

Taken from a plane at whilst travelling over the Carribean Sea. A stunning image... I haven't seen anything like this before. It looks like a supernumerary bow or arc which has caused the multiple rainbow. But to see it under the clouds is fantastic.

Article can be seen here.

Well, this isn't a rainbow after all. It's cause by polarised light seen through the plane window. What confused me (and quite a few others) is how the light appears below the clouds.

However, definitely not an atmospheric effect after all.

While I've seen that kind of effect on plane windows before, the real trompe l'oeil is, as you say, the fact that it only appears under the clouds.

Something to do with the way the light is reflected off the sea, I guess? It certainly looks extremely calm and flat. [Mike gets out slide-rule to work out diffraction angles...]

Alright, so the rainbow effect appears to be explained (although the window polarisation is a bit vague). But now explain this...how the heck do cloud shadows appear on the "rainbow"?!?

But now explain this…how the heck do cloud shadows appear on the “rainbow”

This is what threw me completely, I have to say... which is why my initial thought was that the picture was "genuine" (even though I had a sneaking suspicion that something was wrong... just didn't think it through, as it was such a beautiful image).

The best explanation I've seen is on the Guardian website, here. I suspect that the Guardian are rubbing their hands with glee that the Telegraph splashed this on their front page yesterday (not that the Guardian have ever been known to get anything wrong, oh no).

Key quote is here:

The ocean surface also acts like a polarising filter. When sunlight reflects from the water, it becomes polarised. This means that the rays of light are made to oscillate in a predominant direction.

So that's why we are seeing colour on the ocean's surface and not in the clouds.

...but that still doesn't explain the cloud shadows on the rainbow itself. Its all fine with the light refracting and bouncing off different angles from the atmosphere molecules and the window but its still just light, not a solid real object and as you had said previously, Mike, everyone has their own personal rainbow from their unique position...so how can there be cloud shadows on something that isnt actually physically there?!

but that still doesn’t explain the cloud shadows on the rainbow itself

It does... but you need to think it through. The partial polarisation of light reflecting off of the sea will be greater than that reflecting off of the clouds (one is mirror-like and the other is diffuse).

This partially polarised light then travels through the window (the "birefringent" medium referred to in the article), then on to the camera sensor as a dispersed spectrum.

The cloud shadows are actually on the surface of the ocean. As these are areas where less light is reflected back, they appear as if they are shadows on the "rainbow" (which isn't a rainbow... but you get my point).