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Home Forums Observing and Imaging Group Rainbows and other sky phenomena

This topic contains 40 replies, has 6 voices, and was last updated by  Andy Sawers 2 months, 2 weeks ago.

Viewing 15 posts - 16 through 30 (of 41 total)
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  • #7637

    Mike Meynell
    Moderator
    Topics: 119
    Replies: 753

    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?

    #7638

    Andy Sawers
    Moderator
    Topics: 121
    Replies: 596

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

    Definitely!! 🙂

    • This reply was modified 3 years, 10 months ago by  Andy Sawers. Reason: Can't spell
    • This reply was modified 3 years, 10 months ago by  Andy Sawers. Reason: Still can't spell
    #7639

    Sumitra
    Participant
    Topics: 21
    Replies: 233

    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.

    #7642

    Andy Sawers
    Moderator
    Topics: 121
    Replies: 596

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

    Moderators to the rescue?

    #7643

    Mike Meynell
    Moderator
    Topics: 119
    Replies: 753

    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.

    #7647

    Sumitra
    Participant
    Topics: 21
    Replies: 233

    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”

    #7650

    Mike Meynell
    Moderator
    Topics: 119
    Replies: 753
    #7652

    Sumitra
    Participant
    Topics: 21
    Replies: 233

     

    All done
    http://flamsteed.info/forums/forum/useful-stuff/%5B/quote%5D

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

     

    Lucky Luke

    Lucky Luke

    • This reply was modified 3 years, 10 months ago by  Sumitra.
    #9226

    Mike Meynell
    Moderator
    Topics: 119
    Replies: 753

    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.

    • This reply was modified 3 years, 8 months ago by  Mike Meynell.
    #9233

    Mike Meynell
    Moderator
    Topics: 119
    Replies: 753

    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.

    #9236

    Andy Sawers
    Moderator
    Topics: 121
    Replies: 596

    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…]

    #9238

    Tej
    Participant
    Topics: 38
    Replies: 593

    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”?!?

    #9252

    Mike Meynell
    Moderator
    Topics: 119
    Replies: 753

    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.

    #9264

    Tej
    Participant
    Topics: 38
    Replies: 593

    …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?!

    #9265

    Mike Meynell
    Moderator
    Topics: 119
    Replies: 753

    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).

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