Martin Lewis

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Viewing 14 posts - 21 through 34 (of 34 total)
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  • in reply to: Fullerscopes Finchley Road #582712
    Martin Lewis
    Participant

    Thanks Daryl,

    I remember reading that saga before in your first link.

    I did find the picture in the bottom link which is very good but really wanted the later frontage with the round window I used to stare through!

    Thanks for your help anyway,

    Best wishes

    Martin

    in reply to: Raspberry Pi Camera #582404
    Martin Lewis
    Participant

    That chip size is plenty big enough for a decent all-sky camera and plenty of 180deg fish eye lenses to suit such as the Arecont f2 1.55mm lens. You can see all-sky pictures taken with that lens and a chip just 4.8mm x 3.6mm here; http://skyinspector.co.uk/allsky-camera-ii

    Cheers
    Martin

    in reply to: Advanced Planetary Imaging Workshop #582039
    Martin Lewis
    Participant

    Updated details of the ‘BAA/SPA Advanced Planetary Imaging Workshop’ and the full agenda for the day have recently been posted.

    We are please to announce that the following speakers have confirmed; 

    • David Arditti (planetary imager and BAA Equipment and Techniques section director)
    • Pete Edwards (planetary imager)
    • Chris Garry (planetary imager and author of PIPP)
    • Chris Hooker (planetary imager and BAA Mercury section coordinator)
    • Simon Kidd (planetary imager)
    • Emil Kraaikamp (planetary imager and author of Autostakkert)
    • Martin Lewis (planetary imager and BAA Equipment and Techniques section advisor)
    • Damian Peach (imager and BAA Jupiter section assistant director)

    It promises to be a most interesting and popular event so don’t miss out on the limited places available. Reductions for BAA and SPA members.

    Details given at; https://britastro.org/node/19008

    See you there,

    Martin Lewis & David Arditti- event coordinators

    in reply to: Image Posting on Members Pages #581388
    Martin Lewis
    Participant

    Thanks Andy,
    Wonder why it never suggests anything for those field but always for the fields above then?
    Thanks for the understanding anyway.
    Best wishes
    Martin

    in reply to: Members Pages Enlarged Images #581110
    Martin Lewis
    Participant

    Thanks Andy,
    That is a very comprehensive reply and very helpful.
    Thanks for your testing,

    Martin

    in reply to: Members Pages Enlarged Images #581095
    Martin Lewis
    Participant

    That’s interesting. I wonder why some enlarge further when click and for others nothing happens? Curious. Some of mine are uploaded as jpegs and some as pngs- will see if it relates to that.

    Thanks for the suggestion anyway, Peter

    Martin

    in reply to: Members Pages Enlarged Images #581094
    Martin Lewis
    Participant

    Yes David,

    It would be great if it did that but generally the image is hardly any bigger. Why is that one different?

    Cheers,
    Martin

    in reply to: Planetary Histograms #580948
    Martin Lewis
    Participant

    Hi Ron,

    This is a step I often do to darken the background on planetary images including images of the Ice Giants and particularly images taken in daylight or bright twilight, often Mercury or Venus. I would always do this after wavelet processing as the application of the wavelets will change the histogram distribution quite markedly. You won’t lose planetary data unless it is something very dark like the Crepe ring on Saturn. Removal of the background like this is a simple way of boosting the contrast.

    Martin

    in reply to: Dew shields #580685
    Martin Lewis
    Participant

    As Robin says, a dew shield considerably reduces the amount of cold sky that the lens ‘sees’. Without it the lens will quickly radiate it’s heat to that cold sky and receive little heat from the sky in return. That loss in heat will cause the lens to go below the dew point of the surrounding air and water will then condense on the glass as a result- it will dew up. The night sky typically has a radiative temp in the UK of -10C to -30C. Last night, for example, I measured it as -26C.

    The lens will try to reach radiative equilibrium with that cold sky but is prevented from going too low by the heat it receives by conduction from the bath of warmer air it is sitting in and the warmth it receives again by conduction from the scope tube etc. It is  a battle between radiative loss and conductive gain. That is why a breezy night where the transfer of heat from the air is more efficient the battle between radiative loss and conductive gain is more likely to be won. Also reduce the amount of cold sky you see (reduce the radiative losses) and that makes it more likely to stay dew free.

    A dew cap does not work by trapping warm air as some books will say.

    Cheers

    Martin

    in reply to: Christmas meeting Livestream #580362
    Martin Lewis
    Participant

     The live streaming worked really well for me and allowed me to enjoy a meeting that I had booked for but was unable to attend. Great innovation which I hope will be extended to future meetings. Thanks to those organising this.

    Martin

    in reply to: Animated gifs #578659
    Martin Lewis
    Participant

    Thanks Dominic,

    The animation I wanted to upload was showing the small shift in position of a bright spot on Neptune over a 25min period and a side by side comparison just doesn’t compare in functionality to a gif animation.

    Still if you don’t have the functionality you don’t have it.

    Thanks for the prompt reply anyway,

    Martin

    in reply to: 2.1 binocs #578340
    Martin Lewis
    Participant

    Hi Dave,

    I bought a pair for low power views of constellations and they give a big boost to your vision by adding 1.5 mags without changing the size that much- it’s like having super-eyes.

    They are simple Galilean design and there is some astigmatism and the quality falls off noticeably away from the centre but they are fun in a dark location, especially for sweeping the Milky Way and looking at large clusters like Pleiades, Hyades etc,

    Martin

    in reply to: Atmospheric dispersion #578000
    Martin Lewis
    Participant

    As Damian says, now is a good time to get an ADC if you don’t already have one. About the price of a good eyepiece and a sound investment especially if you want to image or view Mars and Saturn from the UK in the next few years.

    Es Reid and I did a study of the levels of astigmatism generated by ADCs in use and we found that for a given scope the degree of astigmatism generated by a correctly adjusted ADC is primarily related to the altitude of the object. You can read more about this study at; http://www.skyinspector.co.uk/adcs-part2

    I also have a more general page on ADCs those those interested in learning more about these useful devices at; http://www.skyinspector.co.uk/atm-dispersion-corrector–adc

    Cheers, Martin

    in reply to: Images Likes #577959
    Martin Lewis
    Participant

    Thanks Guys, obvious when you know how to do it …..

    Martin

Viewing 14 posts - 21 through 34 (of 34 total)