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The title pretty much explains this one. Can I use a specific solar optical eye piece, or other optical device, in conjunction with the pinhole projector method to focus the Transit of Mercury?

Would anyone have any specific recommendations for specifications, etc if it is possible to achieve this...

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    $\begingroup$ Possible duplicate of Watching the Mercury transit with improvised devices $\endgroup$
    – Mike G
    Apr 26, 2016 at 21:35
  • $\begingroup$ @MikeG Hi Mike. I was rather hoping for specific recommendations on suitable optical pieces too. I think this one is worth keeping open. :) $\endgroup$
    – MichaelJRoberts
    Apr 26, 2016 at 21:36
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    $\begingroup$ @MichaelJRoberts pinhole projection, and eyepiece projection are two different techniques. Eyepiece projection is done by holding a screen behind the eyepiece of a telescope or binocular (or monocular :) ). Are you asking how to combine them together in some new way, or just mixing them up by accident? $\endgroup$
    – uhoh
    Apr 28, 2016 at 9:02

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The whole point of a pin hole projector is that it doesn't need any optics just a pin hole.

If you are after magnification then that is related to the distance you project the solar image behind the pin hole, with a projection distance of 1000mm the solar disc will have a diameter of about 9mm. Increasing the distance will increase the size of the image but also reduce its brightness. Increasing the size of the pin hole will increase the brightness but reduce the sharpness of the image.

I suppose you could use a handheld magnifying glass to look at a small image but would not personally recommend it as unless you are extremely careful there is always a risk of fire or even blinding yourself or someone else when using a lens near an unfiltered solar observation. There is a famous story of an experienced astronomer setting his beard on fire because he left the cap off his telescopes finder.

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  • $\begingroup$ I understand the arguments you are making: but we're talking about the transit of Mercury here. A solar disc of 9mm is incredibly small to discern the transit of Mercury. Hence, rather than losing on brightness I wanted a different projection method. Giving me a larger solar disk and smaller distance between the image and pinhole. $\endgroup$
    – MichaelJRoberts
    Apr 28, 2016 at 8:14
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    $\begingroup$ It would be better to project an image with a refracting telescope if you have access to one. Or if you can find a large room with a window facing the Sun, using curtains, blankets etc block most of the window but leave a small section uncovered in this place your pin hole and project across the darkened room on to white paper, or similar. That way you may be able to get a projection distance of 5m or more and the faint image will be less of a problem due to the darkness of the room. $\endgroup$
    – James Screech
    Apr 28, 2016 at 8:25
  • $\begingroup$ Who was this experienced astronomer ? Do you have any links about this famous story ? $\endgroup$
    – usernumber
    May 26, 2020 at 6:48
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I built an optical projector to observe the Venus transit with a 10x50 monocular. I mounted the monocular inside a box, leaving a small window to observe the projection. The focusing capability of the monocular was necessary to get a good image. The Sun's image was large and bright and detailed, much better than a pinhole projector.

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A 10x25 or similar monocular should be able to project a usable image for a modest cost. Its theoretical angular resolution in yellow light would be 6 arcseconds, significantly smaller than Mercury at inferior conjunction. Focused on a screen 50cm away, the Sun image would be 45mm wide and 30% as bright as direct sunlight. I recommend surrounding the monocular with a sheet of cardboard to shade the screen. Until the next transit in November 2019, it would probably show sunspots too.

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