eyepiece projection question

[davekelley]

This might be a ridiculous question but.......I have a solar filter and I'm enjoying being able to enjoy astronomy during the day and in warm temperatures!  I have seen that projecting the image onto a screen can create a large image that more people can observe and in safety so that seems like a great idea.  My question is, can the same method be used with the moon, after all the moon is extremely bright in the telescope.  Do people ever project an image of the moon onto a screen?  Or is it a completely stupid question?  

Cheers

dave

[oobydooby]

Not a stupid question at all.

I have never considered projecting sun or moon but I would guess that even though the moon seems extremely bright it is nowhere near bright enough to project through a telescope. Others may well prove me wrong.

[johnturley]

It might work around full moon when the moon is at its brightest, but the lunar disc would probably not be bright enough to work around half moon when most detail is visible, it would also be affected by the aperture and focal ratio of the telescope used.

John 

[Starwatcher2001]

Moon projection is certainly an interesting idea, but I'd be surprised if it was bright enough to work.

This is how I did solar projection during a transit of Venus in June 2004. Turned the tube of my home build Dob upside down, and added a thin white screen to provide shade and project downwards:

[Dark Vader]

Apologies if this isn't what you're aiming at here, but I've recently started taking photographs of the moon with a smartphone adapter and phone camera. It's a form of eyepiece projection and when I wasn't actually taking a photo, the moon was still visible on the screen. I had several people looking at the live image on the phone screen, including a neighbour who looked over the garden fence and was amazed by the view. 

[Capt Slog]

I've not tried projecting the moon either, it's an interesting idea, I might have a go.

 

I know that folks on here are going to know the danger of pointing a telescope at the Sun, but just wanted to add a bit about that.   

As part of my work, I was once asked to make a version of this by a colleague...

 

... (three of actually), which I did, and then went onto seeing them tested and used.  

This is supposed to be a fairly safe way of looking at the sun, so it came as a bit of a shock (to me) that when I was adjusting the device, I unknowingly managed to put my hand between the eyepiece and the projection surface, and received a burn for my stupidity.  I must have been close to the EP of course, but it was a timely reminder not to take 'safe' for granted.

[Astro Noodles]

7 hours ago, davekelley said:

This might be a ridiculous question but.......I have a solar filter and I'm enjoying being able to enjoy astronomy during the day and in warm temperatures!  I have seen that projecting the image onto a screen can create a large image that more people can observe and in safety so that seems like a great idea.  My question is, can the same method be used with the moon, after all the moon is extremely bright in the telescope.  Do people ever project an image of the moon onto a screen?  Or is it a completely stupid question?  

Cheers

dave

Hi Dave

You should try it and let us know the results. Sounds like an interesting idea.

[Peter Drew]

The Moon can be projected but it will be very faint unless it's close to the eyepiece and low power.  The Sun is unbelievably brighter than the full Moon, mag-26 compared to mag -12, mentally compare this to the difference between a mag +12 star and one of mag +26 star.  We project the Moon on a 72" monitor by using a DSLR connected to the telescope and the monitor for outreach.        🙂 

[Louis D]

I've projected the full moon onto my palm with the eyepiece removed from my Dob.  It's certainly bright enough to be easily seen at night in a darkened location.  Of course, the image focuses quite close to the top of the focuser, so it would need projected onto a translucent material for easier viewing with a Newt.  Fracs might have enough back focus for front projection.

It should also be doable, though dimmer, with an eyepiece or Barlow in the focuser.  This would allow for the image to be larger and focused farther from the focuser.

Away from full moon, the image will be dimmer, but might still be doable.

This would definitely not work very well during a lunar eclipse.  The moon gets very dim during them.

5 hours ago, Peter Drew said:

The Moon can be projected but it will be very faint unless it's close to the eyepiece and low power.  The Sun is unbelievably brighter than the full Moon, mag-26 compared to mag -12, mentally compare this to the difference between a mag +12 star and one of mag +26 star.  We project the Moon on a 72" monitor by using a DSLR connected to the telescope and the monitor for outreach.        🙂 

Keep in mind how much lower the ambient illumination is at a dark site (that is not too close to or above the Arctic Circle) compared to the daytime.  This helps immensely with viewing the projected ~40000x times dimmer moon.

[CraigT82]

As with Dark Vader above, I've had some success sharing with neighbours a live moon view using a smartphone holder, simply get the phone positioned over the eyepiece properly and open the camera app and viola.... Live image of the moon that people can see clearly from a few feet away.