Black dot on iphone image?

[engstrom]

when I tried my new scope out the other week I got a great view of the moon that filled the eyepiece up so I tried the old iphone up against it but the image of the moon had a black dot on it in the centre. This of course wasn't visible through the eyepiece.

What is this?

[Telrad]

It could be a pixel issue?

[Keiran]

Maybe it could have something to do with the exit pupil of the EP

[engstrom]

It could be a pixel issue?

Sorry , I wasn't clear enough. It was an large dot with fuzzy edges, part of the image rather than dead pixels and moving the image around the screen also moved the dot.

[Telrad]

Oh, I see. NP engstrom ..like Keiran suggests, prehaps it's the exit pupil?

[virtualpilot45]

Sounds like a very large exit pupil, try increasing your magnification.

[engstrom]

Ah right. Interesting. So am I right in thinking that at the distance the lens was from the ep the aperture of the camera is too small?

[Nova]

My wife is always shoving me off my scope to take pictures with her iphone and we have noticed this aswell. It does come and go with different EP's but we think it is the exit pupil. We have to have the camera in exactly the right position.

The pic below was taken on an iphone, if you notice the bright white area that is showing in the shadow this is what happens just before the black spot appears. There doesnt seem to be a lot of room for error and it is actually quite difficult to hold the phone steady in the right place. We found resting you hand on the focusing tube and slowly moving the camera towards the ep was the best way to go

[engstrom]

That's a really nice pic actually! Even with the glow :-)

[Nova]

This is probably the best ive managed with the iphone. Had a bit of a tweak in photoshop too