Why am I seeing my spider and secondary?

[Breakintheclouds]

Okay, sorry if this is a stupid question! I've just go a 38mm Panaview eyepiece for looking at large DSOs and starfields. I've just tried popping it into my scope for a quick daylight test, and as soon as I put my eye up to it I was aware of a faint dark shape, visible in the field of view and moving around as I moved my head.

Pulling my eye back, until it was a few inches back from the eyepiece, I could see in the lens a view which looked a lot like I see when I look into the focuser with the eyepiece missing: a bright circle with the secondary mirror holder and spider visible in the middle. It's this secondary shadow that I'm seeing faintly bobbing around in my vision when I look through the EP.

I hope that description makes sense. Anybody know why this is happening? Is there anything I can do about this?

[tooth_dr]

I can see mine during the day too, with any of my EPs. It's in the path of the light so not much you can do about that. Never noticed at night so I wouldn't worry about it. Alternative - buy a refractor .

[RobH]

It's perfectly normal. Don't worry about it

Cheers

Rob

[Breakintheclouds]

Thanks for the reassurance, guys. That's great.

[Merlin66]

Your seeing the "exit pupil" which is just a scaled down version of the aperture.

If you hold your arm across the end of the tube you'll see the thick black line across the exit pupil.

The size ( diameter) of the disk in the eyepiece is equal to the aperture/ magnification.

Ken

[brianb]

38mm in an f/5 scope? 7.6mm exit pupil .... sorry, that's FAR TOO BIG, you might "get away with it" with a refractor (where the only effect is to lose light grasp) but you will get that "shadowing" effect with a scope with an obstructed aperture.

[wulfrunian]

Will you always get that shadowing effect though? I've got a 40mm (from when I had an f/10 scope), and although I'm planning to replace it now, I have used it in my f/4.8 reflector without noticing that effect.

[brianb]

I've got a 40mm (from when I had an f/10 scope)

The exit pupil size is the focal length of the eyepiece divided by the focal ratio of the scope. 40/10 = 4mm, fine (when it's dark). 40/4.8 = 8.33mm, no-one has a pupil that size ... if it's REALLY dark you may not notice the shadowing, but it's there, all the same.

[John]

If it bothers you the only solution is to go for a shorter focal length eyepiece - a 32mm would probably not show the secondary shadow.