Dust inside eyepiece

[sorrimen]

Hi there

See the attached image. Small hair/scratch looking thing inside the eyepiece. Have used the eyepiece a couple months then after last night’s observing (didn’t actually use it much) it was quite obvious at a certain angle when I looked this morning. Whilst it looks scratch-like, the fact that it is within the lens(es) leads me to think some sort of little hair/fibre instead of a scratch. I’ve bulb blown both ends, removed the lower part of the eyepiece which is a barlow and blown the lower lens (it’s definitely between the lower and upper lens of the actual eyepiece). Sorry if my terminology/knowledge is a little off, I’m still relatively new! What can be done and how the hell did it get there?!

TIA

Ross

p.s. reason for multiple images is so that you can that by the angle it’s visible at it can’t be on the surface. 

[sorrimen]

https://imgur.com/a/UOFICG4

Wasnt letting me upload media.

[Louis D]

Try smacking the eyepiece sideways into your open palm with the debris side facing downward.  You may be able to displace the debris to the side wall.

[DaveL59]

What Louis said. Does it affect the view at all?

If not ignore until you decide you need to open it up further to clean which might be never. Not impossible that it got there during manufacture or its not airtight and found its way in. What eyepiece is it?

Edited August 13, 2022 by DaveL59

[sorrimen]

26 minutes ago, DaveL59 said:

What Louis said. Does it affect the view at all?

If not ignore until you decide you need to open it up further to clean which might be never. Not impossible that it got there during manufacture or its not airtight and found its way in. What eyepiece is it?

I had seen the idea to smack it and tried briefly to no avail, but will try again with more effort. Very much appreciate the tip, Louis. It’s a BST Starguider 18mm. I’m tempted to think it’s got it there very recently as I’ve cleaned the eyepiece before and find it super unlikely that I’d miss something this visible. That’s what’s left me so confused, and my own newbie conclusion was that perhaps it was something on the eyecup threads that got in when I screwed it back down, though I doubt the threads would be in open contact with the lenses so I’m stumped.

[Zeta Reticulan]

It's not unknown for previously unseen debris to migrate into the field. 

[DaveL59]

Things sometimes shake themselves loose over time and use and mysteriously appear. Not sure re the eyecup threads as I don't have those ones but is possible that allowed a gap for something to creep in. Lenses are usually held in place with thin rings that do bear onto the glass at the edge, so its possible that's how that top lens is held in place. But if so the others under it would be too, removing that ring  and up-ending the lens would risk a tumble of glass that you'd then have to figure out the order to refit so take care. You wouldn't be the first to ask how it all goes back together 😉 

Edited August 13, 2022 by DaveL59

[sorrimen]

Given it a few hard whacks into my palm and no movement. Thing seems real glued in there which just adds to the mystery of how it got there. Think I’ll heed that warning carefully, Dave, and see whether it has an effect on views before even thinking about disassembling. As an 18mm in an 8” dob, it’s restricted to DSOs and lunar, the latter of which annoyingly will probably make it the most visible, but the former will hopefully tolerate it well! 

Thanks all so far, and if anyone has any more suggestions/knows how easy Starguider disassembly and dreaded reassembly is, please stick them here!

[DaveL59]

you'll probably be surprised how little it shows up if at all tho because you know its there you'll look for it. Same with cleaning mirrors/lenses etc 🙂 

[Louis D]

It's probably far enough above the focal plane that it won't be very visible.  On the other hand, I had a brand new 30mm APM UFF with debris on one of the lower lenses which is practically coincident with the focal plane, and boy was that visible.  In the far right schematic below, the debris was on either the top of the second lens from the bottom or the bottom of the third lens up from the bottom.  Both are rally close to the internal field stop.  Either way, I exchanged it for another that was clean.

[Ricochet]

17 hours ago, sorrimen said:

Given it a few hard whacks into my palm and no movement. Thing seems real glued in there which just adds to the mystery of how it got there. Think I’ll heed that warning carefully, Dave, and see whether it has an effect on views before even thinking about disassembling. As an 18mm in an 8” dob, it’s restricted to DSOs and lunar, the latter of which annoyingly will probably make it the most visible, but the former will hopefully tolerate it well! 

Thanks all so far, and if anyone has any more suggestions/knows how easy Starguider disassembly and dreaded reassembly is, please stick them here!

I've taken an 18mm Starguider apart before, it's relatively easy. You just have to be really careful when cleaning to make sure you don't reassemble with any dirt or marks inside of it.