Ghosting effect with 10" LB and Stratus/Hyperion EP???

[mbaddah]

Hello all

This is a bit of continuation on from my collimation thread I posted earlier. (http://www.iceinspace.com.au/forum/showthread.php?p=302310#post302310)

Basically, after collimating the scope and taken it out for it's first light, I noticed unless I had my eye dead on in centre, there would be a "ghosting" effect on the object I am looking (e.g. I'd see saturn and then a fainter version next to it which would move relative to my eye placement).

I am using 8mm Orion Stratus, 13mm Hyperion and 21mm Hyperion (also tested with 20mm Bintel Plossl), and it happens with all eyepieces (less with the plossl).

Can anyone shed some light on the matter as to why this is so? Your help is greatly appreciated thankyou.

[wavelandscott]

I think that this is a good question.

While I am no eyepiece expert, since no one else has posted a response yet, I'll try...

There are a couple of potential causes of ghost images that I am aware of…
#1 internal reflections within the eyepiece
#2 counter reflection off of your cornea on to the nearest lens surface to your eye

There may be more causes...based on your comments about the importance of eye placement I'd suspect #2...

Cheers,

[mbaddah]

Thankyou for the reply. I purchased a shroud for the lightbridge haven't tested it yet, would that help you reckon?

Or is having correct eye placement a normal thing to do with large dobs and premium eyepieces? Thanks for your help.

[astronut]

Moh,
Internal reflections within the eyepieces is the usual culprit, i get this with mine as well.
But it only happens on the bright planets and very bright stars.
A Neutral density or polarizing filter helps cut down the glare and ghosting:thumbsup:

[mbaddah]

Thanks mate. I'll purchase a neutral density/polariser filter, recommend any?

Does this effect happen in premium eyepieces such as the Pentax or Nagler?

[astronut]

Go to the Bintel & Andrews site they have filters there.
The Televue's suffer less from this effect, but they are also very expensive eyepieces.

[mark3d]

i'd still work on the collimation before buying much more - the last photo i saw the central circles were not centrally aligned. whether that causes the effect i dont know! :)

[AstralTraveller]

The ghosting you describe is quite common. I imagine that the major culprit is reflection off your cornea to the outer surface of the eye lens. After all your eye isn't multicoated. I remember reading that whether you get ghosting depends on the curvature of the outer surface of the eye lens - which makes sense. Concave will bounce the reflected light back to your eye while convex will send it off to the side. I also recall that plossls (and I think stratus and hyperion are basically plossls) produce ghosting while orthoscopics don't. I've never tested this theory but would like to try. For this reason I am open to donations of premium-quality orthoscopics.

[Starkler]

#1 would result in a fairly static ghost image which moves with eye placement and placement of the bright object within the field.

#2 Gives an effect like tiny flittering moths or dancing speckles of light.

My Pentax and b/tmb planetary ep's dont suffer from internal ghosting.

[janoskiss]

You can also get ghost images from a mirror / tube not in thermal equilibrium with its surround.

[mbaddah]

Looks like i'll have to start saving up for Pentax and Burgess eyepieces then. I wish i knew this before I purchased the Stratus and Hyperions :(

Thanks guys for all the help much appreciated.

[Gargoyle_Steve]

I have an 8mm Stratus & 13 & 17mm Hyperion ep's, used previously in a 10" dob and now in my 12" and I don't get ghosting at all.

I'd be suspicious of external light sources in your observing environment reflecting off your own eye as well. I'd also make sure that your collimation is as good as you can get it, but I don't ever remember seeing ghosting even when my collimaion skills were less than perfect.

[mbaddah]

If tonight is clear I might go test it out again (collimation has improved) and report back see if get same effect. I've also purchased a AstroZap shroud which I've yet to test so i'll give that a go, hopefully it will elliminate it totally :( Cheers.

[mark3d]

i saw a small reflection through my hyperion this morning when looking at jupiter, im guessing because it was so bright. id probably describe it as the small moth as described below. it was annoying but easy enough to ignore.

[mbaddah]

Took the scope out last night,

a) Collimation I'd say was 95% accurate (using new Astrosystem laser I purchased)
b) Last time I didn't turn on fan for primary mirror, made sure was on for atleast half hour before viewing
c) First time used the AstroZap shroud

guess what, NO GHOSTING :):D I moved my eye around the whole eyepiece and image was centered perfectly.

Thanks guys for all the help :thumbsup: Much appreciated.

[Gargoyle_Steve]

That's GREAT news, glad to hear the ghost has moved on to a better resting place now.

Cheers!