BST "Starguider" - possible aberrations?

[Planetesimal]

I got a couple of the BSTs before Christmas, and I've had a couple of looks through the occasional gaps in the clouds.

I've noticed a couple of strange artifacts that I didn't get on the old SW MAs, but given my lack of experience with loads of EPs, I wondered if anyone can tell me if what I'm seeing is normal for this design? The aberrations are noticeable only on very bright objects - specifically Jupiter has caused the effects:

- There is a "ghost" / "eyeball" reflection image, basically this is a small bright fast-moving light that looks a bit like a reflection in the glass but moves about with the movement of the eye

- The second effect is a larger circular disk of light in front of the planet, again moves with the eye and not related to high could / mist, the result of which is you're looking at the planet through a bright disk

- There is a third effect which is more noticeable on the higher power EP, which is like rays of refracted light emanating from the image of the planet and reaching / warping out to the edge of the FOV.

I'd be interested to know if these are known effects that I just need to get used to, or if the EPs are faulty?

[Spec-Chum]

I can attest to seeing the first one in my old 8mm BST, I originally thought it was some kind of firefly buzzing around haha

Not encountered the other 2, but they do sound suspiciously like dew forming on the secondary to me...

[nightfisher]

The third example sounds like tube currants from not letting the scope cool enough, also the EP needs to cool

[Spec-Chum]

Good call, it does add that kind of effects at high mags

[adrianelliott]

The little thing darting around happens on my 8mm BST too! I must admit it didn't occur to me that it was a reflection.

[Planetesimal]

Interesting to hear your experiences!

At least I know the 8mm "firefly" effect is not just me. It's not a major issue once you know it's not a fault - I'll learn to ignore it I'm sure.

The dew forming on the secondary issue could definitely be the problem! I find the latter two happens within about 30 minutes of placing the 'scope outside to cool, so the scope is probably not fully cooled and dew has already started to form. Basically I can't do astronomy until I work out how to deal with the dew issue.

I've got a diy dew shield in place which is three sheets of A4 black cell foam from hobbycraft (about 2mm thick), stuck together with insulating tape. It slots around the secondary thumb screws so probably extends out about 3/4 of the length of A4. Perhaps I need to get some sort of heater to attach directly to the secondary...

[rwilkey]

I have not experienced this personally, but haven't had good enough viewing conditions to use the 5mm. Part of the problem may be the exceptional eye relief of these eyepieces and you are not used to viewing through these. I find it best to use the twist-up eyecup (have you discovered these yet!) fully extended to help get the eye in a good and steady position for viewing. The reflection of the eye is sometimes due to artificial lighting in the vacinity, again the twist-up eyecups will help here.

[russ.will]

- There is a "ghost" / "eyeball" reflection image, basically this is a small bright fast-moving light that looks a bit like a reflection in the glass but moves about with the movement of the eye

I think what you are seeing is the image of Jupiter reflecting off your retina and then the occular lens of the EP. Keeping the occular scrupulously clean and free of condensation helps, as there is less for the reflection to shine on. Keep the condensation down by keeping the high power EPs in your pocket and indeed, a clean piece of glass is less prone to dewing up anyway,

- The second effect is a larger circular disk of light in front of the planet, again moves with the eye and not related to high could / mist, the result of which is you're looking at the planet through a bright disk

This maybe a ghost image as it passes through a very fine layer of condensation, from either your eyeball or breath, on the occular lens. Keep the higher power EPs in your pocket to keep them warm.

- There is a third effect which is more noticeable on the higher power EP, which is like rays of refracted light emanating from the image of the planet and reaching / warping out to the edge of the FOV.

That's the diffraction spikes from you secondary's spider. On sharp points of light like stars, they're clearly defined spikes. On a larger bright point like Jupiter, they're lower in intensity and more diffuse, but they're still diffraction spikes. On something like the moon, they're so wide you can't see them, but they're there, reducing contrast slightly.

-I'd be interested to know if these are known effects that I just need to get used to, or if the EPs are faulty?

They're not faulty.

Russell

[Planetesimal]

Thanks Russell, very useful info. I definitely need to find a way to keep condensation of the lens and and the secondary!

[Naemeth]

Have you tried observing straight away? I know the 150P is 20mm bigger than my 130P, but I find I can observe at low powers straight away with no cool down time.

Dew tends to form if you leave your scope pointing in the same place for a while, and whilst observing this shouldn't happen, so try that way first .

[Planetesimal]

Have you tried observing straight away? I know the 150P is 20mm bigger than my 130P, but I find I can observe at low powers straight away with no cool down time.

Dew tends to form if you leave your scope pointing in the same place for a while, and whilst observing this shouldn't happen, so try that way first .

I do often find myself impatient to get started, and I can take in a few clusters at low power, but Jupiter looks like a bubbly taupe pea for the first 20 minutes or so, even at medium power, and closer observations of stars shows them to be "roiling". After 30 mins on a night of lower humidity Jupiter goes (at about 150x) from a beige circle with 4 grey bands to being a ruddy-brown orb with fine internal structure (swirls, barges and festoons are clearly visible). On a night like that, the scope won't be moving very much so the condensation builds quickly... I hold my breath whenever I'm changing EPs or going anywhere near the telrad!

I think it needs more time to cool down though because the tube is 1.2 metres long, so it takes a bit longer for those air currents to escape! I fear I may have to buy a hair dryer for the first time in my life!

[wookie1965]

My 150p takes a good hour cooling down before i can start to see any detail.

[Naemeth]

I suppose it's different for me, I spend all my time looking at everything through my 26mm EP, rarely going to Jupiter and other Planets .

[chiltonstar]

I get a defocussed white reflection with my 8mm that I assume is due to incomplete anti-reflection coating on one of the elements of the EP - mind you. I tend to look at ultra-bright objects like Jupiter and Sirius, so I suppose I should expect it....

Chris

[Planetesimal]

My 150p takes a good hour cooling down before i can start to see any detail.

How do you get on with the condensation issue wookie?

[inedible_hulk]

I also get the ghost/firefly reflection when looking at bright objects. It seems to happen when humidity is higher. As rwilkey suggested, this does seem to be associated with the eye relief. I've found there is a sweet spot in positioning my eye and I think it's getting my eye square to the eyepiece that makes it go away. I'm guessing that the light is a little more scattered in humid conditions and so more reflects back off my eye onto the surface of the eyepiece. I might be talking complete nonsense though!

[Planetesimal]

I suppose it's different for me, I spend all my time looking at everything through my 26mm EP, rarely going to Jupiter and other Planets .

Have you ever tried upping the magnification to split some coloured doubles - it can be addictive!

[Naemeth]

Have you ever tried upping the magnification to split some coloured doubles - it can be addictive!

Not yet, I'm working my way through all the Messiers I can get until I reach the point I need somewhere that allows me views near to the Horizon, or to travel to a darker site.