Star test - Any ideas what this is?

[Jaxxxxx]

Hello,

Just a quick question as its 2am and I am up early...

I was out earlier with my 80mm refractor and decided to do a quick star test on Polaris and noticed a strange line right through the middle of the defocused star. Please see attached image.

I checked the lens as well as inside the tube and everything appears as it should. I then moved onto trying different eyepieces with a barlow and without just to make sure it was not them and all showed the same line... Any Ideas?

Please note the image was taken very quickly through the eyepiece with my iPhone which is why it is not completely round and I edited the image to make it brighter so you guys can see. Could this possibly be the cheapo 45 degree diagonal?

Thanks

[Merlin66]

Looks like a thread or something in the optical path. Try rotating the diagonal see if it moves...check by focusing without it (using a spacer)

[Saleratus]

I'm wondering if there was something between you and polaris when you took this shot--a power line or maybe a wire holding up a trellis in the garden. If it was close enough to the scope, you wouldn't see it when you focused on polaris, but when you defocused, you might have brought the focus closer to this object.

[Ganymede12]

Polaris is actually a double star! So it's quite possible that when you see a defocused image of polaris you can see some light from both of them. I doubt you would be able to see Polaris's "twin" when your image is in focus though.

I could be wrong though. I'm just giving a theory.

But Polaris is a double star, that much is true!

[brucen]

Polaris is actually a double star! So it's quite possible that when you see a defocused image of polaris you can see some light from both of them. I doubt you would be able to see Polaris's "twin" when your image is in focus though.

I could be wrong though. I'm just giving a theory.

But Polaris is a double star, that much is true!

I went to an astronomy presentation on a cruise a couple of weeks ago and it was mentioned that Hubble discovered a third star in 2006 so it is actually a triple star. As it took Hubble to see it I don't suppose it makes that much difference when viewing from earth!

[E621Keith]

Any chance it may be a overhead cable or a laundry wire in your garden?

It's certainly not a double star, they don't give you any straight line in out of focus image.

[John]

It could be a power line or I have seen something like this when using a 45 degree prism diagonal too - they are not well suited to astronomy to be honest.

[Jaxxxxx]

I tried on Vega as well and the same line was there... I also tried a street light and again same thing so its definatly not a wire in the garden as the scope was being moved. Possibly a thread however I cant actaully see it anywhere in the scope so I am starting to think its the 45 degree prism however I dont have an extension tube to actually test this

Thanks for the replies

[sunshine185]

I get this when the washing line is in the fov.

[Ganymede12]

Aren't we forgetting the obvious?

Someone cut the star in half!

[ollypenrice]

Very close to the EP, probably on the bottom of it. Just maybe a hair across the bottom of the diagonal. It is quite well in focus so it can't be far away in my view. Abosoutely nothing to do with anything at astronomical distance.

Olly

[andrew s]

If you were using a 44 deg diagonal then they can cause such a line to appear. Does it give a diffraction spike when in focus or just fade away? - Andrew

[Peter Drew]

It's the "roof " line of the roof prism in the 45 degree diagonal.

[paul mc c]

It could be a strand of a spiders web,very hard to see but would show up in the eyepiece!

[brantuk]

It's an overhead cable - I had exactly the same view through mine one night - took me 1hr of scratching my head over the otherwise excellent optics before I thought to look up and instantly feel stupid lol

[sunshine185]

I keep tyring to persuade the missus to buy a rotary clothes dryer,I also hate the fact she has to have about 600 pegs attached to the clothes line when the most we ever use is about 20.

[LukeSkywatcher]

It's the "roof " line of the roof prism in the 45 degree diagonal.

Thats what i thought too. You will see this when the scope is out of focus.

[Jaxxxxx]

Hey

Thank you for all the responces!

Armed with a William Optics 1.25" CF and a few breaks in the cloud I managed to get Vega defocused and the line was gone... In goes the 1.25" 45 Degree and the line retuns

It appears that there is some sort of inperfection in the prism a very thin line that can be seen only just in daylight. Problem solved!

Thanks again for the help!!

[Peter Drew]

QED!

[sunshine185]

I still hate the clothes line.