314l and scope help

[astrokat]

i think / sure it some thing to do with the focuser its producing 3 defractions how do i solve this problem also found with ccd imaging there so many wires lol i need to get organised i manage one 5 min sub at -15

i get the feeling this ccd stuff is goin to make me gray

[Steve]

Does your telescope use three metal tabs as lens spacers?

[Whippy]

Does your telescope use three metal tabs as lens spacers?

That's what I'm thinking. It looks as though they're protuding into the light path, giving those funky star shapes like those Telescope House 80mm APO scopes did.

Tony..

[astrokat]

I'm not sure if you mean the focuser is fixed the the scope via 3 grub screws then yes Is this going to be a pain to sort out

[Steve]

Not the focuser, the optics. With air-spaced optics manufacturers use spacers between the lens elements to provide the air gap. They often use an outer ring, a bit like a thin washer, but sometimes they use three metal tabs placed around the outer edge. If the tabs protrude into the light-path they can produce diffraction artefacts like the ones in your image. What telescope are you using?

HTH

[ollypenrice]

If this is the case (and it sounds likely) you could try making a small aperture mask. It needs to be a ring with a circular aperture just a tiny bit smaller than the aperture of the scope, enough to stop light interacting with the little lens spacers. I bet the folks who make Bahtinov masks would make you one. EG Starsharp Masks (Morris Engraving). Ideally it would fit inside the dewsheild, close to the glass, but that might be tricky to cut. Otherwise it could sit on the dewsheild. You'd only lose a couple of mm aperture.

This problem also seems to have cropped up with the WO 132, I think.

Olly

[Steve]

The use of metal spacers is not uncommon, you can find them in scopes ranging from the humble (Skywaycher Startravel) to the exotic (TMB) but when they protrude into the lightpath they do show as artifacts around bright stars. If we have guessed correctly then the ones shown here in this thread are rather prominent. It is probably worth discussing this with your supplier, it might be that your telescope is atypical.

[FLO]

Just spoken with Toby, it is a Megrez-90 supplied by us so we are on the case

Those diffraction spikes are definitely not normal, much too prominent.

[MartinB]

Good diagnosis and response Steve

[astrokat]

thanks guys