Curved spiders

[Mark Porter]

Quick question, does anyone know of a UK based supplier of curved spider vanes (6").

I'm looking for something along the lines of 1800 Destiny's Retrofit 4 Vane spider.

1800 Destiny: Retrofit Curved Vane Spiders

[johninderby]

Orion Optics UK does them to order but be aware that the curved vanes are far more sensitive than the straight vanes to any errors in the fitting causing distortion in the vanes, and if they're not just right they can cause severe diffraction problems.

Worth a chat with Barry or John at OO for their expert opinion on the subject though.

John

[Moonshane]

I've not used them but my understanding is that they don't remove the diffraction, just 'smear' it around (does this reduce contrast?) so you don't see it as obviously as straight vanes? On this basis I think I'd sooner have 'unsmeared' views with an obvious spike.

[Mark Porter]

Thanks for the info guys, I'll give Orion a call tomorrow for a chat.

[Starflyer]

There's an image on this site selling curved spiders, scroll about halfway down and click on the (diffraction comparison image) link;

Protostar Telescope Making & Upgrading

If you look closely at the third image you'll see the 'smear' of diffraction previously mentioned. I'm sure someone wish more knowledge of optics will be around in a moment to help quantify the effect.

[Moonshane]

an off topic but related question. has anyone ever tried to make vanes out of eg beer can aluminium which would be extremely thin and assuming you could get them tensioned correctly would surely be strong enough for most smaller mirrors?

incidentally, I see the diffraction spikes on my 6" f11 much more obviously than my 12" f5.3. anyone know why this might be? they are slightly thicker on the 6", maybe that's the answer?

[perrin6]

I see the diffraction spikes on my 6" f11 much more obviously than my 12" f5.3. QUOTE]

Maybe because the ratio of aperture width to vane thickness is larger and so less apparent in the 12 inch (????)

Alan

[Moonshane]

ahhh - good enough for me!

[johninderby]

OO did a survey last year where they fitted a scope with 0.5mm thick vanes and then with 5mm thick vanes and took images of an artificial star and asked people if they could tell the difference in a "blind" test. The results were split 50 : 50 so it appears that the thickness of the vanes has less impact on the diffraction spikes than expected.

Something to think about

John

[perrin6]

OO did a survey last year where they fitted a scope with 0.5mm thick vanes and then with 5mm thick vanes and took images of an artificial star and asked people if they could tell the difference in a "blind" test. The results were split 50 : 50 so it appears that the thickness of the vanes has less impact on the diffraction spikes than expected.

Something to think about

John

BLIMEY ! I've been fretting over my standard 4-vaned spider with 1mm thick ones ! Perhaps I can relax a bit now.

[Moonshane]

OO did a survey last year where they fitted a scope with 0.5mm thick vanes and then with 5mm thick vanes and took images of an artificial star and asked people if they could tell the difference in a "blind" test. The results were split 50 : 50 so it appears that the thickness of the vanes has less impact on the diffraction spikes than expected.

Something to think about

John

yes, but you're saying 50% could tell....

actually this is great news as I don't really want to mess about with things for no gain!

[Peter Drew]

When Rob Miller and I worked together with designing the Astro-Systems Newtonians our main interest was telescope performance. We tried out every known configuration of secondary support and found by direct comparison, that a single vane support gave the best planetary image. As mentioned in above posts, curved spiders did remove the star "spikes" but smeared the diffraction effect across the field. The ultimate solution was to use an optical window but this added significant cost plus sveral other complications. (Post sent from Tenerife)

[Moonshane]

great post Peter

this is interesting.

plus it's something you could probably make/try out without any permanent mods to the existing spider support. I may have a go at this. I suppose the difficulty is getting the balance of stability and 'slimness' of the support but based on John's post, maybe it could be reasonably thick.