Optical defects gallery - an idea.

[ollypenrice]

While pondering an issue of Ant's on the imaging board it came to me that a gallery of optical and imaging defects might be etremely useful. Some defects come up again and again - guiding errors, backlash, pinched optics, mis-collimation. We tend to re-invent the wheel each time so a gallery of defects and their solutions would be a big help to the afflicted!

Olly

[samtheeagle]

Sounds like a good shout Olly. I've got a few samples in my Mak collimation thread that might fit the bill...?

[Black Knight]

Sounds like a great idea to me

[barkis]

I would imagine the common defects that, are cause identifiable would be a good thing to place on record Ollie.

The ones that Catanonia has been experiencing with the SuperNewt, are seemingly difficult to pin down.

However, as a novice in the field, I'm saying what I think, rather than what I know. I think you have a good suggestion here though.

Ron.

[West End Wendy]

I was looking for something like this on the internet a few days ago, and failed to find anything beyond the Wikipedia entries.

I really don't know when I see a visual defect whether I am seeing astigmatism, pincushion distortion, coma or something else, and it would nice to be able to use the correct description when doing a critical appraisal of a telescope or eyepiece.

The internet is so full of poorly-informed opinion, I don't like to think I could be contributing to it.

Tim

[Sparrow]

Excellent idea Olly. I'll second the suggestion:)

[perfrej]

I'll throw in my extremely pinched Megrez 90 for the show to start

/per

[perfrej]

Oh, and if a site is needed, let me know. I have plenty of servers available.

[barkis]

I'll throw in my extremely pinched Megrez 90 for the show to start

/per

Crikey, is pinched an appropriate description for that ?

More like crushed .

Ron.

[perfrej]

As delivered from WO! And same when returned after service at WO.

They gave me a good rebate towards an FLT-98 instead. I took it... It's good!

/per

[barkis]

As delivered from WO! And same when returned after service at WO.

They gave me a good rebate towards an FLT-98 instead. I took it... It's good!

/per

A fairly amicable solution then. Good one.

[Hypernova]

There was a small list of common optical defects at the bottom of this page on Astro Baby's site. I assume they are computer generated and perhaps not representative of some real-world problems but it's a start.

[Whirlwind]

'Tis an extremely good idea. Also how about including a library of different telescopes and what they look like using a standard imaging setup (e.g DSLR) with and without correctors/flatteners etc. There's no good library of the different scopes out there and between everyone here surely we could put together a decent list of images showing coma, field flatteness etc for most telescopes make and model?

Ian

[AndyUK]

I think this is an excellent idea Olly... says someone who is currently confused whether his refractor has a focuser orthagonality issue or whether it's down to poor polar alignment, poor guiding, differential flexure or possibly non-flush fitting camera.

I think it would be useful to not only see how each issue portrays itself in an image (like Per's), but also how to test and resolve each of them (if possible) and to assist with ruling them out of the investigation...

[Macavity]

A few practical examples of (e.g. eyepiece) aberrations might indeed useful. Many terms - astigmatism, field curvature etc., are bandied about (repeated) on (invariably other? LOL) forums - Without much comprehension on either side.

But, with little remnant shame re. asking stupid questions, I am EVER indebted to those (Elsewhere and here) who take the time and trouble to *gently* ... enlighten - Folks who really know their stuff.

[Gina]

+1 Extremely useful - great idea

[Cath]

Very good idea!

Especially to noobs like myself.

[Nibor]

A vote from me as well!! Especially helpful for "lone" astronomers without access to opinions from another pair of eyes!!

[Darth Takahashi]

Abberator!!!

[Flying Eye]

+1 - sounds invaluable.

[en51nm]

Sounds like a great idea

[michael.h.f.wilkinson]

I would love such a defects gallery to train the "Local PSF estimator" that students might be building this spring. It could then be trained to give an estimate of what is wrong with the scope.

[Gina]

Here's a simple example that pretty much everyone will see - out of focus.

[Macavity]

Bit "theoretical" (but useful?) in explaining eyepiece astigmatism:

Differing significantly from the "high street optician" concept.

[Mike Hawtin]

Here's another for the gallery taken with a WO 80mm Megrez II triplet, seems appropriate really given the three sided star shapes.