General Optics

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Optics Websites

Last post by Don Pensack « Sun Jul 11, 2021 2:35 pm
Replies: 18
by mikemarotta » Fri Jul 02, 2021 6:00 pm

First post

I found this one:

Amateur Telescope Optics by Vladimir Sasek.

it seems all right and several or many others must be out there.
Any other leads?...

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Enjoy Mr. Suiter book when you get to read it. :)

Star Testing Astronomical Telescopes: A Manual for Evaluation and Adjustment by Harold Richard...

18 Replies

13884 Views

Last post by Don Pensack
Sun Jul 11, 2021 2:35 pm
Prism versus diagonal in an old f/9 ED Vixen

Last post by Lady Fraktor « Wed May 25, 2022 4:23 am
Replies: 10
by John Baars » Sun May 22, 2022 11:42 am

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My old f/9 ED Vixen refractor was build in Japan in the nineties of the twentieth century. She is more than 25 years old.

IMG_1154 - kopie final...

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The objective from factory was stopped down to 95 mm due to the design of the lens cell and the tube was very thin walled aluminium tubing.
So thin...

10 Replies

252 Views

Last post by Lady Fraktor
Wed May 25, 2022 4:23 am
Monocular review

Last post by JayTee « Sun Apr 10, 2022 9:37 pm
Replies: 4
by Butterfly Maiden » Thu Apr 07, 2022 3:30 pm

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I have just come across this review - Why Is This £54 Monocular Better Than £3000 Telescopes?

It sounds amazing, but is it too good to be true?...

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One of the reasons why this forum exists -- to help dissuade anyone who wants to spend £54 on optical garbage!

4 Replies

201 Views

Last post by JayTee
Sun Apr 10, 2022 9:37 pm
Straight Spotting Scope???

Last post by Richard « Sat Mar 26, 2022 1:55 pm
Replies: 9
by Colorado Luckydog » Thu Mar 24, 2022 12:46 pm

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I had no idea I was going to develop a taste for star gazing and I just bought a straight spotting scope. It's a Vortex Razor 27-60X85. What would be...

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Though not ideal any scope can be used for Astronomy , spotting scopes , the quality ones are good , but looking up makes it uncomfortable , I wonder...

9 Replies

625 Views

Last post by Richard
Sat Mar 26, 2022 1:55 pm
Understanding the (so-called) Dawes Limit

Last post by helicon « Sun Mar 20, 2022 2:43 pm
Replies: 2
by mikemarotta » Wed Nov 03, 2021 10:20 am

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Hence it follows that the tests of separating power furnished by close double stars are by no means to be relied on as determining the character of a...

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Very interesting piece Mike. Thanks!

2 Replies

15777 Views

Last post by helicon
Sun Mar 20, 2022 2:43 pm
Some lenses to play with on the cloudy days

Last post by j.gardavsky « Sat Oct 30, 2021 8:39 pm
Replies: 5
by j.gardavsky » Thu Oct 21, 2021 11:32 am

First post

Hello all,

I have received from Oberkochen some of their deplorable lenses from the ongoing projects,

lenses group.jpg

Top, left to right:...

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Hello Marshall,

the CaF2 crystal lens has a bright convex rim with a faint bluish coating, otherwise planar. The purpose of the rim is not known to...

5 Replies

3052 Views

Last post by j.gardavsky
Sat Oct 30, 2021 8:39 pm
Change your eye pupil size voluntarily?

Last post by AntennaGuy « Thu Oct 21, 2021 1:03 pm
Replies: 15
by AntennaGuy » Thu Sep 02, 2021 12:14 am

First post

I wonder if this might be a useful skill for visual astronomers to master?
Man Can Change His Pupil Size on Demand, Something Scientists Thought Was...

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...
Of course, it's well-known that pupil's dilate with sexual arousal.....much more pleasant than those awful eyedrops......just sayin :lol:
Joe...

15 Replies

7298 Views

Last post by AntennaGuy
Thu Oct 21, 2021 1:03 pm
Monolithic SCT from single cylider of glass

Last post by Chich « Sun Oct 17, 2021 6:25 pm

by Chich » Sun Oct 17, 2021 6:25 pm

This fellow, Rik ter Horst, makes very small telescopes out of a single cylinder of glass. Very impressive skill set!

0 Replies

2180 Views

Last post by Chich
Sun Oct 17, 2021 6:25 pm
Coma correctors

Last post by turboscrew « Tue Oct 05, 2021 9:47 pm
Replies: 6
by turboscrew » Tue Sep 21, 2021 9:39 pm

First post

How do coma correctors work? Is there only one right place a certain distance from the focal plane (or focal point in the optical axis)?

I wonder,...

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You would lock the focuser and use spacers to get the camera as close as possible to focused, then do any final mm or 2 of focusing using the...

6 Replies

3363 Views

Last post by turboscrew
Tue Oct 05, 2021 9:47 pm
Collimation change by off-center secondary's weight

Last post by Don Pensack « Sun Sep 26, 2021 10:24 pm
Replies: 3
by SkyHiker » Sun Sep 26, 2021 2:46 am

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I always wondered if the collimation would be maintained when the scope changes position. Tonight I tried it and found that this is not the case....

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It could be the spider. It could be the secondary holder sagging.
It could be the focuser flexing the tube differently (many people have had this...

3 Replies

1458 Views

Last post by Don Pensack
Sun Sep 26, 2021 10:24 pm
The Conrady's Chromatic Condition ...

Last post by Lady Fraktor « Thu Jul 29, 2021 5:01 pm
Replies: 7
by j.gardavsky » Sun Jul 18, 2021 8:27 pm

First post

... a historical math approach, not only of interest for our not Fritz Argelander.

From the historical perspective,
there is a downloadable article...

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I do agree Bill, some people seem to be of the opinion that if a refractor shows any colour it needs to be condemed as unusable.
I thoroughly enjoy...

7 Replies

2875 Views

Last post by Lady Fraktor
Thu Jul 29, 2021 5:01 pm
Advances in telescope optics

Last post by Thomas_M44 « Thu Jul 01, 2021 5:56 pm
Replies: 12
by The Happy Parrot » Fri Jun 11, 2021 10:12 pm

First post

Interesting article on optical design for cameras and telescopes at the University of Ottawa. Will telescopes be much shorter than current designs?

Last post

Here is the research paper on the technology...

Absolutely fascinating.

This is clearly state-of-the-art optical technology .

It’s...

12 Replies

3592 Views

Last post by Thomas_M44
Thu Jul 01, 2021 5:56 pm
10 Inch Dob Under Bortle 4 Skies Vs. 6 Inch Refractor Under Bortle 2 Skies

Last post by Ylem « Mon Jun 21, 2021 6:57 pm
Replies: 10
by Refractordude » Tue May 18, 2021 4:39 am

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Which of these will show brighter DSO? Left click the image.

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At a Bortle 6/7 here, I pretty much have to use the C8 to pull anything out. I had a 10 Dob many years ago and sometimes miss it.

That said, my ST80...

10 Replies

3324 Views

Last post by Ylem
Mon Jun 21, 2021 6:57 pm
127mm Lens

Last post by LDW47 « Fri Jun 11, 2021 5:57 pm
Replies: 7
by LDW47 » Tue Jun 08, 2021 4:06 pm

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My info is sparse but I have a chance to buy a 127mm f5 home made refractor with a Jaegers achro lens in like new condition. Anyone know much about...

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Some fairly inexpensive upgrades from the Vixen Porta Mount:
Stellarvue M2C
Explore Scientific Twilight-II mount (now discontinued--have to find a...

7 Replies

2378 Views

Last post by LDW47
Fri Jun 11, 2021 5:57 pm
Collimation tools for faster scopes?

Last post by Don Pensack « Thu Jun 03, 2021 8:54 pm
Replies: 22
by turboscrew » Fri Oct 09, 2020 4:20 pm
1

2
First post

I've been wondering, what kind of tools there are for collimating a 300 mm F/4 scope?
I'm especially interested in getting the secondary right. I...

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And the 3 tool set from Catseye is available, and much better than the Tectron Tools.
The Tectron tools haven't been available since the early '90s....
22 Replies

7715 Views

Last post by Don Pensack
Thu Jun 03, 2021 8:54 pm
How to Calculate the Limits of Your Telescope

Last post by Don Pensack « Sun May 30, 2021 9:09 pm
Replies: 8
by mikemarotta » Tue Mar 16, 2021 10:20 pm

First post

Resolving power (Rayleigh limit) = 138/D arc seconds
Resolving power (Dawes limit) = 116/D arc seconds
Theoretical visual limiting magnitude...

Last post

Limiting magnitude of a telescope is a far more complex thing than a simple formula.
There are many factors influencing the limit:
Diameter of...

8 Replies

3003 Views

Last post by Don Pensack
Sun May 30, 2021 9:09 pm
Issue with my Coronado PST: shift towards green

Last post by Solsearcher « Fri May 07, 2021 3:37 pm
Replies: 4
by c12marin » Thu May 06, 2021 3:20 pm

First post

Hi folks:

I'm having trouble imaging with a Coronado PST and a DLSR APS-C. The thing is the telescope allows more light to enter than it should and...

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Hello Christian
There are people here who can help you , we just need more information about your scope . Your description about too much light...

4 Replies

1891 Views

Last post by Solsearcher
Fri May 07, 2021 3:37 pm
Aperture size and "seeing" conditions

Last post by OzEclipse « Wed Apr 28, 2021 11:00 pm
Replies: 37
by Piet Le Roux » Wed Sep 30, 2020 2:13 pm
1

2
First post

I am placing this in Off Topic because I just realise we don't have a General Observing sub forum!
I have come across this notion, in different...

Last post

Hi Piet, nFA and all. A very interesting thread here. I wanted to add a couple of items on the affects of atmospheric spherules (cells) on the...
37 Replies

11393 Views

Last post by OzEclipse
Wed Apr 28, 2021 11:00 pm
laser ray tracing the zenith prisms

Last post by j.gardavsky « Thu Apr 22, 2021 7:10 pm
Replies: 6
by j.gardavsky » Tue Apr 20, 2021 9:32 am

First post

Hello all,

as there has been recently criticized the mud in the Takahashi 1.25 zenith prism,

tak prism mud.jpg

I became a bit more curious....

Last post

Hello Gabby,

the case with the scattered light is even worse in the pic posted by another user on the CN. It is no to as bad on my sample, but still...

6 Replies

2212 Views

Last post by j.gardavsky
Thu Apr 22, 2021 7:10 pm
Finally it looks as if my Antares Versascope will guide.

Last post by Greenman « Wed Apr 14, 2021 10:18 pm
Replies: 1
by Greenman » Wed Apr 14, 2021 1:05 pm

First post

My I have had some fun with this - very little information on the back focus needed to use this as a guide scope with an astro camera, in my case an...

Last post

Whoops M51, guide scope will focus but too far out of alignment, never mind goo PA and getting good 1min subs.

1 Replies

1466 Views

Last post by Greenman
Wed Apr 14, 2021 10:18 pm
Difraction Rings

Last post by Bigzmey « Mon Apr 05, 2021 4:50 pm
Replies: 1
by Jones » Mon Apr 05, 2021 5:19 am

First post

Why does my 6 f6 GSO newt show a prominent 1st difraction ring,
while the Edmund 6 f8 reveals just a faint one?

Neither could see the 'f' star in...

Last post

I believe it has to do with F-ratio and size of the central obstruction. The larger central obstruction the more light is distributed from the airy...

1 Replies

1492 Views

Last post by Bigzmey
Mon Apr 05, 2021 4:50 pm
Geometrical optics and focuser

Last post by ARock « Thu Feb 11, 2021 1:22 am
Replies: 6
by turboscrew » Sun Jan 10, 2021 1:02 pm

First post

What's the role of the focuser?
I've been playing with geometrical optics of two lens system, and it looks like the image is always formed, either...

Last post

What's the role of the focuser?

In the above image, the role of the focuser is to place the EP (actually the EP lens) at fe distance away from...

6 Replies

2924 Views

Last post by ARock
Thu Feb 11, 2021 1:22 am
night vision

Last post by yobbo89 « Thu Jan 07, 2021 7:46 pm
Replies: 5
by yobbo89 » Tue Dec 01, 2020 5:09 pm

First post

so, my mum is intrested in some night vision binos or monoculars, does anyone know of something under $500 that would be suitable ?,.. a xmas gift...

Last post

hey guys. thanks for the help, i got her some pre paid credit card cash for some online shoping, i'll link her some of these binos, cheers , i had a...

5 Replies

2951 Views

Last post by yobbo89
Thu Jan 07, 2021 7:46 pm

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