General Optics

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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.

Last post

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

5462 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

First post

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

4089 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
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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

12629 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

5197 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

3186 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
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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...

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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

16749 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

3410 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...

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

1 Replies

2219 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...

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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

2146 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

4024 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

3956 Views

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

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