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?...

Last post

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

20004 Views

Last post by Don Pensack
Sun Jul 11, 2021 2:35 pm
Focal Length

Last post by Don Pensack « Thu Sep 28, 2023 5:56 pm
Replies: 13
by Graeme1858 » Mon Sep 11, 2023 10:32 pm

First post

My 9.25 (235mm) F10 SCT has a focal length of 2350mm. I put an F6.3 focal reducer on it which should, according to the maths, reduce my focal length...

Last post

Ah, yes, that makes sense.

So would a 1480mm to 1317mm focal length reduction be considered normal and to be expected?

Also, is it not the case...

13 Replies

250 Views

Last post by Don Pensack
Thu Sep 28, 2023 5:56 pm
Bell Howell Objective 36" F/8 - What type of Lens Elements are in it?

Last post by Michael131313 « Sun Sep 17, 2023 6:20 pm
Replies: 7
by TheButcher » Mon Aug 28, 2023 11:57 pm

First post

I was wondering if anyone here could chime in on what type of lens elements this could be? A friend of mine gave this to me the other day for free. I...

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Thanks for the interesting post .

7 Replies

175 Views

Last post by Michael131313
Sun Sep 17, 2023 6:20 pm
Last chance to purchase :)

Last post by Lady Fraktor « Thu Aug 17, 2023 5:05 pm
Replies: 2
by Lady Fraktor » Mon Aug 14, 2023 6:58 pm

First post

If anyone has considered converting their Synta 150 mm f/8 refractor to a APM 152 mm f/7.9 ED doublet, Teleskop-Service has one left.
APM has decided...

Last post

APM is still continuing to sell the 140 mm doublet lens in cell using FPL-53 and refractor.
The only 152 mm f/7.9 they will be producing is the LZOS...

2 Replies

128 Views

Last post by Lady Fraktor
Thu Aug 17, 2023 5:05 pm
Correcting coma in my 102 f/5 Startravel

Last post by Lady Fraktor « Wed Jun 21, 2023 5:38 pm
Replies: 18
by John Baars » Tue Mar 07, 2023 1:04 pm

First post

In my review I wrote about some flaws in my new 102mm f/5 Startravel.

Near focus the Poisson point was found to be not exactly in the center, but...

Last post

Looking good John!

Hard work pays off, btw how's the focuser on that scope?

I always had fun improving those Synta focusers, with proper cleaning...

18 Replies

1184 Views

Last post by Lady Fraktor
Wed Jun 21, 2023 5:38 pm
The Barlow Lens ?

Last post by Frankskywatcher « Thu Mar 09, 2023 1:50 pm
Replies: 36
by Frankskywatcher » Tue Feb 28, 2023 5:52 pm
1

2
First post

I’m posting this in the hopes of getting some insight about Barlow lenses.

I’m just really curious how often they are used,the results, price ranges...

Last post

Hello Frank. It was my pleasure to send you that fine Barlow lens and I hope that you will have many great views and observing sessions using it with...
36 Replies

1861 Views

Last post by Frankskywatcher
Thu Mar 09, 2023 1:50 pm
Optical Reports

Last post by John Baars « Tue Mar 07, 2023 11:12 pm
Replies: 4
by Lady Fraktor » Thu Feb 16, 2023 9:07 pm

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I was looking around a different astro site when I read a conversation about someone not being able to get a Zygo report for his refractor so was no...

Last post

I agree with Lady Fraktor. One should learn to do his/her own testing if necessary. Most of the time it isn't, one can recognize quality when one...

4 Replies

473 Views

Last post by John Baars
Tue Mar 07, 2023 11:12 pm
Zoom EP questions

Last post by messier 111 « Wed Mar 01, 2023 1:07 am
Replies: 6
by Ylem » Tue Feb 28, 2023 10:47 pm

First post

I have been thinking about snagging one for both solar and vacation use.
What I don't really like about them is it seems FOV Increases with higher...

Last post

hi jeff ,
here is the one I use with my televue 85 .

I like the eye relief and the field of view.
for the price it is very good.
I use it to see the...

6 Replies

440 Views

Last post by messier 111
Wed Mar 01, 2023 1:07 am
Is this ruined?

Last post by Frazman « Sun Jan 15, 2023 11:48 pm
Replies: 10
by Frazman » Thu Dec 29, 2022 12:23 am

First post

304DE053-3BFB-49F6-BF60-E91408E318C6.jpeg

Years ago I found this 102/600 lens for sale and bought it for a project scope, cutting down a 102/1000...

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Weather has been sporadic and on the somewhat clear nights Luna has been in the way.

The one night I was able to get out just a short while I saw...

10 Replies

790 Views

Last post by Frazman
Sun Jan 15, 2023 11:48 pm
Understanding the (so-called) Dawes Limit

Last post by Don Pensack « Sat Oct 29, 2022 3:56 pm
Replies: 3
by mikemarotta » Wed Nov 03, 2021 10:20 am

First post

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...

Last post

Here is a more calculated approach to Rayleigh, Dawes, and Sparrow limits:

Note also that the resolving ability of a scope depends on shape and...

3 Replies

17141 Views

Last post by Don Pensack
Sat Oct 29, 2022 3:56 pm
What has happened with the Explore Scientific love?

Last post by Nakedgun « Tue Oct 18, 2022 3:16 am
Replies: 9
by Lady Fraktor » Sun Oct 16, 2022 5:57 pm

First post

3-4 years ago you could not go a day without reading postings about how great Explore Scientific telescopes are.
Now you hardly see them mentioned,...

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~

In my view, we see the result of the impact that the world-wide economic lockdown has had on production, along with the (now) inflation-driven...

9 Replies

810 Views

Last post by Nakedgun
Tue Oct 18, 2022 3:16 am
Bino-viewing

Last post by Lady Fraktor « Sun Oct 16, 2022 3:50 am
Replies: 1
by Nakedgun » Sun Oct 16, 2022 2:28 am

First post

Vernonscope is distributing this model, which reached my doorstep Thursday, just ahead of cloudy/wet weather. I was able to test it under clear...

Last post

They and the Baader are in the unobtanium class for me currently.
Enjoy the views.

1 Replies

360 Views

Last post by Lady Fraktor
Sun Oct 16, 2022 3:50 am
Purchased a 2" Altair Astro Prism Diagonal

Last post by Bigzmey « Sun Sep 25, 2022 4:54 pm
Replies: 11
by davesellars » Mon Sep 19, 2022 12:40 pm

First post

OK, I finally got round to getting a prism for using in either the 102ED for planetary / lunar or the 80ED for solar observing. Apart from the...

Last post

I know right? Once you look through a good quality prism the difference is obvious.

11 Replies

1038 Views

Last post by Bigzmey
Sun Sep 25, 2022 4:54 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

First post

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...

Last post

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

1256 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

First post

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?...

Last post

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

4 Replies

888 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

First post

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...

Last post

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

1609 Views

Last post by Richard
Sat Mar 26, 2022 1:55 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:...

Last post

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

3936 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...

Last post

...
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

9457 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

2800 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,...

Last post

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

4410 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

First post

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....

Last post

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

2202 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...

Last post

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

3953 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

4902 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

First post

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

4653 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...

Last post

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

7 Replies

3268 Views

Last post by LDW47
Fri Jun 11, 2021 5:57 pm

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