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#1151 davidc135

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Posted 19 February 2021 - 07:39 AM

I found it online and I think it was right here on Cloudy Nights.

I was trying to find the size of the obstruction in a ETX-125.

And I must have spent the entire evening (raining anyway) on the subject because 

the baffle around the secondary mirror is causing confusion, it flairs out larger then

the secondary spot it's self.

Also the primary is actually 5.5" in diameter, adding to the confusion.

Some are saying if we say 5" for the primary and INCLUDE the secondary baffle,

40% central obstruction.

And I can say there is no way the ETX-125 has a 40% obstruction, it's too good.

If we use 5" aperture and the actual secondary spot diameter 1.55" = 31%, that's better

but what about the true size of the primary 5.5" and the true size of the spot?

28% obstruction. I feel this is more inline with what I see in the eyepiece but it

probably isn't correct.confused1.gif

 

Robert

It could be 40%. I tested my 2045 with pieces of masking tape around the co and at the edge and marked the limits when I placed my eye at the focus without an ep. Easier with an sct but maybe stretch masking tape across the whole aperture

I found the aperture was 99mm and the co 45.5mm giving a huge 46% but the image quality is still impressive although it would be put in it's place by a good 3'' refractor. The DX-8 seems to have 35/36%.

 

I wonder how much difference it would make to a Questar 31/2 if a 40% paper disc was stuck on. I expect it could be seen.

David


Edited by davidc135, 19 February 2021 - 07:41 AM.

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#1152 ccwemyss

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Posted 24 February 2021 - 11:31 AM

The AP users group just got permission to post Roland's original 1981 Sky and Telescope article about his NASA glass triplet. It's an interesting read, and the ads are also pretty nostalgic. I notice that one is from a retailer for the AP drive corrector. 

 

https://s3-us-west-1...ve article.pdf"

 

Chip W. 


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#1153 pbealo

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Posted 24 February 2021 - 03:49 PM

Link doesn't work



#1154 DAVIDG

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Posted 24 February 2021 - 04:15 PM

The AP users group just got permission to post Roland's original 1981 Sky and Telescope article about his NASA glass triplet. It's an interesting read, and the ads are also pretty nostalgic. I notice that one is from a retailer for the AP drive corrector. 

 

https://s3-us-west-1...ve article.pdf"

 

Chip W. 

 There was a correction to this article published I believe a month later in Sky and Tel.  Also  Roland had an article in Telescope Making describing his lens and how it came to be. The  original idea was from an Applied Optics article  published many years earlier that showed how to choose the three types of glass. Then Mike Simmons who was one of the co-inventor  of the Astroscan, inventor of the Simak scope and also developed the GOTO systems for Meade and Celestron wrote a program that looked at all the different  three combination of glass that would work with R2=R3  and R4=R5 so those surfaces could be oiled together.

 

                    - Dave 


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#1155 AstroKerr

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Posted 26 February 2021 - 02:09 PM

I found it online and I think it was right here on Cloudy Nights.

I was trying to find the size of the obstruction in a ETX-125.

And I must have spent the entire evening (raining anyway) on the subject because 

the baffle around the secondary mirror is causing confusion, it flairs out larger then

the secondary spot it's self.

Also the primary is actually 5.5" in diameter, adding to the confusion.

Some are saying if we say 5" for the primary and INCLUDE the secondary baffle,

40% central obstruction.

And I can say there is no way the ETX-125 has a 40% obstruction, it's too good.

If we use 5" aperture and the actual secondary spot diameter 1.55" = 31%, that's better

but what about the true size of the primary 5.5" and the true size of the spot?

28% obstruction. I feel this is more inline with what I see in the eyepiece but it

probably isn't correct.confused1.gif

 

Robert

5.00" clear ap, 2.00" 2ndry + Baffle CO, from 'those sources..."

 

127.0mm clear ap, 50.8mm 2ndry + Baffle CO,

 

12,668mm2 pri area & 2,027mm2 CO area, which yields 16.0% Obstruction by Area & 40.0% Diametric Obstruction,

 

10,641mm2 eff Area, 116mm Equivalent or effective Unobstructed Diam, 4.58" in Inches (roughly) which is why it's not "like a 3" aperture" (saw that online) and why it doesn't suck... I think - I haven't calipered any of this directly - this is all 'found online' & should be close enough. Mine didn't suck, or I'd still have it - it was Most Excellent! (worthy of gifting). Are blah-blah and meh-blah affected? Yes they are, most certainly. Are they important? Yes, assuredly. To the extent we imagine? Usually not. Anyways, the ~50mm flared cone baffle seems to be a fact, Meade likes to mention when they oversize a primary and I haven't seen 5.5" - they list 5" / 127mm clear ap, so I think that's what we use?

 

Nitpicky, fun-to-know Math or Fawlty Math aside - the proof is in the views. We can know the Math, but we need the experience - our eyes, our scopes - to interpret it properly. I like the nitpick details so I know roughly why I have good/bad/ugly views.



#1156 ryanr256

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Posted 26 February 2021 - 02:43 PM

A bit late to the aircraft party, but here's a pic of me in front of an SR-71 at Mtn. Home AFB, Idaho in the early 80's:

 

sr71-original.jpg

 

Yes, that's an SP with an M16 in the background. One of the stupidest things I've done in my life.

 

-Bob


Edited by ryanr256, 26 February 2021 - 02:44 PM.

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#1157 Eric P

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Posted 02 March 2021 - 06:09 PM

I love Taks but the plastic knobs on the lower end stuff is just lame.  Finally managed to find a replacement set for my old 76.

 

 

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#1158 Eric P

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Posted 02 March 2021 - 06:15 PM

Also I’ve noticed that packages from Japan are often meticulously taped.

 

 

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#1159 Terra Nova

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Posted 05 March 2021 - 07:36 AM

Another interesting find for those interested in wwii, military surplus, etc:

 

https://sill-www.arm...ULL_EDITION.pdf

 

here’s another one:

 

https://sill-www.arm...ULL_EDITION.pdf

 

(You will see some cool old optical devices here and there.)


Edited by Terra Nova, 05 March 2021 - 07:39 AM.

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#1160 Bobby Dee

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Posted 05 March 2021 - 08:06 AM

Also I’ve noticed that packages from Japan are often meticulously taped.

Speaking of packaging, great sticker on my delivery today.

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#1161 Terra Nova

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Posted 09 March 2021 - 10:35 PM

How about a story concerning classic radio astronomy and a very classic radio telescope:

 

https://www.vice.com...-do-with-aliens


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#1162 GreyDay

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Posted 10 March 2021 - 04:35 AM

Great story Terra, what struck a chord for me personally was the comment,

 

"The tale of channel 37 reflects one thing: Without resistance, a commercial use case will usurp a noncommercial use case for a given resource."

 

This rings so true across many resources, particularly property (real estate) and it's usage. Our local council is so corrupt that many decisions have been made which are contrary to proposals and regulations set out regarding use or ownership of real estate, usually in favour of financial interest and not for the public good.


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#1163 Eric P

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Posted 13 March 2021 - 02:55 PM

My NJP was missing a cast part on the declination axis and sourcing a replacement proved impossible.  So eMachineshop and $214 later I have a part.

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#1164 Garyth64

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Posted 17 March 2021 - 10:42 AM

Well, the spanner wrench came today.  It was from Neewer, spans 10mm to 100mm.

 

attachicon.gifspanner wrench.jpg

 

It seems pretty sturdy, and is a 1000% improvement on what I was using.  It seems like it will really take some torque.

And I think it's made out of SS.

 

I like it.  Thanks for the heads up.

I feel I need to do an update on this spanner wrench.  After using it several times, I suggest not to buy it.

 

Tightening the locking screws as tight as I can with my fingers, they all seem to come loose.  I guess I could use pliers to tighten them, but I felt I shouldn't have to.  I guess if I wanted to, I could retap the holes and use different screws, but it's just not near the top of my to-do list.  So I just work thru the loose screws tightening them as I use it.  I haven't thrown it across the room yet, so there still my be hope.


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#1165 Bomber Bob

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Posted 17 March 2021 - 08:24 PM

Who made What?

 

After I got my first Mizar EQ, I thought it looked very similar to the 1986 Bushnell Banner 1000 that I once owned.  After spending HOURS on ZEN Market, carefully studying (& drooling over!) 100's of vintage Japanese scopes, I can say a couple of things...

 

Circa 1985, these Brands were definitely using common OTA & HINO EQ Hardware:

 

- Bushnell / B&L

- Kenko

- Mizar

- Pentax

 

A couple of ads attributed the mounts and/or OTA castings to Hino Metals.

 

Circa 1976, these Brands were selling EQs almost identical to the venerable Vixen Saturn:

 

- Kenko

- Mizar

- Royal

- Tasco

 

Some of the variations are slight.  One Kenko version has a longer & plainer DEC axis.

 

I hope y'all appreciate how grueling it was, having to look at all those scopes -- many models uncommon or Rare over here in the USA.  You're Welcome!

 

- - - - - - - - - -  EXAMPLES  - - - - - - - - - - 

 

Bushnell / B&L (Mizar) Banner 1000 = Kenko NES:

 

Bushnell Banner 1000 S03 - EQ Mount (Zoom).jpg Kenko NES EQ AS01.jpg

 

100% Identical, including drive motor housing & gearing location.

 

Kenko KES = Vixen SS:

 

K125 - Unpacked S26.jpg

 

Vixen has a few cosmetic differences, but identical large-diameter axis housings, polar scope, etc.

 

Okay, so what?  Well... If you have a Banner 1000, and you need a polar scope, motor drive, hand controller, etc. you can buy the Kenko equivalent if one pops up, and it should fit & function same as the original.


Edited by Bomber Bob, 18 March 2021 - 07:50 PM.

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#1166 Bomber Bob

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Posted 20 March 2021 - 05:24 PM

Uncommon Astro Optical EQ:

 

Typical Tasco 10TE w/ 76mm Cradle

 

Tasco (AO) 76mm EQ 10TE.jpg

 

Uncommon AO w/ 60mm Cradle

 

Tasco (AO) 60mm EQ 10TE Style.jpg

 

Besides all the Eye Candy on ZEN, I'm learning all kinds of cool stuff about the Classic Scopes we go nutz over.  Need a clutch-gear widget for your Classic Vixen Super Polaris?  With patience, you can find one.  Want to use the caps (optical housings) from your favorite .965" eyepieces?  You can buy sets of 3 x 1.25" barrels with adapters - just thread the small format in, and Presto / Chango!  they'll fit standard focusers.  Oh!  And apparently, scopes that are dirtier than average earn the JUNK adjective in their ad titles...


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#1167 blakestree

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Posted 24 March 2021 - 04:41 PM

Is there a better alternative for a 1.25" visual back, for my Swift 839, than Vixen part #3720? Maybe something with a compression ring, instead of set screw?

 

Danke!



#1168 blakestree

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Posted 01 April 2021 - 01:12 PM

Hey, guess what? My Brandon 94 has a 92mm CA. I was slightly perturbed by the stated 94/640/f7 discrepancy. So, I measured. Looks like those early "misprints" may have actually been correct.


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#1169 Steve C.

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Posted 07 April 2021 - 12:09 AM

60AD767A-BE81-4FCD-B3FE-19425C9CE382.jpeg

My little Tasco 11TR, Christmas 1969.

 


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