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Pretty decent deal on a 20"

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#76 stargazer193857

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Posted 19 November 2018 - 11:06 PM

Elvira 24" f/2.75 The very perfect scope . . . .


It will be perfect when they figure out how to do it cheaply. Sure you would not prefer a 36" f2.75?
 

#77 stargazer193857

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Posted 19 November 2018 - 11:08 PM

If the stair case is made shallow enough with deep enough spend of similar hight, a third pair of legs would help keep the weight down.
 

#78 opticsguy

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Posted 20 November 2018 - 01:05 AM

It will be perfect when they figure out how to do it cheaply. Sure you would not prefer a 36" f2.75?

 

No ladder needed for  Elvira 24" f/2.75 The very perfect scope . . . .


 

#79 Shneor

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Posted 20 November 2018 - 02:17 AM

Good points. What depth do you think is the minimum needed for comfort?
Do you mean rubber strops are good? Deep soft rubber? Expanded holly metal?
Yeah, plain flat metal would be slippery too.


With staggered feet aimed 45 degrees to the side, would 8" steps be comfortable? I'm thinking the balls heal base and toe base, not toe tips, are the most important part to support.

I think 8" would work; the Cosco steps look like some kind of plastic, maybe with a thin rubbery coating. If I need a couple of extra inches, I use a piece of 2x8 board on the top step - also when someone is a bit too short for the position of the eyepiece.


Edited by Shneor, 20 November 2018 - 02:19 AM.

 

#80 stargazer193857

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Posted 20 November 2018 - 03:59 PM

A 2 by 8. I did not think of such booster. And as long as it is not deeper than the step, it is easy to step up onto.
 

#81 spaceoddity

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Posted 20 November 2018 - 05:49 PM

An 18" Obsession UC with a feathertouch, sips and a bunch of other upgrades just sold here on the classifieds last week for $2800. That was a steal IMO. If it would have been a little closer I would have been all over it.


 

#82 a__l

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Posted 23 November 2018 - 07:51 AM

No ladder needed for  Elvira 24" f/2.75 The very perfect scope . . . .

It is curious this statement.
Does not need a ladder and less fast telescopes.
For example, my 24" f/3.3 is just a small tabouret (if at zenith).
The faster the parabola, the more (heavier) the secondary, the more likely problems are with manufacturing mirror, collimation, telescope design requirements, etc.


Edited by a__l, 23 November 2018 - 07:53 AM.

 

#83 opticsguy

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Posted 23 November 2018 - 10:22 AM

There can be many perfect telescopes, and I have observed through several perfect telescopes. 

 

I have many hours of observing time in this 24" perfect telescope.  I have been observing for 56 years. 

 

Elvira - 24"  f/2.75  -  the perfect scope. 

 

Nuff said.


 

#84 dgoldb

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Posted 23 November 2018 - 10:29 AM

There can be many perfect telescopes, and I have observed through several perfect telescopes. 

 

I have many hours of observing time in this 24" perfect telescope.  I have been observing for 56 years. 

 

Elvira - 24"  f/2.75  -  the perfect scope. 

 

Nuff said.

Perhaps perfect for now.  Technology marches on... 


 

#85 stargazer193857

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Posted 23 November 2018 - 04:33 PM

It is curious this statement.
Does not need a ladder and less fast telescopes.
For example, my 24" f/3.3 is just a small tabouret (if at zenith).
The faster the parabola, the more (heavier) the secondary, the more likely problems are with manufacturing mirror, collimation, telescope design requirements, etc.


Secondary size is far more affected by focal length than focal ratio.

750mm scopes have a 33% CO regardless of aperture, unless the designer chooses to fully aluminated a big eyepiece.

1200mm FL scopes are around 25% CO, yes, even a 6" f8.

1500mm scopes are around 20%, ladder territory gets you down below 16%.

I'm willing to accept 23% to sit comfortably at 1370mm.

Keeping eyepiece height constant while increasing aperture does increase CO a tiny bit, but no where near as much as shrinking focal length, even if the f# is increased by decreasing aperture.
 

#86 a__l

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Posted 23 November 2018 - 05:12 PM

Secondary size is far more affected by focal length than focal ratio.

750mm scopes have a 33% CO regardless of aperture, unless the designer chooses to fully aluminated a big eyepiece.

1200mm FL scopes are around 25% CO, yes, even a 6" f8.

1500mm scopes are around 20%, ladder territory gets you down below 16%.

I'm willing to accept 23% to sit comfortably at 1370mm.

Keeping eyepiece height constant while increasing aperture does increase CO a tiny bit, but no where near as much as shrinking focal length, even if the f# is increased by decreasing aperture.

In this case, the 24" size is discussed.
Curious one more. For telescopes with a size>=16" (arbitrary digit) there are many statements about 'ideality' and almost never confirmation this. For example, StarTest, Ronchigram or something else. Because both finished optics and finished telescope can be different situations. Of interest is the finished product in complex.

 

For the statement about the 'ideality' of the telescope, there must be an 'ideal' observation condition. In this case, it is easy to confirm StarTest.

 

One of the options to simplify the task is video stream processing (StarTest).
For example RegiStax. As an addition to the 'raw' photo


Edited by a__l, 23 November 2018 - 05:56 PM.

 

#87 a__l

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Posted 23 November 2018 - 06:37 PM

I do not insist, replace the word 'ideal' on 'perfect' (4 of 4) or 'good' (3 of 4)

Or better than L/7 (L/4) as you like ...

 

smile.gif


Edited by a__l, 23 November 2018 - 06:45 PM.

 

#88 CHASLX200

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Posted 23 November 2018 - 06:50 PM

Did anyone jump on that 20" F/5?


 

#89 GShaffer

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Posted 23 November 2018 - 07:20 PM

Finally an on topic post again LOL

 

Was on the verge of locking the thread :)


 

#90 CHASLX200

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Posted 23 November 2018 - 08:02 PM

I sure would trade all my scopes for it.


 

#91 Shneor

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Posted 24 November 2018 - 02:21 AM

Did anyone jump on that 20" F/5?

Don't know. I was actually in Decatur last weekend, but with family, no time to check out the scope...


 

#92 CHASLX200

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Posted 24 November 2018 - 07:05 AM

Well if someone is headed to FL i would pay well for gas money.  I just gotta wonder if it would fit thru my door all setup.  Be the perfect planet scope for my seeing.  Sure not gonna fit in my Corvette.


 

#93 stargazer193857

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Posted 24 November 2018 - 11:35 AM

Planet scopes don't have to point at zenith. Might not need ladders.

A dedicated planet scope can have a shorter base.

Edited by stargazer193857, 24 November 2018 - 11:36 AM.

 

#94 rowdy388

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Posted 24 November 2018 - 12:18 PM

Planet scopes don't have to point at zenith. Might not need ladders.

A dedicated planet scope can have a shorter base.

Good point!


 

#95 stargazer193857

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Posted 24 November 2018 - 12:33 PM

A 10" f9 can have can have a tripple truss and short base and easy collimation, small secondary, and no need for extra corrective glass. Also easy to make the mirror. Cool much faster too. That is why planetary folk don't run out and buy 16" scopes despite all the technological advances.

You could angle the eyepiece down, just for that use.

Edited by stargazer193857, 24 November 2018 - 12:56 PM.

 

#96 GShaffer

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Posted 24 November 2018 - 02:50 PM

The scope this topic was about has been sold......closing this out.


 


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