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TeleVue NP101 vs Genesis SDF

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#26 areyoukiddingme

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Posted 10 February 2020 - 12:10 PM

Interesting. In a camera, there's a ton of coma at the edge.

 

Visually, it looks like very small amounts of astigmatism in perhaps the last 5% of the field.



#27 Phillip Creed

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Posted 10 February 2020 - 01:40 PM

I had no idea the TV101 was an improvement on the SDF.  Interesting!

The question in my mind is--and I'm sure I'm not alone in asking this--WHAT improvement was it between the SDF and the TV-101 that compelled the retirement of the SDF for the TV-101 back in the late 1990s?

Not too many TV-101's pop up used.  It's typically the SDF's or the (non-IS) NP-101's, but not the iteration in between them.

Clear Skies,

Phil



#28 25585

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Posted 10 February 2020 - 03:51 PM

The question in my mind is--and I'm sure I'm not alone in asking this--WHAT improvement was it between the SDF and the TV-101 that compelled the retirement of the SDF for the TV-101 back in the late 1990s?

Not too many TV-101's pop up used.  It's typically the SDF's or the (non-IS) NP-101's, but not the iteration in between them.

Clear Skies,

Phil

Company 7 does not stipulate. Perhaps more cosmetic than anything else e.g. green tube option as 76s & 85s have now.

 

One thing I notice on the 101 specs is its photography is 35mm only, so pre-digital.

" 35mm prime-focus field: 3.7 x 2.6 x 4.5 degrees @ f10.8, 

35mm field with 2x Barlow: 1.9 x 1.3 x 2.4 degrees @ f10.8"

 

 


Edited by 25585, 10 February 2020 - 03:52 PM.


#29 Brent

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Posted 10 February 2020 - 04:45 PM

If I’m not mistaken, the optical design must have changed somewhat, as the Genesis sdf incorporated fluorite, whereas the TV-101 did not. (The “f” in “sdf” stood for fluorite.)


Edited by Brent, 10 February 2020 - 04:46 PM.


#30 Toddeo

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Posted 10 February 2020 - 06:46 PM

My "Mint" 1991 Genesis just has "fluorite" written(under the word Genesis) on the side of the focuser. Here's some paperwork that came with the scope.

Attached Thumbnails

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Edited by Toddeo, 10 February 2020 - 07:11 PM.

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#31 Jon Isaacs

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Posted 10 February 2020 - 08:02 PM

If I’m not mistaken, the optical design must have changed somewhat, as the Genesis sdf incorporated fluorite, whereas the TV-101 did not. (The “f” in “sdf” stood for fluorite.)

I think what maybe confusing is that the Fluorite is not necessarily used in the front objective. By modern standards, the Genesis would not be considered an apo, at least by my standards and the one I looked through.  It was more colorful than an AT-102ED by a ways.

 

Jon



#32 Brent

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Posted 10 February 2020 - 09:25 PM

Jon,

it is my understanding that both the original Genesis and the sdf used fluorite in the rear petzval doublet.  The sdf added an sd element (in the front doublet, I believe, but am not sure).  The innovation of the sdf was not the fluorite, but the sd element.  TeleVue stopped using fluorite with the TV-101.

That is how I remember it.

Brent


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#33 Phillip Creed

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Posted 11 February 2020 - 10:58 AM

I think what maybe confusing is that the Fluorite is not necessarily used in the front objective. By modern standards, the Genesis would not be considered an apo, at least by my standards and the one I looked through.  It was more colorful than an AT-102ED by a ways.

 

Jon

That's about how I remember my f/5 non-SDF Genesis Device.  About the same CA as a 4" ~f/12 achromat.  Tested it alongside an 80mm f/6 achro and a 4" f/15 Edmund Scientific achro.  Much less CA than the former but a little more than the latter.  Still, for a 4" f/5 scope it was quite the versatile performer.

Common talk under dark skies went like this--

Fellow observer: "Where's your finderscope?"
Me:  <silent grin>

The SDF was a different ball game.  The NP-101 is essentially perfect, but I'd say at least visually a used SDF bridges 3/4 of the color correction gap between the original f/5 Genesis and the NP-101 for about half the used price of an NP-101.  Planets may be sharper in scopes that have perfect color correction, but the SDF is no slouch.  I could only see hints of CA at 150X or more on Vega, and none on Jupiter.

As others have noted, iterations prior to the NP-101 aren't that conducive for widefield imaging.  I've tried it through the SDF and while the color correction was okay (minus a little blue bloating), you could clearly see that the illumination dropped off quickly away from center--and this was with a cropped sensor (Canon T6).  No surprise given the fast f/5.4 light cone and smaller reducing element vs. the later NP-101 and NP101is.

Clear Skies,

Phil


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#34 riot1013

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Posted 12 February 2020 - 11:47 AM

The question in my mind is--and I'm sure I'm not alone in asking this--WHAT improvement was it between the SDF and the TV-101 that compelled the retirement of the SDF for the TV-101 back in the late 1990s?

Not too many TV-101's pop up used.  It's typically the SDF's or the (non-IS) NP-101's, but not the iteration in between them.

Clear Skies,

Phil

The TV-101 uses an ED substrate in the front and rear elements.  The SDF used one fluorite lens in the rear element (if I remember correctly).  Both are fundamentally the same design which is paired f11 doublets that together function as an f5.4 optical system.


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#35 25585

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Posted 12 February 2020 - 12:10 PM

The TV-101 uses an ED substrate in the front and rear elements.  The SDF used one fluorite lens in the rear element (if I remember correctly).  Both are fundamentally the same design which is paired f11 doublets that together function as an f5.4 optical system.

I think I would rather have the SDF, given a choice. Fluorite or an unspecified ED glass.

 

Did Vixen provide or make the SDF's lenses for TV?



#36 Jon Isaacs

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Posted 12 February 2020 - 01:36 PM

I think I would rather have the SDF, given a choice. Fluorite or an unspecified ED glass.

 

Did Vixen provide or make the SDF's lenses for TV?

 

It's a little more complicated than that.

 

Both have unspecified ED glass.  The Fluorite is in the rear of the SDF. Both have unspecified glasses in the objective where it's more important.

 

My guess: The TV-101 uses FPL-53 at both ends, the SDF does not use FPL-53 in the objective. 

 

It's hard to imagine that TV would design the TV-101 with inferior correct to the SDF.

 

Jon


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#37 riot1013

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Posted 12 February 2020 - 01:37 PM

I think I would rather have the SDF, given a choice. Fluorite or an unspecified ED glass.

 

Did Vixen provide or make the SDF's lenses for TV?

I don't know about that.  The TV101 was flawless from a color standpoint, the SDF wasn't.  When you are talking about two f11 lens pairings you really shouldn't need super exotic lens elements to correct for color.  FPL 53 or FCD 100 really isn't neccessary.


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#38 areyoukiddingme

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Posted 12 February 2020 - 01:39 PM

Phil's observation is a small amount of CA at ~150x in his SDF.

 

I see zero CA at any power in the 101. So I would think that means better glass in the 101.


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