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Stellarvue 80mm f7 Aplanat question

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#1 BDS316

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Posted 03 December 2021 - 02:22 PM

Hi I have one of these and it's a long discontinued model for sure.

 

I've enjoyed it mostly for low power wide field views of open clusters etc with my 32mm Televue Plossl and occasionally pushed the power up to 100-150x for luna and planets. I say occasionally since I have an 8 inch Dob for this type of observing.

 

The size format  of the scope suits me well as a grab n' go.

 

Would I be considered a candidate to upgrade to something of similar size but far more expensive like a TV85 or AP Stowaway?

 

Thanks

 

 



#2 Jon Isaacs

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Posted 03 December 2021 - 04:12 PM

Bryan:

 

I've had my 80 mm F/7 William Optics Megrez ll FD for more than 15 years.. it's a FPL-53 doublet with very good optics and very good mechanicals.  I had a Pronto and have an NP-101, I like the TeleVue build but I've never figured a reason that would justify a TV -76 or TV-85.. 

 

I think you'd be happy with an upgrade to an 80 mm FPL-53 doublet or even a Pk-61 doublet like the Astro-Tech 80ED..  it would have nearly 4 times better color correction than your current scope.

 

Of course if you want to spend the money... TV and A-P are there waiting as is the AT-92EDT..

 

 Jon



#3 Stahi

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Posted 03 December 2021 - 05:11 PM

I have been using a Stellarvue Aplanat 80mm f7 for the past 13 years. I too also have a dob, mainly for lunar/planetary (in my case a 12.5 f6).

I placed an order recently for an FOA-60q. I know quite different from the aplanat. I may also get a wide field refractor, like a cheap but larger 120mm f5 for those low magnification views - or perhaps use the Tak in q less mode.

I love the aplanat for what it is and how it's served me faithfully, but given how available short tube apos are these days... to me its utility is limited since CA is quite noticeable when you push the power to anything decent. I was impressed at its performance over a decade ago, but now I'm spoiled. Even the views in my Sharpstar 61edph ii I bought solely for beginner level wide field astrophography has so much better color correction at the eyepiece than the aplanat.

#4 BDS316

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Posted 04 December 2021 - 05:31 PM

Thanks guys...

Last night our club had our first open-to-the-public observing sessions in over a year and I brought the 80mm Aplanat. Low power views were excellent: Pleiades, Alberio, Andromeda and especially the double cluster. When I tried to up the magnification on Jupiter and Saturn the views got mushy. Unfortunately no other refractors of similar size for comparison.

I always thought that in terms of performance and color correction the Aplanat should be in between the original achromatic Nighthawk and the 80 ED.

Edited by BDS316, 04 December 2021 - 05:35 PM.


#5 Jon Isaacs

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Posted 04 December 2021 - 06:54 PM

Thanks guys...

Last night our club had our first open-to-the-public observing sessions in over a year and I brought the 80mm Aplanat. Low power views were excellent: Pleiades, Alberio, Andromeda and especially the double cluster. When I tried to up the magnification on Jupiter and Saturn the views got mushy. Unfortunately no other refractors of similar size for comparison.

I always thought that in terms of performance and color correction the Aplanat should be in between the original achromatic Nighthawk and the 80 ED.

 

The Aplanat is an achromat. An aplanatic lens is one that is free of coma and spherical aberration. 

 

As such, the chromatic aberration will be slightly better than the 80mm F/6 Achromat.  The Orion ED-80 is in a different league.  

 

One way to characterize a refractor's color correction is the compare the diameter of the chromatic blur to the diameter of the Airy disk:

 

80 mm F/6 achromat: Chromatic blur =  5.2 x the Airy disk

 

80 mm F/7 achromat: Chromatic blur = 4.4 x the Airy disk

 

ED-80 Orion F/7.5 FPL-53 doublet: Chromatic blur = 0.71 x the Airy disk.

 

The ED-80s chromatic blur is smaller than the Airy disk, essentially free of chromatic aberration.

 

Jon


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#6 Spikey131

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Posted 04 December 2021 - 07:00 PM

You would be very happy with a TV85 or AP Stowaway.  The former is readily available new and good used units show up frequently.  The used ones are often a bargain.  The Stowaway is a bit of a unicorn, not really available new and at a premium used.


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#7 alnitak22

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Posted 04 December 2021 - 07:21 PM

Thanks guys...

Last night our club had our first open-to-the-public observing sessions in over a year and I brought the 80mm Aplanat. Low power views were excellent: Pleiades, Alberio, Andromeda and especially the double cluster. When I tried to up the magnification on Jupiter and Saturn the views got mushy. Unfortunately no other refractors of similar size for comparison.

I always thought that in terms of performance and color correction the Aplanat should be in between the original achromatic Nighthawk and the 80 ED.

Yes, theoretically the performance should fall between the Nighthawk and ED80. Closer to the former than the latter.




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