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Sharpstar 130 f/2.8 for NV?

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#1 Sarkikos

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Posted 11 June 2021 - 08:14 PM

How would this fast Newt be for NV?  Would it be worth the price?

 

https://agenaastro.c...h-13028hnt.html

 

Mike



#2 a__l

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Posted 11 June 2021 - 08:44 PM

If you have it, it makes sense to try it out.
2.5" focuser and promised 44mm flat field.
The only nuance is China and there may be problems with a specific instance.


Edited by a__l, 11 June 2021 - 08:44 PM.

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#3 Mazerski

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Posted 11 June 2021 - 08:51 PM

I have the TS Boren-Simon 8” f/2.8 or f/4 and recommend it.

 

I use the Mod3 and PVS7 NV devices and it’s a great scope - I use it ~ 100% with NV.

Emission nebula look great thru scope as do some galaxies and globulars - I can use the 2x Powermate for f/8 on star stuff.

 

As for the SharpStar - I don’t know anything about it or if the price is reasonable other than reading somewhere that the company / scopes have QC issues. 
 

Note: scope comes with corrector / reducer for f/2.8 and can use scope without it. 
I use with filter wheel most of the time.


Edited by Mazerski, 11 June 2021 - 09:29 PM.

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#4 a__l

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Posted 12 June 2021 - 02:46 AM

I have the TS Boren-Simon 8” f/2.8 or f/4 and recommend it.

 

 

If the SharpStar actually has a 44mm field, it is better for afocal use than the ASA corrector in the TS.
Here you can see the ASA CC https://www.astrofotoblog.eu/?p=856

 

I have a SharpStar 0.95x coma corrector. This works well on my f/4 (for prime focus). There is an inconvenience. It is necessary to move the primary mirror to the focuser ~ 35-40 mm relative to P2.


Edited by a__l, 12 June 2021 - 02:49 AM.


#5 Mazerski

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Posted 12 June 2021 - 07:59 AM

If the SharpStar actually has a 44mm field, it is better for afocal use than the ASA corrector in the TS.

 

I have a SharpStar 0.95x coma corrector. This works well on my f/4 (for prime focus). There is an inconvenience. It is necessary to move the primary mirror to the focuser ~ 35-40 mm relative to P2.

I’ll accept what you say... however, I lack the skills and tools to move primary mirror and I observe in prime mode only. I sold (2) ENVIS lens. As for P2, is this the Televue Paracorr ? For f/4 I use the Baader MPCC (small and lightweight compared to the TV).
 

Unfortunately no paperwork is available for the Boren-Simon scopes... it would be nice to know something about the Focuser (how much weight it can handle).



#6 a__l

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Posted 12 June 2021 - 08:21 AM

SharpStar 0.95x this is a 2" coma corrector. For it need to move the mirror for prime focus. For afocal with TV67 it has vignetting and I don't recommend it.

Sharpstar 130 mm has 2.5" corrector for a hyperbolic mirror. I have no experience with it.
P2 is paracorr -2.
ASA 0.73x is a 2" corrector-reducer.

 

Now I have 4 correctors: P2, modified SIPS module, P1 and SharpStar 0.95x.


Edited by a__l, 12 June 2021 - 08:42 AM.


#7 maxmir

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Posted 12 June 2021 - 12:43 PM

I have had 2 sharp star refractory
I had send back one the optics were so bad
The other has marginal optics
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#8 GeezerGazer

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Posted 12 June 2021 - 02:30 PM

Hi Mike,

You didn't say how you would use the scope with NV; visual at the NV ocular or for photos.  I have seen some really nice, flat field images taken with this scope, but I've forgot where I saw them, sorry.  I would say that it depends on how much you plan to use the Sharpstar which is designed for wide field imaging.  With NV at ~5x you would have an 8° FoV which covers a lot of sky.  I do like seeing that much sky sometimes to see how things fit together.   But as a rule, I like a bit more magnification; I use my 300mm lens a LOT more than my 135mm lens... this is a personal preference.  

 

Although I used a 150mm Newt (parabolic mirror) at f:2.8 for 6 months, I sold it after acquiring an 8" f:4 Newt that is also used at f:2.8.   Like Mazerski and Eddgie, I have the TS .73x reducer which works well with most f:4 parabolic Newts.  Even though it may not have the perfectly flat field of the Sharpstar, it does pretty well and I have no complaints using it visually with NV.  If you go to my gallery, you can look at the first two images (Lobster and Cat's Paw) and then scroll down to the Monkeyhead (and below), where several of the images were taken with the 8" f:4 + .73x reducer at f:2.8, to see if those results are satisfactory for your needs.  https://www.cloudyni...-phonetography/

 

The TS Boren Simon 150mm including the .73x reducer, is less expensive than the Sharpstar if that is of concern.  One advantage of the .73x TS reducer is that it can be used with just about any f:4 Newt having a parabolic mirror.  So if you have more than one f:4 Newtonian scope, it is easily transferred (it just drops in the focuser).  And the price difference between buying a hyperbolic and parabolic scope is fairly substantial, especially in larger apertures.  The TS reducer did work fine in the Orion 150mm Newt I had, but I had to raise the primary about 2cm to reach focus.  It fit perfectly in my ES 8" CF Newt without modification.  

 

There was a review of the Sharpstar in S&T about a year ago and IIRC, the review was mostly positive but had a couple of cons.  It has 55mm of back focus so it should work with NV fine.  

 

To see if you really like the image scale you could try a 135mm camera lens if you have one, although the Sharpstar would provide a brighter image at an equal f:2.8.  

 

Gavster had a fast Tak 130 that he liked pretty well; you might PM him for details.  I don't know anyone who uses their NVD with the Sharpstar.  

Good luck.  If you buy one, please let us know how it works out.  


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#9 Sarkikos

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Posted 12 June 2021 - 02:53 PM

I don't have any NVD's ... yet.  But I've been gathering information about it for a few years now.  I don't do any imaging, I'm 100% visual.  It seems, though, that some of the OTA's and accessories meant for imaging might be good for NV. 

 

I already have two Newts that were actually meant largely for imaging:  the Bresser 208 f/3.9 and TPO 150 f/4.  In order for either to come to focus for visual astronomy, I have to install either an extension at the focuser or put in a filter wheel.  It is convenient sometimes to have a Newt that can come to focus with a filter wheel for visual without having to also put a Barlow or Barlow lens assembly in the optical train.

 

They might also be good for NV when I finally get into that.

 

Mike


Edited by Sarkikos, 12 June 2021 - 02:59 PM.

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#10 a__l

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Posted 12 June 2021 - 03:29 PM

The TS Boren Simon 150mm including the .73x reducer, is less expensive than the Sharpstar if that is of concern.  One advantage of the .73x TS reducer is that it can be used with just about any f:4 Newt having a parabolic mirror.  So if you have more than one f:4 Newtonian scope, it is easily transferred (it just drops in the focuser).  And the price difference between buying a hyperbolic and parabolic scope is fairly substantial, especially in larger apertures.  The TS reducer did work fine in the Orion 150mm Newt I had, but I had to raise the primary about 2cm to reach focus.  It fit perfectly in my ES 8" CF Newt without modification.  

 

 

There is little information on ASA 0.73. Here's what I'm found in the end.

http://xmcvs.free.fr...pe1/reducer.htm

It looks like Philipp KELLER has optimized it for these telescopes.

I doubt it will fit my 18" f/4 (for example).



#11 Mazerski

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Posted 12 June 2021 - 03:44 PM

I purchased the BS8ED in August 2017 and this is the reducer that came with scope. 

 

== The thin adapter is required to use reducer with a 1.25 (standard) filter wheel

== The reducer does not focus in a NewMoon 12.5" f/4.5 Dobsonian. The Antares 2" 0.5x and 0.7x do focus in NewMoon.

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#12 a__l

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Posted 12 June 2021 - 04:16 PM

This is not what I am writing about.
Most likely you need to make truss tubes shorter for your NewMoon.
I am writing about the quality of field correction.

The field curvature of short telescopes differs from that of long ones.
200x4 = 800 mm (8" f/4)
450x4 = 1800 mm (18" f/4)



#13 GeezerGazer

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Posted 12 June 2021 - 06:47 PM

I don't have any NVD's ... yet.  But I've been gathering information about it for a few years now.  I don't do any imaging, I'm 100% visual.  It seems, though, that some of the OTA's and accessories meant for imaging might be good for NV. 

 

I already have two Newts that were actually meant largely for imaging:  the Bresser 208 f/3.9 and TPO 150 f/4.  In order for either to come to focus for visual astronomy, I have to install either an extension at the focuser or put in a filter wheel.  It is convenient sometimes to have a Newt that can come to focus with a filter wheel for visual without having to also put a Barlow or Barlow lens assembly in the optical train.

 

They might also be good for NV when I finally get into that.

 

Mike

Yes, many imaging scopes and accessories are used with NV.  Imaging scopes have two primary advantages.  First, they usually provide a faster focal ratio for a brighter image.  And, no less important, they provide full-sensor illumination.  

 

My ES 208 is the same as your Bresser, @ f:3.9.  So if the edge correction in my photos is satisfactory, you can buy the TS 2KORR reducer, as described above (~$700), and use it in both your 150 & 208 at f:2.8 (the 150 might need adjustment on primary height... longer primary screws should suffice).  Keep in mind that my photos show zero noise/scintillation, which is a function of photo averaging.  The NV ocular image, when using H-a filters, often shows scintillation.  

 

My own experience with NV has revealed f:2.8 to f:4 or even f:5.6 as a sweet spot for H-a filtration with NV.  But I use NV in prime focus almost exclusively.  If you choose to use NV in afocal, there are different solutions.  Choosing how you want to use NV most often (prime or afocal) will determine what solution you should choose for optimal performance.  Jeff, above, described some of the reasons you might use both methods; you need not choose just one method of implementation.  Each has strong points and weaknesses.  Because of TeleVue's entry selling PVS 14 NVDs, many more observers now choose that route as a turnkey unit.  But prime focus does have some advantages too.


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#14 Astrojedi

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Posted 03 July 2021 - 09:06 PM

How would this fast Newt be for NV?  Would it be worth the price?

 

https://agenaastro.c...h-13028hnt.html

 

Mike

Mike,

 

Have you thought about whether you would do afocal or prime NV? I switched to afocal as it was a lot more convenient for me and I could go faster. 
 

The reason I ask is that a slower newt would work just as well with a long FL EP if you are doing afocal. You will get a newt that is easier to collimate, holds collimation better and produces a well corrected field. Plus you can achieve a faster f ratio than is possible with NV at prime.

 

I don’t think you need to spend that much for NV. The imaging scopes you already have should work pretty well. A F4 scope with a 50mm GR plossl and a PVS-14 that I use would produce an effective NV f ratio of 2.1 with a well corrected field.

 

With my 14” f 3.5 Dob it got me to a screaming f1.8. With that scope I have seen the pillars of creation visually.


Edited by Astrojedi, 03 July 2021 - 09:06 PM.


#15 Jeff Morgan

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Posted 04 July 2021 - 03:12 AM

Obviously, a Takahashi Epsilon clone.

 

As a concept, a small aperture flat field astrograph is a huge winner with NV.

 

I owned an Epsilon for three years and it was extremely useful for NV at prime focus. No other 500mm focal length scope brought that much aperture to the table. Optical and mechanical quality was excellent.

 

It was sold it when the Lockwood 16" f/2.8 mirror was imminent. I miss the Epsilon, and have quite a bit of Sellers Remorse on that one.

 

OTOH, China is stilll a crapshoot on quality. Not that you need 1/20th wave optics and bulletproof collimation (though it sure is nice). Many of us have used $300 Celestron Comet Catcher scopes very satisfactorily with NV.

 

I would say if you can afford the NVD, you can afford the Epsilon. You never feel dumb buying Quality.


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