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120mm F5 refractor or 6 inch F4 newt for NV?

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#1 GOLGO13

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Posted 05 September 2019 - 10:09 AM

Let me know what you think or any other suggestions. I have my 10 inch F4.7 newt already and it seems to work pretty well. I have the 1x lens for super low power and the 50mm guide scope which I am liking. But I believe I need something in between. My current 5 inch refractor is F7.4. It's also a pretty big scope to setup. The views in it were not bad though. But I'm wanting to get a faster setup to see how that improves things.

 

My other thought for the above is portability and ease of setup.

 

One reason I may prefer the refractor is cool down. Especially as we get to the winter months. Though I'd guess a 6 inch F4 wouldn't be horrible for cool down.

 

I ordered the .7 reducer from Scope stuff as my .5 GSO one isn't the best for focusing and such.

 

Thanks for your help!



#2 Mazerski

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Posted 05 September 2019 - 12:50 PM

Eddgie has the 6” and I have the 8” - both are f/2.8 (with included corrector) or f/4 without. It’s the best scope I have and provides great wide field views. The scopes accept a filter wheel and it’s great to cycle thru filters on objects.

 

I have a Berlebach Handle, D Plate and the included Finder is well made and easy to center Star at crosshair.

If you want photos, just say. Highly recommend this scope. 

I bought the 8” due to Ed’s writeup of the 6” and he helped me with putting a package together.

 

https://www.teleskop...Astrograph.html



#3 GOLGO13

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Posted 05 September 2019 - 01:00 PM

Wow...that does look sweet, but maybe a bit much for my wallet at this point. But certainly something to consider in the future.

 

Do you also use some sort of coma corrector with it?



#4 The Ardent

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Posted 05 September 2019 - 01:07 PM

The 6” f/4 imaging newt ~ $300 new, find a used one here in the classifieds. A good NV scope.
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#5 Mazerski

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Posted 05 September 2019 - 02:29 PM

The corrector is supplied with scope - from the BS writeup

 

♦ Very good field correction thanks to the ASA corrector/reducer

 

If I recall, Ray (GeezerGazer) has the scope or type of scope that Ray (the Ardent) describes.

Drop Geezer a line for his opinion.

 

Ray did buy the corrector that comes with the Boren scope to use with his scope - ask him to verify.


Edited by Mazerski, 05 September 2019 - 02:43 PM.


#6 GOLGO13

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Posted 05 September 2019 - 02:47 PM

Looks like the reducer/corrector is a good portion of the cost of that setup. So it's not as bad as it appears.



#7 bobhen

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Posted 05 September 2019 - 03:59 PM

Sounds like you are leaning toward the Orion 120mm F5 refractor. NV observer, Vondragonnoggin uses both 120 and 150mm F5 achromats. You might want to Google some of his posts. I use a 102mm F5 and really like that scope with NV.

 

If you get one, you will need to replace the standard focuser with a GSO 2” focuser. That will allow you to use the reducer to get to F3.5 or still use the native F5.

 

You will have to use filters with an achromat. Most NV observing is done with filters anyway.

 

These fast refractors are relatively inexpensive, rugged, fairly compact and portable and should never need collimation. And they are just a whole lot of fun with NV.

 

Of course, Newtonians have advantages as well.

 

Bob



#8 The Ardent

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Posted 05 September 2019 - 05:30 PM

https://astromart.co...5-newtonian-ota

#9 GeezerGazer

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Posted 06 September 2019 - 01:47 AM

Your choices are good ones.  If portability is really important, the 120 is wonderful.  It's light weight (8 lbs... IIRC, mine is 11 lbs with rings, finder, NV, and a handle), small enough to handle easily, is carried nicely on almost any mount, is very fast to set up (no collimation) for quick looks and the price is right either new or used.  If you are using a filter (either long pass IR or H-a bandpass) you will never notice star bloat.  Although I now know I was not getting full field illumination on the NV sensor with mine, it never really bothered me, especially when used visually.  Where I saw it most prominently was in photos.  I used an Orion .8x reducer made for refractors, which took it to f:4 at 480mm.  The 480-600mm FL was very useful for many medium sized nebula.  I also used it occasionally with a 2x barlow when taking images of small globs, galaxies & planetary nebulae.  I took a lot of phone photos with the ST 120 and was happy with most of them.  For visual use, I was completely satisfied.  

 

Advantages of the ST 120 over a 6" Newt are pretty much limited to the convenience factor (size & weight), and under some circumstances, it may have a sharper image of stars that is easier to maintain.  The 6" Newt I had was quite excellent.  It was barely heavier than the ST 120 and was easily mounted and controlled by both my manual alt/az and my AZ Pro goto mount.  It had the extra step of checking collimation, but it held collimation quite well, needing adjustment only occasionally.  The scope is native f:4 with a FL of 600mm which is the same as the ST 120.  The big advantage is using it at f:2.8 as a prime objective with the addition of the ASA reducer.  The drawback is the cost of the reducer from Teleskop Service in Germany.  There is a substantial difference between f:4 and f:2.8 when using a scope visually with filters.  A benefit to you might be double duty of the reducer, as it is probably quite useable in your f:4.7 Dob.  

 

Keep in mind that my use of the ST 120 was pretty much limited to prime focus and I found it very good for my purposes, both visually and for imaging.  I tried it in afocal with a 2" 55 Plossl and a 1.25" 40 Plossl, but was never really satisfied with the image, especially for photos.  This is a personal preference based on my tolerance of outer field aberrations.  But the advantage is that very fast focal ratios can be achieved with the right afocal eyepiece, even more when used with a supplemental reducer.  If your focus is on the center FoV, you many not even notice field curvature or astigmatism toward the edge of field.  

 

A fast objective focal ratio is a friend to NV.  The faster the focal ratio is, the more compelling your NVD image will be.  The faster the focal ratio, the better your H-a filters will seem to perform, as the image will be brighter and will reveal more contrast.  

 

I don't think you will be disappointed by either scope.  Since you already have an f:4.7 Dob, and convenience seems to be a high priority, the ST 120 seems to be the likely candidate.  Good luck. 


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#10 GOLGO13

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Posted 06 September 2019 - 08:38 AM

Well, wife put her foot down on any more spending...so I'll have to wait a while. Beyond all this NV purchases I rediscovered ebay for classic computer stuff...

 

But eventually I'll get something. How much of an improvement do you figure it would be going from my 130mm F7.4 to the 120mm F5. I'll soon be using the .7 reducer. And of course I do have the 10 inch dob which works well.



#11 bobhen

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Posted 06 September 2019 - 12:00 PM

If the .7 reducer works with your 130mm, don't get the 120 F5 get the 102mm F5.

 

Sky Watcher sells a 102mm F5 as the Star Travel 102.  A few retailers offer them.

 

HERE is a link.

 

Bob


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#12 GOLGO13

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Posted 06 September 2019 - 12:40 PM

That sounds good. I wish they had the OTA only version of this in the U.S. I can always look out for the OTA on the used market. The 102 F5 probably fits better with what I currently have, and portability as well. Should ride easy on my Vixen Porta mount with wood legs.

 

I'll keep this in mind for the future.



#13 GeezerGazer

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Posted 06 September 2019 - 02:26 PM

Like your wife, I would say you should hold off on spending more temporarily.  You need to try your reducer in your 130 at prime focus.  Then you need to try the reducer attached to a long FL eyepiece in afocal to see if it suits your needs and tolerance levels.  Afocal makes a much taller stack than prime and adding a reducer to the mix may induce aberrations that you cannot tolerate.  But it may be perfect for your needs and tolerance levels.  So trying what you have first is an important step.  

 

There are long focal length eyepieces, like the Russell Optics 65mm Super Plossl, that provide excellent value and performance in certain afocal optical systems.  The long FL eyepieces from 40-65mm, provide substantial focal reduction, even without a reducer.  You can read about one here, used in several different optical systems:  

You need to read this thread to the end, where chemisted used it in his R-C scope.  I'll soon be testing the Russell 50mm in afocal.  With a Mod 3C you are not limited to just prime or afocal.  You might decide you prefer one method over the other, but you might decide to use both, if each method provides results to your liking.  If you have a Panoptic 40mm, you may find that when used in afocal with your 130, it provides a perfectly flat FoV with zero aberrations while providing .67x of reduction... taking your 130 to f:5.  Adding your .7x reducer to the Panoptic might perform well enough to yield a focal ratio of F:3.5.  You need try it to know for sure, but it's possible.  Using the 65mm Super Plossl in your 130 could reduce it to f:4... without adding a supplemental reducer.  Based on my experiments at f:7, I think there would be some outer field aberrations in your 130, both curvature and astigmatism, but whether you'd even notice them during visual use can only be answered by trying it.  Experience and experiments have shown that different optical systems perform differently with the same eyepiece used in afocal.  You just have to try it to know.   



#14 Doug Culbertson

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Posted 06 September 2019 - 03:13 PM

If the .7 reducer works with your 130mm, don't get the 120 F5 get the 102mm F5.

 

Sky Watcher sells a 102mm F5 as the Star Travel 102.  A few retailers offer them.

 

HERE is a link.

 

Bob

 I just bought one of those to use with a Quark Chromosphere, but I plan to use it with NV as well. . I saved a few pennies by purchasing it at First Light Optics in England.  When you put it in your cart they remove the VAT so the price drops. 



#15 bobhen

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Posted 06 September 2019 - 03:29 PM

 I just bought one of those to use with a Quark Chromosphere, but I plan to use it with NV as well. . I saved a few pennies by purchasing it at First Light Optics in England.  When you put it in your cart they remove the VAT so the price drops. 

Doug,

 

For NV consider a GSO 2” focuser to replace the standard focuser. You can use the Antares 2” .7 reducer at prime focus to get to F3.5. And of course you can still use the native F5.

 

The GSO is a nicer focuser anyway.

 

Bob



#16 Doug Culbertson

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Posted 06 September 2019 - 06:06 PM

Bob, I ordered the GSO linear bearing focuser from Agena Astro the day I ordered the telescope. It’s really nice!



#17 GOLGO13

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Posted 13 September 2019 - 06:42 PM

The .7 Antares reducer arrived and it seems very nice. It threads much nicer onto my scopestuff 1.25 to 2 inch adapter. Now we will see if any of the scopes will work with it without having to go strait through on the refractors.



#18 GOLGO13

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Posted 13 September 2019 - 09:52 PM

Good news. The .7 Antares reducer works great in my AT60 with plenty of room to spare. It was clear but a horrible night for anything but testing. Although I could still see nebulas despite the crazy full moon and sky conditions. But I could tell it was impacting the image across the board. 

 

So based on where that focused, I'm thinking that setup should work with all my scopes (we'll see on the 10 inch dob...hoping I don't need to adjust the mirror in it).

 

So that should set me up for which ever of these scopes I decide to get.



#19 GOLGO13

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Posted 16 September 2019 - 02:03 PM

I sold my Televue 60 and part of my HA solar setup...so I ordered the 6 inch F4 newt (Apertura brand which appears to be similar to all of them). I have to say it's a pretty nice package for $299. I believe the low end nature of this scope favors going with the 6 inch (less likely to have collimation flexure). Plus for me, I prefer lighter weight on my mounts. And the 6 inch is quite a bit lighter. I also believe the smaller diameter would make for mounting on my FTX where I'm unsure the 8 inch version would. Just guessing on that though. 

 

I'm hoping to get away with not using a coma corrector for a bit...but I figure at some point I'll probably need one.

 

I do not use a corrector in my 10 inch, so I don't think I'm as bothered by it. But this is slightly faster optics.

 

I did have a TeleVue Paracorr back in the day and it was pretty nice. But ultimately I sold it to fund other things. It was one heck of a combo at the time. I had the 10 inch dob, a 26mm nagler and the paracorr. pretty sweet. But at that point of my telescope career it was too much money for what it gave me. Still have the 10 inch dob though luckily :)


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#20 Jeff Morgan

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Posted 16 September 2019 - 09:37 PM

I used to have a FTX, and it handled the 28 pound Epsilon e180 easily. The tripod was a medium duty Berelebach UNI. Should handle the 6" quite nicely!

 

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