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6 Inch F5 refractor with NV

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#1 GOLGO13

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Posted 15 May 2021 - 08:51 PM

Finally got the lens spacing right (very close) on my 6 inch F5. I've only tried it out a little bit with NV, but want to give it a good go soon. It's clearish tonight but the thin clouds are around and usually those are terrible for NV. It was quite the effort to get the spacing right, but also a good challenge. Just glad it's not my really good scopes as that would have made me nervous.
 
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I know a lot of us have used 120mm F5 and 100mm F5 scopes, but I haven't seen too many with the 6 inch F5. Last time I checked, it didn't seem to be much of an advantage over the 6 inch F4 newt. But I didn't have the performance correct at the time. 

 

It is of course a bit of a debatable scope as far as usefulness outside of NV. Since the exit pupil is pretty large at low power, and it's really only good at low power. Probably pretty neat in a very dark sky.



#2 Mazerski

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Posted 15 May 2021 - 10:53 PM

GO,

 

You may have read on the galaxies / NV thread that I met up with Jeff Morgan and Sky Ranger in AZ. Drove to a dark location and Jeff used a 5” refractor at f/7 and threw in a 5x Powermate for f/35 on M13. I didn’t know or even consider that high f ratios were possible but the view was clear and was looking at the interior of cluster. Amazing view as I have never seen anything like it. 

 

The same 5” refractor showed way more detail of M51 than I see at my house with 12.5” NewMoon.
 

Your scope should provide very good views. 


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#3 bobhen

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Posted 16 May 2021 - 05:47 AM

There is a review of the Omni 6" F5 on Astromart. HERE is the link.  At the end of the review here is a section titled, the H-Alpha Machine. The author used the refractor for Night Vision observing. Keep in mind that the review was written in 2009. Here is just part of that section.

 

"The normally elusive Horsehead and the surrounding IC 434 were easy to pick out (no imagination necessary!), and the nearby Rosette Nebula displayed many of the finely layered details that it normally reveals only in photographs. For moderately wide-field intensified H-alpha observing, the Omni is an ideal instrument."

 

Bob


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#4 GOLGO13

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Posted 16 May 2021 - 07:35 AM

There is a review of the Omni 6" F5 on Astromart. HERE is the link. At the end of the review here is a section titled, the H-Alpha Machine. The author used the refractor for Night Vision observing. Keep in mind that the review was written in 2009. Here is just part of that section.

"The normally elusive Horsehead and the surrounding IC 434 were easy to pick out (no imagination necessary!), and the nearby Rosette Nebula displayed many of the finely layered details that it normally reveals only in photographs. For moderately wide-field intensified H-alpha observing, the Omni is an ideal instrument."

Bob


Thanks Bobhen. One thing I would say is it looks cool if nothing else. I believe why I had to fix the spacing of the lenses is because the material of the spacers broke down and lost some length. The other fix I had to do was replacing the focuser. Someone had installed a William Optics DDG which had cut the aperture to 5.5 inches. With the Moonlite, it is the full 6 inches. Of course it's slightly crazy to outfit this with such a focuser, but I did get a good amount back by selling the DDG. I look forward to giving it some good comparisons over the next month.

#5 GOLGO13

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Posted 18 May 2021 - 11:49 PM

OK...finally an actually clear night. I got to test the 6 inch F5 and compare it again to the 6 inch F4 newt. My opinion is the 6 inch F5 refractor is just a touch sharper with about the same brightness. Seemed best to use the .7 reducer in prime focus and native F5 (and the same for the newt). I wasn't using the coma corrector on the newt but I was mostly looking at nebulas.

 

This is the best time of the year for me because I can see all of the nebulas from the back porch, not having to go out to the front yard.

 

So I think either scope would be fine in this situation. The newt is a lower cost solution, but does take precise collimation. And overall I like the refractor. However, I'd still take my 10 inch dob for most of these nebulas. The North American and the other nebulas in Cygnus are a bit too zoomed in with the 10 inch dob. But still fun to look at. Of course it maybe best to use the 10 inch dob for zoomed in and a camera lens or the 50mm guide scope for looking at Cygnus.

 

So I guess I wouldn't say the 6 inch F5 is magic and I'm guessing a 120mm F5 would be a better choice in terms of portability and mounting. Though my 6 inch F5 rides like a dream on the Unistar mount. But it is a pretty large scope. I do look forward to using it at low power a bit with glass.

 

One thing that redeems the 6 inch F5 a bit on bright objects is just installing the included aperture mask. That cleans up the CA on the Moon and planets. If nothing else the scope looks crazy cool grin.gif


Edited by GOLGO13, 18 May 2021 - 11:50 PM.

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#6 GOLGO13

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Posted 18 May 2021 - 11:56 PM

I did use the .7 reducer and use the Afocal with a 40mm plossl. this did reduce it pretty good. Still, not sure it's worth going for the 67mm TeleVue and get 2 inch filters. I actually tend to like things zoomed in a bit. I can see that being helpful for certain scopes which are longer focal lengths.

 

And of course the 8 inch SCT is my super zoomed in scope for Globulars and smaller objects.

 

I'm trying to think about what I would want to take to a dark site or star party/club get together if I ever go sometime. My first inclination is the 10 inch dob and 8 inch SCT. But I could substitute the 6 inch F5 or 6 inch F4 for the 10 inch. However, honestly the 10 inch does the best so I'd probably want the best. But I am intrigued with what the 6 inch F5 could do in a darker sky.



#7 bobhen

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Posted 19 May 2021 - 09:17 AM

You might be right about the 120 F5 being a better fit. 

 

For NV I like to use scopes with about half the FL of the next.

 

My 50mm repurposed guide scope is about 190mm FL

My 102 F5 refractor is about 500mm FL

My TaK TSA 120 refractor is about 900mm FL

My C8 is about 2,000mm FL

 

The scopes can all be reduced, but the ratio stays about the same.

 

Bob



#8 GOLGO13

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Posted 30 June 2021 - 02:39 PM

Had a good session with the 6 inch F5 refractor last night. I have the lenses dialed in (recently made a final adjustment) and I won't be messing with the spacing anymore. The scope was performing very well. I'm pretty impressed despite it's CA limitations. For visual, I'd pick a smaller APO probably though. Not that it's bad, but I'm sure there is contrast loss and such going on. I personally think a 130mm F7ish apo is perfect scope (refactor wise). But I don't own one anymore.

 

For NV it does work well. I used it at F5 and F3.5 and both worked well. I think this will take the place of my 6 inch F4 reflector. One nice benefit is it can be used with glass whereas the 6 inch F4 is really more of an imaging only scope. Last time I compared the two scopes the refractor was a bit sharper (for NV). But it's been a little while. They provide similar views with the similar focal length.

 

So I think I'd setup this scope and the 8 inch F10 SCT to cover most NV bases. I can also use the 50mm guide scope and 1x when necessary. 

 

But I'd also be able to use the 8 inch SCT and 6 inch F5 refractor with glass which would be nice. I only have two mounts that can carry these scopes. The Vixen GPD2 (setup with goto) and the Unistar heavy alt/az mount. Both mounts handle the scopes great. Then I just have to decide which scope and which mount. Maybe the 6 inch F5 on the goto mount as it would get the most NV use. Hard to say.

 

I do like the 10 inch dob, but it's hard to say if I would bring it on a trip. My current thought is I would not even though I kind of feel it's the best NV scope all around. It's a pretty huge scope and I think I'd like to be more compact.


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#9 Starman81

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Posted 01 July 2021 - 02:39 PM

 

So I think I'd setup this scope and the 8 inch F10 SCT to cover most NV bases. I can also use the 50mm guide scope and 1x when necessary. 

 

But I'd also be able to use the 8 inch SCT and 6 inch F5 refractor with glass which would be nice. I only have two mounts that can carry these scopes. The Vixen GPD2 (setup with goto) and the Unistar heavy alt/az mount. Both mounts handle the scopes great. Then I just have to decide which scope and which mount. Maybe the 6 inch F5 on the goto mount as it would get the most NV use. Hard to say.

 

 

 

You would probably benefit greatly from an alt-az mount that can mount dual scopes to run the C8 and 150R simultaneously. Less mounts to worry about. 

 

Myself (and bobhen) use the DSV-3 (excellent mount) and the ES Twilight II worked well for me for the many years I had it as well. If you really wanted to splurge on Go-to/tracking, the DSV-3 has that option (though pricey) and then there is also the Orion Atlas Pro AZ/EQ-G.



#10 Doug Culbertson

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Posted 01 July 2021 - 04:35 PM

You would probably benefit greatly from an alt-az mount that can mount dual scopes to run the C8 and 150R simultaneously. Less mounts to worry about. 

 

Myself (and bobhen) use the DSV-3 (excellent mount) and the ES Twilight II worked well for me for the many years I had it as well. If you really wanted to splurge on Go-to/tracking, the DSV-3 has that option (though pricey) and then there is also the Orion Atlas Pro AZ/EQ-G.

 

Yep, I use the SkyTee 2 with a 120mm f/5 and a 6" f/10 Meade ACF for NV. Or, I would if it ever clears up around here. 

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#11 GeezerGazer

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Posted 06 July 2021 - 01:56 AM

Go,

I previously used an Orion .8x refractor reducer with my ST 120 f:5 achro, allowing it to perform very well at f:4.  I really never felt a need to go faster with it.  The ST 120 is definitely a more compact scope than it's 150mm sibling, and it's very light weight.  I put a GSO focuser on it for smoother focusing.  Comparing it to the 6" f:4 Newt I had, the image was very close to equal, but the ST 120 showed tighter stars.  I sold the 6" Newt after I bought an 8" Newt.  I still have the ST 120 though.  When the wind comes up, I remove the 8" Newt from the mount and get out the ST 120, which is much less prone to act like a kite.  

 

vondragonnoggin really enjoyed his ST 150 f:5.  When you use either an H-a filter or a ~140nm long pass filter, you will never see or be annoyed by chromatic issues.  I am slightly biased, but the short tube achromats definitely acquit themselves in the price vs performance category.  I hope you get lots of good use out of your 150.  

Ray


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#12 joelin

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Posted 10 July 2021 - 12:29 AM

I'm also a fan of the short tube achromats. I use the C102 f/5 for the reason that its light enough to fit on my Dwarfstar mount and small enough to fit in a backpack. I have to use prime focus however as any afocal setup would add too much weight. 

 

 

A couple of times I went out for a stroll with a backpack and camera tripod. Throw in a 2" diagona, and a Rigel finder to help point and I have a v very comfortable and portable 102mm f/5 night vision setup that can a lot of targets. 



#13 GOLGO13

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Posted 23 July 2021 - 07:48 PM

I'm also a fan of the short tube achromats. I use the C102 f/5 for the reason that its light enough to fit on my Dwarfstar mount and small enough to fit in a backpack. I have to use prime focus however as any afocal setup would add too much weight.


A couple of times I went out for a stroll with a backpack and camera tripod. Throw in a 2" diagona, and a Rigel finder to help point and I have a v very comfortable and portable 102mm f/5 night vision setup that can a lot of targets.


I just ordered a 102mm F5 for NV purposes. I think I will sell my 6 inch F4 newt since the 6 inch F5 refractor seems to be better. I can also use the 6 inch F5 for visual whereas the imaging newt I feel is best just for NV.

I will admit the 6 inch F4 is a very good scope, just limited in use.

#14 bobhen

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Posted 24 July 2021 - 05:58 AM

I’ve been using a 102 F5 for over 5 years with NV and really like the combination.

 

You should use filters of course. And if you are using prime focus, I would highly recommend the GSO 2” focuser as a replacement for the standard focuser and then you can use a 2” .7 reducer. That combination delivers some very nice wide field NV views.

 

The 102 F5 and NV combination is a very portable yet powerful, wide field, deep sky system that delivers in all light pollution conditions.

 

Here’s mine.

 

Bob

 

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#15 GOLGO13

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Posted 24 July 2021 - 06:57 AM

I ended up canceling my order and will look for a used one. Unfortunately they don't sell an OTA only version. I do want to get one eventually.

#16 bobhen

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Posted 24 July 2021 - 08:28 AM

I ended up canceling my order and will look for a used one. Unfortunately they don't sell an OTA only version. I do want to get one eventually.

 

If you can't get a US retailer to just sell you an OTA, I believe they do across the pond. HERE is a link.

 

You could also run an ad rather than waiting for one to pop up.

 

They are worth seeking out for NV use. A very small investment with big view returns as well. 

 

Good luck.

 

Bob



#17 GOLGO13

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Posted 24 July 2021 - 09:39 AM

If you can't get a US retailer to just sell you an OTA, I believe they do across the pond. HERE is a link.

You could also run an ad rather than waiting for one to pop up.

They are worth seeking out for NV use. A very small investment with big view returns as well.

Good luck.

Bob



That's the one I want

#18 joelin

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Posted 25 July 2021 - 02:03 AM

I just ordered a 102mm F5 for NV purposes. I think I will sell my 6 inch F4 newt since the 6 inch F5 refractor seems to be better. I can also use the 6 inch F5 for visual whereas the imaging newt I feel is best just for NV.

I will admit the 6 inch F4 is a very good scope, just limited in use.

Hmmm, ...the 6 inch f/4 reflector has a few advantages over the 6" f/5 refractor. The refractor is an achromat so it's only really usable for NV when filtered at 685nm or Ha. You can use it for visual but CA will show for bright stars/planets or at higher power. 

 

I think the imaging newt doesn't suffer from CA and you can use it for visual with an extension tube. 



#19 GOLGO13

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Posted 25 July 2021 - 11:04 AM

Hmmm, ...the 6 inch f/4 reflector has a few advantages over the 6" f/5 refractor. The refractor is an achromat so it's only really usable for NV when filtered at 685nm or Ha. You can use it for visual but CA will show for bright stars/planets or at higher power.

I think the imaging newt doesn't suffer from CA and you can use it for visual with an extension tube.


Just comparing the two, the images are sharper with the refractor. They are close though. Yes, some brighter stars get blown out a bit. I only use it heavily filtered. I can do more comparisons, but so far the refractor has won. I am not sold on the 6 inch F5 refractor for visual yet, however, adding the aperture mask works very well on the Moon and Planets. Though smaller aperture. I have not had the chance to use it in a dark sky. Obviously a 5 inch F7 apo would be much better. And maybe even my 103mm Vixen would be better. But it seems to do well for night vision.

The imaging newt has a huge central obstruction and I've found it isn't great for visual. Don't get me wrong, it's a great scope for imaging purposes and NV. Adding a coma corrector makes for a gigantic stack. I know they sell a really expensive one made for these, but doesn't seem worth it.

The only benefit I see with the 6 inch F4 is using a filter wheel is possible. Though I don't personally like using the filter wheel much.

If I wanted a visual newt, a 6 inch F5 with a normal secondary mirror would be much better.


So I think I will sell the 6 inch F4, the filter wheel, and the MPCC. I could use a bit of money anyways as I recently ordered a Tak 76 DCU which I will be using F12.5. I've been doing half visual half night vision recently. I like seeing the color of the stars, the Moon and the planets.

My new Vixen AP mount is really good with my Lunt 50mm double stack. And I figured the Tak 76 was a good match for the mount.


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