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Night vision; next purchase?

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#1 Trentend

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Posted 14 February 2021 - 07:03 AM

Having recently viewed some winter delights for the first time with NV I must admit to feeling a little flat with the hobby thinking (incorrectly I know) things from my city centre location probably wouldn’t get any better. Using an 18” dob, high spec OVNI-B (earlier version with no manual gain) and various filters from 3.5nm to 642 I had a great “nebula evening” seeing the ring, veil, horsehead and other delights for the first time. As mentioned on another astronomy forum I also nearly fell off my chair when I first laid eyes on M42 - an unbelievable sight that I’ll never forget. And here lies the problem, everything I’ve viewed since has been a bit of an anticlimax. I’m guessing I really need to get out to dark skies and / or buy some new kit to take things on to the next level (presume I can’t really improve on the big dob for the backyard without getting an even bigger one...)

 

So, the priority is probably a portable / fast-ish scope with minimal cool down as skies here in Scotland are very unpredictable. I recently received great advice and went to buy the Tak FC100 before Christmas, which would also be very good on the moon and planets with my Binotron. But that sold out and isn’t going to be available until the summer. So that gives me time on my hands again to consider requirements and the best purely NV approach. The Tak is still the front runner but I’m now wondering if I’d get brighter NV views from something more dedicated like the Boren Simon or a faster refractor?

 

The other alternative is to bite the bullet and upgrade to NV goggles with manual gain. Ideally I would have visited the retailer in France to give these a try first but lockdown continues to put paid to that (one day though Joko!).

 

First world problems I know but keen to hear people’s thoughts.


Edited by Trentend, 14 February 2021 - 07:30 AM.

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#2 bobhen

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Posted 14 February 2021 - 07:56 AM

For wider fields and large objects, consider…

 

1. A fast 6 to 8” Newtonian/Dobsonian
2. A fast 102mm or 120mm F5 achromatic refractor
3. The more expensive and fast 100mm apo refractors
4. The more expensive and fast photographic Newtonians

5. Also consider camera lenses or even modified 50-60mm guide scopes for ultra-wide field observing

 

The above will deliver wider fields but you do give up image scale and the details that image scale can provide for certain objects.

 

"And here lies the problem, everything I’ve viewed since has been a bit of an anticlimax. I’m guessing I really need to get out to dark skies and / or buy some new kit to take things on to the next level."

 

You might consider evaluating what will really impress you. Dark skies will certainly be better but I am wondering if dark skies will be “better enough” to meet your expectations.

 

You might want to research what a camera and short exposure EAA will bring to meeting your expectations. Even an exposure of 30 to 60 seconds with a small scope will deliver “a lot” more (read: A LOT MORE) detail than an intensifier and 18” Dobsonian. And EAA can be done in most backyards. EAA is, of course, more like imaging than visual observing. But EAA, like most things, has its own advantages. One 60-second image of galaxy M51 might convince you that EAA is something for you to consider.

 

Good luck.

 

Bob


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#3 Trentend

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Posted 14 February 2021 - 12:31 PM

Thanks Bob. The “nebula night” was fantastic, as were some of the views of globular clusters last summer and these are the objects which really impress and to the scale viewed through the dob (appreciate these will be smaller in some of the suggestions above with wider FOV). I’m currently limited to a narrow-ish south/west outloook being surrounded by tall properties so really hanker after something portable that also provides brighter images. Unfortunately this strand of astronomy is an expensive one to experiment with and lockdown prevents live/direct comparison with kit used by fellow night visioners.

 

Some fantastic photos on-line with EAA but afraid that medium just doesn’t appeal



#4 Gavster

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Posted 14 February 2021 - 03:23 PM

My preference for portable grab and go would be a fast good quality refractor such as the following
https://www.teleskop...-Telescope.html

With a 67mm plossl this would give an effective f ratio of f2 which would give gorgeous widefield nv views of the large nebulae such as California, rosette, heart and soul, North America etc

 

However the number of these large showecase objects is a bit limited and you may get bored pretty quickly with repeated observations (I don’t!). There are a lot more smaller objects including galaxies, globulars and planetary nebulae but for these I find I need aperture to get the image scale AND brightness, which means either my 11 inch sct or 16 inch dob. For trips to a dark site, my C11 is my most common companion due to its relative “portability”


Edited by Gavster, 14 February 2021 - 03:33 PM.

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#5 PEterW

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Posted 14 February 2021 - 05:34 PM

Brackens Astrophotography sky atlas will give a good idea of what’s available to see. With a big scope you can go for the smaller objects, AlanJGreen who’s “over the border” from you has observed pretty much all the Sharpless and has gone looking for things that aren’t listed.
With NV speed is key, you change the focal length to fit what you want to observe.... bigger is not always better. Afocal has made this easier to do. Most of my observing is with my “slightly reduced” 80mm jumbo finder swung round by hand. My 8”f4 went through a whole list of galaxies last year on its eq6.
No one astro tool will do everything, solar telescopes and NV are very potent, but there are things that neither will help with.
Just sweeping round with 1x/3x and some filtration when shielded from lights. Sometimes people focus on seeing specific objects, taking in the wider view can sometimes give a different perspective.

PEter
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#6 GOLGO13

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Posted 14 February 2021 - 11:31 PM

I've had similar feelings sometimes. And it's not a knock on night vision. Certainly night vision provides dark sky like capabilities in a light polluted sky. But, I sometimes question whether it is better to just look at photos someone else has created (astrophotography is not in my future). All that being said I don't think I will get rid of my scopes or night vision. I know this hobby ebbs and flows with interest. I do like the planets and moon generally. But I probably should scale my scopes back a bit. To be perfectly honest I have always had a bit of an on and off interest in this hobby. Even in dark sky situations I tend to just look up at the Milky Way most of the night. And I have never learned the sky too well. I almost enjoyed the tech part of the hobby as much as the observing. I think I am ranting a bit here, but I think I know what you are saying. I think we were hoping night vision would provide astrophotography views, and other than a few objects, it's not there. Close to EAA sometimes. All this being said I have only used night vision in light pollution.
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#7 GeezerGazer

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Posted 14 February 2021 - 11:46 PM

Before making suggestions, allow me to ask a few questions: 

1.  What is the focal ratio of your 18" Dob? 

2.  Does your Dob have motor tracking ability or is it manual?  

3.  What types of subjects do you want to see, nebulae/planetaries or globs/galaxies? 

4.  Is the objective lens on your OVNI B removable... is it a C-mount device? 

5.  You have ruled out EAA; would you have any interest in NV Phonetography?  

6.  How often would you travel to a dark site? 

Ray



#8 Joko

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Posted 17 February 2021 - 06:42 AM

4.  Is the objective lens on your OVNI B removable... is it a C-mount device? 

I can answer this question. smile.gif

Yes the front lens is removable. To add camera lens it has C-mount, M42 (42mm) and T2 (48mm).

OVNI-B also have 1.25" and 2" barrel with filter thread.

 

The 1.25" barrel, 2" barrel, C-mount, M42 (42mm) and T2 (48mm) are possible with only one accessory called "Multi-adapter".


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#9 Trentend

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Posted 17 February 2021 - 04:18 PM

Apologies for the delayed response:

 

1 F3.9

2. Manual only, although has encoders for Nexus DSC fitted (also have AZ GTi and M2 mount, the latter with DSC encoders so have flexibility for different weight scopes)

3. Nebula the priority followed by galaxies, but believe the latter not best suited always to NV

5. Sorry no 

6. Regularly with something genuinely portable (so unfortunately rules out something like the C11 although I’m sure the views through that would be immense!). Amazingly dark skies within 1hour drive but weather here very unpredictable so needs to be something with minimal cool down time.

 

Pretty sure I’ll stick to my original choice of the FC100 when they’re back in stock here in the U.K.

 

Thanks again for the feedback


Edited by Trentend, 17 February 2021 - 04:19 PM.

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#10 GeezerGazer

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Posted 18 February 2021 - 01:35 AM

Apologies for the delayed response:

 

1 F3.9

2. Manual only, although has encoders for Nexus DSC fitted (also have AZ GTi and M2 mount, the latter with DSC encoders so have flexibility for different weight scopes)

3. Nebula the priority followed by galaxies, but believe the latter not best suited always to NV

5. Sorry no 

6. Regularly with something genuinely portable (so unfortunately rules out something like the C11 although I’m sure the views through that would be immense!). Amazingly dark skies within 1hour drive but weather here very unpredictable so needs to be something with minimal cool down time.

 

Pretty sure I’ll stick to my original choice of the FC100 when they’re back in stock here in the U.K.

 

Thanks again for the feedback

OK, thanks.  With your 18" you have globulars, planetary nebulae and galaxies well covered, so I understand your need for wider FoV for medium to large emission nebulae.  With H-a, your need for speed becomes critically important, and although the Tak refractor will provide excellent views with glass eyepieces, you will be under-whelmed using it with NV.  I have owned 9 Tak scopes and I would select none of the refractors for use with NV except the FSQ 85 with either the Tak reducer or preferably using it in afocal to reduce speed.  It is possible to increase the speed of the FC 100 Tak refractor using an eyepiece in afocal, but there are caveats to this method.  I did not like my f:9 FC 100 DL used with NV and subsequently sold it.  

 

Because a fast focal ratio is paramount and because you want it to be portable, I would recommend one of two optical options... perhaps BOTH options.  The first would be a small 6" f:2.8 reflector like the Boren-Simon which uses a .73x reducer in an f:4 native scope.  It produces a flat FoV with no coma and provides full sensor illumination; an important issue for a bright image without vignetting.  The advantage of the B-S system is that you could probably use the reducer in your 18" f:3.9 scope, making it a prime f:2.8 optical system with a wider FoV than you experience at f:3.9.  I have used the TS (ASA) reducer for almost 3 years in 3 different scopes having native focal ratios of f:3.9 to f:4, and the reducer performed flawlessly, although I did need to shorten the light path on one scope by 15mm to use the reducer.  The B-S option is a bit more expensive, but the reducer makes this scope quite excellent with NV for emission nebulae.  

 

Sharpstar offers a similar, more expensive f:2.8 system, but I know nothing about the reducer they use to achieve the faster speed.  IIRC, the Sharpstar uses a hyperbolic instead of a parabolic primary, so I doubt the reducer would be useable in your 18" Dobsonian.  The B-S 6" scope is relatively small, lightweight (CF tube) and has a good record with NV for visual use.  

 

If you choose to go afocal using a small astrograph, like the Askar 108mm or even the 73mm, you can reduce the focal ratio using their proprietary reducer, but it still only gets down to f:3.9.    Using the TeleVue 55/67 Plossl in afocal (instead of the reducer) reduces the to about f:2.2, but makes a much longer stack from the diagonal.

 

The second optical option I can recommend was already listed above by bobhen.  Nikon or Cannon camera lenses used in prime focus offer some excellent wide field images with very fast focal ratios.  And they can be adapted for use with either 1.25" or 2" H-a filters which are probably already in your possession (PM me if you want to know more about using filters with camera lenses).  I have stuck with Nikon lenses only because I used them early in life.  For use with NV, you need only to create or purchase a C-mount adapter to use them with your OVNI B.  Used visually, straight through and hand held, I prefer either a 105mm f:1.8 at 4x or 135mm f:2 lens at 5x using a 3.5nm filter in a LP red zone.  Many others prefer the 180mm which I found too bulky and heavy.  At a dark site I prefer a wider H-a filter of 6-8nm to see more stars.  But a 3 or 3.5nm can be used under any conditions.  Since your OVNI B does not have gain control, you will find that the aperture ring on a camera lens works in a similar fashion to control the brightness of the image.  Take a folding lounge chair and your filtered OVNI for a low-power hand held view of the night sky.  

 

You can also mount your OVNI on your AZ GTi with the camera lens attached, although the straight through method is a pain in the neck, literally.  

 

You can also use a C-mount lens but they often result in vignetting because they are often designed to illuminate smaller sensors.  And longer focal length C-mount lenses often cost more than available Nikon or Cannon camera lenses.  

 

There is a lot of good information in the BEST of NV; click on "NV and Lenses."  Many of the old Nikon AI or AiS lenses are found for a lower price than many astronomical eyepieces.  I recommend sticking with older lenses with manual focus and having an aperture ring.  Many of the auto focus lenses produced today are problematic in use because they require a special adapter that allows manual control of the aperture; many of them do not have an aperture ring on the lens barrel.  Also keep in mind that H-a or long pass filtration must be placed behind most camera lenses, which requires an adapter for the lens, a way to insert a filter and an adapter for the NVD.  But it's not complicated and all parts are available on-line.  

 

Last thing... PEterW above recommended the Bracken Astrophotography atlas.  If you do not have one of these you should seriously consider the $20 price.  Nebulae are shown in different shades of red on the white pages so you can estimate the brightness and the size for optics with an adequate FoV.  It's a valuable NV tool for emission nebulae and it has a very user friendly index.  

 

NOTE:  The recommendation for a camera lens is based on Joko's response that your objective lens is removable.  If it is not removable, as you say, then please disregard the camera lens suggestion.  Good luck.   Ray


Edited by GeezerGazer, 18 February 2021 - 01:54 AM.

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#11 Deadlake

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Posted 18 February 2021 - 03:50 AM

I have owned 9 Tak scopes and I would select none of the refractors for use with NV except the FSQ 85 with either the Tak reducer or preferably using it in afocal to reduce speed. 

Ray did you ever try an FSQ-106 at all? I know Gavster had a FSQ-130 and last time I heard had good result, but after messaging him, he recommend any good 130/F6 for dual use with visual/NV.  

Thanks

 

Martin


Edited by Deadlake, 18 February 2021 - 04:32 AM.


#12 bobhen

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Posted 18 February 2021 - 07:36 AM

Apologies for the delayed response:

 

1 F3.9

2. Manual only, although has encoders for Nexus DSC fitted (also have AZ GTi and M2 mount, the latter with DSC encoders so have flexibility for different weight scopes)

3. Nebula the priority followed by galaxies, but believe the latter not best suited always to NV

5. Sorry no 

6. Regularly with something genuinely portable (so unfortunately rules out something like the C11 although I’m sure the views through that would be immense!). Amazingly dark skies within 1hour drive but weather here very unpredictable so needs to be something with minimal cool down time.

 

Pretty sure I’ll stick to my original choice of the FC100 when they’re back in stock here in the U.K.

 

Thanks again for the feedback

A Tak 100DF should be fine for NV. Consider adding the Tak reducer to get to F5 or an aftermarket reducer for faster speeds.

 

For small objects like globular clusters image scale is important. Consider adding a C8 or C6. Both are extremely portable and lightweight and can easily ride on alt/az mounts. The native F10 will be great for small objects (galaxies globulars etc) and both can be easily reduced to around F7 without distortion. 

 

Although a perfectly acclimated scope is desirable, for deep sky observing, perfect acclimation is not an absolute must.

 

I use a Tak TSA 120 and love it for NV observing. The TSA 120 is my single (when I take out just one scope) do it all NV scope.  I also use a C8 for more image scale for the small stuff when I feel the need. And I use a fast F5 refractor (even at F3.5) for ultra-wide fields.

 

Using an alt/az mount, All are one or two trip setups.

 

Below are my Tak TSA 120 and the 102mm F5 refractor and the C8 and the 102mm F5 refractor on a twin alt/az mount. Of course each scope can be used alone or on an even more portable alt/az mount for an even quicker setup.

 

Bob

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#13 chemisted

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Posted 18 February 2021 - 07:41 AM

If you are willing to try to find a discontinued telescope I recommend the Takahashi Sky 90.  See the following thread to see how I enjoy a perfect, 5.87o flat field at f/2.0 with mine:

 

https://www.cloudyni...opic-tfov-ever/

 

CN member jdbastro has fantastic intensified images taken with his Sky 90 and a Tak reducer.


Edited by chemisted, 18 February 2021 - 08:19 AM.


#14 Joko

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Posted 18 February 2021 - 08:24 AM

In Takashashi brand, Epsilon E130D and Epsilon 180mm ED also have very short focal ratio.

I read some great reviews using NVD and Epsilon 180mm ED from CN members Mazerski and Jeff Morgan.


Edited by Joko, 18 February 2021 - 08:25 AM.


#15 Jeff Morgan

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Posted 18 February 2021 - 12:26 PM

In Takashashi brand, Epsilon E130D and Epsilon 180mm ED also have very short focal ratio.

I read some great reviews using NVD and Epsilon 180mm ED from CN members Mazerski and Jeff Morgan.

 

Yes, the Epsilon e180 was a great NV scope. It showed me the path forward, but at the same time I realized it was only a Stop on the way to the Destination.

 

Largely, the problem is defined by the angular size distribution of the objects you wish to observe, available budget, and portability requirements. (Sound familiar?)

 

Within those parameters and in general terms, you want the fastest large optic you can afford - and something smaller.

 

If you have a f/3 Newtonian, you can always couple it with a Powermate for the small target performance. (Or couple afocally with a short focal length eyepiece if you can't do prime). And the aperture supports resolution on those small targets. Looking at the problem from the other side, it is more problematic to make a medium speed optic faster.

 

And of course, the entire portability thing. With my 16" f/2.8 (a project which is asymptotically approaching completion), each component is manageable weight (less than a medium-duty German Equatorial head). I do not need wheelbarrow handles. I do not need ramps. I do not need a ladder. Ditching those items makes logistics much simpler.

 

The "something smaller" question is fortunately easier (and cheaper) to handle. For the really big targets (and with NV there are many of them), a small fast refractor or short telephoto can be used. SLR lenses up to around 200mm can be hand-held, great for logistics. Note many small refractors used with the Tele Vue 67 Plossl can approximate a 200mm SLR lens, so the largest SLR lens I have is 135mm.

 

That two-optic approach gives you a great range of coverage (in terms of target size) yet remains quite portable.


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#16 GeezerGazer

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Posted 18 February 2021 - 02:08 PM

Ray did you ever try an FSQ-106 at all? I know Gavster had a FSQ-130 and last time I heard had good result, but after messaging him, he recommend any good 130/F6 for dual use with visual/NV.  

Thanks

 

Martin

Hi Martin, the FSQ line are basically alike except with different apertures... I'm sure they are all excellent with NV.  But the OP is interested in a compact system.  In post #1 he says:  "So, the priority is probably a portable / fast-ish scope with minimal cool down as skies here in Scotland are very unpredictable."  The FSQ is a very compact system; mine fit in a medium Pelican with everything needed to observe.  

 

There are many scopes that will perform well with NV, including a TSA 120... I had one of those too.  But the OP seems most interested in being able to see medium to large emission nebulae.  And unless the TSA is used in afocal, it cannot be optimized for H-a.  I did not include the Sky 90 because it is out of production, last I heard, but it might be a good, compact option for NV... I did not own a Sky 90 so I cannot say.  

 

Trentend has most aspects of NV use covered with his 18" f:3.9, and has not been wowed with his subsequent H-a viewing.  To get views that do have a wow factor using narrow-band filters, my feeling is that a fast focal ratio is absolutely necessary.  No other general aspect of NV use requires a particularly fast focal ratio... but using narrow band filters does... in my experience.  And in my experience, reducing a refractor to focal ratios at or below f:3 without using an afocal system is problematic at best.  

 

But this is all academic, until we actually know if Tentend's OVNI B has a C-mount lens connection.  He says it does not; Joko says it does.  If Trentend is actually limited to afocal, it changes all of the parameters in post #10... and many of the other posts in this thread as well.  



#17 Deadlake

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Posted 18 February 2021 - 04:01 PM

Hi Martin, the FSQ line are basically alike except with different apertures... I'm sure they are all excellent with NV.  But the OP is interested in a compact system.  In post #1 he says:  "So, the priority is probably a portable / fast-ish scope with minimal cool down as skies here in Scotland are very unpredictable."  The FSQ is a very compact system; mine fit in a medium Pelican with everything needed to observe.  

 

There are many scopes that will perform well with NV, including a TSA 120... I had one of those too.  But the OP seems most interested in being able to see medium to large emission nebulae.  And unless the TSA is used in afocal, it cannot be optimized for H-a.  I did not include the Sky 90 because it is out of production, last I heard, but it might be a good, compact option for NV... I did not own a Sky 90 so I cannot say.  

 

Trentend has most aspects of NV use covered with his 18" f:3.9, and has not been wowed with his subsequent H-a viewing.  To get views that do have a wow factor using narrow-band filters, my feeling is that a fast focal ratio is absolutely necessary.  No other general aspect of NV use requires a particularly fast focal ratio... but using narrow band filters does... in my experience.  And in my experience, reducing a refractor to focal ratios at or below f:3 without using an afocal system is problematic at best.  

 

But this is all academic, until we actually know if Tentend's OVNI B has a C-mount lens connection.  He says it does not; Joko says it does.  If Trentend is actually limited to afocal, it changes all of the parameters in post #10... and many of the other posts in this thread as well.  

Jeff, apologises for hijacking the thread.  

What is the general rule here. To use a narrow band filter how fast does a refractor need to be before a reducer is fitted, around F6 or is that not fast enough?

 

What are the problems when using a refactor at below F3 (after a reducer is fitted) if not in focal mode?

 

Thanks


Edited by Deadlake, 18 February 2021 - 07:07 PM.


#18 GeezerGazer

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Posted 18 February 2021 - 05:36 PM

Martin, it is not so much a minimum speed at which emission nebulae appear using H-a filters, as it is at what point they are easily discerned from the background sky to see detail... which involves a multitude of variables, not limited to LP.  But I don't think anyone will argue against the concept that a faster focal ratio increases light throughput.  Especially under high levels of LP, it has been related here many times, that the fastest possible focal ratio combined with the narrowest pass band H-a filters provide the best detail for visual use.  

 

When Gavster, under urban London skies, can see much of the Sharpless catalogue using a 3nm filter in optical systems that are well under f:2, it is evidence enough to understand what will enhance a visual image.  While not everyone has an f:1.6 system, I don't think anyone would argue against using an f:1.6 optical system specifically for H-a/emission nebulae.  There are other considerations, like the effect of band shift when using such a fast system, but for visual use, the faster optical system combined with a narrower band filter will always produce greater contrast to discern detail.  

 

In post #1, Trentend says, "The Tak is still the front runner but I’m now wondering if I’d get brighter NV views from something more dedicated like the Boren Simon or a faster refractor?"  And, in Post 9, he makes it clear that his objective is to see nebulae better.  In my experience, yes, there are brighter views available from an "optimized" NV system.  We know that Trentend can see H-a with a slower system such as his intended FC 100, but if he actually intends to create an optical system optimized for emission nebulae, there are better choices.  

 

There are at least 5 variants of the FC 100, the D, DC, DF, DL, and DZ, which range from f:7.4. to f:9.  And Tak makes the FC-35 .66x reducer (only $1,000 more) which nicely reduces these fine scopes.  But the only way you can make them faster than f:5 is by using them in afocal with a long FL eyepiece such as the TV 55/67.  Sometimes extreme reduction works well... and sometimes it does not.  My experience tells me that there are better ways to reach the fastest focal ratios... by starting with a faster native system, explained by Jeff Morgan above.  

 

Again, not knowing if Trentend's OVNI is actually a C-mount device, makes recommending a specific optical system impossible.  If it is not a C-mount device, many prior recommendations become irrelevant.

Ray


Edited by GeezerGazer, 18 February 2021 - 05:54 PM.


#19 Trentend

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Posted 18 February 2021 - 06:42 PM

Yes the OVNI has the c mount and I fortunately already have the 55/67 combo so am ok with long stacks. 



#20 Jeff Morgan

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Posted 18 February 2021 - 06:43 PM

There are other considerations, like the effect of band shift when using such a fast system, but for visual use, the faster optical system combined with a narrower band filter will always produce greater contrast to discern detail.  

 

On the band shift, I have recently acquired a 3nm h-alpha and have done some testing of it.

 

At f/2.8, the 3nm works quite well.

 

With my faster selections (f/1.2 ENVIS, and f/1.4 SLR) I find the band shift extremely unappealing. And that is with the filter mounted ahead of the lens, the optimum position.

 

Visually outer field is quite dark, with good performance only at the center. Kind of a "spotlight" effect. The only situations I would use this configuration for would be for a nebula that was very small, very dim, and well-centered in the field of view.

 

OTOH, with a 7nm filter the band shift is hardly noticeable at all at f/1.2.


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#21 Gavster

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Posted 18 February 2021 - 07:20 PM

I see my Takahashi fsq-130 has been mentioned smile.gif

Coincidentally I was observing with it this evening (first proper clear sky in London for ages it feels). It’s not an obvious choice for  NV work but I like it...Here are some phone shots of traditional nv favourites, Flame/Horsehead, Rosette and Monkeyhead nebulae taken using my ovni-m monocular operating in prime mode (which definitely gives tighter stars across the fov than afocal albeit dimmer views). Taken this evening in the light polluted London gloom with my 3nm

chroma ha filter - I’m itching to get to darker sites now.

 

I would echo Ray’s thoughts in that a f7.4 refractor would be a bit too slow for my nv preferences even with a 67mm eyepiece used afocally. My most used smaller nv scopes are my fsq85 and fsq130 which are both around f5 giving an effective f2 when used with the 67mm - lovely bright contrasty nebulae views with a tight 3nm ha filter. I used to have a fc100df which I used with nv but with a 67mm eyepiece this would give about f3, nice but a little too slow for me.

 

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Edited by Gavster, 18 February 2021 - 07:48 PM.

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#22 GeezerGazer

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Posted 19 February 2021 - 01:52 AM

Nice photos Gavster, as usual.  waytogo.gif

 

Jeff, yes, it is my experience as well that there is a balance concerning the optical focal ratio and the H-a filter bandwidth.  But much of what satisfies different NV observers is subjective.  You will notice in my imaging that I stick pretty much to the 7 or 12nm filter, dropping down to the 3.5nm when needed for fainter H-a.  But visual is different and many observers are not bothered by the effects of band shift, or minor vignetting.  At f:2.8 with a 7nm filter, I see neither band shift nor vignetting with my camera lenses or Newt.  At f:1.4 using my 3.5nm filter, I easily lose the outer 35% to band shift.  One of the good things about having multiple optical systems (camera lenses in my case) is if I'm forced to use the narrower filter, I can slow the optical speed a bit with the aperture ring... or just bump down to a shorter FL lens for a bigger FoV, so that the H-a subject remains fully illuminated in the center.   


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#23 Deadlake

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Posted 19 February 2021 - 04:20 AM

I see my Takahashi fsq-130 has been mentioned smile.gif

Coincidentally I was observing with it this evening (first proper clear sky in London for ages it feels). It’s not an obvious choice for  NV work but I like it...Here are some phone shots of traditional nv favourites, Flame/Horsehead, Rosette and Monkeyhead nebulae taken using my ovni-m monocular operating in prime mode (which definitely gives tighter stars across the fov than afocal albeit dimmer views). Taken this evening in the light polluted London gloom with my 3nm

chroma ha filter - I’m itching to get to darker sites now.

 

I would echo Ray’s thoughts in that a f7.4 refractor would be a bit too slow for my nv preferences even with a 67mm eyepiece used afocally. My most used smaller nv scopes are my fsq85 and fsq130 which are both around f5 giving an effective f2 when used with the 67mm - lovely bright contrasty nebulae views with a tight 3nm ha filter. I used to have a fc100df which I used with nv but with a 67mm eyepiece this would give about f3, nice but a little too slow for me.

Gavin,

 

Nice pictures.

 

You had a better night than me, the Moon was reflecting off some cloud on the horizon making the atmosphere milky (if thats the right word), seeing was not as good as I hope. 

For an F6 scope with the 67 mm EP I should go for a 3 nm filter, not too tight?

Best wishes

 

Martin 
 


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#24 Trentend

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Posted 19 February 2021 - 04:26 AM

Cracking shots! I need to do the maths but presume adding a reducer to the fc100 with the 55/67 combo would be better (or just a marginal gain for quite a chunky price tag)


Edited by Trentend, 19 February 2021 - 04:27 AM.

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#25 Gavster

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Posted 19 February 2021 - 05:11 AM

Gavin,

 

Nice pictures.

 

You had a better night than me, the Moon was reflecting off some cloud on the horizon making the atmosphere milky (if thats the right word), seeing was not as good as I hope. 

For an F6 scope with the 67 mm EP I should go for a 3 nm filter, not too tight?

Best wishes

 

Martin 
 

Martin 

Your mention of my fsq130 prompted me to “dust it off” last night - unfortunately  it’s been quite a while since I last used this scope. It was my best session so far with it  (I haven’t got this scope to a dark site yet) and my first time using the ovni-m with it which in prime mode worked really well with the phone camera. For visual I preferred using my 67mm in afocal mode for brighter views which made the detail easier to see live.

With a f6 scope the 67mm will get you to an effective f2.3 which should be fine for a 3nm ha filter. I’m very happy I bought all my chroma filters before the recent price rise, it’s a real shame they have gone up so much since they are fantastic for nv


Edited by Gavster, 19 February 2021 - 05:20 AM.

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