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Telescope Options for NV

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#1 Alware

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Posted 25 March 2017 - 07:15 AM

I want to make a simple question as I'm looking to get into NV astronomy.

Until now I'd been only a simple visual observer but since a couple of months ago I found this forum and I got hooked up.

I have some questions as follow:

1.- What could be a good choice for a NV? ( I have a PVS-7)

A monocular or goggle?

2.- What could be a nice Telescope complement for the NV?

I had all kind of Telescopes but never really have the chance to fully enjoy (visually).

I have a Teeter's 12.5 Telescope but unfortunately had some bad issues and it can't be operated until get fixed so, I'll prefer to jump into my next Telescope.

 

3.- I have a some ES 100 degrees ep's and basically are new as I had poor opportunities to use them.

Should I sell them ? I found some comments of other members that once you get into the NV you probably will not go back to regular visual with ep's..

 

 



#2 Jeff Morgan

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Posted 25 March 2017 - 10:17 AM

Welcome to the club! As Obi Wan Kenobi said to young Luke Skywalker "you've just taken your first step into a larger universe". Or something like that.

 

1) Use what you already have, assuming it is at least an Omni III tube. Cost effective, and will give you a baseline.

 

2) On scopes, faster is always better. But again, don't hesitate to use whatever you have. When weather and schedule allow I will also start using my two Newtonians, f/7 and f/9.

 

I started experimenting with my monocular in a 90mm f/13.8 Maksutov. Open star clusters were actually quite good! Much better than conventional. Only tried one nebula (the HorseHead). I saw it clearly, but the view was pretty grainy. I suspect I pushed just a little hard on that one.

 

But most scopes are faster than this, and several people on this forum are using f/10 SCT's. Hopefully they will see this and relay their experience. 

 

3) I would not sell your conventional eyepieces yet. Or at all. At a minimum, you'll want to have them planetary and double star work. Also, higher magnifications.

 

I started NV last August, and use it at least 80% of the time. I just don't have much appetite for the dim views of conventional - but I am keeping a reduced set conventional eyepieces.


Edited by Jeff Morgan, 25 March 2017 - 10:19 AM.


#3 PEterW

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Posted 25 March 2017 - 11:53 AM

Rule 1: FAST
Rule 2: see rule 1.
Use a field of view calculator for the fastest f-ratio you can find and tune the aperture to the field of view. A 3x lens and camera lens/jumbo finder will do for most of the big stuff, something a big bigger for the smaller stuff. Not often you are going to need >12".
Remember to get some filters as they make the view more than the aperture, good baffling and stray light shielding is also invaluable too.

Peter

Edited by PEterW, 25 March 2017 - 12:15 PM.


#4 Rickster

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Posted 25 March 2017 - 01:28 PM

The simple, but not very satisfying answer is that NV makes almost any telescope better, and it excels when viewing dim, or previously invisible objects.  Here are some thoughts based on my use of a PVS-7 with various scopes and lenses.  These observations are based on viewing under dark skies and may differ from others observations under urban skies.

 

It is commonly accepted that NV works better with faster scopes, and while this is true in general, and especially true if you need filters to reduce light pollution, I find that NV also works well at higher f ratios.  I have used mine at f25, but in general I stop at f15. 

 

One of the handiest and most enjoyable scopes is one I cobbled from a 50mm sighter scope off an old Meade SCT.  The focal length is somewhere between 200 and 300mm,  which is nearly ideal for scanning the sky and observing large nebula.  The best part is that it weighs so little.

 

I have tried various camera lenses (Canon FD).  All give good views, but are heavy.  My favorite is a 200mm with 1/4x20 tripod mount ring.  The disadvantage is that these lens wont focus using a 45 or 90 degree diagonal, so looking up can be a pain.  But they are great for doing terrestrial surveillance, which is where a 80x200mm zoom lens excels.

 

I have found that I can see as deep (in terms of magnitude) with my lowly 70mm Pronto/PVS-7 combo as I can with my 10 dob and no night vision.  A great general purpose combo is  PVS-7 with a short tube refractor having an objective in the 80 to 120mm range. 

 

If you need or want to use filters, especially narrow band filters, such as a 12nm Ha, aperture and fast focal ratio are king.  Here I find my 10in dob with a .63 focal reducer works best.  And bigger would be even better.  It is big enough to give bright views, yet has a wide enough field of view to observe many nebula.  One problem, of course, is portability.  The views through a bigger dob must be fabulous, but if over 10 or 12 inches, portability can become a limitation. The second problem is that the field of view gets smaller as the telescope gets bigger (due to increasing focal length).  For example, I was trying to observe the North America nebula one night in the 10" dob.  I had a very hard time finding it.  And when I did find it, all I could view was a portion at a time.  Even though the NA nebula stands out when viewed with a smaller scope, it looks like any one of a million others when you can only see part of it.  But hey, the view was bright.

 

NV with SCTs (8 and 10inch in my case) is great for looking at globulars and galaxies.  M15 is spectacular.  The problem that I have with SCTs is that I enjoy NV most for scanning, and the limited FOV of an SCT makes scanning frustrating.  A .63 FR helps, but not enough IMO.  But, now that I have looked through an SCT with NV, I cant bear to look through it with a glass eyepiece.  Using a glass eyepiece in an SCT is like going blind (unless you are looking at bright objects like the moon and planets of course.  There glass is the only way to go.).

 

So this brings me to what I think is probably the best compromise, a 6 or 8in reflector:  The jack of all trades and master of almost none.  It is small enough to be portable and can be easily mounted or even hand held.  In my case, this is a AT6IN.  I adapted it to a homemade dob mount so that I could use it off a table.  Using a 12nm ha filter and a .63 focal reducer, it has a wide enough field of view to observe even the largest nebula, while having enough light grasp to give reasonably bright views.  Without the FR and ha filter, it has enough focal length to recognize that distant galaxies are galaxies, but not much more.  Basically, it will leave you wanting for other more specialized scopes, but it is an excellent place to start, and is the one I use the most.


Edited by Rickster, 25 March 2017 - 01:30 PM.


#5 bobhen

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Posted 25 March 2017 - 01:38 PM

I observe with a NVD Micro from the Philadelphia suburbs in extremely heavy light pollution. I use a NVD Micro, which is a monocular and I really like it but I’m one of those people who has a hard time with binoculars. Night Vision has shone me objects that were just not visible from this location with any size telescope.

 

Night Vision works in any telescope. Faster delivers somewhat smoother views with less scintillation BUT (and it’s a big but) you need longer focal length for image scale and close-in detail. I use scopes from: a 50mm F2 repurposed guide scope (hand held), 102mm F5 achromatic refractor, 120mm F7.5 apo refractor (also at F5.25 with a reducer), and a “slow” Mewlon 210 at F11.5 (and F8 with a reducer). ALL deliver the goods with just different fields of view and image scales. Use what you have to start as NV works in just about any scope.

 

Think of a NV Image Intensifier as a camera. Unlike a telescope that uses eyepieces to get different magnifications and fields of view with NV you need different scopes or reducers or barlows to change image scale and the field of view. For example: My Mewlon’s 2400mm FL is great for gobulars and smaller planetary nebula. The Tak 120 at 650mm or 900mm FL is perfect for the Rosette or the Monkey Head nebula, and my 50mm repurposed guide scope is perfect for sweeping up the large dark nebula in Sagittarius.

 

One night just last week I observed 54 “diverse” deep sky objects from galaxies to planetary nebula: including the Horsehead, Flame, Monkey head, Orion Nebula, Rosette, M82, M3, the Leo Trio, M35 and 2158, NGC 2440 (including its double core and scattered shell) and MANY more. After 40 years of observing from this location and with scopes up to 15”, the best “visual views” I’ve had of these and many other objects is with NV and modest scopes from 102mm to 210mm.

 

In addition you will need a Ha filter for nebula. A 7nm Ha filter is a good compromise between cost and performance and mine delivers the goods in heavy light pollution. Some use 5 and 12 and even 3nm Ha filters as well.

 

For heavy light pollution, I use a 685 Longpass filter. Some use 640 and 610. These work on non-nebula objects like galaxies and dark nebula etc. Open clusters and globulars are also fantastic using NV.

 

I use a 2” .7 reducer on my refractor and Mewlon. Don’t get the 1.25” reducers as edge performance suffers too much IMO.

 

Also be aware that most NV Intensifiers need more in-focus than regular eyepieces. For example: SCTs or scopes with moving mirrors usually work fine. Refractors that have additional back focus extensions that can be removed (like my Tak 120) also work fine. However my 4” F5 refractor does come to focus but only using a 1.25-inch diagonal.

 

I would keep the eyepieces for now. You can always sell them later. Having said that, I haven’t really used eyepieces for deep sky viewing since I got the NVD Micro.

 

HERE is a great website that will answer more of your questions.

 

Bob



#6 bandhunter

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Posted 26 March 2017 - 11:38 PM

I use my Psv-7 with my 10 inch f/4.7 and my WO 66 f/5.9 with very pleasing results.  I've had my NVs a year but consider myself nv beginner due to my limited amount I've actually been able to observe.  That being said I've been able to see alot.  Just this week I was able to get views of the rosette nebula, flame nebula, ring nebula, dumbbell nebula, extremely detailed Orion nebula, m63, m51, m81/82, m37, m36, and the list goes on with just 66mm and camera tripod in a red/white zone.  It's amazing. And the faster f/4.7 is a lot better, of course there is 10 inches as well.

 

 But with the dob I don't get the field of view I want on the larger objects.  I get a good field of view with my 66 but not quite the detail I'm craving with simultaneous wide fields.  After reading Doug Culbertson's awesome report on his experience with the 120st f/5, I decided I wanted an f/5 refractor for NV as well for high detail wide field.  Someone else mentioned /implied that this type of scope is fine for filtered NV but maybe not for without a filter.  I didn't understand that, we want faster right? Is this a CA problem? I haven't had to deal with CA in NV before due to the scopes I'm using. I thought, I guess naively that color correction wouldn't be a big deal cause I'm seeing all green anyway. Could use some clarity on this.

 

 I have a twilight ii on the way.  Plan on getting a much bigger refractor for it to use for NV wide sweeps.  Probably gonna be the 120st but got the twilight ii because I was considering the Omni 150r f/5.  Anyone used this with NV?  I thought it could be epic but now I'm worried about CA.  Also what about newtonian astrographs f/3.8 anyone have experience with them as a NV rig?



#7 bobhen

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Posted 27 March 2017 - 07:22 AM

CA is an issue with achromatic refractors because the Image Intensifier will intensify the unfocused light resulting in bloated stars. Ha and Longpass filters do a good job of reducing this. In addition, with Night Vision and an F5 refractor you will be using lowish powers anyway and low power helps minimize the appearance of CA as well.

 

One of the telescopes I use is a 4” F5 refractor (with filters) and the views are really wonderful. Get the 120mm F5 (or the 150 F5) and use it with filters and it will amaze you.

 

Below is a section from a review of the Omni 150 F5 refractor taken from a 2009 A-Mart Review. This section of the review deals with the 150 F5 when used with NV...

 

"THE H-ALPHA MACHINE

One of the primary reasons I purchased the Omni was my previous experience with a Collins I3 image intensifier coupled to a narrow-band hydrogen-alpha filter. This combination had given me some magnificent views of some faint and elusive diffuse nebulae with both small refractors and larger Newtonians. The aperture and fast optics of the Celestron scope seemed like the perfect match for some impressive vistas.

 

On a dark, moonless night with a naked-eye limiting magnitude of 5.5, I used the I3/H-alpha set-up at magnification of 50x with the 150R. The resulting views were spectacular. Because of the narrow H-alpha bandpass, the image intensifier was able to operate at close to its maximum 50,000x efficiency, darkening the sky background to pitch black and generating outstanding contrast. The Great Orion Nebula was so bright and detailed that it was enough to cause a loss of dark adaptation, albeit its monochrome green coloration. 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



#8 Doug Culbertson

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Posted 27 March 2017 - 07:34 AM

FWIW, I am still greatly enjoying my 120ST with PVS-7 and Ha filter. I had also been warned that these fast achromats may not be suitable for NV observing but, thanks to Bob and Vondragonnoggin reassuring me, I gave it a go and have not regretted it. 



#9 bandhunter

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Posted 27 March 2017 - 07:44 AM

Thanks for the input on the F/5 refractors! Makes me feel better. I'm going to try and hold out for one with an upgraded focuser, but we will see. Vondragonnoggin reviews and opinions were why I went with the Twilight II as well, he uses some big refractors with his NV

 

I currently have a Ha 13nm filter, but no long pass filter.  I meant to get one when I was first getting my NV set up but it slipped my mind.  I have also read that for AP and fast achromats, you can reduce/eliminate CA with a V-block and a yellow filter combo.  I wonder if this would also apply to image intensifiers.  A yellow or dark yellow filter are cheap and easy to come by, just a thought.


Edited by bandhunter, 27 March 2017 - 08:04 AM.


#10 bobhen

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Posted 27 March 2017 - 10:12 AM

Thanks for the input on the F/5 refractors! Makes me feel better. I'm going to try and hold out for one with an upgraded focuser, but we will see. Vondragonnoggin reviews and opinions were why I went with the Twilight II as well, he uses some big refractors with his NV

 

I currently have a Ha 13nm filter, but no long pass filter.  I meant to get one when I was first getting my NV set up but it slipped my mind.  I have also read that for AP and fast achromats, you can reduce/eliminate CA with a V-block and a yellow filter combo.  I wonder if this would also apply to image intensifiers.  A yellow or dark yellow filter are cheap and easy to come by, just a thought.

Consider a 7nm Ha filter as well. Its more aggressive but can really pull out nebula without diminishing the stars all that much. With my heavily light polluted sky, I use 7 and 6nm Ha filters.

 

The long pass filters help block light pollution something a yellow filter doesn’t really do. Remember your image intensifier intensifies all light – even some light like unfocused CA and light pollution that you don’t want.

 

A twin mount with a 66mm refractor on one side and a 120mm or 150mm F5 refractor on the other would be a nice set up – especially for large to mid-size nebula and clusters etc.

 

You can also add a barlow to increase image scale for globulars and the small stuff. TV Powermates do not add additional in-focus if that becomes an issue.

 

Have fun.

 

Bob



#11 PEterW

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Posted 27 March 2017 - 01:25 PM

I used to do very nice lunar observing with an st120 and a yellow filter... why did i sell it???!!

Cheers

Peter

#12 pwang99

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Posted 27 March 2017 - 06:16 PM

I currently have a Ha 13nm filter, but no long pass filter.  I meant to get one when I was first getting my NV set up but it slipped my mind.  I have also read that for AP and fast achromats, you can reduce/eliminate CA with a V-block and a yellow filter combo.  I wonder if this would also apply to image intensifiers.  A yellow or dark yellow filter are cheap and easy to come by, just a thought.

 

Just an FYI - I find my 7nm H-a to be a big step up in contrast from even a 10nm, and I am also in red/white zone skies... With summer coming up, it might be worth saving your nickels for one, if it's not already on your wishlist.  :-)



#13 shams42

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Posted 28 March 2017 - 11:07 AM

Don't use a yellow filter with NV. Use a red filter or IR pass. These devices are most sensitive to the red and near-IR band.

 

As an aside, would anyone want to swap their Baader 7nm for my Astrodon 5mm for a few weeks? I'd like to evaluate the 7nm. The 5nm has great contrast, but I wonder if I went too narrow. PM me if interested.




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