68 replies to this topic

[Gavster]

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)

I‘ve found adding a reducer in addition to my 67mm eyepiece to be a bit of a lottery. Standard photographic reducers often don’t work well since they require a very short (eg 55mm) distance to the focal plane which isn’t good with a 2inch diagonal and 67mm Televue eyepiece. With my refractors I’ve had the best results just using the 67mm eyepiece on its own without a reducer and hence like to start with a fast f5 refractor in the first place. I’ve had much more success using reducers with my c11 but in that case it’s reducing it from f10 to f7, not f7.4 to f5.5 which may be the reason. 
I think others have tried using a reducer and 67mm combo but generally I think the experience is that it’s better to just use the 67mm only.

[Deadlake]

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

The luxury of having a FSQ-130 lying around to 'dust off'  

What would you give up or gain do you think between a 85/100 mm FSQ. I think you've mentioned that you like the FSQ-85 but the number of objects you would use it for is limited compared with a 130mm or C11?

Note: Sharpstar is now stocked by FLO and they will bench test the scope, hopefully no hit for manufactures QA process.  

[Gavster]

The luxury of having a FSQ-130 lying around to 'dust off'  

What would you give up or gain do you think between a 85/100 mm FSQ. I think you've mentioned that you like the FSQ-85 but the number of objects you would use it for is limited compared with a 130mm or C11?

Note: Sharpstar is now stocked by FLO and they will bench test the scope, hopefully no hit for manufactures QA process.  

The fsq 85 and 106 are so close in focal length (450 vs 530) which means for nv use there wouldn’t be much between them and therefore imo the 85 wins by being much more portable. My 130 has a bigger jump to 650 focal length so provides a noticeable step up in image scale - this was apparent to me last night.

The focal length gap is even bigger between the 130 and the c11 so the c11 is much better for smaller objects such as galaxies imo since it gives you much more image scale. There are many more smaller objects to observe than larger ones so if I had to have only one scope (and having already viewed most of the best larger objects) I would go with my c11 (which is portable enough to easily transport by car with the TTS-160 Panther mount)

Edited by Gavster, 19 February 2021 - 06:15 AM.

[chemisted]

The fsq 85 and 106 are so close in focal length (450 vs 530) which means for nv use there wouldn’t be much between them and therefore imo the 85 wins by being much more portable. My 130 has a bigger jump to 650 focal length so provides a noticeable step up in image scale - this was apparent to me last night.

The focal length gap is even bigger between the 130 and the c11 so the c11 is much better for smaller objects such as galaxies imo since it gives you much more image scale. There are many more smaller objects to observe than larger ones so if I had to have only one scope (and having already viewed most of the best larger objects) I would go with my c11 (which is portable enough to easily transport by car with the TTS-160 Panther mount)

This is absolutely spot on and, as Ray has pointed out, very nice wide field views are always available with inexpensive manual focus camera lenses.

[Trentend]

A C11 looks great but I’d need a new mount, tripod etc and ideally looking for something to compliment my existing Gitzo and M2. Perhaps a C8 or 9.25 with a reducer? Although then back to potential collimation and cool down issues. 

[Gavster]

A C11 looks great but I’d need a new mount, tripod etc and ideally looking for something to compliment my existing Gitzo and M2. Perhaps a C8 or 9.25 with a reducer? Although then back to potential collimation and cool down issues. 

Given that night vision observing is done at low power, collimation and cool down isn’t a big issue imo.
However a new mount is! You will get an extra perspective on the skies with a smaller scope (whether refractor or reflector) and nv at a dark site. Certainly worth trying...

 

I’m biased to refractors but either of these scopes would be tasty as a grab and go nv option (the 600 is quite heavy though)

https://www.firstlig...astrograph.html

https://www.firstlig...astrograph.html

 

After my success with my c11, I tried a c6 with nv but I didn’t like it, I could only use a 1.25 40mm plossl and I think the smaller scts don’t works as well with 2 inch diagonals needed for the 67mm whereas the c11 is great. I also think for the smaller objects (and to keep the effective speed as fast as f3 or so), you really need about 25x mag which equates to a scope with a 10 inch aperture.

Edited by Gavster, 19 February 2021 - 03:29 PM.

[GeezerGazer]

I agree with with Gavster.  Trentend has 18" f:3.9 Dob with a focal length of roughly 1780mm.  A 600mm f:5.6 refractor would would be a great addition that could be used in prime at f:5.6 or with the 55/67 eyepiece at 235mm and ~f:2.2.  That would be a really nice combination.  The smaller Askar scope could be used for an even wider FoV.  

 

Keep in mind that a 6" B-S comes with the TS (ASA) .73x reducer that yields an f:2.8 scope at about 430mm in PRIME mode.  And, that same reducer could be used in his 18" scope giving him a wider range of focal lengths for an additional FoV.  His focal length in the 18" would drop to ~1300 at f:2.8, which would be great on medium small H-a.  And the 6" would pick up the larger H-a with a respectable FoV.  The Askar 108 is heavier than the B-S 6" scope, but is a little more compact.  There are always tradeoffs!

 

Since Trentend does have a C-mount device, he should consider selecting a system that can be used effectively in both prime and afocal.  If going the way of the B-S 150, since it is roughly $1000 less than the Askar 108, he would have ample $ left for one or two lenses mounted to his C-mount NVD for very wide field, hand held use at 3x-5x.  Lots to consider there.

Ray

[a__l]

Keep in mind that a 6" B-S comes with the TS (ASA) .73x reducer that yields an f:2.8 scope at about 430mm in PRIME mode.  And, that same reducer could be used in his 18" scope giving him a wider range of focal lengths for an additional FoV.  His focal length in the 18" would drop to ~1300 at f:2.8, which would be great on medium small H-a.  And the 6" would pick up the larger H-a with a respectable FoV.  The Askar 108 is heavier than the B-S 6" scope, but is a little more compact.  There are always tradeoffs!

 

 

I have exactly the same 18" f/3.9
At this point I think the best option was to use a 0.95x coma corrector. In afocal mode with 67mm TV, no need for another telescope. There is only one thing left, an experiment with a coma corrector in afocal. Waiting for the warmth.

[Trentend]

Appreciate all the continued feedback! I should perhaps just reiterate I’m happy with the views through the dob (although always want more!) but the priority is for something that yields a similar field of view and magnification but with the added bonus of being portable as I’m limited to a narrow part of the skies in the back garden. Plus I’d really like to see some of the existing targets that I can but at a dark site. 

[Gavster]

Appreciate all the continued feedback! I should perhaps just reiterate I’m happy with the views through the dob (although always want more!) but the priority is for something that yields a similar field of view and magnification but with the added bonus of being portable as I’m limited to a narrow part of the skies in the back garden. Plus I’d really like to see some of the existing targets that I can but at a dark site. 

You can get a similar field of view and magnification to your dob with a smaller instrument just by using a higher power eyepiece eg With a 67mm I calculate you are getting roughly 30x mag with your dob (and operating at an effective f1.8). If say you got a 6 inch f2.8 boren Simon then you could get 30x mag by using a 14mm eyepiece.

However the big issue with nv is that with this eyepiece you are operating at an effective f5.2 which will give much dimmer views. To get similar bright views to your dob at 30x you will need a similar 18 inch aperture and that’s not going to be portable. For a portable option, you do need to accept that it will work best with nv at a much lower mag (and bigger fov) than your dob. Some objects such as globular clusters will be ok at f5 but nebulae objects with ha filters will be much better at the fast speeds of sub f3 (hence why Televue developed the 67mm add on for night vision).

[Deadlake]

The trade off in the smaller APO mentions is say three groups of focal length F6, F5.5 and F5.3 using the Takahashi FSQ-85. Going to the F5 is almost a trebling of price, I know the FSQ-85 is a more flexible system, is it worth it?

 

Given the flexibility of these portable scopes if I moved site from a backyard location of 20.6 SQM to 21.24 SQM (local dark site, 45 mins) and then 21.78 SQM (relatives location, 5 hours drive), would this really have that much of an impact? Visually yes, so I'd expect NV to be more sensitive?

The 85 mm APO are around 4 kg which means you can use a light weight mount like a Scopetech Zero which adds to mobility, another plus point and also you can turn up and the scope would be ready to go without any cool down issues ( I know someone will say cool down is not needed for NV), but you might also want to look at some other object.

 

Edited by Deadlake, 20 February 2021 - 01:12 PM.

[Jeff Morgan]

However the big issue with nv is that with this eyepiece you are operating at an effective f5.2 which will give much dimmer views. 

 

Dimmer yes, but how about a little perspective here?

 

It's not like all nebula require the very fastest speed and very tightest bandpass filter to be seen well, or to be pleasing to the eye.

 

Any nebula with high surface brightness (which includes many Messiers, and a large number of Planetary Nebula) still look pretty good at f/5.2. And that view will be light years ahead of a conventional eyepiece/nebular filter.

 

Yes, they will be brighter faster. And once you start getting into the dimmer emission nebula (and there are hundreds in that category), speed becomes critical.

 

But you can still get very nice views at medium focal ratios. I do this frequently in my native f/7 refractor. After getting the "bright view" with the 67 Plossl, I go prime for the higher magnification. On some nebula (especially PN's) I will use a barlow and only realizing effective speeds in the f/10-f/20 range.

[Gavster]

Dimmer yes, but how about a little perspective here?

 

It's not like all nebula require the very fastest speed and very tightest bandpass filter to be seen well, or to be pleasing to the eye.

 

Any nebula with high surface brightness (which includes many Messiers, and a large number of Planetary Nebula) still look pretty good at f/5.2. And that view will be light years ahead of a conventional eyepiece/nebular filter.

 

Yes, they will be brighter faster. And once you start getting into the dimmer emission nebula (and there are hundreds in that category), speed becomes critical.

 

But you can still get very nice views at medium focal ratios. I do this frequently in my native f/7 refractor. After getting the "bright view" with the 67 Plossl, I go prime for the higher magnification. On some nebula (especially PN's) I will use a barlow and only realizing effective speeds in the f/10-f/20 range.

Jeff, Maybe the reason I personally feel f5 is too slow is that I live under very light polluted skies (sqm 18ish) and don’t often observe under dark skies. In these poor conditions I find I need a very narrow 3nm filter to cut through the light pollution for virtually all nebulae (not m42). With this very narrow ha filter f5 is just too dim visually for me. I have tried slower systems often to get more image scale and unfortunately I just haven’t liked the views. A very recent example was this week with my f5 fsq130. The live views on flame, horsehead, rosette etc with my 67mm plossl in afocal mode effective f2 were much better than in prime mode at f5. (That’s nearly 3 f stops or 8 times more light at f2 cf f5)

 

My preference remains that speed is king for nv (even globs I prefer fast setups )

Edited by Gavster, 20 February 2021 - 02:03 PM.

[ButterFly]

Between the options presented in the original post, I would suggest the adjustable gain.  Adjusting the gain is a huge advantage.  If the tube isn't running at the right gain for the conditions and the target, another scope won't fix that.

 

Should that be taken care of, my dob's best friend is my 80mm f/6 refractor, and vice versa.  You can reduce a native system down to around f/3 before the 67 PP becomes wasteful.  Field curvature becomes the enemy of artificial reduction at some point, because it is an imaging system after all.

 

 

 ... but the priority is for something that yields a similar field of view and magnification but with the added bonus of being portable as I’m limited to a narrow part of the skies in the back garden.

These are conflicting goals.  I can always use a zoom eyepiece with my 80mm, which are great, but at the expense of brightness.  The resolution will never match the dob.  If you want those brightly resolved high magnification views, you need the aperture, which is just less portable.

[Trentend]

Had the mini Mak127 out tonight taking a peek at the moon with the binoviewers. Usual crisp/sharp views pretty much straight away (that scope really punches above its weight) but started to cloud over after just 10 minutes. Noticed though it was momentarily clear around Orion so thought I’d try the NV kit on M42 with the 55/67 a-focal stack. Completely inappropriate for NV I know but the view was actually pretty good, nice large scale filling the whole FOV, could easily make out the trapezium, minimal scintillation and not bad detail with the 642 and 12nm filters. Only had a further 5 minutes before the skies clouded over completely but a nice mini session and great being able to do some genuine grab and go NVing with a scope (a first for me).

[Deadlake]

I‘ve found adding a reducer in addition to my 67mm eyepiece to be a bit of a lottery. Standard photographic reducers often don’t work well since they require a very short (eg 55mm) distance to the focal plane which isn’t good with a 2inch diagonal and 67mm Televue eyepiece. With my refractors I’ve had the best results just using the 67mm eyepiece on its own without a reducer and hence like to start with a fast f5 refractor in the first place. I’ve had much more success using reducers with my c11 but in that case it’s reducing it from f10 to f7, not f7.4 to f5.5 which may be the reason. 
I think others have tried using a reducer and 67mm combo but generally I think the experience is that it’s better to just use the 67mm only.

Have you ever tried reducing your FSQ telescopes, to get closer to a native NV speed of F1.2, or you think it will bump into stoping you finding focus?
At SQM 18-18.4 any little helps.

[Gavster]

Have you ever tried reducing your FSQ telescopes, to get closer to a native NV speed of F1.2, or you think it will bump into stoping you finding focus?
At SQM 18-18.4 any little helps.

Yes I have tried but with cheaper gso rc 0.75x reducers. It works but there are two issues 1) image scale is pretty small eg for the Tak fsq85 with reducer and 67mm the magnification is only 5x and 2) I think the quality of the view is adversely affected for a bit of an increase in brightness. So in general I just stick to 67mm with my refractors and Binoscope. For the dob and c11 the reduction in image scale is not do important as they naturally give significantly higher mag due to the extra aperture.

Edited by Gavster, 25 February 2021 - 09:52 AM.

[Deadlake]

Yes I have tried but with cheaper gso rc 0.75x reducers. It works but there are two issues 1) image scale is pretty small eg for the Tak fsq85 with reducer and 67mm the magnification is only 5x and 2) I think the quality of the view is adversely affected for a bit of an increase in brightness. So in general I just stick to 67mm with my refractors and Binoscope. For the dob and c11 the reduction in image scale is not do important as they naturally give significantly higher mag due to the extra aperture.

I should of stated FSQ-130. but you've not tried it on the 130mm/F5 then?

Edited by Deadlake, 25 February 2021 - 10:26 AM.

[Gavster]

I should of stated FSQ-130. but you've not tried it on the 130mm/F5 then?

I’m not sure I have but even with the fsq130 the mag would be only 7x (fov nearly 6 degrees) which is generally a bit too small for my preferences. For extreme reduction I’d want to use the bigger apertures.

[chemisted]

Have you ever tried reducing your FSQ telescopes, to get closer to a native NV speed of F1.2, or you think it will bump into stoping you finding focus?
At SQM 18-18.4 any little helps.

I have a TV-140 which is Al Nagler's Petzval design.  To get maximal reduction I used, very successfully, a Russell Optics 85mm Super-Plossl.  See post #8 in the following thread:

 

https://www.cloudyni...al-with-ovni-m/

 

This took the native f/5 down to f/1.56.

[Scopeman61]

Hello Folks -

 

I'm thinking about purchasing a vintage Starlight TVS-2B night NV scope. has anyone owned or used one?

 

It a crew served Vietnam era device. 7x 5.5/6" aperture. gen 2 tube i think. This unit is in working order and has all the original accessories and case. even the mercury battery.

I was going to diy an eyepiece for my scopes, and saw this guy. Just thought I would reach out and ask here.

 

any input would be greatly appreciated.

 

Thanks

 

 

 

 

[gatorengineer]

I can't comprehend why anyone would put an NV device in an fsq.  I have one and tried and was very disappointed. 

 

Going back to the ops question your next purchase should be an Asa or ts optiks 0.73 reducer corrector.  After that either a 6f4or an 8f4 newt.  With the reducer they will make you forget about putting NV in a lens thingy. 

 

Last question is no old NV isn't worth bothering with even more recent Gen 2+.

[Gavster]

I can't comprehend why anyone would put an NV device in an fsq.  I have one and tried and was very disappointed. 

 

 

Its personal preference. With the televue 67mm my fsqs give an effective speed of f2 which is fast enough to give great and bright views even with very narrow 3nm ha filters. I know that ChemistEd also gets great views with his very similar Televue 140, so I don't think its just me

 

With the 67mm the fsq give very wide fov of around 4-5 degrees which frame the larger nebulae such as the North American, butterfly, California, heart and soul and rosette very nicely. For smaller nebulae and galaxies, it is worthwhile to use significantly bigger aperture scopes to get bigger image scale (and still retain the fast effective speed).

 

I have tried achros and "small" reflectors (5-6 inches) but I just prefer the aesthetics that my fsqs give (eg lovely tight stars right to the edge). Refractors also have an advantage over reflectors of similar size in that  reflectors only have about 85% light transmission due to light loss from mirror reflectivity and secondary shading, whereas with refractors its close to 100% light transmission. But refractors don't size up well so for smaller objects (of which there are far more), my C11 edge and 16 inch dob are my instruments of choice. 

Edited by Gavster, 18 March 2021 - 04:43 AM.

[Deadlake]

Its personal preference. With the televue 67mm my fsqs give an effective speed of f2 which is fast enough to give great and bright views even with very narrow 3nm ha filters. I know that ChemistEd also gets great views with his very similar Televue 140, so I don't think its just me

Even given the speed of the FSQ Wimbledon is around 18-18.43 SQM, have you tried using a Russel Optics 85 mm EP for a little more speed?

Edited by Deadlake, 18 March 2021 - 09:48 AM.

[Gavster]

Even given the speed of the FSQ Wimbledon is around 18-18.43 SQM, have you tried using a Russel Optics 85 mm EP for a little more speed?

There comes a point where the image scale becomes too small to be worthwhile to get a bit of additional speed. Also I do have a 50mm Russell but I wasn’t happy with the edge stars so decided to stick with my Televue eyepieces.