Binoviewing Mars

[JeremyS]

Had a first outing of the binoviewers on Mars this apparition. They are the standard WO version with 1.6x Barlow. I used them on the Takahashi TSA 120. 

I’d forgotten just how well Mars looks in binoviewers. Generally, more relaxing to observe over long periods, allowing detail to be seen. Wonderful to see the very dark Solis Lacus coming onto the disc. The trouble is I only have two pairs of bino eyepieces: 20mm and 8mm. Obviously, I used the latter, giving x 180. However, I could have done with more as I was using the Vixen HR 3.4 (x265) in cyclops mode and the seeing was quite good (but not as good as earlier this week). I’m not sure about binoviewing at such a high mag – and I certainly don’t want to buy a second HR 3.4. By the way, the HR 3.4 in standard cyclops mode (no binoviewer in the train) gave superior views, especially in moments of good seeing. Maybe due to the higher mag, but I’m also thinking it might be because it forces one to concentrate more and one is more attuned to picking of those moments. Is this a case of generally better observing whilst binoviewing, but those exquisite “high spots” are more accessible to cyclops? I don’t know: needs more experimentation.

I tried out several single eyepieces in the binoviewer to get higher mags than with the 8mm’s.  Established 5 mm is probably about what I’d want to try in bino mode (x180). Rather than ordering another pair of eyepieces, I’ve gone for a WO x2 Barlow, which should also give x180 with the 8mm’s. We’ll see. Is anyone aware of other Barlows that fit the WO nosepiece (by other makers), e.g. x1.8 or x2.2?
 

[Robindonne]

4 minutes ago, JeremyS said:

Is anyone aware of other Barlows that fit the WO nosepiece (by other makers), e.g. x1.8 or x2.2?

I think we are lucky with the thread on these wo binoviewers.   Thread seems to be a slightly bigger one of all available threads, and accept all items i tried.  Barlows/filters etc.  

[Sky-searcher]

Hi Jeremy, TS have a 2.6X GPC which I use on my WO binoviewers. It also gives you 180mm of back focus which is why I bought it. Purchased mine from 365 astronomy. I observe with binoviewers 80% of the time nowadays. Thanks Andy.

[Paz]

Where you put the Barlow in the optical train will also vary the magnification it provides and may give more magnification options if focusing allows, i.e. placing it before or after the diagonal.

[Robindonne]

1 hour ago, Paz said:

Where you put the Barlow in the optical train will also vary the magnification it provides and may give more magnification options if focusing allows, i.e. placing it before or after the diagonal.

Hm ok.   So you mean a normal x2 barlow element will possible not magnify x2 in a binoviewer?
Thats interesting, because i used that x2 element tonight, in a binoviewer with the standard 20 mm ep’s.

Switched to monoview using a 4 and 5 mm, and was actually asking myself if the bino wasn’t showing the objects the same or larger?

Those 20mm’s were possibly not barlowed to 10 mm’s when you are right. But could they really bring those to 20mm’s to almost 5mm’s?

And thinking of what you just said, is that longer gso 3x barlow maybe the same element as the 2x?  With only the eyepiece further away from the barlow element? I was considering buying one of those, more to not having to buy all sorts of elements designed for that binoviewer.  But it wouldn’t possibly have worked.  

Edited September 19, 2020 by Robindonne

[Louis D]

The equation for Barlow magnification is M = 1 - L / f_b where L is the distance from the Barlow lens to the eyepiece's field stop and f_b is the Barlow focal length (always a negative number for magnifying Barlows).

Regardless of the Barlow focal length, which is never reported by any Barlow makers to my knowledge, it is clear that increasing the working distance between the Barlow lens and the eyepiece is going to increase the magnification.  That's why using Barlow elements in front of a binoviewer generally yields more magnification than when the Barlow is used as designed.  This assumes that the Barlow had a shorter working distance as designed than the optical path length of the binoviewer.  There are vintage long Barlows for which this might not be the case, but they didn't generally have removable lens cells.

[HollyHound]

22 hours ago, JeremyS said:

Had a first outing of the binoviewers on Mars this apparition. They are the standard WO version with 1.6x Barlow. I used them on the Takahashi TSA 120. 

I’d forgotten just how well Mars looks in binoviewers. Generally, more relaxing to observe over long periods, allowing detail to be seen.
 

Thank you so much for this thread, I had completely forgotten about trying my WO Binoviewer on Mars, just used on the moon so far 👍

I do have matched 16mm and 20mm eyepieces, plus a 1.6x and 2.25x Barlow, so I reckon this could work on the Mak 127... will give it a go 🤞

[mikeDnight]

12 hours ago, Robindonne said:

Hm ok.   So you mean a normal x2 barlow element will possible not magnify x2 in a binoviewer?
Thats interesting, because i used that x2 element tonight, in a binoviewer with the standard 20 mm ep’s.

Switched to monoview using a 4 and 5 mm, and was actually asking myself if the bino wasn’t showing the objects the same or larger?

Those 20mm’s were possibly not barlowed to 10 mm’s when you are right. But could they really bring those to 20mm’s to almost 5mm’s?

And thinking of what you just said, is that longer gso 3x barlow maybe the same element as the 2x?  With only the eyepiece further away from the barlow element? I was considering buying one of those, more to not having to buy all sorts of elements designed for that binoviewer.  But it wouldn’t possibly have worked.  

If you were to use a standard shortly barlow and insert your binoviewer nose piece into it, you'd get around 4X amplification. Screwing the barlow lens directly into the bv nose piece would reduce the amplification. So if using a WO or similar bv you can reach meaningful planetary magnifications by using a short tube barlow such as a 2X Ultima sv or 2X SW Delux, while using longer focal length eyepieces. I generally use 18mm Ultima's or 16.8mm Abbe Ortho's for most of my lunar and planetary observing when using my revelation binoviewer and Ultima barlow, giving approx X178 & X190 respectively in my 100mm F8 refractor.

Edited September 19, 2020 by mikeDnight

[Robindonne]

48 minutes ago, mikeDnight said:

If you were to use a standard shortly barlow and insert your binoviewer nose piece into it, you'd get around 4X amplification. Screwing the barlow lens directly into the bv nose piece would reduce the amplification. 

My only paired ep’s are the ones that came with the bv.   20mm.  I indeed screwed that barlow element directly in the bv nose piece.  According to what you estimated, i would have barlowed 3.5x? Going further would make no sense probably.  And im too inexperienced to tell how much it effect the view quality with such high “barlowed” magnifications.   If the quality is affected, i might be better of buying a second of on of my 4 or 5 mm eyepieces to make a pair.  
 

 But im stealing op’s question😬.  Sorry.  

Edited September 19, 2020 by Robindonne

[Louis D]

Generally, Barlowing binoviewers works really well because it helps to reach focus in telescopes with limited in-focus travel, slows down the light cone, and seemingly makes merging high power images easier than when using pairs of short focal length eyepieces.  Even with SCTs and Maks that can natively reach focus with binoviewers, Barlows allow the telescope to operate much closer to its designed focal length which minimizes induced spherical aberration.

All in all, Barlows play really nicely with binoviewers.

Edited September 19, 2020 by Louis D

[Robindonne]

On 19/09/2020 at 15:13, Louis D said:

All in all, Barlows play really nicely with binoviewers.

And do have any idea about differences between normal barlows and ES barlows?   Like the op opened this thread, will an ES fit in the binos nocepiece? 

[Louis D]

Focal extenders don't increase magnification very much with increasing working distance, so they would tend to continue to yield their rated magnification when used ahead of a binoviewer.  Since they are made up of two sections, the negative Barlow section below and the positive section above it to parfocalize the diverging rays, the nose piece alone would most likely be negative only.  I would try it as-is ahead of the binoviewer.

[jetstream]

I like lower power eyepieces as they are easier to merge and relax the eye. I use the Binotron 27's with their powerswitch giving 1.4x, 2.4x and 3x approx depending on config. Using 10mm eyepieces I can get 300x easy but prefer to stay a bit lower.

[Ricochet]

On 18/09/2020 at 13:55, JeremyS said:

Is this a case of generally better observing whilst binoviewing, but those exquisite “high spots” are more accessible to cyclops? I don’t know: needs more experimentation.

I suspect it is down to the difference in equipment being used. The Vixen HR series has meticulous optical design, expensive glass types, a high level of polishing, top coatings, and excellent stray light control via internal blackening and baffles. The binoviewers and barlow have none of these things. In moments of exceptional seeing it could be that the BVs become the limiting factor, and this is why the HR mono view pulls ahead. My cheap BVs definitely could be better with regards to scattering and stray light control, and I would guess yours might be the same. 

[F15Rules]

Jeremy,

I have both a WO 1.6x nosepiece and Baader Hyperion zoom 2.25x Barlow..both thread perfectly into my Revelation binoviewer 1.25" nosepiece, so their threads must be the same?

Both work very well. The Baader gives much higher magnification than the usual 2.25x when in the BV, I'd estimate a bit over 3.5x (not scientific, but based on visual comparisons between high power short FL eyepieces and longer focal length pairings with Barlow 2.25x screwed  into the BV 1.25" nosepiece). Assuming I'm correct in this, you'd probably want a pair around the 12.5mm (eg BGO or Ultima 12.5s, or best of all a pair of Morpheus 12.5s) mark to give you the equivalent of your solo Vixen HR 3.4mm. And of course, a pair of 12.5s would give you more eye relief than the 8s..

In my FS128 F8 (1040mm) such a combo would give me c 291x. In your TSA120  F7.5 the same combo would give c 252x, a pair of 10mms would give c x315 - both well within your scopes' comfort zone on decent nights..😊.

HTH

Dave

Edited September 21, 2020 by F15Rules