8 replies to this topic

[bsavoie]

I have been thinking of buying two Vixen 39208 NPL 30mm Telescope Eyepieces for my Williams Optics Binoviewer. I kind of think these 4- element PLOSSL series eyepieces are about as large as a 1.25 barrel will allow.

 

My reasoning has two objectives, 1) widest possible views, and 2) with many of my optical systems, I have to barlow with an Orion shorty 2x (with body removed) to bring about focus. When I am forced to use a barlow, I don't want all that magnification.

 

Yesterday I took my Lunt LS60T Ha B1200 out and looked at the Sun. Since Eddgie said somewhere that the B1200 allowed him enough backfocus to use his bino, I tried my more primitive WO. First without any barlow, and that didn't work, so I tried the 1.6 that comes with the WO binoviewer package. That didn't work, but it almost did, it just ran out of adjustment back space. I almost gave up and was about to order a WO 2x barlow that screws into the nose piece, when I remembered a bag of odd optics that came with my used Vixen (Orion) R200SS. In there was an Orion Shorty 2x and I remember reading that it can be taken apart. The optics screwed into the nosepiece and I had plenty of backspace. (loved showing my wife what the sun looked like with two eyes!)

 

Looking at the sun with two 20mm lens was almost too big, the sun just barely fit into full view. It felt like a 9 mm in mono view, a bit too close for my manual tracking with a Vixen 3992mini Mini Porta Mount. Every two minutes I had to re-center the sun.

 

I suspect 30mm will work OK for solar observation, because there is lots of light, and a little distortion around the edges may not be a distraction. But I want to do a variety of sky viewing. I want to buy a Vixen 2604 R130Sf Telescope, because it seems to be the ideal grab and go telescope. I also suspect that a binoviewer will work If I connect in with a T-2 adapter. It seems that the Vixen R200SS and smaller R130Sf both allow T-2 threads half way off the focuser and before the eyepiece. This backfocus was to allow camera connections, but it seems to me to also allow a binoviewer to fit nicely into the optical path. Why not try to have two eyes on the sky?

 

Having fallen in love with astronomy, I want to have several choices in equipment. I have the 'big aperture' covered with a 17.5 inch F6 dob, and a NS11 GPS. (just bought a Hyperstar III so in a few weeks M11 will be my focus). I also put the R200SS on a Celestron Cg-5, which leaves an unused GP2 mount. That will nicely hold a R130Sf. My hope is to have appropriate equipment to quickly get some sky viewing time in. Even better if I can use both eyes.

 

(M11 is my current favorite using the C-11 and WO bino raw. My next favorite is mono viewing with a 2 inch 16mm 100 degree Zhumell) (With my 17.5 inch F6 Dob my favorite is M5, but It is hard for me to find.)

 

I have been reading these binoviewer posts and no one talks about the little Vixen 30mm eyepiece. Is there something I am missing? My hope is that it will work well for the money spent. Has any one tried using these in a binoviewer, and did they have any success?

[Eddgie]

Since Eddgie said somewhere that the B1200 allowed him enough backfocus to use his bino, I tried my more primitive WO.

 

Sorry, but I think I said that you have to use a B1200 for binoviewers, which is true, but I did a long post on this about 6 months ago to tell how it was possible, and to make it work, I had to use a 1.25X GPC mounted in front of the BF1200.

 

Again, there is a post on how I was able to do this, but the 1.25x GPC mounted in front of the BF1200 works at about 1.5x.

 

As for whether it will work, the limit of field size is set more by the rear apeture of the binoviwer than by the field stop of the eyepecie.   What happens is that the field stop of these eyepecies tends to be close to the bottom of the barrel, and becuase of this, the rear apture of the binoviewer is so close to tthe field stop that it comes into focus.   When you look into the eyepiece, what you are really seeing at the edge of the field is the rear apeture of the BV.

 

This means that in these kinds of eyepeices, the effect will be that the apparent field of view is reduced.   Rather than be 50 degrees, it may appear as less than 40 degrees.  Depends on the eyepeice and binoviewer and other factors.  Bottom line though is that you may find that you don't get much bigger true field than you would get in the higher power eyepeice.

 

At least that is the experience I had when I tried using 32mm and 40mm Plossls with a Burgess, which is very similar to the WO.

 

Now you still get the lower power, but the true field never got bigger.  

 

As an example, the 40mm TV Plossl wound up having an apparent field of about 36 degrees (vs about 44 degrees).

 

The Baader GPC approach is expensive, and won't work unless you can direclty connect your binoviewers to the top of the BF1200 (which has T2 Threads the same as a Baader diagonal).

So, to reach focus, I needed to remove the eyepiece holder and attach the binoviewers directly (I bought a pair of Maxbrights), use a 1.25x GPC mounted inside the front extension tube on the BF1200, and I needed an externally threaded ring to hold the GPC in place in the extension tube.

 

Again, I posted on this about 6 months ago..  Lots of pictures.

[REC]

FYI....I also tried my WO w/20mm in my 1200mm Mak and it was just a little to big for the sun.  Filled the entire view.  I backed up to my 26mm SP pair and that was just right.

[bsavoie]

Thank you both for informing me. I like the idea of getting a $118 Glass Pack Corrector probably the 1.7, and placing it before the B1200. I did not know there were threads there (on the input side of the B1200). I guess that the GPC 1:1.7 does not just thread on, but needs another adapter. Then again it looks like, in the pdf manual that the GPC has three threads, so it might just easily attach to the B1200.

 

By placing the magnification before the Binoviewer, it will help to integrate the vision between the two eyes, by keeping the differences to a minimum. At least that is my current understanding.

 

By choosing 1.7 I might also have a better chance of using the WO bino on my big 17.5 inch F6 Dob.

 

I still like the idea of using 30mm Vixens which are $50.27 each on Amazon. I have two 26mm plossl eyepieces, but one is Meade and the other is another brand, and they are of different heights. Don't have much of a 1.25 inch eyepiece collection. Yesterday I found two Zhummel Zooms for $75, so with the one I already have, I will pick the two that are best matched and sell the other. The idea of zooming, rather than swapping out eyepieces would be most convenient (especially when the snow is falling).

 

Binoviewers are great, but they must first reach focus, then a selection of eyepieces becomes important.

Edited by bsavoie, 21 August 2014 - 01:25 PM.

[JustaBoy]

These are cheaper.

 

http://agenaastro.co...l-eyepiece.html

[bsavoie]

Thank you Chuck. This time it was too late, but I will always check a bit better next time. Win some lose some. Thanks for the information.

 

Optimizing equipment is always challenging. Fortunately we have that wonderful sky, waiting for a clear night. I love looking at the sky and recognizing how unbounded it is. The beauty of the sky is amazing and I don't mind spending some to see that beauty. I like the way the Vixen eyepiece looked on paper. I will check out the field of view and probably write it up. Maybe it is completely like Eddgie claims, but 30mm is not like 32mm, and the added effect of GPC 1.7 might open the view up a bit too. A 2x in front of the WO bino was probably not a good as the 1.7x in front of the B1200 blocking filter. The thinner and more expensive GPC operates up the optical stream, which seems a better way to go. I suspect the view will be wider and perhaps even contain more contrast. It is worth exploring, after all the equipment ecosystem is constantly evolving and changing. I think there is a place for both lower costing binovisors and lower costing eyepieces. Once I find that economic sweet spot, I till let others know and together we will make this hobby more accessible to all.

[Messyone]

 

Well here you go a photo of 30mm NPL's with WO Bino's on my former 6" f8 refractor. Nice eyepieces, but lots and lots of vignetting. 

 

I really don't use the 30's now prefering 25mm orthos with a razor sharp field stop.

 

I have read the 25mm plossls don't vignette and give much the same TFOV as the 30's.

 

Possibly Agena Astro 20mm WA eyepieces are the cheap but good way out, I also have AA 15 and 20mm SWA pairs, not that I use them anymore either! Prefer 18mm orthos for that razor sharp field stop combined with various barlows gives me all the mags I need....so far.

 

Matt

[Eddgie]

Thank you both for informing me. I like the idea of getting a $118 Glass Pack Corrector probably the 1.7, and placing it before the B1200. I did not know there were threads there (on the input side of the B1200). I guess that the GPC 1:1.7 does not just thread on, but needs another adapter. Then again it looks like, in the pdf manual that the GPC has three threads, so it might just easily attach to the B1200.

 

 

 

There are no threads on the GPC.

 

Here is how I did it...

 

http://www.cloudynig...pc#entry5950821

 

 

Also, when used in front of the diagonal, the 1.25x gives about 1.5x, and I think that  the 1.7X is going to give much more than 1.7x, so you might get tight on true field. 

 

 It is unlikely that you will reach focus in the reflector with the standard 1.7x GPC.

 

The right part for a Newt is the 1.7x Newtonian Glass Path/Coma corrector, but you need a T2 compatible binoivewer (or after-market adapter with a WO or clone)  for this to work.  Not all Newts will reach focus with this unit, but most will. 

Edited by Eddgie, 23 August 2014 - 06:26 PM.

[areyoukiddingme]

Also be careful. I tried these eyepieces, but ordered the two a few months apart. I managed to get two slightly different models. One has a wider TFOV than the other (perhaps an extra 5 degrees) which messed up binoviewing big time.