Binoviewer Compatibility with my TMB 130

[John]

My new-to-me TMB 130mm F/9.2 refractor has a built in extension section between the bottom of the scope tube and the focuser which effectively allows the tube length of the scope to be varied by up to 10cm. When using the scope with a single eyepiece and a 2" diagonal, the extension section is extended around 90mm-100mm. The Feathertouch focuser on the scope has 65mm of travel of it's own. 

I'm tempted to give binoviewing another try with this scope and I'm wondering if sliding the extended section inwards by the amount indicated above would enable a binoviewer to reach focus without the need to use a barlow lens / extender to reach focus. I suspect this feature may be incorporated just for this purpose but is 100mm enough inwards movement ?

Thanks for any advice offered

 

[jetstream]

Congratulations for your fine purchase John, what an excellent scope.

My reply is off topic a bit, but may be of interest to you. I have heard that binoviewers function better with a barlow or OCS in my case-  I am not sure exactly why. Of course I had to try my binos "native" with no OCS and the results were poor. The OCS was put back in front of the diagonal and the views were razor sharp again.

If you select a well matched binoviewer system, the views through that TMB 130mm just might make your knees go weak

[John]

Thats interesting Gerry - thanks for the feedback

I've been reading up on the Baader Maxbrights and they use glass path correctors of various strengths which seem to do more than just reduce the amount of back focus required - they also correct CA apparently.

More to research on this before jumping in I think.

 

 

[jetstream]

Research is is a good thing espc for binoviewing IMHO- there is a lot going on with binoviewers. Baader is releasing a new version of the Maxbright this summer they told me, but had no details. They use excellent optics including the flexible GPC's and lets hope they have made collimation easy for when they need a tweak. The "false exit pupil" theory holds true in practise and has many implications really. Many positives with it but one negative- so far- the binos are too dim for use with filters on nebs but I'm playing with large true exit pupils to raise the "false exit pupil" light volume... so far 6.7mm exit isn't cutting it... the 15" might be able to afford an aperture robbing 7.5mm+ exit, we'll see.

Rumor has it that the GPC, OCS can reduce/eliminate bino spherical abberation if the mag factor is high enough. Some see SA with no barlow/OCS/GPC or low factors. My own set up induces no changes in my star tests but I never checked native as the views were so poor...

I expect your flexible TMB 130mm to accomodate binos easily and if it were me I'd pick a GPC factor that allows a 1.5mm-2mm exit pupil with a lowish FL, sharp eyepiece that barlows well for lunar/planetary.

When everything is matched up nicely with binos the views are jaw dropping. Can't wait to hear your first report with them!

Sorry to ramble John.

[YKSE]

John,

That build-in 10cm extension is surely an addition nice feature of this great scope.

Baader Maxbright needs 110mm back focus when using T2 connection to a diagonal. With you present T2 diagonaal, if you can reach focus with intended binoviewer EP AND with the build-in extension fully extended, then you're certainly be able to use Maxbright without GPC, since the Baader clicklock 1.25" EP holder is 33mm long, this 133mm is good enough. (To be more exact, it's enough to have the build-in entension extended 80mm).

With binoviewers without direct T2 connection, you'll need ca another 40mm for added light path, you can make similar back focus check by using 2" diagonal with 1.25" reducer and fully extended build-in extension.

[John]

Thanks very much for that advice Yong - much appreciated

Baader certainly seem to think things through.

[YKSE]

Yes, T2 connection is very thoughtful implemented in many of Baader products

Some larger binoviewers have T2 connection too, such Denkmeier Binotron (127mm light path, 27mm free aperture), Baader Mark V (123mm light path, 28mm free aperture), Televue's Bino Vue(133-139mm measured light pass, 28mm free aperture).

For low power without GPC (OCS),

24mm 68° EPs should work with Mark V or Bino Vue without vignetting, while 21mm Denk is recomended by Denk as lowest for Binotron without vignetting.

Maxbright has 23mm free aperture, same as TS binoviewer, a pair of 20mm 68° should be the lowest power. While for WO bino with 20mm free aperture, a pair of 18mm 68°(if there exists such) should be the limit.

[Dude_with_the_tube]

John,

firstly grats on the Tmb

that 10cm adjustment should be sufficient for you to be able to achieve focus in "Native". However,i would suggest to use 1.25" prism and not the 2"  to reduce the light pass.(basically,keep your light pass as short as possible to save every bit of light coming through).

Not sure what equipment Gerry is using,but i have been using binoviewers in "native" and I am unable to report "poor" performance.Quite the opposite.Performance has been excellent.I have observed Venus with a pair of 7mm orthos(native focus) and have seen masses of detail.

Any sort of ideas on what binoviewers,Ep`s you will be running?

I got the new Baader BBHS silver prism(T2) sitting and waiting on a test run,but weather hasnt been cooperating  and as such,nothing to report.

[John]

Not sure about which BV's to go for. I've not got on too well with them in the past so I may try an "entry level" one to see how I get on.

 

[Stu]

31 minutes ago, John said:

Not sure about which BV's to go for. I've not got on too well with them in the past so I may try an "entry level" one to see how I get on.

 

I found the TS ones to be very good for an entry level pair. Self centring eyepiece holders with dioptre adjustment, good sized prisms and only 100mm optical path length. Good price too, although no eyepieces included.

http://www.teleskop-express.de/shop/product_info.php/info/p1855_TS-Astro-Binoviewer-for-telescopes--with-compression-ring.html

[John]

Thanks for that recommendation Stu - it's appreciated

[Dude_with_the_tube]

agree with Stu,

if buying new go for TS or William Optics ones,or maybe play smart and get a s/h from ABS in likes of Baader maxbrights they do pop up quite often .Price will go higher as bigger the prisms in the viewer.But to get the feeling TS or WO will do the trick.You will be unable to use 24mm Pans or ES 24mm EPs in them as they will vignette due to the prism size,however,they will do fantastically good for planetary observations.

Just one thing to remember,you dont need to push magnification in binoviewers! What you used to observe in cyclops mode with lets say 7mm EP,you will see the same but with 14mm pairs in bino.Cheap pair or orthos,plossls or erfles will work perfectly fine,no need for expensive pairs or glass like Naglers etc.unless money is burning your pocket   I use 2 sets of meade research grade orthos and erfles  from 10mm and up (very rarely i get the opportunity to do critical observation with less than 10mm pairs due to weather and seeing conditions)and for low power i use 35mm Baader eudiascopics. i binoview now 100% of my observations.Takes time to get used to it and i would say the best target to start off with is Moon and Jupiter to get the hang of the binoviewers.

[John]

Thanks Dude

I've got some BST Starguiders that I use for public viewing sessions. Maybe I'll turn those into pairs which won't break the bank and they are pretty decent eyepieces I think.

 

[Stu]

As an observation, I have had multiple pairs of binoviewers. I did not really get on with the Maxbrights or the WO ones because of the eyepiece holders, I found collimation a problem. The TS ones just seemed very well aligned and the self centring eyepiece holders help with keeping the alignment. I would quite happily go back from my Baaders to a pair of TS ones if I had to.

[nicoscy]

I agree with Stu as well on all comments. I have a pair of these (had the maxbrights in the past) and I just sent them to Denis Levatik in Croatia to supercharge them for a measly EUR 90. 

For that money, I get collimation to a very high degree, blackened prisms, better screws to hold the prisms and enlarged diameter of 25mm both on eyepiece side and telescope side. He is also fabricating for an additional EUR 45 an adapter for these binoviewers to my T2 Prism diagonal.

Keep in mind that Prism diagonals work better with f7 and slower scopes , so your scope might benefit from one of these. Prism diagonals also allow you some "breathing room" when you use binoviewers, affording you a bit more back focus.

I figure the only path to upgrade is if I want to use 24mm Pans. Currently there is a new binoviewer in the works from China which will have 27 - 28mm prisms to use with 24 Pans but there is no time frame.

FYI my binoviewers will be used with the infamous Vite 23mm aspherics with 62 degrees AFOV which are dirty cheap and would also work great with your long focal length telescope. In my case, these will be used also for wide field views with my soon-to-come Borg 90mm, yielding about 2.7 degrees TFOV.

[Dude_with_the_tube]

apparently rumors are that the new chinese binos will have 30mm prisms but these are only rumors and nothing has been confirmed.but for sure 30mm prisms will be a big game changer as this opens up the possibility to use not only 24mm pans but also 35mm 1.25" Ep`s like baader eudiascopics and so on for low power widefield observations.Obviously quality of binoviewers,prisms quality will be important.

I havent tried WO or TS ones so i will leave it to you guys to comment on them.I did use Denks 2 to start off with and they where the ones what hooked me to binoviewing.My next step was a custom order in cooperation with Deniss mentioned by Nicos and the end result was a custom made binoviewer with 30mm prisms and openings on both ends to allow me to use 35mm Ep`s,prisms where off ultra high polishing accuracy and Zeiss T* coated for high light pass,click lock Ep holders and T2 telescope end connection so i can use Baader OCS if i desire. 

I have tried numerous Ep pairs like cheap plossls,BGO orthos,Explore scientific,Maxvisions,Naglers ,TAL, Celestron etc.etc. and came to conclusion that simple orthos,plossls and erfles work perfectly fine for a fraction of price of more expensive multiple lens Ep`s,thats also taking into consideration of the weight of bino+Ep`s and possibly + powermate/barlow combo if you do not have muliple Ep pairs to use.however.i would say that my most used pairs so far: 35mm for low power. 20mm for general, 15mm and 12mm for high power.Only in really good seeing conditions i will use pairs below 10mm for critical details,but its more easier to stick a 2X barlow or powermate or OCS with 15mm pair and you are set.To sum up 3 pairs or even we can say 2 pairs of ep`s+ powermate/barlow/OCS will have you covered.

P.S. previous model of Baader:Mark IV has 30mm prisms and screw type Ep holder can be replaced with click locks