Tak 76 & binoviewers

[IB20]

I’ve been gifted some lovely Revelation binoviewers which I tried to use today for white solar viewing. Lo and behold the Tak 76 had too little inward travel to focus with the 1.25” Herschel wedge. I tried both with and without a 2x barlow but no luck. Can anyone help me identify what adapter or add-on I’d need to reach focus? I don’t know if I can get them to focus at night using the Tak prism either. Is this a Herschel wedge problem or will I also struggle during night sessions?

Interestingly the barlow & BVs (15mms EPs) worked in the Starbase 80, but the image I was getting was floater city and I guess the barlow was increasing their mag to something which the scope struggled with, it’s also a longer and slower scope which will probably contributed to what I was seeing.

I guess the other option is to buy a pair of lower mag EPs for the Starbase. Maybe some nice TV 25mm plossls? 

There was a fleeting moment where I could see why people rave about BVs, so any help getting this to work would be very much appreciated.
 

 

[jock1958]

Ahhh the curse of insufficient inwards focus!
I bought a pair of WO BV’s 18 months ago for my Tak FC-100DL and initially used the supplied 20mm eyepieces, Baader mirror diagonal, Baader 2.25x barlow or TV 2.5x power mate to reach focus.

Since then I’ve also been using a Baader ultra short clamp and prism diagonal (shorter light path) to reach focus natively with a variety of eyepieces.

I’ve found its a bit of a challenge with lots of trial and error but the rewards are well worth the effort. 

Edited April 20, 2022 by jock1958

[IB20]

10 hours ago, jock1958 said:

 

Since then I’ve also been using a Baader ultra short clamp and prism diagonal (shorter light path) to reach focus natively with a variety of eyepieces.

 

Is that replacing some or all of the Tak visual back? Seems inexpensive so might be worth a go. There are so many Tak and Baader adapters it’s really hard to know where to start. 

[jock1958]

2 hours ago, IB20 said:

Is that replacing some or all of the Tak visual back? Seems inexpensive so might be worth a go. There are so many Tak and Baader adapters it’s really hard to know where to start. 

I use the original Tak 2” visual back or a Baader 2” ultra short clamp depending whether I’m using my mirror or prism diagonals and what magnification I want to achieve.

Not sure what the visual back is on your FC 76 but if it’s similar to my Tak FS 60Q then my BV’s work on that with a screw on Tak 2” visual back that came as an extra. 

I would experiment and get some experience with what you already have before buying stuff that you probably won’t be able to use.

Some pics below with my different configurations.
 

 

[F15Rules]

I agree with Jock, an Ultrashort clamp and Baader T2 prism gives you the best chance to get focus without a Barlow lens. 

Alternatively a Baader 1.25x OCS gets you quite close to native magnification, but they are hard to find used or new at the moment and not cheap when new...🥴.

It's definitely worth perseverance though..when you get it right the views are wonderful!

HTH,

Dave

[Louis D]

4 hours ago, F15Rules said:

I agree with Jock, an Ultrashort clamp and Baader T2 prism gives you the best chance to get focus without a Barlow lens. 

No applicable for Herschel wedge usage.

[Louis D]

I use the nosepiece of a vintage Meade 140 2x Barlow on my Arcturus BV to reach focus even in my Dob which has only 20mm of in-focus left.  It operates at 3x in that configuration.  Check the astro classifieds and maybe put out a wanted ad.  There are some other screw in Barlow/OCA/OCS/GPC options out there as well to help reach focus.

[IB20]

Have just tried every conceivable configuration before/after the BVs with a Celestron Omni 2x barlow and a longer TV 2x barlow. No luck however! It’s not far off focus, but I’m not quite sure what I’m supposed to be lengthening when i have too little inward focus travel.

[jock1958]

2 minutes ago, IB20 said:

Have just tried every conceivable configuration before/after the BVs with a Celestron Omni 2x barlow and a longer TV 2x barlow. No luck however! It’s not far off focus, but I’m not quite sure what I’m supposed to be lengthening when i have too little inward focus travel.

Any chance of a photo of your set up?
BV’s extend the light path so anyway you can reduce that by shorter adapters in front of your diagonal will help, that’s how I managed that with the ultra short clamp. As I said a prism diagonal has a shorter light path than a mirrored one. 

[jock1958]

Hi @IB20 have a read of this thread from a few years ago it might be of some help. 
 

 

[IB20]

1 hour ago, jock1958 said:

Any chance of a photo of your set up?
BV’s extend the light path so anyway you can reduce that by shorter adapters in front of your diagonal will help, that’s how I managed that with the ultra short clamp. As I said a prism diagonal has a shorter light path than a mirrored one. 

I think I’m best to tackle the set-up at night. I have a Tak prism which has a short light path and I may be able to achieve focus. If it’s the wedge introducing problems perhaps I can use solar film (are wedges mirrors?). First go I get at trying at night I’ll take a pic!

[Stu]

I’m able to achieve focus, just, using a Baader CoolWedge which must have a much longer light path than the 1.25” ones.

I use a x2.6 GPC and connect directly using T2 connection to the Wedge. This won’t be possible with the Binoviewers you have, but is one of the advantages of the ones with a Baader style connection.

This is with a Feathertouch focuser, but I don’t think that makes a difference. My FC100DC has a lot more inwards focus available which does reach focus without barlows with a normal diagonal.

[F15Rules]

22 hours ago, IB20 said:

I don’t know if I can get them to focus at night using the Tak prism either. Is this a Herschel wedge problem or will I also struggle during night sessions?

 

2 hours ago, Louis D said:

No applicable for Herschel wedge usage.

..but very relevant for night sky usage.

Dave

[IB20]

I think the orange circled section is the bit I need to add something to. The blue area is where I’m adding the barlow and it’s very close to focus. 

[Stu]

29 minutes ago, IB20 said:

I think the orange circled section is the bit I need to add something to. The blue area is where I’m adding the barlow and it’s very close to focus. 

My x2.6 GPC is in the section circled orange.

Can you post a pic of your setup?

[IB20]

Please ignore the golf clubs, also something I’m terrible at. For night use I’d also expect to just swap in the Tak 1.25” prism, which I need to check if I can focus with.

[Louis D]

Did you try putting the Barlow into the wedge?  It's too bad the threads on the TV Barlow nosepiece aren't 1.25" filter threaded, then you could dispense with the long Barlow barrel and definitely reach focus.

Why the long train of step down adapters (three by my count) on the back of the focuser?  If it did the step down in one low profile go, I'm sure you could reach focus.

[jock1958]

1 hour ago, IB20 said:

Please ignore the golf clubs, also something I’m terrible at. For night use I’d also expect to just swap in the Tak 1.25” prism, which I need to check if I can focus with.

Looks like the same visual back that’s on my Tak FS-60C/Q but not 💯 sure? just wondering if you can unscrew the lens on your barlow and screw it into the nose piece of your BV’s, I did this with my Baader barlow and achieved focus but magnification was a bit too much. Some pics below and ignore my last photo as you wouldn’t require the barlow tube. 

 

 

Edited April 21, 2022 by jock1958

[JeremyS]

Ian at FLO has always been able to advise me on which precise Tak part is needed.

[Louis D]

7 minutes ago, jock1958 said:

just wondering if you can unscrew the lens on your barlow and screw it into the nose piece of your BV’s

The TV Barlows are not 1.25" filter threaded.  They're somewhat smaller and won't engage.

[IB20]

6 minutes ago, Louis D said:

Did you try putting the Barlow into the wedge?  It's too bad the threads on the TV Barlow nosepiece aren't 1.25" filter threaded, then you could dispense with the long Barlow barrel and definitely reach focus.

Why the long train of step down adapters (three by my count) on the back of the focuser?  If it did the step down in one low profile go, I'm sure you could reach focus.

On the Celestron Omni barlow the end piece does screw onto the BV nosepiece, I tried this but it was still out of focus. Don’t really know if the visual back is how it’s supposed to be but it’s how I interpreted the Japanese schematics though and it does focus.

I’ll try it with the Tak prism now.

[jock1958]

24 minutes ago, JeremyS said:

Ian at FLO has always been able to advise me on which precise Tak part is needed.

Good call Jeremy,  Ian King is the man! 

[Louis D]

27 minutes ago, IB20 said:

On the Celestron Omni barlow the end piece does screw onto the BV nosepiece, I tried this but it was still out of focus.

I'm not familiar with that Barlow.  It could be because it's a relatively short Barlow.  Bummer that didn't work either.

[jock1958]

42 minutes ago, IB20 said:

On the Celestron Omni barlow the end piece does screw onto the BV nosepiece, I tried this but it was still out of focus. Don’t really know if the visual back is how it’s supposed to be but it’s how I interpreted the Japanese schematics though and it does focus.

I’ll try it with the Tak prism now.

Hope it works with your prism diagonal, if not and it’s more in-focus you need then it might be a case of getting a Tak 2” visual back and a prism diagonal with a 2” nose piece. Before going down that route I would contact Ian at FLO as suggested earlier. Good luck 🤞

https://www.firstlightoptics.com/takahashi-adapters/takahashi-2-inch-eyepiece-holder-for-fs-60-and-fs-78fc100dc.html

[JeremyS]

4 minutes ago, jock1958 said:

Hope it works with your prism diagonal, if not and it’s more in-focus you need then it might be a case of getting a Tak 2” visual back and a prism diagonal with a 2” nose piece. Before going down that route I would contact Ian at FLO as suggested earlier. Good luck 🤞

https://www.firstlightoptics.com/takahashi-adapters/takahashi-2-inch-eyepiece-holder-for-fs-60-and-fs-78fc100dc.html

I did something similar with my FS 60Q. The Tak 2” back saves quite a bit of in-focus. Can use a low profile 2 to 1.25 inch reducer which will then accommodate a 1.25 inch diagonal