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Takahashi FC-100 and FC-76 advice


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What diagonals do people.use with the FC100 (and FC76) to bring binoviewers to native focus (ie without a Barlow/OCS)?  I think it has to be a prism for the light path length, but what is good for holding binoviewers securely?

Does the Tak 1.25 prism do a good job securing the load or does it need to be the Baader T2 prism?

Also, would the T2 be wide enough to take 2" wide field EPs like TV Ethos without vignetting?

Edited by Commanderfish
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9 hours ago, Commanderfish said:

What diagonals do people.use with the FC100 (and FC76) to bring binoviewers to native focus (ie without a Barlow/OCS)?  I think it has to be a prism for the light path length, but what is good for holding binoviewers securely?

Does the Tak 1.25 prism do a good job securing the load or does it need to be the Baader T2 prism?

Also, would the T2 be wide enough to take 2" wide field EPs like TV Ethos without vignetting?

I would go with a Baader Zeiss T2 prism if wanting the shortest light path and best quality. Depending on the Binoviewer you get, you can attach directly to the prism saving more distance.

According to TS website, up to 40mm field stop can be used with minimal vignetting. That is my experience too, you eyes are not that sensitive to vignetting up to a certain point. Obviously you may want to end up with a prism for binoviewers and a full 2” mirror diagonal for your larger ethos.

https://www.teleskop-express.de/shop/product_info.php/info/p609_Baader-ZEISS-90--diagonal---T2-thread-on-both-sides.html

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6 hours ago, Stu said:

I would go with a Baader Zeiss T2 prism if wanting the shortest light path and best quality. Depending on the Binoviewer you get, you can attach directly to the prism saving more distance.

According to TS website, up to 40mm field stop can be used with minimal vignetting. That is my experience too, you eyes are not that sensitive to vignetting up to a certain point. Obviously you may want to end up with a prism for binoviewers and a full 2” mirror diagonal for your larger ethos.

https://www.teleskop-express.de/shop/product_info.php/info/p609_Baader-ZEISS-90--diagonal---T2-thread-on-both-sides.html

Thanks. I would definitely need  2" to T2  adapter at the telescope end (where there's a Baader 2" Clicklock). 

My binoviewers (your old binoviewers, since supercharged by Denis L) have a 1.25" nosepiece.  Guess I would either need a T2 to 1.25" adapter at the Eyepiece end OR a T2 to 2" Baader clicklock and then a 2" to 1.25" adapter.  The Clicklock would be more versatile. 

I imagine there's not a lot of difference in the lightpath between a T2- 2" clicklock (36.6mm plus adapter) and a T2-1.25" nose piece (lighpath not listed)? 

 

 

Edited by Commanderfish
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On 28/04/2021 at 01:21, Commanderfish said:

Just double checked and it definitely is just a matter of unscrewing, just needs sufficient grip, which is easier with the silver ring still screwed on to the OTA. There are definite advantages to shortening the OTA by removing the blue extension tube!

No matter how much force I use, even (carefully) tried a pipe wrench, I can’t remove that blue extension... so unfortunately (for now) it will have to stay 😬

Fortunately, my binoviewer comes easily to focus with the Hyperion 2.2x Barlow (albeit giving x5) and I’ve just received a WO 2x binoviewer Barlow nosepiece. This should be enough for my needs, as I didn’t plan on binoviewing anything other than the moon or planets.

Strange though that mine seems to be so tight, almost like it’s had glue or paint applied in the screw threads 🤔

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1 hour ago, Commanderfish said:

Thanks. I would definitely need  2" to T2  adapter at the telescope end (where there's a Baader 2" Clicklock). 

My binoviewers (your old binoviewers, since supercharged by Denis L) have a 1.25" nosepiece.  Guess I would either need a T2 to 1.25" adapter at the Eyepiece end OR a T2 to 2" Baader clicklock and then a 2" to 1.25" adapter.  The Clicklock would be more versatile. 

I imagine there's not a lot of difference in the lightpath between a T2- 2" clicklock (36.6mm plus adapter) and a T2-1.25" nose piece (lighpath not listed)? 

 

 

FLO ordered this custom for me:

https://www.firstlightoptics.com/adapters/baader-reducing-ring-2i-t-2a-with-15mm-optical-length.html

Maybe you should order intake for the next delivery in two weeks. 

Edited by Deadlake
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27 minutes ago, Commanderfish said:

That could be great, but it's for a male SC thread... What did you connect that to?

It’s not turned up, it’s for connecting telescope side UFC 2” to a T2 prism

 

781094EA-48D6-45B7-9A1C-B0AF4C030459.jpeg
 

so I can swap between a 2” or T2 diagonal.

https://www.baader-planetarium.com/en/downloads/dl/file/id/1617/product/1237/baader_star_diagonals_t_2_and_2.pdf

page 16

Edited by Deadlake
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5 hours ago, Commanderfish said:

So would that connect straight onto the back of a Tak without an adaptor or clicklock?

It would connect to a 2” nose telescope side to a T2 diagonal side in theory. I’ll let you know. 

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On 03/04/2021 at 13:42, mikeDnight said:

I think if I needed to take an FC on a plane, I'd remove the focuser, and if a DC or DF, the dewshield too. It would just mean I'd need to find a suitable cap for the lens cell and open tube.

That’s what I do Mike. The Lenscoat Hoodies work very well to cover the ends. I can’t recall which sizes I bought, so worth measuring to check.

https://www.wexphotovideo.com/lenscoat-hoodie-lens-cap-medium-black-1019928/

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On 28/04/2021 at 01:21, Commanderfish said:

Just double checked and it definitely is just a matter of unscrewing, just needs sufficient grip, which is easier with the silver ring still screwed on to the OTA. There are definite advantages to shortening the OTA by removing the blue extension tube!

I’m happy to report that I (finally) managed to unscrew that blue extension... just had to settle it carefully on a large towel, grip the whole tube and silver end ring in one hand and the extension in the other and give it some welly 😬🤣

Does make the OTA much more flexible now 😃

Thanks for the advice, it gave me the confidence to keep persevering 👍

F5FC161D-7028-4DF8-83B7-31914E67285E.jpeg

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This morning I tried to separate these two parts on my FC100DC but I failed. To much resistance...even with help of my friend. It seems to me that these two elements are also glued to each other !?Has anyone else had similar problems?

With 2.6x GPC I can reach focus, but with 1.6x GPC don't have much in focus...

Screenshot_20210503-230856.jpg

Edited by godra
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1 hour ago, godra said:

This morning I tried to separate these two parts on my FC100DC but I failed. To much resistance...even with help of my friend. It seems to me that these two elements are also glued to each other !?Has anyone else had similar problems?

I had exactly this issue (read the post directly above yours) and solved it by keeping that silver ring attached and laying it on a table and just gripping both parts and giving it a really solid twist. 

I think the parts might be stuck due to the black paint they use inside the tube, rather than glue 🤔

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My blue extension tube was tighter than the black extensions, yes it could well be the black paint that does it (no sign of glue or other fixings), and indeed the trick is to keep the silver ring tightly screwed to the white main tube to give yourself more grip on the silver section.

I might have used a towel for extra grip on the white/silver section too.

Give it some Welly, it's just a stuck screw fit.

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20 minutes ago, HollyHound said:

I had exactly this issue (read the post directly above yours) and solved it by keeping that silver ring attached and laying it on a table and just gripping both parts and giving it a really solid twist. 

I think the parts might be stuck due to the black paint they use inside the tube, rather than glue 🤔

 

13 minutes ago, Commanderfish said:

My blue extension tube was tighter than the black extensions, yes it could well be the black paint that does it (no sign of glue or other fixings), and indeed the trick is to keep the silver ring tightly screwed to the white main tube to give yourself more grip on the silver section.

I might have used a towel for extra grip on the white/silver section too.

Give it some Welly, it's just a stuck screw fit.

Careful guys - you’ll have the Taks protection league after you 

 

🤣

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Hi everyone,

Has anyone managed to bring binoviewers to focus with the DC or DF using a Baader 2" BBHS PRISM?

Just trying to work out what to replace my diagonal with.

I have a 1.25" Tak prism, I need a lightweight 2" diagonal for my EPs.  I was simply going to go with a lightweight 99% dielectric like the Explore Scientific one I had before. 

Is there any reason to buy a 2" prism over a 2" diagonal when I know I can bring my 2" EPs to focus with a 2" mirror and bring the binoviewers to focus with a 1.25" diagonal?

Cheers,

 

Fish

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4 hours ago, Commanderfish said:

Has anyone managed to bring binoviewers to focus with the DC or DF using a Baader 2" BBHS PRISM?

Just trying to work out what to replace my diagonal with.

As it happens, I’ve just taken delivery of this very prism today and as soon as I can get some clear sky, I’ll be checking it with my WO binoviewers on my FC-100DC.

However, although I did remove that blue section before the focuser, I may be putting that back and just using a Barlow/Focal Extender with the binoviewer. I’ll try both though if I can 👍

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4 hours ago, Commanderfish said:

s there any reason to buy a 2" prism over a 2" diagonal when I know I can bring my 2" EPs to focus with a 2" mirror and bring the binoviewers to focus with a 1.25" diagonal?

I have the same thought... I have the Baader BBHS 2” mirror and prism now, plus the Baader 1.25” prism. It’s very likely I will just use the binoviewer with the 1.25” and swap back to one of the others depending on target (I have Clicklock).

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5 hours ago, Commanderfish said:

Hi everyone,

Has anyone managed to bring binoviewers to focus with the DC or DF using a Baader 2" BBHS PRISM?

Just trying to work out what to replace my diagonal with.

I have a 1.25" Tak prism, I need a lightweight 2" diagonal for my EPs.  I was simply going to go with a lightweight 99% dielectric like the Explore Scientific one I had before. 

Is there any reason to buy a 2" prism over a 2" diagonal when I know I can bring my 2" EPs to focus with a 2" mirror and bring the binoviewers to focus with a 1.25" diagonal?

Cheers,

 

Fish

What do you want to use the binoviewers for? If mainly for high power lunar and planetary high power then it will be no problem as a GPC can gain you any additional back focus needed. Personally I still prefer single eyepieces for low and medium power use.

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15 minutes ago, Stu said:

What do you want to use the binoviewers for? If mainly for high power lunar and planetary high power then it will be no problem as a GPC can gain you any additional back focus needed. Personally I still prefer single eyepieces for low and medium power use.

This is my thinking now too... it’s good to have the option for low power binoviewing, but realistically I’ll stick with single eyepieces for this 🤔

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I would certainly like the option of using binoviewers at low to medium power on larger objects like open clusters, Orion's sword region including M41, maybe even the Pleiades/Beehive etc.

Pan 24s at native would give 2.2 degrees at x31 in the FC100DC/DF.

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2 hours ago, Commanderfish said:

Anyway, the question is:  is there a reason to get a 2" prism rather than a 2" diagonal, other than getting a shorter light path?

Technically the prism won't display light scatter in the same way that a mirror diagonal will. Having said that, I've never been bothered, or even noticed much light scatter from a quality mirror diagonal. Perhaps it's more academic than a major real world issue? May be the prism would have the edge at high magnifications?

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On 01/05/2021 at 06:15, Deadlake said:

It would connect to a 2” nose telescope side to a T2 diagonal side in theory. I’ll let you know. 

The above had turned up and works perfectly. Now can swap the UFC between a T2 or 2" without having to pull the nose out. 

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