Help focusing a Tak FC100DZ with a 2” Baader BBHS mirror diagonal

[Nicola Fletcher]

Hi all,

I’m looking for a bit of help - I bought a 2” Baader BBHS mirror diagonal for a Takahashi FC100DZ and I can - almost - focus with a 41mm Panoptic and a Baader 8-24mm Mk IV zoom. These are the only 2” EPs I have. If I pull the nosepiece out of the focuser a bit it does focus both EPs (photo below), so I think I need a short extender. Has anyone used this diagonal with this scope and if so, could you offer any advice?

The System Chart doesn’t show any particular extender with 2” diagonals and FLO weren’t sure if I would be able to focus but they did point out that 2” EPs reach focus with the DL: http://www.scopeviews.co.uk/TakFC-100DL.htm. I’d hate to have to return this so any advice would be very much appreciated. Thanks in advance! 

[John]

I reckon you might need a 35mm 2 inch extension between the scope drawtube and the diagonal. Something like this:

StellaLyra 35mm 2" Extension Tube | First Light Optics

I found that I needed one when I used a 2 inch diagonal with my Tak FC100-DL

Other 35mm extenders are available of course. Baader have a click lock one I think.

 

 

Edited July 25, 2023 by John

[Franklin]

Tak 71S/71L 2"extension, on your chart.

[John]

13 minutes ago, Franklin said:

Tak 71S/71L 2"extension, on your chart.

I have the 71L and can't use it because it's too long. My scope is the FC100-DL. The 71S might be the one of those two. 

Edit: The 71S has an optical length of 35mm so may well do the trick. It costs though - £149.00 !!

Edited July 25, 2023 by John

[Franklin]

2 minutes ago, John said:

I have the 71L and can't use it because it's too long. My scope is the FC100-DL. The 71S might be the one of those two. 

Yes I agree looking at the amount the diagonal nosepiece is pulled out and your suggestion will be a lot more economical as well.

[Nicola Fletcher]

Thanks all - I tried the 71L and it’s too long - I can’t quite focus. However, I’ve also tried 71L with all the extenders that came with the scope and none of my 1.25 EPs (I tried a 24 Panoptic, 9mm Nagler and 18mm BST) focus with a 1.25 Tak prism diagonal either - there isn’t enough inward travel on the focuser. Removing the 71L extender doesn’t work either. Do I need 71S or a 35mm extender to use this with a 1.25” setup as well?

Edited July 25, 2023 by Nicola Fletcher

[John]

If you want to use 1.25 inch eyepieces in the 2 inch diagonal I think you will need a 35mm 2 inch fit extension of some sort.

 

[Nicola Fletcher]

1 minute ago, John said:

If you want to use 1.25 inch eyepieces in the 2 inch diagonal I think you will need a 35mm 2 inch fit extension of some sort.

 

No, apologies, this is the Tak 1.25 prism diagonal. It seems neither the  2 inch or 1.25 diagonals focus with the supplied extensions. 

[John]

Just now, Nicola Fletcher said:

No, apologies, this is the Tak 1.25 prism diagonal. It seems neither the  2 inch or 1.25 diagonals focus with the supplied extensions. 

I use a Baader T2 Zeiss prism diagonal with 1.25 inch fittings front and back. That goes straight into the 2 inch fitting on the end of the drawtube without the 71L extension. All my 1.25 inch eyepieces reach focus somewhere around the central part of the drawtube travel with that arrangement (pic below).

 

[JeremyS]

Here’s the back end of my DZ in 1.25 inch mode

[John]

Your 1.25 inch Tak adapter seems a little different from Nicola's and mine Jeremy ?

The 2nd knurled ring seems deeper ?

 

[Nicola Fletcher]

Thank you both very much - looks like I need to remove the long extender (71L on the system chart) and it should be the same as both of yours. I will wait a while and try it on something other than the moon which is just over a neighbouring house. The 1.25 prism should focus according to your experience. I appreciate your help very much.

[Nicola Fletcher]

3 minutes ago, John said:

Your 1.25 inch Tak adapter seems a little different from Nicola's and mine Jeremy ?

The 2nd knurled ring seems deeper ?

 

Yes good point - I see that too.

[JeremyS]

Here’s the DZ with 2 inch BBHS mirror and Pan 35 (I don’t have 41). It reaches focus at maximum focus extension. So I raised the the eyepiece a couple of mm

Edited July 25, 2023 by JeremyS

[JeremyS]

This is the first time I’ve used the Pan 35 in the DZ (normally use in my M210). It does need more back focus that my Ethos range or the Pentax 40 or Apollo 11.

Edited July 25, 2023 by JeremyS

[Franklin]

16 minutes ago, John said:

The 2nd knurled ring seems deeper ?

Maybe No14 on the system chart?

[JeremyS]

Gratuitous pic whilst set up 😊

I normally use in 1.25 inch mode.

Edited July 25, 2023 by JeremyS

[John]

6 minutes ago, JeremyS said:

....I normally use in 1.25 inch mode.

 

I have my FC100-DL out as well.

I'm normally in 1.25 inch mode with that too 🙂

[John]

25 minutes ago, JeremyS said:

Here’s the DZ with 2 inch BBHS mirror and Pan 35 (I don’t have 41). It reaches focus at maximum focus extension. So I raised the the eyepiece a couple of mm

 

The Panoptic 35 has a different focal plane position to the Pan 41 according to the TV specs page:

Tele Vue Optics: Tele Vue Eyepiece Specifications

 

Edited July 25, 2023 by John

[Nicola Fletcher]

Maybe the 41 Pan won’t work out for me. I’ll get the 35mm extender you suggested @John and see if that works.

The 1.25 inch Tak diagonal not letting me focus is a surprise though - I didn’t expect to have any problems with it. It is definitely not correct - I can’t focus on Vega either. I wonder if the 35mm extender will allow me to focus the 1.25 setup as well? @JeremyS, do you remember if you bought part 14 separately as it doesn’t come with the DZ?

[JeremyS]

3 minutes ago, Nicola Fletcher said:

Maybe the 41 Pan won’t work out for me. I’ll get the 35mm extender you suggested @John and see if that works.

The 1.25 inch Tak diagonal not letting me focus is a surprise though - I didn’t expect to have any problems with it. It is definitely not correct - I can’t focus on Vega either. I wonder if the 35mm extender will allow me to focus the 1.25 setup as well? @JeremyS, do you remember if you bought part 14 separately as it doesn’t come with the DZ?

It’s all part of the original setup I bought brand new in 2020

Edited July 25, 2023 by JeremyS

[JeremyS]

1 minute ago, Nicola Fletcher said:

Maybe the 41 Pan won’t work out for me. I’ll get the 35mm extender you suggested @John and see if that works.

The 1.25 inch Tak diagonal not letting me focus is a surprise though - I didn’t expect to have any problems with it. It is definitely not correct - I can’t focus on Vega either. I wonder if the 35mm extender will allow me to focus the 1.25 setup as well? @JeremyS, do you remember if you bought part 14 separately as it doesn’t come with the DZ?

Does your Tak FC 76 have the same back end? Worth swapping?

[Nicola Fletcher]

Just now, JeremyS said:

Does your Tak FC 76 have the same back end? Worth swapping?

Good idea - I’ll have a look at that and see if there are any bits I can use off it. It has the smaller focuser that I think is the same as on the DC so I might be able to use it.

[Mr Spock]

Here's my FC100. Works just fine with a Baader clicklock for both 2" and 1.25" eyepieces..

[Don Pensack]

7 hours ago, John said:

I reckon you might need a 35mm 2 inch extension between the scope drawtube and the diagonal. Something like this:

StellaLyra 35mm 2" Extension Tube | First Light Optics

I found that I needed one when I used a 2 inch diagonal with my Tak FC100-DL

Other 35mm extenders are available of course. Baader have a click lock one I think.

 

 

This would push the eyepiece back so far he's need 2" of in-travel.

He might have that 2", looking at the picture.

But:

The best solutions are:

--Parfocalizing ring on the eyepiece so the eyepiece stops before it is fully inserted.

--2" barrel extender on the eyepiece

--2" barrel extender on the diagonal nosepiece.

Barrel extenders are inexpensive and come in lengths of 5mm to 50mm.