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FC100DC with Binoviewers, no barlow


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Not sure why I haven't tried this before, but I've just checked out my Baader Mark IVs in the Tak without any barlow or GPC element and they do come to focus no problem.

For full disclosure I'm using a FT2025-BCR focuser and an A20-302 adaptor, can check exactly what length that is. Also, a T2 BBHS diagonal with the Binoviewer connected directly via a T2 quick changer ring to keep the light path short.

Lovely views of the DC, with 25mm 50 degree eyepieces the field of view felt plenty wide enough.

 

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That's interesting Stu. Does the FT have greater in-focus than the FC's original focuser? I know my own binoviewer doesn't reach focus without a Barlow. I daren't leave my Tak unattended near Peter Drew, as Peter likes to shorten tubes allowing binoviewers to reach focus. :eek:

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25 minutes ago, mikeDnight said:

That's interesting Stu. Does the FT have greater in-focus than the FC's original focuser? I know my own binoviewer doesn't reach focus without a Barlow. I daren't leave my Tak unattended near Peter Drew, as Peter likes to shorten tubes allowing binoviewers to reach focus. :eek:

Stu can give his take but when I installed the feathertouch on my FC100DF it did increase the infocus such that I had to buy a 2 inch extension tube to get my normal mono eyepieces to come into focus. 

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17 minutes ago, mikeDnight said:

That's interesting Stu. Does the FT have greater in-focus than the FC's original focuser? I know my own binoviewer doesn't reach focus without a Barlow. I daren't leave my Tak unattended near Peter Drew, as Peter likes to shorten tubes allowing binoviewers to reach focus. :eek:

I've not done a direct comparison Mike but yes I believe it does. I've actually just got an 80mm extension so that I can reach focus with my Tak Prism which has a very short light path. I've still got the original focuser so I can put them side by side and let you know.

The only difference between Gavin's setup and mine is that he uses the correct adaptor (A20-304?) and I use an A20-302 which I had originally from my FS-60C/FC76DC scopes. It works fine but is possibly a little shorter than the 304. Hopefully I'm seeing Gavin on Friday so we can compare.

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So the answer is an emphatic yes :) 

Hard to be exact based on a quick look, but there are 2x40mm extensions plus the Baader clicklock in my FT, so probably 100mm maybe more difference.

IMG_3340.JPG

IMG_3341.JPG

IMG_3342.JPG

IMG_3343.JPG

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3 minutes ago, marcus_z said:

Note the extension tube in the original DC focuser. If you remove that you gain approximately 65mm backfocus. That might help...

I removed that in the first three images, put it back in the last one just to show how long it is then!

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10 minutes ago, Piero said:

That's very short indeed! 

I have to say that so far I haven't had any inward issue with my DF + 2" BBHS. I don't binoview though.

It will only be an issue if you want to binoview with no barlow Piero

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I just measured the distance for my FC-100DF.

15cm, from the beginning of the focuser to the 1.25" adapter. 10.5cm if used in 2" mode.

 

Edit: measures taken with drawtube completely retracted.

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I'll measure mine in a minute Piero. I think my pictures show that Tak design is sensibly thought out as it is almost exactly the same length as mine with extension tubes for 1.25", and allows for it to be shortened to accommodate 2" diagonals. But, I'm sure with a different design they could also allow for binoviewing, the tube length itself is short enough.

I did wonder if the front section of the Tak focuser could be removed but I don't think so (unless that is what Marcus was referring to?)

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Just measured mine

The full Tak focuser including extensions is  257mm to the end of the 1.25" adaptor

With the extensions removed and in 1.25" mode, it is 187mm to the end of the 1.25" adaptor

The FeatherTouch is 76mm to the end of the 2" drawtube (or end of the focuser, it is the same), so over 100mm shorter even including a 1.25" adaptor but I use a 2" on my diagonal so probably only lose a mm or 2.

Quite a dramatic difference.

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9 hours ago, Piero said:

I just measured the distance for my FC-100DF.

15cm, from the beginning of the focuser to the 1.25" adapter. 10.5cm if used in 2" mode.

 

Edit: measures taken with drawtube completely retracted.

Here's a question, is the tube length the same between the DC and DF models? I had always assumed yes, but not totally sure.

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1 hour ago, Stu said:

Here's a question, is the tube length the same between the DC and DF models? I had always assumed yes, but not totally sure.

I believe so. They are both f7.4, so the focal point of the DF + 2" diagonal path should be the same as the focal point of the DC + 1.25" diagonal path.

 

EDIT: My measurement doesn't include the 2" extension tube. I didn't include this as the telescope doesn't reach focus with it using a diagonal, but only in straight through mode.

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11 hours ago, Piero said:

I just measured the distance for my FC-100DF.

15cm, from the beginning of the focuser to the 1.25" adapter. 10.5cm if used in 2" mode.

Edit: measures taken with drawtube completely retracted.

 

2 hours ago, Stu said:

Just measured mine

The full Tak focuser including extensions is  257mm to the end of the 1.25" adaptor

With the extensions removed and in 1.25" mode, it is 187mm to the end of the 1.25" adaptor

The FeatherTouch is 76mm to the end of the 2" drawtube (or end of the focuser, it is the same), so over 100mm shorter even including a 1.25" adaptor but I use a 2" on my diagonal so probably only lose a mm or 2.

Quite a dramatic difference.

 

I'd have expected the FT to be around 8cm and I went rather close. Your focuser is essentially 30mm shorter than the DF. :) 

I haven't measured but from what I read it seems to me that the DF drawtube is 2.5". 

 

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7 minutes ago, Piero said:
50 minutes ago, Stu said:

 

I believe so. They are both f7.4, so the focal point of the DF + 2" diagonal path should be the same as the focal point of the DC + 1.25" diagonal path.

 

 

I guess I'm wondering whether the DF focuser is the same length as the DC focuser in 2" vs 2" and 1.25" vs 1.25" modes? If there is any difference then it would be made up by a different tube length?

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According to this I'm correct, the DF has a shorter tube length than the DC, specifically to allow more backfocus for imaging and for the reducer. Im not sure if this is just that the focuser itself is shorter (which it obviouslynis) or if the tube is shorter too.

This does mean that if you are wanting to binoview with no barlow then the DF makes sense to buy over the DC unless you want to upgrade to an FT which was something I always intended to do. All interesting stuff, I had no idea this thread would lead here :)

I bought the DC because it was cheaper and lighter so it suited my purposes but the DF definitely makes sense too :) 

I wonder if the reducer can be used visually? Would be nice a f5.4 :) 

IMG_3345.PNG

IMG_3346.PNG

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1 hour ago, Stu said:

According to this I'm correct, the DF has a shorter tube length than the DC, specifically to allow more backfocus for imaging and for the reducer. Im not sure if this is just that the focuser itself is shorter (which it obviouslynis) or if the tube is shorter too.

This does mean that if you are wanting to binoview with no barlow then the DF makes sense to buy over the DC unless you want to upgrade to an FT which was something I always intended to do. All interesting stuff, I had no idea this thread would lead here :)

I bought the DC because it was cheaper and lighter so it suited my purposes but the DF definitely makes sense too :) 

I wonder if the reducer can be used visually? Would be nice a f5.4 :) 

 

A nice photo here of the two siblings (DF and DC) here: :) 

https://www.cloudynights.com/topic/535739-takahashi-fc-100-dc-basic-questions/#entry7193389

 

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12 hours ago, mikeDnight said:

That's interesting Stu. Does the FT have greater in-focus than the FC's original focuser? I know my own binoviewer doesn't reach focus without a Barlow. I daren't leave my Tak unattended near Peter Drew, as Peter likes to shorten tubes allowing binoviewers to reach focus. :eek:

FT  £500?, hacksaw blade £1, my time and skill £499.  No brainer really!   :grin:

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22 minutes ago, Piero said:

 

A nice photo here of the two siblings (DF and DC) here: :) 

https://www.cloudynights.com/topic/535739-takahashi-fc-100-dc-basic-questions/#entry7193389

 

Thanks Piero, so, tube length the same but the DF focuser much shorter so you have more backfocus available.

The FT still has a bit in reserve so I will check how much I used to see whether the DF would take the binoviewers without Barlow.

IMG_3348.JPG

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I remember I read a post from a gentleman on CN who stated how much travel was needed for binoviewing using the DF. According to those measures, the 2" diagonal was not suitable (at least with the 2" clamp), but the T2 diagonal (that you have if I remember correctly) works fine. 

I think this post is in one of these threads (.. haven't double checked!): 

https://www.cloudynights.com/topic/535739-takahashi-fc-100-dc-basic-questions/ 

https://www.cloudynights.com/topic/513141-takahashi-fc-100dc-vs-takahashi-fc-100df/ 

https://www.cloudynights.com/topic/507650-question-on-tak-fc100-dc/ 

https://www.cloudynights.com/topic/511658-takahashi-fc-100df-first-light-report/ 

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I quickly checked those threads I posted before, and they don't contain the post I was referring to. Apologise for this.

Here some reference: 

"The FC100DF handles my Baader Mark V with 2x Panoptic 24mm without any issues." https://www.cloudynights.com/topic/507650-question-on-tak-fc100-dc/#entry6725143  , https://www.cloudynights.com/topic/507650-question-on-tak-fc100-dc/#entry6725501 

 

https://www.cloudynights.com/topic/459189-help-with-bino-configuration/ (using Tak-fc100)

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