TCF-S focuser

[Zuts]

Hi Guys,

I am thinking of purchasing a TCF-S focuser. One reason is that i will be able to use it on multiple scopes and it also works with CCDSoft.

With the SBIG my imaging train consists of 80mm extension tube, field reducer, SBIG. All up i only have 10 mm or a bit less of back focus after achieving focus.

I received the following reply from OPTEC and was wondering if i should go ahead. My thoughts are a bit confused but I still think it may be possible to drop the extension tube and/or maybe get some sort of spacer to achieve focus.

Your thoughts greatly appreciated.

A reply from OPTEC

Dear Paul,

I was going by the picture of the telescope on the Televue website since they don't seem to publish the BF distance. If you are correct, then I think there might be room for the TCF-S.

Our 17459 2" diameter nose piece for the TCF-S might be the best adapter. This would add 0.1" to the BF. The TCF-S would add 3.5" to the mid point of travel (travel of the drawtube would be +/-0.3" from this center position). The 17664 2" to T-thread adapter would add the last 0.1". The total to the center position would be then 3.7". From your calculation you have 90mm or 3.5". This would mean that the drawtube would have to go in another 0.2" to reach focus. This would work but barely leaving only 0.1" of IN focus. It might be possible to squeeze another 0.2" by making or modifying some part. If you are really interested in mounting a TCF-S, we are willing to help engineer a solution. It might be necessary to make a custom adatper.

You can see pictures of these adapters on our web site.



Thanks Paul

[gbeal]

Paul,
you are looking to integrate the TCF-S into the existing scope, retaining the existing focuser, or to start all over with the TCF-S as a replacement focuser?
While not against the Optec product, my suggestion is to "replace" your existing focuser with the Feather Touch, and the digital drive system, complete with temp probe for temperature control. I have yet to try the temp probe for mine, but as soon as it arrives I will let you know. The F/T and digital drive really is stunning. I can point you in the direction of a similar unit a few hours from where you are, if you need to see one in the flesh.
Gary

[Zuts]

Hi Gary,

I was intending to just plug the TCF-S into the existing focuser drawtube.

If I were to go the feathertouch route what would I need for computerised focusing with my TV85 and SBIG and are you suggesting that I should replace the existing TV focuser?

Ideally i would like to use the system on a C9.25 (if and when i get one).

Currently, with my existing imaging train (see first post) I only have 5 to 10mm of backfocus remaining. Would this be a problem with the feathertouch?

On the feathertouch site there only appears to be one motor attachment and electronics box, is this the unit you are suggesting?

Thanks Paul

[Bassnut]

Paul.

On my set up an AP 0.67f reducer on the SBIG nose piece actually goes inside the TCF-S (does your televue?) and takes up no back focus at all outside the TCF-S. Why do you need an 80mm extension tube?. With an SBIG, filterwheel, nosepiece, reducer, TCF-S, on an LX200R, I have more than enough back focus left - even for an A07 !, how come yours is so short? (will it be, on a C9.25?)

You will probably end up uesing Focus max for autofocus, its the best by far, make sure if buy focuser that it is compatible with focusmax (TCF-S is).

[gbeal]

Paul,
OK, than that is why you are slurping up the back-focus. And if you use the FT in this way it will be no different I suspect. My suggestion would have been to replace the existing focuser with either the TCF or the F/T. In my situation I have the FT202BCR, plus the digital motor, and hub, as well as the hand controller. These are all detailed on the Starlight site. If you change later to using the C9.52" then it is a simple matter of sourcing the correct adaptor to fit onto the C9.25, and the FT unit attaches in minutes. Mind you I can't see why the TCF won't do this as well.
With the AP67CCD Telecompressor (I use one as well) it soaks up quite a bit of in-focus, and in the case of my imaging newt it won't allow it to come to focus. In my Zeiss ED80/840 refractor, it will, just, but the focuser is racked virtually all the way in, no biggie, but it serves to show that the reducer brings the focus point well in.
The Feather Touch motor unit is designed to work with the FocusMax program, and I use it almost exclusively.
Gary

[Louwai]

I've got a motorised Feathertouch on my C8. Coupled with the Micro Focuser on the primary, it is awesome.

Haven't mastered the remote PC focus ctrl yet, but I'm getting there.

[Zuts]

Hi Guys,

Getting out my tape measure and doing a rough measurement

(1) The TV 85 has 7cm of focus travel.

(2) With a 80mm extension i only have around 3 mm of focus travel left. The focusser is racked all the way in bar 3mm. So this is why I need an extension tube.

(3) Logically though I should also be able to come to focus with a 35 or 50 mm extension.

(4) From Optecs reply the TCF-S by itself adds 3.5 inches or 88.9 mm, so if i had the tv focuser completely racked in the TCF itself is like a 88.9mm extension and so i dont think i could come to focus. Even with the 0.3 inch of focus travel available each side of focus with the TCF-S.

Anybody agree with (4) above or have i got it wrong.

Thanks Paul

[gbeal]

Without actually having the bits in the hand it is difficult, but it would seem the Optec will be too "fat" to allow the focus, yes.
Bear in mind also that the ST2K soaks up about 35mm of back focus.
Gary