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PGM

Takahashi FC-100DC focuser

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I have a Takahashi FC-100DC with the original focuser, plus a Giro Ercole and a Gitzo.

The focuser seems to shake a lot whenever I'm trying to really find the perfect focus, starting with a magnification as low as 90x or so. Of course, my hands shake a little, and that surely doesn't help... It starts shaking as soon as I place a finger on the wheel. I'm trying to find out if that's a problem I'd be able to fix with a better focuser.
The focuser also seems to have just a little more difficulty handling the weight of my Pentax XWs. It works just as well, but feels the extra weight. In the future I'd like to try a Lunt Herschel Wedge and a binoviewer, so that would be even worse.

A Feather Touch focuser is on my list, but very high prices aside, I'd hate to lose that little Tak plate with the scope's serial number and the Tak blue parts. Maybe a Tak MEF-3 then. Anyway, I'd like to know what the real benefits would be with such an upgrade, regarding focusing/shaking.

 

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It sounds more like a mounting issue than a focusser user issue to me, 90 X mag is not high ?and I wouldn’t put Pentax XW’s in the hefty lump category.

 

Edited by Pig
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Maybe try a more hefty steel tripod in order to keep the centre of the mass closer to the ground? Your current combination is quite likely top heavy (less stable) with the lightweight carbon fibre Gitzo.

Edited by KP82
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Most scopes have a settlement period of between a split second and a few seconds depending on the scope and mount. It may be a mounting issue but a dual speed focuser would definitely improve things especially on the current mount but also possibly even on a better mount.

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With the Giro mount balance is critical. And you need a sturdy tripod. What you can try is to to tighten the altitude and azimuth knobs a little more so the movement is more stiff.

I have successfully used the Giro mount in the past with dual setup.

639604859_20170120_small-Copy.thumb.jpg.0092f0c3b46432adad67dc1973ec4fc9.jpg

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I find my Gitzo very stable even when fully extended so I'm surprised you are having this issue. I think a dual speed may help but I would investigate where the vibration is coming from first.

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The DC focuser will handle XW's and binoviewer without any problem, so the shake almost certainly comes from elsewhere.  Sometimes however, Tak focusers can feel a little stiff. This can be rectified by adjusting the tension screws on the top of the focuser body and which have been sealed by glue, after being factory set by Shrek. (Its a very delicate and critical process on the Tak RPF, as each screw needs to be precisely and equally adjusted)! You could consider a Tak micro focuser to allow critical fine focus.

With regard to the Lunt Herschel Wedge, I found there wasn't enough inward travel without using my 2" adapter and a low profile 2" to 1.25" adapter.

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I agree that the problem will be the mount/ tripod combination. My binoviewers are quite heavy compared to most, but the Tak focuser handles it easily.

After trying AZ4/AZ5 mounts I changed recently to this little Berlebach mount, and the problem that I was having is sorted. Damping time down to less than a second at 154x

IMG_0745.JPG

Edited by Saganite
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Hi Alan,

 

It is a UNI 18, bought from Dobbie. I had always  used the 2" s/s Skywatcher tripod, which came with the NEQ6, perfectly solid, but quite heavy, and nowhere near as handsome as the Berlebach. When all things are equal, beauty carries THE DAY ! :grin:

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7 hours ago, Stardust1 said:

With the Giro mount balance is critical. And you need a sturdy tripod. What you can try is to to tighten the altitude and azimuth knobs a little more so the movement is more stiff.

I have successfully used the Giro mount in the past with dual setup.

639604859_20170120_small-Copy.thumb.jpg.0092f0c3b46432adad67dc1973ec4fc9.jpg

Yes, this type of mount is the first  that I have owned, and getting  the balance correct is important, But I am getting there ! :smiley:

Edited by Saganite
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8 hours ago, Stardust1 said:

With the Giro mount balance is critical. And you need a sturdy tripod. What you can try is to to tighten the altitude and azimuth knobs a little more so the movement is more stiff.

I have successfully used the Giro mount in the past with dual setup.

639604859_20170120_small-Copy.thumb.jpg.0092f0c3b46432adad67dc1973ec4fc9.jpg

That looks like it was a chilly night! :)

I find that dual setups work very well and are perhaps slightly more stable than a single scope on a giro style mount from a balance perspective.

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10 hours ago, PGM said:

It starts shaking as soon as I place a finger on the wheel

As I learned how to adjust the Tak focuser I noticed you can end up with enough slop or play in it that could induce interesting results... there is an interesting relationship between the shaft cover and the underlying adjustment screws as well.

My focuser is now butter smooth with no image shift and holds a bunch of weight (thanks Kunama on CN!)

A mal adusted focuser could possibly induce the shakes in a less than stable tripod/mount set up IMHO.

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Thank you all for some very helpful posts.
I previously used a Tak Vixen plate that came with the clamshell and a Berlebach clamp to hold it, so I removed it to see if it improved things. No difference, so I now use the clamshell directly screwed on to the mount.

I investigated further and although the DC focuser does seem a bit stiff at times, which introduces further vibration, it does not seem to be the only culprit. I tried to tap my finger on several parts of the setup:
- Gitzo tripod: it's not fully extended (I observe sitting down) and seems rock solid - no vibration.
- Giro mount: knobs completely tightened; the arm that holds the scope shows some minor vibration; much less on the other (unused) side.
- Telescope: as I tap along the tube, there's more and more vibration, peaking at the diagonal.

Anyway, I'm probably making too much of it, it's just that me and my wife take turns observing, so it would be nice to really find the right focus spot more easily. But it's not the end of the world.

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On 19/01/2019 at 12:46, mikeDnight said:

The DC focuser will handle XW's and binoviewer without any problem, so the shake almost certainly comes from elsewhere.  Sometimes however, Tak focusers can feel a little stiff. This can be rectified by adjusting the tension screws on the top of the focuser body and which have been sealed by glue, after being factory set by Shrek. (Its a very delicate and critical process on the Tak RPF, as each screw needs to be precisely and equally adjusted)! You could consider a Tak micro focuser to allow critical fine focus.

With regard to the Lunt Herschel Wedge, I found there wasn't enough inward travel without using my 2" adapter and a low profile 2" to 1.25" adapter.

Those are some bad news about the Lunt wedge. I hate chasing adapters so much that I might give up on getting a wedge just because of that.

 

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On 19/01/2019 at 20:19, jetstream said:

As I learned how to adjust the Tak focuser I noticed you can end up with enough slop or play in it that could induce interesting results... there is an interesting relationship between the shaft cover and the underlying adjustment screws as well.

My focuser is now butter smooth with no image shift and holds a bunch of weight (thanks Kunama on CN!)

A mal adusted focuser could possibly induce the shakes in a less than stable tripod/mount set up IMHO.

Any advice on how to do that?

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On 19/01/2019 at 11:41, Stardust1 said:

With the Giro mount balance is critical. And you need a sturdy tripod. What you can try is to to tighten the altitude and azimuth knobs a little more so the movement is more stiff.

I have successfully used the Giro mount in the past with dual setup.

639604859_20170120_small-Copy.thumb.jpg.0092f0c3b46432adad67dc1973ec4fc9.jpg

You know, I saved this photo just to remind myself what an easy life my Tak has ?

 

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Thank you PGM!

These Taks are superb. 

Your FC-100DC is one of the most beautiful 4" Tak ever made, it has a classic look and finish. It balances well. Mine gave stunning views!

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5 hours ago, PGM said:

Any advice on how to do that?

It is actually simple- and I don't hold to the belief that "only adjust a tiny amount" . It might only need a tiny amount of adjustment but my approach is to see how things work. The most interesting thing in that focuser is the backlash adjustment IMHO .

Have you tried adjusting it yet?

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5 hours ago, PGM said:

Any advice on how to do that?

@Rainmaker Hey Matt, could we get your input on adjusting a Tak focuser? btw, mine works great- thanks :thumbsup:

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1 hour ago, jetstream said:

Have you tried adjusting it yet?

Not at all. Very interested to know what Matt has to say.

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I like the original Tak focusers as they are very easy to adjust at home with just very basic tools.

The best way is to first remove the pinion shaft cover plate, then the two screws under it and take off the pinion.

Then check the movement of the draw tube, it should be smooth with slight resistance to sliding and no side to side movement.

If there is side to side movement or very loose slide action then the glide strip needs to be adjusted.  The glide strips are tensioned by small set scores, on the top of the focuser on most you will see small spots covered with a lacquer. you need a drop of acetone on those spots to soften the lacquer so that an Allen key can be inserted to turn the grub screw to slightly add pressure to the glide strip.  Do that evenly front to back so the draw tube travels smoothly through its whole length.

Once that is done, re install the pinion shaft and gold coloured tension plate setting the backlash using the two mounting screws.  Then replace the cover plate. Voila....

 

 

Edited by Rainmaker
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49 minutes ago, Rainmaker said:

I like the original Tak focusers as they are very easy to adjust at home with just very basic tools.

The best way is to first remove the pinion shaft cover plate, then the two screws under it and take off the pinion.

Then check the movement of the draw tube, it should be smooth with slight resistance to sliding and no side to side movement.

If there is side to side movement or very loose slide action then the glide strip needs to be adjusted.  The glide strips are tensioned by small set scores, on the top of the focuser on most you will see small spots covered with a lacquer. you need a drop of acetone on those spots to soften the lacquer so that an Allen key can be inserted to turn the grub screw to slightly add pressure to the glide strip.  Do that evenly front to back so the draw tube travels smoothly through its whole length.

Once that is done, re install the pinion shaft and gold coloured tension plate setting the backlash using the two mounting screws.  Then replace the cover plate. Voila....

 

 

Spot on. That is just what I did with my Tak FC-100DL and it worked like a charm :smiley:

If I have a heavy eyepiece on board and the scope is pointed upwards I just add a tiny dab of tension from the large tension knob on top of the focuser to avoid the chance of any "creep".

 

 

taksolar01.JPG

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In conversation with a couple of friends it became apparent that some might have found adjusting the backlash precisely "interesting". Once the tension plate is set up and the cover plate is put back on there can be a bit of gear depth reduction- affecting the backlash when the cover plate is tightened. I believe it lifts up on the tension plate or something a bit.             

 This is a great method of yours to use to adjust the focuser @Rainmaker

Edited by jetstream
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