Skywatcher Star Adventurer

[alcol620]

Just now, alcol620 said:

Apologies, getting in a muddle as always. The focuser is the one that comes with the TS60 but it has a stepper motor on it. Its my 120ED that has the moonlite. Will take an image tomorrow to illustrate the set up. i would have thought the distances would be the same. The distance requirement of the reducer should make the distances the same.

Should have said that the stepper motor is not used as I have no controller fitted as yet, I focus manually with the stepper not connected although fitted. Obviously adds nothing to the distance

[alcol620]

On 24/08/2018 at 22:20, GuLinux said:

There's an extra white ring in the scope package, you should unscrew the focuser, and add the ring to the tube. It's an extension.

 

I'm using the same plate as well, but I moved the attach point so it's closer to the focuser (and with said extension you also get some extra room).

I have to keep the focuser on the top side (reversed) in order to get the balance point as close to the focuser as possible:

Very many thanks for that, most helpful. I wondered what that extra tube in the case was for! Tomorrow I will check the polarscope calibration and extend the tube. thanks again. Alec

[alcol620]

Morning GuLinux

My set up is as shown. Tube extension added, 70 mm spacing between Photoline 0.79x reducer and sensor (made up of 63.5mm spacers and 6.5mm ASI1600 backfocus). Focuser racked right in to the scope body and still a bit more required to get to focus.

I am probably doing something wrong, but not sure what it is?

[GuLinux]

Mmh, no idea honestly..

I can't see anything wrong, and btw I have the same configuration (I use a shorter spacer, but only because the filter wheel takes another 20mm).

[alcol620]

Thanks for reply, bit of a mystery. I have emailed Teleskop-Service in Germany for any thoughts they might have. In the meantime I will try it out again, but I can't see how anything will change

[RayD]

I think the FR from TS is 70mm up to 350mm FL, so at 360mm (65mm up to 420mm) you're a tad over so you could try removing 5mm of spacing and having another go.

[alcol620]

Thanks Ray, I was under the impression that with the reducer/flattener in the chain that the FL is down to 260?

[RayD]

Just now, alcol620 said:

Thanks Ray, I was under the impression that with the reducer/flattener in the chain that the FL is down to 260?

I could be wrong (I often am) but I've always calculated it using the native FL of the OTA it is being fitted to.  This is what I did on my TS80 with the TS2.5 and it worked perfectly.  Certainly worth a go if you have some short spacers in there that you can remove.

[RayD]

I just looked on the TS site and it does refer to this being dependant on the focal length of the telescope, and then gives the relative figures, so I think it is the native FL of the telescope (360mm in your case) which determines the spacing.

[GuLinux]

5 minutes ago, RayD said:

I just looked on the TS site and it does refer to this being dependant on the focal length of the telescope, and then gives the relative figures, so I think it is the native FL of the telescope (360mm in your case) which determines the spacing.

Indeed. But the 60/360 scope is the newer model. Mine (and I assume, his as well) are 60/330. He mentioned he gets a focal length of 260, which is 330 * 0.79, so I think he has the older model too.

And with FL < 350 the distance should indeed be 70mm.

But possibly there's been some miscalculation in the length of the spacer, so maybe trying a shorter distance might help indeed.

Edited August 26, 2018 by GuLinux

[alcol620]

Thanks Ray

When I was setting the TS60 up last year the guy from TS Germany said that the recommended back focus for the TSRED279 reducer/flattener was 70mm and I had it working with that, it gave the best "flat" image out to the corners. 

It seems to be the addition of the tube extender on the scope (added to get better balance of the set up) which has stopped the focuser reaching focus. I will await further feedback, thanks again for interest

2 minutes ago, GuLinux said:

Indeed. But the 60/360 scope is the newer model. Mine (and I assume, his as well) are 60/330. He mentioned he gets a focal length of 260, which is 330 * 0.79, so I think he has the older model too.

And with FL < 350 the distance should indeed be 70mm.

But possibly there's been some miscalculation in the length of the spacer, so maybe trying a shorter distance might help indeed.

presumably we are increasing the focal length by adding the tube extension?

[RayD]

2 minutes ago, GuLinux said:

Indeed. But the 60/360 scope is the newer model. Mine (and I assume, his as well) are 60/330. He mentioned he gets a focal length of 260, which is 330 * 0.79, so I think he has the older model too.

And with FL < 350 the distance should indeed be 70mm.

But possibly there's been some miscalculation in the length of the spacer, so maybe trying a shorter distance might help indeed.

No problem, I didn't know there were older and newer versions with different focal lengths, just trying to help.  I've found that with focal reducers intended for varying focal length scopes there is often some fettling to do. 

[RayD]

12 minutes ago, alcol620 said:

presumably we are increasing the focal length by adding the tube extension?

I don't think this changes it.  The focal length is the point from the lens cell that the light converges and effectively comes to focus (in simplified terms) so this doesn't change with an extension as it will still be 360mm (or maybe 330mm in your case) until you add the FR then this then changes to 260mm.

As always I could be wrong and this is only my understanding in my tiny brain.

Edited August 26, 2018 by RayD

[GuLinux]

1 minute ago, RayD said:

I don't think this changes it.  The focal length is the point from the lens cell that the light converges and effectively comes to focus (in simplified terms) so this doesn't change with an extension as it will still be 360mm ( or maybe 330mm in your case) until you add the FR then this then changes to 260mm.

As always, I could be wrong and this is only my understanding in my tiny brain.

Absolutely right, it doesn't ?

That's only a tube, with no optical elements whatsoever, so the focal length is still 330mm

[alcol620]

Thanks Guys, there is obviously something else that I have introduced into the mix. I had the set up working without the tube extension. The only reason I changed things, as you can see from earlier posts, was to get better balance of the set up as I was getting star trails. But it was focusing OK.

I can't see anything else that is obvious to have changed the focusing so much. Probably something I am doing that I didn't do before.

[alcol620]

Further research suggests to me that adding an extension tube to the existing scope will move the focal point also forward by the length of the extension tube. (please correct me if I am wrong). This would have the effect of having to move the focuser tube also forward by the same amount? (quite a long way). Hence it could move the focus point so far forward that it is not possible to focus the image - the situation I find myself in.

However, the only issue here is that GuLinex has an almost identical set up but can achieve focus.

Regards Alec

[RayD]

6 minutes ago, alcol620 said:

Further research suggests to me that adding an extension tube to the existing scope will move the focal point also forward by the length of the extension tube. (please correct me if I am wrong). This would have the effect of having to move the focuser tube also forward by the same amount? (quite a long way). Hence it could move the focus point so far forward that it is not possible to focus the image - the situation I find myself in.

However, the only issue here is that GuLinex has an almost identical set up but can achieve focus.

Regards Alec

Yes.  The only reason you would normally add an extension tube is if you need to extend the tube to reach the focal point, such as using a guide camera on Celestron Startravel OTA.  In your case, whatever the length of the extender between the end of the draw tube and the FR, is the amount the draw tube needs to go in, so actually doesn't achieve anything as this would put the camera sensor in the same place anyway.

[alcol620]

3 minutes ago, RayD said:

Yes.  The only reason you would normally add an extension tube is if you need to extend the tube to reach the focal point, such as using a guide camera on Celestron Startravel OTA.  In your case, whatever the length of the extender between the end of the draw tube and the FR, is the amount the draw tube needs to go in, so actually doesn't achieve anything as this would put the camera sensor in the same place anyway.

But could put it out of the range of the focuser??

[RayD]

Just now, alcol620 said:

But could put it out of the range of the focuser??

Yes if you then can't rack the draw tube in far enough to get the sensor to the focal point. 

[RayD]

By way of example.  If you imagine you have everything working and focusing with no extensions between your draw tube and your FR.  You have the correct (70mm) spacers between your FR and your camera sensor.  Now imagine at this point your draw tube is sticking out 50mm.  Add a 25mm spacer to the end of the draw tube, and the camera sensor will be 25mm out from where it needs to be to achieve focus, so you will need to wind the draw tube in 25mm to bring the sensor back to the focal point.

In your case if you have an extension between the draw tube and the FR, that distance is how far your draw tube needs to go in, and if this is more than what would be sticking out with no extension, then it won't be possible to achieve focus.

Edited August 26, 2018 by RayD

[alcol620]

Thanks Ray, that seems to be the answer, except that GuLinex can still focus with similar set up. The answer for me seems to be to remove the tube extension I added and find another way of achieving a better balance of the set up

[RayD]

5 minutes ago, alcol620 said:

Thanks Ray, that seems to be the answer, except that GuLinex can still focus with similar set up. The answer for me seems to be to remove the tube extension I added and find another way of achieving a better balance of the set up

Definitely I would say.  I struggle with balance also with my FSQ106, and just use external weights and longer dovetails in various manners to get there.

Edited August 26, 2018 by RayD

[MattJenko]

I have the old version and the x0.79 reducer as well. I screw reducer directly into the end of the focuser and certainly don't use an extension, as the focuser is racked right in on the focuser as it is! If you are struggling, you could try inserting the reducer into the focuser as opposed to screwing in the end. This is less secure I found, but it means you can push it in further if it doesn't quite reach focus.

 

[alcol620]

Hi Matt, good to see you are still around. I think I have sorted the balancing with a longer dovetail and no longer need to use the tube extension to aid balancing. Now need a clear sky. Thanks everyone for feedback.

[GuLinux]

Maybe the problem is me then, I might have set my spacer too short.

I'll check home and see what distance I'm currently using, however I don't think I saw anything wrong around the edges of my frames