1.25 focuser too long.

[Nigel G]

Hi.

My 1.25 focuser on the SW 150p has a thread to connect a camera t ring direct, or a theat on the x2 barlow which connects direct to the t ring.

The camera and barlow connection is fine and focuses fine.   The direct connection without barlow will not focus in enough, so wider angle photos can not be taken, example is I cannot photo M 81 -  M82 together. 

The camera needs to be about half inch closer to secondary mirror. 

I'm looking into modifying the focuser or maybe getting a  shorter focuser if available without breaking the bank. 

Unless anyone knows a trick ?

Nige. 

PS. Every time I observe I see new things,  I never new I would see so much through my scopes.

Totally hooked.

[Alan64]

With the "Star Discovery" mount as the imaging platform, you have a few options...

1.  http://www.firstlightoptics.com/reflectors/skywatcher-explorer-130p-ds-ota.html

The "P-DS" Newtonians are primarily designed for imaging, and will come to focus for deep-sky imaging without a barlow.

2.  Modifying or replacing the focusser as originally planned, and for a lower profile.

3.  Moving the primary mirror said half-inch up from the end of the tube.  This option will require removing at least said amount from the back of the tube, then drilling out new holes for the screws that hold the primary mirror cell in place.

[Cornelius Varley]

8 hours ago, Alan64 said:

With the "Star Discovery" mount as the imaging platform, you have a few options...

1.  http://www.firstlightoptics.com/reflectors/skywatcher-explorer-130p-ds-ota.html

The "P-DS" Newtonians are primarily designed for imaging, and will come to focus for deep-sky imaging without a barlow.

2.  Modifying or replacing the focusser as originally planned, and for a lower profile.

3.  Moving the primary mirror said half-inch up from the end of the tube.  This option will require removing at least said amount from the back of the tube, then drilling out new holes for the screws that hold the primary mirror cell in place.

The last option is probably the hardest thing to do with the Star Discovery. The telescope doesn't have any collimation screws at the rear so any modifications to the tube would have to be precise and would, of course, invalidate the warranty.
Changing the focuser, likewise, is also going to be difficult. A low profile focuser, like the version used on the PDS tubes, will require some surgery to the tube. Modifying the existing focuser may not be practical and if you get it wrong you will end up with a nonfunctioning telescope.
Purchasing a 130PDS ota would be less expensive than a new low profile focuser and would be guaranteed to work.

You might be able to get focus if you just use the barlow lens element screwed into a 1.25" nosepiece. The magnification of the barlow lens will be reduced using this method so you will get a wider field of view.

[Nigel G]

Thanks guys.

One of my barlow end eliment screws directly into a 1.25 camera adapter so I will give that a try first, hopefully that will be enough.

Cheers. 

 

[Nigel G]

 

I decided to modify the focuser. 

I cut 1/4" off the fixed focuser tube which makes no difference to the focuser it's self. 

I then unscrewed the eyepiece holder from the running  tube.

Then machined from an abs 1.5" plastic pipe fitting, a bush which screws on to running focuser tube and screws into t ring adapter. 

The camera is 3/4" closer to mirror allowing full focusing.

 

In the picture is the internal tube with eyepiece holder removed and t ring with bush fitted. Also the off cut of external tube bottom left. The other piece in the middle is removed from the t ring by undoing 3 grub screws to allow new plastic bush to be fitted.

I have ended up with a very sturdy direct camera mount which has enough travel to focus and no loss of movement. 

The only slight penalty is the focuser tube extends 3/4" more into the main scope reducing a slight amount of light to primary mirror. 

I have yet to check if any can be removed but I think the loss is minimal. 

Nige.

[Nigel G]

The barlow trick did not work enough so the above was done.

Total cost £0 as I  had the pipe fitting in the van 

[Alan64]

When the element from the barlow is removed, it's no longer a 2x, but a 1.5x?

[Nigel G]

Sure, it's a good idea and gives me an extra magnification but still not quite wide enough. With the modified piece I have a wider field of view than the camera connected direct to my dob.

Thanks for the idea I would neve have known I could do that.

Nige.

[Nigel G]

The alterations to my focuser has allowed me to get better photos with the star discovery, I'm pleased with this..  20 seconds exposure. 

Before I  could  only get one cluster in the shot. 

[Alan64]

Not bad at all, and most judicious in taking only 1/4" from the top of the sleeve, and then making up for the rest with the T-adaptor.

I wouldn't remove any from the bottom of the drawtube, as then the use for visual would be restricted, but you can do something else in addition.  I have the same exact focusser on my Synta 6" f/5, and blackened the lower portion of the drawtube with ultra-flat black spray, aka "chalkboard" paint, and flocked the interior...

It's best to sand the chrome plating prior, and if flocking the drawtube, the inside should be glossed for improved adhesion if using self-adhesive flocking.

If and when you feel comfortable in so doing, you can flock and blacken the entire telescope, for improved contrast and blacker sky backgrounds, and as I did for my own...

 

 

 

[Nigel G]

1 hour ago, Alan64 said:

Not bad at all, and most judicious in taking only 1/4" from the top of the sleeve, and then making up for the rest with the T-adaptor.

I wouldn't remove any from the bottom of the drawtube, as then the use for visual would be restricted, but you can do something else in addition.  I have the same exact focusser on my Synta 6" f/5, and blackened the lower portion of the drawtube with ultra-flat black spray, aka "chalkboard" paint, and flocked the interior...

It's best to sand the chrome plating prior, and if flocking the drawtube, the inside should be glossed for improved adhesion if using self-adhesive flocking.

If and when you feel comfortable in so doing, you can flock and blacken the entire telescope, for improved contrast and blacker sky backgrounds, and as I did for my own...

 

 

 

I shall be blackening the draw tube for sure, I was wondering why it has Been left chrome plated, seems odd to leave that amount of shine tube within the telescopes main tube. I can see a dim glow in the viewer when the camera is attached, and sometimes when I have barlows in, I'm guessing it's the draw tube.

[Alan64]

There's one more thing.  You may have noticed the shims within the focusser cavity for the drawtube...

I replaced the plastic ribbed shims with strips of the same size and length, and of self-adhesive felt, and as I did for this plastic refractor focusser...

I found the focusser to be tighter yet smoother in operation.  I would use black felt, and would remove the plastic shims very slowly and carefully in case you wish to put them back if you find that the felt shims are not to your liking.