150 PDS focusing

[LR Watanabe]

Backstory: Recently, I blasted quite a bit of my money on the EQ5 and a SW 150 PDS, and the mount's been working just fine!

Okay, now for the problem; yesterday, my father took me to the Torami beach in Chiba (A LOT OF MOIST) and the feeling of excitement overwhelmed me, for it was my first time letting the light from astronomical objects go through my telescope– which was what I hoped to achieve.

The problem occurred when I looked through my telescope; no matter what I pointed my 150 PDS at, whether it be Jupiter or some random star I have yet to learn the name of, what greeted me through the eyepiece wasn't the sparkle of countless stars– instead, I could only see one large dot, with the mirror crosshairs. I couldn't focus properly, no matter how hard I tried. 

Now this leads me to question what is it that's gone wrong that led to these most unfortunate results.

Any help would be much appreciated.

 

[Merlin66]

LR,

You don't mention which eyepiece(s) you were using...

I assume the collimation is acceptable.

Assuming you start with the longest fl eyepiece ( to give the lowest magnification) - then point at a bright object/ star and check that with the focuser all the way in towards the tube that there is no focus....slowly wind the focuser outwards and continue to check for a focus.... if still no focus at the end of the travel you'll need a spacer adaptor to hold the eyepiece further out. You may be able to verify this by slightly sliding the eyepiece out of the focuser but still maintaining locking/ and control....

It sounds like the 150 PDS is designed for imaging and has an "allowance" usually around 55mm for the camera body - you need a spacer to compensate this distance for visual.

(If you have the end dust cover for the tube....it has a small cap about 50mm diameter built in. You can leave the cover in place, remove the smaller cap and point the scope to the sun. DON"T look through the focuser!!!! Place a card behind the focuser and see where the image of the sun comes to focus - this will give some idea of the spacer required.)

 

[Cornelius Varley]

The 150PDS is equipped with a 2" focuser that also uses a 1.25" adapter. A common mistake when using  a 1.25" eyepiece is using both adapters together.

[Merlin66]

Peter,

Hmmm, how do you then use a 1.25” eyepiece without an adaptor?

 

[Cornelius Varley]

The focuser has two adapters. One is for 2" eyepieces and the other for 1.25". The 1.25" adapter can be fitted into the 2" adapter tube which means a 1.25" eyepiece will then be too far away from the secondary to reach focus. 

[spillage]

As the OP has the PDS will he not need an extender on the focuser to enable him to use an eyepiece?

[Grahlom]

1 hour ago, Merlin66 said:

You can leave the cover in place, remove the smaller cap and point the scope to the sun. DON"T look through the focuser!!!! Place a card behind the focuser and see where the image of the sun comes to focus - this will give some idea of the spacer required.)

I wouldn't advise you to point your telescope towards the sun, that can be bad not just for you but also for the telescope. I heard viewfinder strings can burn in an instant if you do that.

The same can be achieved by pointing at something outside during the day from a window. Just point your telescope at something that has contrast in brightness, like roof of a house. Sky will be a lot brighter so you will be able to see the shape of a house clearly when you move a card into focus.

[adyj1]

You'll need to get an extension tube, or rack the focuser right out and see whether you can get focus without one. You should see your star get smaller and smaller (and the cross-hairs disappear) until it comes into sharp focus. You should carry on slightly past the focal point until it starts blurring again and then reverse back into focus so you get a good feel of the sensitivity of your focuser (and with the 10:1 Crayford focuser on the 150PDS, it is quite sensitive). 

I have a 150 PDS. The drawtube is only 1 to 1.5 cm out when my dslr is in focus. If I use an eyepiece, I use an extension tube of something like 6 to 7cm, and that brings the eyepiece to focus in roughly the same place. I haven't tried without the extension tube, so am not sure whether you can get focus without it. 

Hope this helos

Ady 

[LR Watanabe]

MERLIN66

YOU ARE A LEGEND

I CAN'T EMPHASISE ENOUGH MY FEELING OF GRATITUDE TOWARDS YOU MATE

ABSOLUTE  LEGEND

THANK YOU!

[Merlin66]

<Blushing>.....

We're all here to help each other...

"Hold hands in the traffic"

 

 

[Geoff_L]

FWIW, I have a 150 PDS on an EQ5 Pro. The 150 PDS doesn't need an extension tube with any of the eyepieces I possess (either 2" or 1.25"). Although the OTA is a little shorter than the 150 P to optimise it for astrophotography, the focuser has enough backtravel to cope with visual obs IME. Since the OP mentions crosshairs, I wonder whether the "eyepiece" is a colimator rather than a reticle eyepiece? That said, I also have a Baader Q turret, which doesn't work with the 150 PDS as the turret 'pushes' the eyepiece further out and makes it impossible to focus, so the comments about trying to use the 1.25" adapter in the 2" adapter make sense. Both adapters are threaded and you need to remove the 2" adapter and screw in the 1.25" one to use 1.25" eyepieces. I hope the above makes sense and helps. Geoff

[LR Watanabe]

7 hours ago, Geoff_L said:

FWIW, I have a 150 PDS on an EQ5 Pro. The 150 PDS doesn't need an extension tube with any of the eyepieces I possess (either 2" or 1.25"). Although the OTA is a little shorter than the 150 P to optimise it for astrophotography, the focuser has enough backtravel to cope with visual obs IME. Since the OP mentions crosshairs, I wonder whether the "eyepiece" is a colimator rather than a reticle eyepiece? That said, I also have a Baader Q turret, which doesn't work with the 150 PDS as the turret 'pushes' the eyepiece further out and makes it impossible to focus, so the comments about trying to use the 1.25" adapter in the 2" adapter make sense. Both adapters are threaded and you need to remove the 2" adapter and screw in the 1.25" one to use 1.25" eyepieces. I hope the above makes sense and helps. Geoff

I found some extension tube, so I s'pose I need to put that in. Btw, it's not a collimator. It's the SW 28mm standard 2" eyepiece.

[Ronclarke]

I too own a 150PDS, the DSLR is in focus at 1-1.5 cm but I use a 45 mm extension tube to get an eyepiece into focus as has been said above. Good collimation is a must!!

Good luck, it's a cracking scope!!

Ron