Skywatcher 150PDS + 2x Barlow + DSLR = No focus.

[guiseppe]

So, I tried using my newly purchased 2x Barlow (bought it specifically for astrophotography) but when I tried it tonight I couldn't get it to focus. When using the eyepiece, I need to extend the focuser to get a focal point, but with the Barlow and the DSLR I need to get further in than what seems possible. I tried every configuration imaginable and nothing worked. I need to get further in with the focuser. So first of all, can I solve this? And if so, how? Secondly, why do I need to go further out without the Barlow, but further in with the it?

Any help would be appreciated.

[Avocette]

A Barlow will place the focal point further out than without, so the DSLR will need to be further out from the scope tube. You should find the same thing with the eyepiece when used with the Barlow. You may need to use an extension tube to take the DSLR further away. 

[Leveye]

Look into the Antares twistlock extension tubes i use one with a 2' inch extender and it works great using my 3x Televue

[dobbie]

if you got your scope from new you should have a extension tube that came with it , I did on my 200pds ,dobbie.

[guiseppe]

But I used the extension tube I got with and the further out I got, the worse the image got. Only when putting the Barlow with the DSLR mount on it directly to the scope did I get a more focused image. So it seemed like I needed to go further in, rather than out.

[knobby]

Weird... Isn't the PDS version the one that is designed for DSLR imaging, maybe it needs a short Barlow. Which Barlow do you have?

[guiseppe]

http://agenaastro.com/media/catalog/product/o/b/obar-gs-gs22b-2_3.jpg this is the one that I have. It was recommended to me on this very site (if I'm not mistaken).

[dobbie]

I use the tal very small barlow, no problem..

[knobby]

Looks a good Barlow... Have you got the 2" and the 1.25" adaptor both on? Try just the 1.25" on its own if so.<br />

Failing that if you still can't focus, its a bit extreme but you could move the primary up the tube slightly with the collimation adjusters... See if something simple gets suggested first though :-)

[jambouk]

A barlow will effectively give you inwards travel on the focus.

If you need more inwards travel, you need a lower profile focuser. I don't know if a 3x (say) barlow fives you even more inwards travel than a 2x barlow.

James

[dobbie]

I must try this with mine to see if I get the same problem , but the last time I used it with a dslr I don't recall any?

[guiseppe]

Looks a good Barlow... Have you got the 2" and the 1.25" adaptor both on? Try just the 1.25" on its own if so.<br />

Failing that if you still can't focus, its a bit extreme but you could move the primary up the tube slightly with the collimation adjusters... See if something simple gets suggested first though :-)

No, I've removed the 1,25 adaptor, to fit my extender and / or camera.

[dobbie]

mmmm I just tried this on my barlow tal, the lens elements are all at the bottom with unscrews , my cannon 1.25 adapter as a thread on it so I unscrews the bottom of the barlow and screws in onto the 1.25 adapter then puts it into the focuser given me more inward travel , not sure if it works as it raining and cant test it..

[Tinker1947]

I'm not sure why your using a barlow if you need more inward travel this will just put the DSLR further out from the focus tube, have you tried with just the DSLR attached to the focuser,,,,

[guiseppe]

I'm not sure why your using a barlow if you need more inward travel this will just put the DSLR further out from the focus tube, have you tried with just the DSLR attached to the focuser,,,,

Yes, and that works just fine. But I want to be able to use the Barlow for, well the features of a Barlow. Unless I've missed something.

[bogdog]

from the flo website regarding 150 pds

"The SkyWatcher EXPLORER-150PDS Newtonian telescope incorporates the same superb mirror-set as the Explorer-150P Black Diamond Series, but with two significant advantages: A Dual-Speed 10:1 ratio focuser and a slightly shortened tube-length optimised for prime-focus photography."

so you shouldn't need a barlow as the tube is shorter...so no need for primary mirror movement up the tube!

have you tried just the dslr attached to the focusser?

or unscrew the lens from the bottom of your barlow and use tube what difference if any does that make?

[Tinker1947]

Yes, and that works just fine. But I want to be able to use the Barlow for, well the features of a Barlow. Unless I've missed something.

Seems a barlow won't work you can buy EP's that allow the DSLR to be attached to them so you have DSLR-EP-Focus tube, the lower the MM of the EP the more magnification you get ......

[guiseppe]

In other words, buying the Barlow was a complete waste of money for me? Sure it works for observing, but that's not what I bought it for.

[Tinker1947]

In other words, buying the Barlow was a complete waste of money for me? Sure it works for observing, but that's not what I bought it for.

Properly.... you could use it with a Webcam, for Planets and the Moon