Can't achieve focus with Barlow 2x

[upahill]

Hi All,

Got a cheap 2x barlow from astroboot but cant achieve focus on my 6" meade newt, I need about another half-3/4 turn of inward focus. Do I understand it correctly that I need to move the mirror cell further up the tube with longer bolts?

I am also considering a mod which will allow me to rotate one end of the tube, allowing me to place the eypiece in the most convenient location. Has anyone ever modded their newt to allow this to be done?

Sam

[Lonestar70]

Hi Sam,

A barlow lens will/should make the focal point further out from the focusser so would require greater OUTWARD travel to bring an eyepiece, or camera, to focus.

Have you tried focussing over the full range of focusser travel?... go slowly, as it's quite easy to miss the correct position.

As for modifying your tube to allow front end rotation... NOT a good idea as it would certainly play havoc with collimation.

The normal course would be to slacken both the tube rings and rotate the whole OTA to bring the eyepiece to a more suitable position for viewing, then tighten the rings again.

A third ring fitted to the OTA just above and just touching the top ring but not attached to the dovetail bar will prevent the whole OTA slipping down when adjusting the orientation.

Do a search for "rotation ring" on the forum... there have been several posts showing how these can be easily made and fitted.

Hope this helps.

Best Regards.

[Stargazer_00]

Try only putting the barlow half in the focuser and fixing it there. Odds are that will work.

[upahill]

Hi Sam,

A barlow lens will/should make the focal point further out from the focusser so would require greater OUTWARD travel to bring an eyepiece, or camera, to focus.

Have you tried focussing over the full range of focusser travel?... go slowly, as it's quite easy to miss the correct position.

As for modifying your tube to allow front end rotation... NOT a good idea as it would certainly play havoc with collimation.

The normal course would be to slacken both the tube rings and rotate the whole OTA to bring the eyepiece to a more suitable position for viewing, then tighten the rings again.

A third ring fitted to the OTA just above and just touching the top ring but not attached to the dovetail bar will prevent the whole OTA slipping down when adjusting the orientation.

Do a search for "rotation ring" on the forum... there have been several posts showing how these can be easily made and fitted.

Hope this helps.

Best Regards.

Focussing out makes everything bigger, to the point where I can see the secondary reflection and mirror clips, bringing it in gets it SOOOO close to being in focus,

The barlow is a plastic affair which doesnt split apart or anything, I did think about cutting the barlow down, but still unsure, the idea that it should bring the focus out is confusing the matter even more now.

Forecase cloud for the next decade so wont have a chance to test.

[upahill]

Fixed it!

It turns out there was a 2" extension on the focusser, it was so tight and flush I assumed it was part and parcel of the focusser, I decided to brute force it and woohoo it unscrewed.

1.25" adapter screwed straight back on and it worked a treat on my neighbours trampoline (about 3 miles away)

Very happy I dont need to replace anything.

Will need to upgrade the barlow I think though, the plastic quality and glass quality is a bit suspect :S

[Lonestar70]

Hi Sam,

Ok, that explains a lot...

I have just been looking at the manual for your scope and it would appear that the 2" extension is required to achieve focus when using standard eyepieces... so you may find you have to re-fit it when you dont use the barlow.

It also appears that the focuser is a low profile unit which is good for achieving focus (prime) with a DSLR camera.

It clearly states that the extension should be removed and the t-ring directly attached to the focusser tube.

The Meade #140 barlow,Quite a long looking afair, is also shown in the manual, and seems to have the extension built in so again the normal extension would need to be removed.

Seems a very strange way of arranging the optics though... but Meade tend to do strange things at times.

Anyway, you have got it sorted for the time being.

That just leaves the tube rotation to sort out and you will be away and running.

Have fun.

Best regards.

[upahill]

Yeah its not the end of the word loosening the tube rings and rotating tube, but with an ST80 bolted to the top and a red dot finder, i find either the finder obstructs the st80 or it renders the rdf unusable because the ST80 is in the way. I may just ditch the ST80 until im ready to give imaging a go.