Barlows/Tele Extenders and inward focusing

[Mark at Beaufort]

A Barlow lens has many advantages and are usually 2X or 2.25X. Sometimes you can remove the bottom element and this can be screwed into the eyepiece to give an increase of 1.5X approx. One of the disadvantages is the Barlow increases the eye relief which on some eyepieces can create vignetting.

Al Nagler resolved some of these negative problems by creating the Powermates. Over the years other companies have created Tele Extenders which resolves the eye relief situation. However, I understand that using Tele Extenders require more inward travel which might be a problem on certain scopes and focusers.

My question has anyone used a Tele Extender/ Powermate and not been able to gain focus. If you are able to gain focus what extra inward distance was required.

I have an Orion VX8 and the focuser is not low profile so I need this type of information before I commit to a purchase.

[Knighty2112]

Awaiting a Powermate from Orion Optics, so can't answer the focusing issue. Just hope it's worth it for what you pay for them. Hopefully should get it (fingers crossed) early next week. 

[Star Struck]

Mark,

I have used a 2.5x 1.25 PowerMate on a SkyWatcher 8 inch dob and not had any problems with a lack of inward focus.

I tried it with a number of different eyepieces e.g BGO, TeleVue and Vixen and found the inward focus was increased by between 3-5mm. Nothing like the 20mm needed by my barlow which I have discovered I cannot use on the dob (works great with the refractors though).

Tony

 

[Mark at Beaufort]

1 hour ago, Star Struck said:

Mark,

I have used a 2.5x 1.25 PowerMate on a SkyWatcher 8 inch dob and not had any problems with a lack of inward focus.

I tried it with a number of different eyepieces e.g BGO, TeleVue and Vixen and found the inward focus was increased by between 3-5mm. Nothing like the 20mm needed by my barlow which I have discovered I cannot use on the dob (works great with the refractors though).

Tony

 

Thanks Tony that is very helpful.

[David Levi]

I have a question related to the opening message so I hope you don't mind if I ask it on this thread. I saw a video on YouTube demonstrating how to remove the lens from a 2x barlow and screw it onto the eyepiece. The presenter said like Mark at Beaufort that this would produce a 1.5x additional magnification. I have just bought my first telescope, a Skywatcher 200P, which came with a 2x barlow. The lens on the barlow can be unscrewed and attached to the eyepiece. Is this then a 1.5x (approx.) magnification? I intend to try it out but it would be good to get other people's knowledge on the matter.

[Mark at Beaufort]

Hello David and welcome to SGL.

From what you have stated I would guess that the bottom part of your barlow will give you a mag of approx 1.5X. I use this system to gain enough inward focus so that I can use binoviewers.