not enough focus ?

[ninjageezer]

Ok so I am quite new to this, I have a few eyepieces and a 2x barlow and a TV 5x powermate i just acquired for a great price used.

with my eyepieces and my 2 x barlow everything looks great but i tried the Tv powermate tonight and i cannot get it to focus its as though the focuser does not quite travel outwards enough if that makes sense, please advise how i can combat this.

the scope is a sky-watcher 250p flex dob. F4.7

[Don Pensack]

Already responded to the same post on CN.  Can you achieve focus by pulling the eyepiece + PowerMate out of the focuser a bit?

How much.  For 1/4", don't sweat it, just do it and tighten it down.

For 1/2" or more, look into getting an extension tube (available everywhere).

[ninjageezer]

1 minute ago, Don Pensack said:

Already responded to the same post on CN.  Can you achieve focus by pulling the eyepiece + PowerMate out of the focuser a bit?

How much.  For 1/4", don't sweat it, just do it and tighten it down.

For 1/2" or more, look into getting an extension tube (available everywhere).

thanks don will get to test that out this week weather permitting ,if I can get focus buy doing that I'm guessing I need some kind of adapter to extend the focuser ?

[Don Pensack]

Just now, ninjageezer said:

thanks don will get to test that out this week weather permitting ,if I can get focus buy doing that I'm guessing I need some kind of adapter to extend the focuser ?

Yes, it's called an Extension Tube.  FLO sells them, as do many other retailers.

[ninjageezer]

4 minutes ago, Don Pensack said:

Yes, it's called an Extension Tube.  FLO sells them, as do many other retailers.

spot on thanks again will report back when i can test.

[Louis D]

🤔 And here I thought the Powermates weren't supposed to alter focus position of an eyepiece by much, if any.

Try pulling the eyepiece upward out of the PM to see if that helps at all as well as pulling the PM up out of the focuser.  Seems weird that focus position is so far off as with a long Barlow.  At least with the latter, it has a 2" to 3" insertion tube, so you just insert it partway and lock it down once focus is reached.

[Don Pensack]

The 5X Powermate also has a significant change in magnification with distance from the lens.

See:

https://www.televue.com/engine/TV3b_page.asp?id=53&Tab=_app

I think it is unlikely it is the same optical confoguration as the other PowerMates.

[Louis D]

Crazily enough, on that webpage, TV says their 1.25" PMs are parfocal in ALL (their caps) 1.25" diagonals and prisms.  I would expect them to be parfocal in Newtonian focusers as well.

@ninjageezer Double check that your truss poles are extended all the way and locked.  However, if the eyepiece focuses without the PM, it should focus with it based on my reading of the above TV PM webpage.

[ninjageezer]

Thanks to all ,had a play yesterday and yes i just pulled the TV out slightly and it worked on my DSLR and with a 25mm eypeiece.😉