Quick, quick! need some help!

[blinkity-blonk]

I got a new diagonal, 2x barlow and eyepiece a few weeks back, cloud has meant Im only able to get out there now to test it all out.

When I use all 3 bits of kit together the scope doesn't seem to focus on anything far away e.g the moon but it will focus on stuff close by like trees.

Any ideas why or any ideas how to fix it?

Cheers B-B

[johninderby]

First of all some info is needed. What scope are you using and also what eyepiece and barlow?

John

[blinkity-blonk]

Its a 4" Helios refractor, focal length = 1000mm

The eyepiece is the Revelation 2" 26mm

Barlow is a 2" 2x Revelation

And the diagonal is "2 90deg Revelation (I quite like revelation stuff )

Oh, the more I wind the focuser out the worse it gets - its like the focal length is too long or something

[RobH]

Remove the barlow and see if you can get focus with just the eyepiece. If you still can't get focus with any eyepice position, then remove the diagonal and try with just the eyepiece.

Cheers

Rob

[blinkity-blonk]

Ok, with just the diagonal and the eyepiece it makes it a little better but the focusing tube is still right up against the stop. Without the diagonal it works fine, but I'm at funny angles viewing, which was the point of the diagonal.

If i go back to my original setup of 1.25" stuff but keep the 2" diagonal in its still not focusing. Why is the extra .75" causing issues?

[ollypenrice]

To focus on something nearby your EP has to be further back than for something at infinity, like a star. This should give you an insight into what is going on.

Olly

[johninderby]

I wouldn't have expected that a lack of in-focus travel would be a problem with this scope but that's what it seems to be.

The scope or it's SkyWatcher or Celestron equivalent is common enough so there should be more than a few here on SGL that have experience with using a 2" diagonal on this scope. Perhaps one of them will be able to comment.

John

[blinkity-blonk]

Thanks for the assistance I suppose technically that makes my scope short sighted. lol

[John]

A 2" diagonal swallows up some of the in-focus travel as the light path through it is longer than a 1.25". The Barlow (depending which it is) will probably swallow up some more - my Antares 1.6x 2" barlow needs an additional 17mm of in-focus.

The Revelation 26mm may have it's focal plane higher up the barrel than other eyepieces (they do all vary quite a bit) and that could be using up the last few mm of in-focus as well.

I have a similar issue but fortunately Tele Vues use a little more out-focus than other brands so I've not run out of in-travel as yet with my 4" and 6" refractors.

[blinkity-blonk]

Thanks John. I'm guessing a focal reducer would fix it, or another tube (I was already toying with the idea of a nice reflector)

Are there any other (cheaper) fixes I can use in the meantime?

[John]

I'm not sure a focal reducer would help but I could be wrong as I've not tried it.

Perhaps stop using the barlow with the 26mm EP and get a 13mm 1.25" EP instead - that will probably come to focus OK.