Cant focus 2.5 barlow on 130mm scope

[eoinzy]

Hi,

I was looking at Jupiter on my Skywatcher Heritage 130p using both my 25mm and my 10mm lenses. It looks great in the 10mm and I can see some moons etc.

Anyway, I bought a Revelation 2.5x Barlow and tried it tonight after looking through my 10mm at Jupiter. I could see it perfect through my 10mm, until I added the barlow. Now its a white circle with a black "lollipop" in the middle. It looks like its out of focus with both my 10mm and 25mm and I can't seem to focus it.

Is there anything I need to do to the barlow when I take it out of the box? There was no instructions with it.

Thanks.

[nephilim]

You've probably pushed it too far, although the 130p is capable of greater magnification than that, if the seeings not to good then you wont get a good view, I cant get a decent image in my 130 with a 9mm EP & 2xbarlow no matter what the conditions, I may be wrong.

[nephilim]

Hi,

I was looking at Jupiter on my Skywatcher Heritage 130p using both my 25mm and my 10mm lenses. It looks great in the 10mm and I can see some moons etc.

Anyway, I bought a Revelation 2.5x Barlow and tried it tonight after looking through my 10mm at Jupiter. I could see it perfect through my 10mm, until I added the barlow. Now its a white circle with a black "lollipop" in the middle. It looks like its out of focus with both my 10mm and 25mm and I can't seem to focus it.

Is there anything I need to do to the barlow when I take it out of the box? There was no instructions with it.

Thanks.

Sorry just re read your post, if u cant achieve focus with the 25mm either then it could be a collimation issue (have you checked that?) I can barlow my 25mm perfectly well, theres no real wrong way of using a barlow, just pop it in the focusor and put in the EP.

Steve.

[eoinzy]

Hi, thanks for the reply.

I should clarify. I can focus perfectly with my 10mm and 25mm WITHOUT the barlow.

With both the 10mm and 25mm WITH the barlow, I cannot focus.

[eoinzy]

Also, I found someone online having a similar issue and they resolved it by "removing the diagonal".

What does that mean, and how do I do it?

[nephilim]

Also, I found someone online having a similar issue and they resolved it by "removing the diagonal".

What does that mean, and how do I do it?

The diagonal is a seperate lense which turns the flipped image you get in a astro scope the right way round http://www.astronomics.com/astro-tech-1-25-inch-99-percent-reflectivity-dielectric-mirror-diagonal_p10475.aspx you'd know if you had one & altho they can affect the image as the light has more lenses to go thru i cant see how it would affect it that badly (im a novice myself) I use the revelation 2.5x and find it works well. I really dont know the answer to this then & can only hope someone else can help you.

[eoinzy]

Hmm, I have the Skywatcher Heritage 130p. which has a kinda retractable top. See here:

http://www.astrotreff.de/upload/Stathis/20100525/heritage130_1.jpg

A funny thing happened earlier. I had the scope about 99% extended, and I looked through the lense, with the barlow, and I could make out Jupiter. It was still a bit blurry as if it still wasnt in perfect focus, but I think this means that at least it works, and its just a focus issue.

[Peter Drew]

It seems to me that the focus has not been reached. Do you have the diagonal fitted in first, then the Barlow, then the eyepiece?. If you put the Barlow in front of the diagonal it will greatly affect the power of the Barlow and you might not have enough focus travel to focus it.

[RikM]

You don't normally use a star diagonal with a Dobsonian. The heritage 130P has a helical focuser and I am not sure how much focus travel it has. If it came to focus with the truss collapsed a bit then you need to wind the focuser in a bit. Barlows normally move the focus position out, so you shouldn't have a problem.

[knobby]

Not sure if the revelation Barlow can do this but you could unscrew the bottom part of the Barlow and screw it to the bottom of your ep... Worth a try

[LeeB]

It sounds like you don't have enough focus travel, a friend has the same scope i'll look tommorrow and get back to you. To find best solution.

[eoinzy]

It seems to me that the focus has not been reached. Do you have the diagonal fitted in first, then the Barlow, then the eyepiece?. If you put the Barlow in front of the diagonal it will greatly affect the power of the Barlow and you might not have enough focus travel to focus it.

I don't have a diagonal at all. It was just something I read online somewhere, but afterwards found out it was a separate eyepiece, which I don't have.

You don't normally use a star diagonal with a Dobsonian. The heritage 130P has a helical focuser and I am not sure how much focus travel it has. If it came to focus with the truss collapsed a bit then you need to wind the focuser in a bit. Barlows normally move the focus position out, so you shouldn't have a problem.

OK, when you say the "focuser", do you mean that piece below where the Eyepieces go in that I can twist to focus the image? If so, I tried twisting that from one end to the other, until it totally came off, and it never got into focus.

Not sure if the revelation Barlow can do this but you could unscrew the bottom part of the Barlow and screw it to the bottom of your ep... Worth a try

I tried that already. There's a silver bit at the bottom that I unscrewed, however, it just didnt fit into the bottom of my eyepiece.

[bombassa]

The black lollipop must be the reflection of the secondary due to lack of focus.

Try inserting the barlow and then the 25 mm and unscrew the focuser as far as possible. Then look while slowly retracting the 25 mm and see if it reaches focus at any point.

I've had this scope and watching jupiter with this magnification was usually possible.

Sorry bout bad english.

Good luck.

[brantuk]

Your scope has a focal length of 650 mm - with a 10mm eyepiece you get 65x magnification. if you pop a 2.5x barlow in with the 10mm you will be getting 162.5x magnification because you are effectively extending the focal length - this should be perfectly do'able on a night of good seeing. The standard focal length of the scope puts the focal point somewhere within the range of the focuser tube (which is helical on that scope IIRC)

However - when you extend the focal length the focal point get's pushed further out of the focuser tube so you could be lacking "backward focus". The usual solution is an extension tube. Also be prepared for "inward focus" issues if you reduce the focal length with a reducer - for which some folks replace the focuser with a low profile model.

Some things to try - set the eyepiece a bit further out of the barlow, and set the barlow a bit further out of the focuser tube. It'll make the arrangement a little less solid so be careful they're firmly screwed in so as not to drop anything in use. Now try focusing slowly across the full range of movement and you might just get there. Otherwise try for a cheap extension tube. Hth

[glowjet]

Just a note to those using a diagonal and Barlow, if you have a diagonal/Barlow/eye piece set up, you will achieve the stated increase in mag, however, if on the other hand you use a Barlow/diagonal/eye piece set up, you will increase the mag by a further 50%

John.

[eoinzy]

OK so I broke out the telescope tonight to try resolve this. I used my 10mm lense and the revelation 2,5x barlow.

I started off with the scope collapsed and moved it as far up as possible, while focusing each time. I was able to focus in up to a certain point. This point was about half a centimetre short of having the scope fully extended. By that stage, I had twisted the focuser as far as it could go in the one direction. If I could twist it another short bit, I would be able to fully extend the scope and focus with the revelation 2.5x barlow.

Is it possible for me to tweak (collimate?) the scope so that I can get a clean focus with both the barlow and my normal 10mm and 25mm lenses? Or any other tips?

I see people have used this type of Barlow with my exact model of scope so it must be a configuration issue.

[LukeSkywatcher]

Using a 10mm eyepiece with a 2.5X barlow on a Heritage 130P is never going to work. Its pushing the scope well above its means in this part of the world. It should be ok to use with a 25mm eyepiece.

I live in Dublin also and i own a Heritage 130P and a 2x Revelation barlow.

10mm+2x is ok with this scope in theory but we just dont get the seeing conditions often enough to do this.

Forget the barlow and just observe with 10mm.