I can't focus with my barlow

[tomw28]

Hi!

I have recently purchased a Sky-Watcher Heritage 76. I am really pleased with it but when I put a 2X barlow lens in with either a 25mm eyepiece or the 10mm eyepiece the only things that will focus are things that are within a few metres of me. Stars and planets just look like a black splodge with a ring around it. It appears to focus slightly more when (I don't know the technical term) the focusing thing is close to the main body of the telescope.

Does anyone know if the scope just won't work with a barlow or if it is the barlow I'm using (a cheap one I'm afraid) or even how I'm using it?

Thanks

Tom

P.S. The focal length of the telescope is 300mm and the mirror is 76mm. Thanks!

Edited April 21, 2010 by tomw28

[Cornelius Varley]

Did the barlow lens come with the telescope or is it from elsewhere? Also, do you have anymore focus travel left when try to focus using the barlow?

Peter

[Astorix]

Hi Tom, welcome to SGL

First off let me say, if you are using the barlow that came with the scope it should work fine. However when you are using the Barlow with the 10/25mm you are looking at objects with a much higher mag.

If your FL is 300mm then a 10mm with barlow would give you a 60x mag and with the 25mm a 24x mag. This should be fine to focus on pretty much anything in the sky.

With higher magnifications you will find that the exact spot of focus is actually very small. To the point where even turning the focus just 2 to 3mm more to the left or right can mess up the focus. I find that it is easiest to put the focus all the way to one end and then extremely slowly move the focus untill you find the focus.

You could also be experiencing vibrations which gives the effect of unfocused images. Are you placing the scope on a sturdy object and away from traffic which can send vibrations through the ground.

Hope this helps,

[pvaz]

Depending on the barlow you may need more in travel to focus on that scope. But usually, with barlows it works the other way around, it usually needs more out focus though I guess infocus may be needed with some.

Unlock the barlow + EP from the focuser and slowly bring it out and see if you can reach focus. If you do you can either lock the barlow on the focuser keeping it out a bit or buy an extension tube.

If you really need infocus then the only solution would be a low profile focuser and this cost more as many scopes, so it's cheaper to find another barlow that will focus on your scope. You can also use the collimation screws to bring the mirror a bit up the tube but that can be tricky to do and will only add a little infocus.

Edited April 21, 2010 by pvaz

[sn00p]

i have one of these scopes and use my SW 2x deluxe barlow from my skymax 127 with 10 and 25mm SW EP's NO issues. Its a nice quick grab and plonk on your car roof scope.... great for the moon but so far useless on saturn :-( I do however find im nearly always fully wound IN on the focusser. I'll double check tonight and let you know

[gareththegeek]

When using my scope the focuser must we wound a long way out for normal eyepieces and wound a long way in when I add a Barlow to the same eye piece.

[tomw28]

Thanks for the advice. The people I brought it from have finally got back to me and said that I should return it and they will send me the "deluxe" model. He didn't explain what the problem was though, just saying that the new one would work. I'm pretty sure the lens works because it will focus very crisply on plants a few metres away with the increased magnification, but not on planets and stars slot further away! And no, the barlow wasn't included with the set, I ordered it seperatley. I'll let you now if the deluxe lens helps.

Thanks

Tom

Edited April 22, 2010 by tomw28

[sn00p]

i have one of these scopes and use my SW 2x deluxe barlow from my skymax 127 with 10 and 25mm SW EP's NO issues. Its a nice quick grab and plonk on your car roof scope.... great for the moon but so far useless on saturn :-( I do however find im nearly always fully wound IN on the focusser. I'll double check tonight and let you know

Ok i checked for you late last night regarding focussing with the 10mm and x2 barlow (both SW) and i can confirm i CAN focus on the moon NO issues and VERY pleasing views.... I then turned my attention to Saturn.... well i can get a crisp clear bright slighlty larger star... I DO NOT see the rings its just too small for me to be able to see them.

Now i wonder if mine has issues??? how big did you see saturn??? what lens blah blah blah... I will mention i didnt let mine cool but then they are tiny so didnt think it would need much and my skies are polluted with light :-(

[pvaz]

With the 10mm + barlow on your scope you get 60x. That's only enough to see it as a tine disc with a line crossing it, cuting it in half. That very small line is the rings, they are on edge now, will open by next year.

[sn00p]

You can also use the collimation screws to bring the mirror a bit up the tube but that can be tricky to do and will only add a little infocus.

Do you have any instructions on this??? my colmination is deffo out and i can see i need to raise the mirror but seems to be nice and round but off centre... i noticed the stalk to raise the mirror and the 3 screws on back of mirror i guessed for colmination?

will i need a colminating tool???

[pvaz]

Well you could buy a smaller EP for higher power, but I'm afraid the problem is fundamentally in the scope. The heritage 76 is a portable option more suited for wide field views of the moon and the largest/brightest DSOs. It will always strugle with planets, but on a good "seeing" night you could probably see the shape of the rings. Anyway now they are a bit featureless.

Edited April 22, 2010 by pvaz

[sn00p]

yes thanks i got that... i also have a skymax 127 which is great for Saturn. I would like some info on shifting the mirror in the mini dob and colmination technics for it you have any info??? the booklet has NOTHING mentioned for it

[pvaz]

This is the best collimation guide I know Astro Babys Guide to Collimation

To move the mirror up you need to unscrew the adjust bolts to the limit, then collimate. I never did this, just read about it, I think there is a risk of setting the mirror free which can then be difficult to attach again, not sure though.

[Dave73]

Thanks for the advice. The people I brought it from have finally got back to me and said that I should return it and they will send me the "deluxe" model. He didn't explain what the problem was though, just saying that the new one would work. I'm pretty sure the lens works because it will focus very crisply on plants a few metres away with the increased magnification, but not on planets and stars slot further away! And no, the barlow wasn't included with the set, I ordered it seperatley. I'll let you now if the deluxe lens helps.

Thanks

Tom

I have just searched this site for info regarding Barlow focus problems, i have the same telescope and have recently received a x2 barlow which i just cant get to focus.

The first time i used it to look at the moon with a 25mm eye piece it became very apparent that its not in focus at all and you cant turn the focus rack far back enough to get any sharp image.

I will prob keep this for future use with any new telescope but will also try purchasing the short "deluxe" Barlow or contact shop for more advice.

[Uwe]

Hi, I know this is an old post, but as I just went through a day of experimenting, I thought I share my findings - someone might have the same issue in the future. 

The crucial bit in Tom's post/scenario is: All is blurry with Barlow lens in the distance, but actually near objects can be focused. 

Same was true for me. I have a 70mm Celestron Travel Scope and it came with a 3x Barlow lens (testing it with a 20mm eyepiece and prism - but also tried without prism). All blurry in distance and sharp with very near objects. Looking into the manual, it talks about a barlow lens - but only for the 50mm version of the telescope. That should have been a hint to me :). I seem to remember that when I bought the telescope, it advertised to give a Barlow lens for free :). 

Peter's response up there talks about increasing the focus length. That prompted me to look into the Barlow lens. The actual lens is in the plastic part, not the tube - and can be moved around with a chop stick. The closer I moved it to the tube end, the further away near objects could be. So I took the lens holder out of top part and of course it does not fit into the tube. I put it into the prism part and then inserted the tube of the Barlow lens as far as possible to keep it tight and voilà, I can sharpen distant objects. I have not tried it with the moon as yet, or even planets - appears too much of a shaky construction to me - but at least I know I did not do something wrong. I got the wrong Barlow for my type of telescope. 

 

Hope it helps someone. Uwe

[McQ]

2X barlow won't work on my 76mm either, not on space, it works on terrestrial. I have a Russell 19mm that won't work in the 76 at all. Not that it matters, I'll probably sell the 76mm in a few weeks. 

[Mandy D]

14 hours ago, McQ said:

2X barlow won't work on my 76mm either, not on space, it works on terrestrial. I have a Russell 19mm that won't work in the 76 at all. Not that it matters, I'll probably sell the 76mm in a few weeks. 

I'm having problems with a Barlow at the moment and have started another thread asking questions.

All I know at the moment is that I need another 75 mm or so of back-focus on my RC6 to get anything distant into focus with a 2x Barlow. If you fit a 25 mm eyepiece in the Barlow, then rack the focusser out as far as you can it will not focus. Pull the Barlow and eyepiece further out of the focusser taking care to maintain alignment and eventually you wil achieve focus.

It appears that Barlows need to be further away from the objective or main mirror than an eyepiece without one. I am struggling to find information on the web and getting answers in forums that explain it all.

This also seems to apply equally to focal extenders.

I have ordered some more extensions for my RC6, which should fix this.

[Louis D]

I generally don't insert Barlows all the way into the focuser to avoid racking the focuser out so much.  Of course, this assumes the Barlow is long enough to allow this to work.

Focal extenders are just the opposite.  They need lots of in-focus to work.  As such, many focusers can't be racked in far enough to reach focus with them.

[Mandy D]

3 hours ago, Louis D said:

I generally don't insert Barlows all the way into the focuser to avoid racking the focuser out so much.  Of course, this assumes the Barlow is long enough to allow this to work.

Focal extenders are just the opposite.  They need lots of in-focus to work.  As such, many focusers can't be racked in far enough to reach focus with them.

Mine is on an RC6 and with 100 mm of spacers (all it came with) and I have to use all the spacers, rack the focusser fully out and add about another 65 mm to get focus. I'm told this is due to not using a diagonal, but I wanted to keep everything in one line.

I'm now curious about focal extenders because mine appears to need the same as my Barlow! I have the extensions I need, now, so I'll test all of this as soon as I can