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Jay F

Is a shorty Barlow harder to focus than a standard size?

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Jay F    22

Looking for a little advice.  I have an Orion 2x shorty Barlow that came with my telescope.  It seems to be much harder to focus when I use that with any of my eyepieces than my actual eyepieces are.  I have a new Orion 6mm planetary eyepiece, which if terrific, actually, but when I pair it with my shorty 2x, I can't really get a clear focus on it, which is a little disappointing.  I am thinking of buying a TeleVue 3x Barlow, which is much longer.  It seems like with a longer eyepiece like that, it wouldn't require so many micro-adjustments to try to get a good, clean focus.  (I could be wrong about that also, I know.)  I Since they are quite a bit more expensive than the one I have, I want to make sure that it would be a good choice at this point.  I am a beginner and am working with a 114 Reflector.  

Any thoughts or suggestions much appreciated.

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Charic    2,197

Could be the 114 reflector itself, and by using a Barlow, your expecting too much! Barlowing the 6mm is simple to say, but difficult to achieve, due to the amount of magnification, plus the scope itself. I had a 127EQ, same issues, I couldn't get away trying to Barlow the short focal length eyepiece. Do you have the same issue with the longer focal length eyepiece?
Also, you can often remove the Barlow lens cell from its extension tube, the lens sits in a cell, and sometimes can be removed from the Barlow and attached/screwed onto the base of an eyepiece. This alone will reduce the multiplication factor of the Barlow, so a 2x will feel more like a 1.5x Barlow. Try it see if theres any difference.

I think you would be wasting good money on a 3x Tele View on your present scope.
Whats the focal ratio on the telescopes data plate, use that as a guide to your shortest focal length eyepiece (highest power) if its an f/5 scope then a 5mm lens is a good limit! If your trying to Barlow a 6mm eyepiece by a factor of TWO, the effectively your using the 6mm as though it was a 3mm, far in excess to what is achievable?

 

Edited by Charic

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Jay F    22

Thanks for the suggestion.  I just checked, and yeah, it will unscrew and I can screw directly on to any eyepiece.  Who knew? I never would have thought of trying that.  :-)

I'll give it a try tonight and see if it makes a difference.

(I do realize that I can't expect too much from a lower-end telescope, but it was a bit of a compromise for me at this point.  Hope to upgrade as finances progress.) 

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Charic    2,197

It will just be less powerful. 

Magnification of a telescope is determined by the telescopes focal length and the focal length of the eyepiece.

If your scope has a focal length of 1000mm and you use an eyepiece of 6mm you achieve a magnification or power of @ 166x written as 166x.

The Barlow, for want of a better excuse doubles the focal length of the telescope? Your 1000mm focal length is now 2000mm when you insert a Barlow of 2x into the focuser, and depending on which eyepiece you use next, will determine the power.

1000/6=166x
(two times Barlow ) 2000/6=333x

(TeleVue 3x ) 3000/6=500 Lol!

There lies a problem

Edited by Charic
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Floater    2,251

It hasn’t to do with a ‘lower-end’ scope, Jay. It’s just that you are probably trying for too high a magnification. That’s not necessarily a good thing. (Magnification = scope focal length/eyepiece focal length.)

Using a higher factor of Barlow - TV or other - will definitely not help!

Edit: @Charic beat me to it.

Edited by Floater
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Jay F    22

Thanks Floater,

I kind of thought it might be a limitation of the telescope more than the eyepieces, but it was worth a shot. :-(

Thanks to Charic also for the calculations.  This telescope has a focal length of 500mm, so a 6mm with a 2x barlow would bring it to 166x, if my calculations are right.  The max magnification they recommend is 200x, so a 3x would apparently not be a good idea.  This is most likely the max magnification I should attempt to achieve at this point.

Thanks to both of you for saving me some money that wouldn't make much difference.

Not disappointed at all, I am actually really pleased with what I can see, even with a low-end scope like this.  It was so amazing the first time I looked a Jupiter and saw it not only as a more than just a bright light, but one with actual small moons in an orbital pattern.  I was so excited, I don't think I'll ever forget that.  So learning as I go, maybe some day a more advanced setup, but there is still so much to learn and see right now with this one, that I'm not too worried. 

Thanks again for the great advice.  I really appreciate it.

Edited by Jay F
changed focal length and results of calculations

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Charic    2,197

Which scope do you have Jay F.

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Jay F    22

It's an Orion Starblast 4.5 on an EQ1 mount.  (I may want to upgrade the mount before I do the telescope :-))

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Louis D    983

I have a generic version of that shorty barlow I paid about $30 for years ago.  It's not that sharp of a barlow compared to a Televue 2x or Meade 140 2x.  I loaned it to a beginner friend and told him he could keep it indefinitely since I wasn't using it.  It came back to me within 6 months because he had also found it not that great.  I literally couldn't convince him to keep it, so now it sits in my box of sidelined equipment on a shelf in my closet.

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Jay F    22

Well, I tried screwing the Barlow lens in directly to my eyepiece, and there was some improvement that way.  I was able to focus in pretty tightly on Crater Schickard this morning with my 3mm planetary eyepiece and it looked crisp and clear. That eyepiece with the Barlow was pretty good, but the focus is still just slightly off when compared with the 6mm without it.   Thanks again for that suggestion, @Charic.

@Louis D I appreciate that information.  I think that is probably part of the problem.  It is an inexpensive Barlow.  I guess you get what you pay for!  Possibly I would have better luck with TV 2x at some point down the line, might be my next upgrade.  (but not a 3x :-)) 

Thanks, again.

Kind regards, Jay

 

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Charic    2,197
11 minutes ago, Jay F said:

.......... I was able to focus in pretty tightly on Crater Schickard this morning with my 3mm planetary eyepiece and it looked crisp and clear. That eyepiece with the Barlow was pretty good, but the focus is still just slightly off when compared with the 6mm without it. 

 

Can I suggest you 2x Barlow the 6mm to give you your 3mm 'eyepiece' rather than 2x Barlow your 3mm eyepiece!

That's how I'm reading/understanding your text? 

The Meade #140 that Louis D mentions is a good tele negative Barlow and probably cheaper than a TeleVue, should the need arise.

Edited by Charic

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Jay F    22

@Charic  I only have a 6mm eyepiece, not a 3mm one.  I mistyped that in the post above.  Sorry about that, I just reread the post and it's pretty confusing, even to me :-) 

I do get it that, with my telescope specs, the 6mm with the 2x should be the highest magnification I should try, and I'm good with that. 

You saved me some money :-)

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Louis D    983
2 hours ago, Jay F said:

@Charic  I only have a 6mm eyepiece, not a 3mm one.  I mistyped that in the post above.  Sorry about that, I just reread the post and it's pretty confusing, even to me :-) 

I do get it that, with my telescope specs, the 6mm with the 2x should be the highest magnification I should try, and I'm good with that. 

You saved me some money :-)

I'm thinking your best bet is to get a 3.2mm BST Starguider from FLO rather than keep trying to find a good barlow-eyepiece combo.  That eyepiece is already a negative-positive (barlow/smyth + konig variation) eyepiece.  It should be a well matched combination.

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Jay F    22

Thanks Louis D,

That does sound like a better option, now that you mention it, with a reasonable price also.  I have it bookmarked and on my wish list.

Kind regards, Jay

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