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Barlow lens and finderscope

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#1 newtoastronomy1993

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Posted 15 January 2020 - 10:25 AM

So I have an Orion 130st EQ Reflector Telescope, and I have no problem finding the moon until I try using a Barlow lens, which, in my experience, has made seeing anything in the night sky more difficult. I understand that the Barlow lens is meant to increase the magnification of the eyepiece by a factor of 2, but I was wondering, is there an easy way for me to use the finder scope and the Barlow lens simultaneously so that focusing on objects like the moon doesn't feel like I'm looking at the sky with a straw?

 

One thing I've noticed is that If I orient the telescope in such a way that the cross-hairs of the finder scope are positioned like the x and y axes of a graph, and the moon is visible in the upper right quadrant of that graph, then I can see the moon in the eyepiece no problem without making any major adjustments to the scope's position (ie. using the RIA and declination knobs). However, when I try and put the Barlow lens in with the eyepiece, I notice that I always have to orient the telescope in such a way that the moon appears in the upper left quadrant of the finder scopes cross-hairs, and ensure that it's close enough to the origin, in order for me to see it. The problem is, I'm only sometimes successful at doing this, and other times, not so much. I'll find myself spending about 5 minutes or so just trying to get a part of the moon in a viewable position. So my question is: is there a secret, specific way for me to make better make use of the finder scope and Barlow lens so that I don't spend as much time trying to spot the moon? or is it a matter of spending more time with my telescope?

 

Thanks!


Edited by newtoastronomy1993, 15 January 2020 - 10:40 AM.


#2 banjaxed

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Posted 15 January 2020 - 10:39 AM

Have you aligned your finder scope with your telescope ?



#3 newtoastronomy1993

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Posted 15 January 2020 - 10:44 AM

Have you aligned your finder scope with your telescope ?

What do you mean? Like if I position the finder scope perpendicular to the ground?



#4 banjaxed

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Posted 15 January 2020 - 10:52 AM

No, the idea is to centre your telescope at a distant object (preferably in daylight) then adjust your finder scope so the object is centred also. The reason is that when you centre your finder scope at your object the telescope is also entered.



#5 newtoastronomy1993

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Posted 15 January 2020 - 10:56 AM

No, the idea is to centre your telescope at a distant object (preferably in daylight) then adjust your finder scope so the object is centred also. The reason is that when you centre your finder scope at your object the telescope is also entered.

Oh, I've never done that. I don't think I can because my finderscope isn't adjustable. Once I put it on, I can't change its position. It pretty much moves with the optical tube in whatever direction.


Edited by newtoastronomy1993, 15 January 2020 - 10:57 AM.


#6 banjaxed

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Posted 15 January 2020 - 11:03 AM

Are you sure it is not adjustable? They normally have 2 thumb screws, it would be useless as a finder scope if you can’t adjust it.



#7 msl615

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Posted 15 January 2020 - 11:16 AM

Does your telescope look like this one?  If so, see the small screws/bolts that stick out of the finder scope bracket towards the back?  Those are used to tilt the finder scope so that it can be aligned with the image in the main scope.

 

The process is as described above.

Use a low power eyepiece and find a distant object in the daylight in the main scope

Use the tilting screws in the back of the finder bracket to align the image in the finder to that of the main scope.

This can be easily banged, or mis-aligned, so it is best to get to a bright star at the start of each session, and give it a tune-up.

 

Let us know how this works!

 

Mike

Attached Thumbnails

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#8 Barlowbill

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Posted 15 January 2020 - 11:27 AM

You can definitely align the finder with your scope.  It takes a bit to get it right but you will get better as time goes on.  You want to align your object in the exact center of the scopes eyepiece, then align the finder scope so that the exact center is on the object.  You never want to use a Barlow when trying to find an object.  You want to use a "finder" eyepiece without Barlow to locate your object.  The "finder eyepiece will be your lowest magnification eyepiece....preferably a 25mm or 30ish mm eyepiece.  If you don't have one, get one.  The bigger the Field Of View the better so you can see more sky.



#9 newtoastronomy1993

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Posted 15 January 2020 - 11:34 AM

Does your telescope look like this one?  If so, see the small screws/bolts that stick out of the finder scope bracket towards the back?  Those are used to tilt the finder scope so that it can be aligned with the image in the main scope.

 

The process is as described above.

Use a low power eyepiece and find a distant object in the daylight in the main scope

Use the tilting screws in the back of the finder bracket to align the image in the finder to that of the main scope.

This can be easily banged, or mis-aligned, so it is best to get to a bright star at the start of each session, and give it a tune-up.

 

Let us know how this works!

 

Mike

Yes that's the telescope I have, but I guess I'm not understanding what you mean by "aligning" the image in the finder to the image of the main scope.

 

So say I go ahead and focus the finder on a distant tree. Do I make sure the tree is in the center of the finder and then look through the eyepiece to see if it is also centered?



#10 newtoastronomy1993

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Posted 15 January 2020 - 11:37 AM

You can definitely align the finder with your scope.  It takes a bit to get it right but you will get better as time goes on.  You want to align your object in the exact center of the scopes eyepiece, then align the finder scope so that the exact center is on the object.  You never want to use a Barlow when trying to find an object.  You want to use a "finder" eyepiece without Barlow to locate your object.  The "finder eyepiece will be your lowest magnification eyepiece....preferably a 25mm or 30ish mm eyepiece.  If you don't have one, get one.  The bigger the Field Of View the better so you can see more sky.

Oh ok. so what you're saying is

1) align finder scope so the exact center is on the object

2) then make sure the object in the eye piece is also in the exact center as well...but what if it isn't? do i then adjust the finder scope using the bolts on the brackets and play around with it so that eventually the image in both the finder and eyepiece is centered?



#11 banjaxed

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Posted 15 January 2020 - 12:09 PM

It is best to find a distant target,something like an aerial or mast then focus your scope on a precise part, you can now adjust the finder so it is pointing at the exact same part. When you get it right it will make life a lot easier.


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#12 havasman

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Posted 15 January 2020 - 12:14 PM

What you need is for the optical axis of the two to be coincident. That way when you center an object in the finder it will appear in the scope. The finder is the one that is adjustable. So the method is to focus the telescope on a distant object and then use the finder adjustment screws to center the object in the finder field. Then your finder should be aligned with your scope and should become useful. The better aligned, the more useful.

 

And yes, the more time you spend observing the more effective, natural and pleasing your observing will be.


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#13 BFaucett

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Posted 15 January 2020 - 04:51 PM

Oh ok. so what you're saying is

1) align finder scope so the exact center is on the object

2) then make sure the object in the eye piece is also in the exact center as well...but what if it isn't? do i then adjust the finder scope using the bolts on the brackets and play around with it so that eventually the image in both the finder and eyepiece is centered?

 

Did you read the user's manual that came with the scope?  (I'm assuming that you bought the scope new and that a manual was included.)

 

Here's a link to the manual:

 

Orion SpaceProbe 130ST EQ 

https://images-na.ss...81bz-JpMHtL.pdf

 

See "Aligning the Finder Scope" on page 6. 

 

The attached images below are from the user's manual.

 

Bob F.

 

 

130st.jpg

 

130finder.jpg


Edited by BFaucett, 15 January 2020 - 04:58 PM.

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#14 epee

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Posted 16 January 2020 - 09:12 AM

Oh ok. so what you're saying is

1) align finder scope so the exact center is on the object

2) then make sure the object in the eye piece is also in the exact center as well...but what if it isn't? do i then adjust the finder scope using the bolts on the brackets and play around with it so that eventually the image in both the finder and eyepiece is centered?

Nope, other way around.

  1. Center the most distant, non-moving, terrestrial object you can see in the main telescope.
  2. Start with your lowest powered eyepiece and then increase the magnification gradually, while keeping the object centered. Maximum magnification isn't necessary or desirable.
  3. Lock the scope down on that object as best you can. 
  4. Then adjust the finderscope so that the crosshair points to the part of the distant object that is in the middle of your telescope's field of view.

You can then "fine tune" your finderscope's alignment on a bright star or even a spot on the Moon, if necessary.


Edited by epee, 16 January 2020 - 09:14 AM.

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#15 csa/montana

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Posted 16 January 2020 - 10:29 AM

Moved to Equipment, for better fit of topic.



#16 Voyageur

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Posted 16 January 2020 - 11:27 AM

Oh ok. so what you're saying is

1) align finder scope so the exact center is on the object

2) then make sure the object in the eye piece is also in the exact center as well...but what if it isn't? do i then adjust the finder scope using the bolts on the brackets and play around with it so that eventually the image in both the finder and eyepiece is centered?

Good explanations above, but I wanted to refine the approach a bit.

 

In the day time, take your scope outside to where you can see a distant object clearly against the sky, in a part of the sky far away from where the Sun is at that time.

The top of a cell phone tower makes an ideal target.

Using your lowest-power eyepiece, which with your scope is probably a 25mm, adjust the mount until you can see the object in the eyepiece of the main scope (NOT the finder scope). This may take a minute, but be patient; you'll find it. You can sight along the top of the main scope tube to assist your positioning.

Fine-tune the scope position so that the object is as close to the center of the EP as possible. This is where a cell phone tower is better to use than a distant mountain, for example - you can better center the exact top of the tower. The corner of a tall building will also work. At this point, you can switch to a higher-power EP if you have one, as Jim has suggested above, to center the object even more precisely.

 

Lock your scope in position. Now look through the finder scope and make adjustments with the alignment bolts until your object is centered in the cross hairs of the finder scope.

 

When night falls, you might want to adjust the finder slightly using a star as a pinpoint object.

 

This should work okay, but in fact, a 6 x 30 finder scope is really not the best tool. It is hard to locate an object in those little finder scopes, so many people replace them with a larger finder scope such as a 9 x 50 RACI (right-angle, correct image) finder.

 

Others prefer a reflex (1x) finder such as a Telrad. It doesn't magnify what you are aiming at but rather, through the miracle of reflective surfaces, superimposes a bull's-eye image over the night night sky where it is pointed. 

 

There are other good reflex sights such as the Rigel Quickfinder.

 

Avoid cheap red-dot finder scopes. They are a piece of junk; I had one once and threw it away, and I am not a throwaway kind of person. Apologies to anyone who likes them; that's my opinion.

 

None of these is a "laser finder" even though people sometimes incorrectly call RDF finders laser finders.

 

A true laser, the green laser pointer, can be a nice addition to your pointing arsenal. They send out a beam of green light that you can see for some distance, and which appears to point right onto a star or other object, I love mine, but it requires caution in use. If you are anywhere near an airport or flight path of aircraft, its best to avoid them. Different countries, states, provinces, municipalities, etc. may have strict laws about their use and purchase.


Edited by Voyageur, 16 January 2020 - 11:37 AM.


#17 airbleeder

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Posted 16 January 2020 - 11:44 AM

    Learn to correctly adjust and use the finder you have before you think about replacing it. As great as CNers are, they can be loose with YOUR money.


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#18 grif 678

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Posted 16 January 2020 - 12:37 PM

The higher power you use to adjust your finder scope, the more accurate it will be. Say for instance, if you have your scope at 35X, and if the object is not centered exactly in the middle of the cross hairs of your finder,  if you then go to say 100X, the object may be near the edge of the FOV of the finder. So I would use at least 100X to set the finder scope.


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#19 Voyageur

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Posted 16 January 2020 - 01:17 PM

    Learn to correctly adjust and use the finder you have before you think about replacing it. As great as CNers are, they can be loose with YOUR money.

Good point. Never buy any piece of new astro gear until you have

1) become thoroughly familiar with the gear you already have

2) explored your current equipment to its fullest and determined that it fails to meet your needs

3) attempted a cheap or DIY workaround to the issue(s)

4) identified the proper commercially-available solution to solve your specific problem

5) enough money to afford the new piece of gear without economic and/or marital strife

 

I admit that I have not always taken that advice to its full mile...


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#20 Jon Isaacs

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Posted 17 January 2020 - 02:02 AM

This should work okay, but in fact, a 6 x 30 finder scope is really not the best tool. It is hard to locate an object in those little finder scopes, so many people replace them with a larger finder scope such as a 9 x 50 RACI (right-angle, correct image) finder.

 

I think they're actually quite good.

 

The basic technique with a straight through finder is to start out with both eyes open, one looking through the finder and one looking at the night sky.  What you will see is the finder cross hairs superimposed on the night sky.  

 

You then move the scope so that the cross hairs are moving towards the bright star you have chosen to start off with.  Suddenly it will pop into view in the finder.  At that point, you close the one eye and just use the finder.  

 

This is the advantage of straight through finders over RACI finders, you don't need a red dot or Telrad to get started.

 

Jon



#21 Jeff Struve

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Posted 17 January 2020 - 09:25 AM

Good point. Never buy any piece of new astro gear until you have

1) become thoroughly familiar with the gear you already have

2) explored your current equipment to its fullest and determined that it fails to meet your needs

3) attempted a cheap or DIY workaround to the issue(s)

4) identified the proper commercially-available solution to solve your specific problem

5) enough money to afford the new piece of gear without economic and/or marital strife

 

I admit that I have not always taken that advice to its full mile...

 

Yep! My modus operandi except I dont do #3...



#22 aeajr

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Posted 17 January 2020 - 09:43 AM

A finder scope on a telescope is like the sights on a gun. You adjust the sight until it matches where the gun shoots.

 

Finder Scopes
https://telescopicwa...n-finderscopes/


I do this during the day.

Using the lowest power eyepiece (HIGHEST NUMBER) I point the scope at a distant phone or power pole using the cross arm as my center.  Note that you have a Newtonian reflector so the image will be upside down.  That is normal. 

 

I then look through the eyepiece of the telescope (not the finder) and get the target centered in the eyepiece.  Now I lock the scope in position if I can.  

Now adjust the screws on the finder scope till that same cross arm is centered in the finder.  And make sure the image is in focus.  You focus your finder by turning the front lens of the finder, as shown in your manual. 

 

Go back to the telescope eyepiece and make sure it has not moved, that the target is still centered.  Now check the finder again and make sure both images are centered on the same thing.

 

You can go to your high power eyepiece to get this more precisely matched, but I typically don't do that. I find the low power eyepiece gets me close enough. 

 

This is what we mean by aligning the finder to the telescope. 

Done.

 

 

At Night

 

When I first use the scope at night, every night, I pick a bright star and center it in the low power eyepiece then I make a minor adjustment on the finder so it is centered in the finder too.  Finders tend to get bumped so a quick adjustment at the start of your session is normal and quick and very important to a successful evening. 


Edited by aeajr, 17 January 2020 - 12:23 PM.

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#23 Voyageur

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Posted 17 January 2020 - 11:05 AM

This should work okay, but in fact, a 6 x 30 finder scope is really not the best tool. It is hard to locate an object in those little finder scopes, so many people replace them with a larger finder scope such as a 9 x 50 RACI (right-angle, correct image) finder.

 

I think they're actually quite good.

 

The basic technique with a straight through finder is to start out with both eyes open, one looking through the finder and one looking at the night sky.  What you will see is the finder cross hairs superimposed on the night sky.  

 

You then move the scope so that the cross hairs are moving towards the bright star you have chosen to start off with.  Suddenly it will pop into view in the finder.  At that point, you close the one eye and just use the finder.  

 

This is the advantage of straight through finders over RACI finders, you don't need a red dot or Telrad to get started.

 

Jon

Jon, evidently you intended to quote my post, but it didn't show up as a quote in your post, making your post appear somewhat self-contradictory!

 

If someone is struggling with a piece of equipment, of course the first step is to try to get the existing equipment to work. That's why I made some suggestions on how to use the finder he has before mentioning some other solutions.

 

The OP doesn't need to spend a single penny more to enjoy his new scope. I just provided some information about options in case that might be helpful, and did not endorse any particular solution or urge him to another purchase.



#24 aeajr

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Posted 17 January 2020 - 11:17 AM

Nothing wrong with a 6x30 finder. Certainly there are better finders at higher cost but these work.

I have cited along the optical tube and used a low power eyepiece to find my targets. In fact this works pretty well on a short focal length scope.

A red dot finder costing $15 can also be effective. In fact, on a short FL scope I prefer the RDF in combination with a 25 to 32 mm Plossl or wider eyepiece.

Edited by aeajr, 17 January 2020 - 11:18 AM.


#25 aeajr

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Posted 17 January 2020 - 11:47 AM

Let's take a look at the scope, the tools and the task.  The task is to point the scope at bright targets or at guide stars for star hopping.  You have to target something you can see.

 

130STEQ

https://www.telescop...7caAuOFEALw_wcB

 

650 mm FL

  • two 1.25" Sirius Plossl eyepieces (25mm/26X and 10mm/65X)
  • 6x30 finder scope

I presume these are the only eyepieces the original poster, OP, owns.  BTW, the Orion Sirius Plossl eyepieces are pretty good eyepieces.  I own both of these. 

 

650/25 = 26X      52 degree AFOV/ 26x = 2 degree FOV, approximately.   Fairly wide

 

A an inexpensive 6X30 finder has about a 6 degree field of view.  More than wide enough.  

 

So, if the finder is aligned and focused properly he has a 6 degree field of view to find his target area.  Then he goes to a 2 degree field of view in his low power eyepiece.  That should be a pretty effective finder combination.

 

Now, I am assuming that the finder optics are reasonably good, not the best.  So if it is aligned properly it should be quite effective. 

 

If it were my scope and I wanted a different finder, knowing my low power had a 2 degree field of view, I would probably add a red dot finder rather than an 8X50 that would have about a 5.5 degree field of view. 

 

In fact,  I own a cheap 80 mm F5 refractor that came with a 6X30 finder.  Works fine, but I had a RDF that I could just slip on and that is what I use with this scope.  But the 6X30 worked too. 

 

 

 

The OP asked about using a 2X barlow with this scope and having a problem keeping the target in the field of view.   There are three things to remember:

  • As you go up in magnification you go down in field of view
  • Targets move faster through a higher power narrower field of view
  • The longer you take to switch eyepieces the more the target will move
  • Take note of which direction your target is moving through the field of view

If you change your eyepiece fairly quickly, your target may still be in the field of view or it may have moved just outside the field of view.  But you know which way it is moving so all you have to do is to move the scope a little and you should get it back easily.   

 

Understanding and using a Barlow Lens
https://telescopicwatch.com/?s=barlow

 

So, the OP needs to understand that as you go up in magnification your field of view will decrease. This is true if you use a shorter focal length eyepiece for higher power or if you use a barlow lens.  This is the result of magnification, not specific to a barlow lens.

 

25 mm eyepiece = 26X and 2 degrees FOV when using the 25 mm Sirius Plossl eyepiece. 

 

Put that in a 2X barlow and you get the equivalent of a 12.5 mm Plossl eyepiece.

 

FL scope / FL eyepiece = magnification

 

650/12.5 = 52X

 

AFOV of eyepiece / mag of eyepiece = approximate field of view

 

52 degree AFOV eyepiece / 52X = 1 degree FOV

 

This is true whether you use a 25 mm Plossl with a 2X barlow or a 12.5 mm Plossl eyepiece. 

 

Understanding Telescope Eyepieces-

There are recommendations, based on budget, but the meat of the article

is about understanding the issues when selecting eyepieces.
https://telescopicwa...cope-eyepieces/


Edited by aeajr, 17 January 2020 - 11:55 AM.



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