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Barlow Lens for Celestron 76mm cometron / firstscope / funscope

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#1 MoonFrog

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Posted 24 September 2020 - 03:14 AM

Good morning / evening gang so after much research and very conflicting advice I have a question to any of you with the cometron / firstscope / funscope etc I’m trying to find a Barlow lens that is compatabke with my little scope I bought a cheapie one (yes I know 🤦‍♂️ just to try ) it’s the longer variety and I. Can’t achieve focus most day stay away from the shortys but I would like to know what people are using ?? Links please I have some nice eyepieces (def not what came with this ) and am modifying this setup as I go along any help will be great as I don’t want to keep spending money on useless cr@p 🤦‍♂️ I don’t want to upgrade the scope itself as I’m extremely limited by space so this fits nicely on the windowsill many thabks in advance
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#2 Hesiod

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Posted 24 September 2020 - 04:07 AM

My advice is to stick with the eyepiece you have and start saving money for a more powerful telescope.
Mind that once start purchasing eyepiece and other accessories you have already paid a good fraction of the price for a more capable telescope; but while eyepieces would give you only a marginal improvement, getting an AWB Onesky would be a major improvement (I have both the Celestron Firstscope76 and the Heritage130, Skywatcher's version of the OneSky) for a very small increase of encumbrance

Edited by Hesiod, 24 September 2020 - 04:08 AM.

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#3 Wouter1981

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Posted 24 September 2020 - 04:15 AM

100% agree with Hesiod. Trying to upgrade such a telescope is not worth it. I've never used the AWB onesky but it's remarkably small for a 130mm telescope.


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#4 MoonFrog

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Posted 24 September 2020 - 04:38 AM

My advice is to stick with the eyepiece you have and start saving money for a more powerful telescope.
Mind that once start purchasing eyepiece and other accessories you have already paid a good fraction of the price for a more capable telescope; but while eyepieces would give you only a marginal improvement, getting an AWB Onesky would be a major improvement (I have both the Celestron Firstscope76 and the Heritage130, Skywatcher's version of the OneSky) for a very small increase of encumbrance

Thanks for your reply , unfortunately as I said above I do not have any space to keep a larger scope hence why I asked the question . You say you have the firstscope have you tried a Barlow on it ? Getting another scope in this property isn’t going to happen so I must make do with what I have .... do you have any Barlows (2x) that you could try and see if they work ?? Is there a formula to working out what I need ?? Many thabks 



#5 MoonFrog

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Posted 24 September 2020 - 04:41 AM

100% agree with Hesiod. Trying to upgrade such a telescope is not worth it. I've never used the AWB onesky but it's remarkably small for a 130mm telescope.

Getting the best Out of any piece of equiptment is surely the overall goal here no ?? Be it a firstscope or a large maxitov... have you tried the cometron ? Mine was out of collimation when it arrived and after collimating the secondary the performance gained was night and day getting a larger scope here simply wouldn’t work so is out of the question so am looking to improve on what I have here bud ....



#6 Hesiod

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Posted 24 September 2020 - 06:18 AM

Those 76/300 do not have a good main mirror, being a fast spherical one.
Therefore views at "high" power will be truly soft.

If recall correctly, you should have a 4mm eyepiece and trust me, that is how high you want to go.
If want higher magnification and sharper view you need another telescope, not pricey accessories; on the other hand, too cheap eyepieces are not better than your current ones so in any case would be just a waste of money
At ca 75x can already perceive some features of planets e.g. the rings of Saturn, the Great Red Spot of Jupiter and hints of its banding, Venus' and Mercury's phases, and some albedo features on Mars, especially under opposition as it is happening now).
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#7 Sky Muse

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Posted 24 September 2020 - 06:29 AM

Hi MoonFrog,

 

I have the next size up from your telescope, a 100mm f/4 Newtonian...

 

comparison2.jpg

 

That's one of pics I took of it, and to illustrate its size.

 

Just recently, I had it outdoors with a 4mm eyepiece inserted into a 2x-barlow, and observed Mars.

 

Yours is a 76mm f/4 Newtonian.  You most certainly can get a barlow for your telescope.  If it fails to satisfy with your telescope, in that the primary-mirror is spherical instead of parabolic, it can be used with any others that might be acquired in future...

 

https://agenaastro.c...arlow-lens.html

 

You do want a short-bodied barlow for a Newtonian, to keep the overall height of the eyepiece and barlow at a minimum, and there's nothing wrong with a shorter one versus a longer one.  I have three barlows, and all three are considered short...

 

barlows2.jpg

 

I've had much success with those Antares barlows.  The one in the middle is ideal for Newtonians, optically, and arguably, but it hasn't been sold new for many, many years, sadly.  The Antares barlows are still available however...

 

2x... http://www.scopestuff.com/ss_eba4.htm

3x... http://www.scopestuff.com/ss_eba3.htm

 

Your telescope has a 300mm focal-length, and rather short, therefore you can definitely make use of a 3x-barlow.


Edited by Sky Muse, 24 September 2020 - 06:33 AM.

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#8 noobwatcher

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Posted 24 September 2020 - 08:40 AM

I don't know much about telescopes nor eyepieces, but I would say go ahead and get an inexpensive barlow (svbony 2x Barlow on Amazon for <$20). You can try some inexpensive Svbony eyepieces too, they're typically less than $20 each too. Also, don't forget Amazon's generous return policy in case they don't work out for you. Worst case you're out a drive to UPS to drop off the return package. Best case, you're happy.



#9 Wouter1981

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Posted 25 September 2020 - 12:30 PM

Getting the best Out of any piece of equiptment is surely the overall goal here no ?? Be it a firstscope or a large maxitov... have you tried the cometron ? Mine was out of collimation when it arrived and after collimating the secondary the performance gained was night and day getting a larger scope here simply wouldn’t work so is out of the question so am looking to improve on what I have here bud ....

Yes, but the danger is of spending much money and time in something that will never achieve the result another telescope easily can do. No matter what upgrades, eyepieces, or modifications you do on your 76mm telescope, a small 60mm ED refractor will be superior, especially at higher magnifications while also being very small.
But don't let that stop you if you like really like doing that. Building and modifying a telescope is huge fun.


Edited by Wouter1981, 25 September 2020 - 12:31 PM.


#10 RobertMaples

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Posted 25 September 2020 - 09:18 PM

Good morning / evening gang so after much research and very conflicting advice I have a question to any of you with the cometron / firstscope / funscope etc I’m trying to find a Barlow lens that is compatabke with my little scope I bought a cheapie one (yes I know 🤦‍♂️ just to try ) it’s the longer variety and I. Can’t achieve focus most day stay away from the shortys but I would like to know what people are using ?? Links please I have some nice eyepieces (def not what came with this ) and am modifying this setup as I go along any help will be great as I don’t want to keep spending money on useless cr@p 🤦‍♂️ I don’t want to upgrade the scope itself as I’m extremely limited by space so this fits nicely on the windowsill many thabks in advance

The Orion Shorty 2x Barlow(https://www.telescop...?keyword=barlow) works with it.



#11 aeajr

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Posted 27 September 2020 - 03:36 PM

Good morning / evening gang so after much research and very conflicting advice I have a question to any of you with the cometron / firstscope / funscope etc I’m trying to find a Barlow lens that is compatabke with my little scope I bought a cheapie one (yes I know ‍♂ just to try ) it’s the longer variety and I. Can’t achieve focus most day stay away from the shortys but I would like to know what people are using ?? Links please I have some nice eyepieces (def not what came with this ) and am modifying this setup as I go along any help will be great as I don’t want to keep spending money on useless cr@p ‍♂ I don’t want to upgrade the scope itself as I’m extremely limited by space so this fits nicely on the windowsill many thabks in advance

 

 

Thanks for your reply , unfortunately as I said above I do not have any space to keep a larger scope hence why I asked the question . You say you have the firstscope have you tried a Barlow on it ? Getting another scope in this property isn’t going to happen so I must make do with what I have .... do you have any Barlows (2x) that you could try and see if they work ?? Is there a formula to working out what I need ?? Many thabks 

 

OK, first question, what Barlow did you buy? Can you provide a link?   Not sure why you should have a focus problem and I can't think of any reason why a shorty barlow would be a problem. All of my Barlows are shorties. 

 

I don't have a cometron, first scope or fun scope.  Let's make sure we know what you have.  One of these?

https://www.telescop...eyword=funscope

 

Orion lists 90X as the highest useful mag with that scope, and on some days you may not be able to go that high.  How high are you trying to go and what are you trying to see? 

 

FL Scope / FL eyepiece = magnification.   

 

So a 3.3 mm eyepiece would be about the max mag you would expect, and that would be under very good conditions.    You could achieve that with a 3.3 mm eyepiece, 10 mm in a 3X barlow or a 6.6 mm in a 2X barlow. 

 

You might be able to push 120X on the Moon on an excellent night, maybe. 

 

Among my other scopes I have a SkyScanner 100, an F4 tabletop, so a size up from yours.  Works fine with a 2X barlow and a 3X barlow up to a reasonable magnification.  In this scope up to about 120X is reasonable and I have pushed to 150X under superb conditions.

https://www.telescop...pe/p/102007.uts



#12 MoonFrog

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Posted 27 September 2020 - 05:07 PM

Hey buddy thanks for the reply I have a firstscope with spherical mirror it’s a 300x76 model the Barlow was junk I have ordered a celestron one now which should be far superior in every way should be here tommorow hopefully and will find out 😊
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#13 neildo

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Posted 27 September 2020 - 06:49 PM

I started with a Celestron Firstscope and ran into the same issue using a Meade 3x barlow ($40) where I could not get any EPs to focus because the focuser bottomed out about 5mm short of being able to focus. I can confirm that the Svbony 2x barlow does work with the Firstscope without getting close to bottoming or topping out on the focuser. I have since upgraded to a Z130 and find myself using the Meade 3x barlow (over the Svbony 2x) just because the image quality seems better at all equivalent focal lengths. And I haven't hade any problems with focusing using the Meade 3x with the Z130.


Edited by neildo, 27 September 2020 - 06:58 PM.

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#14 Tony Flanders

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Posted 28 September 2020 - 05:40 AM

I started with a Celestron Firstscope and ran into the same issue using a Meade 3x barlow ($40) where I could not get any EPs to focus because the focuser bottomed out about 5mm short of being able to focus. I can confirm that the Svbony 2x barlow does work with the Firstscope without getting close to bottoming or topping out on the focuser. I have since upgraded to a Z130 and find myself using the Meade 3x barlow (over the Svbony 2x) just because the image quality seems better at all equivalent focal lengths. And I haven't hade any problems with focusing using the Meade 3x with the Z130.

It's worth pointing out that one of the many problems with the FirstScope and its clones is that the focuser travel is very short. That's not a design issue so much as simple physics; there simply isn't much distance from the tube to the secondary mirror, so if you build the scope with lots of in-focus, the focuser will bump into the secondary.

 

With larger apertures, its much easier to have a focuser with a reasonably big length of travel.

 

That's one of the reasons why the FirstScope is more likely than most Newtonians to run out of focuser travel when using different eyepieces, and even more so when using Barlows. It's also one of the reasons why refractors far outnumber Newtonians in apertures smaller than 100 mm.


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#15 aeajr

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Posted 28 September 2020 - 07:12 AM

Tony,

Real good point about focuser travel. I was not aware of this but it makes sense. Thanks for the mechanical lesson.

#16 neildo

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Posted 28 September 2020 - 09:00 AM

Forgot to mention that it’s also rather futile to try to push the Firstscope past the 75x magnification that you get with the included 4mm EP. You can maybe go as high as 100x but the results will not change what you can really see. This scope is good for viewing the moon. You can see the moons of Jupiter but Jupiter will just look like a bright ball. Saturn will look like a star with ears. It wasn’t until I got the Z130 that I really saw the planets with their distinctive features. 
 

Since the space is a limitation from upgrading to a 130mm tabletop, you might consider a 90m tabletop maksutov like an Orion Starmax: https://www.amazon.c...e/dp/B002JO06PO. It’s only 6.5 lbs and will be a nice step up from the Firstscope for planetary viewing. 


Edited by neildo, 28 September 2020 - 09:01 AM.


#17 Sky Muse

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Posted 28 September 2020 - 10:29 PM

Forgot to mention that it’s also rather futile to try to push the Firstscope past the 75x magnification that you get with the included 4mm EP. You can maybe go as high as 100x but the results will not change what you can really see. This scope is good for viewing the moon. You can see the moons of Jupiter but Jupiter will just look like a bright ball. Saturn will look like a star with ears. It wasn’t until I got the Z130 that I really saw the planets with their distinctive features. 
 

Since the space is a limitation from upgrading to a 130mm tabletop, you might consider a 90m tabletop maksutov like an Orion Starmax: https://www.amazon.c...e/dp/B002JO06PO. It’s only 6.5 lbs and will be a nice step up from the Firstscope for planetary viewing. 

With the 130mm f/5 trained on Jupiter, at what power were you observing to where you were able to the discern the planet's features, and which features exactly?



#18 neildo

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Posted 28 September 2020 - 11:27 PM

With the 130mm f/5 trained on Jupiter, at what power were you observing to where you were able to the discern the planet's features, and which features exactly?

Under best atmospheric conditions I am between 3.5mm and 5mm so 130x to 185x. I can see the Cassini division and very subtle lines in the rings and slight banding on Saturn itself. On Jupiter, I can see 2 distinct red bands, and on really good nights I can see slight streaks in the red bands. 4 moons of Jupiter are distinct but haven't caught a moon in transit across the face though I haven't really tried. When Mars is high, I can see a polar ice cap as a bright white dot and I can see a large brownish area on the very orange face of Mars.

 

Overall the thing I wish I got more of is contrast like you see in the pictures. The planets are plenty bright even at 180x, they just dont have great contrast as I push the magnification limits.


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#19 Sky Muse

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Posted 29 September 2020 - 04:41 AM

Under best atmospheric conditions I am between 3.5mm and 5mm so 130x to 185x. I can see the Cassini division and very subtle lines in the rings and slight banding on Saturn itself. On Jupiter, I can see 2 distinct red bands, and on really good nights I can see slight streaks in the red bands. 4 moons of Jupiter are distinct but haven't caught a moon in transit across the face though I haven't really tried. When Mars is high, I can see a polar ice cap as a bright white dot and I can see a large brownish area on the very orange face of Mars.

 

Overall the thing I wish I got more of is contrast like you see in the pictures. The planets are plenty bright even at 180x, they just dont have great contrast as I push the magnification limits.

Congratulations upon that sighting of Mars.

 

Your highest attempt, at 185x, that's somewhat above what I had used with my 150mm f/5 one night, whilst observing Jupiter, and with a simulated 4.3mm(12mm + 2,8x barlow = 174x).  But the planet was still a white orb, washed-out.  I then used a variable-polariser to dim the image a bit, and enough to where nothing could have prepared me for what I then saw: the festoons and whorls within the equatorial-bands; like colours of paint being swirled about with a toothpick, and nigh tack-sharp.  But that was during a few moments when the atmosphere had steadied; otherwise, the bands are blank.  Brightness is not always our friend.

 

For the lack of a better analogy, the event is as the early bird in catching the worm.  In other words, great patience is required, and in waiting for those most special moments in time.  If you look away from the eyepiece, even for a few seconds, you will have missed it.  But then it appears yet again, teasingly, temptingly.  The atmosphere can be cruel in that.

 

For maximum contrast, blacken and flock the telescope's interior.  There are only two things inside a Newtonian that are to reflect, at all, even in the slightest: the two mirrors.  All else must be dead to light, as this...

 

focusser3b.jpg

 

I had to brighten that image considerably afterwards.  During the taking of it, the camera balked, and could not focus upon it, to look upon it even.

 

Then, for the sharpest images possible, learn to love, yea, the process of collimation.


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#20 MoonFrog

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Posted 29 September 2020 - 04:53 AM

What wondeful replies I have gotten from this thread 😊
Many thabks to all that have helped out here I’m aware that this budget bit of kit has limits and I’m well aware of them the ideal scenario would be a larger apeture or a maksutov I totally agree but I will co tongue on my quest of getting some pleasing results out of this basic scope all comments have been useful both the initial and later replies and I wnat to thank you all for your time for this I will be doing a comparison between how this came out of the box and What I have ended up with so that others may follow this trail should they wish to at their own pace again Thabkyou so much
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#21 RobertMaples

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Posted 30 September 2020 - 09:46 AM

Forgot to mention that it’s also rather futile to try to push the Firstscope past the 75x magnification that you get with the included 4mm EP. You can maybe go as high as 100x but the results will not change what you can really see. This scope is good for viewing the moon. You can see the moons of Jupiter but Jupiter will just look like a bright ball. Saturn will look like a star with ears...

I've compared 100x to 75x with mine and the difference is noticeable.  At 75x, I can see a hint of two cloud bands on Jupiter, but at 100x, they are much more noticeable.  I can also more clearly see that there is a gap between Saturn and its rings.

 

Hey buddy thanks for the reply I have a firstscope with spherical mirror it’s a 300x76 model the Barlow was junk I have ordered a celestron one now which should be far superior in every way should be here tommorow hopefully and will find out

The Celestron barlow should work because it's probably a similar design to the Orion shorty, but if not, again, the Orion one definitely does.  I suggest getting a 6mm Plossl eyepiece (https://www.astronom...l.html?___SID=U).  The 4mm with a barlow will give you 150x, which seems to be a bit much for that scope.  The 6mm with a barlow would give you 100x, significantly more than the 75x you get with the 4mm alone, but still seems to be quite useable with that scope.

 

If you have not collimated it, do.  You cannot collimate the main mirror (at least not easily), but you can collimate the secondary and it can make a big difference.


Edited by RobertMaples, 30 September 2020 - 09:46 AM.



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