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Am I right?

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#1 moonman60

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Posted 06 December 2021 - 11:35 AM

I was looking at adding a 9mm eyepiece. I did some figuring. I have a 18mm eyepiece that when I add my 2x Barlow, equals 166.66 power. The 9mm equals 166.66 power and adding a 2x Barlow reaches max power for my scope. Thus it would be foolish to buy the 9mm eyepiece. Am I right?
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#2 Dobs O Fun

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Posted 06 December 2021 - 11:45 AM

Not necessarily. You may not like using a barlow. However if you are on a budget you could opt for buying another FL EP and still have 9mm for your barlow.
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#3 SeattleScott

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Posted 06 December 2021 - 11:49 AM

Your 6” SCT should be able to hit 200-300x magnification in good seeing. If you bought something around 9-12mm you could max out the magnification on stable nights by barlowing the eyepiece.

 

Also there is the convenience aspect. Personally I don’t want to mess with swapping a barlow in and out for a commonly used magnification. I will mess with a barlow on rare nights of steady seeing rather than buying another $250 eyepiece.

 

 I would certainly want the ability to go higher than 166x. You might look for a 12mm. With the barlow, that would give you 18, 12, 9 and 6. A nice spread and enough power to do justice to your scope during good seeing, if not quite max it out.

 

scott


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#4 zakry3323

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Posted 06 December 2021 - 12:05 PM

I just don't care for swapping out and adding the barlow- most of the time for me that means rebalancing, which also means I'll probably lose my target at higher magnifications anyways. I'd rather have an inexpensive set that's just about parfocal and just about weighs the same in 1.25" format. I find myself using my Astro-tech Paradigms more frequently than some of my more expensive eyepieces for this reason. 


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#5 Voyageur

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Posted 06 December 2021 - 12:08 PM

What is the 18mm eyepiece? Do you like it? How about the Barlow? Is it of good quality? Are you happy with the field of view and eye relief when you use the two in combination?

 

Do you find yourself using that combination often? If you use it often, but are less than satisfied with the view, maybe a better quality 9mm eyepiece would be a good investment. Which one are you thinking of?
 

If you don’t use that combination often, because it’s too much power for most nights in your viewing conditions, maybe a different eyepiece would be a better choice, or maybe more than one. Did another eyepiece come with your scope? If so, I’m guessing maybe 25mm. You should get at least one eyepiece in between 9mm and 25mm!

 

 If you give us a budget, people can make specific suggestions! 


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#6 Mike Allen

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Posted 06 December 2021 - 01:44 PM

If you don’t mind using the 2X barlow in combination with your 18mm eyepiece, then purchasing a 9mm eyepiece would be redundant.  Some observers appreciate the benefits that a barlow brings to the table, others don’t.

 

If I was in your position, I would purchase an eyepiece around 12mm, which would give you 125 and 250x.  I would get an exit pupil of 0.6mm with this eyepiece/barlow combination.  My opinion is that this is the smallest exit pupil I can tolerate without making the image too faint.


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#7 Exnihilo

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Posted 06 December 2021 - 02:14 PM

I just don't care for swapping out and adding the barlow- most of the time for me that means rebalancing, which also means I'll probably lose my target at higher magnifications anyways. I'd rather have an inexpensive set that's just about parfocal and just about weighs the same in 1.25" format. I find myself using my Astro-tech Paradigms more frequently than some of my more expensive eyepieces for this reason. 

Yeah, I’m in the same camp, even though I have a perfectly good Barlow, I almost never use it.  Too much weight differential.  


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#8 helpwanted

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Posted 06 December 2021 - 02:55 PM

Also the quality of the eyepieces & barlow matter. If using a high quality eyepiece in a cheap barlow, you loose the quality. Your view is only as good as the weakest part of the optical train. 


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#9 kongqk

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Posted 06 December 2021 - 03:15 PM

Good suggestions so far. Depending on the quality of the eyepiece and barlow, if you have a good quality barlow and eyepiec, and don't mind swap in and out of the barlow, go for it. Some of the budget barlows degrades the view which is better to have a fixed length eyepiece. Also, some eyepieces and barlows have the parfocal features, which is really a nice feature that you don't need to re-adjust the focuser once you put in/out of the barlow, such as the TV delos and the TV 2x barlow. 


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#10 moonman60

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Posted 06 December 2021 - 03:22 PM

I have a 12mm, 18mm, 25mm, and 2x Barlow. All are Celestron X Cell LX. I've tried the Barlow with the 18mm and 12mm. I didn't like it with the 12mm. I like the field of view of the 25mm.



#11 zakry3323

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Posted 06 December 2021 - 04:01 PM

I have a 12mm, 18mm, 25mm, and 2x Barlow. All are Celestron X Cell LX. I've tried the Barlow with the 18mm and 12mm. I didn't like it with the 12mm. I like the field of view of the 25mm.

Your 12mm with a 2x Barlow would give you around 250x. What is it about the view that you don't like? We share a lot of the same weather and 250x around here is usually only possible a couple times a year- the seeing just stinks, generally. Personally 120-160x ish is my bread and butter.


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#12 moonman60

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Posted 06 December 2021 - 05:21 PM

The view seemed to lack clarity as I increased power by adding the Barlow to the 12mm. You are right about the weather and that was probably a contributing factor. That being said, Jupiter still looked cool and I could make out the bands on the surface. We've been sitting out back all this summer with my binoculars (10x50) and a knock at the door brought me my birthday present that being the 6SE. Clear sky's all summer and now that I have a good telescope, nothing but clouds. Truth be told, I should wait and see with better conditions.


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#13 zakry3323

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Posted 06 December 2021 - 05:29 PM

The view seemed to lack clarity as I increased power by adding the Barlow to the 12mm. You are right about the weather and that was probably a contributing factor. That being said, Jupiter still looked cool and I could make out the bands on the surface. We've been sitting out back all this summer with my binoculars (10x50) and a knock at the door brought me my birthday present that being the 6SE. Clear sky's all summer and now that I have a good telescope, nothing but clouds. Truth be told, I should wait and see with better conditions.

Ahh, so you're the one that brought the curse down upon us :) The cloud gods HATE new equipment :)


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#14 Jon Isaacs

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Posted 07 December 2021 - 08:23 AM

Also the quality of the eyepieces & barlow matter. If using a high quality eyepiece in a cheap barlow, you loose the quality. Your view is only as good as the weakest part of the optical train. 

 

I use Barlows frequently. The Barlow is rarely the weakest link in the optical train.

 

"Cheap Barlows" are not recommended but a good solid 1.25 inch 2x Barlow can be purchased for $30-$40. 

 

https://www.astronom...-eyepieces.html

 

I recently initiated a thread about my experiences using the 2X, 2 inch $60 GSO Barlow in my faster Dobs using a Paracorr 2 and the 13mm, 10 mm and 8 mm TeleVue Ethos eyepieces.

 

It works very well. 

 

Jon



#15 Jon Isaacs

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Posted 07 December 2021 - 08:27 AM

The view seemed to lack clarity as I increased power by adding the Barlow to the 12mm. You are right about the weather and that was probably a contributing factor. That being said, Jupiter still looked cool and I could make out the bands on the surface. We've been sitting out back all this summer with my binoculars (10x50) and a knock at the door brought me my birthday present that being the 6SE. Clear sky's all summer and now that I have a good telescope, nothing but clouds. Truth be told, I should wait and see with better conditions.

 

Increasing the power from 125x to 250x can very often result in a lack of clarity. That's not the the fault of the Barlow, that would have happened using a 6 mm eyepiece...

 

Jon


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#16 eric_zeiner

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Posted 10 December 2021 - 10:26 AM

I built my EP collection so I would not have to use a Barlow.  I have enough f/l range so I can get close to what I am looking for in terms of magnification.  My thoughts on Barlow's are this:. Too much fiddling around in the dark, two or more elements additional for light to have to travel through, and then, as mentioned before, too much weight differential.  I have one, though not a good one, I don't think I have ever used it.

 

As a final thought, it took me several years to build my EP collection as it stands.  Most of them are used but they perform very well.  Take your time and assess what it is you are trying to do then go from there.


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#17 barbie

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Posted 10 December 2021 - 12:22 PM

I use my $50.00 Meade Barlow quite often in my faster apos to achieve high magnification on the moon & planets but relatively infrequently in my 80mm f15 achromat because of its inherently longer focal length. A decent quality Barlow is a very useful accessory for me to have on hand. I have a 2x Barlow in both of my eyepiece cases for that reason.


Edited by barbie, 10 December 2021 - 12:31 PM.

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#18 PKDfan

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Posted 10 December 2021 - 01:10 PM

My eyepieces have been very carefully chosen to be at ideal exit pupils and at powers I can frequently use.

My 2x 2" Barlow is used to achieve very high powers such as using my 6.5mm(6.7) Morpheus in tandem to get to a 3.35mm effective eyepiece to view Mars, which to this date is the only time I have used a very high power to excellent effect.

The other crucial use application is for a very stable base for my Baader Mk.IV zoom as a 80x-220x lunar exploration tool.

These are critical applications for me, when the use of a good Barlow is utterly invaluable and is the only solution to be found.


I AM considering wasting perfectly good money on a single focal length for Mars at 3.3mm but thats a step too far right now. Though with Jupiter rising and at very high inclination in a couple of years a companion for my 4mm T.O.E. might become necessary.



Clear skies & Good seeing
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#19 MitchAlsup

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Posted 10 December 2021 - 09:10 PM

I was looking at adding a 9mm eyepiece. I did some figuring. I have a 18mm eyepiece that when I add my 2x Barlow, equals 166.66 power. The 9mm equals 166.66 power and adding a 2x Barlow reaches max power for my scope. Thus it would be foolish to buy the 9mm eyepiece. Am I right?

If you only "look" t magnification (or equivalent exit pupil) then you are correct.

 

If you look at FoV, there is no 18mm EP with a FoV as big as 9ES120.

If you look at lack of scatter there is no EP as free from scatter as monocentrics.

.

.

.



#20 luxo II

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Posted 11 December 2021 - 04:16 AM

Your 6” SCT should be able to hit 200-300x magnification in good seeing.

Technically possible, but improbable. 100-200 more likely; IMHO the optimum for a 150mm SCT is about 150-180X.


Edited by luxo II, 11 December 2021 - 05:12 AM.

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#21 Jon Isaacs

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Posted 11 December 2021 - 05:26 AM

I built my EP collection so I would not have to use a Barlow.  I have enough f/l range so I can get close to what I am looking for in terms of magnification.  My thoughts on Barlow's are this:. Too much fiddling around in the dark, two or more elements additional for light to have to travel through, and then, as mentioned before, too much weight differential.  I have one, though not a good one, I don't think I have ever used it.

 

As a final thought, it took me several years to build my EP collection as it stands.  Most of them are used but they perform very well.  Take your time and assess what it is you are trying to do then go from there.

 

I do not understand the weight concern.. A 1.25 inch 2X GSO Barlow weighs 2.6 ounces, a 1.25 inch 2X TeleVue Barlow weighs 4.6 ounces.  From my point of view, a few ounces causes balance problems, there are bigger problems with the mount.

 

As far as fiddling around in the dark... once my eyes are dark adapted, it's straightforward, everything has it's place, it only takes a few seconds.  

 

The usefulness of a Barlow depends in part on the seeing as well as the focal ratio of the scope.  In an F/5 scope under excellent seeing, effective focal lengths under 3 mm can be required for things like very close doubles.  A Barlow is an effective tool for using high quality wide field eyepieces at such focal lengths and magnifications.  

 

I Barlow my 5mm and 3.5 mm type 6 Nagler quite frequently.  TeleVue doesn't make a 1.7mm eyepiece.  

 

Another neat thing about Barlows is that they can be used as zooms.  If you pull the eyepiece out 1/2 inch from that 2x Televue it's now a 2.17x Barlow, pull it out an 1 inch if you can and you now have a 2.34x Barlow.

 

Jon



#22 SeattleScott

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Posted 11 December 2021 - 06:17 AM

Technically possible, but improbable. 100-200 more likely; IMHO the optimum for a 150mm SCT is about 150-180X.

Geez, I’m glad I opted for a 6” Mak instead of the 6” SCT.

Scott
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#23 Jon Isaacs

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Posted 11 December 2021 - 06:57 AM

Geez, I’m glad I opted for a 6” Mak instead of the 6” SCT.

Scott

Don't believe everything you read.

 

Jon


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#24 moonman60

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Posted 11 December 2021 - 11:34 AM

A whole nother discussion would be the possibility of adding one of those really expensive ( Tel-Vue ) eyepieces to the herd. Expensive being subjective as I thought $90 eyepieces expensive. $300 for an eyepiece, well that's a whole nother conundrum.

#25 SeattleScott

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Posted 11 December 2021 - 12:08 PM

On a 6” SCT I would use eyepieces shorter than 18mm pretty regularly so I would want a fixed focal length. Now once you get down to 5-6mm you need pretty good seeing, so maybe just rely on a barlow at that point since it wouldn’t be something you could use everyday.

The biggest difference with the truly expensive eyepieces versus $90 (which is reportedly below median price for a new eyepiece, so technically on the affordable side) is wider AFOV and/or long ER. Especially with a SCT you don’t need to spend $300 for good edge correction. But for $90 it is hard to exceed 60-70 AFOV. For $300 you can get 80-100 AFOV. Or maybe 76 AFOV with long eye relief.

Scott


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