Minimum eyepice

[Bivo]

Dears,

I have a Refractor Meade with 90mm aperture and 1000mm

At the moment I have an 32mm and 12mm eyepices.

Would be a good choice to buy a 6mm eyepice to see more details of planets?

Based on some searchs I did, 6mm are the minimum size to my telescope 

Edited June 27, 2023 by Bivo

[Franklin]

Yes, 6mm would be about max for your scope but it would need good seeing conditions to be much use, maybe a 9mm or 8mm would be more usable in practical terms. Your scope is an achromat and will show some color aberration at high magnifications so backing off from the max will give better results, though a smaller image scale.

[Carbon Brush]

Hi. Something to add to the good advice from @Franklin.
As you increase magnification, mount stability becomes important.
You haven't said what mount you are using. As a general rule the package supplied mounts are a bit flexible.
How steady is the image with a 12mm eyepiece? It will be twice the perceived wobble with a 6mm eyepiece.
 

[Don Pensack]

12 hours ago, Bivo said:

Dears,

I have a Refractor Meade with 90mm aperture and 1000mm

At the moment I have an 32mm and 12mm eyepieces.

Would be a good choice to buy a 6mm eyepiece to see more details of planets?

Based on some searches I did, 6mm are the minimum size to my telescope 

F/11.1.

Maximum focal length 78mm eyepiece (doesn't exist).

Minimum focal length eyepiece 5.5mm

The vast majority of your observing will be in the 55mm to 11mm range, with the sharpest views with eyepieces of 22-33mm.

But, a decent 90mm does pretty well at 100x, or a 9mm eyepiece.

once you get into the 100-180x range, though, seeing will determine how high you can go.

If well corrected, an f/11.1 doublet in that aperture will not suffer from chromatic aberration, so seeing will be the main problem above 100x.

90mm is aperture-limited when looking at higher powers, but Jupiter and Saturn look fine at around 150x (6mm eyepiece), so I don't think there is necessarily

anything wrong with having that focal length, but buying a 6mm eyepiece that will stay in the case most nights is not economical.

 

So I advise getting a 2X Barlow lens, which would turn the 32mm into a 16mm and the 12mm into a 6mm.

And if it is the type of Barlow (like a Celestron Omni or something like it), that the lens detaches from the Barlow and attaches to the eyepiece, that that Barlow could give you

1.5x with the Barlow's lens threaded directly on the eyepieces (resulting in 21mm and 8mm focal lengths)

2x under the eyepiece in the Barlow's original configuration (resulting in 16mm and 6mm focal lengths)

3x in front of the star diagonal (resulting in 10.7mm and 4mm focal lengths).

Because a simple 2X Barlow lens can effectively double or triple your entire eyepiece collection, it is VERY cost-effective.

And if your star diagonal is threaded for filters on its inserted nosepiece, the Barlow's lens can also be threaded there for roughly a 2.5x magnification, quadrupling your eyepiece collection.

You could have 1x, 1.5x, 2x, 2.5x, and 3x, or 10 magnifications with just 2 eyepieces.

 

For a variety of reasons, you might want to get separate eyepieces at discrete magnifications at some point, but the Barlow lens should give you what you want.

FLO has one for only £27

https://www.firstlightoptics.com/barlow-eyepieces.html

[bosun21]

I am in complete agreement with @Don Pensack regarding the single purchase of a 2x barlow. It gives you such a variety of magnification to choose from at a very reasonable price.

[Mr Spock]

17 hours ago, Bivo said:

At the moment I have an 32mm and 12mm eyepices.

I'd agree that a x2 Barlow would fit those eyepieces well. 32 - 16 - 12 - 6 looks a decent spread.

[bomberbaz]

Love a good barlow in any setup. Such a flexible, simple & low costing bit of kit.

I still have two and always take one out with me on any field trip.

[Bivo]

Thanks Don and other colleagues.

I'll definitely to buy a 2x Barlow Celestron Omni

[Don Pensack]

The Omni Barlow changed from its original, and the lens is now in a housing ever-so-slightly smaller than 1.25".

That might mean they changed the threads on the lens, so be sure to ask if it still threads directly to a 1.25" eyepiece.

FLO sells others that do, in case the Celestron is no longer usable that way.

Of course you could still use it under the eyepiece in its own tube (2x) or in front of the diagonal in its own tube (3x) if you didn't want the other magnifications possible.

Used in front of the diagonal, it usually requires a lot of infocus.  It depends on your scope if that is possible or not.

[Bivo]

Thanks again Don!

Please, could you confirm if its this one in the picture?

[bomberbaz]

That seems expensive although not sure of the actual currency come to think of it, this is the same one 

https://www.firstlightoptics.com/barlow-eyepieces/celestron-2x-universal-125-barlow-old.html

Edited July 2, 2023 by bomberbaz

[Mr Spock]

At current exchange rates R$145.04 is £23.83 

[Bivo]

6 hours ago, bomberbaz said:

That seems expensive although not sure of the actual currency come to think of it, this is the same one 

https://www.firstlightoptics.com/barlow-eyepieces/celestron-2x-universal-125-barlow-old.html

So... Does it wort according Don''s comments?

[bomberbaz]

2 hours ago, Bivo said:

So... Does it wort according Don''s comments?

Oh yes, I have used regularly myself, found the nosepiece very useful for my now sold binoviewers. 

Don's comments around it's versatility are spot on.  A barlow can save you a lot of money by making use of it's versatile nature. 

[Cosmic Geoff]

The pictured Omni looks like mine. I found I could screw the nosepiece onto ZWO cameras.

[Bivo]

Good to kkow Dears!

Thanks a lot!

[Gfamily]

There is a Celestron Barlow that has a T-thread at the top so you can easily attach a camera (mirrorless/DSLR). 

I have to say I'd not known about the ability to re-purpose the nosepiece lens from the Barlow on the ep or on the diagonal, but it makes sense and is something to try. Thanks @Don Pensack

Edited July 6, 2023 by Gfamily

[AstralFields]

No Telescope is complete (truly any telescope) without a 2x Barlow (the one that unscrews and can be made into a 1.5x)

I have the Celestron Omni 2x. Even if I have a 6mm that gives 200x, sometimes I put it for a 300x on very very good conditions.

[bosun21]

I no longer use a barlow as all my eyepieces have a very good eye relief and I don’t like the fact that a 2x barlow doubles this. I find trying to refind the correct eye position an unnecessary inconvenience. Saying this they are great for eyepieces with short or mediocre eye relief. I have settled on a 2x ES extender with a future upgrade to a 2.5x powermate in the pipeline.

[Second Time Around]

28 minutes ago, bosun21 said:

I no longer use a barlow as all my eyepieces have a very good eye relief and I don’t like the fact that a 2x barlow doubles this. 

Author Bill Paolini's tests found that the increase is typically only 20-40%, depending on the focal length of the Barlow, with "shorty" Barlows having a greater increase.

[bosun21]

1 hour ago, Second Time Around said:

Author Bill Paolini's tests found that the increase is typically only 20-40%, depending on the focal length of the Barlow, with "shorty" Barlows having a greater increase.

My experience is that’s it’s a lot more than 20%. Most modern barlows are of  the short variety. I used to own a longer Vixen barlow which was tack sharp but I foolishly sold it. I try my hardest to reach the desired magnification with just a short focal length eyepiece. (With good eye relief).

Edited July 21, 2023 by bosun21

[Second Time Around]

For further data points, Bill found 20% with a Televue Barlow and an APM 2.7x, 40% with a Klee 2.8x Shorty.

I have the 2.7x APM and several other Barlows:

1.3x/1.6x Omegon GPC

1.5/2x shorty

2.25x Baader Hyperion

I can see some experiments in my future........

Edited August 15, 2023 by Second Time Around

[Louis D]

5 hours ago, bosun21 said:

I used to own a longer Vixen barlow which was tack sharp but I foolishly sold it.

Funny you should mention a long, Japanese made Barlow.  The best affordable Barlow I've owned and used is a 1990s vintage Orion Deluxe 2x (Japan).  It's about 6 inches long, baffled, and has a full aperture negative lens in a very thin barrel.

In direct comparisons, I found it to be sharper and has less scatter than my 1999 vintage TV Barlow 2x, 1990s vintage Meade 140 APO 2x Barlow (Japan), and 1990s vintage Parks GS 2X Shorty Barlow (Japan).  The latter is the same as the Celestron Ultima Shorty and Orion Shorty-Plus.  The problem is, it's only usable in Newtonian telescopes due to the required insertion distance.  I suppose it could be used in a Mak or SCT, but I've never had the inclination to double their already long focal lengths.  In my refractors, I prefer the Parks Barlow because I never have trouble reaching focus, and it is basically as sharp and contrasty as the Meade and TV Barlows without causing exit pupil issues.

[Bivo]

Hi Dears!

Recently during my searchs for Celestron Omini 2x Barlow, I found the zoom eye piece below.

Does anybody have any experience with it to make a comment?

 

Edited August 11, 2023 by Bivo

[Jim L]

I have several of those eyepieces (SV135), and they’re excellent. Here are two very good reviews of the eyepiece from Ernest’s website, Astro Talks,

https://astro--talks-ru.translate.goog/forum/viewtopic.php?t=4542&_x_tr_sl=ru&_x_tr_tl=en&_x_tr_hl=en-US&_x_tr_pto=wapp&_x_tr_sch=http
 

https://astro--talks-ru.translate.goog/forum/viewtopic.php?t=4585&_x_tr_sl=ru&_x_tr_tl=en&_x_tr_hl=en-US&_x_tr_pto=wapp&_x_tr_sch=http
 

They’re my most often used eyepiece; light, versatile, decent eye relief, and sharp.