Fast 10" Dob - To Barlow or Not to Barlow... ? HELP!

[JS81North]

Hi all!

I have inherited a 10" f4.7 Skywatcher 250 Flex-tube Dob with the kit lenses of 10 and 25mm.

I gather these lenses aren't brilliant so I'd like to upgrade the high power one for improved planet & moon observing.

However, I only have a small budget of around £50 - 60.

On the high power, Ian at the awesome FLO recommended a Baader Classic Plossl.

My conundrum is 10mm with barlow or 6mm without? Ian says he prefers not to use a barlow as it adds extra glass, but so many people seem to have them!

I live in North Devon and (when it's not raining) have a Bortle Class 4 sky. I mostly wear contact lenses and occasionally glasses.

I would love your thoughts, advice or suggestions!

Many thanks,

John

 

Edited June 4, 2020 by JS81North

[maw lod qan]

First, welcome to an incredible forum.

I'm not the expert so many here are, but what I've found is that for the money a Barlow is a good addition because it allows you to almost double your eyepiece collection without spending a lot of money

Just remember, when you do buy more, take in account what you already have and what the Barlow gives you. If you have a 20mm, and a Barlow, dont buy a 10mm.

[JS81North]

1 hour ago, maw lod qan said:

First, welcome to an incredible forum.

I'm not the expert so many here are, but what I've found is that for the money a Barlow is a good addition because it allows you to almost double your eyepiece collection without spending a lot of money

Just remember, when you do buy more, take in account what you already have and what the Barlow gives you. If you have a 20mm, and a Barlow, dont buy a 10mm.

Thank you Sir for your welcome and your thoughts!

[Shaun VS]

From what I understand, at the moment you don’t own a Barlow. I would therefore suggest that you try out the eyepieces you have. A Barlow will not improve the eyepiece that you use, but if you buy a decent one it will double the magnifications of both eyepieces and be useful with any additional eyepieces you buy in the future. If however you are not happy with the eyepieces, in particular the 10mm then I would take the advice from flo. For what it’s worth I never use a Barlow on my 10” f4.

[Ricochet]

The problem with the 6mm Ortho is that it only has 5mm eye relief (the distance between the lens and your eye). The 10mm Ortho, plus a 2x barlow will be much more comfortable to use. If you buy a good barlow the effect on the views is negligible. I do realise this requires buying two things instead of one and exceeds your budget. 

Alternatively, if you prefer comfort over the high quality views of the BCO line, you could buy a BST Starguider (5/8/12mm). These are not quite as good optically, but are great all round eyepieces, with a 60° field and 16mm eye relief across the range. 

[NGC 1502]

The much maligned Barlow gets a lot of stick.  But a good quality Barlow can actually improve the performance of an eyepiece.   A low or mid power inexpensive eyepiece will probably have poor performance away from the centre of the field of view in an F4.7 reflector, but adding a good Barlow will often improve the eyepiece performance especially away from the centre of field.

But a high power eyepiece when Barlowed may easily give a too high magnification and therefore a fuzzy view.  It is of course your decision whether to spend out on a good Barlow or use the same money for better eyepieces......

The performance of your 10” reflector will be compromised by the stock eyepieces, but as already suggested, perhaps have a few sessions and see how you get on.  You don’t have to spend top dollar for better eyepieces, there’s mid quality kit available that does a great job.

Ed.

 

 

[Alan White]

Either BCO is a no go with glasses, the eye relief is too shallow.
They would be fine with contacts.
The 10mm is more comfortable to use, I felt like my eyeball was welded to the 6mm's eyelens.

As Ed says above, a barlow is a good option as is a mid priced eyepiece.
 

[JS81North]

On 04/06/2020 at 16:37, Shaun VS said:

From what I understand, at the moment you don’t own a Barlow. I would therefore suggest that you try out the eyepieces you have. A Barlow will not improve the eyepiece that you use, but if you buy a decent one it will double the magnifications of both eyepieces and be useful with any additional eyepieces you buy in the future. If however you are not happy with the eyepieces, in particular the 10mm then I would take the advice from flo. For what it’s worth I never use a Barlow on my 10” f4.

Thank you Shaun! Intrigued what eyepieces you do have and how you find them? Thanks again!

[JS81North]

On 04/06/2020 at 18:33, Ricochet said:

The problem with the 6mm Ortho is that it only has 5mm eye relief (the distance between the lens and your eye). The 10mm Ortho, plus a 2x barlow will be much more comfortable to use. If you buy a good barlow the effect on the views is negligible. I do realise this requires buying two things instead of one and exceeds your budget. 

Alternatively, if you prefer comfort over the high quality views of the BCO line, you could buy a BST Starguider (5/8/12mm). These are not quite as good optically, but are great all round eyepieces, with a 60° field and 16mm eye relief across the range. 

Thanks Ricochet! I mainly wear lenses so in my novice research the shallow eye relief doesn't worry me too much. My aim is to get the highest quality views within my small budget! I may have to save for a decent barlow!

[JS81North]

On 04/06/2020 at 19:45, Alan White said:

Either BCO is a no go with glasses, the eye relief is too shallow.
They would be fine with contacts.
The 10mm is more comfortable to use, I felt like my eyeball was welded to the 6mm's eyelens.

As Ed says above, a barlow is a good option as is a mid priced eyepiece.
 

Ah gosh, if you've tried the 6mm may I ask how you found it optically? Compared to the 10mm if you don't mind me asking?! Seems the barlow has strong support! Thanks again!

 

[JS81North]

On 04/06/2020 at 19:37, NGC 1502 said:

The much maligned Barlow gets a lot of stick.  But a good quality Barlow can actually improve the performance of an eyepiece.   A low or mid power inexpensive eyepiece will probably have poor performance away from the centre of the field of view in an F4.7 reflector, but adding a good Barlow will often improve the eyepiece performance especially away from the centre of field.

But a high power eyepiece when Barlowed may easily give a too high magnification and therefore a fuzzy view.  It is of course your decision whether to spend out on a good Barlow or use the same money for better eyepieces......

The performance of your 10” reflector will be compromised by the stock eyepieces, but as already suggested, perhaps have a few sessions and see how you get on.  You don’t have to spend top dollar for better eyepieces, there’s mid quality kit available that does a great job.

Ed.

 

 

Thanks so much Ed, really appreciate your thoughts. I wonder whether a decent barlow would help improve a 10mm BCO?! Johh

[Ricochet]

11 hours ago, JS81North said:

I mainly wear lenses

I assume you mean contact lenses. If you are using glasses instead of contact lenses then the need to wear them while observing depends on the amount of astigmatism in your observing eye. See the following chart:

Astigmatism is given on your glasses/contact lens prescription as the cylinder/CYL value.

Exit pupil is eyepiece focal length / telescope focal ratio.

11 hours ago, JS81North said:

My aim is to get the highest quality views within my small budget

In this case, the BCOs are the way to go.

Edited June 6, 2020 by Ricochet
Typo

[John]

BGO = Baader Genuine Ortho = out of production for some years now. Really superb quality if you can get hold of one.

BCO = Baader Classic Ortho = in production at just under £50 each. Focal lengths available are 6mm, 10mm and 18mm. The 10 and 18mm are really good eyepieces and, IMHO still probably the best in terms of pure optical quality that you can get for £50. The 6mm is not quite as good as the 10mm and 18mm but still a comptant 6mm eyepiece.

The Baader Classic Orthos work very well with the Baader Q-Turret 2.25x barlow lens which can also give 1.3x amplification if the optical element alone is used in the 1.25 inch barrels of the Orthos.

All the above come with the standard ortho characteristics of eye relief that is around 80% of the focal length of the eyepiece. The Baader Classic Orthos have a slightly wider apparent field than the Baader Genuine Orthos (50 degrees vs 42 degrees) but the outer 5% or so of the Classic's field is what I call "framing field" and not quite as well corrected as the rest of the view. I believe this was a deliberated design decision by Baader. The eye lenses of the Baader Classic Orthos are slightly larger and easier to find in the dark than the Baader Genuine Orthos.

The above includes the Baader Classic 32mm which is a plossl rather than an ortho design.

 

[Ricochet]

6 minutes ago, John said:

BGO = Baader Genuine Ortho = out of production for some years now. Really superb quality if you can get hold of one.

BCO = Baader Classic Ortho = in production at just under £50 each. Focal lengths available are 6mm, 10mm and 18mm. The 10 and 18mm are really good eyepieces and, IMHO still probably the best in terms of pure optical quality that you can get for £50. The 6mm is not quite as good as the 10mm and 18mm but still a comptant 6mm eyepiece.

Cheers John, I meant BCO, I even thought that's what I'd typed.

[JS81North]

25 minutes ago, John said:

BGO = Baader Genuine Ortho = out of production for some years now. Really superb quality if you can get hold of one.

BCO = Baader Classic Ortho = in production at just under £50 each. Focal lengths available are 6mm, 10mm and 18mm. The 10 and 18mm are really good eyepieces and, IMHO still probably the best in terms of pure optical quality that you can get for £50. The 6mm is not quite as good as the 10mm and 18mm but still a comptant 6mm eyepiece.

The Baader Classic Orthos work very well with the Baader Q-Turret 2.25x barlow lens which can also give 1.3x amplification if the optical element alone is used in the 1.25 inch barrels of the Orthos.

All the above come with the standard ortho characteristics of eye relief that is around 80% of the focal length of the eyepiece. The Baader Classic Orthos have a slightly wider apparent field than the Baader Genuine Orthos (50 degrees vs 42 degrees) but the outer 5% or so of the Classic's field is what I call "framing field" and not quite as well corrected as the rest of the view. I believe this was a deliberated design decision by Baader. The eye lenses of the Baader Classic Orthos are slightly larger and easier to find in the dark than the Baader Genuine Orthos.

The above includes the Baader Classic 32mm which is a plossl rather than an ortho design.

 

Thanks so much John! I’ve devoured a lot of what you’ve written here etc! 
 

Excellent to hear you think 10mm slightly better than 6mm. If I may ask your opinion on two smaller points? Firstly would say the 10mm plus 2.25 Barlow would usually outperform the 6 on its own?

Second, good to know the Baader Barlow is decent. Would something like a TV 2x Barlow be 3 time better (it’s 3 times the price at FLO)?

 Huge thanks again!

[John]

The 10mm plus the 2.25x barlow in standard form would create a virtual 4.44mm eyepiece so quite a lot more magnification than a 6mm - 270x vs 200x. Seeing conditons and target would come into play more than optical differences I think.

The barlow + 10mm combination would deliver more eye relief than the 6mm on it's own. Barlow lenses lengthen eye relief a little and the 10mm ortho already has longer eye relief than the 6mm of course.

The Tele Vue 2x barlow is excellent but it's been a long time since I owned one. I would guess that the performance is similar in quality to the Baader barlow but the Tele Vue is better built.

Nothing is ever 3x as good as anything that costs 3x less. The performance differences are incremental and get smaller as the quality / cost increases. The step between the stock eyepieces and the next step up (eg: £50 eyepieces) is the largest (even then not 3x whatever that means !) and then improvements get smaller from there.

If you look at the eyepiece section you will see that people are still happy to spend a lot of money on these small gains though 

[cletrac1922]

John

First of all welcome from Land Down Under

I have exactly the same scope

For the moon I use a 25mm eyepiece

When out doing presentations with my club K-7 primary schools, cubs and joeys, scout groups for Jupiter, Saturn and other deep sky objects use either a 15mm or 17mm wide-angle eyepiece, which gives good eye relief

Very rarely ever use barlow, even though I have a 2X

John

 

[JS81North]

1 hour ago, John said:

The 10mm plus the 2.25x barlow in standard form would create a virtual 4.44mm eyepiece so quite a lot more magnification than a 6mm - 270x vs 200x. Seeing conditons and target would come into play more than optical differences I think.

The barlow + 10mm combination would deliver more eye relief than the 6mm on it's own. Barlow lenses lengthen eye relief a little and the 10mm ortho already has longer eye relief than the 6mm of course.

The Tele Vue 2x barlow is excellent but it's been a long time since I owned one. I would guess that the performance is similar in quality to the Baader barlow but the Tele Vue is better built.

Nothing is ever 3x as good as anything that costs 3x less. The performance differences are incremental and get smaller as the quality / cost increases. The step between the stock eyepieces and the next step up (eg: £50 eyepieces) is the largest (even then not 3x whatever that means !) and then improvements get smaller from there.

If you look at the eyepiece section you will see that people are still happy to spend a lot of money on these small gains though 

Amazing food for thought and so helpful, thank you! I see you're in North Somerset and I'm in North Devon we perhaps have comparable seeing! Thanks again, John

[JS81North]

1 hour ago, cletrac1922 said:

John

First of all welcome from Land Down Under

I have exactly the same scope

For the moon I use a 25mm eyepiece

When out doing presentations with my club K-7 primary schools, cubs and joeys, scout groups for Jupiter, Saturn and other deep sky objects use either a 15mm or 17mm wide-angle eyepiece, which gives good eye relief

Very rarely ever use barlow, even though I have a 2X

John

 

Thanks John! Especially from such a cool location! Almost as cool as Devon 🙂

The most valuable thing I'm  learning (thankfully before spending big money) is that chasing magnification isn't where the jackpot's at!

You get enough magnification from a 17mm for the planets?

Thanks again!

John

 

[John]

With a 10 inch scope you will find magnifications between 150x - 250x work well on the moon and planets as long as the seeing conditions are reasonable.

So eyepiece focal lengths in the range 8mm to 5mm will be useful. Using a good barlow is certainly one way to achieve that.

Maybe John in Australia is referring to keeping the magnifications more modest at outreach events, which does make some sense because higher powers can be tricky to use for folks who have never observed with a scope.

 

 

[cletrac1922]

On 06/06/2020 at 21:42, JS81North said:

Thanks John! Especially from such a cool location! Almost as cool as Devon 🙂

The most valuable thing I'm  learning (thankfully before spending big money) is that chasing magnification isn't where the jackpot's at!

You get enough magnification from a 17mm for the planets?

Thanks again!

John

 

John

Yes with either 15mm or 17mm

Couple of other things

Get yourself a right angle finderscope

Saves laying on damp ground, when trying to observe things directly overhead

As the base of the Dob is also chipboard construction, I use a small waterproof ground sheet under the base to protect

John

 

 

[markse68]

On 06/06/2020 at 09:56, John said:

The 6mm is not quite as good as the 10mm and 18mm but still a comptant 6mm eyepiece.

Hi John, I recently picked up a 6mm BCO and reading up about it found your early review. I noticed your image of the inside of the barrel and it’s quite different to mine. Mine has a long thin central micro ridged tube containing the optics and field stop but yours looked to be mounted flush. Looks like an improved design- it must surely help with eliminating reflections from the glossy anodised barrel interior from getting into the lenses? Sorry if this is already common knowledge- couldn’t find anything about it.

Mark

[HollyHound]

On 17/06/2020 at 12:16, markse68 said:

Hi John, I recently picked up a 6mm BCO and reading up about it found your early review. I noticed your image of the inside of the barrel and it’s quite different to mine. Mine has a long thin central micro ridged tube containing the optics and field stop but yours looked to be mounted flush. Looks like an improved design- it must surely help with eliminating reflections from the glossy anodised barrel interior from getting into the lenses? Sorry if this is already common knowledge- couldn’t find anything about it.

 

Mine has the same design... long thin central tube (not mounted flush)... hopeful it's an improvement 🤞