barlow and planetary observing

[bambuko]

As we all know slow Newts are better for planetary observing, and Barlow has an effect of extending effective focal length of the Newt, so my question is:

For my f/5 Newt when observing planets am I better off using Barlow and (for example) 16mm eyepiece or directly 8mm eyepiece (without Barlow).

[ronin]

Why are slow newtonians better for planetary viewing?

I know an f/3 scope that was used to detect planets around other stars.

[rory]

I never knew newts were the choice for planetary viewing ? Is that to do with c/a.

I thought refractors were more favourable. ?

[bambuko]

High contrast performance.

It is a matter of an opinion (and YMMV) of course, but typically "planet killers" are slow f scopes.

[bambuko]

I never knew newts were the choice for planetary viewing ? Is that to do with c/a.

I thought refractors were more favourable. ?

You possibly are right? but if we exclude refractors ve reflectors question and stick to my question (about the use of Barlow to extend effective focal length) and the effect it has please?

[andyman]

Have done with it and get a dob they kill everything

[bambuko]

Have done with it and get a dob they kill everything

Isn't there no place safe from dob fanatics

[andyman]

Isn't there no place safe from dob fanatics

you no what the dob mobs like 

[John]

Setting aside the issue of the focal ratio, a good quality barlow can work very well on the planets and can give you high power views without the need for short focal length eyepieces which can have tight eye relief and be less comfortable to use. 

Adding a barlow does add at least two extra glass elements though so they need to be of excellent optical quality to ensure that they don't bring any unwanted artifacts / aberrations to the view.

A dob is just a newtonian mounted a different way   

[andyman]

As john says if you do decide on a barlow invest in a quality one

And yes a newt is a dob silly me 

[knobby]

As john says if you do decide on a barlow invest in a quality one

And yes a newt is a dob silly me

Imagine if it has been John Dickinson that invented that mount :-)

[bambuko]

And yes a newt is a dob silly me 

Wrong way round...

dob is always a newt, but newt is only a dob when mounted on dobsonian mount

[andyman]

I get the drift coats already on 

[rory]

There's a quality Barlow on astro b&s right now . @£45 an Orion shorty plus.

As john mentions , your putting more glass in front of your eyes. , so good quality is the order of the day.

Although you ask weather your better off with an eyepiece or Barlow . I'd say it depends the eyepiece you go for and what your like with tight eye relief ? As you know it's well documented ortho's perform as good as anything but with tight eye relief at higher magnification , same with plossls. But other eyepieces are available that give better eye relief by design .

Of course an advantage of a Barlow is the fact that a set of three or four eyepieces becomes effectively a set of six or eight focal lengths , if you plan the spread.

[Charic]

bambuko..........If your a purist, you would just stick to a primary lens. If like me and you change your mind, a Barlow can be a good thing. remember its the telescopes focal length that is theoretically adjusted, so Barlowing an 8mm lens, the lens is still 8mm, only working with a higher focal length, therefore increasing magnification, less view and darkening of contrast. All these things, the eye accomodates for. If you barlow a lens, its not like your closing the curtains, and the image gets to dark. and because the lens stays the same, you may find that your 16mm lens is more comfortable to use in respect to AFOV/TFOV and eye relief. The Barlow keeps those properties, if not slightly increases them. I tried to Barlow the 8mm on Jupiter, conditions not  great,  not in  Zenith, and the image was blurred,  however, I was blown away by the views of the Moon at 375x power. The Revelation  Astro was my choice and I secured one at a decent price, but they retail for about £33 

[andyman]

There's a quality Barlow on astro b&s right now . @£45 an Orion shorty plus.

As john mentions , your putting more glass in front of your eyes. , so good quality is the order of the day.

Although you ask weather your better off with an eyepiece or Barlow . I'd say it depends the eyepiece you go for and what your like with tight eye relief ? As you know it's well documented ortho's perform as good as anything but with tight eye relief at higher magnification , same with plossls. But other eyepieces are available that give better eye relief by design .

Of course an advantage of a Barlow is the fact that a set of three or four eyepieces becomes effectively a set of six or eight focal lengths , if you plan the spread.

Yes rory its mine 

[Moonshane]

I have three main scopes. a 16" f4, a 12" f4 and a 6" f11, all newts/dobs. to my eyes, the 6" provides views with the most contrast. this is most likely due to the smaller exit pupil, at the same magnifications, and smaller secondary/secondary:primary ratio cf. the other two scopes. that said, the 12" and 16" scopes (at full aperture) provide finer detail when the seeing is best. they provide brighter views and sometimes you have to work harder to get the detail but it's certainly there. ironically, the greater mirror sizes compared with the vane area also creates smaller diffraction effects in the bigger scopes which I feel to some extent mitigates the apparent loss of visual contrast caused by the larger secondaries/faster focal ratio of these scopes.

in short I feel that if you see past the individual characteristics of the scope you are using the detail visible, at the same magnification, will be very similar other than in extreme cases where you have paid a lot more for the scope. I am doubtful that using a barlow of good quality or a prime eyepiece to get to the same magnification will show much difference. I don't use barlows for convenience as much as any other reason.

[rory]

Yes rory its mine

Oh right. I'll be wanting commission then Andy . Lol. They are the same as the ultima arnt they ? If I had a scope ( don't ask ) I'd have snapped that up myself.

[bambuko]

I have three main scopes. a 16" f4, a 12" f4 and a 6" f11, all newts/dobs. to my eyes, the 6" provides views with the most contrast. this is most likely due to the smaller exit pupil, at the same magnifications, and smaller secondary/secondary:primary ratio cf. the other two scopes....

Glad to be back on topic (after all the banter and distractions ) - thank you Moonshane!

...in short I feel that if you see past the individual characteristics of the scope you are using the detail visible, at the same magnification, will be very similar other than in extreme cases where you have paid a lot more for the scope. I am doubtful that using a barlow of good quality or a prime eyepiece to get to the same magnification will show much difference. I don't use barlows for convenience as much as any other reason.

That answers my question directly!

I am not bothered by eye relief, so wouldn't use this as a justification for Barlow.

I am not bothered about getting six eyepieces for the price of three with Barlow (or eight for four, etc), so this wouldn't be my justification for Barlow.

You are telling me (if I understand you correctly) that Barlow wouldn't help with contrast, even though it extends effective focal length (making the scope in effect "slower").

My question also was related to http://stargazerslounge.com/topic/202124-tal-120/  another topic of mine, that got 0 response

The Russians produced two versions of the same scope, one straight newtonian and another one a shorter version of it with integral "multi-coated negative achromatic lens in the base of the focuser" and I was wondering how they would compare (everything else, apart from tube length being equal).

I think I got my answer now...

[andyman]

Oh right. I'll be wanting commission then Andy . Lol. They are the same as the ultima arnt they ? If I had a scope ( don't ask ) I'd have snapped that up myself.

Yes they are the same as the ultima which sold on abs the other week for £65 

I am surprised it hasnt gone yet for £45 as its a cracking barlow.Only selling it has i have two

Hows a pint sound 

[Qualia]

My general experience echoes that of Moonshane - although I have less telescopes On nights of reasonably good seeing, the 10" f/5 blows away the 4" f/10 on planetary viewing. There really is no contest. Again, not being troubled by exit pupil, I prefer a run of tight little orthos for planetary rather than Barlowing the heavy, longer focal length wide-field eyepieces. 

[bambuko]

Thanks Qualia ,

It was also my view (ie that Barlows are not worth the trouble) until I discovered this strange Russian reflector with built in Barlow and it started me wondering...

[RikM]

There are plenty of telescopes with a barlow built into the optical train. Normally referred to as 'Bird-Jones' type Newtonians. They are generally made so the manufacturer can use a cheaper/poorer spherical primary rather than a parabolic mirror. They are widely held to be difficult to collimate and giving pretty poor views. Personally, I have only used one, the Celestron Astromaster 114, and it was worth every penny that my Son paid for it (he got it for 10p )

I personally can't tell the difference between a 14mm + 2x Barlow and a 7mm eyepiece on it's own other than the difference in eye relief. I also don't think it makes much difference how many bits of glass you have in the optical train. A 9mm Japanese Ortho plus a Televue Barlow won't be radically different from a 4.5mm Delos (FOV aside), both should be excellent. Similarly, there won't be much difference between a SW 10mm + 2x deluxe barlow and a SW 5mm eyepiece (other than eyerelief as already mentioned).

I currently use a 2.5x Barlow but am moving to an EP only set because it's one less fiddly screw to fight with in the cold!

[cotterless45]

If you unscrew the bottom end of a x2 Barlow and screw it onto the bottom of your ep you'll get a possibly more manageable x1.6 focal length.

Whatever you're using the salient factor will be seeing conditions which may change from moment to moment. I prefer to use 5-6mm Plossls to give 240-200x on super seeing. Usually 130-160 x is enough to pick out sharp details.

Using refractors, Newts and Dobs side by side, I'd say that nothing beats the views of my 10" Dob very tightly collimated,

Nick.