Barlow & Lens - best combos

[Dominic]

Hi all. Glasses/contact wearer new to Astronomy, so would appreciate some advice in respect of best (initial) Barlow and lens combos.

I know this is a confusing topic for most starting out, so hopefully the feedback to this post will help others as well as myself. 

I have an Evostar short tube 90/660 refractor F7.3 with a max mag of x180. It comes with the usual cheap 25mm and 10mm lenses. Having looked through some articles, it seems the 25mm is not worth replacing (initially), but 10mm needs swapping out asap.

So my initial upgrade involves getting a Plossl 10mm, a 15mm and a x2 Barlow. This will give me (if I have worked this out right) in lenses and mags:

5mm (x132); 7.5mm (x88); 10mm (x66); 12.5mm (x52); 15mm (x44); 25mm (x26).

Is this a good combo for mixed viewing, so deep sky, moon and planets? 

I was considering a 7.5mm (which with Barlow would get me to max mag, but I felt that would be too close to scope limits). I also toyed with getting a 17mm rather than a 15mm, to give me 8.5mm.

Hopefully what I’ve settled on is a good choice???

Confirmation/other recommendations needed! 

🙂

Cheers!  

Edited February 3, 2022 by Dominic
Grammar corrections

[cajen2]

The range of mags you're looking at seem fine to me. I'd avoid a 10mm Plossl, as the eye relief is unlikely to be very comfortable and go for a BST Starguider 8 or 12mm - very good VFM eyepieces. In fact, I'd recommend them for all three.

[cajen2]

Do remember that cheap Barlows can degrade the image somewhat, especially by making it darker, so buy the best you can afford. A nice compromise on quality and expense would again be a BST Starguider one.

Obviously, all three EPs can be improved upon, but not without spending some serious money. The BSTs are that good

 

Edited February 3, 2022 by cajen2

[alex_stars]

Hi Dominic,

it obviously depends on your budget. I agree with @cajen2 watch out on the Plössls for short eye relief (probably around 5 mm, depending on focal length). This is very uncomfortable for most beginners. Especially if you observe with glasses, that will not work. The BST Starguider are good and then there is no limit on the upper side.

I personally do a lot of planetary observing and use Vixen SLVs but they are more costly and have a narrow field of view.

As a good rule of thumb you need a spacing between EP focal length of about 1.6x, so if you stick to the BST starguider world you could get these EPs and the BST Starguider Barlow

• 25 mm (26x) and with the Barlow its a 12.5 mm (52x)
• 15 mm (44x) and with the Barlow its a 7.5 mm (88x)

I'd start there, with 88x you already gonna have fun on Jupiter. If you feel the need for higher magnifications you can add the 8 mm (82x) which obviously is as 4 mm in the Barlow (165x) and then approaching the x180 theoretical limit.

However the Barlow is about the price of an EP, so you could also just get another EP instead and skip switching the Barlow in and out.

Another option, just to confusion matters more, would be to get a decent Zoom EP and start exploring what magnifications you like (and if you like Zoom EPs more than fixed length). A really good one is the Hyperflex (7.2 mm - 21.5 mm).

I personally started out with a decent Zoom EP, learned (and probably still learn) the magnifications I like for my targets. Then I figured out I don't want to zoom around all the time and ended up with fixed focal length EPs. However that is personal preference and one should try that out oneself.

Hope this helps. Great scope BTW.

CS

Alex

Edited February 3, 2022 by alex_stars

[cajen2]

Yep, good advice from Alex. I also have an OVL Hyperflex Zoom but, rather like a Barlow, there may be downsides. You need one EP with a low mag / wide field of view as a way of centring on your target and viewing large objects like the Andromeda galaxy. All zooms tend towards a narrow FOV at lower mags, so they're no substitute. Personally, I use a Vixen 30mm  NPL - great EP for the price. The 25mm BST would do the same job.

So I'd consider a zoom as an adjunct to fixed f/l EPs, not a replacement. Other people are of different opinions, of course!😄

Edited February 3, 2022 by cajen2

[Carbon Brush]

Another consideration to throw in. Are you using varifocal specs?
if so,they are bad news for almost any eyepiece, though some are worse than others.

Then if you do not have astigmatism correction in your prescription, forget the specs anyway and just adjust the focus.

If you do want to be able to see away from the sope,  then you have the best choice in eyepieces if you use contact lenses.

Big subject that has been discussed in other threads.

[Louis D]

6 hours ago, Dominic said:

Glasses/contact wearer new to Astronomy

How many diopters of astigmatism do you have in your observing eye?  If it is low, you can probably get away with not wearing eyeglasses at mid to high powers.  I have 2.0 diopters of astigmatism, so I can see an improvement wearing them at all but the very highest powers.  The relationship actually revolves around exit pupil size rather than magnification, but the two are in inverse proportion to each other.

In your situation, I would probably get a 32mm Plossl for 20x, a 12mm BST Starguider for 55x, and an 8mm BST Starguider for 83x.  Since your scope is an achromat at f7.3, it's going to show a lot of false color even with the 8mm eyepiece.  All of these eyepieces will have enough eye relief to be usable with eyeglasses.

I don't find myself using in-between powers very often.  I generally go for lowest/widest power, move up to mid-power for most observing, and then jump to highest power if conditions and the object warrant it.  Technically, both the 8mm and 12mm yield mid to mid-low powers, but your scope isn't really suited to reaching for high powers above 100x due to aperture and false color.  If you mask off false violet/blue and orange/red colors with a light green filter, you could push your power up to 130x with a 5mm BST Starguider on bright objects like the planets and luna and get a rewardingly sharp image.

Even in my 8" Dob, I generally observe planets at around 100x to 125x on most nights because I get the best contrast on planetary details in that range.  The moon and globular clusters are where I push to 200x or more.  Your scope simply doesn't have enough aperture to ever resolve globulars, so they will always look like fuzzy blobs.  That said, open clusters and bright planetary nebula should make for interesting observing in your scope.

[Zermelo]

Some good advice already given.
If you did end up wanting a straight replacement for the 10mm (a length that isn't available in the Starguider range), then this has the same field of view, similar image quality and slightly better eye relief.

[SuburbanMak]

+ 1 for a zoom eyepiece. I have the Baader Hyperion MkIV 8-24mm & it’s great. Also has a dedicated 2.35x Barlow.  Really comes into its own on freezing cold nights when fiddling with eyepieces is at its most unappealing!
Lots of people speak well of the Hyperflex zoom too at a lower price point. 

 

 

 

[Neil H]

Hi if you want a baader hyperion zoom and matching Barlow there one on Astro buy and sell for £150

Edited February 3, 2022 by Neil H

[Dominic]

Thanks everyone for your advice. Very much appreciated. It seems majority view is that BST Starguiders are the way to go. Cheers! 

[Guest]

+2 on a variable eyepiece.  I run the Orion 8 to 24 and it is the eyepiece I use on the planets the most.  It does very well on planets and I was pleasantly surprised how well it did on the Orion Nebula, The Ring Nebula and The Hecules Cluster.  The Orion has better light transmission then the Celestron but not quite as good as the Baader in the scopes we have tried it in.  It was 200 USD well spent.  As far as a Barlow I have two that I like to use both are 4 element Orion Barlows.  One is a 1.25 inch 3X and the other is a 2X 2 inch.  I have no complaints with either of them.

Edited February 6, 2022 by Guest

[Mr Spock]

BSTs are good value for money. They don't do much wrong.

[Second Time Around]

+3 on a zoom eyepiece.

Many 2x Barlows can also be used at 1.5x.  Look for those with a black section at the telescope end.  If you screw this off and screw it into the filter thread of your eyepiece this will give you approx 1.5x.