What refractor to get

[Neil H]

Hi all i already have the orion optics VX8L on the HEQ5 pro mount . I have about £280 and am looking at a refractor out of 2 on flo whats the better one to go for 

https://www.firstlightoptics.com/startravel/skywatcher-startravel-120t-ota.html

https://www.firstlightoptics.com/evostar/skywatcher-evostar-120-ota.html

[John]

What are you looking for from the refractor - deep sky observing or planetary / lunar observing ?

To compliment your VX8L I'm tending towards the shorter Startravel 120 as a portable deep sky / wide field scope but that might not be how you see things ?

 

[Ruud]

The f/5 with 45º direct image diagonal are  two disadvantages : this type of diagonal degrades the image, and the fast focal ratio is too fast for an 120 mm achromat, causing much chromatic aberration.

My vote is against the Startravel.

The f/8.35 Evostar with its 90° star diagonal is two steps ahead: better focal ratio for chromatic aberration and better images from the diagonal.

[mikeDnight]

I bought a 120 F8.3 Helios refractor back in 1999 and really enjoyed it. I remember vividly my first thoughts as I aimed it at a crescent Moon - "where is the false colour"?  Obviously it was there, but it wasn't as destructive or as obvious as I'd expected. At F8 the 120 is still a rich field refractor and capable of giving some wonderful views of brighter DSO's. Personally I feel it has a performance edge over the F5 version, and yet it's still easily mounted and carried around. The only thing to be aware of with the SW's is that they are not all well figured, and can suffer from quite severe spherical aberration. On the other hand some are really quite wonderful. I suppose if you get a poor one, you could always return it and get a replacement. 

[John]

I agree about changing the diagonal to a 90 degree mirror one.

I just feel that the F/5 120mm will offer something a bit different from the VX8L.

If the intention is to use the scope for observing the planets, moon etc I think the longer one will be better. The VX8L would out perform it by some margin on these targets though.

 

 

[johninderby]

The 120 f/5 is quite good at low power widefield but the diagonal should be replaced by a better quality one. Makes a great white light solar scope when used with a wedge.

The Evostar 120 still has CA but much reduced at higher magnification so much better on lunar / planetary.

Edited September 7, 2020 by johninderby

[Neil H]

Thanks guys i do enjoy planets , lunar, and would like deep space i would like to pop my asl224 camera on it to see if its better than the VX8L 

I have just got in double stars and wookie1965 said that a refractor is good at that 

How do you know if its good or needs to be sent back sorry for the stupid question but i have only been doing this for less an a year and with this lovely british weather it feels like a few days lol

[johninderby]

If it’s double stars then this is a great scope. No noticable CA and great Japanese optics and lightweght.

https://www.firstlightoptics.com/scopetech-telescopes/scopetech-stl-80a-maxi-80mm-f15-classical-refractor.html

Also great on lunar / planetary but too narrow a fov really for DSOs.

[R26 oldtimer]

8 minutes ago, Neil H said:

Thanks guys i do enjoy planets , lunar, and would like deep space i would like to pop my asl224 camera on it to see if its better than the VX8L 

If you practice eeva, then fast optics rule, so the 120 F/5 will be a better choice. Combine that with the Asi224 and even an l-enhance filter and sharpcap and you can start dso hunting. You'll need a tracking or a goto mount though.

[mikeDnight]

1 hour ago, Neil H said:

How do you know if its good or needs to be sent back sorry for the stupid question but i have only been doing this for less an a year and with this lovely british weather it feels like a few days lol

In a thermally stable refractor the focused star at 100X should present itself as a perfect Airy disk, appearing somewhat like a tiny pingpong ball, which if bright enough should show a single concentric diffraction ring encircling it. Inside and outside focus, the star image should appear as concentric rings either side of focus. If one side of focus shows no rings, that's a sign of spherical aberration. If the in focused star image appears furry around its edge, or the diffraction rings are washed out, this too indicates spherical aberration. Aiming the scope at a bright star such as Polaris and removing the eyepiece,  then using a fine toothed comb held against the focuser, you'll see dark lines set against the starlight. Winding the focuser slightly inside or outside of focus until you see five lines, you can check the basic figure of the lens. A refractor should show the lines as straight. If there's any barreling of the lines the scope has spherical aberration.  If the lines appear straight the scope is spherical and essentially perfect.

In short, if the stars are sharp points of light the scope is good. If they are soft then you may have a problem.

[Neil H]

2 hours ago, johninderby said:

If it’s double stars then this is a great scope. No noticable CA and great Japanese optics and lightweght.

https://www.firstlightoptics.com/scopetech-telescopes/scopetech-stl-80a-maxi-80mm-f15-classical-refractor.html

Also great on lunar / planetary but too narrow a fov really for DSOs.

A lot over my price also its very long too  will need extension.  Does look nice  tho 

 

2 hours ago, R26 oldtimer said:

If you practice eeva, then fast optics rule, so the 120 F/5 will be a better choice. Combine that with the Asi224 and even an l-enhance filter and sharpcap and you can start dso hunting. You'll need a tracking or a goto mount though.

Mine is goto HEQ5 pro

[DaveL59]

there's been a couple nice TAL100's on the bay recently and in your range when they sold. Solid and to me nice to use, but... they are quite long at 1M for the OTA

[Alan64]

3 hours ago, johninderby said:

If it’s double stars then this is a great scope. No noticable CA and great Japanese optics and lightweght.

https://www.firstlightoptics.com/scopetech-telescopes/scopetech-stl-80a-maxi-80mm-f15-classical-refractor.html

Also great on lunar / planetary but too narrow a fov really for DSOs.

That's beautiful, and the HEQ-5 is more than capable in supporting it.

Edited September 7, 2020 by Alan64

[John]

You are more likely to see optical issues with the F/5 but they are not designed for high power observing so it might not matter too much.

The F/8.3's are generally optically sound but you can still get some spherical aberration - it's very common with the chinese achromat refractors.

Both will show some chromatic aberration, the F/5 quite a bit more than the F/8.3.

If you are looking for optical perfection in these low cost scopes you may have to reject a lot of samples.

 

[Neil H]

I sort of understand that low price is never going to be as good as a top scope but i am not sure i know enough about this hobby to bag a good second hand one 

 So it looks like the 2 i ear marked in my price range my not be any good 

[John]

Either of the could be good - there are happy and satisfied owners of both types on this forum.

They both have strengths and weaknesses though so I guess its a case of deciding what you are hoping for from this new scope and the extent to which the two you have initially selected might match those aspirations or if there is a better option out there within your budget.

 

[johninderby]

How about one of the Bresser scopes?

https://www.firstlightoptics.com/bresser-telescopes/bresser-messier-ar-102l-1000-refractor-ota.html

https://www.firstlightoptics.com/bresser-telescopes/bresser-messier-ar-127l-1200-refractor-ota.html

 

[Alan64]

A 100mm Maksutov is the closest of the mirrored-designs to a long-focus refractor...

https://www.rothervalleyoptics.co.uk/bresser-messier-mc-1001400-optical-tube-assembly.html

That one is at f/14, and with a somewhat smaller secondary-obstruction when compared to Celestron's and Sky-Watcher's offerings at f/12.9 and f/12.7, respectively; the smaller the obstruction the better, albeit negligible.  

Edited September 7, 2020 by Alan64

[DaveL59]

if you have a chat with Astroboot, they had some F15 frac's recently around £300 as I recall

[johninderby]

4 minutes ago, Alan64 said:

A 100mm Maksutov is the closest of the mirrored-designs to a long-focus refractor...

https://www.rothervalleyoptics.co.uk/bresser-messier-mc-1001400-optical-tube-assembly.html

That one is at f/14, and with a somewhat smaller secondary-obstruction when compared to Celestron's and Sky-Watcher's offerings at f/12.7; the smaller the obstruction the better, albeit negligible.  

And a fine grab’n’go setup indeed. 👍🏻👍🏻👍🏻

[PaulG_SF]

I've had the evostar 120 for 10 years. Although it has been laid up for half that time due to time issues. I have recently started using alongside by Reflector.

I found it to be very sharp, Lunar views are amazing. I discovered the joy of splitting double stars and  Bright DSOs are also pleasing. You can get great planetary views, but I struggled to get focus with anything bigger than a 2x barlow.

CA is present. It's well controlled but you can't escape it.  

I did some really basic imaging - mainly luna with a webcam. I also fixed my DSLR to the end and did some shots of M42, Andromeda and M51.  The stars were blue fringed, as you would expect - but given I was more visual biased at the time I was not overly bothered.

Not particularly specific, but hope that helps.  I'd say it's a good choice if you are on a budget and imaging isn't in your future or you just want to dabble a bit with imaging.

[Neil H]

12 minutes ago, DaveL59 said:

if you have a chat with Astroboot, they had some F15 frac's recently around £300 as I recall

Just had a look they dont have any good ones cheap tho £29 

[DaveL59]

2 minutes ago, Neil H said:

Just had a look they dont have any good ones cheap tho £29 

don't think they're listed, hence have a chat. They mentioned to me if I was interested a week or so back when I had some bits on order. So tempting but I've too many that aren't looking at anything most nights to add another lol

oh, there's aslo a 120XLT down my way on the bay tho the finder bracket is broken.

Edited September 7, 2020 by DaveL59

[Neil H]

Ok Dave i will have a chat 

[DaveL59]

be warned tho, F15 will be a very long scope 😉