38 replies to this topic

[Chris1485]

Hi,

recently I've been looking for a lightweight 70mm Achro.

Years ago I had a SW F7.1 70mm Achro that I used a lot. Even with a bino viewer, but the weight killed the plastic focuser.

I liked it because of the ultra light set up and it gave quite good views.

But try as I might I can't find a 70mm achro with a metal focuser.

There's plenty of ED scopes out there but I wanted something with a bit longer focal length, around F8-F10.

I even struggle to find a retro fit focuser for a 70mm tube.

 

Does anyone have any suggestions of where I can find a scope like this?

 

Thanks,

 

Chris (UK)

[Lagrange]

You can get 80mm achromats with metal focusers from J-Scope (f/7 and f/15 versions) and Starbase (f/10).

 

I've not seen any currently manufactured 70mm achromats with this kind of build quality, so if you wanted one of that aperture you'd probably have to find an older model on the secondhand market.

 

The reason you don't see them making a small achromat to that standard puts its cost in the ballpark of ED scopes, and the latter can be made more compact for a given level of colour correction. Small achromats are generally aimed at very budget conscious customers so they're built to a very low price point and have cheap components.

[betacygni]

You’d need to bump up to 80mm, but the Starbase 80 otherwise meets your criteria: https://www.firstlig...nt-package.html

That said, a long focal ratio achromat largely loses the portability advantage of a small refractor. Unless it’s for nostalgia reasons the modern ED scopes are better in every way, and not much more expensive.

Edited by betacygni, 04 April 2025 - 04:49 AM.

[Jon Isaacs]

You’d need to bump up to 80mm, but the Starbase 80 otherwise meets your criteria: https://www.firstlig...nt-package.html

That said, a long focal ratio achromat largely loses the portability advantage of a small refractor. Unless it’s for nostalgia reasons the modern ED scopes are better in every way, and not much more expensive.

 

I think is easier to answer the question posed by the threads title than finding an quality metal focuser on a 70mm achromat.  

 

I recently acquired a second hand AT-70ED..  They are $329 shipped.  The 2 speed 2 inch rack and pinion focuser is awesome. I think you would have to pay $300 or more just to buy the focuser as an aftermarket item. The barebones scope weighs 4.1 lbs... 

 

70mm achromats are entry level scopes so plastic focusers are standard.  There is always to the TeleVue Pronto but it's more expensive used than the AT-70ED is new and it's heavier and not a true ED scope.  Fitting a aftermarket focuser to a 70mm is problematic because a 2 inch focuser is typically too large in diameter for the 70mm's OTA..  It's tough to find a quality 1.25 inch focuser.

 

And somehow, lightweight and binoviewer seem incompatible.  

 

A 70mm F/8 has a focal length of 560mm, an 80 mm F/7 has a focal length of 560mm and you can buy an AT-80ED for $439.. It weighs about 6.2 lbs with rings and a dovetail.. 

 

Jon

[Chris1485]

You're right of cause, step up to an 80mm or go for an ED.
And it is a bit of nostalgia thinking of when I was using my SW 70mm. I like to push boundaries so why not use a bino viewer with a small scope..
Also I find the stock Synta metal focusers ok.
They make a 1.25" for 80mm scopes but don't for anything smaller. Which I find hard to understand.
They are entry level but would be a better proposition with a metal focuser.

[rob1986]

I think ive seen 1.25 vixen standard focusers on SW70 OTAs which were metal.

But it would be nice if skywatch offered replacement focusers with proper qc

The exampke on my C80 could be decent if not for poor QC

Edited by rob1986, 04 April 2025 - 07:06 AM.

[Jon Isaacs]

 

 

They make a 1.25" for 80mm scopes but don't for anything smaller. Which I find hard to understand.
They are entry level but would be a better proposition with a metal focuser.

 

I think comes down to the basic question:

 

An 80 mm achromat with a metal focuser is quite affordable.

 

They are trying to make the 70 mm significantly less expensive than the 80 mm and that means a plastic focuser among other things..

 

Jon

[VA3DSO]

I've got the same SW 70mm f/7.1 scope that has several issues - one being that there's a "bald" spot on the draw tube rack. Fortunately, it's right at one end, and not where I'd typically be focusing the scope. Still, it's a bit of a pain, and I've often thought about buying a metal rack and pinion to try and upgrade my draw tube. Something like this:

 

https://www.amazon.com/dp/B0D94QXBHX

 

But right now my scope has something wrong with the objective lens and I'm trying to source a replacement for that part first.

 

Otherwise, yeah, going to an ED scope would be my choice.

 

Clear skies!
 

Rick

Edited by Rick-T137, 04 April 2025 - 10:08 PM.

[betacygni]

You're right of cause, step up to an 80mm or go for an ED.
And it is a bit of nostalgia thinking of when I was using my SW 70mm. I like to push boundaries so why not use a bino viewer with a small scope..
Also I find the stock Synta metal focusers ok.
They make a 1.25" for 80mm scopes but don't for anything smaller. Which I find hard to understand.
They are entry level but would be a better proposition with a metal focuser.

There is certainly nothing wrong with pushing boundaries, I use binoviewers in scopes as small as 60mm. But there is no reason to limit your capabilities either. The astrotech 60mm AT60ED for example has a superb focuser that handles binoviewers with ease (TS optics is the European equivalent of these scopes I believe, perhaps others too, https://www.teleskop...-red-line-10095 ). Similarly their 72mm and 80mm scopes as well, while being essentially color free. It’s great fun to see what can be seen with smaller scopes, but to paraphrase a famous telescope maker, if you’re going to use a small scope you want all the light you’re getting to be going the right place, as you have little to start with. As long as budget allows go for one of these modern ED scopes with excellent dual speed focusers, the experience will be very much better. Particularly if this will be your only or primary scope.

 

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Edited by betacygni, 04 April 2025 - 10:53 AM.

[25585]

Find a pre-owned TV Pronto or Ranger, they are achros with metal focusers.

[John R.]

Looking at the title I thought, 'what's wrong with plastic focusers?' Then read the body of your question and understood your dilemma. I have a short tube 70 (and admittedly cheap) that, although it has a plastic focuser works fine, no play, rocking or lash, very positive and smooth. It even has top focusing bearing rail adjustment. But I don't know how it would handle weight, maybe I attach my 18 oz. EM10 mirrorless just as a test. 

Well, the focuser still is smooth with the weight of my mirrorless camera attached. But you can tell the extra weight is there. There is a distinct 'heaviness' to the focusing feel that is not there with just a diagonal and eyepiece. It feels secure, still no play, but.....just heavy, is how I would describe it. 

I'm with Jon and others on this, upgrade to an AT70, or possibly the AT72ED2. Their focusers are amazing.  

 

Edit. The other great thing about the ATxx focusers is that they take either 1.25 or 2 inch visual accessories. And they come with a really very nice included case.  

Edited by John R., 05 April 2025 - 05:29 AM.

[hfjacinto]

Here you go. 50 mm achromatic with metal focuser.

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[Chris1485]

Many thanks for all your replies.

I don't actually mind a plastic focuser, it just has a cheap feel to it, to my mind.

And the SW 70 I had was fine with light weight eyepieces like plossls etc.

I have my SW ED80 which gives very sharp images that have a quality to them that my obstructed scopes don't have, but isn't a light scope.

I had the opportunity a few years ago to get a TV Ranger but at the time decided against it, but I do like the idea of a small, quality achro.

I think I will look at an ED70 / 72, I'm just a bit concerned about the quality of the views from mass produced short focal length lenses.

I had a SW72ED a couple of years ago that just didn't give me the views I wanted and seemed to max out at about x105. Maybe it was a bad example? I remember vividly the SW70 achro I had at that magnification showed a swirling storm following the GRS on Jupiter, and was super light weight on an AZ-3 mount..nostalgia.. definitely..

[25585]

An 80mm finder will be small and light. They have a helical focuser and can take 1.25" eyepieces. This one is an example

 

https://www.apm-tele...-90-erect-image

[Chris1485]

Looks like a nice little scope, I'm assuming it will be F5?
Might be a little to fast for me..

[dmgriff]

I think the Vixen A70Lf 70mm/900mm ota has a metal focuser, made by Synta in China for Vixen (the "f" designation). The tube may be nonmetal. There are many threads on the A70Lf, has a following as a grab and go (2.5kg ota). The A80Mf is all metal. 

 

https://www.bresser....al-tube-X000321

Edited by dmgriff, 05 April 2025 - 03:52 PM.

[maniack]

I think the Vixen A70Lf 70mm/900mm ota has a metal focuser, made by Synta in China for Vixen (the "f" designation). The tube may be nonmetal. There are many threads on the A70Lf, has a following as a grab and go (2.5kg ota). The A80Mf is all metal. 
 
https://www.bresser....al-tube-X000321

From Scope Views:

To this end, the 1.25” focuser has a lightweight, but high-quality, plastic body with a metal draw tube. Focusing is well-weighted and precise, however – better than the Synta all-metal 1.25” unit found on the ST80.

So partially metal, but possibly more usable than standard Synta all-metal focusers.

[RichA]

Find a pre-owned TV Pronto or Ranger, they are achros with metal focusers.

The Rangers I've used all had a small amount of backlash in the helical focusing.  Not enough to really matter, just annoying. 

[Granite Glasser]

My trusted TeleVue Ranger 70mm has the all metal, yet somewhat peculiar, helical focuser.

[Chris1485]

That's interesting about the Vixen A70lf as I had the SW version a few years back that was exceptionally light, very easy to mount and practically colour free but had an all plastic focuser.

I think a focuser with a plastic body and metal draw tube would work fine and I may keep my eyes open for one..

[Chris1485]

Can anyone comment on the optical quality of the Synta ED72?

Like I've said the one I had seemed to max out at x105 with my (genuine) TMB 4mm.

My ED80, which is FPL-53 glass keeps going beyond x160...

[Oldfracguy]

There are a number of "70-ish" mm refractors with metal focusers.  Indeed, here is one scope with a metal focuser that should rightly sell for the price of the entire scope:

 

 

 

 

 

Edited by Oldfracguy, 06 April 2025 - 09:29 AM.

[Terra Nova]

This is a great little 70 with a metal focuser! And it’s readily available:

 

https://astronomics....-ota-fpl-53-f-6

[Chris1485]

They are nice looking scopes, in my last post I was just questioning how good the optics were at F6..

[maniack]

They are nice looking scopes, in my last post I was just questioning how good the optics were at F6..

The AT72EDII has excellent optics. No false color or other issues as far as I can see when viewing Jupiter at 144x. It's also mechanically excellent, far better than any achromat I've seen.