The humble ST80

[Stu]

I bought this scope second hand a while back, intending to give it to my young daughter to experiment with, but for various reasons that never happened and it remained unopened.

This afternoon, I had a look at it for the first time and discovered it is in beautiful, as new condition with all accessories present and boxed. There is even a 1.25” moon and sky glow filter. The only thing I could see missing is the rubber O ring off the finder.

It came with the standard bar which fits on a photo tripod, but also included was a surprisingly solid 3D printed Vixen dovetail which I fitted.

I thought I would have a play around with it this evening as the skies were not worth bothering with anything bigger, plenty of cloud passing through. I then thought why don’t I see what the difference is between the standard accessories and some top quality kit. This is only a very brief comparison due to the cloud, but it was interesting nonetheless. I just wanted to see what a new starter would see if they used the standard kit, ie 45 degree prism diagonal, 2x Barlow, 10mm and 25mm eyepieces.

By way of comparison I used a Baader BBHS T2 mirror and 5mm BGO for a direct comparison with the 2x Barlow with 10mm at 80x.

I only managed two targets; the Moon and Jupiter. 

Simple results:

On Jupiter I could only see a blank disk with no real detail at all. The moons were visible as well obviously. Perhaps with better conditions I might have seen more.

With similar conditions and the BGO/BBHS, Jupiter was sharper and showed the two main equatorial belts, similarly possibly a bit more would have been visible if conditions had been better.

On the Moon with standard kit it looked ok up to the 10mm, it seemed snap into focus well enough, but in adding the Barlow it seemed to lose that sharpness, going through focus without ever reaching a satisfactory image. I specifically looked at Theophilus and its central peaks.

With standard kit, all I could really see was one central peak, perhaps with a bit of complexity to it indicating it might be more than one. With the BGO/BBHS four peaks were visible, two large and two small. The scope snapped into focus nicely; even though the focuser is not the most refined it was perfectly useable.

CA was certainly present mainly around the limb and also washing around the craters, but I must admit I didn’t find it as colourful or objectionable as I expected; I’m a bit of an apo nut and don’t like CA, but I guess the small aperture helps to keep it controlled. I may compare it against the Telementor to see how two achromats of very different focal lengths compare.

So, overall I was more impressed than I expected to be. The standard eyepieces/Barlow/ prism are quite limited, but then it is packaged to be useful as a spotting scope as well as Astro and supplied accessories are limited by the need to keep to a price.

I’ll do a few more comparisons under better conditions, with a few doubles thrown in for good measure.

I had been thinking of selling it on, but I will likely keep it for some cheap fun and I may well use it as a mega finder on the 16” with a 32mm Plossl 👍

[vlaiv]

Out of interest, what is ID of focuser tube and how long is it?

I recently did some calculations for 80mm scopes (F/7.5 in my case, not as fast as F/5) - and it turns out that it is quite hard to illuminated larger field with regular focuser specs.

I suspect that situation might be even worse for ST80 given that it is F/5 and has focuser that is probably around 40ish mm in diameter (If I recall correctly - it has T2 thread on end of focuser tube, so focuser tube can't be much wider).

[Stu]

1 hour ago, vlaiv said:

Out of interest, what is ID of focuser tube and how long is it?

I recently did some calculations for 80mm scopes (F/7.5 in my case, not as fast as F/5) - and it turns out that it is quite hard to illuminated larger field with regular focuser specs.

I suspect that situation might be even worse for ST80 given that it is F/5 and has focuser that is probably around 40ish mm in diameter (If I recall correctly - it has T2 thread on end of focuser tube, so focuser tube can't be much wider).

I’ll have a look Vlad. Seems to make sense. I didn’t know there was a T2 fitting on the end, may be able to connect directly to that which would be better.

[Pixies]

1 hour ago, vlaiv said:

it has T2 thread on end of focuser tube,

Not exactly. It has a female m43 with1.0mm pitch (old Vixen). You need an adapter to get it down to T-2!

Edited January 27, 2023 by Pixies

[vlaiv]

3 minutes ago, Pixies said:

Not exactly. It has a female m43 with1.0mm pitch (old Vixen). You need an adapter to get it down to T-2!

Are you sure?

I was referring to this bit here:

not the thread that black 1.25" receptacle screws in (one on the inside of silver draw tube).

[Pixies]

Just now, vlaiv said:

Are you sure?

I was referring to this bit here:

not the thread that black 1.25" receptacle screws in (one on the inside of silver draw tube).

OK - yes. That's correct - the visual back.

I was talking about the internal thread at the end of the silver tube.

[Louis D]

Try a Yellow #8 to lightly filter out the purple haze.  It can sharpen up the views a bit.  I've found the appearance of lunar mare become more contrasty in my ST80 with a light yellow filter.

Try a Green #56 to improve the snappiness of the focus by filtering out both ends of the spectrum that focus at different distances from green, which is what the achromat is optimized for.  Even with premium eyepieces and dielectric diagonal, the only way I could make out the phase of Venus in my ST80 was with a light green filter.

It could be that there's nothing that can be done to improve the view with the included diagonal and eyepieces, but it might be worth a shot.

[Stu]

9 hours ago, vlaiv said:

Are you sure?

I was referring to this bit here:

not the thread that black 1.25" receptacle screws in (one on the inside of silver draw tube).

I tried that quickly last night and the BBHS screws right on there, makes it very secure and no marring of the diagonal barrel from those horrid screws.

[badhex]

Super interesting read @Stu.

Being that it is Synta, the construction similarities between this and the Travelscope 70 are pretty clear, although the ST80 has some metal parts and is generally better made. The focuser on the TS70 is pretty rubbish unfortunately and has some obstruction in the form of an inner sleeve in the draw tube. 

Anyway, I've said this many times before but optically speaking the TS70 is surprisingly good for such a cheap achro, once you put some decent accessories with it, so it doesn't surprise me that the ST80 performs similarly (even better, by the sound of it). 

I was pretty amazed at how much better it was with a decent diagonal and the Morpheus 17.5mm, so it goes to show that often the issue with beginner gear is not necessarily the scope itself, but the accessories. 

[Peter Drew]

I have three ST80's, two as a binoscope and one as a finder on one of my large telescopes.  As Stu, and others have found, the accessories tend to limit the performance of the comparatively good objective.  Another interesting experiment would be to use the supplied basic accessories on a higher end refractor to see by how much they diminish the performance.     🙂

[vlaiv]

Can anyone measure length of focuser tube on their ST80 (preferably stock / not modified version of focuser)?

[Stu]

1 hour ago, vlaiv said:

Can anyone measure length of focuser tube on their ST80 (preferably stock / not modified version of focuser)?

I’ll have to remove the focuser Vlad but may be able to do that later if no one else has by then.

[Stu]

1 hour ago, Peter Drew said:

Another interesting experiment would be to use the supplied basic accessories on a higher end refractor to see by how much they diminish the performance. 

I’ll give that a go.

What would also being interesting is working out which are the weakest links. I suspect the 45 degree prism and the Barlow based on initial try out but will see with more time.

[badhex]

19 minutes ago, Stu said:

I’ll give that a go.

What would also being interesting is working out which are the weakest links. I suspect the 45 degree prism and the Barlow based on initial try out but will see with more time.

If it is the same 45° prism that came with the TS70, and I suspect it is looking at the pictures, I would heartily agree - barely passable at best IMO. For one thing there's a pretty wide lip on the inside of the barrels, at the prism surface, possibly on both sides, so vignetting will obviously be an issue when using lower power EPs. 

[badhex]

30 minutes ago, Stu said:

I’ll have to remove the focuser Vlad but may be able to do that later if no one else has by then.

If you do end up removing the focuser I'd be interested to know the OD of the focuser where it attaches to the main tube (or the ID of the tube of course, might be easier to measure). I imagine it is probably bigger than the TS70 one but worth seeing if it could be possible to fit the ST80 focuser on the TS70 tube. 

[Stu]

6 hours ago, badhex said:

If you do end up removing the focuser I'd be interested to know the OD of the focuser where it attaches to the main tube (or the ID of the tube of course, might be easier to measure). I imagine it is probably bigger than the TS70 one but worth seeing if it could be possible to fit the ST80 focuser on the TS70 tube. 

Will do 👍

[ollypenrice]

Certainly a great finderscope and, even more certainly, the world's best guidescope. Who visited those festering little finder-guiders on the world? I'm now using two of the wretched things and they are a constant faff, forever losing focus. I would be embarrassed to admit how long it is since I last refocused my ST80 guidescope and even more embarrassed to admit how much time goes by between occasions on which I scrape the accumulated crud from off the lens...

Everyone should have an ST80!

lly

[lunator]

I wouldn't be without my ST80.

I use it for grab and go on the horizon tripod. It is my white light solar observing scope. I have used it for terrestrial observing when on holiday. The lightness combined with the flexibility means it's a very useful scope. 

Cheers

Ian

 

[fozzybear]

On 27/01/2023 at 21:27, vlaiv said:

Out of interest, what is ID of focuser tube and how long is it?

I recently did some calculations for 80mm scopes (F/7.5 in my case, not as fast as F/5) - and it turns out that it is quite hard to illuminated larger field with regular focuser specs.

I suspect that situation might be even worse for ST80 given that it is F/5 and has focuser that is probably around 40ish mm in diameter (If I recall correctly - it has T2 thread on end of focuser tube, so focuser tube can't be much wider).

Here you go from my st80

[fozzybear]

[fozzybear]

sorry my calipers dead battery. Duh

[vlaiv]

Those numbers don't paint pretty picture.

It looks like ST80 is almost stopped down if used with regular diagonal mirror.

I went with following numbers:

Draw tube length - 135mm (last image with 1.25" visual back).

Draw tube inner diameter - 43mm (which makes sense if it has M43x1 inner thread - but also looks like that from images).

Any diagonal mirror that has more than 80mm optical length will stop down aperture - or rather, focuser tube will act as aperture stop.

If we go by this:

and assume that shortest path diagonal mirror has something like 70mm of optical path  - that gives us 4mm diameter fully illuminated circle.

Interestingly enough - illumination level at edge of 1.25" field stop is not significant - in fact, I don't think it can easily be seen by human eye.

Above is simulation of what edge of 1.25" field stop is seeing with 70mm optical length diagonal. Outer circle is objective lens and smaller circle (or rather arc) is edge of the focuser tube. Area between two is effectively blocked, but all the rest is available.

Does not seem like much (not sure if I can easily calculate percentage).

 

[fozzybear]

47 minutes ago, lunator said:

I wouldn't be without my ST80.

I use it for grab and go on the horizon tripod. It is my white light solar observing scope. I have used it for terrestrial observing when on holiday. The lightness combined with the flexibility means it's a very useful scope. 

Cheers

Ian

 

i pimped mine with a dual speed focuser god knows why but hey ho. it works a treat as a grab n go. thus the photo's the original

Edited January 28, 2023 by fozzybear
spelling

[fozzybear]

7 minutes ago, fozzybear said:

i pimped mine with a dual speed focuser god knows why but hey ho. it works a treat as a grab n go. thus the photo's the original