ScopeTech 80mm Fraunhofer Telescopes

[Adam J]

On 22/05/2020 at 14:54, John said:

Very interesting scopes - good to see.

I wonder if 4" inch achromats of similar specs might be in the pipeline as well ? 

A side by side comparison between the Stellamira ED F/10 80mm and one of these slow 80mm achromats would be fascinating

I reckon it might need to be the F/15 to match the colour correction of the ED F/10 ?

half the price mind you.

[F15Rules]

On 22/05/2020 at 18:25, AdeKing said:

Yes, they look lovely and very tempting.

I was interested by the claim that they could be mounted on an AZ5.

Although the OTA is light, I'd have thought the moment arm of both might make mounting on an AZ5 a bit optimistic.

I'd love one but then reality bites when I consider how little use my 102 f/11 gets due to its shakiness on my EQ5 and Vixen GP mounts.

🤔☹️😢

Ade,

I  mounted similar scopes on a Celestron CG5 around 10 years ago with good results: however, I did invest in an ADM saddle and puck upgrade at a cost of c £100 at the time, and this upgrade made all the difference. It transformed the rigidity of the holding of the scope, which was essential as this type of long focus refractor can eat up significant magnification - up to c 300x on doubles- and so needs to be able to be as firmly held as possible. I confess I'm quite surprised if you can't get your 102 F1l to hold firm on a VIxen GP? I had a Lyra version of this scope also at F11 and had no problems with its' rigidity on my CG5. I should probably say that the CG5 was a heavier duty version of the EQ5, with more solid 2" tubular steel legs, ball bearings and of course the ADM upgrade.

On 22/05/2020 at 19:13, John said:

I've found some more photos of these on another forum. They remind me very, very much of the Pentax J series refractors. Goodness how I wanted one of those way back when !

These Scopetech refractors look practically identical to the Pentax J80.

 

John,

You may recall I had a J80 Pentax some 10 years ago (it was bought from me by "Ant" McKewan who posted a review on SGL). I've managed to find some photos of when I had the scope, which I attach below.

I posted several times that this scope delivered some of the best images of any scope that I have ever seen in any scope, and that still holds true: the airy disks of stars were superb.

The only thing about the scope that I found odd was that the (excellent) 6x30 finderscope was mounted dead centre on the focuser mount, not either to right or left as is normally the case, and it made it rather difficult to place your head at times on certain elevations and targets!

But a lovely scope and I would buy one again in future if one came up at the right price.

I agree with you that the new Scopetech scope does look remarkably similar - apart from the finderscope mounting!

Hope you like the pics of the J80.. a couple of them show the J80 mounted on a Towa Topic 80mm F15 mount. I'd love to have put the J 80 F12 up against the Towa F15!😎😀

Dave

Edited May 26, 2020 by F15Rules

[F15Rules]

On 23/05/2020 at 10:29, Shaun_Astro said:

Wonder how it would compare to an evostar 120 with an apo filter.

My son in law has an Evo 120 F8 which I've compared with my Moonraker (Towa lens) 80mm F15. IMO there is no comparison in terms of image quality: the 80/F15  puts up far nicer images, with almost zero CA and beautiful airy disks on stars.                                                                                                  I've used anti-CA filters from Baader etc with the Evo, but to my eyes they all impart an unpleasant yellowish-green cast to the image , which I really don't like.

Others may of course see things differently..                                              Dave 

Edited May 27, 2020 by F15Rules

[Guest]

On 23/05/2020 at 17:14, John said:

Does it deal with the moment arm issue John ?

 

Can I ask what that is, please?

[johninderby]

6 minutes ago, merlin100 said:

Can I ask what that is, please?

https://www.teleskop-express.de/shop/product_info.php/info/p10777_TS-Optics-Adapter-Plate-for-alt-azimuth-Mounts-with-perfect-Weight-Compensation.html

[Shaun_Astro]

Interestingly I found these telescopes being discussed from 2016. They mentioned making a batch of 100, and 50 were finished, I wonder if these being sold here are from that batch. If they really are that good, having one of only 100 made is quite a rarity, and enticing. Surely an exclusive club these long Fl achromats. https://www.cloudynights.com/topic/553726-currently-available-standard-achromats/page-5

Also, the seeing in the SE UK was phenomenal last night. The moon at 200x was as steady as I have ever seen it. The terminator was directly over Theophilus , illuminating it's central peak. Here is a picture from my Meade 70/900 with a shaky phone camera (hence blurring at the top), I can imagine the 80/1200 would have delivered a much better view.

 

 

 

Edited May 28, 2020 by Shaun_Astro

[Trikeflyer]

It was rubbish in the Midlands -glad you had a good night though

steve 

[GazOC]

Awful in N Wales too, I didn't even bother setting up 

[FLO]

Apologies for not responding earlier. Sales of astronomy equipment during the lockdown are at an all-time high so we are working overtime to keep up. 

Most will be surprised to hear it was Ian King who prompted us to stock these Japanese-made telescopes (Ian wrote the product descriptions). He has a collection of vintage long focal-ratio achromat telescopes, including the ScopeTech f15 model discussed here. It outperforms them all! He wanted to import them when he was at 'Ian King Imaging' but had to admit they didn't fit his websites focus on astrophotography. When he joined FLO, importing them was one of the very first suggestions he made. It took us a while (you'd be surprised how difficult it currently is to export telescopes from Japan) but here they are, albeit in small numbers. Ian now also owns the f12.5 model 🙂  

Traditional telescopes like this are very niche. They do include some plastic components but they don't feel cheap and the lighter weight is welcome. Indeed anyone comparing them with Chinese-made achromats is, with respect, missing the point. The optics are very - very - well made and the views are sublime. It is not an expensive Sky-Watcher or Bresser, it is more like an affordable achromatic Takahashi. 

HTH, 

Steve 

[johninderby]

if I didn’t already have the StellaMira 80 f/10 not to mention the Carton 100 f13 I would seriously be considering the 80 f/15. Did think about getting one in order to do a comparison then selling it on. 🤔

Edit: Thinking 🤔

Edited May 29, 2020 by johninderby

[dweller25]

SKywatcher 80ED v Scopetech 80 F/15

That would be an interesting shootout ........

[johninderby]

Had a good morning selling on eBay so a ScopeTech STL-80A Maxi 80mm F15 Classical Refractor has been ordered from FLO. 🥳🙂👍🏻

[Ricochet]

40 minutes ago, johninderby said:

Had a good morning selling on eBay so a ScopeTech STL-80A Maxi 80mm F15 Classical Refractor has been ordered from FLO. 🥳🙂👍🏻

Nice.  I look forward on your report on which 80mm scope is the one to buy. 

[johninderby]

2 hours ago, Ricochet said:

Nice.  I look forward on your report on which 80mm scope is the one to buy. 

Think it will be the StellaMira that is the better all rounder but the ScopeTech will be a close second on planetary. So for a purely planetary scope the ScopeTech should be the better buy but if you want more the StellaMira would be the one.

Edited May 30, 2020 by johninderby

[heliumstar]

@FLO

Interesting scopes but I will hijack this thread for something else. I heard one particular mount from the same manufacturer is heading your way

 

 

[F15Rules]

22 hours ago, dweller25 said:

SKywatcher 80ED v Scopetech 80 F/15

That would be an interesting shootout ........

It certainly would. I'd expect the overall optical quality to be very similar in terms of sharpness and CA.

However, these are two very different scopes which excel in different areas: I'd expect the F15 to win on stellar points presentation, double stars and depth of focus (ease of obtaining a sharp image at high powers), ability to take higher powers and show more planetary/lunar detail in less than ideal seeing, while I think the ED80 would win on wider field of view, slightly better star colours due to the ED glass, and better for imaging if that's your thing.

I would expect contrast to be very good in both scopes. Finally, the ED80 would be more easy and convenient to mount and handle, while the F15 would be far nicer to look at.

All of the above just my opinion of course, feel free to disagree😊.

I like F15 refractors😁

Dave

[dweller25]

Spot on 👍

[John]

With the aperture the same, the airy disk should be the same apparent diameter in both scopes. Have I got that right ?

So if the F/7.5 has a similar figuring accuracy to the F/15 and care is taken to achieve accurate focus, I would have thought that the actual resolving power would be pretty much the same ?

Or are other factors at work here ?

 

[johninderby]

Some useful info on the subject here.

http://www.astropix.com/html/i_astrop/focus/defs.html

[Merlin66]

John,

With the same aperture the angular size of the Airy disk will be the same, but the linear size at focus will depend on the focal length. You get larger star "images" with longer focal lengths,

(In spectroscopy we have to consider the linear size of the seeing disk for the various focal lengths we use to set the optimum slit gap. With seeing of 1 sec arc... on the C11 @f10 (2800mm fl) the star size is 13.6 micron (FWHM), whereas the same scope working at f5 (1400mm fl) the star is only 6.8 micron)

[F15Rules]

9 hours ago, John said:

With the aperture the same, the airy disk should be the same apparent diameter in both scopes. Have I got that right ?

So if the F/7.5 has a similar figuring accuracy to the F/15 and care is taken to achieve accurate focus, I would have thought that the actual resolving power would be pretty much the same ?

Or are other factors at work here ?

 

 

8 hours ago, johninderby said:

Some useful info on the subject here.

http://www.astropix.com/html/i_astrop/focus/defs.html

 

8 hours ago, Merlin66 said:

With the same aperture the angular size of the Airy disk will be the same, but the linear size at focus will depend on the focal length. You get larger star "images" with longer focal lengths,

This is all fascinating stuff. I am a visual only observer and never "got" serious maths, my limit being reasonably competent at arithmetic, so all the above is very helpful.

I can only go by what I see through my scopes, and the airy disk image shown in the article is a great representation of what I see with my 80mm F15 in most conditions - a large, steady disk with one complete diffraction ring surrounding the disk. Even my FS128 F8 doesn't always show a single steady disk as clearly as that, and the disk looks smaller..

It appears, from the data in the article above that this is what the theory/maths predicts. Same with depth of focus - my Moonraker F15 has a dual speed focuser but I rarely need to use the fine focus facility. Conversely, my FS128 has a stock single speed focuser and I do use a Baader fine focusing eyepiece holder to assist in getting the best focus at high powers.

I wonder if this "superior" ease of fine focusing on longer focal lengths is one reason that Takahashi offered both F7.4 and F9 doublets..? Better able to get critical high power focus for planetary/double star observing perhaps?

https://stargazerslounge.com/topic/268106-takahashi-fc100-f74-vs-f9/

Discuss!

Dave

Edited May 31, 2020 by F15Rules

[andrew s]

9 hours ago, John said:

With the aperture the same, the airy disk should be the same apparent diameter in both scopes. Have I got that right ?

So if the F/7.5 has a similar figuring accuracy to the F/15 and care is taken to achieve accurate focus, I would have thought that the actual resolving power would be pretty much the same ?

Or are other factors at work here ?

 

Only if you view them at the same magnification which would mean two very different fl eyepieces.

Regards  Andrew 

Edited May 31, 2020 by andrew s

[Stu]

46 minutes ago, F15Rules said:

 

I can only go by what I see through my scopes, and the airy disk image shown in the article is a great representation of what I see with my 80mm F15 in most conditions - a large, steady disk with one complete diffraction ring surrounding the disk. Even my FS128 F8 doesn't always show a single steady disk as clearly as that, and the disk looks smaller..

I wasn’t aware of the link with focal ratio before reading this thread; I thought airy disk size was only related to aperture so that’s very interesting to know.

What I’ve been seeing lately when using my little Telementor and Alkor recently, is that they do produce much larger airy disks than larger scopes, so they show them much more easily. Your FS128 will show them under the right conditions, they are just smaller and harder to see if conditions don’t support high power. That’s the reason larger scopes show more detail.

Strangely I do actually enjoy the larger disks in the smaller scopes; they easily present textbook star patterns and I guess this in some way accounts for doubles like Izar looking so neat in them, you are just looking at two disks and a diffraction ring around each. In a larger scope if the conditions aren’t so good then it can look a little messier, but that’s just because you are seeing more of what is going on.

[F15Rules]

Exactly Stu, well put.

And much as I like my views in the 80/F15, I won't be letting my FS128 go anywhere, anytime!😁

Dave

[johninderby]

How could anyone get by with just one scope? 😁

Looking forward to finding out just how good the 80mm f/15 is. Will it find a permanemt home or will it be good try but not quite up to it? 🤔🤔🤔