First scope advice – Evostar 102 v 120?

[Roy Challen]

10 hours ago, vlaiv said:

No, just an image I found online - it shows nicely lid type aperture mask. In fact, I think there is a blog dedicated to making and using mask - maybe it has make of scope and details.

https://10minuteastronomy.wordpress.com/2017/02/11/why-and-how-to-make-a-sub-aperture-mask-for-a-refractor/

Yep, it seems to be Bresser Messier AR102S Comet Edition. Not sure if it is available any more.

Luckily, the TAL 100RS lens cap has a removable centre section 30mm in diameter turning f/10 into f/33. I've never even tried it, should be good for lunar and solar.

Edited February 18, 2021 by Roy Challen

[Stu1smartcookie]

10 hours ago, ecuador said:

Oh my! I just checked online prices and the Evostar 80ED is £480 new now! I am sure it was just under £350 when I got it... Well, of course back then I could also buy almost $2 with a pound sterling... 😪

Yes , Prices have taken quite a hike ..which in turn brings to the fore the secondhand market . But , even those prices are inflated now as savvy sellers( or maybe unscrupulous)  in some cases are over pricing their unwanted gear . I saw an ST102 with EQ3 mount secondhand , for sale on FB  for sale at £450 !!!! thats a ridiculous price . The message here is to know the value of the product before you commit ! 

Especially as you do not get the guarantees that you get when buying new . Fortunately , with a dedicated site like SGL you can trust the quality you are buying . 

 

 

[Basementboy]

12 hours ago, KP82 said:

Some of these 4" f/7 ED doublets are actually in stock unlike many Skywatcher & Celestron stuffs which are still months away from reaching the shore of UK. But since you also need a mount, you won't be able to get the full kit in a couple of months.

Other than the Altairs, can you recommend any good 4" f/7 ed doublets? I might be able to pick up a mount secondhand. Would an AZ5 suffice?

[Stu1smartcookie]

3 minutes ago, Basementboy said:

I might be able to pick up a mount secondhand. Would an AZ5 suffice?

FLO had an AZ5 mount head still in stock when i last looked .

[Basementboy]

11 hours ago, ecuador said:

As for the discussion about the ST120 and aperture masks etc, CA is above all a matter of preference, as it is a very "special" kind of artefact, so some users would actually prefer the unobstructed 120mm view, others might not. The 80ED or similar offers better views, it is just a matter of price, which is why I'd try to get one second hand (here, astrobuysell UK, FB etc).

Interesting – it hadn't occured to me that I might find CA appealing in some sense. Again, because I'm colourblind, I'm very unlikely to be bothered by "incorrect" colours – as long as it doesn't also mean a serious reduction in sharpness of detail/contrast (which is what my brain hunts for visually/aesthetically, instead of colour).

I'll keep a lookout on the secondhand forums. Why an 80mm over a 4"? Just for price, you mean?

11 hours ago, ecuador said:

Oh my! I just checked online prices and the Evostar 80ED is £480 new now! I am sure it was just under £350 when I got it... Well, of course back then I could also buy almost $2 with a pound sterling... 😪

Yep. That's what started this whole thing off for me. The setup for which I was *just about* willing to pay £539 jumped to £679. Although now I'm very glad I didn't buy it! (Evostar 120 on EQ5 mount.) I think it would have been a bit of an albatross to handle in the park at night.

 

[Basementboy]

3 hours ago, Roy Challen said:

Luckily, the TAL 100RS lens cap has a removable centre section 30mm in diameter turning f/10 into f/33. I've never even tried it, should be good for lunar and solar.

I hear a lot about these TAL 100RS scopes but don't see them retailed anywhere. Quite old school? They look v cool in a Cold War way

[Basementboy]

Also (and apologies if this should be raised in a more specific forum) – but of these two Altairs, why is the one with the smaller aperture more expensive?

https://www.altairastro.com/starwave-80ed-r-ed-doublet-refractor-telescope-466-p.asp

https://www.altairastro.com/starwave-ascent-102ed-f7-refractor-telescope-geared-focuser-468-p.asp

 

[KP82]

9 minutes ago, Basementboy said:

Other than the Altairs, can you recommend any good 4" f/7 ed doublets? I might be able to pick up a mount secondhand. Would an AZ5 suffice?

TS Optics, Astro-tech and Tecnosky offer similarly spec'ed 4" f/7 ED doublets as they all share the same source manufacturers (KUO, Longpern, etc.). The difference between them is usually the focuser, rotatable vs non-rotatable or 2" vs 2.5". So go with whichever is the cheapest. But beware of the import tax if you're going to order from TS Optics in Germany directly for example.

Yes, AZ5 works well with a 4" f/7. Get the mount head only and attach it to either a heavy duty photo tripod if you already own one or the SW 1.75" steel leg tripod.

[Basementboy]

6 minutes ago, KP82 said:

TS Optics, Astro-tech and Tecnosky offer similarly spec'ed 4" f/7 ED doublets as they all share the same source manufacturers (KUO, Longpern, etc.). The difference between them is usually the focuser, rotatable vs non-rotatable or 2" vs 2.5". So go with whichever is the cheapest. But beware of the import tax if you're going to order from TS Optics in Germany directly for example.

Yes, AZ5 works well with a 4" f/7. Get the mount head only and attach it to either a heavy duty photo tripod if you already own one or the SW 1.75" steel leg tripod.

Thanks. That's really clear and helpful.

[KP82]

11 minutes ago, Basementboy said:

Also (and apologies if this should be raised in a more specific forum) – but of these two Altairs, why is the one with the smaller aperture more expensive?

https://www.altairastro.com/starwave-80ed-r-ed-doublet-refractor-telescope-466-p.asp

https://www.altairastro.com/starwave-ascent-102ed-f7-refractor-telescope-geared-focuser-468-p.asp

 

The 80ED-R is a FPL53 doublet with a rotatable focuser whereas the Ascent 102ED uses FPL51 and non-rotatable.

FPL53 ED glass is slightly superior to FPL51 in terms of dispersion characteristics. The difference matters more to astrophotographers than visual users although if budget allows, 53 is always more desirable than 51 assuming the rest of the spec is the same. I remember there is a recent review of the Ascent 102ED in the user equipment review section here. You may want to have a read on that.

[vlaiv]

4 hours ago, Roy Challen said:

Luckily, the TAL 100RS lens cap has a removable centre section 30mm in diameter turning f/10 into f/33. I've never even tried it, should be good for lunar and solar.

Skywatcher scopes also have 2"  and that was really handy on my ST102 - turns scope into 2" F/10 and Jupiter from blurry mess into proper planet (but limited to about x100 mag)

36 minutes ago, Basementboy said:

Other than the Altairs, can you recommend any good 4" f/7 ed doublets? I might be able to pick up a mount secondhand. Would an AZ5 suffice?

TS, Stellarvue, AltairAstro, Technosky and some other brands all source the scopes at the same manufacturer so they are in principle the same scopes except for detail and branding.

Just keep in mind that there are few models of 4" F/7 - one with FPL51 glass (worse color correction) and one with FPL53 glass (better color correction). I think I've seen two different focusers used - 2" crayford and 2.5" R&P.

That 2.5" rack and pinion unit is actually very good. I have it on one of my scopes (80mm F/6 TS triplet APO).

I think that AZ5 will be ok. I have AZ4 and 80mm F/6 and 102mm F/5 both sit perfectly on it. 102mm F/10 does not - it is too long OTA and vibrations are too large for my liking.

36 minutes ago, Basementboy said:

Interesting – it hadn't occured to me that I might find CA appealing in some sense. Again, because I'm colourblind, I'm very unlikely to be bothered by "incorrect" colours – as long as it doesn't also mean a serious reduction in sharpness of detail/contrast (which is what my brain hunts for visually/aesthetically, instead of colour).

Look at this diagram:

It explains a lot about chromatic aberration in short focus achromats like ST102. What is called false color is actually color blur created by out of focus light. If you put 540nm wavelength (green) of light in focus - all the rest wavelengths of light will be out of focus - some by small amount some by large amount. When you are out of focus - that blurs the details. It is not just about image having the wrong / false color - it is about it being blurry because you can't focus it properly - as soon as you focus some wavelength properly - others go out of focus. You can focus only two wavelengths of light at the same time.

Point of color correction is - how much out of focus are other colors and can you see it. ED doublets use special kind of glass that does not "produce rainbow" as much - and while they have curve similar to above - level of defocus is much much smaller - almost unnoticeable (or even completely absent in top models).

33 minutes ago, Basementboy said:

Also (and apologies if this should be raised in a more specific forum) – but of these two Altairs, why is the one with the smaller aperture more expensive?

Because it has more exotic glass type. These glasses contain rare earth elements and are hard to produce. They have certain level of purity.

One is more expensive than the other.

80ED-R uses FPL-53 glass and that is more expensive glass than FPL51. There is also 102 model with such glass:

https://www.altairastro.com/starwave-102ed-r-fpl53-refractor-459-p.asp

That is £500 more expensive than FPL-51 4" F/7

 

 

[Roy Challen]

2 hours ago, Basementboy said:

I hear a lot about these TAL 100RS scopes but don't see them retailed anywhere. Quite old school? They look v cool in a Cold War way

Tal stopped making telescopes a few years ago. Definitely old school, good quality but nothing fancy. Good achromatic lenses though, I'm certainly happy with mine. They do come up for sale every now and again, usually for not much money (mine was £110 posted back 2015). Put one on an AZ4/5 and you have a lightweight, portable 4" setup that performs well, that shouldn't be anywhere near approaching your budget. But I suppose the same could be said of the Evostar.

[Tiny Clanger]

vlaiv  

as usual has the technical aspect nailed ... for chromatic aberration you need to think of light colour as a product of the wavelength , send light through a simple

lens and precisely where focus in longer wavelength light (e.g. red) falls is different to where focus in shorter wavelength (e.g. blue)  light falls, In refracting 'scopes , expensive glass types, and combinations of several types and shapes of  lens are used to try and minimize this, whilst trying to not introduce any of the other aberrations lend based optical instruments are prey to . That's why 'good'  fracs are expensive , or long ( long focal length minimizes C.A.) or both ....

By the way,chromatic aberration is only found in refractors , not reflectors  , bouncing the light off a mirror does not cause the same problems (naturally, other problems arise tho', nothing is perfect  !)

Heather

[Stu1smartcookie]

Ok so i apologise in advance if you think  the following words are harsh  ... they are not meant as a criticism to any one person . I know words can sometimes appear harsh when written as well as spoken 

This thing about CA is , imho , blown out of proportion . To others its almost a crime ! .. I wonder how on earth Galileo got on ? yes i know , tech has moved on , 

Anyway , 

I can see a planet in our solar system !! i can see a beautiful pattern of stars and the smudge of a galaxy ... to me , that is fantastic ... if i want to see something perfect then i will look in a book or maybe watch in awe as Trevor Jones(AstroBackyard)  produces a magnificent image of a far flung galaxy that i can't even see in my scope . Sure i have owned APO refractors before , but now i own two achromats ! I do not do justice to an expensive set up , just for viewing and taking the occasional photo . I am , compared to most , not as good at the finer details of imaging . Lets go back to the initial post by the op on this thread ... he asks about the comparison between two scopes and he has a limited budget ... he is new to the hobby ... Maybe  after a year his first scope will be sitting in a cupboard gathering dust , maybe after 2 months he will be desperate to upgrade to the latest and greatest . 

We ALL know ( some more than others ...Ahem ) that this CAN be the most expensive , frustrating hard ....and more importantly , easy hobby imaginable . Nothing i have read on here has been wrong ... but , i think the post has gone so far from the initial question ( btw i am as guilty of this as anyone ) that the op probably feels so bombarded with the science and recommendations that he is as confused as anyone would be . 

He has expressed gratitude to everyone for their input as any polite person would . I just think we are taking everything a bit further than we need to . 

I really hope nobody takes these comments the wrong way , after all EVERYONE is doing their bit to help the OP . 

[Tiny Clanger]

1 hour ago, Stu1smartcookie said:

Ok so i apologise in advance if you think  the following words are harsh  ... they are not meant as a criticism to any one person . I know words can sometimes appear harsh when written as well as spoken 

This thing about CA is , imho , blown out of proportion . To others its almost a crime ! .. I wonder how on earth Galileo got on ? yes i know , tech has moved on , 

Anyway , 

I can see a planet in our solar system !! i can see a beautiful pattern of stars and the smudge of a galaxy ... to me , that is fantastic ... if i want to see something perfect then i will look in a book or maybe watch in awe as Trevor Jones(AstroBackyard)  produces a magnificent image of a far flung galaxy that i can't even see in my scope . Sure i have owned APO refractors before , but now i own two achromats ! I do not do justice to an expensive set up , just for viewing and taking the occasional photo . I am , compared to most , not as good at the finer details of imaging . Lets go back to the initial post by the op on this thread ... he asks about the comparison between two scopes and he has a limited budget ... he is new to the hobby ... Maybe  after a year his first scope will be sitting in a cupboard gathering dust , maybe after 2 months he will be desperate to upgrade to the latest and greatest . 

We ALL know ( some more than others ...Ahem ) that this CAN be the most expensive , frustrating hard ....and more importantly , easy hobby imaginable . Nothing i have read on here has been wrong ... but , i think the post has gone so far from the initial question ( btw i am as guilty of this as anyone ) that the op probably feels so bombarded with the science and recommendations that he is as confused as anyone would be . 

He has expressed gratitude to everyone for their input as any polite person would . I just think we are taking everything a bit further than we need to . 

I really hope nobody takes these comments the wrong way , after all EVERYONE is doing their bit to help the OP . 

Yep, it is too easy to chase the impossible goal of technical perfection and lose sight of the point of it all, something I said way back in this thread ...

The OP has not looked at the night sky through any telescope yet . As for everyone over the past  year it's a shame he can't go along to a local club meet and do so,  try a few options out and see the 'scopes and mounts size and heft. That would give him an idea of if CA was or was not an important factor for him I don't think we can gauge this at all .

Step back from the black hole of ever higher priced , incremental quality improvements Basementboy , think about what is a truly sensible budget for you to spend,  when you really don't know if this will be an interest which holds you for long. Then on a clear night get out in the park to look up at the sky with whatever you have, unaided eyes are better than you may think, any binoculars at all will show you some amazing stuff. You will be amazed.

(Don't forget your friend to watch your back while you are amazed and engrossed though, we only want you stunned in the emotional sense, not the 'and then they took my wallet and 'phone' sense )

Heather

[John]

I think CA is often over-emphasized as an optical issue. As long as the scope I'm using is showing as much CA as it's spec (aperture / focal ratio / glass type) suggests it should then I'm OK with it. What I do find a problem is Spherical Aberration (SA). SA does scrub off resolution and contrast and limits the scopes usefulness at higher magnifications.

The TAL 100's were very good and low cost achromat refractors. This was mine from 1999 and it performed as well as the somewhat more expensive Vixen SP102 that I had owned previously:

 

 

 

[vlaiv]

I agree with what has been said - I don't mind achromat scope at all, as long as one is aware of its drawbacks (as with pretty much any other design).

We have just touched upon F/5 and F/10 achromats - and F/10 will be much better optically but not as good for wide field, while F/5 will be good for wide field and portable but not as good for planets.

I personally find Evostar 102 on AZ4 mount not to be as stable as I would like.

How about going in between then? It turns out that there is very good scope that is in between - unfortunately it is too expensive in my opinion in comparison to other offerings. It almost has the same price as ED F/7 with FPL-51 glass.

https://explorescientificusa.com/products/ar102-air-spaced-doublet-refractor

This is 4" achromat at F/6.5.

Another interesting choice - if one is willing to sacrifice some of light grasp is:

https://www.firstlightoptics.com/beginner-telescopes/sky-watcher-evostar-90-660-az-pronto.html

That is F/7.3 scope - but only 90mm of aperture.

Another scope worth mentioning is this one:

https://www.firstlightoptics.com/bresser-telescopes/bresser-messier-ar-102s-600-refractor-ota.html

although I'm seriously annoyed with plastic finder and non standard shoe on that one.

I also don't care much for those oversized dew shields that Bresser and sister company ES have on their scopes.

[Basementboy]

If I'm being very honest, I'm actually really grateful and a little stunned that you've all taken the time to essentially help me patiently take halting steps forward. You must get asked these questions all the time. I'm not at all worried about being bombarded – in fact, the best result has been that I DIDN'T buy that Evostar 120 I was nearly ready to pull the trigger on. And that's all thanks to you. I also would not have had any idea about the ED doublet refractors, or actual real-world advice about cooldown times and portability and FOV and what really matters and what kinda doesn't. And I would almost certainly have bought an EQ mount, too, because I had zero clue about something as basic as the fact that you have to carry the counterweights, and maybe that's a total faff to deal with in a park at night.

In other words, I would have made an early mistake trying to get the Biggest and Best scope, instead of something that suited my criteria properly, and ended up instead with an overcomplicated, unwieldy beast that just stressed me out.

I'm particularly grateful, also, because of what Tiny says – namely that I can't actually see any of the scopes in person or meet anyone to chat it through.

So to understand what CA really is (totally get it now about the light wavelengths!), and to hear how much it matters in real life, I'm treating like gold dust – because when I do decide to buy something I've now got a wealth of information specifically about the things I'm interested in.

And that's kinda the biggest thing of all – which is that you've convinced me not to buy anything yet, but instead to get a feel for the sky and bide my time until a good scope comes up in a secondhand sale, or restock actually arrives. And then, crucially, not to worry too much about buying the "wrong" scope, either – because clearly there's a healthy resale market for this stuff (and a healthy percentage of that market cornered by Stu 😉 ), and as long as I don't blow the budget then I might even end up with two telescopes. And that would be OK. And looking through binoculars until I get there is OK, too.

So while I appreciate you guys looking out to not overload me, it's precisely for this level of detail and interest in my own totally unoriginal and dull newbie situation that I posted in the first place, having read dozens of threads over the past few months and got the feeling that it was a safe place to ask a stupid question.

More stupid questions to come. Until then, binoculars on the roof tonight. Fingers crossed for clear skies. 

Chris

[Tiny Clanger]

8 minutes ago, Basementboy said:

More stupid questions to come. Until then, binoculars on the roof tonight. Fingers crossed for clear skies. 

Chris

ROOF ?! You didn't mention roof ! Whole new landscapes of possibility open up ...  🙂 Take a chair & blanket  up there and some binos and lean back in comfort !

Heather

[Basementboy]

1 hour ago, Tiny Clanger said:

ROOF ?! You didn't mention roof ! Whole new landscapes of possibility open up ...  🙂 Take a chair & blanket  up there and some binos and lean back in comfort !

 

Lol. Office not home, unfortunately

[Tiny Clanger]

2 minutes ago, Basementboy said:

Lol. Office not home, unfortunately

Volunteer for overtime ! 🙂

[ecuador]

13 hours ago, Basementboy said:

Interesting – it hadn't occured to me that I might find CA appealing in some sense. Again, because I'm colourblind, I'm very unlikely to be bothered by "incorrect" colours – as long as it doesn't also mean a serious reduction in sharpness of detail/contrast (which is what my brain hunts for visually/aesthetically, instead of colour).

I'll keep a lookout on the secondhand forums. Why an 80mm over a 4"? Just for price, you mean?

Yep. That's what started this whole thing off for me. The setup for which I was *just about* willing to pay £539 jumped to £679. Although now I'm very glad I didn't buy it! (Evostar 120 on EQ5 mount.) I think it would have been a bit of an albatross to handle in the park at night.

 

I did not mean CA is appealing. I was saying 120mm with more CA, i.e. more light out of focus vs 76mm that has less CA but also less resolution is not an easy comparison and some people will prefer the first others the latter. Some people will prefer the 120mm with a violet blocking filter, which gives you a reduced CA view that is also a matter of subjective opinion.

Otherwise, the 80mm vs 4" was because of price and portability. I find the 80mm the max for what I'd call "grab n go" portable, and also a good enough size for most uses. Lots of info to digest in this thread, I see they started you on the Ohara glass types  

[Basementboy]

8 hours ago, ecuador said:

Lots of info to digest in this thread, I see they started you on the Ohara glass types  

Yeah I'm gonna have to make a spreadsheet

[Soligor Rob]

I have the Helios 120 which is the same as the Sky Watcher 120 and have to say optically it's an excellent tool for a beginner, the problem with my set-up is I find the EQ3 mount has a bit too much play for my comfort and the Tripod just isn't stable enough.

I have done as much as I can to eliminate the backlash in the mount but there is still that little bit there when going from one direction to the other.

I have bought better quality eye pieces and a 9x50mm finder scope which makes setting up easier, next upgrade for me is a better diagonal and I'm also thinking maybe a 2" eyepiece for a better FOV.

One thing for certain the guys and their knowledge on here are a very valuable commodity.

[Stu1smartcookie]

5 minutes ago, Soligor Rob said:

I have the Helios 120 which is the same as the Sky Watcher 120 and have to say optically it's an excellent tool for a beginner, the problem with my set-up is I find the EQ3 mount has a bit too much play for my comfort and the Tripod just isn't stable enough.

I have the skywatcher version on a steel tripod and AZ5 ... out last night in a strong breeze but it was really steady . Brilliant views of the moon & Plaides. ( scope is surprisingly light too )