Small aperture APO for visual

[Elp]

Based on what the OP has, I do genuinely believe there needs to be more of a FL gap between the scopes, otherwise they may find one will quickly become redundant. That's why my three are 60/370mm (ref), 102/714mm (ref) and 150/1500mm (sct).

Edited January 16 by Elp

[SwiMatt]

I do enjoy hearing about Takahashis and other marvels, but for that kind of scope I would need to renounce other plans I have in life (or get a mortgage), so it's definitely not in the cards as my second telescope. It's up there among the best, and my wallet isn't big enough... nice to dream though

It's amazing to see the love that people have for small refractors. This is going to be a tough choice for sure. All in all, the quality and pleasure of use of small apos make it feel like the way to go.

And please keep discussimg, I just got the popcorn out

[Stu]

1 hour ago, SwiMatt said:

I do enjoy hearing about Takahashis and other marvels, but for that kind of scope I would need to renounce other plans I have in life (or get a mortgage), so it's definitely not in the cards as my second telescope. It's up there among the best, and my wallet isn't big enough... nice to dream though

It's amazing to see the love that people have for small refractors. This is going to be a tough choice for sure. All in all, the quality and pleasure of use of small apos make it feel like the way to go.

And please keep discussimg, I just got the popcorn out

Yep, definitely doesn’t need to be a Tak, in fact shouldn’t be a Tak, plenty of these small apos with decent glass will do the trick for way less money.

As I think you’ve realised, the big decision is whether to go 60/70mm or 100. Personally I wouldn’t go as low as 60mm as I think there are real benefits to a little more aperture. 72mm is a bit of a sweet spot, still very portable in a way that even some 80mm aren’t, but very capable. This is the one I had from TS, although if buying from Europe you need to check out duties etc; I believe they ship them with everything paid but do check.

https://www.teleskop-express.de/shop/product_info.php/info/p8866_TS-Optics-Doublet-SD-Apo-72-mm-f-6---FPL53---Lanthanum-Glass-Objective.html

FLO do an 80mm f6.25 but that is 3kg vs 2.2kg for the TS. I think Altair probably do a similar 72mm spec too.

They do:

https://www.altairastro.com/altair-72-edf-refractor-dual-speed-rp-focuser-optical-test-report-451-p.asp

If going 100mm, I reckon the Starfield is hard to beat. Not had one, but the spec is great and the reviews equally good.

https://www.firstlightoptics.com/starfield-telescopes/starfield-102mm-f7-ed-doublet-refractor.html

Hard decision to make! Portability and widefield vs full 4” performance and a bit less portable. You decide! 🤣🤣

[Paz]

I would flag the question of weight. What size and weight of mount will you want to use and what amount of vibes will you tolerate. This can guide what weight of a small scope it is ok to go for.

I have a 72mm f6 apo that is my main travel scope now. I have an ST80 that has two advantages over the 72mm, one obviously is aperture but the other is light weight so less vibes, and thus latter point matters a lot when using light portable mounts.

My 72mm apo doesn't have a rotating focuser, I avoided scopes withose to save weight.

The reasons why the 72mm gets used most are that it has a better focuser, more available infocus, and stronger/better facilities to mount finders on it.

I also have a 102mm f7 apo, but to me that is a completely different class and not what I would call small. A 102mm apo would compete with your maksutov, but a 70-80mm apo would be complimentary.

I admit I would not want to go below 70mm of aperture myself.

[GrumpiusMaximus]

This is the scope that I own:

https://www.altairastro.com/altair-starwave-ascent-70ed-telescope---visual-and-astrophotography-bundle-464-p.asp

The 72s that @Stu has posted are slightly more premium, with better glass.  Mine does exhibit some CA around 100x on Jupiter (on a very clear night, with a passing wind) but nothing unacceptable.

I'd be tempted to go for the 100 Starfield but my mount is only an AZ-GTI.  Which also brings up the question of mounting.  I like a setup I can grab with one hand and put on my patio if I get a ten minute break in the clouds.  But that's my priority, which may not match your priority.

[RobertI]

24 minutes ago, Stu said:

72mm is a bit of a sweet spot,

I almost used the very same words, then chickened out! I have to say if budget is important the Sky-Watcher 72mm is hard to beat at £329. Glass type unknown I think but apparently very good for visual annd imaging.  Apparently the dewshield, though not retractable, does easily slide off for transport. 

[josefk]

i would chip in another datapoint for wide field viewing @SwiMatt if the priority use case would be a wide field compliment to your mak - beware the quality of your skies!

I've got more wide field capability in my shortest-focal-length-smallest-aperture-scope than i can regularly access usefully; simply because at the big exit pupils (>4mm) generated for these wide field views the sky is fairly grey. I trust i will be blown away when i take it to a B1/B2 location but in my regular B4 location i don't use it for the very widest views as much as i thought i would, i self limit to about 3.4 degrees (4mm exit pupil) and prefer about 1.5...2 degrees at exit pupils around 1.5...2mm. Achieving this balance is also a matter of the AFOV the eyepiece not only the focal length of the scope.

That doesn't detract from all the other small scope APO loveliness others have mentioned.

 

Edited January 17 by josefk

[badhex]

Another vote here for 72mm-ish. I have a William Optics Zenithstar 73 (ED doublet, FPL-53) and it's an incredible little scope. I take it abroad with me regularly and everything fits easily into one cabin sized backpack with the tripod on the side - one year we even went island hopping in Greece and stayed on a volcano in the sea with Bortle 2 skies.

This is an older photo with an AZ-GTi but I normally take my Scopetech Mount Zero. There is also room for a 2" diagonal and EPs - 6° TFOV is easy in a scope like this. I also managed to squeeze a 2" Herschel wedge in there on one holiday. 

 

This photo is from last summer in Italy, searching for Enceladus - which was probably a tall order for a scope this small but not by much! Tethys was no problem which gives you an idea of performance, though for planetary the image scale will always be small (even if it is super sharp). I've also seen the entire veil with an Oiii filter (under good conditions) and many other faint targets which you might not expect for scope so small. 

 

 

It is not quite the all rounder you'd get with a 4" but I've had zero issues with CA even when pushing above sensible magnifications, and in my experience the portability definitely makes up for the loss of aperture. I wouldn't feel comfortable taking my 4" away, but this is pretty easy. It's a heavy backpack once full, of course - about 10kg - but I'm not shy with the hefty EPs, 2" diagonal etc, so you could easily shave weight off. 

 

Edited January 17 by badhex

[Bivanus]

I use a SW72ED. It's ok , however I'm pondering selling it and switchings to a TS 80mm f/7 FPL53-Lanthan

https://www.teleskop-express.de/shop/product_info.php/info/p8637_TS-Optics-Doublet-SD-Apo-80-mm-f-7---FPL-53---Lanthanum-Objective.html

[badhex]

30 minutes ago, josefk said:

i would chip in another datapoint for wide field viewing @SwiMatt if the priority use case would be a wide field compliment to your mak - beware the quality of your skies!

I've got more wide field capability in my shortest-focal-length-smallest-aperture-scope than i can regularly access usefully; simply because at the big exit pupils (>4mm) generated for these wide field views the sky is fairly grey. I trust i will be blown away when i take it to a B1/B2 location but in my regular B4 location i don't use it for the very widest views as much as i thought i would, i self limit to about 3.4 degrees (4mm exit pupil) and prefer about 1.5...2 degrees at exit pupils around 1.5...2mm. Achieving this balance is also a matter of the AFOV the eyepiece not only the focal length of the scope.

That doesn't detract from all the other small scope APO loveliness others have mentioned.

 

This is a very good point - and will add my own experience as well. Under none-ideal skies there's no getting away from the grey sky at large exit pupils. My home locations have been Bortle 7 or 8 for the whole time I've had the scope and I definitely prefer to use it in darker skies. Having said that, many of my trips away have not been specifically for astronomy, so on average have had a lot of Bortle 4 and 5 skies, and still thoroughly enjoyed it. Of course, it's all personal preference, but as @josefk says its something you should definitely take into consideration. 

[dweller25]

Hello @SwiMatt,

Given that everything has to fit into a backpack then a 70-80mm refractor would probably be the best option ?

As already mentioned, Telescope Express do a really nice very light and short 72mm with FPL53 glass and a dual speed focuser …..

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p8866_TS-Optics-Doublet-SD-Apo-72-mm-f-6---FPL53---Lanthanum-Glass-Objective.html

They also sell a great 80mm which is just a little bit longer and heavier…..

https://www.teleskop-express.de/shop/product_info.php/info/p8637_TS-Optics-Doublet-SD-Apo-80-mm-f-7---FPL-53---Lanthanum-Objective.html

Good luck in your search 👍

Edited January 17 by dweller25

[Mr Spock]

Some small scopes can be really crisp - and not necessarily that expensive. I like the look of the Evolux 62ED - very nice and only £329.

The only real negative for me with my FS60 is the brightness of the image. It gives lovely sharp views of Jupiter but at any kind of magnification the image is really dark and floaters become a problem.

[SwiMatt]

2 hours ago, josefk said:

i would chip in another datapoint for wide field viewing @SwiMatt if the priority use case would be a wide field compliment to your mak - beware the quality of your skies!

I've got more wide field capability in my shortest-focal-length-smallest-aperture-scope than i can regularly access usefully; simply because at the big exit pupils (>4mm) generated for these wide field views the sky is fairly grey. I trust i will be blown away when i take it to a B1/B2 location but in my regular B4 location i don't use it for the very widest views as much as i thought i would, i self limit to about 3.4 degrees (4mm exit pupil) and prefer about 1.5...2 degrees at exit pupils around 1.5...2mm. Achieving this balance is also a matter of the AFOV the eyepiece not only the focal length of the scope.

That doesn't detract from all the other small scope APO loveliness others have mentioned.

 

I never thought that B4 would be considered as "bad sky quality" 😂 consider that I live in B7-B8. It would be a dream to have fast access to B4 every time I want.

Quality of skies isn't really something I can control, unfortunately. And because portability is so important to be able to get away from streetlights - limiting me to shorter refractors - all of a sudden I don't see a way to avoid larger exit pupils when getting the widest views. For sure a small refractor will get more use when I travel: my Mak at the moment is already bulky and big enough that I would hesitate to fly with it. Do you think however that given the same sky conditions a 70-80 apo is a better choice than an ST80 or similar achros, considering the higher price tag?

All things combined, I will probably not go for an apo that requires me to change my whole set up (I have an AZ5, and will soon upgrade my tripod to something more solid): this probably rules out the 4 inches. There is always a chance to upgrade the whole set up to only a 4" apo as a my work horse, but it's not in the cards as of yet. I will say that it is nice to dream about it

For sure you all gave me so much to think about. I read and re-read all of your comments because it's just a pleasure, and a very good cure against that terrible disease that is aperture fever.

Edited January 17 by SwiMatt

[badhex]

8 minutes ago, SwiMatt said:

Do you think however that given the same sky conditions a 70-80 apo is a better choice than an ST80 or similar achros, considering the higher price tag?

I would say yes, for things like planetary, doubles, PNs etc with the obvious caveat that you can't beat the physics so image scale will always be small, but with better colour correction and sharpness, and overall better build quality, focuser etc. As mentioned I've had no issues with CA in the ZS73. At higher powers, you won't have to worry much about the sky contrast, and from my experience a small, well built APO or ED doublet can take the magnification well.

I must also caveat that I do not have an ST80 with which to compare, though I do have a Celestron Travelscope 70, Synta made, which has surprisingly good optics - they are apparently very hit and miss but I seem to have been lucky. The ZS73 is objectively better by any criterion you wish to examine, except of course price. 

[Nik271]

16 minutes ago, SwiMatt said:

Do you think however that given the same sky conditions a 70-80 apo is a better choice than an ST80 or similar achros, considering the higher price tag?

Yes I think an APO  or least an ED doublet is a better choice than an achromat, and not just because of the glass. The more expensive scopes also have better focusers which at F/5 or F/6 is important as the focus point is very shallow.

[Stu]

48 minutes ago, SwiMatt said:

Do you think however that given the same sky conditions a 70-80 apo is a better choice than an ST80 or similar achros, considering the higher price tag?

Absolutely yes! An Apo just opens up a whole new world in crispness, double stars and planetary that the ST80, good though it is at the price just can’t match. I have an ST80 and know the difference, in fact I did a post on what I called a very unfair fight with my Tak FC-76DCU here. Results would be nearly as good with a 72mm fpl-53 apo although the Tak is f7.5 vs f6 for the 72mms normally.

As Badhex says too, build quality, focuser all so much better and that’s also part of what makes these little scopes a joy to own and use.

[Elp]

I've always wondered what a Borg 90FL will be like, as it's great aperture and light weight, and uses Canon fluorite glass I think. But the photographic images I've seen show blue or magenta star glow so I don't think it's that well corrected. If it works, this would be my goal scope, but my Z61 does so well at near everything (I've used it visual, AP, planets (small but some detail visible), white light solar, ha solar and it's excelled at everything), I'd be curious how it'd compare to more premium scopes.

[Stu]

1 minute ago, Elp said:

I've always wondered what a Borg 90FL will be like, as it's great aperture and light weight, and uses Canon fluorite glass I think. But the photographic images I've seen show blue or magenta star glow so I don't think it's that well corrected. If it works, this would be my goal scope, but my Z61 does so well at near everything (I've used it visual, AP, planets (small but some detail visible), white light solar, ha solar and it's excelled at everything), I'd be curious how it'd compare to more premium scopes.

The 90FL is f5.6 which is pretty fast. Even with premium optics there is a limit to correction including for field curvature etc. It is a factor for all short focal length doublets.

[Roy Challen]

14 hours ago, SwiMatt said:

Yeah the weight of a 4" is a bit of a turn off: at 3.2 kg, the Mak is great but already on the heavier side for a truly portable set up (especially when travelling - I do have access to better skies from time to time, but meed to fly). I see lots of advantages in getting down to 72 (or even 60?? Your passionate speech didn't fall on deaf ears @MalcolmM). But it's a lot more money for something similar in weight and portability to a ST80 or ST102, which is why I'm loving to hear all your positive experiences. It seems worth it.

Now that I think about it, I have yet to hear someone complain about small apos...

I'll second what @MalcolmMsaid. I'd go for a Takahashi FS60-CB too. Which I did! 

Whilst it cannot compete with the resolution of a 100mm for planetary use, it can still make out the most interesting features, certainly well enough for a short session abroad. It is also a lot more money than an ST80/102,  but it is a lot better optically too. 

60mm is also my most used aperture, my Daystar is also a 60😁

Edited January 17 by Roy Challen

[Ian McCallum]

Hopefully, I'm not too late to the discussion...  I've got a couple of achros, specifically the SW ST120 and EV120.  Both of these experience some for of CA, which I tend to filter with a Baader Fringe Killer filter (from memory).   Before I got these, I was using a SW 200p Classic Dobbie.

[SwiMatt]

1 hour ago, Stu said:

The 90FL is f5.6 which is pretty fast. Even with premium optics there is a limit to correction including for field curvature etc. It is a factor for all short focal length doublets.

Besides, for visual use the aberration might be more tolerable. If one has the money, the 90FL seems like a great portable scope - although maybe not quite small enough to fly easily with it.

By the way, another unseen advantage for a light frac with smaller aperture is how convenient it would be for solar observation. Smaller filters (easier to carry for, and easier to replace if the foil tears), smaller set up. I could almost think about putting the setup in the backpack for a lunch session.

I think, as a summary, there is not one person here who thinks that a committed astronomer should go for a fast achromat if money isn't the main issue at hand. Apo wins in basically every respect for this type of usage. A good apo regularly seem to punch above its weight - a thing that is not easily said for any other scope that I heard discussed. But at this point I might slowly update other things and go for a big purchase later in the year (I'm thinking that Williams Optics instruments look veeeeeery sleek and beautiful)...

[glafnazur]

1 hour ago, SwiMatt said:

Besides, for visual use the aberration might be more tolerable. If one has the money, the 90FL seems like a great portable scope - although maybe not quite small enough to fly easily with it.

By the way, another unseen advantage for a light frac with smaller aperture is how convenient it would be for solar observation. Smaller filters (easier to carry for, and easier to replace if the foil tears), smaller set up. I could almost think about putting the setup in the backpack for a lunch session.

I think, as a summary, there is not one person here who thinks that a committed astronomer should go for a fast achromat if money isn't the main issue at hand. Apo wins in basically every respect for this type of usage. A good apo regularly seem to punch above its weight - a thing that is not easily said for any other scope that I heard discussed. But at this point I might slowly update other things and go for a big purchase later in the year (I'm thinking that Williams Optics instruments look veeeeeery sleek and beautiful)...

I have the William Optics ZS61 and it is a lovely scope, my most used scope last year. I used to have the ZS66 but I sold it on and immediately regretted it.

[MalcolmM]

3 hours ago, SwiMatt said:

Do you think however that given the same sky conditions a 70-80 apo is a better choice than an ST80 or similar achros, considering the higher price tag?

I had a Skywatcher Startravel 102 for a couple of years. I really enjoyed it. For lunar and planetary, the FS60CB, despite being much smaller, gave much better views. I would imagine a 70mm would be even better. I felt it was also better for many DSOs simply because of the high contrast and very sharp images. I would strongly endorse the APO over the achro as long as the wallet can stand it!

Malcolm 

[Elp]

1 hour ago, SwiMatt said:

Williams Optics

They can be overpriced though compared to equivalents. Id quite like to add a Pleiades 68 or 111 but look at how much they cost, one of the latest Askar triplets seem more like a better buy if you were on the market for that focal length.

[michael.h.f.wilkinson]

Quite some years ago, I added an APM 80 mm F/6 triplet APO as wide-field visual scope and imaging scope to complement my Celestron C8. At only 2.5 kg it is wonderfully light, and can be taken abroad in cabin luggage easily. The wide-field views with the Nagler 31T5 and Vixen LVW 42 mm are just awesome. My best view of M33 was definitely with the  Nagler 22T4. It also serves as my main solar imaging scope, and travelled with me to the USA for the 2017 eclipse, and got me the most memorable astrophoto ever. A scope like this is also different from a pair of big binoculars. I did a comparison a few years back

They can pry this scope out of my cold dead hands.