Minimum Useful Scope Aperture: Outdated concept ?

[John]

2 hours ago, Xilman said:

....You clearly meant to write "visual observing".

Yes indeed !

 

[Rob]

Excellent post @John its a real interesting one. I've also been a visual observer since 1985!.. I started out with a Patrick Moore book from the Science Museum.. years ago friends from over the pond suggested "Nightwatch' by Terence Dickenson. That opened my world!. I find in the last 10 years with the improvement of optics and telescope builds, all apertures have there place, and can certainly offer massive enjoyment in observing. All my scopes get frequent use on many targets.

Rob

[Peter Drew]

I've been involved in this "game" longer than most but my main take from all this is ("Thank my lucky stars that I couldn't afford to buy a telescope!").  Why?, because it forced me to make my own which lead me on to being a telescope maker both as an amateur and a professional.     🙂

Edited November 19, 2020 by Peter Drew

[Xilman]

On 19/11/2020 at 16:07, Peter Drew said:

I've been involved in this "game" longer than most but my main take from all this is ("Thank my lucky stars that I couldn't afford to buy a telescope!").  Why?, because it forced me to make my own which lead me on to being a telescope maker both as an amateur and a professional.     🙂

Remember the 27.5cm Mak-Cas you made for the Oxford University Astronomical Society?

I made good use of that one.

[AlexK]

I'm in the hobby since 1979. The aperture does matters still. Even though the physics is gradually changing and even being revolutionized, it's not that drastic
You just being confused by the psychological transformation of your hobby attitude. I'm enjoying it even naked eye as nearly every starry region I see is linked with amazing observations memories. But certain treats are physically unreachable without some optics. And the rule of thumb still stands: 80mm refractor, 150mm reflector - is the way to go beyond learning basics. I'm personally wouldn't go any less than 12" without feeling I'm sacrificing the views.
In addition, AP-ers have lowered the plank in unprepared minds a lot lately, thanks to the computational power at their disposal. They are creating really inspiring masterpieces with just 60mm lenses every day around the world. But the eye is a very different instrument.

Edited December 30, 2020 by AlexK

[Xilman]

9 minutes ago, AlexK said:

I'm in the hobby since 1979. The aperture does matters still. Even though the physics is gradually changing and even being revolutionized, it's not that drastic
You just being confused by the psychological transformation of your hobby attitude. I'm enjoying it even naked eye. But certain treats are physically unreachable without some optics. And the rule of thumb still stands: 80mm refractor, 150mm reflector - is the way to go beyond learning basics. I'm personally wouldn't go any less than 12" without feeling I'm sacrificing the views.

I think we are in violent agreement! You can do real science with almost anything but bigger is almost always better.

I have been in the hobby since 1975. Since then technology has added 5 or 6 magnitudes to our light grasp. Seeing Pluto used to be a real challenge in a 250mm reflector back then. Now it is almost trivial to image it. Millimagnitude accuracy photometry was impossible for the vast majority of professionals let alone the likes of us. Now it is straightforward (though it does require careful attention to details) ror bright targets such as many exoplanetary transits.

Astrophotography used to be a challenge for hard-core geeks. Now anyone with a smartphone pointed at an eyepiece can do much the same sort of thing.

Finding out about pretty much anything but solar system objects and the Messier catalogue used to be realy difficult. The interweb-thingy now gives easy access to bleeding edge research.

As Supermac once said: you've never had it so good.  IMO, it is only going to get better.

I would love to own (a) active optics yielding diffraction-limited resolution, (b) a telescope with an aperture >=2m and (c) a camera which works out into the infrared. The first and third may well become available to amateurs within my lifetime.

 

[neil phillips]

On 01/03/2019 at 16:00, John said:

There are a number of terms used in some older books that deserve to be questioned, for example  "useful planetary work".

Perhaps today you need a launch vehicle, a robotic spacecraft, a team of engineers and scientists and a few million $'s to do useful planetary work ?   

 

 

Not necessarily. Impacts on Jupiter have often been picked up by amatures. Bringing it to the attention of professionals. New and interesting storms have been picked up on Neptune by amatures Like Kokatha man . I even got one in 2016 with a bog standard SW 300p

Uranus and Neptune 30th August 2016 - Imaging - Planetary - Stargazers Lounge

Theres always a place for something new to potentially show up on planets. Like the begining of a storm outbreak on Saturn. professionals dont have time to do this kind of monitoring. So a heads up is always a possibility. 

As a comment on the thread. Presently enjoying some nice views with a SW 70mm F12.8 refractor. lunar detail is actually quite good. Could easily see the horse shoe appearance of the Orion nebula, At the very least with the 80mm frac 150 reflector advice. My current 70mm frac is very enjoyable. Surely thats all that matters

Edited January 2, 2021 by neil phillips

[John]

16 minutes ago, neil phillips said:

..... My current 70mm frac is very enjoyable. Surely thats all that matters

Very much so Neil

 

[Xilman]

Other "planetary" (more accurately, solar system objects) research-quality work that can be done by amateurs includes astrometry and photometry of smaller bodies. Admittedly you are not going to do it visually with a 80mm refractor but a 200mm or more aperture on a good drive and fitted with a camera can certainly do useful work.

[mikeDnight]

John started this thread in March 2019 and I'm wondering if he's finished that book he wasn't intending to write, as I'd like to buy it?! ☺

I still believe minimum useful aperture is an outdated concept. It only serves to stop us observing before we begin. Sadly, many observers still harbour this concept in their heart, and so assume as fact that a certain aperture is unable to show an object well, without ever actually having first hand experience. 

 

Edited January 2, 2021 by mikeDnight

[Piero]

I think it all depends on the kind of objects one wants to observe.

With my TV-60, I've spotted/observed about 250-300 targets. I intentionally wrote spotted/observed, because a few of those targets can only be spotted on that telescope given the limited aperture. Said this, it has been a great learning curve. In contrast to a larger telescope, a small wide field refractor can let one find many objects, which means the knowledge of the sky increases considerably. 

There are so many classes of objects that that telescope doesn't / cannot show well though. My 100mm Tak is a bit better on this, but it is still rather limited. I don't want to sound dismissing about small apertures though. They do have a lot of potential. 

To me, the class of telescopes whose future is uncertain is the long focal length / small aperture, like the classic 60/70mm F10-F15 acromats, which were popular in the past. I see these more like piece of nice furniture, but nowadays quite limited in the field. In contrast, a 60 ED short tube shows similar optical quality, but it is much more portable, possibly lighter, and can show a massive (!) FOV with normal 1.25" eyepieces.

[Mark at Beaufort]

Although I have a range of scopes up to a 12" Dob I often use my 15x70 Apollo binos. If I screw a H.Beta filter on one side and my TeleVue Nebustar UHC on the other I have been able to obtain a nice view of the California Nebula. I assume I could obtain a similar view using a 60/70mm ish frac with a wide FOV eyepiece.

The pleasure sitting under the stars and using whatever size scope just gives me huge enjoyment.

 

[John]

I've just read through the posts in this thread and they do make some very interesting and valid points. Thanks to all who have contributed.

I have owned quite a few smaller aperture scopes over the past few years, while I have often been pleasantly surprised at what they could show, I didn't seem to hang onto the ones that were less than 100mm in aperture for very long.

I don't try and undertake any particularly serious observing programmes and I've often described myself as a "space tourist" but I suppose 100mm and above is where there seems to be enough observing potential to keep me interested for the long term and to keep coming back for more.

From the views expressed in this thread I can see that this is definitely a case of "Your Mileage May Vary" though

 

 

 

Edited January 3, 2021 by John

[Spile]

Interesting thread as I came through the same journey as many of you. 

I was given a "toy" 2" refractor as a child and I do not regret getting it for one bit. It was a delight to see our moon, the Jovian moons and the rings of Saturn. It sparked my interest in the subject and half a century later I have reconnected to the world of telescopes. Toys can also be very useful as anyone who has made a pin-hole camera from a toilet roll with know.

I have just looked at Partrick's (no Sir then) 'Atlas of the Universe' from just over 20 years ago and the Dobsonian is referred to once - "unsuitable for lunar and planetary observations". 

How things change.

Edited January 3, 2021 by Spile

[Stu1smartcookie]

On 01/03/2019 at 00:45, John said:

Does the old advice on minimum apertures still have some merit though ?

Just to add to this thread ... some people are actually using the Sky-Watcher EvoGuide 50ED Guidescope as a portable scope !!! and why not ?.Anything that works for astronomy is worth looking through imo . 

[Alien 13]

I think every scope has its uses, you certainly cant see things in a 30 inch dob that you can see with the 6 mm scope in your eye and vise versa.

Real science can be done with tiny optics, remember the Russian meteorite that was tracked by security/dash cams..

Alan

Edited January 3, 2021 by Alien 13

[Highburymark]

I’ve just bought (new) a book on lunar and planetary observing which states early on that: “The smallest size of refractor useful for visual work is 4 inches.” There’s that “useful” word again.... 
I don’t want to broadcast the name of the book because it’s generally very good, and written by a respected author. But on the issue of minimum refractor aperture, I think he’s got it wrong.  The amount of joy and satisfaction to be squeezed from the Moon alone with a 3” frac is almost infinite. I’ve often imagined what it would have been like to have had access to a modern scope like an 80ED as a kid - we’re talking the 1970s here - particularly as it was the only time in my life when I haven’t lived with serious light pollution. It would have been a dream. Though I’d have been forced to give up school due to complete exhaustion.
Forty years later, I actually bought one. A beautiful SW Equinox 80. June 2016, it was. Just a few weeks later, I took it to some semi-dark (though far from perfect) skies in Spain. And I’ve just checked my notes from that week-long trip - reading the list of Messiers, NGCs and planets, looks like my little, not very “useful”, 80mm did rather good 😁

[John]

Looking back at my notes from the mid 1980's I managed to see quite a lot of stuff with my old Tasco 60mm refractor. All I could afford / justify back then but it got me hooked.

 

 

 

[Piero]

In `Observational Astronomy for Amateurs` Sidgwick mentioned magnifications of at least 400x for critical lunar observing. Assuming crisps views, his comment can offer an idea of what kind of minimal aperture he meant!

Again, I think we all have different tastes on this. At mags over 400x, one can seriously study the moon for years, due to the small image scale. Said this, some of the very best views of the moon I had were when it was full, slightly above the horizon, and using my TV-60 at 15x. In particular, the Moon was coming up from bushes and tree branches with a bird or two crossing the FOV time to time. Yes, it was 100% artistic and 0% scientific, but oh man, how beautiful it was to my eye! 

[John]

4 hours ago, Piero said:

...some of the very best views of the moon I had were when it was full, slightly above the horizon, and using my TV-60 at 15x. In particular, the Moon was coming up from bushes and tree branches with a bird or two crossing the FOV time to time. Yes, it was 100% artistic and 0% scientific, but oh man, how beautiful it was to my eye! 

I had a similar observing experience at my 1st SGL star party. The campsite is overlooked by a hill covered mostly by pine forest. A spotted the Moon rising behind the trees and used a very low magnfication in my Vixen ED102SS to watch it gradually appear peeking out from behind the silhouetted pine trees as it rose. A memorable view 

 

Edited January 4, 2021 by John

[JeremyS]

2 hours ago, John said:

I had a similar observing experience at my 1st SGL star party. The campsite is overlooked by a hill covered mostly by pine forest. A spotted the Moon rising behind the trees and used a very low magnfication in my Vixen ED102SS to watch it gradually appear peeking out from behind the silhouetted pine trees as it rose. A memorable view 

 

Ah yes: star parties 

😥