In Praise of Small-Scope Astronomy

[gregl]

The header is the title of an article in the current Sky and Telescope email newsletter. The author sets out a number of reasons why small scopes are worthwhile. And the article is also worthwhile: https://skyandtelescope.org/astronomy-b ... newsletter

[Thefatkitty]

That doesn’t mean I’ve given up on anything bigger than my 114mm tabletop, but this yearning for more has to be tempered by real-world circumstances like budgets, physical limitations, and storage space.

Thanks Greg, I thought that was a well written article, and I couldn't agree more on every level. Light-buckets are great, but my smaller scopes get the most use for sure. I'm more into the grab and go than the lug it out...

All the best,

[gregl]

I know a guy who teaches astronomy at the local community college. He has 17 telescopes, and the one he uses most is a small refractor with an objective that's not much larger than an Oreo cookie. His favorite instrument is his image stabilized binoculars.

[notFritzArgelander]

It's nice to have a variety so one can pick depending on conditions and targets. But I use the smaller scopes more, for sure

[Lady Fraktor]

Variety is good but ease of execution to get out is best.

[DeanD]

I must admit to being amazed by what the smaller scopes can see. I often set up my 12" dob alongside my 4" refractor when I am at a dark sky site, and I find I spend most time with the refractor: even when I have borrowed a peek through a nearby 24".

It is really only the very faint fuzzies that I can't see with the refractor: but it is pretty rare that I have been unable to find something through it once I have spotted it in the 12" (or 24").

Plus I love the clean views in the refactor...

At home in suburban skies I almost never set up the 12", preferring the ease of the smaller scope.

When you think about it, the difference in brightness between naked-eye viewing (assuming a pupil size of 6mm) and a 100mm refractor is roughly a factor of 280x, while between a 100 refractor and a 300 dob is only a factor of around 9x, and even with a 600mm dob it is "only" 36x. That is of course very significant, but nowhere near as much as from naked eye to small scope!

[Unitron48]

Most of my early years of astronomy were accomplished with a 60mm, f/15 refractor. I'm still amazed at the endless number of objects that can be viewed with that small aperture.

The ideal situation is to have, or have access to, a large aperture scope in an observatory!

Dave

[turboscrew]

First:

I can ask the CloudyNights forums for advice on choosing my next scope.

Wrong forum. :wink:

I think, the size of the scope depends on what you like to see.
Like, my Omegon is handy, but somewhat limited when it comes to dimmer targets.
I'd like to use my VX12, but the equipment problems keep bugging me. OTOH, I don't think the equipment problems depend on the size of the telescope. You can have technical problems with binoculars as well.

[gregl]

I think, the size of the scope depends on what you like to see.
...

I think that's what it really comes to. There is lots to see with any instrument including naked eye, and it's all different. I well remember a couple of nights, one out in Death Valley when I saw stuff naked eye that just blew me away, and I had the same feeling once up at 8000 ft. in the mountains when I saw the Swan through a 20-inch dob and an OIII filter.

[SkyHiker]

The author used an SCT which is not easy to use as you have to align it first and the scope has a narrow FOV. When I use my Z12 with DIY "analog" setting circles and a DIY leveling base, alignment is quite quick and easy. Finding targets is not too hard because it has a wide FOV. Taking it to a dark site is problematic of course even when I converted it to a collapsible - the base is quite big.

I like the ease of use of my ES ED80 on a simple Nano tripod for wide views. I found that my Mak-Newt offers very clear and crisp views but of course you need to align it with the AVX controller first, which is a pain then the eyepiece can be in inconvenient places. Sometimes it's even too high up and I'm 6'3" (1m90).

If the binos didn't give me neck cramps, they would be my favorite, so I'll stick with the Z12 most of the time.

[gregl]

...
If the binos didn't give me neck cramps, they would be my favorite....

That's what recliners are for!

[WilliamPaolini]

Observing a celestial object is about more than simply aperture. So aperture does not get you to the finish line. I know many a skilled 8" SCT owner that has observed more with their scope than probably most owners of 12" Dobs. Every aperture has within its operating range many thousands of objects that it can effectively and aesthetically render. Every aperture has challenge objects so no advantage one way or the other. Larger apertures are not effective for some objects (i.e., insufficient TFOV or too much light gathering thereby needing filtration, or just makes no sense like using a 12" Dob for white light solar observing). Smaller apertures are not effective for some objects (i.e., insufficient light gathering or resolution). In the end, what makes a "lifetime" scope is the observer wielding the instrument and not the instrument itself or its aperture. There is no shortage of awe inspiring views, enjoyment, and challenge with any aperture.

FWIW, I have had scopes from 50mm to 254mm aperture, and have used in the field scopes of others for my observing up to 508mm aperture. In the end, where I came to rest was in the 80-102mm range for the vast majority of my observing, keeping a 152 and 203mm on hand should something catch my interest where more umpf is needed at my brighter observing locations. When I went to a Bortle 1 site at 4000' altitude I took a 90mm Apo and was awe struck at the views it showed and the multitude of details on even galaxies. Basically whatever aperture makes an observer the most fulfilled in this hobby is without question the absolute "best" aperture!

[Bigzmey]

"Then on a Zoom call with the club’s telescope workshop, another member pulled out a NexStar 8 and called it his “little scope.”

I am with that member. While I would not necessary call 8" SCT little, for me it is a grab and go light bucket. As easy to use and to deploy as 80mm refractor. It takes ~10 min for me to get it out of the car set and align, and after that in 2-3 min I will be on my first target. However, I did not buy it as a kit, I got OTA, manual mount and finders separately to tailor setup for my observing style.

So, it is not about how big or small is your scope per se. It is about picking the scope which provide right balance between aperture, targets and enjoyment. If you dread setting up or using your scope this is a wrong scope for you.

It sounds that the old 8" SCT did not click with the author. It happens, some don't like SCTs, some DOBs. But it would be wrong to generalize about the aperture limits just based on this experience.

If one can have more than one scope than sure, there is utility of having a small scope in your stable. However, if you are one scope person, one need to get the LARGEST scope they can handle COMFORTABLY. For visual aperture still is the queen, so if one can enjoy using 10" scope there is no reason to settle for 6".

[Bigzmey]

Also, what it is about SCTs having narrow FOV? If you take SCT, refractor and DOB (or any other scope design) of equal aperture they will have exactly the same true field of view at the same power.

[Johnny Carter]

I read this article when it came out, it has a lot of good points. I have a 10” DOB, and just bought a 150 MAK to have something lighter, but I almost bought a Williams 60, I have seen so much good written about them.

[WilliamPaolini]

Also, what it is about SCTs having narrow FOV? If you take SCT, refractor and DOB (or any other scope design) of equal aperture they will have exactly the same true field of view at the same power.

This is quite true. It should be that they are limited in minimum magnification due to their long focal length (reducers do not help as these cannot utilize the full field stop size of a 2" eyepiece). TFOV also due to the central baffle aperture but only on the 6" and smaller aperture SCTs.

[SkyHiker]

Also, what it is about SCTs having narrow FOV? If you take SCT, refractor and DOB (or any other scope design) of equal aperture they will have exactly the same true field of view at the same power.

I keep forgetting that because I'm an AP-er. But the useful range of magnifications for the average collection of eyepieces will be different. The Dob will be useful for lower magnifications that make it still easier to find targets.

About handling, I'm not sure if a 12" SCT handles easier than a 12" Dob because you need a hefty mount for it, too, if you can even lift it on there. You don't have to lift a Dob above your shoulder, and the collapsibles or trusses are quite transportable. Up to 10" any Dob is easy to throw around.

[OzEclipse]

I have posted before about my 6"f7. Two articles, originally posted on the old astronomyforum.net, now reside on my website.
One article describes my first night using the scope after a high grade mirror recoating following many years using a poor quality coating
https://joe-cali.com/astronomy/articles ... Essay.html

The other article describes a night comparing views through a 6" f7.5 Takahashi TOA150 and my 6" f7 reflector.
https://joe-cali.com/astronomy/articles ... ctors.html

Of note in the above comparison is that views of emission nebulae revealed dropouts of certain emission in the refractor which may be due to the AR coatings.

The 7.5" tube of the 6" is not "light" being a zinc annealed steel tube. I have never measured the tube weight but it is probably a bit heavier than an 8" SCT. I have a Vixen 8" VC200L which is nice but not as pleasing as the 6". However I don't want to re-tube the 6". It has machined tube rotation rings bored and fitted to the tube diameter that allow the eyepiece to be easily rotated to a position of viewing comfort in almost any sky orientation.

You will see from my signature or reports that I also have an 18" push to dob. It's on a wheelbarrow mount and from a physical handling viewpoint, setting up the 18" is about the same as setting up the 6". BUT...I have both instruments permanently stored at my home in dark skies. The 18" is not an easily transported instrument. If I had to transport the scope, I would not own that 18". In fact, I talked a friend out of buying a similarly constructed 16" scope just 2 weeks ago for that same reason. He lives in the city and would need to transport the scope out of the city in order to take advantage of the scopes full capability. However, given the relative ease of setup of the scopes, I probable use the 6" and the 18" equally. After buying the house, I installed two ramps both for visitor safety at night and also to make it easier for me to roll the scope out of my studio onto the rear deck then off the rear deck into the back yard.

Both scopes have excellent optics. I enjoy the greater light grasp of the 18" and the slightly wider field of the 6". During the recent apparition of comet Leonard, I left both setup for a few weeks and used both and as well as a pair of 9x63mm binoculars every night. Each provided their own unique views.

The widest useable fields, taking my own estimated pupil dilation and other scope limitations into account, are not that different:-

6"f7: small diagonal minimises diffraction from central obstruction but limits the scope to 1.25" eyepieces.
40mm 1.25" eyepiece 40deg AFOV, 1.5deg true field at 26x magnification.

18"f5.5: 2" eyepieces are possible but at f5.5, 31mm eyepiece results in a 5.5mm exit pupil, my maximum dialation.
31mm Nagler yields just under 1 deg true field at 80x magnification

But even if I put a 25mm 45 deg Orthoscopic eyepiece into the 6" yielding about 1deg at 42X, the perception of a 1 deg FOV at 42x is very very different to the perception of the same 1deg at 80X through the larger instrument.

I do agree that finding a scope that you can physically handle is important. However, I think these assessments are very complex and dependent on so many personal variables, that broad generalisations about ideal scope size are of limited value.

Astronomy Club Telescope Libraries that allow members to borrow and test drive scopes of different sizes and types especially testing yourself against the physical handling and setup, are very valuable facilities and a big plus factor for astronomy club membership.

As a qualified Work Health and Safety practitioner, there are a plethora of commercial handling and rolling aids in addition to bespoke solutions such as wheelbarrow dob trundles that can make moving and setting up larger equipment much easier than simple strongman handling.

Joe

[Bigzmey]

Also, what it is about SCTs having narrow FOV? If you take SCT, refractor and DOB (or any other scope design) of equal aperture they will have exactly the same true field of view at the same power.

I keep forgetting that because I'm an AP-er. But the useful range of magnifications for the average collection of eyepieces will be different. The Dob will be useful for lower magnifications that make it still easier to find targets.

About handling, I'm not sure if a 12" SCT handles easier than a 12" Dob because you need a hefty mount for it, too, if you can even lift it on there. You don't have to lift a Dob above your shoulder, and the collapsibles or trusses are quite transportable. Up to 10" any Dob is easy to throw around.

As Joe indicated for visual it is not the range of powers but range of useful exit pupils. True, it is easier to get 6-7mm exit pupil out of F5 DOB compared to F10 SCT. But unless you observe under very dark skies the views at 6-7mm exit pupil are not very pleasant lacking contrast and details with bright background sky. And typical useful range of 1mm to 4mm easily achieved in both DOBs and SCTs. Not even talking about reducer which brings SCT F-ratio close to DOBs.

I agree though that starting from 11" SCT are a hustle to handle and DOBs could be more manageable.

[Ylem]

My C90 Mak does seem to get the most use of all my scopes, other than my binos.

I recently purchased a C5 SCT, which may become one of my new favorites, it rides nice on the Porta Mount. Normally I choose which mount I want to use, then pick the scope.