Is aperture king?

[5haan_A]

Hi,

I am currently the proud owner of a 200p skywatcher dob. A great scope that has so far served me really well and I'm really happy with the whole learning experience I have had in 2018.

But now I'm beginning to get the itch and I find myself on cloudy nights browsing other scopes and seeing what the next level might look like for me.

One thing I consistently see is that some of the long thin scopes are often times in the 1000s of pounds. Which goes against what I'd previously held as an absolute truth: Aperture is king.

So why are these long thin refractors so much more expensive, and how do they compare against the performance of a scope like the 200p dob?

Thanks,

[Ricochet]

5 minutes ago, 5haan_A said:

So why are these long thin refractors so much more expensive

Because in order to get apochromatic colour correction extremely expensive high quality glass must be used. In addition, there are two faces to each lens and at least two lenses which is additional work compared to a mirror with only one face. 

[Sunshine]

In a nutshell, refractors are inherently quite a bit more costly to manufacture than reflectors, grinding lenses is far more costly per inch of aperture than mirrors. Each design has its strengths, mirrors being easier to make in large apertures do offer better light gathering capabilities for those faint deep sky fuzzies, but refractors on the other hand offer sharper more contrast views per aperture than do mirrors. For planetary views for example you can’t beat a quality refractors when it comes to beautiful contrast and color, but again they are very costly. For faint deep sky objects, you can’t beat a large reflector for bringing out detail in those whispy spiral galaxies. 

When one chooses a scope, having an idea of what one likes to observe is vital in deciding on a scope, also, astrophotography plays a large role in the decision, refractors are fantastic for this, offering wide field views in a compact design and are easily mountable on equatorial mounts which is needed for astrophotography. A large dobsonian on the other hand is not suited for AP.

 

[Beulah]

I used to believe that aperture was king...I truly think that light pollution-free skies have toppled aperture from its place.

Especially when you consider that the larger the optical equipment, the more hassle it is to set up, etc.

This year I have tried remote observing (getting away from night-lit communities into the countryside) with all manner of apertures and have found that all perform excellently - I have had an amazing year using telescopes of 16" apertures and below, 10x50s and 25x100 binoculars and the unaided eye. The biggest rewards I have had is with the unaided eyes, binoculars and 8" telescope, due to their comparatively light weights and being able to take them out to remote sites.

It's been truly a revelation...

Get out there if you can, guys...even a holiday to remote sites a few times a year will pay dividends (if it is clear) 

However, this is just a personal opinion and others mileage may vary.

The 8" telescope is a highly underrated scope and needs testing under a dark sky before considering future purchases.

[Charic]

The 200P was a good choice, and you found it quite useable, but going bigger makes the scope larger, heavier and more expensive.
That said, the more aperture you have, the more photons it will gather, giving you more detail and a brighter image. But if it's too large is it manageable.
I would really like for someone to pitch their 12" Skyliner classic right next to mine in my own back yard, just to get a feel and see for my own eyes under the same viewing conditions, to see just how much better the extra aperture would be, and would I see a real improvement over what I have now.
I'm waiting for a gap in the weather to test my scope under the reduced lighting levels that are present here at my observatory, maybe I can stay longer with the 8".

Is Aperture King! It's probably the most important aspect of any telescope for visual observing. The sole task of a telescope is to gather light.
Without aperture you have no light, nothing, but the more you have, the better it gets. Just remember your own personal limitations.

[mikeDnight]

No, aperture is not King! Definition is King, as without it, aperture counts for very little.

A few years ago, a friend loaned me a 200mm Sky Watcher Dob. I set the scope up in the garden mid afternoon, alongside my then 120mm Skywatcher Equinox ED refractor. It wasn't until around 9pm  when another friend and myself decided to take a quick look at the Moon and Saturn. Looking first at the moon through the 200mm, the view was truly excellent. I thought to myself that the 120ED wouldn't be able to match the view through the Newtonian. You could have knocked me down with a feather, as the 120ED was in a different league altogether. The view through the 120ED was far better defined, offering a view that was unimaginably sharp and detailed.

Turning both scopes onto Saturn, again I genuinely felt the ED wouldn't be able to touch the 200 mm Newt. Again I was completely wrong, as the 120ED revealed laser etched detail in Saturn's rings not even hinted at in the 200mm. Obviously the 200mm has greater light grasp, but that's where its advantage ended on the night in question. Both scopes were thermally stable having stood outside for more than six hours, and the seeing was steady and transparent, and both were working at a mere X180 (approximately), so any theoretical advantage in resolution that the 200mm should have had, was lost on the objects observed. 

There are numerous reasons that refractors tend to carry high price tags, not least of which is that they deliver outstanding views of pretty much everything within their light grasp. 

[Charic]

8 minutes ago, Beulah said:

........I truly think that light pollution-free skies......

Makes a huge difference to my scope, its as if the scope has morphed  into something special by the time I get there. 
Ive often heard  it said that the 6" would give more joy under the right sky than my 8" under my present sky?

 

[Beulah]

14 minutes ago, Charic said:

Makes a huge difference to my scope, its as if the scope has morphed  into something special by the time I get there. 
Ive often heard  it said that the 6" would give more joy under the right sky than my 8" under my present sky?

 

I know what I have written is anecdotal...but it feels like I've been going in the wrong direction for years, thinking larger scopes would improve the observing experience - but primary mirrors do not discriminate between natural light and man-made light! Even though there are improvements to detail and picking up fainter fuzzies, the differences are significant in a dark sky.

Someone on SGL wrote a scientific/more coherent observation on this some years ago and I can't find it ATM.

Better to stick to portability and load the car/use a trolley and walk to a site if possible. For the few that live in areas with no direct neighbours...lucky you! 

Large telescopes do lead to incredible observing experiences but far fewer in comparision to using something that's easily set up. Using the word "joy" is very appropriate, as that's what it's all about. 

 

[vlaiv]

Aperture is the king, all other things being equal

But they really never are.

I echo above comments on sky quality. I've got 8" SW dob and smaller scopes and observe from my very light polluted back yard. This year around spring time for galaxy season I managed to get to very dark skies, compared to my regular conditions, but it was not as dark as can be - my average conditions at home are about 18.5mag and I was observing from around 21mag (but you can 1 mag darker still down to 22mag). I had 2 scopes with me on that occasion - 8" dob and 4" short frac for wide field. Small 100mm refractor showed me more galaxies that evening than I ever seen in 8" in all my observing from light polluted location put together. Then again 8" dob was just jaw dropping experience - those things kept popping out from background regardless where I pointed my scope to

Aperture is also key for planetary performance. I often hear people say that smaller instrument - apo refractor, will outclass larger instrument - reflector on planets. I have opposite experience. My 80mm apo refractor is very good quality wise - tested more than strehl 0.95 (0.98 in red part of spectrum if I remember correctly). Dob on the other hand is about average - it is above 0.8 system strehl (so both primary and secondary combined). Dob simply blows refractor out of the water when conditions are right. In every respect - detail, contrast, you name it.

Theory also says that 8" obstructed instrument will perform better in this regard (even contrast) to 5" unobstructed instrument if they are of equal optical quality.

4" Apo will certainly have its strengths and is on my wish list along 8" Dob. Wide field, planetary, even deep sky under dark skies - very versatile instrument and easily transported and mounted.

[Moonshane]

Aperture is king but as above other factors contribute. E.g. see below with a 100cm slow scope in great conditions (not my image). In the same conditions a 100mm scope would never compete

However in average UK conditions and looking at planets, moon etc, seeing conditions matter more than aperture. For things like globular and open  clusters aperture steps ahead again. In other words, both is best ?

[Peter Drew]

I think you have to be careful comparing a 120ed with a 200p Newtonian despite the difference in size. The 200p costs £275 and a 120ED over £1100. I'm pretty sure that a premium 8" planetary Newtonian of similar value to the 120ED would be more than a match for it on planetary detail in most circumstances and do better on faint DSO's which are in the majority.   ?

[barkis]

Anyone owning an 8" f5 Newtonian must never despair over their inability to
spend loadsa money on a highly sophisticated instrument. 

The 8" has been a stalwart for the humble Amateur observer for many years, and will continue to be so.
There is so much satisfaction to be gleaned from that  instrument, it surely deserves it's place in 
the annals of practical  amateurs  observational astronomy.

Besides, star parties will always offer the means to at least peak through any of the Rolls Royce
telescopes at said SP's.  No owner of the expensive scopes would so churlish as to deny anyone a peek.

Then go back to your 8" Newt, and be pleased that you own one of the best servants there has ever  been to this great activity we all indulge in.
Remember the Late John Dobson folks.

Ron.

 

[nebulaeman]

DARK SKIES ARE KING!!!!!  What ever instrument you use including just your Naked Eyes show AMAZING VIEWS in a DARK SKY!!!  Then the trick is knowing what instrument will best show the many objects you may want to see.  There is no instrument that will show them all best!  Naked Eyes show some while small scopes with wide angled eyepieces show others and large scopes will also show some as well, but you need to know which ones handle each objects best - DARK SKIES are needed to begin with if it is Deep Sky Objects you are discussing!  At least this is one of the main points in my new book - Bright and Dark Nebulae!!!!  Note the difference in Dr. Gaposchkin's drawing of the Milky Way (center drawn at the Dark Sky of Mt. Stromlo Observatory and the rest from Boston - Hardly a dark sky).  I am certain you will want the dark sky once you have tasted it!

[estwing]

Dark skies rule....with big mirrors under them...

[MartinB]

I have observed with the same  3 scopes for the past 8 years ago, a 12" SW F5 dob, a 10" Meade ACF SCT, and a SW ED120. I have suburb skies.

The dob delivers the best planetary resolution with good seeing, however, the problem is that you have to keep nudging a dob at high mags which seriously impacts on the brains ability to do it's own "stacking".  In less than perfect seeing I prefer to use a motorized mount.  In all but poor seeing my SCT clearly shows more planetary detail than my ED120 albeit with less contrast.  In poor seeing the ED120 wins out in view of better colour and contrast.

Star clusters are at their prettiest through the ED120.  For other deep sky targets the dob shows significantly more faint wispy stuff than the SCT and the 120 is way off the pace.

The SCT is used least because it needs a chunky mount requiring some effort.  It is also sometimes on imaging duty.  The dob is ok to set up as is the ed120 on a small mount.

I couldn't pick a favourite!

[Paul73]

44 minutes ago, Peter Drew said:

I think you have to be careful comparing a 120ed with a 200p Newtonian despite the difference in size. The 200p costs £275 and a 120ED over £1100. I'm pretty sure that a premium 8" planetary Newtonian of similar value to the 120ED would be more than a match for it on planetary detail in most circumstances and do better on faint DSO's which are in the majority.   ?

I’m a Dob man at heart. So obviously bigger is better......

But, ED120 planetary viewes have blown away any Dob that I’ve pointed at a planet. Largely because I’m to busy hunting fuzzies to spend long on planetary.??.   Maybe I need to re-evaluate?

What commercially available mirror less than 12” would beat a standard SW ED120? 

Paul

[MartinB]

I'm 4 hours drive from a half way decent dark sky.  You might as well add that a cloudless sky helps.  That's even further away most of the time.

[Stu]

I'm with Sam on this. Dark skies rule, with any kind of optical aid, even none. Most of my best observing has been with 4" refractors when away camping under reasonably dark skies. Lovely widefield views of those lovely Southern Milky Way objects, plus plenty more too. Any scope under a good sky will perform brilliantly; don't allow yourself to be kidded that you have to take a huge dob in order to enjoy the skies, you don't. Of course, if you want to go chasing small, faint galaxies then a big dob is what you need, but if, like me, you often have a car packed full of camping gear and a family on your dark site trip, a decent frac on an alt-az mount will do a fantastic job too. There are plenty of targets out there to suit a range of apertures.

[Moonshane]

Agreed about dark skies but a big scope at dark skies albeit not necessary to have a great time will open up more objects and provide better views than a small scope particularly of faint objects.

Agreeing with you again though, a small scope is better than no scope albeit this still supports the aperture is king hypothesis.

[Charic]

Dark Sky or Dark Site!!!!!

 It's the site that's important for me.  I want to be able to see NO man-made lighting from any direction.
Last time I achieved this and the conditions were just about perfect, there was so much natural Star light from the Milky Way, it cast a body shadow, so in all honesty, quite bright considering I'm at a dark site, but oh what a sight, what a night!

[5haan_A]

Really insightful posts there. 

Aperture is king but a Dark Sky is the Queen.  ?

 

I live in a semi-rural part of Yorkshire. The LP isn't terrible, but it's still some way of a Dark site. In my short time of backyard visual astronomy I haven't managed to take my scope out to a proper Dark sky. It's something to look forward to in 2019. I'm planning on taking the scope out to the Yorkshire Dales, just need to find the time to do it although after reading these posts I'm more compelled to make the trip. 

As a new entrant into this hobby seeing the amount of variations in scopes available can be challenging, but the responses in this thread have provided with a little more insight. 

 

Thanks a lot. 

[Alien 13]

For me focal length is King, the shorter the better 

Alan

[Stu]

2 minutes ago, Moonshane said:

Agreed about dark skies but a big scope at dark skies albeit not necessary to have a great time will open up more objects and provide better views than a small scope particularly of faint objects.

Agreeing with you again though, a small scope is better than no scope albeit this still supports the aperture is king hypothesis.

Shane, I don't think we are disagreeing ??, but I guess my point is similar to the arguments around light pollution. I don't subscribe to the dark skies or nothing mantra any more than I do large aperture or nothing. If my only observing has to be under light polluted skies then I would rather do that than give up the hobby, likewise small scope vs big scope. If using a small scope helps me observe regularly then it will keep my interest in the hobby rather than giving up. I couldn't take a 20" dob with me on most of my limited dark sky trips, so would rather take something that can fit in in order to enjoy the views. Equally if the moon is up, it's clear and I have the time and energy to observe, I will observe the moon rather than saying there is no point.

Many folk end up getting aperture fever, then using their scope less as a result, which to me defeats the object.

The question was, is aperture king, and if that is relating to views of most DSOs then yes of course it is king, no question, end of.

The boundary becomes far more blurred if you include a desire to observe widefield objects, solar and planetary, throw in practicality/fitting into a family life and it becomes more balanced still.

To the OP's question, long thin scopes can have their advantages with lovely star shapes, contrast and an ability to cut through seeing. My Tak generally gives very stable planetary views that allow you to tease out the detail when a larger scope might struggle ie would produce a more variable image as the seeing comes and goes. I recall observing Jupiter side by side with the Tak and an 8" Edge SCT. The refractor gave lovely stable views, with muted colour and in a manner that I could spend time enjoying. The SCT gave a much more colourful view, with better resolution but it was very variable as the seeing came and went. I actually found it more frustrating and preferred the stability of the frac.

Another example which kind of counters my point (??), was observing Jupiter with Shane's 16" dob at the Peak Star Party quite a number of years ago. With an aperture mask giving effectively a 170mm unobstructed scope, there was plenty of detail, colour and a reasonably stable image. Unmasked at 16", there was ultimately more resolution and therefore detail than most normal (ie affordable) refractors, but the seeing had a much bigger impact on the stability of the view; we had to wait longer for each clear view.

Now, this post has gone on for quite some time, what was my point actually, and did I actually just argue against myself?? ??. Yes and no. Aperture IS king for deep sky objects, but don't lose sight of the practicalities and other factors and end up with a scope you never use.

Over and out ?

[Peter Drew]

1 hour ago, Paul73 said:

I’m a Dob man at heart. So obviously bigger is better......

But, ED120 planetary viewes have blown away any Dob that I’ve pointed at a planet. Largely because I’m to busy hunting fuzzies to spend long on planetary.??.   Maybe I need to re-evaluate?

What commercially available mirror less than 12” would beat a standard SW ED120? 

Paul

Any David Hinds "A" quality 8.5" and upwards and probably top end OOUK optics. Refractors are best for what small telescopes are best at, wide field visual and imaging, double stars and solar. For most else there are better options IMO.     ?

[Moonshane]

As it happens I have been using my 120ed a lot lately in favour of my 12" dob and even my bins for a quick shufty so I think we are agreeing ??