Which gives better image at 160x? A 110m f7 ED doublet or 80mm f6 Apo Triplet?

[Saturninus]

In the 110m ED doublet, i would be using a 5mm EP to get to 157x, at about 37x per inch of aperture.<br />

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In the 80mm apo triplet, I would be using a 3mm EP to get to 160x at 50x per inch of aperture. <br />

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All other things being equal, which image has better contrast and resolution? Assume the ED is corrected well enough that chromatic aberration is not bothersome. Does the bigger scope operating below it's maximum outperform the smaller, superior scope that is being pushed to it's limit?

[John]

..... Does the bigger scope operating below it's maximum outperform the smaller, superior scope that is being pushed to it's limit?

All other things being equal, yes it does. 

My personal experience was moving from an 80mm ED doublet to a 102mm ED doublet and the difference there was noticeable on all objects viewed. I would not expect a markedly different result had the 80mm been a triplet.

[Brian Nordstrom]

The difference between my 90mm Takahashi SKY90 with one Fluorite lens that is as colour free and perfectly figured and polished ( as perfect as a 90mm f5.5 can be )as a scopes lens set can be , and my 127mm Istar f8 doublet is a huge jump in resolution , detail seen , available magnification and brightness on any object.

Of course there is CA ( very faint ) in the 127mm , but it sees so much more due to its extra light gathering power .

I could imagine the 80mm triplet giving those perfect views of star clusters , double stars , etc that only a short focal length quality APO can give , like my Tak does , very ,very beautiful and hard to beat .

The 110mm ED would go much deeper , show more detail on the moon and planets and still show stars very well as only refractors can , just not quite as nice as the smaller 80mm APO will.

Another thing to consider in mounting either scope , my Istar needs its HEQ5 as its physically much larger than my SKY90 that sits perfectly on its Vixen SP mount . The difference in size and weight between these 2 mounts is a lot .

Then there is trying to acheave high magnifications of 150x plus in a short fl small APO , that is tough , and unless you have good quality small fl eyepieces like TV , Pentax , Denk etc that are very expensive just using and enjoying what its capable of is an exercise in frustration , ever looked thru sat a cheap 4mm plossl ? 3mm eye relief and tunnel vision , not much fun sorry to say , but true .

I use all TV eyepieces from 3mm to 31mm as well as a TV 2x Powermate , so high power views in my 500mm fl Tak are enjoyable , and its capable of 250x easy .

Then there is portability , that goes without saying , the 80mm triplet is the winner here .

If it were me , as sexy as the smaller 80mm might be , I would opt for the larger 110mm if mounting was not an issue and a CG5 size mount will be plenty and because if you got the small 80mm ,, you would always be thinking ....... What if ?

my 5c.

Brian.

[Saturninus]

all sounds very reasonable.  and I know where this will lead: Get both!

One day...

I guess the larger exit pupil at any given magnification for the larger scope overwhelms the glass quality, assuming that the larger scope is of reasonably good quality.

What about on objects where surface brightness is not an issue - such as Jupiter? Or a more extreme example - for solar observation? 

Sometimes, when viewing jupiter, a thin cloud will pass over head and darken the image slightly, and it seems like I can see even more detail!?

[Brian Nordstrom]

The cloud thing is only a contrast thing , you will see the image dimmer , but the scope will still be gathering the same amount or light eg 110mm's worth .

I see the same thing when viewing the sun thru my 127mm Istar fitted with Lunt wedge as clouds pass over and the sun spots show up better.

I have a friend down here with a Long Perng 110mm Ed and its a very nice telescope , very well made with good ED optics , there is a very slight CA seen Jupiter at 200x but its very dark and close in against the planet , to me its basically invisible .

Great scope for only $1400aud .

Brian.

[alan potts]

Funny enough I was doing something very similar last night but the other way around, a 115mm triplet and a 70mm ED doublet. With about the same power.

I would not say CA was a major factor at X160 even on the Moon but the one thing that stood out was the brighter image, that was really noticable.

Alan.

[ronin]

Very likely pushing the 80mm triplet towards it's limit, also a 3mm eyepiece is also chancing your luck. In effect both items are getting thrashed. But at the same magnification the 110mm would simply be collecting nearly 2x the amount of light, which would go into what you see.

As with most things it is not a cut and dry situation.

Is the ED glass in both the same, a triplet with FPL-51 and the ED with FPL-53 makes a difference, if the other way round the triplet is FPL-53 and the ED FPL-51 then the triplet may win.

I have seen interferometer data on an 80mm LZOS lens that was a close to perfect as you will ever get. That lens/scope would likely beat anything like an 110 f/7 doublet.

[John]

....Is the ED glass in both the same, a triplet with FPL-51 and the ED with FPL-53 makes a difference, if the other way round the triplet is FPL-53 and the ED FPL-51 then the triplet may win.

I have seen interferometer data on an 80mm LZOS lens that was a close to perfect as you will ever get. That lens/scope would likely beat anything like an 110 f/7 doublet.

The OP did say "All other things being equal...."