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Mamba
04-12-2015, 08:28 PM
Some two months ago I purchased my last telescope, again, and this time I mean it, again.
The scope is 130 mm F7 triplet and cost the high end of the four thousands so although this is a substantial amount of money it is not in the big league of Taks/TV/AP and all the other super stars.
In buying this scope I had certain expectations in mind and not to go into a long list of them I will give two examples. I expected to be able to see the four craterlets in Plato, I expected to be able to see the E and F stars in the Trapezium, Dawes' limits indicate that both these targets should not be a problem with this size of refractor, indeed Dawes' indicate that E and F are a challenge for a 100 mm refractor implying the it is not impossible, whereas I'm using a 130. This was not the case. I have had the scope out under the stars on about a dozen occasions and have ended my session sometimes decidedly unimpressed and sometimes content, damned by faint praise indeed.
I am using a WO Quartz diagonal and a WO 4mm UWAN eyepiece and eyes that are 69 years old but I am the original owner. My skies are reasonable as I live in the outer northern suburbs of Melbourne and even my aged eyes can detect 4.5 mag stars.
My question to the more experienced of you is, have I overestimated the capabilities of such an instrument and am I doomed to purchase another last scope, again.
Mamba

casstony
04-12-2015, 09:18 PM
With the 4mm eyepiece giving 225x magnification, a possible explanation is that you're exceeding the limit imposed by unstable skies. Are stars steady in the eyepiece or dancing around? Have you tried lower magnifications?

Other possibilities include the lens in your eye getting cloudy with age (cataracts) or a poor quality objective in your scope.

raymo
04-12-2015, 10:39 PM
Hi Mamba, Where to start? Firstly, as you age, your pupils dilate less,
letting in less light, about 7mm when young, and by your age, about 5mm or so. As Casstony said, a lower mag could very well help. Also, as Casstony said, your eyes can become cloudy during the early stages of cataract formation without you realising it.
I am in my late 70s, and frequently have trouble spotting E and/or F
in my 8" Newt; only when the seeing is really good, and my eyes are
fully dark adapted can I do it. A couple of years ago I just managed to
see them in a friend's 150mm Mak. Last year I could see them most
times in a 10" Dob, but still had to look hard.
To sum up, I imagine that your scope is fine, and your problem is
probably, like mine, old eyes.[and too much magnification; I think
around 150-175x would be good.]
raymo

dannat
05-12-2015, 05:16 AM
it would be good for you to compare a similar scope say at a star party, which suburb in nth'ern Melb could also make a bit of difference, i can fairly easilyy see E in my 5" achro on most nights, but it is a doublet which needs almost no cooling time, F is a little more challenging

The Mekon
05-12-2015, 07:58 AM
David, can I ask how often you observe? I can recall many nights in the first couple of years ownership of my AP 130EDT F8 (a similar scope to yours) that I would get frustrated as none of my targets would show up well in the scope. I would say to myself this scope is useless! I soon learned that it was the seeing and transparency, not the scope that was the problem. E & F trapezium were easy for this scope on the right night. I recall one night at Ilford where I picked up E & F well before the end of twilight. So maybe you have not struck those good conditions yet?
I also concur with Casstony 225X is too much. Get the magnification around 120X to 150X for best results.
I do wonder whether our age greatly affects what we see in the eyepiece. At 60 I don't need glasses to look through a scope, but do to read the charts or see distance clearly, and I can repeat most all the observations I made 20 years ago in the right conditions.

LewisM
05-12-2015, 08:21 AM
Heck, I observe at around 33X... OCCASIONALLY go to 100X.

I saw E&F several times with my sadly-sold Tak FC-100. I doubt I will be able to with the FC-76.

casstony
05-12-2015, 08:34 AM
At my recent optometrist visit I was told I had slight cloudiness in my eyes, very early stages of cataracts, and that I would end up needing new lenses at some point in the future. (partly related to medication I take). I'm 51 now.

I wonder if we get a choice of lenses...... thinking I might go for an flp53 doublet, or maybe a fluorite singlet? :)

Allan
05-12-2015, 11:06 AM
Suburban skies are probably not helping you, also considering the aperture you are using. What's your experience with the scope when observing under dark skies? I can see E and F in the trap in my TV85 under dark skies. At home where it's brighter they are not easy to see at all in the little scope, but the 4" shows them clearly.

So that would be my suggestion, get out under dark skies somewhere and I'm sure you will realise what a great scope you have.

raymo
05-12-2015, 12:32 PM
If your eyes are healthy and free of cataracts, age won't noticeably affect what you see, resolution wise. There is no point in using an eyepiece
that has an exit pupil larger than your own diminished one, because a lot of the light falls outside the area of the rods and cones. Provided that the
eyes are free of aberrations, you should be able to use a scope without
glasses at any age, I'm nearly 80 and can see through my scope just fine
without specs.
Reasonable seeing last night, but no sign of E or F through my 8" Newt
at any magnification, but my exit pupils are less than 5mm, so I'm not
surprised.
My colour perception has definitely diminished considerably over recent
years; I used to be able to see green in M42 through my old 6" Newt,
but now can't see any colour at all , even through a 12" Dob.

N1
05-12-2015, 01:05 PM
Saw E through an FC76 last year. EP was an Abbe.

Mamba
06-12-2015, 09:48 AM
Thanks to all who replied to this thread.
The concensus seems to be that the telescope is probably good and the owner is knackered, l think l would have preferred it the other way round.
The glass is certainly very big and heavy and cool down times will be long and l will certainly take on board the advice of less magnification
Mamba

casstony
06-12-2015, 10:12 AM
If you haven't been to an optometrist in a long while (or ever) it's well worth a visit to guard against diseases/conditions which can wreck your vision but are very treatable if caught early. While there you can ask about the general condition of your eyes and lenses.

jenchris
06-12-2015, 10:27 AM
Get the optometrist to graft in a couple of Atik sensors on your retina...
It'll be possible soon.

Profiler
10-12-2015, 05:44 PM
As food for thought last night I took a look through the most impressive 4' refractor I have ever looked through so far in my life. This was a Takahashi FC-100DC fitted with a dedicated extender-Q 1.6 which brought it up to f12. I could clearly see the E and hints of the F stars.

I have not been able to see these before in many other 100mm or smaller refractors such as Televues (NP101,TV85,TV76), WO110, SW ED100, ED80, Vixen ED81s, ED103s

Don Pensack
11-12-2015, 08:57 AM
The 3 "C"s:
Cooling. How long was the scope outdoors? A 130mm triplet can sharpen optically over an hour or two after it's been brought out.

Collimation. Have you checked the collimation? Just because it's a triplet doesn't necessarily mean the scope is collimated. I use a "daytime star" to collimate my triplet refractor, i.e. the reflection of the sun off a Christmas tree ornament hung on a tree at least 100 meters away. I recommend green for visual acuity.

Conditions. Seeing can be broken down into two components: lateral motion and scintillation. Lateral motion won't influence the ability to see the E and F stars in the Trapezium (though I think it takes 32cm to see the G and H1 members, and perhaps a 15" to see the H2 and I components), but scintillation will blur the stars to the point where E and F are pretty much invisible. In average seeing, 15-20x per inch of aperture (77-102x) should be best to see them. In good seeing, 20-25x/inch of aperture (102-128x), and in exceptional seeing, 25-60x/inch (128x-307x). That last will be a rare night.

All 3 "C"s have to be right to see things at the limit of the scope, like some of the craterlets in the floor of Plato (most visible 1-2 days after the sun has appeared at Plato).

Tinderboxsky
11-12-2015, 02:45 PM
I have multiple observations of the E&F stars in the Trapezium using a Vixen ED103s, all in at least average to good seeing conditions as Don has noted. Clearest views have been at 113x, that is, 28x per inch of aperture.

Cheers

Steve