have i done the math?

[estwing]

the f13.3 on my telementor means that a 10mm ep is near it's limit, 50x per "= 125x mag is also the norm..so why do i read that this scope can be pushed to 80x per"= 200 even 240x mag, or do people lie on the internet?!

[Merlin66]

Yes,

you already know that people lie on the Internet ;-)

The maximum usable magnification shouldn't get mixed up with the working limit.

The atmospherics in Europe usually limit your 'useful" magnification to a max. of around x250 - with any telescope! Sure, on those very infrequent steady nights or on close double stars you may get up to x300 or so, but those are "once in a blue moon"

x50 per " is a fair limit for most scopes ie a 6" would give x300.

x80 per " is a memorable night that you'll talk about forever.

[andrew s]

I don't think there is a right answer. One way to approach it is to look at what magnification allows your eye to fully resolve all the detail in the diffraction limited image produced by the primary lens. Another is to look at the smallest diameter exit pupil the eye can accommodate with out impairing your vision. In Amateur Astronomers Handbook by J B Sidgwick he states "these limits are not hard and fast" and quotes figures from 10D to 25D (D in cm). This was first published in 1955! Double star observers may go even higher to split close doubles.

I am sure some people may lie on the internet but that is a different issue.

Andrew

[AndyH]

The higher quality the optic is, the more you can eak out, magnificaion wise.

[Moonshane]

I think it depends what you are looking at. if you want to tease fine detail from the surface of Jupiter then you'll get away with less magnification. if splitting doubles then you'll get away with more.

e.g. with my 6" f11 dob, and when objects are high or near the zenith I can often achieve 350x-500x on double stars and on great nights even on the moon. this is 83x aperture in inches with a 1/6PV scope on an equatorial platform. the view is often sharp too with decent airy disks/rings visible. I am certainly not telling lies (although I don't dispute that some do for some reason). the view comes and goes a bit but the split is there with patience.

[ronin]

Back when the telemetor was made they said 1.5x dia in mm, so 37.5x per inch.

What has happened since is that we made better glass types and can now get 50x per inch - FPL-51 and FPL-53. That will however mean on a good apo triplet, say a TMB.

You cannot compare an achro to the modern triplets. If they all produced a sharp image at 50x per inch there is no point in making a triplet or anyone paying the extra for one. Your point holds only if all refractors perform similarily, regardless of number of lens and glass types used. Which they pretty obviously don't.

The net can say anything, stick a 5mm eyepiece in with a 5x teleview barlow and you have 840x on your scope. The maths say it, and someone on the web will say it.

If one manufacturer says 50x per inch, say someone like TMB or Astro Physics then the rest will have to say the same. It is called marketing.

The Zeiss may be good, expect it is, but it isn't going to perform as well as a TMB 130SS.

[estwing]

so close-ups of the moon and great views of saturn maybe beyond my reach...

[Moonshane]

not at all - don't believe the doubters and try things out. if I believed what people often say, I have never tried such daft mags on my scopes. push it and you may just be surprised. you may not but why worry, go your own way.

[estwing]

and at that price i'd expect the tbm 130ss to be better!

[AndyH]

If you can't get 150-160x most nights, I'll eat my hat.

The Zeiss lens is one of the truly GREAT small lenses ever made !!

I get superb views of the planets on my carton 60mm lens. The Zeiss will at least equal it.

[great_bear]

What has happened since is that we made better glass types and can now get 50x per inch - FPL-51 and FPL-53.

You've been misinformed, I'm afraid.

FPL-51 and FPL-53 are not "better" glass types that permit higher resolution. They allow (in combination with other glass types) lens designers to create better corrected lenses at fast focal ratios, that's all.

This is great for those imagers who need fast ratios, and it's also good news for visual observers who want a lighter, more compact scope. That's quite a big market who will pay the premium price, but for visual observation the scopes are not intrinsically "better" than a quality long-focus achromat.

Thomas Back (TMB) and Roland Christen (Astro-Physics) have been quite clear on this point in the past.

The resolution of telescopes (in terms of aperture-to-magnification ratios) has remained unchanged for many years, now being limited more by the laws of physics than the quality of the optics (although it's true that on poorer quality scopes the image gets "messy" very quickly once you get past 25x per inch). On scopes that hold the image well at higher magnification, some people do prefer the larger image scale or the reduced planetary glare, but there's no extra detail there. The main consideration for choosing telescope powers is the object type, since some take (or require) more power than others.

The power ranges (expressed as power-per-inch) for all telescopes, remain very roughly as follows:

1) 4-8x pi - for open clusters and general sky-sweeping

2) 8-16x pi - for galaxies, nebulae and globular clusters

3) 16-32x pi - for lunar and planetary observing

4) 32-64x pi - for double stars

- not forgetting of course, to factor in atmospheric conditions when arriving at magnification figures for a particular scope.

[AndyH]

Very well put, g_b

Good post.

Andy.

[estwing]

so my 16-0rtho is great on the planets..

[AndyH]

so my 16-0rtho is great on the planets..

53x wont show much of a disc, I'm afraid. It'll be nice, but very, very small. Try at least 100x, preferably more, imho.

[great_bear]

I'd go for the best quality 10mm I could find...

[Later] - within limits!

[even later] - Ooops - I forgot this is only a 60mm scope. 10mm isn't really enough magnification to get a satisfying experience on planets, so you'll probably want to push a bit harder than that...

[estwing]

there's one on flebay at £139, £70 more like it for me but thats not gonna happen?

[great_bear]

Yes, I should have added "within limits" (and now have! )

About £70 would be reasonable unless you want to go for a very wide field.

Oh - and it's best to never buy eyepieces from eBay unless you're an expert...

It's worth bearing in mind that with the limited magnification of this scope, tracking the moon and planets will not be difficult, so the choice of a wide-field eyepiece would be an aesthetic rather than practical one.

Has it been modified to take 1.25" eyepieces?

[John]

Are you sticking to .965" or can you use 1.25" eyepieces now ?.

And are you looking to stay with Zeiss accessories ?

[AndyH]

Regarding planets - On my 60mm, I start at 100x and work my way up, using different eyepieces, until the image quality gets no better, or breaks down. I usually max out, around the 160x(ish) mark, but often 140x is nice.

I use mine on an alt/az mount, so the slo-mo knobs on the telementor mount should make tracking the object, hell of an easier job.

[AndyH]

I'd be tempted to get a decent 2x barlow, to use with the 16mm Zeiss ortho, making it in effect an 8mm. Sure the field of view won't be wide, but you'll struggle to find a sharper/contrastier(sp?) eyepiece. Should be a beautiful planetary/moon combo.

You'd need to use the 0.965"-1.25" adapter that I mentioned in the other thread.

All this is just my opinion, by the way ! I'd just want to get as much use out of the Zeiss ortho as possible.

Cheers,

Andy.

[John]

With my old Tasco (Japanese 1960's) 60mm F/13, looking back at my observation notes, I was often using 133x for planetary viewing when the observing conditions were good. I would have thought your Zeiss 63mm objective lens would have a better figure and polish than the old Tasco so 120x-140x should be usable. Something like a 7mm Baader Genuine Orthoscopic should work very well.

By the way, this web site might be of interest, if you have not already discovered it:

Unofficial Zeiss Telementor Web site

[AndyH]

Hehehe.

This is why in your other thread, I mentioned eyepiece recommendation, warrantied a seperate discussion !!

Possibilities are endless.....

Andy.

[great_bear]

- and estwing, if you're trying to resolve the seemingly contradictory advice here, it boils down to what I said earlier:

On scopes that hold the image well at higher magnification, some people do prefer the larger image scale or the reduced planetary glare, but there's no extra detail there.

Since (as Andy says) you really want to be starting at 100x upwards on a scope like this, the ordinary limits tend to get pushed a lot; a tiny planetary image isn't very satisfying to look at

[estwing]

the wife says she'll get me all the bits that andyH recommends to convert it to take 1.25 ep's for xmas!!!! i've got a cheap x2 meade 0.965 barlow which isn't bad but the image is still small-ish, that's why the 10mm on fleabay is tempting...or get the conversion then a BGO with a shorty barlow..my my where's that piggybank