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Chromatic aberration in an apochromat.

osbourne one-nil

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ollypenrice

ollypenrice

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Yep - all fracts show CA and why Issac Newton invented the Newt . OK Apos are better but still fracts and if you're into imaging with modern CCDs you need to kill cam IR sensitivity as IR won't be focused - all reflecting scopes bring all radiation to same ficus !

...but need coma correctors make of glass...  :BangHead:

You can't win in this game.

:grin: lly

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osbourne one-nil

osbourne one-nil

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You mentioned in your original post that you were having problems withe the ports mount being a bit unsteady. Well has about this as an upgrade?

Remember a mount can never be too solid! I love Takahashi, they never do anything by halves!attachicon.gifIMG_20150315_222323.jpg

Mike

Looks like a pier though so how would I get my vibration suppression pads under it?

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paulastro

paulastro

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I've been told by a well respected telescope dealer, who certainly knows his refractors, that the new Takahashi  FC-100  (fluorite doublet) will perform better visually on the planets than the TSA-102 (triplet).  The person explained that the TSA may have the edge on colour for imaging purposes, but the FC's better contrast and sharpness will give it the edge visually for Lunar and planetary observers. This is in-keeping with my own experience, having used both FS fluorite doublets and TSA triplets.

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paulastro

paulastro

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Yes Jules, and some of  us revel in using shorter focal length achromats. :smiley:   I have an Ostara 152mm f5.9 achromat which performs way beyond what most people would expect - me included before I bought it from a friend.  (this scope also comes in other versions such as Altair and TS)  Peter Drew (from The Astronomy Centre) observed with me using it on Jupiter a week or so ago.  Using a binoviewer with an equivalent view of between x150 and x200, Peter commented that the view was more like that from a 6 inch of f10 or f11. (with regard to the lack of CA)

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Gina

Gina

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And I'm using two ST80 guide scopes for imaging in my 400mm triple imaging rig for narrow band imaging :D  I was amazed at the image quality :)  5nm and 3nm bandwidth effectively removes CA.

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mikeDnight

mikeDnight

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CA is the nature of the beast. Its amusing that we buy a top refractor and then spend our time trying to find fault with it. I've never heard a reflector lover condem his Newtonian for having coma and spider diffraction, which is also the nature of the beast, and is more destructive to definition than is CA in an apo.

Some time back I read a review comparing a 5" Fluorite doublet to two high end triplets. The reviewers compared the scopes side by side over several nights. At the end of it all, the reviewers agreed the Fluorite doublet delivered superior contrast to either of the triplets. They also complained that a tiny amount of CA was visible in the doublet, while feeling that one of the triplets, displaying ASTIGMATISM, was nothing to grumble over. HAS THE WORLD GONE MAD?

When I buy myself a 10" Takahashi Apo you can all come and play, critics and all. I'll still have the biggest smile in the world.

It might be a while yet though, as I think they're around £250000.00. I'm not certain if that's just for the tube assembly!

Mike

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Mr Spock

Mr Spock

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If you have £10k you could have a 24" dob. Great for deep sky, but, you could have a sub aperture mask of around 10" with no obsctructions. That would give you a true 10" apo with no loss in contrast due to a secondary :)

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paulastro

paulastro

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Mike, I hope that you remember I'm your bestist  (only? :grin: ) friend when you buy your 10inch Tak.  If I were you I'd move house unless you want me to be round every clear night!  Come to think of it, I think I'd move to Burnley to save the 20 odd mile round trip - but I don't know where the wife is going to live? :grin:

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mikeDnight

mikeDnight

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As always Spock your logic is undeniable! However, I am a weak human compared to you and logic is rarely found in me.

A refractor to me is something beautiful. Looking upon a top class refractor, apochromat or achromat, is like looking upon the most beautiful woman I've ever cast eyes on. My legs go weak, my heart rate increases, everything is in slow motion and I begin panting like a dog. All that occurs before I even look through it.

Reflectors on the other hand simply don't do it for me, through my ilogical eyes they're more like a pig in a frock. I don't mean that to come across as cruel and unkind, beauty after all is in the eye of the beholder, and love is blind, or in my case partially sighted. As proof of that fact you should take a look at some of my friends wives.

I hear what youre saying about stopping down a reflector and I agree with it. However, it still remains a large cumbersome beast with the eyepiece at the wrong end, and no matter how you dress it, it will always look like a pig in a frock to me.

If only you could do that Vulcan mind thingy on me and give me some of your cold logic. Without that I'm doomed to live out my life falling desperately in love with one calcium fluorite chrystal lens after another draped in its transparent, almost nude, anti reflection coating. Help! Its an illness! And its that's cost me thousands and there seems to be no cure!

Mike

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John

John

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I used to think like that. I then found I could afford "pigs in frocks" that would handily outperform my refractors. They now live happily side by side :smiley:

The "pig" gets used a lot more though and is a 12" apo :grin:

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ollypenrice

ollypenrice

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I like 'Pigs in frocks!' Heheh.

I have to say that when I go round to the Observatoire des Barronnies on a social visit I'm wowed by their 0.8 metre reseach grade RC but the scope which always makes my heart ache is the 8 inch TMB apo. Ohhhhh, such an instrument! Swoons.

Olly

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Piero

Piero

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Maybe I am too naive on this but (in a crude way) I like to judge refractors as tools for more inclined to (light) quality and reflector as tools more inclined (light) quantity. Unless you have a specific reason for quality, for astronomy you need quantity. 

Then of course you have all the other important variables (e.g. portability, fov, eyepiece position, cooling time, weight, user experience, ...).

We can be proud of our tools, love them too, but they remain tools for seeing the sky and that is eventually the point of all of this. I think it is important to spend some time evaluating and saving for the best tool that we can afford and that satisfies our target interests.

However, after buying something, I also think people spend too much time wondering what they need to add or what is wrong with their equipment. 

So, here is the point:

How much time (and money) would we save AND how much would we enjoy this hobby more IF we just accepted our equipment for what it is, with its cons BUT also with its pros (!)? 

It is weird because there are many discussions here in sgl, cn, iis, ..., regarding how we can improve our equipment but it seems this is a never ending story. I am not saying that we should stop talking about equipment. I am just saying that I feel there is something wrong if we spend tons of money in equipment to afford the best we can, and then we spend more time on thinking about the defects instead of enjoying what this equipment is able to show us, namely some of the beauties of this universe. 

I apologise if I offended some people saying this, but I think this is actually an important point which can improve our way to progress with this hobby. 

Piero

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