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Your choice of focal ratio?

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#26 Jon Isaacs

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Posted 14 July 2013 - 06:46 PM

For such long focal ratios ~f20. Would you consider a split tube design where the two parts would come apart for easy storage and transportation?


Absolutely.


Clear skies!
Thomas, Denmark


At F/20, the mount required is substantial and for a reasonably capable aperture, basically impractical as a refractor or Newtonian. An F/20 may provide good performance per inch of aperture but is a poor performer in terms of inch of focal length.

Jon

#27 Starhawk

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Posted 14 July 2013 - 07:12 PM

My AP130 EDFGT is ideal at f/6.3. The entire suite of practical eyepieces from 3mm to 42 mm is immediately usable for an enormous practical magnification range. And, of course, for photography, nothing succeeds like a low f/#.

-Rich

#28 Astrojensen

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Posted 15 July 2013 - 02:11 AM

At F/20, the mount required is substantial and for a reasonably capable aperture, basically impractical as a refractor or Newtonian. An F/20 may provide good performance per inch of aperture but is a poor performer in terms of inch of focal length.


I guess you could put it that way, but I never said my choice was based on logic.


Clear skies!
Thomas, Denmark

#29 Jon Isaacs

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Posted 15 July 2013 - 04:34 AM

At F/20, the mount required is substantial and for a reasonably capable aperture, basically impractical as a refractor or Newtonian. An F/20 may provide good performance per inch of aperture but is a poor performer in terms of inch of focal length.


I guess you could put it that way, but I never said my choice was based on logic.


Clear skies!
Thomas, Denmark


Thomas:

I love the views in a native F/13+ scope, there is something pure and pristine about such gentle bending the light. But as aperture increases they quickly become quite problematic in terms of transport and mounting and the field of view becomes very narrow.

It all comes down to the fact that there is no perfect scope. If our choices were all based on rationality and logic, we would be in bed sleeping rather than outside fighting with the elements trying to get a glimpse of some tiny object that is much better seen in a photo.

Such is the nature of a passion.

Jon

#30 Stellarfire

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Posted 15 July 2013 - 04:58 AM

As a mainly lunar and planetary observer, I prefer native f/8, or slower.

Stephan

#31 Scott99

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Posted 15 July 2013 - 02:06 PM

>>Even if you would have rather liked it to be f/9, I can think of worser fates than having to live with a 160mm f/7.5 Astro-Physics refractor...

Thomas - It's easy to say I like f/9 better now that I have f/7.5. It's likely the f/9 would not have fit into my current car - I may be singing a different tune if I actually had the F/9!

These guys (TEC, AP, Tak, APM, etc) know what SELLS. They probably know what's best for us whether we think so or not! Getting a 5 or 6 inch apo with an f/6 or f/7 length tube is a pretty amazing feat of engineering and design.

If I had an f/9 tube I'd be more smug about it but I'd probably use it less, these manufacturers know that portability is everything with these scopes.

#32 vahe

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Posted 15 July 2013 - 02:41 PM

These guys (TEC, AP, Tak, APM, etc) know what SELLS. They probably know what's best for us whether we think so or not!



Along the same lines we received word that TEC is starting another run of their 160FL f/7, I contacted Yuri to see if he would make me a f/9 version of the same, he did not say no but he gave me a 1:1000000 chance for producing such a scope, oh well!!!!!

I do not want these scope makers to tell me what is best for me, that is my decision, instead I will tell them what I would like to have and if they decline, well, there are other options.

Vahe

#33 KaStern

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Posted 15 July 2013 - 04:38 PM

Hi Pedro,

Hi all,

if telescope length were not a concern, nor were optics type (achro, Apo), which focal ratio would you pick for visual observation, both some deep sky and planetary.

Too short and eyepieces will suffer, but too long and exit pupil will diminish.

What do you think?

I think I can live in the f8-12 range.


unfortunately the optics type is of concern, like the tube length is,
and the aperture is...

But if I were to buy a refractor to complement my 8"f/6 Newt
I would chose a 4"f/6.4 apochromat.
It would give me a nice aproximately 4° field of view.

If I would buy me a 4" achromat I would buy at least an f/20

Cheers, Karsten

#34 Paul G

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Posted 15 July 2013 - 06:51 PM

These guys (TEC, AP, Tak, APM, etc) know what SELLS.


When AP sold both a fast and a slow version of 5 and 6 inch scopes the fast scopes outsold the slower versions by a very large margin.

My personal preference is around f7, can ride a smaller mount and can be barlowed for those times I want a longer fl scope.






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