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Equipment Discussions >> Refractors

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DarkStar1984
member


Reged: 07/10/12

Re: Strengths of a long focal length Achromat new [Re: covey]
      #5519400 - 11/14/12 11:31 AM

Do you live in New England

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Jon Isaacs
Postmaster
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Strengths of a long focal length Achromat new [Re: Mr Onions]
      #5519491 - 11/14/12 12:45 PM

Quote:

I'm very happy with my 60mm Skylight using the Carton lens.
Razor sharp and super high contrast.




Slow refractors are great in the smaller apertures, 60mm is about right, I really like my Asahi-Pentax 60mm F/13.3. But for planetary detail, contrast is a function of aperture so while it does about all that can be done with a 60mm scope, it can only show so much.

Jon


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BarrySimon615
Pa Bear
*****

Reged: 03/01/04

Loc: New Orleans, LA
Re: Strengths of a long focal length Achromat new [Re: Jon Isaacs]
      #5519519 - 11/14/12 01:10 PM Attachment (84 downloads)

Strengths - classic look, long focal length or rather slow f/ratio (don't confuse the two - a large reflector can be very fast, but have a long focal length if it has a very large aperture) can make focusing easier and make it easier to correct out aberrations. Appearance makes for an impressive look at outreach events.

Weaknesses - more difficult to mount appropriately, harder to display or store, harder to transport, more prone to tube flexure particularly with extremely long tubes and with thin wall tubes. More difficult to set up. Much more difficult to get a large exit pupil. Advantages pretty much minimized by the introduction of faster apo refractors.

Don't get me wrong, I like fast achromats and I have several that are f/15 ratio or slower in 60mm, 76mm and 105mm. But, go much bigger than that and they beg for an observatory. Length and weight do not allow for easy transport. Go from a 4" f/15 Unitron to a 5" f/15 Unitron and you increase weight from 100 lbs. to 275 lbs. Something to consider when your age is going up and your physical abilities are going down.

Check out this photo of me with a 5" Unitron. The tripod legs had been shortened (not by me) to get the mount into a garage.

Barry Simon

Edited by BarrySimon615 (11/14/12 01:14 PM)


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covey
member


Reged: 07/02/11

Re: Strengths of a long focal length Achromat new [Re: BarrySimon615]
      #5519531 - 11/14/12 01:19 PM

No doubt they are great scopes.....
But I gave up masochism for a very good C8.


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nightfisher
super member


Reged: 11/06/11

Loc: Huddersfield UK
Re: Strengths of a long focal length Achromat new [Re: Mr Onions]
      #5519641 - 11/14/12 02:53 PM

I guess my Antares 105 f15.......stopped down to 80mm f19 sort of counts

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astrogeezer41
super member
*****

Reged: 08/27/10

Re: Strengths of a long focal length Achromat new [Re: stevew]
      #5519833 - 11/14/12 05:21 PM

Yes, that image steadiness can be wonderful. I find the following about f-ratios with my scopes:
I can work with an f/7 when the seeing is fair-good (SV80F7 Aplanat)

I can work with f/9.4 if the seeing is fair or better (SV80/9D)

I can work with f/11 when the seeing is fair or better (SV102F11)

If the seeing is poor-fair only my old 75mm, f/16, Unitron will do.
In fact the depth of focus is so deep with the f/16 that I could make a U-turn with a semi in it (or so it seems).

I have owned several f/6 scopes over the years but they were so tweeky in focus that I never fell in love with them.

I would also add that my 6"f/8 Planetary Newtonian has served me pretty well but I wish that I had been able to make it an f/9.

Steady views,
Robert


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jrbarnett
Eyepiece Hooligan
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Reged: 02/28/06

Loc: Petaluma, CA
Re: Strengths of a long focal length Achromat new [Re: astrogeezer41]
      #5519846 - 11/14/12 05:32 PM

21. Doubles as a tool for removing cobwebs from the rafters of the observatory.

22. It compensates...er...for something.

23. So long as the two elements of the objective are roughly in the same county, collimation is adequate.

24. Using one allows you to (credibly) pull off the cardigan sweater and briarwood pipe look in the field.

25. Visitors will address you as "sir".

26. Really kind visitors will instead address you as "Sir".

27. You can pull off "mine's bigger" and "some are longer than others" jokes at star parties.

28. They're great if you like to talk to your guests at a star party. You'll be describing endlessly what it is those little dots and dim patch represent. Dobs are for introverts; they let the image do the talking.

29. People ask you about your grand children. Even if you don't have any grand children. Or children. Or haven't even completed secondary school yet.

30. They created a market for MV filters.

31. They created a market for apochromats.

32. Most of all, they are long on nostalgia as much as focal length. While you can never go home, you can briefly relive the observations of yesteryear.


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rockethead26
Carpal Tunnel
*****

Reged: 10/21/09

Loc: Arizona, USA
Re: Strengths of a long focal length Achromat new [Re: jrbarnett]
      #5519862 - 11/14/12 05:48 PM



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stevew
Now I've done it


Reged: 03/03/06

Loc: British Columbia Canada
Re: Strengths of a long focal length Achromat new [Re: rockethead26]
      #5520226 - 11/14/12 09:58 PM

33. Most long F-ratio achromatic lenses are better figured than their shorter counterparts.
Reducing seidel aberrations to very low levels.


Steve


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Sky Muse
sage


Reged: 10/26/12

Loc: De Soto County, MS
Re: Strengths of a long focal length Achromat new [Re: jrbarnett]
      #5520464 - 11/15/12 01:31 AM



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Ziggy943
Post Laureate


Reged: 08/11/06

Loc: Utah
Re: Strengths of a long focal length Achromat new [Re: mikey cee]
      #5521316 - 11/15/12 02:18 PM

Quote:

#18. Never again needing to upgrade! Mike




That's just mean!


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ken hubal
Pooh-Bah
*****

Reged: 05/01/07

Re: Strengths of a long focal length Achromat new [Re: Ziggy943]
      #5521458 - 11/15/12 03:45 PM

Stevew hit the nail square on the head!!

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Ziggy943
Post Laureate


Reged: 08/11/06

Loc: Utah
Re: Strengths of a long focal length Achromat new [Re: ken hubal]
      #5521515 - 11/15/12 04:25 PM Attachment (39 downloads)

34. They double a clothes rack

Post # 3,000


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Andy Taylor
Twisted, but in a Good Way
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Reged: 09/24/08

Loc: Epsom - UK
Re: Strengths of a long focal length Achromat new [Re: Ziggy943]
      #5521564 - 11/15/12 04:49 PM

Quote:

34. They double a clothes rack




Blimey!!! You could pole dance with that one...

Now there's an idea.


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dan_h
Carpal Tunnel


Reged: 12/10/07

Re: Strengths of a long focal length Achromat new [Re: Ziggy943]
      #5521806 - 11/15/12 07:45 PM

Quote:


Post # 3,000




Congrats!


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t.r.
Post Laureate
*****

Reged: 02/14/08

Loc: Upstate NY
Re: Strengths of a long focal length Achromat new [Re: dan_h]
      #5522407 - 11/16/12 08:14 AM

35. They get you closer to the object your viewing. Always a bonus!

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csrlice12
Postmaster
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Reged: 05/22/12

Loc: Denver, CO
Re: Strengths of a long focal length Achromat new [Re: t.r.]
      #5523104 - 11/16/12 03:55 PM

Quote:

35. They get you closer to the object your viewing. Always a bonus!




Nah; haven't you read: Objects APPEAR closer then they actually are. Of course, that was a reflective surface and not an objective lens...


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rwiederrich
Goldfinger
*****

Reged: 11/17/05

Loc: Always Dark skies of Belfair W...
Re: Strengths of a long focal length Achromat new [Re: csrlice12]
      #5523217 - 11/16/12 05:13 PM Attachment (35 downloads)

Strengths of long focus refractors.......Hmmmm...let me see.

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chboss
professor emeritus


Reged: 03/24/08

Loc: Zurich Switzerland
Re: Strengths of a long focal length Achromat new [Re: rwiederrich]
      #5523370 - 11/16/12 07:45 PM

You have to own a weekend house?

cheers
Chris

P.S. I love the look of this scope, I am sure the views are fantastic?


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jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Strengths of a long focal length Achromat new [Re: chboss]
      #5523437 - 11/16/12 08:33 PM

36. If you should ever be so fortunate as to have a beach house (I don't) you'll have the right kind of telescope to set up in the family room next to the ocean-view window.

37. They provide a reason to hang on to all of those old design eyepieces like Plossl, Orthoscopics, Erfles, Kellners, Ramsdens, Huygenians and such.

38. There is no better weapon for instilling "shock and awe" on lines of ants.

39. They give you instant credibility. Folks at star parties figure that there must be some reason your scope is so different. They're afraid that you know something they don't, so they reflexively treat you as an "authority".

40. They add weight to your case to the spouse that you need a new, larger vehicle.

41. They are highly "floater" resistant. The TFOV is typically so small that the probability of it and a floater occupying the same space at the same time is almost nil.

42. They resist dew without need for heated dew strips and batteries. All you need do is slew near zenith and allow the objective to poke through the upper atmosphere.

42. They are lovely scopes in action. For outreach I put the 105/1500 Antares on a CG5-GT head, atop a 60" tall pier. This places the tube saddle at almost 6.5-feet off the ground and the objective when aimed at Polaris just over eight feet up. It's absolutely majestic to watch the massive slow arcs the objective carves as the scope slews from horizon to zenith. It's like mechanical ballet. I found that by going from a 48" to a 60" pier, my outreach lines almost doubled. Talk about "advertising".

- Jim

Edited by jrbarnett (11/17/12 01:44 PM)


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