DarkStar1984
member
Reged: 07/10/12
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Re: Strengths of a long focal length Achromat
[Re: covey]
#5519400 - 11/14/12 11:31 AM
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Do you live in New England 
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Jon Isaacs
Postmaster
Reged: 06/16/04
Loc: San Diego and Boulevard, CA
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Re: Strengths of a long focal length Achromat
[Re: Mr Onions]
#5519491 - 11/14/12 12:45 PM
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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
Carpal Tunnel
Reged: 03/01/04
Loc: New Orleans, LA
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Re: Strengths of a long focal length Achromat
[Re: Jon Isaacs]
#5519519 - 11/14/12 01:10 PM Attachment (81 downloads)
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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
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Re: Strengths of a long focal length Achromat
[Re: BarrySimon615]
#5519531 - 11/14/12 01:19 PM
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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
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Re: Strengths of a long focal length Achromat
[Re: Mr Onions]
#5519641 - 11/14/12 02:53 PM
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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
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Re: Strengths of a long focal length Achromat
[Re: stevew]
#5519833 - 11/14/12 05:21 PM
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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
Reged: 02/28/06
Loc: Petaluma, CA
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Re: Strengths of a long focal length Achromat
[Re: astrogeezer41]
#5519846 - 11/14/12 05:32 PM
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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: Indiana, USA
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Re: Strengths of a long focal length Achromat
[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
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Re: Strengths of a long focal length Achromat
[Re: rockethead26]
#5520226 - 11/14/12 09:58 PM
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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
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Re: Strengths of a long focal length Achromat
[Re: jrbarnett]
#5520464 - 11/15/12 01:31 AM
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Ziggy943
Post Laureate
Reged: 08/11/06
Loc: Utah
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Re: Strengths of a long focal length Achromat
[Re: mikey cee]
#5521316 - 11/15/12 02:18 PM
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#18. Never again needing to upgrade!   Mike
That's just mean!
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ken hubal
Pooh-Bah
Reged: 05/01/07
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Re: Strengths of a long focal length Achromat
[Re: Ziggy943]
#5521458 - 11/15/12 03:45 PM
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Stevew hit the nail square on the head!! 
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Ziggy943
Post Laureate
Reged: 08/11/06
Loc: Utah
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Re: Strengths of a long focal length Achromat
[Re: ken hubal]
#5521515 - 11/15/12 04:25 PM Attachment (38 downloads)
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34. They double a clothes rack
Post # 3,000
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Andy Taylor
Twisted, but in a Good Way
Reged: 09/24/08
Loc: The Pub. UK
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Re: Strengths of a long focal length Achromat
[Re: Ziggy943]
#5521564 - 11/15/12 04:49 PM
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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
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Re: Strengths of a long focal length Achromat
[Re: Ziggy943]
#5521806 - 11/15/12 07:45 PM
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Post # 3,000
Congrats!
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t.r.
Post Laureate
Reged: 02/14/08
Loc: Upstate NY
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Re: Strengths of a long focal length Achromat
[Re: dan_h]
#5522407 - 11/16/12 08:14 AM
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35. They get you closer to the object your viewing. Always a bonus!
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csrlice12
Post Laureate
Reged: 05/22/12
Loc: Denver, CO
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Re: Strengths of a long focal length Achromat
[Re: t.r.]
#5523104 - 11/16/12 03:55 PM
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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...
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Re: Strengths of a long focal length Achromat
[Re: csrlice12]
#5523217 - 11/16/12 05:13 PM Attachment (32 downloads)
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Strengths of long focus refractors.......Hmmmm...let me see.
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chboss
professor emeritus
Reged: 03/24/08
Loc: Tokyo Japan
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Re: Strengths of a long focal length Achromat
[Re: rwiederrich]
#5523370 - 11/16/12 07:45 PM
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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
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Re: Strengths of a long focal length Achromat
[Re: chboss]
#5523437 - 11/16/12 08:33 PM
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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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