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Why would you want a 6 inch Achromat?

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287 replies to this topic

#276 mitsos68

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Posted 29 July 2020 - 12:49 AM

This is my six inch f/8, achromat plus Aries Chromacor II. A nice a very capable instrument.

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Edited by mitsos68, 29 July 2020 - 12:50 AM.

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#277 Bob Myler

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Posted 31 July 2020 - 11:02 AM

After an additional 10 years in storage, I'm still wondering what to do with this:

 

6" f/15 J. W. Fecker Refractor....

 

https://www.cloudyni...cker-refractor/

 

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#278 StarAlert

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Posted 31 July 2020 - 11:15 AM

After an additional 10 years in storage, I'm still wondering what to do with this:

 

6" f/15 J. W. Fecker Refractor....

 

https://www.cloudyni...cker-refractor/

It looks great as a centerpiece on your table. You just might start a new trend with that pic. 



#279 oliver55

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Posted 31 July 2020 - 11:58 AM

After an additional 10 years in storage, I'm still wondering what to do with this:

 

6" f/15 J. W. Fecker Refractor....

 

https://www.cloudyni...cker-refractor/

 

You can give me it! smile.gif



#280 Jeff B

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Posted 31 July 2020 - 06:28 PM

After an additional 10 years in storage, I'm still wondering what to do with this:

 

6" f/15 J. W. Fecker Refractor....

 

https://www.cloudyni...cker-refractor/

Have you considered looking through it? question.gif


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#281 Bob Myler

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Posted 31 July 2020 - 09:22 PM

Have you considered looking through it? question.gif

Yes, I even purchased a huge Richard Berry tripod in an attempt to mount it....

However, diminished health and intervening years (now 72) are beginning to exact their toll.  undecided.gif 


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#282 Marc-Andre

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Posted 01 August 2020 - 07:56 AM

Yes, I even purchased a huge Richard Berry tripod in an attempt to mount it....

However, diminished health and intervening years (now 72) are beginning to exact their toll.  undecided.gif 

I've had a D&G 6" f15 undercover in a spare bedroom for 16 years (now 67).  Finally I'm building a pier from a section of Al light pole that will support a Meade 16", 1-1/2" shaft mount and have legs similar to a Richard Berry mount.  However, it will be movable on 10"pneumatic wheels.  I only vacillate on whether I should rather top it with a Alt-az mount.



#283 CHASLX200

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Posted 01 August 2020 - 08:37 AM

Not unless there is no color. The faster one's i could never live with.



#284 CHASLX200

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Posted 01 August 2020 - 06:07 PM

After an additional 10 years in storage, I'm still wondering what to do with this:

 

6" f/15 J. W. Fecker Refractor....

 

https://www.cloudyni...cker-refractor/

Sell it and make a killing if it is not being used. I loved to buy scopes like that back in the day.



#285 gnowellsct

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Posted 03 August 2020 - 08:52 PM

I am confused by this.  I clearly misunderstand something, so please put me straight.

 

If I want to look at doubles or planets I use my 5" refractor.  If I want to chase DSO's I get out my Dob.  I can see getting a larger refractor if you want to observe doubles and planetary and to snap up a few DSO's while you're there, but if you are primarily after DSO's then surely a 8" Dob is both cheaper (a lot) and better than a 6" refractor for DSO's.  And if you want to put it on your mount, you can even get a set of rings to mount the OTA.  Que No?

That's not much of a vote of confidence in your Dob that you don't trust it on doubles and planets.  I have fun planet viewing and doubles viewing in my refractors (92 mm and 130 mm) but really the C8 and C14 do a better job, the c8 being roughly equal with the GT 130 on star splitting, inferior to it on wide field, superior to it in deep sky, and employable in h-alpha solar (the c8 is not configured for that).  Unless you have a really long 130 mm aperture, like f/20 or more, the exit pupil for planet viewing at a given power is going to be smaller than the exit pupil on the larger aperture instrument.  

 

Thus the exit pupil on a hypothetical f/4.5 15" would be just shy of 2mm at 200x, this big Newt wouldn't even be breaking a sweat.   A 5" f/8 refractor would be at 0.635 exit pupil.  Guess which one offers the more comfortable views for settling in for a long look?  

 

As for double stars they are a lot of fun but we need a list of easy ones for 5" and smaller apos.  At higher magnifications the view is of the highly artificial looking "airy disk."  Those aren't "refractor like" star images at all.  In larger apertures the Airy disk is not often detectable.  

 

Mind you, I have refractors, love 'em and use 'em, and they are among the quickest setups out there.  I'm just always puzzled as to why people consider them superior to larger instruments for doubles and planets.  Maybe if what people mean is, the smaller scope gets set up more often and therefore I view more doubles and planets because I'm in a suburban light zone, or some such, that would make more sense to me.

 

Greg N


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#286 Jon Isaacs

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Posted 04 August 2020 - 06:06 AM

Unless you have a really long 130 mm aperture, like f/20 or more, the exit pupil for planet viewing at a given power is going to be smaller than the exit pupil on the larger aperture instrument.

 

 

Exit pupil = Aperture / Magnification

 

The exit pupil only depends on aperture and magnification. All 130mm scopes at 200 x provide the same 1.54mm exit pupil.

 

I use my Dobs for splitting close doubles.

 

There are plenty of good reasons to own a 6 inch achromat.  None of them apply to my situation.  

 

Jon



#287 beanerds

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Posted 04 August 2020 - 07:23 AM

If I may embellish, ..your first true, really good, triplet Apo is something like your first taste of a truly good, top shelf, Kentucky bourbon....

Scotch ! my friends ,, but I have owned a few awesome Fluorite Doublets ,,, still have one stashed away with a bottle of Irish Whisky ,,, and that's trouble with a capital ' T ' ,,  ' I '. .. we will argue !

 

Beanerds .


Edited by beanerds, 04 August 2020 - 07:25 AM.


#288 gnowellsct

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Posted 04 August 2020 - 09:00 AM

Exit pupil = Aperture / Magnification

The exit pupil only depends on aperture and magnification. All 130mm scopes at 200 x provide the same 1.54mm exit pupil.

I use my Dobs for splitting close doubles.

There are plenty of good reasons to own a 6 inch achromat. None of them apply to my situation.

Jon


Yes. It is too simple. Allow me to amend the statement. More aperture provides more generous exit pupil at equivalent magnifications. End of story.
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