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5" Refractors

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#26 BillP

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Posted 20 August 2014 - 01:33 PM

I think just as others...the 130-140mm is in the goldilocks zone (as t.r. said) for refractors...it's the place where size, weight, form factor, and performance all come together in an easy to handle spot.  Go to 152 and you have to then "deal" with some issues like maybe weight, for sure length, making moving more complicated.  For reflectors I would posit that the 8-10" ones are similarly in that goldilocks zone.  Sure we all like the greater capability of the larger apertures...but then means we need to put up with hassles in other areas.  All just a matter of balancing all the issues so the scope can be a "personable" performer.



#27 Ed Holland

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Posted 20 August 2014 - 01:34 PM

I was lucky enough to acquire a Meade 5" f/9.3 achromatic refractor quite out of the blue - an irresistible offer rather than a conscious choice.

 

After living with this scope for a few years, I have come to love it, and it makes a regular appearance when I observe. It is ready to go fairly soon after setup, and is a good all-rounder for the visual observing I enjoy. It is big, and although a larger refractor seems attractive (cost aside), I can use the same mount with my C8 and views are just as steady... I have a 4" achro as well (the renowned 102mm Celestron special offer). The 5" is a reasonable jump in performance - 50% more light on paper (actually nearer 70% more, since the 102mm is actually working at 97mm). There is more chromatic aberration in the 5" of course, but it is well enough controlled and not something that upsets me.

 

Now, my scope is not an ED doublet or triplet APO, so represents a small corner of the field of 5"ers represented here, even so, as one goes bigger, and with more elements, holding that weight of glass steady at the end of a tube becomes progressively more challenging. It is very functional.

 

Cheers

 

Ed


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#28 dlapoint

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Posted 20 August 2014 - 02:18 PM

I have owned many refractors from 60mm to 152mm.  I preferred the 100 and 152 scopes over a 127mm.  I find 4 inches to be awesome for G&G, and the 6 incher great for DSO.  I found little difference going from 4 to 5 inches.  But a huge difference going from 5 to 6.  If I could only have one refractor, it would be either a 4 or 6 inch.  I guess I'm the opposite of the majority here. 


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#29 Mark Costello

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Posted 20 August 2014 - 04:25 PM

I was lucky enough to acquire a Meade 5" f/9.3 achromatic refractor quite out of the blue - an irresistible offer rather than a conscious choice.

 

After living with this scope for a few years, I have come to love it, and it makes a regular appearance when I observe. It is ready to go fairly soon after setup, and is a good all-rounder for the visual observing I enjoy. It is big, and although a larger refractor seems attractive (cost aside), I can use the same mount with my C8 and views are just as steady... I have a 4" achro as well (the renowned 102mm Celestron special offer). The 5" is a reasonable jump in performance - 50% more light on paper (actually nearer 70% more, since the 102mm is actually working at 97mm). There is more chromatic aberration in the 5" of course, but it is well enough controlled and not something that upsets me.

 

Now, my scope is not an ED doublet or triplet APO, so represents a small corner of the field of 5"ers represented here, even so, as one goes bigger, and with more elements, holding that weight of glass steady at the end of a tube becomes progressively more challenging. It is very functional.

 

Cheers

 

Ed

 

Much of this is behind my decision to go have a 5" refractor.  Ever since in the 60s-70s I saw the very first ads or photos of (1) a 5" Alvan Clark refractor on a tripod, (2) a Jaegers 5"F5 refractor, and (3) the very first Astro-Physics 5" refractor, I decided then and there I wanted one of these.  Also, I had a 4" achro, and for a while was considering getting a complimentary scope for it.  But instead the 5" itch came back and I could only scratch it by getting one, which I did.  The increase in reach was noticeable, objects like M1 and M51 became a good bit easier to see and in particular observe.  My rig at 50 lb is not that much heavier than my 4" rig was and not that big a burden for me.  But I'm afraid that any refractor 6" or larger would be a burden.  So I'm not interested in getting a larger refractor.  Any larger scope I get will work mostly with mirrors.

 

Best,


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#30 seafury

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Posted 20 August 2014 - 04:29 PM

Hi this my 127mm Bresser alongside my 60mm

 

 

gordonAttached File  post-23291-0-98817500-1403195051_thumb.jpg   48.53KB   20 downloads


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#31 Starlon

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Posted 20 August 2014 - 08:22 PM

A 5" refractor is a great scope to have.  I enjoyed what astroneil had to report when he tested a 127mm f/9.5 and a 4" refractor.  This is how he put it:  http://neilenglish.n...rom-the-ashes/


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#32 BigC

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Posted 21 August 2014 - 12:32 AM

I'm not sure weight and size of the nominal 5" are as much the reason directly as the related increased cost of a 6" refractor scope  and the increased cost of its mounting.Although I find the CG4 class works well for my C6R.There is likely a psychological or justification factor in scope purchases for many,that is, once you go above the high hundreds into the thousands of $$$ for a 6" ED it can be a concern to your spouse or yourself if that is a significant part of your budget,even though it is something that should literally last a lifetime.



#33 x-ray

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Posted 21 August 2014 - 12:51 AM

5 inch refractors (in this case a Zeiss 130mm) can be quite a handful for two strong people.  I don't know what the Germans were thinking, but it's all two coordinated, strong people can do to set this up, 3 is better yet.  When the tube is in it's case, it's at the threshold of pain for two to carry.  I just finished restoring this for a friend, and made the mobile base for it to make it manageable.  It uses medical grade casters that lock in both rotation and swivel for solid performance.

Attached Files


Edited by x-ray, 21 August 2014 - 12:52 AM.

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#34 waso29

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Posted 21 August 2014 - 11:24 PM

:bigshock:  :jawdrop: Is that >f/15?



#35 Eddgie

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Posted 22 August 2014 - 09:04 AM

There seems to be a real following of folks here who use 5" refractors (120-140mm). Why 5"?  Is it that a 6" costs so very much more for that one inch gain in aperture? If you use a 5" can you tell us why?

 

 

As refractors get bigger, to perform well, the focal ratio usually has to get slower, and this means that you loose one of the biggest advantages that a refractor has over a reflector, and that is the wide, well illumnated, coma free field of view, and the mounting starts to get difficult.

 

I have owned several refractors in the 120mm to 140mm range, and these were usually faster scopes that would allow a nice 2.5 degree or larger coma free, well illuminated true field.

 

All would mount on something like a GM8, which is a very light but high quality GEM, making them somewhat easy to set up.  Not more effort than a 4" on a Great Polaris really. 

 

Mostly I liked them for the wide field abilities.   

 

But once the refractor gets to be 6" and f/8, you can get the same lovely wide field coma free views from a 10" f/5 Newt with a coma corrector.

 

And that is why my own 6" f/8 refractor is such a big paperweight.   To much weight and effort for the 2 degree field of view I can get from it.   I rarely use it for anything anymore, and keep saying I am going to sell it, but just never get around to it.

 

But in the end, I did not find the 5" scopes to be all that rewarding to use either, so as much as I like the 5" refractor for size and weight, I just find them a tad to small for my personal enjoyment.



#36 PeterR280

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Posted 22 August 2014 - 09:48 AM

I see a significant difference between the AP130GT and the AP155EDFS for observing. Light gathering and planetary detail is very evident, The AP155 is on par with the C8 as far as image brightness but gives better detail. I can use the Pentax 3.5XW with no problem on the AP155 whereas it is pushing the AP130, but there i also a big difference in size and weight. If I could only keep one, I would keep the AP155EDFS.



#37 BillP

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Posted 22 August 2014 - 09:59 AM

I notice in this thread, and others as well, a common expression that going from 5" to 6" is a lot more dramatic than going from 4" to 5".  From and observational perspective, I would agree with this also, that reaching 6" seems to activate some sort of threshold and it appears more significant.  Running the numbers for light gathering and resolution however, reveals that the 4" to 5" is actually slightly more significant.  That being the case, I wonder what the driver might be that makes us feel that the 5" to 6" jump is a more significant one.  Interesting.  :hmm:


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#38 SteveC

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Posted 22 August 2014 - 10:28 AM

I notice in this thread others as well, a common expression that going from 5" to 6" is a lot more dramatic than going from 4" to 5".  From and observational perspective, I would agree with this also, that reaching 6" seems to activate some sort of threshold and it appears more significant.  Running the numbers for light gathering and resolution however, reveals that the 4" to 5" is actually slightly more significant.  That being the case, I wonder what the driver might be that makes us feel that the 5" to 6" jump is a more significant one.  Interesting.  :hmm:

It's rather sad that I came up 12mm short of that magical 6" threshold, story of my life I guess. I look at my TEC140 now, and wonder what could have been.



#39 BillP

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Posted 22 August 2014 - 10:37 AM

 

It's rather sad that I came up 12mm short of that magical 6" threshold, story of my life I guess. I look at my TEC140 now, and wonder what could have been.

 

 

 

Don't fret...just bring up Hubble pics on your PC to get the 6" experience you are missing.  Sorry. :lol:


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#40 mblack

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Posted 22 August 2014 - 11:24 AM

 

 

It's rather sad that I came up 12mm short of that magical 6" threshold, story of my life I guess. I look at my TEC140 now, and wonder what could have been.

 

 

 

Don't fret...just bring up Hubble pics on your PC to get the 6" experience you are missing.  Sorry. :lol:

 

 

Flag on the play, Intentional taunting.   :grin:


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#41 bremms

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Posted 22 August 2014 - 12:37 PM

6" F10 Jaegers, 5" F12 D&G and 4" F15 Jaegers. Had all three at the same time. 6" F10 has the best resolution and light grasp. Only slightly harder to mount than the 5" F12. The 5" F12 was sold and the 6" F10 remained. Still have the 4" F15 and use it on occasion. I like the 6" and up category. a 5" would have to be an APO for me to even think about it over the 6"F10. 100mm is smaller than I really like to observe with.No matter how good.



#42 Jon_Doh

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Posted 22 August 2014 - 12:48 PM

 

I notice in this thread others as well, a common expression that going from 5" to 6" is a lot more dramatic than going from 4" to 5".  From and observational perspective, I would agree with this also, that reaching 6" seems to activate some sort of threshold and it appears more significant.  Running the numbers for light gathering and resolution however, reveals that the 4" to 5" is actually slightly more significant.  That being the case, I wonder what the driver might be that makes us feel that the 5" to 6" jump is a more significant one.  Interesting.  :hmm:

It's rather sad that I came up 12mm short of that magical 6" threshold, story of my life I guess. I look at my TEC140 now, and wonder what could have been.

 

Yes, sad, very sad indeed.  You should give me that terrible undersized TEC and go and buy yourself a 6" scope!  The magical threshold awaits you!  :)

 



#43 dweller25

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Posted 22 August 2014 - 01:46 PM

Once upon a time, there was a little girl named Goldilocks. 

She  went for a walk in the forest. 

Pretty soon, she came upon a house.  She knocked and, when no one answered, she walked right in.

In the house there were three refractors, a 4" a 5" and a 6" which she decided to look through.

First she looked through the 4" - "This scope is too small" she exclaimed.

So, she looked through the 6" - "This scope is too heavy," she said

So, she tried the 5" - "Ahhh, this scope is just right," she said and happily observed all night long.

And she lived happily ever after.

The end. :) :flowerred: :flowerred: :flowerred:


Edited by dweller25, 22 August 2014 - 01:48 PM.

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#44 SteveC

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Posted 22 August 2014 - 03:30 PM

 

 

I e in this thread others as well, a common expression that going from 5" to 6" is a lot more dramatic than going from 4" to 5".  From and observational perspective, I would agree with this also, that reaching 6" seems to activate some sort of threshold and it appears more significant.  Running the numbers for light gathering and resolution however, reveals that the 4" to 5" is actually slightly more significant.  That being the case, I wonder what the driver might be that makes us feel that the 5" to 6" jump is a more significant one.  Interesting.  :hmm:

It's rather sad that I came up 12mm short of that magical 6" threshold, story of my life I guess. I look at my TEC140 now, and wonder what could have been.

 

Yes, sad, very sad indeed.  You should give me that terrible undersized TEC and go and buy yourself a 6" scope!  The magical threshold awaits you!   :)

 

 

Both you and Bill are real sensitive types. I'm in pain and all you guys can think of doing is rub salt in my wounds. At least I'm not a 150mm owner - so close, yet no cigar



#45 JimP

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Posted 22 August 2014 - 04:20 PM

I see a significant difference between the AP130GT and the AP155EDFS for observing. Light gathering and planetary detail is very evident, The AP155 is on par with the C8 as far as image brightness but gives better detail. I can use the Pentax 3.5XW with no problem on the AP155 whereas it is pushing the AP130, but there i also a big difference in size and weight. If I could only keep one, I would keep the AP155EDFS.

 

I have to agree. My AP 155 was a wonderful scope and I kick myself regularly for letting it go. Now, I am looking for something portable (apo or semi-app) for double stars and while I would like a 6" with an AP 155 at the very top of the list, the going price of $11-12K is out of my league now that I am semi-retired. So, my next choice is something in the 5" range. I think 5" for doubles and general lunar/planetary viewing on nights when I don't want to open up the observatory or pull out the Big stuff seems reasonable.



#46 Mark Costello

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Posted 22 August 2014 - 04:30 PM

Once upon a time, there was a little girl named Goldilocks. 

She  went for a walk in the forest. 

Pretty soon, she came upon a house.  She knocked and, when no one answered, she walked right in.

In the house there were three refractors, a 4" a 5" and a 6" which she decided to look through.

First she looked through the 4" - "This scope is too small" she exclaimed.

So, she looked through the 6" - "This scope is too heavy," she said

So, she tried the 5" - "Ahhh, this scope is just right," she said and happily observed all night long.

And she lived happily ever after.

The end. :) :flowerred: :flowerred: :flowerred:

:rofl:



#47 Eddgie

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Posted 22 August 2014 - 04:49 PM

That being the case, I wonder what the driver might be that makes us feel that the 5" to 6" jump is a more significant one.

I personally don't think the jump from 5" to 6" is as noticeable as the jump from 4" to 5".

 

I have own maybe a dozen 4"  refractors, from fast achromats to APOs.    Honestly, I could never love any of them.   Just to small and for my own observing, incapable of giving a satisfying result.

 

The step to 5" to me was quite good, while the step from 5" to 6" was not as dramatic.

 

And that is why back to the original question, I think a lot of people are content with 5" to 140mm.   The level of commitment is far smaller than going to 6", and the difference in performance is not that great, vs 4" to 5".

 

There was a time 10 years ago where ED and APO scopes bigger than 4" were quite uncommon.

 

Today, they are like roaches.  You'll find them all over in the dark.  But 15 years ago, they were not common at all.

 

By comparison, 6" ED and APO scopes, while far less expensive than they used to be, I think still do not sell in proportion to the 120mm to 140mm models.  Lots of reasons for this, but as has been pointed out, the size, weight, and commitment required to use a 6" and larger refractor is much more of a step up than the performance step up would be.



#48 drollere

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Posted 22 August 2014 - 05:06 PM

There seems to be a real following of folks here who use 5" refractors (120-140mm). Why 5"?  Is it that a 6" costs so very much more for that one inch gain in aperture? If you use a 5" can you tell us why?

 

i became interested in refractors after having the opportunity to experience them at a dark sky party hosted by jim barnett, and by views with a D&G ƒ/10 owned by a neighbor. the fundamental attraction was image esthetics on double stars; there was also the cool down reputation.

 

the dimensions of my observatory and pier limited aperture to about 6", which would be an advantage in the poor seeing where i live. i went with a TEC 140 ƒ/7 in order to have a fine quality instrument to learn with and one that would be easily portable.

 

i was surprised by the large increase in price between the TEC 140 and 180, which implies some kind of manufacturing challenge that makes slightly larger scopes more costly to build.

 

i have been so happy with the scope that i completed with it 5/6ths of an observing campaign across the entire struve STF catalog. ergonomically the fast ƒ has been a pleasure to work with and with a 20 mm eyepiece the exit pupil is around 3 mm, the optimal sky darkening through magnification, and the field is 1.5º in a 70º eyepiece. a 40 mm eyepiece yields 6 mm and 2.5º. high magnification shows clean airy disks, and great star test.



#49 TG

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Posted 22 August 2014 - 07:37 PM

5 inch refractors (in this case a Zeiss 130mm) can be quite a handful for two strong people.  I don't know what the Germans were thinking, but it's all two coordinated, strong people can do to set this up, 3 is better yet.  When the tube is in it's case, it's at the threshold of pain for two to carry.  I just finished restoring this for a friend, and made the mobile base for it to make it manageable.  It uses medical grade casters that lock in both rotation and swivel for solid performance.

 

Why so heavy? I used to have a 5" D&G achromat that was maybe 15lbs and a good 5lbs of that was due to the A-P focuser it had.

 

Is it made out of brass or something?

 

Tanveer.



#50 drollere

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Posted 22 August 2014 - 08:04 PM

i posted this in a different topic, but it's to the point.

 

the horizontal scale is aperture, from the minimum useful to the largest practicable. the actual dimensions used are 10 mm to 760 mm (1/2" to 30"), but the curves remain the same unless the aperture range strongly limited (less than 250 mm maximum).

 

the two curves show the proportion of maximum resolution or maximum light grasp obtained by each aperture. 95% of the resolution of a 760mm instrument is obtained with an instrument 1/5 that size, or 150 mm. if the maximum feasible aperture is 24", the resolution break comes at 120 mm.

 

in contrast, 95% of the light grasp is only obtained with 98% of the maximum aperture.

 

this illustrates the contrast between the resolution and light grasp capabilities of different apertures within a feasible range, and shows the resolution advantage of the small (1/5 maximum) apertures; the smaller apertures can fully utilize this advantage because they are also less sensitive to atmospheric or instrument thermals. refractors dominate in this aperture range.

 

resLG.gif








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