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How much increase in aperture to see a difference?

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#1 JimP

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Posted 04 June 2017 - 05:56 PM

I have an AP 130 F/6 which I use for visual observations primarily of double stars although anything is game. I have read so many impressive things about CFF I have thought about getting one. What is your experience in terms of the need for increased aperture moving from a 130 refractor to see a difference? Is a move to 140 enough or would I really need to get a 160 to make a visible difference?


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#2 LewisM

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Posted 04 June 2017 - 06:04 PM

I think you'd need to go 185 to notice any WORTHWHILE difference.



#3 walt99

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Posted 04 June 2017 - 06:29 PM

Using a compass  draw circles of  4, 5, 6, and 7 inches in diameter.  Put an image of Jupiter in the 4" circle and the same image scaled up in the other circles as they would all appear with a 5mm eyepiece.  

 

Just as in the scopes,  the Jupiter Image will be much larger in the 7"  circle,  and as I understand it,  it will be a larger image with the same resolution as the smaller images in smaller scopes.

 

For me,  the difference between 5" and 4"  made me trade up to a 5".


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#4 junomike

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Posted 04 June 2017 - 06:31 PM

160 would make enough of a difference IMO but 180 would be far more noticeable.

 

Mie


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#5 donadani

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Posted 04 June 2017 - 06:35 PM

I had a 5" too and went with the 160 - much better - but only while waiting to jump to the 185...

 

First Jupiter in the 185 and you know you arrived :)


Edited by donadani, 04 June 2017 - 06:37 PM.

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#6 Badger1992

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Posted 04 June 2017 - 06:38 PM

There will be increased planetary detail at 160 if the seeing is good.  The 180 would be a large "jump" from a 130, and certainly noticeable to anyone.



#7 donadani

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Posted 04 June 2017 - 06:41 PM

Btw. forget about the jump to 140 - not worth it comin from a 130!

 

Cs



#8 JimP

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Posted 04 June 2017 - 06:41 PM

I only mentioned going to a 140 or a 160. A 180 is not an option. LOL


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#9 SeymoreStars

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Posted 04 June 2017 - 06:47 PM

I have an AP-140 and having owned an AP-180 EDT I must agree with the majority of posters, a move to a 180+ is noticeable. I suspect the other increments will be marginal. 



#10 LewisM

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Posted 04 June 2017 - 06:53 PM

If only going 10mm (all of 1cm lol), it's not noticeable.

 

Personally, I can't see the hooplah everyone raves about going from a 4" to a 5", but there ya go - some think it is, some don't.


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#11 Heywood

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Posted 04 June 2017 - 06:58 PM

160 would make enough of a difference IMO but 180 would be far more noticeable.

 

Mie

 

What he said.  

 

Going from 130 to 160 is an increase of 30 mm, or 1.2 inches, quite a lot for an apo refractor.


Edited by Heywood, 04 June 2017 - 07:03 PM.

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#12 JimP

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Posted 04 June 2017 - 07:36 PM

 That's pretty much what I thought. Going from a 130 to a 140 is likely not enough  to make a real difference. Going from 130 to 160, being over an inch in aperture, and at this size,  is likely significant. Thanks for your input! Much appreciated.



#13 Richard Whalen

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Posted 04 June 2017 - 07:46 PM

25mm makes a difference at the eyepiece given equal optical quality in the 3" to 8" size range. I have observed side by side at WSP a AP 130 and 155. Difference was noticeable. Same using my 125mm and 150mm D&Gs.



#14 Jon Isaacs

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Posted 04 June 2017 - 08:11 PM

If only going 10mm (all of 1cm lol), it's not noticeable.

 

Personally, I can't see the hooplah everyone raves about going from a 4" to a 5", but there ya go - some think it is, some don't.

 

I see the difference between a 4 inch and a 120 mm as significant.. On the hand, the difference between a 4 inch and a 16 is substantially more significant.

 

Jon



#15 SeymoreStars

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Posted 04 June 2017 - 08:37 PM

Use Pi R/Squared and work it out as a percentage in square mm's.

 

160/130 = 1.23 squared = 1.5129 The 160 has 51% more light grasp.

 

I stole the calculations from this thread.

https://www.cloudyni...ht-grasp-chart/


Edited by sink45ny, 04 June 2017 - 08:38 PM.

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#16 junomike

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Posted 04 June 2017 - 08:44 PM

Use Pi R/Squared and work it out as a percentage in square mm's.

 

160/130 = 1.23 squared = 1.5129 The 160 has 51% more light grasp.

 

I stole the calculations from this thread.

https://www.cloudyni...ht-grasp-chart/

True, but far too much work IMO.

The "Pi" is common to both and thus, can be eliminated and just "squaring" the full Aperture worke the same.

 

   (160mm)2   /   (130mm)2

= 25600/16900

= 51.4%

 

Mike


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#17 BillP

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Posted 04 June 2017 - 08:44 PM

I think you'd need to go 185 to notice any WORTHWHILE difference.

 

200mm if you want it to be a WoW


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#18 SeymoreStars

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Posted 04 June 2017 - 08:45 PM

 

Use Pi R/Squared and work it out as a percentage in square mm's.

 

160/130 = 1.23 squared = 1.5129 The 160 has 51% more light grasp.

 

I stole the calculations from this thread.

https://www.cloudyni...ht-grasp-chart/

True, but far too much work IMO.

The "Pi" is common to both and thus, can be eliminated and just "squaring" the full Aperture worke the same.

 

   (160mm)2   /   (130mm)2

= 25600/16900

= 51.4%

 

Mike

 

What's the matter you don't like work?


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#19 junomike

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Posted 04 June 2017 - 09:07 PM

 

 

Use Pi R/Squared and work it out as a percentage in square mm's.

 

160/130 = 1.23 squared = 1.5129 The 160 has 51% more light grasp.

 

I stole the calculations from this thread.

https://www.cloudyni...ht-grasp-chart/

True, but far too much work IMO.

The "Pi" is common to both and thus, can be eliminated and just "squaring" the full Aperture worke the same.

 

   (160mm)2   /   (130mm)2

= 25600/16900

= 51.4%

 

Mike

 

What's the matter you don't like work?

 

LBD (Lazy By Design)

 

Mike


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#20 mogur

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Posted 04 June 2017 - 09:25 PM

Use Pi R/Squared and work it out as a percentage in square mm's.

 

160/130 = 1.23 squared = 1.5129 The 160 has 51% more light grasp.

 

I stole the calculations from this thread.

https://www.cloudyni...ht-grasp-chart/

...and the difference between 4" and 5" is even greater!


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#21 SeattleScott

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Posted 04 June 2017 - 11:09 PM

I believe the reason people upgrade from 4" to 5" is practicality. Personally I have viewed thru an 8" newt and a 10" newt side by side, and while the difference was quite noticeable, it probably makes more sense to upgrade from 8" to 12 or 15. But in refractor land, that is like upgrading from a 4" to a 6 or 7. Now you just went from $1000-2000 up to $5000-20000. And the mounting requirements increase exponentially too. With reflectors on the other hand, a 12 or 15 isn't going to be exponentially bigger, heavier, and costlier than a 8". So while going from a 4" to 5" isn't gonna wow anyone, a 5" can still go on a VX mount and can be had for under $1500. So if you primarily observe with refractors, it may be worthwhile to make a 1" jump. It isn't going to be a big difference, but it will be noticeable, and it is probably all you can afford!

 

Scott


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#22 Erik Bakker

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Posted 05 June 2017 - 05:36 AM

When upgrading from 130 to 140mm, you will be looking more at differences in design and manufacturing quality of the optics. So a great 130 will do as good or better than a good 140. Since your 130 f/6 is an Astro-Physics, no 140mm will be a big step forward. A 160mm has better chances of showing you more of the universe. But make no mistake in the difference in size and heft between an AP 130 f/6 and any 160mm APO. You will likely need to upgrade your mount too, putting the 160 on it's new mount in a whole new ballpark. If your 130 is already on a very solid permanent mount in an observatory, than a step up to 160mm will have a lot of benefits and few downsides of course.


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#23 Illinois

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Posted 05 June 2017 - 06:12 AM

Few weeks ago, I set up my two refractors. 100 and 127mm refractor to look at Jupiter. Both look great but I noticed that tiny details as Great Red Spot is better in 127mm than 100mm. Little bigger scope get better in small details!  Picture is from my 5 inch refractor!

 

I plan to buy 6 inch soon when I have money and I see that there 's not many 6 to 7 inch apo with at least f 8 out there! Lunt and Explore Sciencfic  is all I know and you might waiting to get it! Tak is too much $$$$!

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#24 Foc

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Posted 05 June 2017 - 06:25 AM

In terms of general observing, a 130mm is pretty similar to a 140mm and and variations in telescope design, construction or collimation will often come into play.

A short focal length CFF 160mm is not much heavier (except on the wallet) than my  CFF 140mm f7.5    And going beyond 160mm you have a great scope for many things.     If you get the chance to look before you buy, you will make the best decision for you own eyes and circumstances. Subjectively in my urban conditions and aged eyes I find in going from a 102mm refractor to a 140mm refractor many pairs become more enjoyable for me to observe.

 

 

A little more objectively the differences seen with increasing aperture for pairs are discussed in many articles and I think nicely presented in this popularized summary below: 

 

 

 

https://www.handprin...RO/bineye1.html

 

 

About 1/2 way down this long article are some nice if rough graphs on for example  increasing number of pairs seen with aperture increases.  I am sure someone has put up some more detailed versions before.  There is certainly a difference in what is seen for an increase from 140mm to 160mm for instance but each individual must decide if it is a worthwhile one.

 

To help locate the graphs the text around the graphs is given below.

 

"The chart (right) illustrates the relative decrease in the resolution limit (1/Do) and the increase in the light grasp (D2) as aperture gets larger. The resolution limit falls dramatically with increasing aperture and the gains bottom out quickly, so that an aperture increase that is just 20% of the maximum affordable or practicable aperture (~140 mm) delivers 75% of the potential resolution gain; half the maximum aperture (250 mm) achieves 93% of the largest aperture resolution. (Magnification increases linearly with aperture and follows the dotted diagonal line.)

In contrast, the chart shows that light grasp accumulates rapidly only in the largest apertures — half the maximum aperture yields less than 30% of the total possible gain in light grasp, and 75% of the gain in light grasp is obtained only with 85% of the maximum feasible aperture (425 mm or about 17 inches). Although not shown in the diagram, limit magnitude changes in the same way as resolution. A 140 mm aperture achieves roughly 50% of the total possible gain in limit magnitude, and a 250 mm aperture achieves 75% of the practicable gain.

These contrasts divide the range of practical or affordable apertures that an astronomer might use into two regimes. Across the smaller half of the affordable or practical aperture range, increasing aperture primarily benefits resolution and limit magnitude; across the larger half of the range, increasing aperture primarily benefits the light grasp useful to see extended targets with low surface brightness. This is the origin of the "aperture fever" that affects deep sky astronomers and their preference for apertures in the "light grasp" half of the aperture range. For the double star astronomer, however, resolution and limit magnitude are the most important image quality criteria, which shifts the aperture preference to the smaller or "resolution" half of the practicable aperture range.'

 

 

I liked the fact that 140mm had a favorable mention. And so for double star observing it seems from this summary you can be fairly satisfied when you have a 9 inch scope as any additional increase in aperture will be associated with a diminishing number of further cataloged pairs you can resolve


Edited by Foc, 05 June 2017 - 06:38 AM.

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#25 mogur

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Posted 05 June 2017 - 06:57 AM

Is there a simple formula for determining the increase in detail visible as aperture increases? Just like we have for determining brightness?




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