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APM 120 vs 100

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23 replies to this topic

#1 RickyD85

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Posted 27 May 2018 - 05:52 AM

Guys

I've been looking at the APM 120mm's with interest.

Are they a worthwhile upgrade from the 100mm's?

What are the benefits over the 100's and how noticeable are they?

I would sell the 100's if I got the 120's, they wouldn't complement each other.

Thanks

Edited by RickyD85, 27 May 2018 - 05:53 AM.


#2 Mad Matt

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Posted 27 May 2018 - 05:59 AM

I personally do not feel the need to upgrade. If I where to buy new and choose between the two I would probably go for the 120’s

#3 Neptune

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Posted 27 May 2018 - 08:59 AM

If you are looking for more resolving power and light grasp, I would go with a 130 or better yet a 140. That would be a more significant and noticeable jump in dia.



#4 range88

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Posted 27 May 2018 - 09:46 AM

SD is better than ED. 53 vs 51. Easily noticeable in the daylight.



#5 Mad Matt

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Posted 27 May 2018 - 10:07 AM

I recently had a chance to do an quick comparison star test with my APO 100mm and an APO 120mm. SA and secondary spectrum where practically identical. Views of the last quarter moon at all available high magnifications (Nagler 6-3mm zoom) where free from false color in both instruments. As expected, at the same magnification (both at 110x) the 120mm showed better resolution but neither showed any CA.

The 120mm have SD because then need it in order to reach the same level of performance as the 100mm. Remember, with the focal ratio remaining constant, secondary spectrum will increase exponential as aperture increases. This means with increased aperture glass with a higher Abbe number is required to compensate for the increased secondary spectrum.

Edited by Mad Matt, 27 May 2018 - 10:20 AM.

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#6 RickyD85

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Posted 27 May 2018 - 10:55 AM

I don't feel like i need to upgrade, i really like my pair.

As I dont use any other binoculars or telescopes i was thinking of getting the bigger ones if there would be a noticeable difference

#7 jdown

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Posted 27 May 2018 - 11:00 AM

Guys

I've been looking at the APM 120mm's with interest.

Are they a worthwhile upgrade from the 100mm's?

What are the benefits over the 100's and how noticeable are they?

I would sell the 100's if I got the 120's, they wouldn't complement each other.

Thanks

Ricky,

   I've owned both BTs (still have the APM 100mm).  From my experience both BTs are about equal in quality.  What you get with the 120mm is 44% more light-gathering power.  This translates into being able to see stars that are about 0.3 to 0.4 magnitudes dimmer than can be seen with the 100.  The 120 is superior when it comes to galaxy hunting.  However, in both instruments nearly all galaxies still appear to me as faint fuzzy spots.  Even with the 120, I see only the core of M31, for example.  If observing galaxies is a big thing for you, you'd be better off with a large telescope that can gather the needed light.

   Having said that, though, I'm glad I bought the 120.  It's the best astronomical instrument I've ever owned for looking at the moon, OCs, GCs, double stars, and the brighter nebulae.  It's large enough to reveal the heavens, but still light enough to qualify as grab 'n go binoculars.   


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#8 edwincjones

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Posted 27 May 2018 - 12:17 PM

I think going from 100mm to 150mm makes more sense-twice the light gathering;
but consider the size, weight, cost and lack of portability.

That is what I did-miyauchi 100 to fuji 150 and back to miyas.
If choosing between 100mm and 120mm, I might go with 120.

Probably like 4" to 5" to 6" scopes

edj

Edited by edwincjones, 27 May 2018 - 12:19 PM.


#9 Allan Wade

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Posted 28 May 2018 - 01:10 AM

I don't feel like i need to upgrade, i really like my pair.

As I dont use any other binoculars or telescopes i was thinking of getting the bigger ones if there would be a noticeable difference

As I was starting out fresh with binoscopes, it was an easy decision for me to get the 120's. There is going to be a noticeable difference in upgrading to the 120's from your 100's, but it won't be earth shattering. You say you don't feel the need to upgrade, so why do it? Spend the money on a larger aperture telescope and see a significant difference on the smaller, fainter objects. The APM 100's and a larger dob are a very good and complementary lineup.  

 

I couldn't resist showing off my APM 120's again.

 

1.jpg


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#10 edwincjones

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Posted 28 May 2018 - 04:29 AM

............... Spend the money on a larger aperture telescope and see a significant difference on the smaller, fainter objects. The APM 100's and a larger dob are a very good and complementary lineup.  
 

 
attachicon.gif 1.jpg


I know that this is the binocular forum,
and not to say something like this,
but Allan makes a good point.

edj

Edited by edwincjones, 28 May 2018 - 04:31 AM.

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#11 Northern

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Posted 28 May 2018 - 06:07 AM

If one where to only use the Doctor 12,5mm eyepieces, which would you suggest?

 

I understood it that you get a larger FOV with the 100mm compared to the 120mm?



#12 Mad Matt

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Posted 28 May 2018 - 07:10 AM

If one where to only use the Doctor 12,5mm eyepieces, which would you suggest?

I understood it that you get a larger FOV with the 100mm compared to the 120mm?

100mm:
My personal and very subjective feeling is that there is a certain “magic” with 44x and 2* FoV. It frames even small objects nicely and with a red dot finder, point the 100 in the general area and the object is usually in the FoV. I find finding objects is so easy I don’t feel the need for DSC’s.

120mm:
At 53x, pointing gets a little more difficult but there are more details visible. Of course the trade off is that you have less context.

If context is what you like then go with the 100mm. If more visible detail is your thing then go with the 120. 😁

Edited by Mad Matt, 28 May 2018 - 08:57 AM.

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#13 edwincjones

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Posted 28 May 2018 - 08:38 AM

I personal and very subjective feeling is that there is a certain “magic” with.........


Yes-this is the goal!

edj

Edited by edwincjones, 28 May 2018 - 08:38 AM.

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#14 RickyD85

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Posted 29 May 2018 - 05:21 AM

Thanks for the input and good opinions/advice as always. All appreciated.

Had a good think about it, and it seems that it all comes down to trade-offs when comparing the 100's and 120's.

APM 100's are smaller and more portable, and dont require such a substantial mount/tripod

APM 120's obviously have the benefit of the wider aperture, with slight trade off in size/weight and mounting requirements.

It seems past the APM100's you start getting into very beefy mount territory. I'm going to stick with the 100's as I feel they suit my needs a little better. The 100's are at the limit of what I would consider practical for transport.

The 120's aren't going to allow me to suddenly start resolving globular clusters and galaxies, so i'm now telescope hunting instead. That's another subject however for another thread!

Edited by RickyD85, 29 May 2018 - 05:22 AM.


#15 Erik Bakker

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Posted 29 May 2018 - 05:55 AM

Isn't it all about the magic and our personal search to experience that?

 

 love.gif


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#16 Erik Bakker

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Posted 29 May 2018 - 06:01 AM

I think Mad Matt hints at a very important point: every instrument has it's own unique "magic". Experienced that from small 8x20 binoculars to 16" f/5 dob's and instruments in between. But also learned the value of an instrument actually having with you and out under the stars to observe with. That's why our naked eyes can still show their magic, even if we have far bigger instruments at our disposal. Personally, I love every instrument that brings me in contact with the beauty and magic of our universe flowerred.gif


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#17 RickyD85

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Posted 29 May 2018 - 06:17 AM

Hi Erik, i agree.

When i got my 12.5mm morpheus the APM's really started to show a kind of 'magic'.

Looking at the Beehive cluster is one of my favourites, it seems made for my set up. I had my first wow monent looking at that for the first time.
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#18 janapier

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Posted 29 May 2018 - 06:38 AM

In my experience, the Docters are indeed fantastic eps for the APMs. However, there are certain objects that call for the 24 Pans as far as I'm concerned. The veil and h/X come to mind. The view of h and X through my APM 100 EDs with 24 Pans is among my favorites of all. I'd be curious if the slightly higher mag in the 120 SDs would still allow for the same magic.

 


Edited by janapier, 29 May 2018 - 06:38 AM.

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#19 range88

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Posted 29 May 2018 - 07:03 AM

I recently had a chance to do an quick comparison star test with my APO 100mm and an APO 120mm. SA and secondary spectrum where practically identical. Views of the last quarter moon at all available high magnifications (Nagler 6-3mm zoom) where free from false color in both instruments. As expected, at the same magnification (both at 110x) the 120mm showed better resolution but neither showed any CA.

The 120mm have SD because then need it in order to reach the same level of performance as the 100mm. Remember, with the focal ratio remaining constant, secondary spectrum will increase exponential as aperture increases. This means with increased aperture glass with a higher Abbe number is required to compensate for the increased secondary spectrum.

Is there anybody who actually think 120sd is better color corrected than 100ed?

To calculate the secondary spectrum:

120sd: 920x120/10000/5.5=2.01

100ed: 920x100/6000/5.5=2.79



#20 Mad Matt

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Posted 29 May 2018 - 07:14 AM

Is there anybody who actually think 120sd is better color corrected than 100ed?

To calculate the secondary spectrum:

120sd: 920x120/10000/5.5=2.01

100ed: 920x100/6000/5.5=2.79

They could very well be but if the secondary spectrum of the 100mm are all ready under a detectable limit for the given magnification  I observed with (110x) then the 120 may be better but its simply not detectable. (You can't see less then what the cone and rod cells can resolve grin.gif ) 

 

I imagine that if I where to compare the CA specifically on the limb of the moon at equal exit pupils (100mm at 183x,120mm at 220x) they would be about equal... This would mean the 120mm has the better absolute correction because, in comparison, its magnification is 20% more wink.gif

 

What are the numbers you are using? 120, 100 and 5.5 are clear but the others? I thought that to calculate the secondary spectrum all curves and glass types must be known blush.gif flowerred.gif


Edited by Mad Matt, 29 May 2018 - 07:30 AM.


#21 range88

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Posted 29 May 2018 - 08:46 AM

1/6000 and 1/10000 are empirical numbers of 51 doublet and 53 doublet when calculating ss of a doublet; 920 is the constant Zeiss used.

Their could be variations of different mating glass, but usually not too much.  And in this case both are lanthanum.

I see a lot of color in my 100ed when observing in the broad sun light, but no so much in 120sd. At night that's a different story.


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#22 RickyD85

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Posted 29 May 2018 - 09:33 AM

I get very minor yellow edge to the moon at night when its very bright, is that an issue with colour correction, or my eyesight?

I find if i look at the edge it goes, but if when looking at the centre it i get this very small yellow edge, only happens on the moon.

Its better with the 12.5 morpheus than the 20mm UWA that came with them.


Edited by RickyD85, 29 May 2018 - 05:12 PM.


#23 Rich V.

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Posted 29 May 2018 - 10:01 AM

Ricky, you're very likely seeing lateral chromatic aberration caused at the eyepieces.  This causes fringes on the Moon like you describe. 

 

With lateral CA, different wavelengths of light come to focus at different positions on the focal plane.  The further off axis you move the Moon, the more fringing appears. You may see a yellow fringe on one side of the Moon and perhaps green or purple on the other.  The further away from the center of the FOV, the more pronounced the CA will be.  On axis, it won't be so noticeable.

 

Rich



#24 Mad Matt

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Posted 29 May 2018 - 11:36 AM

1/6000 and 1/10000 are empirical numbers of 51 doublet and 53 doublet when calculating ss of a doublet; 920 is the constant Zeiss used.
Their could be variations of different mating glass, but usually not too much.  

Thanks for that! Yes, 1/6000 and 1/10000 ring a bell but I cant remember from where.
 

I see a lot of color in my 100ed when observing in the broad sun light, but no so much in 120sd. At night that's a different story.

Interesting! Maybe with daytime viewing the secondary spectrum of the 100's is then bright enough to activate the cone cells. 


Edited by Mad Matt, 29 May 2018 - 11:39 AM.



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