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Does anyone have experience with the ED Doublets?

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#1 thornhale

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Posted 07 April 2021 - 10:00 AM

Hi community,

 

Recently, I came across an interesting combination: a doublet but not with  normal flint glass but with ED glass.

 

https://www.svbony.c...nomy-telescope/

 

What I am wondering is what ED glass (S-FPL51) gives me in this case since it's not a triplet to fully get rid of chromatic aberration.

What I am also wondering is: Is this scope within the price-performance range? Is it a total rip off? Is it a good deal?

 

Does anyone have experiences with this specific scope...or with ED doublets in general (for astrophotography)?


Edited by thornhale, 07 April 2021 - 01:20 PM.


#2 Nippon

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Posted 07 April 2021 - 02:09 PM

ED doublets can be virtually free of false color visually providing it is either fluorite or FPL53 or an equivalent glass to FPL53 as the low dispersion element. And the scope has a focal ratio of F/7 or slower. According to the specs of the scope in your link it is F/6 and uses FPL51. If properly made it will have less false color than an achromat of the same F ratio but will still have false color visually. I guess it could be called a semi apo although there is no clear definition for the term. Some would say that no doublet, even the highly regarded Takahashi fluorite doublets are true apochromats.


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#3 aeajr

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Posted 07 April 2021 - 02:14 PM

I can't comment on the SVBony scope you reference. 

 

The Astro Tech ED doublet refractors are very popular. 

I have a 102ED on order and know several people who have them. They LOVE them.

https://www.astronom...ractor-ota.html

 

The AT 102ED uses FK-61 ED glass.  Visually they are virtually CA free.  AP wise they are still not EDL triplets, but they are close, at a fraction of the price. 

 

The SVBony you listed looks very similar to this AT 72ED

https://www.astronom...fpl-53-f-6.html

 

I can't comment on the different ED glass specifications so can't help.  You might find some help here:

https://en.wikipedia...ispersion_glass

 

FK61 and FPL 53

https://www.cloudyni...-61-and-fpl-53/


Edited by aeajr, 07 April 2021 - 02:34 PM.


#4 russell23

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Posted 07 April 2021 - 02:57 PM

Hi community,

 

Recently, I came across an interesting combination: a doublet but not with  normal flint glass but with ED glass.

 

https://www.svbony.c...nomy-telescope/

 

What I am wondering is what ED glass (S-FPL51) gives me in this case since it's not a triplet to fully get rid of chromatic aberration.

What I am also wondering is: Is this scope within the price-performance range? Is it a total rip off? Is it a good deal?

 

Does anyone have experiences with this specific scope...or with ED doublets in general (for astrophotography)?

This particular scope will show some CA for visual observations as does its larger aperture 102mm f/7 cousin.   However, even the 102mm f/7 version is a very good performing scope. 

 

I have a 102mm f/11 ED doublet with fpl-51 or equivalent and has zero visible CA that I can see so it matches my 102mm f/7 fpl-53 doublet.   That is not surprising as the longer focal length works better with fpl-51 glass.

 

It really depends upon your intended purpose and tolerance.  If you are going for visual the fpl-51 f/7 ED doublets will show a little visible CA.  If you are ok with that then the scopes are a great option.  If you are looking for essentially zero visible CA then the fpl-53 doublets or the f/11 fpl-51 doublet are the better choices.

 

Dave



#5 SeattleScott

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Posted 07 April 2021 - 03:00 PM

Because it is a FPL51 doublet, it will have some CA in the images. One can ignore it. One can process it out. Or one can buy a better scope. Those are the options.

Scott

#6 BlueMoon

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Posted 07 April 2021 - 03:07 PM

I'd stick with FPL-53 glass if possible. FPL-53 glass in doublets is pretty wide spread with a reasonable decent cost factor. So, just my opinion here, I see no reason to buy any doublet with FPL-51 unless one's budget just won't allow anything else.

 

Anecdote: My SW 100ED APO is a doublet with a BK-7 and FPL-53 glass objective, gives amazing views and virtually no CA.

 

Clear skies.


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#7 dagadget

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Posted 07 April 2021 - 03:12 PM

I can't comment on the SVBony scope you reference. 

 

The Astro Tech ED doublet refractors are very popular. 

I have a 102ED on order and know several people who have them. They LOVE them.

https://www.astronom...ractor-ota.html

 

The AT 102ED uses FK-61 ED glass.  Visually they are virtually CA free.  AP wise they are still not EDL triplets, but they are close, at a fraction of the price. 

 

The SVBony you listed looks very similar to this AT 72ED

https://www.astronom...fpl-53-f-6.html

 

I can't comment on the different ED glass specifications so can't help.  You might find some help here:

https://en.wikipedia...ispersion_glass

 

FK61 and FPL 53

https://www.cloudyni...-61-and-fpl-53/

The AT72EDII with FPL-53 glass will out preform that SVBony 70 with FPL-51 glass. I am waiting on my AT72EDII and did a lot of reviews on scopes the AT scope was the best in that size range.



#8 russell23

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Posted 07 April 2021 - 03:18 PM

I'd stick with FPL-53 glass if possible. FPL-53 glsdd in doublets is pretty wide spread with a reasonable decent cost factor. So, just my opinion here, I see no reason to buy any doublet with FPL-51 unless one's budget just won't allow anything else.

 

Anecdote: My SW 100ED APO is a doublet with a BK-7 and FPL-53 glass objective, gives amazing views and virtually no CA.

 

Clear skies.

Hi Jeff,

 

The Starwave 102mm f/11 fpl-51 ED doublet should be an exception from what you are suggesting.  I have done direct comparison with my fpl-53 102mm f/7 SV Access and it is a match for color correction (no visible CA) and in fact general provides a sharper image than the f/7 scope.

 

There is no question that in fast ED doublets (faster than f/8) the fpl-53 or equivalent (FCD-100) scopes provide visual images free of detectable CA whereas the fpl-51 scopes generally show a little visible CA. 

 

Dave

 

 

 

 



#9 BlueMoon

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Posted 07 April 2021 - 03:28 PM

 

The Starwave 102mm f/11 fpl-51 ED doublet should be an exception from what you are suggesting.

Your point is well taken and there are exceptions to everything. However, at approx. $988US, (converted from British pounds) the OP could buy a SW 100ED APO doublet for instance.

 

My own opinion is that I would probably stay away from the scope he's linked to as there are many other "tried and true" brands to choose from.

 

Clear skies.



#10 RichA

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Posted 07 April 2021 - 03:46 PM

I can't comment on the SVBony scope you reference. 

 

The Astro Tech ED doublet refractors are very popular. 

I have a 102ED on order and know several people who have them. They LOVE them.

https://www.astronom...ractor-ota.html

 

The AT 102ED uses FK-61 ED glass.  Visually they are virtually CA free.  AP wise they are still not EDL triplets, but they are close, at a fraction of the price. 

 

 

At f9 such a scope will show about 2x (arbitrary) the colour error of an f6 triplet with the best glass, but f7, you are going to see some mild colour.  Best advice as always, keep you eye dead-centre of the image.

 



#11 McGarnicle

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Posted 07 April 2021 - 03:54 PM

I had an AT80ED (FK-61) and an AT60ED (FPL-53 & lanthanum) and really enjoyed both. Sharp, crisp views with no false color that I ever noticed. Also the focusers and just overall build quality are fantastic. I basically “rented” them while waiting for my AT102ED to arrive, knowing I could resell them for what I paid. These scopes are very well regarded for their quality & value and in great demand. 

 

I know the 102 is a great scope that I’ll use often, but I think I may still miss the 80. It’s the perfect size, compact yet large enough to view plenty of objects, wide field yet capable of high magnification, and just fun to use. 

 

Off-topic musing....if I could buy a set of rings to make two AT80EDs into a bino scope, I’d do that in a second. No idea if that’s a thing. 


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#12 russell23

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Posted 07 April 2021 - 03:58 PM

Your point is well taken and there are exceptions to everything. However, at approx. $988US, (converted from British pounds) the OP could buy a SW 100ED APO doublet for instance.

 

My own opinion is that I would probably stay away from the scope he's linked to as there are many other "tried and true" brands to choose from.

 

Clear skies.

That would be an interesting comparison.  I don't think anyone has reported a direct comparison yet between the 100mm f/9 fpl-53 and the 102mm f/11 fpl-51. 

 

I have the SW120ED and find the Starwave 102 has better contrast and comes with a significantly better focuser. The SW120ED also seems to suffer in cold weather from the objective cell compressing the lens as over the years I have found the scope is never as sharp in sub ~25 deg weather as it is during the summer months.  The Starwave has shown perfect tight, round star images in the cold temps this winter.  Probably I need to loosen the retaining ring slightly on my 120ED, but I've generally found that if I mess with the mechanical aspects of equipment I am more likely to make things worse than better! lol.gif


Edited by russell23, 07 April 2021 - 03:58 PM.


#13 SeattleScott

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Posted 07 April 2021 - 04:31 PM

Hi Jeff,

The Starwave 102mm f/11 fpl-51 ED doublet should be an exception from what you are suggesting. I have done direct comparison with my fpl-53 102mm f/7 SV Access and it is a match for color correction (no visible CA) and in fact general provides a sharper image than the f/7 scope.

There is no question that in fast ED doublets (faster than f/8) the fpl-53 or equivalent (FCD-100) scopes provide visual images free of detectable CA whereas the fpl-51 scopes generally show a little visible CA.

Dave

The OP is looking for an imaging scope though.

Scott
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#14 F.Meiresonne

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Posted 07 April 2021 - 04:45 PM

I have an 102 mm doublet. Virtual color free. FPL53 and Lanthanum. You easily can image with such. F/7

I have also a 70 mm FPL51 doublet. Fine scope for visual and quite better then an achromat but not good enough for AP.


Edited by F.Meiresonne, 07 April 2021 - 04:46 PM.


#15 russell23

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Posted 07 April 2021 - 04:58 PM

The OP is looking for an imaging scope though.

Scott

I think the OP added that after starting the thread.  I do not believe that was in the original post when first posted even though it is there now.  That doesn’t rule out the 102mm f/11 ED although for imaging most people want something faster and definitely the fpl-51 f/7 scopes are not as optimal.  If looking for an imaging scope then it is pretty much guaranteed any of the SW scopes will need a focuser upgrade.  


Edited by russell23, 07 April 2021 - 04:59 PM.

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#16 BlueMoon

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Posted 07 April 2021 - 06:22 PM

 

The OP is looking for an imaging scope though.

I thought the question was more general and the (for astrophotography) was more or less an after-thought and added on.

 

 

What I am wondering is what ED glass (S-FPL51) gives me in this case since it's not a triplet to fully get rid of chromatic aberration.

The point to me is this: it comes down not so much to a particular scope as would a person prefer FPL-51 glass at a nice price point, or spend a bit more perhaps for FPL-53 or better.

 

Clear skies.


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#17 thornhale

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Posted 07 April 2021 - 06:45 PM

I thought the question was more general and the (for astrophotography) was more or less an after-thought and added on.

 

The point to me is this: it comes down not so much to a particular scope as would a person prefer FPL-51 glass at a nice price point, or spend a bit more perhaps for FPL-53 or better.

 

Clear skies.

 

Clear skies.

That's exactly right, BlueMoon. So for example, one could get:

 

1.) A 80mm F5 Achromat with normal flint glass for $179: https://optcorp.com/...SMaAvsrEALw_wcB

2.) A 70mm F6 FPL-51 ED Doublet for $359: https://www.svbony.c...nomy-telescope/

3.) A 70mm F6 FPL-53 ED Doublet for $489: https://www.astronom...fpl-53-f-6.html

4.) A 80mm F6 Tripplet APO refractor for $849: https://www.astronom...ractor-ota.html

5.) A 70mm F5 Quadruplet APO refractor for $1199:https://www.google.c...HX_7CkoQ8wIIrQY

6.) A 80mm F5 FPL-53 Tripplet APO refractor for $1699: https://www.highpoin...elescope-s11400

7.) A 85mm F5.3 four element double ED Petzval system APO refractor for $3900: https://www.highpoin...ttener-tqe08541

 

The pay range for telescopes of relatively similar sizes and F-factors is truly astounding!

 

Is the doublet I referred to in the beginning relatively speaking on the price/performance curve? Is it a total rip off? Or are we getting comparatively more value out of this for the price we are paying? I am looking for a relatively affordable and transportable grab-n-go telescope but would prefer not to spend so much.


Edited by thornhale, 07 April 2021 - 06:51 PM.

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#18 BlueMoon

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Posted 07 April 2021 - 06:58 PM

 

Is it a total rip off?

I try to not think in those terms when possible. I have some Svbony hardware and it seems of reasonable quality. However, if I were to spend my hard-earned $$$ for a scope I would prefer a company who has a longer "track record" and better focus on the optical aspects. Quite honestly, one doesn't see a lot of reviews for the Svbony scopes it seems. There could be any number of reasons why but only some research and diligence will tell the tale.

 

 

I am looking for a relatively affordable and transportable grab-n-go telescope but would prefer not to spend so much.

This is sort of a "grey area" as folks have differing definitions of "grab n go". For me, I'd recommend the SW 72ED APO without reservation. I use one for both casual AP and "grab n go" I've found it to be very affordable (sub-$500US), has fine optics and versatility. But like the alternatives you listed there are quite a few good candidates for that usage. All the major brands sell decent scopes in the smaller apertures that could prove suitable.

 

Clear skies.



#19 thornhale

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Posted 07 April 2021 - 08:12 PM

I try to not think in those terms when possible. I have some Svbony hardware and it seems of reasonable quality. However, if I were to spend my hard-earned $$$ for a scope I would prefer a company who has a longer "track record" and better focus on the optical aspects. Quite honestly, one doesn't see a lot of reviews for the Svbony scopes it seems. There could be any number of reasons why but only some research and diligence will tell the tale.

 

This is sort of a "grey area" as folks have differing definitions of "grab n go". For me, I'd recommend the SW 72ED APO without reservation. I use one for both casual AP and "grab n go" I've found it to be very affordable (sub-$500US), has fine optics and versatile. But like the alternatives you listed there are quite a few good candidates for that usage. All the major brands sell decent scopes in the smaller apertures that could prove suitable.

 

Clear skies.

Could you provide the link for your SW72ED APO?     



#20 BlueMoon

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Posted 07 April 2021 - 08:36 PM

Could you provide the link for your SW72ED APO?     

There you go. https://www.skywatch...2-apo-refractor

 

I use this little guy for grab n go, fit it with a Lunt Solar Wedge for white light solar and I'm using it with a 12 Mpixel Raspberry Pi HQ camera for a EAA AP project I'm developing. Its been used with a Nikon D5300 DSLR for more conventional AP as well. The 72 been incredibly versatile in all it's uses, the optics are first rate and trouble-free. Here's a couple of pics, one set up for solar, the other for night work. Both on a Vixen Porta II mount.

 

Clear skies.

Attached Thumbnails

  • 72_sun_2_400x300.jpg
  • 72mm_400x533.jpg

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#21 Challenger75

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Posted 07 April 2021 - 09:05 PM

I'd stick with FPL-53 glass if possible. FPL-53 glass in doublets is pretty wide spread with a reasonable decent cost factor. So, just my opinion here, I see no reason to buy any doublet with FPL-51 unless one's budget just won't allow anything else.

 

Anecdote: My SW 100ED APO is a doublet with a BK-7 and FPL-53 glass objective, gives amazing views and virtually no CA.

 

Clear skies.

Good to know. My SW 100ED Pro is being delivered tomorrow.


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#22 Challenger75

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Posted 07 April 2021 - 09:23 PM

If you go right to their ad for the scope on Amazon and scroll down, they show  pictures that have a lot of purple fringe/halos around stars. If they are showing that, it's safe to assume that's what you'll see if you get one. 

 

https://www.amazon.c...17848249&sr=8-2


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#23 alphatripleplus

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Posted 08 April 2021 - 08:02 AM

The AT72EDII with FPL-53 glass will out preform that SVBony 70 with FPL-51 glass. I am waiting on my AT72EDII and did a lot of reviews on scopes the AT scope was the best in that size range.

Yeah, the better colour correction is the main reason I chose the FPL-53 glass  AT72EDII over similar scopes with FPL-51 glass.


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#24 JoshUrban

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Posted 08 April 2021 - 06:53 PM

I've got an AT102ED doublet, and there is some CA.  It's not too bad, but it's not entirely color-free.  (Then again, I got it lightly used for $475 with a 2" diagonal, so that's a pretty solid value in my book.)   



#25 Nippon

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Posted 09 April 2021 - 06:34 AM

I don't think it is a ripoff. People happily payed far more for the Tele Vue Pronto which was an ED but nowhere near being an APO.




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