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Svbony SV135 7-21mm Zoom Eyepiece - A Noob’s Perspective

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#1 FlyingV74

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Posted 10 January 2021 - 11:11 AM

If you are like me.......just purchased your first “real scope”, which for many of us is an 8” 1200mm dob......and you are trying to figure out what eyepieces to buy to help improve your view, then you might enjoy what I have written here.

After obsessing about the lower cost options in the eyepiece market, I couldn’t make up my mind. Should I go with a 15mm wide field eyepiece? But what if I really want 12mm? Or 18mm? I finally decided to give this Svbony 7-21mm zoom eyepiece a try. After all, how bad could it be? I liked the idea of being able to go from 21mm to 7mm with the twist of the wrist. The photos made it look like a nice piece. And at $52, it seemed like a good value overall.

The Svbony eyepiece arrived a few weeks ago. I won’t go into the details of the packaging. It arrived safe and sound and worked as it should out of the package. The night that I got it, I took it out to give Jupiter a view through it. Jupiter is obviously getting lower and lower in the sky, making the view worse and worse. I wanted to compare it to the 9mm Plossl that was included with my scope before the view of Jupiter got too bad. In my opinion, the overall view of Jupiter was pretty good, on par with the Plossl. In the center of the image, both the zoom and the Plossl showed good detail and looked very similar to my eye. What I did notice though was a bit of chromatic aberration at the very, very edge of the image. It wasn’t enough to really bother me. But it was definitely there right as Jupiter drifted out of view. The other thing that I noticed was that at 21mm, the view took on that “soda straw” or “porthole” view that I read about. Again, this didn’t bother me all that much. But those that want a low power, wide field of view will not particularly enjoy this aspect of this EP. Finally, the last thing that I noticed is when zoomed in all the way to 7mm, if I got my eye too close to the eye piece, the image would black out. I guess that is an eyepiece’s way of telling you to back up. I always find myself wanting to mash my eye right up against the eyepiece, partly because it helps block out the neighborhood lights. But I’m slowly learning that sometimes you’ve just gotta back up.

I also wanted to give this eye piece a fair comparison at the lower end of its magnification. So I purchased a used 25mm Orion Sirius Plossl so that I could objectively compare this eyepiece to one that is pretty standard in this hobby. I chose to focus on the Orion Nebula for this evaluation. While the zoom eyepiece performed well, I did find myself thinking that the Plossl was ever so slightly crisper. This evaluation was done with and without a 2x Svbony barlow lens screwed into end of the Plossl (for approximately 1.5x). I swapped back and forth between the zoom and the Plossl several times. The contrast of both looked identical to my eye. And don’t get me wrong, the sharpness of the zoom was pretty darn good. But the Plossl just seemed to be a little bit crisper. So for hardcore, low power, wider field of view, the Plossl wins easily. But can the 25mm Plossl zoom to 7mm with the flick of the wrist? Nope. And that is what makes the zoom EP so much fun to use. I can go from viewing the trapezium at 21mm to 7mm, and all points in between, just by giving the eye piece a twist. This really does let a person find that “sweet spot” in magnification where they enjoy viewing the most.

As I have used this 7-21mm eyepiece and considered that my scope included a 9mm Plossl and 30mm Superview, I have found myself wondering why manufacturers of entry level scopes don’t forego the various low cost eyepieces and the Barlow lens and include an 8-24mm zoom eyepiece in these kits? Would it cost more to do this? I don’t know. But I believe that most “noobs” like myself would enjoy the experience of being able to zoom in and out. This would allow us to figure out exactly how much power we enjoy using for viewing different things in the sky. And then when we take the plunge into a TV or ES eyepiece that sets us back $200+, we will likely be quite satisfied since we aren’t purchasing a focal length that is completely foreign to us. And if nothing else, it is just cool to be able to zoom in and out when it strikes you to do so. Though I did not give it a Wayne’s World unnecessary zoom, I think it would hold up just fine! :p
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#2 sevenofnine

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Posted 10 January 2021 - 11:56 AM

Yep, I'm a zoom fan too lol.gif  What they do makes them really attractive especially when you're first starting out. So much better than the plossls included with scopes these days. I'm sure that mfgr's cost has a lot to do with why they don't include them instead. The plossls are probably $5 ea. and the zoom might be $20. There are other really nice eyepieces out there too. The view through a good 2 inch wide is breath taking on some objects. A good wide and zoom "might" be all you need waytogo.gif


Edited by sevenofnine, 10 January 2021 - 11:42 PM.

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#3 Taosmath

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Posted 10 January 2021 - 12:50 PM

I'm with 7of9.  

 

For 90% of my viewing with my Dobs I use a Baader zoom and a wide angle (usually my 31mm Axiom LX). I also always have a low midrange wide angle Ep around if I need wider field of view than the 24mm zoom can give me (I use a 23 mm Axiom LX) but I only use that  once or twice each session.

 

I did a comparison of Baader vs, Celestron vs SV Bony 8-24mm. https://www.cloudyni...oom/?p=10551885

 

 Baader was the best (no surprise) but it wasn't SO much better than the others (certainly not the 3x better indicated by the price).  I thought the SV Bony may have been a little sharper than the Celestron/Meade/Agena (all the same) but the FOV was narrower.  Also people have noted that at low temperatures, the SV Bony can get stiff to the point of immovable in some cases Mine was stiff at the long focal length setting the other night when temperature were 25F. Not something I have found with the Celestron.

 

I  suspect that  7of9 is also correct about the production cost deciding which Ep's to provide with a new scope.


Edited by Taosmath, 10 January 2021 - 12:53 PM.

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#4 LDW47

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Posted 10 January 2021 - 12:50 PM

If you are like me.......just purchased your first “real scope”, which for many of us is an 8” 1200mm dob......and you are trying to figure out what eyepieces to buy to help improve your view, then you might enjoy what I have written here.

After obsessing about the lower cost options in the eyepiece market, I couldn’t make up my mind. Should I go with a 15mm wide field eyepiece? But what if I really want 12mm? Or 18mm? I finally decided to give this Svbony 7-21mm zoom eyepiece a try. After all, how bad could it be? I liked the idea of being able to go from 21mm to 7mm with the twist of the wrist. The photos made it look like a nice piece. And at $52, it seemed like a good value overall.

The Svbony eyepiece arrived a few weeks ago. I won’t go into the details of the packaging. It arrived safe and sound and worked as it should out of the package. The night that I got it, I took it out to give Jupiter a view through it. Jupiter is obviously getting lower and lower in the sky, making the view worse and worse. I wanted to compare it to the 9mm Plossl that was included with my scope before the view of Jupiter got too bad. In my opinion, the overall view of Jupiter was pretty good, on par with the Plossl. In the center of the image, both the zoom and the Plossl showed good detail and looked very similar to my eye. What I did notice though was a bit of chromatic aberration at the very, very edge of the image. It wasn’t enough to really bother me. But it was definitely there right as Jupiter drifted out of view. The other thing that I noticed was that at 21mm, the view took on that “soda straw” or “porthole” view that I read about. Again, this didn’t bother me all that much. But those that want a low power, wide field of view will not particularly enjoy this aspect of this EP. Finally, the last thing that I noticed is when zoomed in all the way to 7mm, if I got my eye too close to the eye piece, the image would black out. I guess that is an eyepiece’s way of telling you to back up. I always find myself wanting to mash my eye right up against the eyepiece, partly because it helps block out the neighborhood lights. But I’m slowly learning that sometimes you’ve just gotta back up.

I also wanted to give this eye piece a fair comparison at the lower end of its magnification. So I purchased a used 25mm Orion Sirius Plossl so that I could objectively compare this eyepiece to one that is pretty standard in this hobby. I chose to focus on the Orion Nebula for this evaluation. While the zoom eyepiece performed well, I did find myself thinking that the Plossl was ever so slightly crisper. This evaluation was done with and without a 2x Svbony barlow lens screwed into end of the Plossl (for approximately 1.5x). I swapped back and forth between the zoom and the Plossl several times. The contrast of both looked identical to my eye. And don’t get me wrong, the sharpness of the zoom was pretty darn good. But the Plossl just seemed to be a little bit crisper. So for hardcore, low power, wider field of view, the Plossl wins easily. But can the 25mm Plossl zoom to 7mm with the flick of the wrist? Nope. And that is what makes the zoom EP so much fun to use. I can go from viewing the trapezium at 21mm to 7mm, and all points in between, just by giving the eye piece a twist. This really does let a person find that “sweet spot” in magnification where they enjoy viewing the most.

As I have used this 7-21mm eyepiece and considered that my scope included a 9mm Plossl and 30mm Superview, I have found myself wondering why manufacturers of entry level scopes don’t forego the various low cost eyepieces and the Barlow lens and include an 8-24mm zoom eyepiece in these kits? Would it cost more to do this? I don’t know. But I believe that most “noobs” like myself would enjoy the experience of being able to zoom in and out. This would allow us to figure out exactly how much power we enjoy using for viewing different things in the sky. And then when we take the plunge into a TV or ES eyepiece that sets us back $200+, we will likely be quite satisfied since we aren’t purchasing a focal length that is completely foreign to us. And if nothing else, it is just cool to be able to zoom in and out when it strikes you to do so. Though I did not give it a Wayne’s World unnecessary zoom, I think it would hold up just fine! tongue2.gif

 

If you are like me.......just purchased your first “real scope”, which for many of us is an 8” 1200mm dob......and you are trying to figure out what eyepieces to buy to help improve your view, then you might enjoy what I have written here.

After obsessing about the lower cost options in the eyepiece market, I couldn’t make up my mind. Should I go with a 15mm wide field eyepiece? But what if I really want 12mm? Or 18mm? I finally decided to give this Svbony 7-21mm zoom eyepiece a try. After all, how bad could it be? I liked the idea of being able to go from 21mm to 7mm with the twist of the wrist. The photos made it look like a nice piece. And at $52, it seemed like a good value overall.

The Svbony eyepiece arrived a few weeks ago. I won’t go into the details of the packaging. It arrived safe and sound and worked as it should out of the package. The night that I got it, I took it out to give Jupiter a view through it. Jupiter is obviously getting lower and lower in the sky, making the view worse and worse. I wanted to compare it to the 9mm Plossl that was included with my scope before the view of Jupiter got too bad. In my opinion, the overall view of Jupiter was pretty good, on par with the Plossl. In the center of the image, both the zoom and the Plossl showed good detail and looked very similar to my eye. What I did notice though was a bit of chromatic aberration at the very, very edge of the image. It wasn’t enough to really bother me. But it was definitely there right as Jupiter drifted out of view. The other thing that I noticed was that at 21mm, the view took on that “soda straw” or “porthole” view that I read about. Again, this didn’t bother me all that much. But those that want a low power, wide field of view will not particularly enjoy this aspect of this EP. Finally, the last thing that I noticed is when zoomed in all the way to 7mm, if I got my eye too close to the eye piece, the image would black out. I guess that is an eyepiece’s way of telling you to back up. I always find myself wanting to mash my eye right up against the eyepiece, partly because it helps block out the neighborhood lights. But I’m slowly learning that sometimes you’ve just gotta back up.

I also wanted to give this eye piece a fair comparison at the lower end of its magnification. So I purchased a used 25mm Orion Sirius Plossl so that I could objectively compare this eyepiece to one that is pretty standard in this hobby. I chose to focus on the Orion Nebula for this evaluation. While the zoom eyepiece performed well, I did find myself thinking that the Plossl was ever so slightly crisper. This evaluation was done with and without a 2x Svbony barlow lens screwed into end of the Plossl (for approximately 1.5x). I swapped back and forth between the zoom and the Plossl several times. The contrast of both looked identical to my eye. And don’t get me wrong, the sharpness of the zoom was pretty darn good. But the Plossl just seemed to be a little bit crisper. So for hardcore, low power, wider field of view, the Plossl wins easily. But can the 25mm Plossl zoom to 7mm with the flick of the wrist? Nope. And that is what makes the zoom EP so much fun to use. I can go from viewing the trapezium at 21mm to 7mm, and all points in between, just by giving the eye piece a twist. This really does let a person find that “sweet spot” in magnification where they enjoy viewing the most.
 

They throw in the basic eps hoping / knowing that you will buy a better ep(s), its common sense ! And I have 2 Svbony zooms, the larger 8-24 and the 10-30 and the slight difference in FOV vs other brands is hardly notable contrary to what many will say. What do you think you see different between 41° and 38° or 58° and 55° ? Calculate it and see for yourself while you are busy concentrating on those black, clear skize. My 3 older Meade 4000 zooms and my new Orion E zoom are no different and they all function like they should in temps down to about 10° F !


Edited by LDW47, 10 January 2021 - 01:34 PM.

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#5 LDW47

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Posted 10 January 2021 - 01:39 PM

I'm with 7of9.  

 

For 90% of my viewing with my Dobs I use a Baader zoom and a wide angle (usually my 31mm Axiom LX). I also always have a low midrange wide angle Ep around if I need wider field of view than the 24mm zoom can give me (I use a 23 mm Axiom LX) but I only use that  once or twice each session.

 

I did a comparison of Baader vs, Celestron vs SV Bony 8-24mm. https://www.cloudyni...oom/?p=10551885

 

 Baader was the best (no surprise) but it wasn't SO much better than the others (certainly not the 3x better indicated by the price).  I thought the SV Bony may have been a little sharper than the Celestron/Meade/Agena (all the same) but the FOV was narrower.  Also people have noted that at low temperatures, the SV Bony can get stiff to the point of immovable in some cases Mine was stiff at the long focal length setting the other night when temperature were 25F. Not something I have found with the Celestron.

 

I  suspect that  7of9 is also correct about the production cost deciding which Ep's to provide with a new scope.

If its the Mark IV its more like 4-5x the price ! Big difference vs very little in performance !



#6 teashea

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Posted 10 January 2021 - 01:54 PM

I have the Svbony 7-21 and the 10-30.  Both are excellent.  Performance is very fine and the build quality is excellent.  There should be no stigma anymore regarding optics made in China.  They can be quite good. 

 

I also have purchased several eyepieces and accessories from Svbony.  They have all been high quality.  

 

Quite impressive.


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#7 LDW47

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Posted 10 January 2021 - 03:02 PM

I have the Svbony 7-21 and the 10-30.  Both are excellent.  Performance is very fine and the build quality is excellent.  There should be no stigma anymore regarding optics made in China.  They can be quite good. 

 

I also have purchased several eyepieces and accessories from Svbony.  They have all been high quality.  

 

Quite impressive.

Dead on !


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#8 aeajr

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Posted 10 January 2021 - 10:39 PM

Just received my SVBony 7-21 

 

First look, daytime, through my 127 mm F15 Mak.   Compared it to the Celestron and the Baader Hyperion.

 

Used a power pole about 1/4 mile away.   Optically I would put it with the Celestron so far.   No obvious defects around the edge as compared to the others.  Power lines seemed straight and even and in focus to the edges from 60X to 230X.

 

Daytime targets at high mag during the day are not really good for evaluation.  However, it did confirm that my sample has no apparent defects.

 

I had read posts with concerns that it stiffens up in the cold.  It has been outside for 3 days with below freezing temps each night.  Tonight it was 32 F when I went to check it.  Smooth operation with no hint of stiffening.  

 

Next time I will get it into a scope at night. 

 

Looking forward to getting it out at night.


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#9 Enceladust

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Posted 14 January 2021 - 08:43 PM

I received my SVBony 7-21 eyepiece yesterday.

I used my SVBony 7-21 eyepiece yesterday.

 

I used it as one of my tools to see Uranus for the first time with it yesterday. It was great zooming in and out on the Orion nebula with it. It was chilly but not super cold, and it performed well smoothly.

 

I have the feeling that I will be using it a lot! I agree with most people, for this price, it's a steal !


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#10 mr_helios

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Posted 07 February 2022 - 12:43 PM

Just ordered the 7-21 and am returning the Celestron 8-24 if I find it to be better. I have to say I was pretty disappointed with the clarity of the Celestron 8-24mm compared with my C6-supplied 25mm eyepiece. The 25mm was considerably crisper, even with just lunar observing. Looking forward to giving the SVBony a shot. 

 

Side question: Do you think the depth that an eyepiece seats into a star diagonal effects optical quality? Is it possible for eyepieces to perform differently relative to each other with different scopes? 


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#11 LDW47

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Posted 07 February 2022 - 12:54 PM

I received my SVBony 7-21 eyepiece yesterday.

I used my SVBony 7-21 eyepiece yesterday.

 

I used it as one of my tools to see Uranus for the first time with it yesterday. It was great zooming in and out on the Orion nebula with it. It was chilly but not super cold, and it performed well smoothly.

 

I have the feeling that I will be using it a lot! I agree with most people, for this price, it's a steal !

That why I have 3 different models, lol.


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#12 Sainso23

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Posted 07 February 2022 - 01:05 PM

I have the 7 to 21mm and the 9 to 27mm svbony zooms. Both perform well. The 9 to 27mm has a wider fov throughout most settings, it is with the extra cost. I find the 7 to 21mm has a smoother action to zoom.

#13 Sainso23

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Posted 07 February 2022 - 01:18 PM

That why I have 3 different models, lol.


Also why I got a second one. Plus to give me a slightly different range of magnifications.

#14 LDW47

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Posted 07 February 2022 - 01:45 PM

I have the 7 to 21mm and the 9 to 27mm svbony zooms. Both perform well. The 9 to 27mm has a wider fov throughout most settings, it is with the extra cost. I find the 7 to 21mm has a smoother action to zoom.

The 7.2-21.6 model has the widest FOV.


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#15 Neanderthal

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Posted 07 February 2022 - 02:15 PM

The 7.2-21.6 model has the widest FOV.

Just to avoid any confusion - this is the SV-191 model. waytogo.gif


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#16 Sainso23

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Posted 07 February 2022 - 02:57 PM

[quote name="LDW47" post="11695626" timestamp="1644259514"]

The 7.2-21.6 model has the widest FOV.[/quote

Yep that is true. Was comparing my two. The 9 to 27mm is wider throughout compared to the older 7 to 21 model. Both are good eyepieces though 😀

Edited by Sainso23, 07 February 2022 - 03:01 PM.

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#17 Lagrange

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Posted 08 February 2022 - 06:59 PM

Just ordered the 7-21 and am returning the Celestron 8-24 if I find it to be better. I have to say I was pretty disappointed with the clarity of the Celestron 8-24mm compared with my C6-supplied 25mm eyepiece. The 25mm was considerably crisper, even with just lunar observing. Looking forward to giving the SVBony a shot. 

 

Side question: Do you think the depth that an eyepiece seats into a star diagonal effects optical quality? Is it possible for eyepieces to perform differently relative to each other with different scopes? 

I don't know whether the seating of an eyepiece into the diagonal would affect image quality (I'd doubt it but could be wrong), but different scopes can cause eyepieces to perform very differently.

 

Using an eyepiece in a scope that has significant field curvature such as a short focal length refractor can make it seem like it loses sharpness away from the centre of the image, but the same eyepiece in an SCT which has a much flatter field could look great edge to edge. The eyepiece itself can have field curvature which might cancel out that of the scope and deliver a great image, or it could amplify the effect and look terrible.

 

The focal ratio of the scope is also important. A relatively simple and/or cheap eyepiece that delivers great images with a long focal ratio scope like an SCT will often struggle when used with much faster optics. Creating an eyepiece that can work well down to f/4 is difficult and expensive but the benefit of its sophisticated optical design will be much less obvious at f/10 and in the slower scope it might not seem that much better than a cheaper alternative.


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#18 mr_helios

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Posted 08 February 2022 - 10:22 PM

Well I'm very pleased with the 7-21. It certainly performs better than the Celestron 8-24 for whatever reason. I had some nice, clear skies tonight and a great moon. Here is a picture I too. Please note this is the first time I've taken a picture of anything and I don't have proper equipment. I just held up my iPhone to the 7-21mm (zoom set @ 21). Also, the site is really compressing it - original picture is a lot sharper, and real life is of course even more.
 
moon_iphone_c6.jpg

Edited by mr_helios, 08 February 2022 - 10:22 PM.

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#19 SteveG

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Posted 09 February 2022 - 02:25 PM

 

 

Side question: Do you think the depth that an eyepiece seats into a star diagonal effects optical quality? Is it possible for eyepieces to perform differently relative to each other with different scopes? 

Answer is: no to how it works with a diagonal, but yes to using different scopes.

 

Glad you're happy with the SvBony zoom. I purchased their 8-24, and was quite surprised at how nice it is.



#20 seasparky89

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Posted 10 February 2022 - 03:14 PM

I wanted an inexpensive zoom for use with mr AT-102ed and Herschel wedge for public solar sessions.  The SV zoom performs very well at all focal lengths, and I don’t worry about the public handling/mishandling it.  After two years of use, no issues.


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#21 llas

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Posted 04 April 2022 - 08:48 AM

I have a question regarding the true magnification capabilities of the Svbony Zoom 7-21mm eyepiece.

 

First, I would say that I am very pleased with its performance, delivering very sharp, clear and comfortable views with my AT70ED. The aforementioned question emerged when I measured the exit pupil within the several magnifications of the eyepiece, achieving contradictory results.  

 

I understand the calculation for exit pupil is aperture of the objective lens of the telescope divided by the magnification produced by the eyepiece.

  • The AT70ED scope has 70mm of aperture and 420 mm of focal length. In principle, the exit pupils should be:
    • at 21mm (20x) = 3,5mm
    • at 7mm (60x) = 1,16mm
  • However, I measured the exit pupils with a ruler and the results are:
    • at 21mm (?) = 3,4 mm
    • a 7mm (?) = 1,9 mm
  • With this experiment, I could preliminarily  conclude that the magnification at 7mm is not compatible with the official information about the eyepiece. Right now, a 1,9mm exit pupil means a magnification of 36,8x and not 60x as it should be.  I could achieve a 1mm exit pupil with a Svbony 2x barlow, however. 

Does anyone has achieved controversial magnification results with this eyepiece? Thanks a lot!



#22 emilslomi

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Posted 04 April 2022 - 09:33 AM

I have a question regarding the true magnification capabilities of the Svbony Zoom 7-21mm eyepiece.

 

First, I would say that I am very pleased with its performance, delivering very sharp, clear and comfortable views with my AT70ED. The aforementioned question emerged when I measured the exit pupil within the several magnifications of the eyepiece, achieving contradictory results.  

 

I understand the calculation for exit pupil is aperture of the objective lens of the telescope divided by the magnification produced by the eyepiece.

  • The AT70ED scope has 70mm of aperture and 420 mm of focal length. In principle, the exit pupils should be:
    • at 21mm (20x) = 3,5mm
    • at 7mm (60x) = 1,16mm
  • However, I measured the exit pupils with a ruler and the results are:
    • at 21mm (?) = 3,4 mm
    • a 7mm (?) = 1,9 mm
  • With this experiment, I could preliminarily  conclude that the magnification at 7mm is not compatible with the official information about the eyepiece. Right now, a 1,9mm exit pupil means a magnification of 36,8x and not 60x as it should be.  I could achieve a 1mm exit pupil with a Svbony 2x barlow, however. 

Does anyone has achieved controversial magnification results with this eyepiece? Thanks a lot!

 

How are you measuring the exit pupil to a precision of 0.1 mm with a ruler? There are rulers that can, but they are rather special. What about looking at how much the eyepiece magnifies an object going from 21mm to 7mm. It should be three times longer/wider at 7mm than at 21mm, whereas your measurements indicate that it is less than twice as big. That should be pretty quick to check out. Little (negligible) deviations abound and are of no consequence (unless one counts oneself an Asperger member), but that big a difference suggests that there is a measurement error somewhere.

 

Oh, and I have the 7-21 and it seems to magnify fine - no clue about the exit pupil though.

 

Emil



#23 llas

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Posted 05 April 2022 - 03:32 AM

How are you measuring the exit pupil to a precision of 0.1 mm with a ruler? There are rulers that can, but they are rather special. What about looking at how much the eyepiece magnifies an object going from 21mm to 7mm. It should be three times longer/wider at 7mm than at 21mm, whereas your measurements indicate that it is less than twice as big. That should be pretty quick to check out. Little (negligible) deviations abound and are of no consequence (unless one counts oneself an Asperger member), but that big a difference suggests that there is a measurement error somewhere.

 

Oh, and I have the 7-21 and it seems to magnify fine - no clue about the exit pupil though.

 

Emil

 

Thanks. It does seem to magnify 3x, indeed. Although the ruler measurement is not precise enough, the deviations of the exit pupil size are clear visible, that's why I would like to hear if anyone have noted that.



#24 davidgmd

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Posted 05 April 2022 - 03:49 PM

How does one directly measure (as opposed to calculate) exit pupil? Diameter of a circle of light at the manufacturer’s stated eye relief? If a zoom’s eye relief varies at different magnifications, how do you know where to take the measurements?




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