115 replies to this topic

[Inkie]

What exactly is a semi-apo. An achromat by another name? Maybe they stretched the focal length by 25 mm? Or enlarged the internal baffle to reduce the effective aperture?

Greg N

There is obviously a lot of range for the responses.  When I left the hobby about 25 years ago, an ED refractor was both expensive and rare, and they had 'some kinda spiffy glass' in them.  They weren't Roland Christen class neither, and nobody with any time in the hobby was under any illusions.

 

Now, ED means, to me, a higher quality glass as a component of a doublet meant to reduce CA substantially.....not entirely.  A lot better than the achromats less than F10 at the time I left the hobby.  Except now they're F8-ish.

 

To me, APO means at least a doublet with FPL-53 and another high quality glass with lanthanum, or whatever, but that's taking some liberties with the term.  Really a triplet is a true APO if it has FPL-53 or equivalent.  I can't give you numbers the way the 'grownup's can about Strehl, or percentage of gathered energy inside of the central 6% of the donut slightly out of focus, or whatever.  You should be able to see virtually no discernible CA in a true APO.

[Jon Isaacs]

Marketing term.  The lens had ED glass but not good enough ED glass or a long enough focal ration to make it a true apo.   I beleive the Celestron ED 80mm APOs came out about the same time and they had a Focal ration near 7.   It was a good scope just not a great one.

 

The Orion Express came out after the ED-80. The Express had no ED glass.

 

The ED-80 was F/7.5 with FPL-53, excellent color correction. The Celestron version was called a spotting scope and used the same objective.

 

I calculate the chromatic blur is 75% of the Airy disk.. 

 

Jon

[Redbetter]

I don't recall how the Pronto/Rangers were marketed; they weren't apo's, but folks were raving about them when they came out.  When I hear "semi-apo" I think of them, a somewhat better corrected short focal length achromat, sharp, but still obviously an achro.

 

Many/most of the FPL-51 doublets are somewhere in between the semi-apo's and the visually apochromatic ED doublets.  The visually apochromatic ones typically use something like FPL-53.    

[Jon Isaacs]

I don't recall how the Pronto/Rangers were marketed; they weren't apo's, but folks were raving about them when they came out.  When I hear "semi-apo" I think of them, a somewhat better corrected short focal length achromat, sharp, but still obviously an achro.

 

Many/most of the FPL-51 doublets are somewhere in between the semi-apo's and the visually apochromatic ED doublets.  The visually apochromatic ones typically use something like FPL-53.    

I have a Ranger, I had a Pronto.  When they came out, affordable ED scopes did not exist.  Both have ED on the name plate but again, according to Roland Christen, they used FK-5.  From the Astromart thread:

 

"Note one interesting glass that was touted some years ago as a "semi-ED" glass, which is FK5. "FK" is the Schott designation for Flour-crown, and this type of glass has some fluorite in it, but in this case not much at all. In any case, as you can see, there really are no mates far enough separated in dispersion (Vd) that would produce any sort of meaningful color correction, any better that the plain vanilla BK7-F4 variety."

 

The optics are very good, I recently was given a SkyWatcher 70mm x 500mm achromat. It probably had slightly more CA than my Ranger, pretty similar.

 

An FPL-51 doublet has about 3.7x better color correction than an achromat of the same focal ratio and aperture. Roland called them ED Doublet apos, given his role in developing the modern apo triplet and the fact that Astro-Physics has never made a FPL-51 doublet, I defer to him.

 

Jon

[Japetus Eye]

I have both tubes. I assume your Starfield must be very similar to my SV503. I have often mounted them side by side. The most noticeable difference in viewing has been when observing Jupiter and Saturn, and the Moon. Less so for other objects. The superior optics of the SW 100ED provide a quality of sharpness and contrast in detail that the 80ED cannot match; obviously there is a resolving power factor in favor of the 100ED that plays a role as well. As mentioned, the weakest link in the 100ED's chain is its Crayford focuser, which is smooth but can slips when retracted by the weight of the diagonal and 2" eyepieces in overhead positions.

 

Now, I think you're mistaken if you think you'll perceive a noticeable difference in light gathering between the 100 and the 80, as in my experience the difference comes from the different resolution capabilities and the difference in optics quality. So is it worth it? For me, yes. They are two different tubes. Even with the reducer, you still get a larger field of view with your 80. But keep in mind that the reducer will be used for photographic purposes, it won't give you visual focus, at least with the diagonal in the optical train. Your 80 is also less heavy and much shorter, so you can mount it on lighter supports and transport it more easily: an 80mm is, in fact, a great companion for travel, many observers have a similar telescope in a grab 'n' go setup. For me they are perfectly compatible and complementary tubes, and the offer for the SW 100ED looks quite tempting.

 

An acro 150mm wins... in light gathering, yes. But you must consider that it is a long, heavy tube and will require a very sturdy, and possibly expensive, support. On the other hand, you will use that tube basically at low and medium powers, since as soon as you exceed approx. 120x it will start to noticeably show chromatic aberration, which reduces the sharpness and contrast of the views. In short, an R150mm is a great tube for deep sky objects, but for lunar and planetary observation at high magnification it is not so good.

[Arkade]

I have both tubes. I assume your Starfield must be very similar to my SV503. I have often mounted them side by side. The most noticeable difference in viewing has been when observing Jupiter and Saturn, and the Moon. Less so for other objects. The superior optics of the SW 100ED provide a quality of sharpness and contrast in detail that the 80ED cannot match; obviously there is a resolving power factor in favor of the 100ED that plays a role as well. As mentioned, the weakest link in the 100ED's chain is its Crayford focuser, which is smooth but can slips when retracted by the weight of the diagonal and 2" eyepieces in overhead positions.

Now, I think you're mistaken if you think you'll perceive a noticeable difference in light gathering between the 100 and the 80, as in my experience the difference comes from the different resolution capabilities and the difference in optics quality. So is it worth it? For me, yes. They are two different tubes. Even with the reducer, you still get a larger field of view with your 80. But keep in mind that the reducer will be used for photographic purposes, it won't give you visual focus, at least with the diagonal in the optical train. Your 80 is also less heavy and much shorter, so you can mount it on lighter supports and transport it more easily: an 80mm is, in fact, a great companion for travel, many observers have a similar telescope in a grab 'n' go setup. For me they are perfectly compatible and complementary tubes, and the offer for the SW 100ED looks quite tempting.

An acro 150mm wins... in light gathering, yes. But you must consider that it is a long, heavy tube and will require a very sturdy, and possibly expensive, support. On the other hand, you will use that tube basically at low and medium powers, since as soon as you exceed approx. 120x it will start to noticeably show chromatic aberration, which reduces the sharpness and contrast of the views. In short, an R150mm is a great tube for deep sky objects, but for lunar and planetary observation at high magnification it is not so good.

I agree, the 150 achro will be used for dso mainly even though i have read people with the 750mm fl say it isnt bad on planets and the moon, given it being a fast scope.

About your SV503 80ed, I purchased my starfield 80mm as an apo, it clearly states it is an apo whereas the sv503 is not? If you know something i do not know regarding this as the price of the starfield was $887(in us dollars, i did conversion). Can they sell a telescope and advertise it as an apo when it is not? As i have looked on their website and a number of stores and it states it is an apo

[Japetus Eye]

I agree, the 150 achro will be used for dso mainly even though i have read people with the 750mm fl say it isnt bad on planets and the moon, given it being a fast scope.

About your SV503 80ed, I purchased my starfield 80mm as an apo, it clearly states it is an apo whereas the sv503 is not? If you know something i do not know regarding this as the price of the starfield was $887(in us dollars, i did conversion). Can they sell a telescope and advertise it as an apo when it is not? As i have looked on their website and a number of stores and it states it is an apo

I assumed at first that your 80mm was an ED doublet very similar to mine. But your comment has made me look at it more closely. It is indeed sold as an ED doublet, but they do include the term APO in the description. However, when we go to review the characteristics of the doublet they do not specify what kind of lenses it uses.

 

In ED doublets, the crown component is usually made of a special type of glass, sometimes with very expensive natural fluorite (calcium fluoride), or more frequently with synthetic fluorides. Lenses with these materials have the property of generating a very low dispersion of white light in its different wavelengths, or colors (hence the acronym "ED", extra-low dispersion). However, within ED lenses there are several different qualities, in fact, they are characterized by their Abbe numbers, which is a standardized indicator of the refractive index of any kind of lens, and in the case of crown lenses it ranges from approximately V=60 to V=95: the higher the V (Abbe number), the higher the refractive quality and the more expensive the lens. For example, doublets that incorporate a FPL-53 lens (V=94.96) are more expensive than those that incorporate a FPL-51 lens (V=81.61).

 

Why is it important to know this data? Because precisely one of the main aberrations that refractors suffer (although not the only one) is chromatic aberration (CA), which manifests itself in the form of colored halos (generally purple) around bright objects, as in the case of nighttime observation of the main planets, first magnitude stars or the Moon. The evolution of refractor lenses has always sought to reduce to a minimum the presence of this "false color" in the image (whether visual or photographic). With the invention of the achromatic doublet around the middle of the 18th century (positive crown lens + negative flint lens) it was possible to reduce to practically zero the so-called primary color spectrum, which, broadly speaking, was the very notable chromatic aberration generated by the archaic single-lens objective of, for example, Galileo's telescope. With the achromatic doublet it was also possible to greatly improve the sharpness and contrast of vision. Even so, the so-called secondary color spectrum persisted, which was (is) a remnant of CA that the (achromatic) doublet is not able to eradicate... although it can minimize it with very high focal ratios.

 

To control the secondary color spectrum at moderate focal lengths, the triplet objective was developed approximately a century later. It consisted of three lenses and was much more complex to build than the doublet. If the achromatic doublet bring two wavelengths (usually in the blue and red colors, that is, from the extremes of the visible spectrum) to the same focal plane, the triplet was capable of bringing three wavelengths in the blue, green and red region. These types of objectives were called apochromatic, or, to simplify, APO, which basically means "colorless." They were characterized by minimizing practically to 0 the chromatic aberration generated by the telescope tube objective. CA not only generates those unwanted color fringes around bright objects or details, but also reduces to some extent the sharpness and contrast of the view. So, although the achromatic telescope already offered very good views compared to the old Galileo, Kepler or Huygens telescopes, the apochromatic telescope improved these performances even further and, in addition, achieved this without the need to increase the focal ratio of the system. But about 60 years ago, new lens manufacturing materials appeared whose exceptional refractive properties gave new life to the old doublet objective, the ED lenses. The use of this type of low light dispersion lenses provides a control of the CA "similar" or close to that which a triplet objective can give, that is, it can minimize the secondary spectrum to practically 0. For this reason, telescopes with ED lenses are sometimes given the title of APO. But they are also often referred to as semi-APO, or simply ED.

 

Strictly speaking, from the point of view of chromatism, an APO refractor is one that can bring three wavelengths to the same focal plane. It is not stated whether this should be achieved with two, three, four or five lenses. Is it possible that a doublet with a high-quality ED element and an optimized construction design could do it? It seems to be. I think the SW 100ED Evostar is a good example of this. In fact, FLO doesn't promote it as APO (https://www.firstlig...pro-outfit.html), but Astronomics does (https://astronomics.com/collections/refractors/products/sky-watcher-evostar-100ed-100mm-f-9-ed-doublet-apochromatic-refractor?_pos=8&_fid=4df15ba87&_ss=c). I would say that visually it is practically impossible to find any false color in the views it offers. Likewise, I think we have all heard of triplets that, just because they are triplets, do not guarantee APO status, simply because their build quality is not fully optimized.

 

Finally, on the issue of the coveted APO label, I must also say that there is a certain amount of marketing involved, and it has become more of a "hook" for the buyer than a meaningful description of the optical quality of the refractor. If not, and considering that the Sky Watcher Evostar 100ED doublet is APO, what difference can there be then with the SW triplet Esprit 100, which is supposedly the "authentic" APO, apart from a difference of more than a thousand dollars, a lower focal ratio and a larger field of view? Well, there has to be a difference, and this is where the "crux" of the matter often lies. In visual observation, as far as chromaticity is concerned, there is probably no difference at all. And from a photographic point of view, much more sensitive to remnants of the secondary spectrum, the triplet, which also has an ED element of the same quality as the doublet, may, with a much lower focal ratio, give a better result. Furthermore, something similar is likely to happen with other non-chromatic aberrations that are also present in refractors and that are relevant in photography, such as field curvature, spherical aberration or comatic aberration. For this reason, some doublets are often classified as APO, provided that they are used primarily for visual purposes, and for this reason astrophotographers often use triplets, quadruplets or even quintuplets instead of doublets, since they normally guarantee a higher degree of correction in photographic shots at low or very low focal ratios.

 

In the case of your Starfield, since the type of ED lens used in the doublet is not indicated, it is likely to be an FPL-51, FCD-1 or equivalent, that is, a "basic" type of ED lens. By "basic" I do not mean "bad", but simply that it will probably not be one of those with the highest Abbe number, that is, one with the highest refractive index. Generally, the lower the dispersion index of an ED lens, the more expensive it is and the more they state this in the description in order to justify the price of the optical tube. That said, you don't have to worry too much about this kind of thing either, since "one lens does not make a spring". You always have to evaluate the whole picture, and this includes another lens (in the case of the doublet), the design of the lens, the quality of the overall construction of the tube and also of the lenses and their cell, etc., etc. In the end, optical quality and therefore viewing quality is a very complex issue involving many variables, which often can only be really evaluated in practice or experience.

 

I hope I haven't bored you. Here is this thread if you want to learn more:
https://www.cloudyni...y-ed-refractor/

Edited by Japetus Eye, 30 January 2025 - 12:03 PM.

[maniack]

I agree, the 150 achro will be used for dso mainly even though i have read people with the 750mm fl say it isnt bad on planets and the moon, given it being a fast scope.

About your SV503 80ed, I purchased my starfield 80mm as an apo, it clearly states it is an apo whereas the sv503 is not? If you know something i do not know regarding this as the price of the starfield was $887(in us dollars, i did conversion). Can they sell a telescope and advertise it as an apo when it is not? As i have looked on their website and a number of stores and it states it is an apo

Putting the marketing speak aside, the Starfield 80mm doublet is undoubtedly not a true apo - it's a plain ED scope or "semi-apo", just like the SV503.

 

Starfield does not state the glass used in the 80mm while they clearly state the 102mm has FPL53. Therefore the 80mm does not have FPL53 or its FCD100 equivalent, and its "ED element" is going to be in the FPL51/FK61/FCD1 class.

[Arkade]

I assumed at first that your 80mm was an ED doublet very similar to mine. But your comment has made me look at it more closely. It is indeed sold as an ED doublet, but they do include the term APO in the description. However, when we go to review the characteristics of the doublet they do not specify what kind of lenses it uses.

In ED doublets, the crown component is usually made of a special type of glass, sometimes with very expensive natural fluorite (calcium fluoride), or more frequently with synthetic fluorides. Lenses with these materials have the property of generating a very low dispersion of white light in its different wavelengths, or colors (hence the acronym "ED", extra-low dispersion). However, within ED lenses there are several different qualities, in fact, they are characterized by their Abbe numbers, which is a standardized indicator of the refractive index of any kind of lens, and in the case of crown lenses it ranges from approximately V=60 to V=95: the higher the V (Abbe number), the higher the refractive quality and the more expensive the lens. For example, doublets that incorporate a FPL-53 lens (V=94.96) are more expensive than those that incorporate a FPL-51 lens (V=81.61).

Why is it important to know this data? Because precisely one of the main aberrations that refractors suffer (although not the only one) is chromatic aberration (CA), which manifests itself in the form of colored halos (generally purple) around bright objects, as in the case of nighttime observation of the main planets, first magnitude stars or the Moon. The evolution of refractor lenses has always sought to reduce to a minimum the presence of this "false color" in the image (whether visual or photographic). With the invention of the achromatic doublet around the middle of the 18th century (positive crown lens + negative flint lens) it was possible to reduce to practically zero the so-called primary color spectrum, which, broadly speaking, was the very notable chromatic aberration generated by the archaic single-lens objective of, for example, Galileo's telescope. With the achromatic doublet it was also possible to greatly improve the sharpness and contrast of vision. Even so, the so-called secondary color spectrum persisted, which was (is) a remnant of CA that the (achromatic) doublet is not able to eradicate... although it can minimize it with very high focal ratios.

To control the secondary color spectrum at moderate focal lengths, the triplet objective was developed approximately a century later. It consisted of three lenses and was much more complex to build than the doublet. If the achromatic doublet bring two wavelengths (usually in the blue and red colors, that is, from the extremes of the visible spectrum) to the same focal plane, the triplet was capable of bringing three wavelengths in the blue, green and red region. These types of objectives were called apochromatic, or, to simplify, APO, which basically means "colorless." They were characterized by minimizing practically to 0 the chromatic aberration generated by the telescope tube objective. CA not only generates those unwanted color fringes around bright objects or details, but also reduces to some extent the sharpness and contrast of the view. So, although the achromatic telescope already offered very good views compared to the old Galileo, Kepler or Huygens telescopes, the apochromatic telescope improved these performances even further and, in addition, achieved this without the need to increase the focal ratio of the system. But about 60 years ago, new lens manufacturing materials appeared whose exceptional refractive properties gave new life to the old doublet objective, the ED lenses. The use of this type of low light dispersion lenses provides a control of the CA "similar" or close to that which a triplet objective can give, that is, it can minimize the secondary spectrum to practically 0. For this reason, telescopes with ED lenses are sometimes given the title of APO. But they are also often referred to as semi-APO, or simply ED.

Strictly speaking, from the point of view of chromatism, an APO refractor is one that can bring three wavelengths to the same focal plane. It is not stated whether this should be achieved with two, three, four or five lenses. Is it possible that a doublet with a high-quality ED element and an optimized construction design could do it? It seems to be. I think the SW 100ED Evostar is a good example of this. In fact, FLO doesn't promote it as APO (https://www.firstlig...pro-outfit.html), but Astronomics does (https://astronomics....4df15ba87&_ss=c). I would say that visually it is practically impossible to find any false color in the views it offers. Likewise, I think we have all heard of triplets that, just because they are triplets, do not guarantee APO status, simply because their build quality is not fully optimized.

Finally, on the issue of the coveted APO label, I must also say that there is a certain amount of marketing involved, and it has become more of a "hook" for the buyer than a meaningful description of the optical quality of the refractor. If not, and considering that the Sky Watcher Evostar 100ED doublet is APO, what difference can there be then with the SW triplet Esprit 100, which is supposedly the "authentic" APO, apart from a difference of more than a thousand dollars, a lower focal ratio and a larger field of view? Well, there has to be a difference, and this is where the "crux" of the matter often lies. In visual observation, as far as chromaticity is concerned, there is probably no difference at all. And from a photographic point of view, much more sensitive to remnants of the secondary spectrum, the triplet, which also has an ED element of the same quality as the doublet, may, with a much lower focal ratio, give a better result. Furthermore, something similar is likely to happen with other non-chromatic aberrations that are also present in refractors and that are relevant in photography, such as field curvature, spherical aberration or comatic aberration. For this reason, some doublets are often classified as APO, provided that they are used primarily for visual purposes, and for this reason astrophotographers often use triplets, quadruplets or even quintuplets instead of doublets, since they normally guarantee a higher degree of correction in photographic shots at low or very low focal ratios.

In the case of your Starfield, since the type of ED lens used in the doublet is not indicated, it is likely to be an FPL-51, FCD-1 or equivalent, that is, a "basic" type of ED lens. By "basic" I do not mean "bad", but simply that it will probably not be one of those with the highest Abbe number, that is, one with the highest refractive index. Generally, the lower the dispersion index of an ED lens, the more expensive it is and the more they state this in the description in order to justify the price of the optical tube. That said, you don't have to worry too much about this kind of thing either, since "one lens does not make a spring". You always have to evaluate the whole picture, and this includes another lens (in the case of the doublet), the design of the lens, the quality of the overall construction of the tube and also of the lenses and their cell, etc., etc. In the end, optical quality and therefore viewing quality is a very complex issue involving many variables, which often can only be really evaluated in practice or experience.

I hope I haven't bored you. Here is this thread if you want to learn more:
https://www.cloudyni...y-ed-refractor/

No, deffo didnt bore me at all. It was all very interesting and i read every word.
It was funny as i read the whole article you wrote and then the last paragraph, you basically gave the reason for my scope being over priced by several hundred dollars lol. I feel that i was better off gettimg the svbony achro 102mm for only £186 ($230 US DOLLARS) . I could have got 3 svbonys and 20mm larger aperture. I really feel many newbies would make similar mistakes. If anyone can offer any reason we may have got it wrong, please do so.

Thank you. I do find the 80/560 to show no blue fringe around moon or planets where the 100/660 achros do.

Really appreciate your essay, it was very educational

[Arkade]

Putting the marketing speak aside, the Starfield 80mm doublet is undoubtedly not a true apo - it's a plain ED scope or "semi-apo", just like the SV503.

Starfield does not state the glass used in the 80mm while they clearly state the 102mm has FPL53. Therefore the 80mm does not have FPL53 or its FCD100 equivalent, and its "ED element" is going to be in the FPL51/FK61/FCD1 class.

The reason it may be an apo is firstly, it is a small canadian company and If a telescope company in Canada is advertising a telescope as an APO but it does not meet the standards, this could be considered misleading or deceptive advertising. Under the Canadian Competition Act, businesses are prohibited from making false or misleading claims about their product

[dnrmilspec]

Because this is the beginners forum I would like to make a bit of a clarification.  The main difference between a semi APO and a "true" APO is money. 

 

Once one gets into any kind of ED glass the difference between scopes is generally not that much.  For example, my 130 Triplet does show the tiniest bit of color.  Did I say tiny?  It is .982 Strehl which is quite good indeed.  One could opt for more exotic glass and a famous manufacturer and spend seven times what mine cost.  At the eyepiece would someone see the difference?  Perhaps.  Sometimes.  But in general use, not so much. 

 

I have a few ED doublets.  In comparing the SVBony 102 Ed with the Skywatcher 100 ED with FPL 53 glass, the difference on solar system objects is somewhat noticeable.  But the comparison is difficult because of the differences in focal length which also favors the FPL53 scope. 

 

Someone mentioned the 152 Achromat.  I have one of those also.  For DSOs it rocks.   Just beautiful views.  For planetary it is no slouch.  People at star parties live to point it at the moon.   Sweeping the star fields of Sagitarius it (like its little brother the 120 F5) are just stunning.  For that sort of viewing it has left many the APO scope owners shaking their heads.

 

So my advice to new people is certainly to consider upgrades but do it with a modicum of caution. 

[vtornado]

For visual "back-in-the-day"  an 80mm f/15 refractor CA ratio of 5 was thought acceptible for planets and bright objects.

If one is willing to slum it and stay at a CR of 5.

 

https://www.cloudyni...73834301145.jpg

 

FPL-51 glass multiply the focal ratio by 3

FPL-53 glass multiply the focal ratio by 5.

 

My new to me svbony 70mm f/6 FPL51 scope has a CR ratio around 6.  I can see the CA but, it is not distracting.

My Orion ED80 f7.5 with fpl53 is nearly colorless to my eyes.

My 100 ED100 f9 with fpl53 is nearly colorless to my eyes.  Daytime solar images I can see some CA.

 

I wish they made an affordable 150 f/8 with FPL-51.  Nearly a CR of 5.  Could they do this for a small increment over the traditional achromat?

[maniack]

I wish they made an affordable 150 f/8 with FPL-51.  Nearly a CR of 5.  Could they do this for a small increment over the traditional achromat?

Well, iStar made an ED (presumably FPL51) version of the 204mm f/6. There's even one for sale near me. So if a 204mm f/6 can be done a 150 f/8 should be easy .

[Japetus Eye]

I wish they made an affordable 150 f/8 with FPL-51.  Nearly a CR of 5.  Could they do this for a small increment over the traditional achromat?

Well, such tubes do exist... although unfortunately I'm afraid they don't meet the "for a small increase over the price of the achromatic version" condition...

 

https://agenaastro.c...tor-s11190.html
This Sky Watcher Evostar is supposed to meet the Conrady standard, however observers who have tested it have noted that it has slight colour halos around very bright objects, such as the brightest stars. On the Moon it also has a very slight halo in the high contrast area of ​​the terminator, but, forced to 740x it still offers a minimally decent image. Still, with good seeing it would be better not to exceed 650x with it on the Moon, and 450x on planets. These figures give an idea of ​​its good optical quality, sharpness and ability to transmit contrast. On bright extended deep sky objects it gives great performance, especially in open clusters; In other types of objects, it can be surpassed by 8" or 10" reflectors due to their greater resolution and light gathering capacity. As far as I understand, this is the ED refractor with that aperture with the best quality/price ratio currently on the market. The APM would be practically equivalent from an optical point of view, although it has some differences in the mechanical part, such as the focuser: https://www.apm-tele...with-25-focuser .

 

https://www.teleskop...ap-auszug-14000
This marvel would be closer to the Sidgwick standard, so it should present more CA than the previous ones, although its shorter length and focal distance would guarantee less instability and vibrations on suitable supports, and of course wider fields of view.

[Japetus Eye]

No, deffo didnt bore me at all. It was all very interesting and i read every word.
It was funny as i read the whole article you wrote and then the last paragraph, you basically gave the reason for my scope being over priced by several hundred dollars lol. I feel that i was better off gettimg the svbony achro 102mm for only £186 ($230 US DOLLARS) . I could have got 3 svbonys and 20mm larger aperture. I really feel many newbies would make similar mistakes. If anyone can offer any reason we may have got it wrong, please do so.

Thank you. I do find the 80/560 to show no blue fringe around moon or planets where the 100/660 achros do.

Really appreciate your essay, it was very educational

Thank you for your kind words. Above all else, the most important thing is that you are satisfied with the performance of your optical tube. I think that sometimes a manufacturer or a small dealer can take better care of the quality of construction and quality control of the products than large companies such as the most widely distributed brands (such as Sky Watcher or Celestron). In the case of Starfield it seems that it is a company linked to Bresser and, therefore, to Jinghua Optical Electronics Co., Ltd. (JOC).

Edited by Japetus Eye, 31 January 2025 - 10:39 AM.

[Arkade]

[quote name="Japetus Eye" post="13942839" timestamp="1738337387"]

Thank you for your kind words. Above all else, the most important thing is that you are satisfied with the performance of your optical tube. I think that sometimes a manufacturer or a small dealer can take better care of the quality of construction and quality control of the products than large companies such as the most widely distributed brands (such as Sky Watcher or Celestron). In the case of Starfield it seems that it is a company linked to Bresser and, therefore, to Jinghua Optical Electronics Co., Ltd. (JOC).[/quote

Thank you. I purchased it from the owner of starfield. He works in a store located in bolton, toronto. He seemed a very honest man. He was very helpful. He just seemed a good guy and he was very proud of his line of starfield telescopes.

He is laid back, no trying to push you to buy. Very helpful and actually helped me save money ( buying other acessories and somethknt for someone else)

I think that too, as he is a small company, he cares a lot more about the standard of hos telescopes as he was proudly showing me a prototype of the one i purchased.

Whereas svbony, i have read people have had issues due to their quality control. I had issues with svbony also but one thing i can say, they are very good as there was a small fault in a £60 eyepiece and they sent me a new one. The old one, i fixed it recently but they let me keep it.

[gnowellsct]

It can be worth upgrading from an 80mm to a 76mm if the 76mm is a hotshot and the 80mm is mediocre.  Or upgrade from an 80mm to an 81mm (there is an 81mm Vixen, a very elegant little scope and a performer in its class).

 

These things are always a question of from what, to what, and the impact of the expenditure on your lifestyle.  If it means you eat rocks all month, maybe not do it.   If it means that at worst you find out the new scope is not what you want, but you can sell it and recover much of the outlay and then go on with extra wisdom from the experience, then it may indeed be worth the change.  

 

Greg N

[Arkade]

It can be worth upgrading from an 80mm to a 76mm if the 76mm is a hotshot and the 80mm is mediocre. Or upgrade from an 80mm to an 81mm (there is an 81mm Vixen, a very elegant little scope and a performer in its class).

These things are always a question of from what, to what, and the impact of the expenditure on your lifestyle. If it means you eat rocks all month, maybe not do it. If it means that at worst you find out the new scope is not what you want, but you can sell it and recover much of the outlay and then go on with extra wisdom from the experience, then it may indeed be worth the change.

Greg N

I havent used my scope all thar much ( starfield 80/560mm apo or ed,no idea ) . I would usually observe the moon at a max mag of 160 but today, I went up to 486 if i calculated correctly using a 7mm with 2 barlows, 3x barlow and another 2x balow.
I have limited use of telescopes but the images were breathtaking.

The craters for the first time, it felt like I could really see the depth and the see the shadows, whereas before I have never seen anything like this.Is this normal?

I tried my 127/1500 mak at 250 magnification and it was underwhelming. Dim, it didnt "pop" like my 80mm apo/ed. Didn't bother increasing the zoom as I didn't feel it would improve image.

[maniack]

I havent used my scope all thar much ( starfield 80/560mm apo or ed,no idea ) . I would usually observe the moon at a max mag of 160 but today, I went up to 486 if i calculated correctly using a 7mm with 2 barlows, 3x barlow and another 2x balow.
I have limited use of telescopes but the images were breathtaking.

The craters for the first time, it felt like I could really see the depth and the see the shadows, whereas before I have never seen anything like this.Is this normal?

I tried my 127/1500 mak at 250 magnification and it was underwhelming. Dim, it didnt "pop" like my 80mm apo/ed. Didn't bother increasing the zoom as I didn't feel it would improve image.

If you weren't doing this comparison side-by-side differences in atmospheric seeing can have a significant impact on the view. Also the 127 needs to be thermally acclimated to perform decently.

[Arkade]

If you weren't doing this comparison side-by-side differences in atmospheric seeing can have a significant impact on the view. Also the 127 needs to be thermally acclimated to perform decently.

I did it side by side...had the 80mm out first and then had the mak out shortly afer. I gave it 45 minutes, had it & used it for about 10 mintues at the end of my session.
I am not sure if 45 mins is enough as it is 21 degees inside and about 6-8 degrees outside.

Venus looked very nice through the mak.
Very nice with 80mm apo.
A lot of blue with the 100/660mm celestron achro.

[dnrmilspec]

I havent used my scope all thar much ( starfield 80/560mm apo or ed,no idea ) . I would usually observe the moon at a max mag of 160 but today, I went up to 486 if i calculated correctly using a 7mm with 2 barlows, 3x barlow and another 2x balow.
I have limited use of telescopes but the images were breathtaking.

The craters for the first time, it felt like I could really see the depth and the see the shadows, whereas before I have never seen anything like this.Is this normal?

I tried my 127/1500 mak at 250 magnification and it was underwhelming. Dim, it didnt "pop" like my 80mm apo/ed. Didn't bother increasing the zoom as I didn't feel it would improve image.

There is something very suspicious here.  Your Mak should be every bit as good as  your 80mm frac on the moon.  At higher mags it should be quite a bit better.  What eyepieces are you using with the mak?  Try your 7mm alone on the Mak for 214X and tell us how it looks.

 

Your 80mm scope should not be doing well at 480X.  I find your conclusion that it looks breathtaking highly unusual.  I am going to assume that there is a miscalculation here.  I have a very nice 80mm FPL53 scope and it has occasionally performed ok at 200X but 460 is way beyond what is reasonable.  160X is considered the highest useful mag for an 80mm triplet.  Astro-Phyics claims that their wonderful Stowaway can do 360X and that is pretty outrageous for a 92mm scope. 

 

I am sure I will lure the "oh yea?  Well I got my 60mm whizbang to 500X" crowd with this one  But seriously.  Recheck your numbers and let us know if that is correct.. 

 

One of the best lunar experiences I have ever had was a magical night in my driveway with my 127 Mak on a Porta Two.  AP diagonal and Nagler 7mm for 214X and the  view was stunning.  I had just gone out for a quick look and stayed for a long time. 

 

It is possible, as a new user, to appreciate a view which with more experience you may be more critical.  But try your Mak at the 214X then push it to double that with the 2x Barlow and let us know what you think.
 

[Jon Isaacs]

Now, I think you're mistaken if you think you'll perceive a noticeable difference in light gathering between the 100 and the 80, as in my experience the difference comes from the different resolution capabilities and the difference in optics quality.

 

 

I have both 80 mm and 4 inch apo/ed refractors.  At the same magnification, the 4 inch is 60% brighter.  That is easy to see but also allows one to use greater magnification at the same brightness.  At planetary magnifications in scopes of these apertures, brightness is an important part of the equation because the exit pupils are small, the images are dim.  

 

The greater resolution and contrast of the larger scope is an important factor but brightness also plays a role.

 

Jon

[gnowellsct]

I havent used my scope all thar much ( starfield 80/560mm apo or ed,no idea ) . I would usually observe the moon at a max mag of 160 but today, I went up to 486 if i calculated correctly using a 7mm with 2 barlows, 3x barlow and another 2x balow.
I have limited use of telescopes but the images were breathtaking.

The craters for the first time, it felt like I could really see the depth and the see the shadows, whereas before I have never seen anything like this.Is this normal?

I tried my 127/1500 mak at 250 magnification and it was underwhelming. Dim, it didnt "pop" like my 80mm apo/ed. Didn't bother increasing the zoom as I didn't feel it would improve image.

I think you'll find that's 480x. I think many of us would find anything over 3x per millimeter or 240X on your scope to be over magnified.

Speaking for myself I would probably stop somewhere below 200x. Things get too dim and the narrow exit pupil, a consequence of the extreme magnification, mostly just lights up the junk in an old person's eyes.

But you're not breaking any laws. You can over magnify all you like.

I can't speak to what's going on with your Mak. It should easily outperform an 80 mm refractor.

If the Mak has a 1.25 inch diagonal and only accepts 1.25-in eyepieces the view can seem cramped if you're used to wider field eyepieces.

Greg N

[Arkade]

There is something very suspicious here. Your Mak should be every bit as good as your 80mm frac on the moon. At higher mags it should be quite a bit better. What eyepieces are you using with the mak? Try your 7mm alone on the Mak for 214X and tell us how it looks.

Your 80mm scope should not be doing well at 480X. I find your conclusion that it looks breathtaking highly unusual. I am going to assume that there is a miscalculation here. I have a very nice 80mm FPL53 scope and it has occasionally performed ok at 200X but 460 is way beyond what is reasonable. 160X is considered the highest useful mag for an 80mm triplet. Astro-Phyics claims that their wonderful Stowaway can do 360X and that is pretty outrageous for a 92mm scope.

I am sure I will lure the "oh yea? Well I got my 60mm whizbang to 500X" crowd with this one But seriously. Recheck your numbers and let us know if that is correct..

One of the best lunar experiences I have ever had was a magical night in my driveway with my 127 Mak on a Porta Two. AP diagonal and Nagler 7mm for 214X and the view was stunning. I had just gone out for a quick look and stayed for a long time.

It is possible, as a new user, to appreciate a view which with more experience you may be more critical. But try your Mak at the 214X then push it to double that with the 2x Barlow and let us know what you think.

I will try again this week and see. Who knows, this time I will be more mindful about what everyone has said and try with 7mm, also leave mak out for longer.

[maniack]

I will try again this week and see. Who knows, this time I will be more mindful about what everyone has said and try with 7mm, also leave mak out for longer.

Leaving the mak out longer is a good idea - I don't think 45 minutes is enough for the temperature delta you mentioned.