#21  
Old 07-03-2019, 03:54 AM
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Ukastronomer (Jeremy)
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"Am I right in assuming that Hoya FCD100 and Ohara FPL53 are broadly equivalent?

Calvin"

I bet no one could tell the difference visually


I have an argument with other photographers about prime v zoom lenses ED glass, I prefer zoom and use them as a paid sports photographer.

Put the same back on an 80-400 ED zoom such as the Nikkor and get three other bodies place a Nikkor 80-200-400 prime on each, shoot the same image NOT in a lab but real life, same settings and I challenge anyone to see any difference.

Last edited by Ukastronomer; 08-03-2019 at 11:24 PM.
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  #22  
Old 07-03-2019, 03:56 AM
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CaF2 “Fluorite” (Various manufacturers): 94.99 (incredibly expensive and hard to work with, often has inhomogeneity, internal stresses, can fracture during polishing, not very stable in a chemical or thermal sense).

S-FPL-53 (Ohara Japan): 94.94 (more even internal structure, freedom from internal stresses can be attained by baking and annealing, more chemically stable, less expensive and easier to work with than Fluorite, but harder to work with than S-FPL51).

S-FPL-51 (Ohara Japan): 81.54 (easier to work with, and much less expensive than S-FPL53, very stable by comparison).

FCD-100 (Hoya): 94.66 (less expensive than S-PL53, thanks Hoya!)

By combining multiple lens elements and using ED glasses in the same refractor lens cell, we can get very good or essentially perfect “colour correction” in a refractor, such that there are no false colours visible in the in-focus image. This is particularly evident in our FPL-53 based triplet refractors which have perfect colour correction to the eye both inside and outside of focus, and amongst the best photographic colour correction on the market today, especially in the red and blue ends of the spectrum which CCD cameras are very sensitive to. This is borne out in the profusion of images taken with our telescopes on the internet. It’s important to remember, however, that glass type and the Abbe number of that glass type isn’t the only factor in controlling colour correction or optical quality overall. The geometry of the surface being polished, the relative spacing between the lens elements, coatings, surface smoothness, and deviation from the ideal design, plus the final figuring process are all very important. In fact, we are able to get near perfect colour correction in focus in our FPL-51 based triplets, and better blue colour correction than many FCD1 and H-FK61 based lenses we’ve tested. This is achieved by using a better match of mating elements and geometry, and taking time to adjust the lens arrangement and surfaces during production. Once again, this is borne out by the images taken with our larger FPL-51 based refractors which show better blue channel colour correction than some competing refractors with FCD1 and H-FK61 lenses. The point is that, while a lower dispersion element helps, it's not the only factor. But for now, let’s concentrate on the main ED glass types we use:
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  #23  
Old 07-03-2019, 09:11 AM
casstony
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The difference between fpl53, fpl55, fcd100 and fluorite is negligible compared to how well the overall lens and cell are made.

Some fpl53 doublets and fpl51 triplets are fine for imaging too, such as the two scopes in my signature.
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  #24  
Old 07-03-2019, 10:10 AM
glend (Glen)
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Quote:
Originally Posted by casstony View Post
The difference between fpl53, fpl55, fcd100 and fluorite is negligible compared to how well the overall lens and cell are made.

Some fpl53 doublets and fpl51 triplets are fine for imaging too, such as the two scopes in my signature.
Yes indeed, FPL-51 Triplets which include a Lanthanum partner element, are highly regarded. The TS115 being a good example.
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  #25  
Old 07-03-2019, 11:50 AM
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A lot of theory. I would want to simply evaluate images taken with the scopes/ The images tell you if the lens is OK or not.

I have used several fluorite scopes and they are a slight cut above FPL53 scopes. Usually better colour in the images and a little bit brighter image.

Fluorite allows the optical designer the freedom to achieve a faster F ratio without sacrificing optical performance. It also has less light scatter.

But a fluorite doublet - is it really an APO? Tak calls them APOs but I my old FS152 was superb as a visual instrument but you did get the odd blue ringed bright star with it imaging.

These ED glass/Lanthanum element lenses look interesting. I have not heard of one in a triplet yet only doublets. Which scopes have them in a triplet?



Greg.
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  #26  
Old 07-03-2019, 12:21 PM
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+1 for the ED80 Triplet.
It has better colour correction than a doublet, shorter FL so easier on the guiding, plus it has a focal ratio of f/5 which cuts down imaging time.
This does not cut down imaging time. Only a larger aperture in mm cuts down image time to get the same faint objects.

But, indeed a triplet wins over a doublet if you are a real pixel peeper. Otherwise, rather get a 100...120mm ED doublet plus reducer.
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  #27  
Old 07-03-2019, 04:11 PM
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I bought and Esprit 100 a few years ago and I image with it (almost) all the time. Well corrected and super sharp. If you can spring for it, it’s well worth it. Note that these are not rebadged and sold by someone else, the Esprit are made by Skywatcher for Skywatcher.

On a practical note, the few shield is huge and I rarely use a few heater in SE QLD...
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  #28  
Old 07-03-2019, 05:28 PM
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Originally Posted by skysurfer View Post
This does not cut down imaging time. Only a larger aperture in mm cuts down image time to get the same faint objects.

But, indeed a triplet wins over a doublet if you are a real pixel peeper. Otherwise, rather get a 100...120mm ED doublet plus reducer.
F5 is indeed quicker but yes aperture is the key. F5 means a wider swath of the field ends up on the same real estate of the sensor. So its collecting more total light.

I think also you'll find that more of the light that enters the lens actually lands on the sensor rather than only a large slice of it with a substantial amount missing the sides of the sensor.

Greg.
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  #29  
Old 08-03-2019, 06:12 PM
JA
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Originally Posted by Ukastronomer View Post
I have an argument with other photographers about prime v zoom lenses, I prefer zoom and use them as a paid sports photographer.

Put the same back on an 80-400 ED zoom such as the Nikkor and get three other bodies place a Nikkor 80-200-400 prime on each, shoot the same image NOT in a lab but real life, same settings and I challenge anyone to see any difference.
Hi J,

At the risk of opening a second front , I can't agree: I think one would see differences in image quality between the Nikkor 80-400 ED and certain Nikkor primes in the same focal length range. Demonstrating that over the internet is not an easy task, since it would require identical subjects photographed with the same settings and then analysed in some way: quantitatively or qualitatively.

Identical images to compare are difficult to come by (unless one owns all the lenses) or is prepared to accept images of optical test charts (ąsome analysis). You also expressed a certain reluctance/disinterest in LAB tests. If that extends to images of optical test charts, it may be difficult to provide objective evidence of any differences.

As the discussion may grow and it's a little off-topic already, It may be better to discuss this in a new thread, if you want to.

Best
JA

Last edited by JA; 08-03-2019 at 06:34 PM.
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  #30  
Old 08-03-2019, 07:28 PM
glend (Glen)
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Originally Posted by gregbradley View Post
A lot of theory. ........

These ED glass/Lanthanum element lenses look interesting. I have not heard of one in a triplet yet only doublets. Which scopes have them in a triplet?

Greg.

Greg, my TS115 Triplet uses FPL-51 and Lanthanum elements. I am very happy with it.

To quote TS:

Triplet Apo Objective with two special glasses (Lanthanum glass and FPL51) - Ohara Japan - colour correction comparable with FPL53 triplet objective
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  #31  
Old 08-03-2019, 07:59 PM
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Ukastronomer (Jeremy)
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Originally Posted by JA View Post
Hi J,

At the risk of opening a second front , I can't agree: I think one would see differences in image quality between the Nikkor 80-400 ED and certain Nikkor primes in the same focal length range. Demonstrating that over the internet is not an easy task, since it would require identical subjects photographed with the same settings and then analysed in some way: quantitatively or qualitatively.

Identical images to compare are difficult to come by (unless one owns all the lenses) or is prepared to accept images of optical test charts (ąsome analysis). You also expressed a certain reluctance/disinterest in LAB tests. If that extends to images of optical test charts, it may be difficult to provide objective evidence of any differences.

As the discussion may grow and it's a little off-topic already, It may be better to discuss this in a new thread, if you want to.

Best
JA
It has been done by us as a club, and at A3+ there is NO visible difference
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  #32  
Old 08-03-2019, 08:08 PM
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Originally Posted by Ukastronomer View Post
It has been done by us as a club, and at A3+ there is NO visible difference
Hi J,
May I ask: which Nikkor lenses and camera did you use and what was the subject image?

Best
JA

Last edited by JA; 08-03-2019 at 09:10 PM.
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  #33  
Old 08-03-2019, 09:15 PM
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Hi J,
May I ask: Exactly which Nikkor lenses and camera did you use and what was the subject image?

Best
JA
No problem

D4s, D810, My Nikkor 80-400, 70-210 f2.8 and Nikkor 14-24 with others Nikon 200mm f4 AF Micro, Nikon 300mm f4, Nikon 24mm f1.8

Outdoors, same conditions/lighting etc, real life situation, sports and landscape
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  #34  
Old 08-03-2019, 11:09 PM
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What do all these camera lenses post have to do with the OPs question? Highjacked by the Brit again.
Over here that would be considered racist, sorry for being WELSH and NOT a BRIT, please get it right, thank you

In fact my Mother was born in Swansea, Wales and my father Scotland I am actually a Cornish living in Wales my son is Devonian born Devon/Cornwall

I was simply making the comparison that most people would not see any difference between different types of GLASS used in scopes, fluorite etc, may be a bit complicated to understand, whicgh I have now highlighted in my earlier response to make it easier to understand the relevance, sorry

http://projectbritain.com/nationality.htm[/QUOTE]

Last edited by Ukastronomer; 08-03-2019 at 11:22 PM.
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  #35  
Old 09-03-2019, 10:23 AM
Astronovice (Calvin)
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Originally Posted by Ukastronomer View Post
Over here that would be considered racist, sorry for being WELSH and NOT a BRIT, please get it right, thank you

In fact my Mother was born in Swansea, Wales and my father Scotland I am actually a Cornish living in Wales my son is Devonian born Devon/Cornwall

I was simply making the comparison that most people would not see any difference between different types of GLASS used in scopes, fluorite etc, may be a bit complicated to understand, whicgh I have now highlighted in my earlier response to make it easier to understand the relevance, sorry

http://projectbritain.com/nationality.htm
[/QUOTE]

Hi Jeremy,

As the originator of this topic I fail to see what you find offensive or incorrect about being called a Brit. I was born in England and to my knowledge all of us born in Great Britain (which includes Wales, as the website you linked quite clearly points out) are labelled as British, colloquially known as Brits.

Back to the original topic, I have found your input informative in regard to the differences between FCD100 and FPL53 as it addresses the question whether there would be a significant glass driven difference between the Saxon scope and the SkyWatcher alternatives. Having acknowledged that, the ongoing discussion relating to zoom or fixed focus camera lenses is spurious to the original post as it contributes nothing to making the choice of which scope to buy.
Thanks again for your input. Calvin, naturalised Australian.
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  #36  
Old 09-03-2019, 10:37 AM
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Life is a conversation. Sometimes it wanders from person to person as people dropout of the discussion and/or make a point that someone picks up on and shows interest in discussing further.

Best
JA
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  #37  
Old 09-03-2019, 11:33 AM
glend (Glen)
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Greg, you wanted to see some TS115 images, here are the ones Astrobin finds:

https://www.astrobin.com/gear/13409/...0-triplet-apo/
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