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Old 27-01-2021, 08:17 PM
TareqPhoto (Tareq)
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Design or optical quality???

Hi,


I want to know when buying a refractor, which is more important to have:


1. A triplet but with ED optics


2. A doublet but with Fluorite or FPL-53 optics


So if can't afford both or the type of scope i want can't be in both of above and only one of above, what will be the choice?


All scopes are well made and nice quality manufactured so no one will come to say that this build quality is better than the other one, so assume all are with excellent build quality.
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Old 28-01-2021, 12:44 PM
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The_bluester (Paul)
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Funny enough after another thread on here I was reading Vic Maris's (Stellarvue telescopes) thoughts on exactly this topic.

It is really a hard question to answer but to paraphrase him, a very well figured objective of "ED" glass is likely to outperform a mass produced and only "OK" objective of FPL-53 or similar. Snip from this page below. https://www.stellarvue.com/optical-glass-types/

Quote:
Glass type is not the most important thing: When someone chooses a relatively inexpensive, mass produced telescope because it is advertised as using FPL53 over a telescope using FCD100 that is much more accurately figured, the customer is clearly using the wrong criteria to determine quality. Let's imagine the less expensive telescope focuses 90% of the light where it is supposed to go and the other focuses 99% of the light where it is supposed to go. Choosing the less accurate optic simply because it uses a particular glass type is silly when both glasses are equivalent. The difference between two telescopes under a steady sky will be obvious. In this case the FCD100 telescope will win, not because it has better glass but because a lot more time has been spent to bring it to a higher standard.
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Old 28-01-2021, 12:56 PM
TareqPhoto (Tareq)
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The problem is how to trust if there are not many options with conditions we look for, so if i request a certain things in a scope, and i only found 3 scopes and i don't know their quality either the optics or the design and mechanica system itself, then it is hard to choose which one.
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Old 28-01-2021, 01:03 PM
JA
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Hi Tarek,

There is only 1 REAL approach:
1. test them yourself
2. review quantitative test results for both devices
3. get back to back images for comparison

In the absence of these, all one potentially has is supposition, generalization or reliance on a good reputation, which is a concern if you want to lay down your hard earned $ on one on a cost/performance basis .

Best
JA
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Old 28-01-2021, 01:47 PM
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Quote:
Originally Posted by JA View Post
Hi Tarek,

There is only 1 REAL approach:
1. test them yourself
2. review quantitative test results for both devices
3. get back to back images for comparison

In the absence of these, all one potentially has is supposition, generalization or reliance on a good reputation, which is a concern if you want to lay down your hard earned $ on one on a cost/performance basis .

Best
JA
Absence of all above
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Old 28-01-2021, 01:52 PM
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One avenue to follow is to search for images on sites like Astrobin for images shot with the scopes you are looking at as candidates.

The best scope on earth will still produce poor results out of poor processing, but if you find a healthy number of good images from different people (In case someone has found some processing tricks, fair or foul, to overcome problems with a scope) using a scope you are considering then there is a fair chance they are a good scope.

It is not a sure thing. I bought my Stellarvue SVX80 on the basis of shooting with a friends SV70. If there had been an SVX70 (Which replaced the SV70) available at the time, I would have bought one like a shot, but what I was comparing it to was a Celestron RASA 8".

I could not find many images shot through the RASA 8" that I would have been happy to publish at that time, so I bought the SVX80 (Which I am still very happy with) but now there are some really good images appearing from the RASA.
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Old 28-01-2021, 06:51 PM
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Some info from Tele Vue on APO design.

https://televue.com/televueopticstal.../#.YBJ4t8rZWhA

I think build quality and testing and buying from a reputable manufacturer should be considered in the decision process.
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Old 28-01-2021, 11:34 PM
TareqPhoto (Tareq)
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Quote:
Originally Posted by The_bluester View Post
One avenue to follow is to search for images on sites like Astrobin for images shot with the scopes you are looking at as candidates.

The best scope on earth will still produce poor results out of poor processing, but if you find a healthy number of good images from different people (In case someone has found some processing tricks, fair or foul, to overcome problems with a scope) using a scope you are considering then there is a fair chance they are a good scope.

It is not a sure thing. I bought my Stellarvue SVX80 on the basis of shooting with a friends SV70. If there had been an SVX70 (Which replaced the SV70) available at the time, I would have bought one like a shot, but what I was comparing it to was a Celestron RASA 8".

I could not find many images shot through the RASA 8" that I would have been happy to publish at that time, so I bought the SVX80 (Which I am still very happy with) but now there are some really good images appearing from the RASA.
I really wish if i bought that Stellarvue 70T back in the past, i might be so happy now and successful with images, but i ignored it due to prices and running after expensive Takahashi scope and i end up with only two Newt and one Mak, and funny i still using my ST80 guide scope as imaging, and last year i ordered my first APO refr which is 90mm F/6 triplet, but the store online delaying it over and over, so i will expect it later this year.

For that above scope i ordered, i was in rush, the budget was for getting 14" Dobsonian i was eye-ing for a while, but the site destroyed me and said they don't ship, so while i am desperate i just ordered whatever i saw later on another site, 90mm f/6 FPL55 triplet, and while i was waiting i did test my ST80 with my new 0.8x reducer and i shocked amazed of the results, i mean FOV, i felt like it was the first time i saw that although i used my Canon 300mm, but the lens has much more issues i see than a guide scope i use, so because of that i changed my plan, or say added so many things in my plan.

I looked around on Astrobin, i saw like two or three images, that i liked, i was trying to eye something like Andromeda or M45 or Horsehead, because those targets are the real test for LRGB or color cameras, not narrowbanding, so i don't know if i have to judge a scope from narrowbanding targets or those LRGB targets, and yet in another forum someone still finding issues within those nice results, and i told him that if that is the case then there is no perfect refractor scope at all, and even the best one that will be way way way out of my reach my entire life, so i don't know if i should be that much strict to issues details in any image only to reject it, but i liked the results after all.
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Old 28-01-2021, 11:36 PM
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Quote:
Originally Posted by astro744 View Post
Some info from Tele Vue on APO design.

https://televue.com/televueopticstal.../#.YBJ4t8rZWhA

I think build quality and testing and buying from a reputable manufacturer should be considered in the decision process.
Only if i have the budget and the scope is matching my requirements, in fact there is a scope that has that my requirements perfectly perfect, but it is above US$6000, so i better not put impossible in my list yet, and if i think about saving for it then it means i have to stop for few years until i have the budget, those few years new people will get into astro and having amazing results already.
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Old 29-01-2021, 06:47 AM
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It is a pity that shipping would be prohibitive, there is an SV70T that will probably be up for sale here in Australia. It is an SV70T not the later SVX70T, they only ever made a handful of those (I thought about an SVX70T instead of my SVX80T but the wait time was an unknown) and I don't think they are making any more, it made no sense for them to spend so many hours hand figuring an objective for a scope that was about $1600 USD when they had back orders on $8000 USD scopes.
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Old 29-01-2021, 09:11 AM
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Quote:
Originally Posted by The_bluester View Post
It is a pity that shipping would be prohibitive, there is an SV70T that will probably be up for sale here in Australia. It is an SV70T not the later SVX70T, they only ever made a handful of those (I thought about an SVX70T instead of my SVX80T but the wait time was an unknown) and I don't think they are making any more, it made no sense for them to spend so many hours hand figuring an objective for a scope that was about $1600 USD when they had back orders on $8000 USD scopes.
No second hand for me, and no waiting to unknown model production time if they are planning for it, so i try to see what is almost available now within 2-4 months, i wish if i went with Stellarvue SVX70T when it was available back in time, but things happens, it is gone, and i have to move on.

At the end i am looking for this scope only to use either Ha filter or Lum, and sounds Ha isn't a problem at all, any scope can do the job, but with Lum because it covers all visible wavelength, then it should be well corrected scope, so i hope to find that well corrected scope at range 280mm up to 320mm if possible, and hopefully it won't cause like blue halo or CA whatever you call it with lum filter in the final results.

Many tried to give me options like Redcat at 250mm or 70mm something at 360mm, i know them long time ago, if i need them then i won't ask, but not interested in both, i asked if i can try using something like 0.7x or at least 0.65x reducer with 70mm triplet scope, almost all said i will risk for incompatibility then, so either i didn't give them any chance or they didn't give me any possibilities.
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Old 05-02-2021, 01:21 PM
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For my first scope I went with an unknown manufacturer (Askar FRA400/5.6) and quintuplet design for completely flat imaging, with whatever glass it came with. I love it and haven't regretted my decision one bit. I then purchased the "notoriously difficult" and "poor quality" GSO Ritchey-Cretien scope (204mm@f/8) and loved every moment with it. Yes, a learning curve, but satisfying and I got images (forgettable, but present) from my very first night out.

If you need to pick glass vs optical quality, I'd go optical quality all the way.
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Old 06-02-2021, 01:02 AM
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Originally Posted by kalon View Post
For my first scope I went with an unknown manufacturer (Askar FRA400/5.6) and quintuplet design for completely flat imaging, with whatever glass it came with. I love it and haven't regretted my decision one bit. I then purchased the "notoriously difficult" and "poor quality" GSO Ritchey-Cretien scope (204mm@f/8) and loved every moment with it. Yes, a learning curve, but satisfying and I got images (forgettable, but present) from my very first night out.

If you need to pick glass vs optical quality, I'd go optical quality all the way.

Actually those two scopes are in my list, more is that Askar FRA400, and i am almost confirmed or decided to get it finally, but i still have time before i order if anything will happen to change my mind, but from some results i saw out of this scope i feel good and accepting what i see, and it will match one camera i already have, so it will be done.


Now i am searching for third same focal length or FOV of FRA400, for my other cameras, i have three and i might add one more, so having 4 cameras is so much flexible, and for that i prefer to use two or three scopes, one is ordered which is a triplet new model FPL-55, second could be strongly this FRA400 [it matches QHY294M which i have nicely], then i am left with QHY163M and ASI1600MM, both have 3.8um pixel size, and i don't want to go longer focal length only to match pixel size for sampling as many told me, but who knows.
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Old 10-02-2021, 08:31 AM
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...i am left with QHY163M and ASI1600MM, both have 3.8um pixel size, and i don't want to go longer focal length only to match pixel size for sampling as many told me, but who knows.
I have the 1600MM. The FRA400/5.6 comes with an adaptor that you can screw straight in to the ZWO filter wheel and 1600MM camera to give you perfect backfocus.

I now also use the 1600MM on my GSO 8" RC giving me 1625mm focal length, and that is meant to be slight oversampling, but that doesn't seem to be the case (to my eye)... Check out some of my work using both scopes at https://telescopius.com/profile/kalon
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Old 16-02-2021, 05:40 AM
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Quote:
Originally Posted by kalon View Post
I have the 1600MM. The FRA400/5.6 comes with an adaptor that you can screw straight in to the ZWO filter wheel and 1600MM camera to give you perfect backfocus.

I now also use the 1600MM on my GSO 8" RC giving me 1625mm focal length, and that is meant to be slight oversampling, but that doesn't seem to be the case (to my eye)... Check out some of my work using both scopes at https://telescopius.com/profile/kalon

The worse case is under sampling, this is what i read, so using longer focal length isn't a problem, i don't have long focal length scopes except my 8" F5 which is 1000mm perfect one and Mak 180mm which 2700mm but it is not for DSO anyway.
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