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How much strehl difference is actually detectable?

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#51 RLK1

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Posted 04 May 2021 - 11:00 AM

What have you read? That you can visually see the difference?

Again, read the thread:

1. On an 'average night...' I don't think you can tell the difference between 0.94 and 0.98." But, on a VERY GOOD night that another thing."

2."I can visually detect differences between my FC76DCU-EX (quad, which probably has a polystrehl around 0.98 or better), FC-100 (Polystrehl ~0.96), Vixen SD81S (never measured but probably around 0.94-0.95 Strehl judging from other CN'ers estimates) and ED100, ED80. The differences between the first three (all Japan-made optics) are subtle,"


 

#52 gnowellsct

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Posted 04 May 2021 - 11:44 AM

Strehl anxiety and optical quality obsession seems to be solely a disease of the refractor lovers community. I know it's true of me when I use my refractor. But the mirror scope folks seem to spend more time enjoying the night sky than worrying about optics and this is also true of me when I use my mirror scope:)

It's an obsession which makes sense, really.  A larger optic with lower strehl will deliver a better view than a much smaller optic with a high strehl.  In the Newtonian world it's always possible to add another inch or two or ten to the observing program and do so at costs that do not break budgets.  The Meade 16" Lighbridge is only $3600 and that is with go-to.  In all but the very worst cases it will outperform a four inch apo with a .98 strehl.  

 

But if you have decided that refractors are for you, the range of affordable apertures is much more limited and the cost of mounting is not included in the price.  To improve performance and remain a refractor user the only real option for improved performance is to chase a higher strehl (and in the usual case, a better mount).

 

Inherent to refractor design are:

 

1.  rapid escalation in cost at the margin

2.  diminishing real returns to performance with increasing Strehl

 

Two years ago at a public event I had my GT130 which was doing a fine job at high powers (on Jupiter) but the 10 and 12" Skywatchers that belonged to two friends next to me were blowing it away.  I'm dead certain I had the higher strehl.  My friends rather gleefully pointed out that their two scopes together cost less than mine.  They were right.   But at least my AP "looked like a telescope."

 

 

Greg N


 

#53 kel123

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Posted 04 May 2021 - 11:53 AM

Again, read the thread:
1. On an 'average night...' I don't think you can tell the difference between 0.94 and 0.98." But, on a VERY GOOD night that another thing."
2."I can visually detect differences between my FC76DCU-EX (quad, which probably has a polystrehl around 0.98 or better), FC-100 (Polystrehl ~0.96), Vixen SD81S (never measured but probably around 0.94-0.95 Strehl judging from other CN'ers estimates) and ED100, ED80. The differences between the first three (all Japan-made optics) are subtle,"


Read other threads. There are variety of opinions here. I can quote other threads for you too. But this is so unnecessary. Just focus on your own opinion rather than looking for something to be worked up about in threads.
I really find it difficult to understand why some people do this.
 

#54 RLK1

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Posted 04 May 2021 - 12:00 PM

Read other threads. There are variety of opinions here. I can quote other threads for you too. But this is so unnecessary. Just focus on your own opinion rather than looking for something to be worked up about in threads.

What?! Are you serious or just trolling? I haven't referenced "other threads" since I'm responding to the one in which the discussion is occurring.  And, I'll remind you that you responded and questioned my post regarding what other people have stated specific to question of the OP in this thread. But, you're right, this is so unnecessary if only you had read and comprehend the posts in this thread...


 

#55 kel123

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Posted 04 May 2021 - 12:10 PM

What?! Are you serious or just trolling? I haven't referenced "other threads" since I'm responding to the one in which the discussion is occurring. And, I'll remind you that you responded and questioned my post regarding what other people have stated specific to question of the OP in this thread. But, you're right, this is so unnecessary if only you had read and comprehend the posts in this thread...


I mean other posts, not other threads. That was an error. I was referencing the fact that the you quoted other posts which conformed to your own query. I couldn't have been the one trolling. You were the one that responded to my post initially. And it was very unnecessary. Just share your own views and leave others. Just enjoy the hobby.
 

#56 Joe1950

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Posted 04 May 2021 - 12:56 PM

The ‘This versus That’ topics get old really quickly. It’s like a pooch chasing its tail.

 

BTW: Roland said in one of his informative essays that he could make an APO lens that would give an identical inside and outside focus star test. But it wouldn’t be the best lens he could make. I’m paraphrasing, of course. He judges an optic by the in-focus Airy disk/diffraction pattern.

 

So even the vaunted star test can be misleading.

 

Someone once said that optical testing has ruined more good telescopes than any other cause!

 

Quality is determined by price? Something most often said by someone with a very high priced product listed in his/her signature. I’d agree that generally a higher priced telescope is of a higher quality, but one cannot use that as hard and fast rule. PRICE is determined by many factors, quality being one perhaps, but not the only one.

 

Anyway, that’s my humble and often flawed opinion. If anyone disagrees, that’s fine as well. I will give opposing opinions my utmost attention and consideration!

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lol.gif

 

 

 


 

#57 RLK1

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Posted 04 May 2021 - 12:57 PM

I mean other posts, not other threads. That was an error. I was referencing the fact that the you quoted other posts which conformed to your own query. I couldn't have been the one trolling. You were the one that responded to my post initially. And it was very unnecessary. Just share your own views and leave others. Just enjoy the hobby.

I was responding to your original error when you posted, "As every other poster has noted, you can never possibly see the difference visually". Two other posts in the thread, previously noted, stated otherwise.


 

#58 kel123

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Posted 04 May 2021 - 01:09 PM

All is well
 

#59 SeattleScott

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Posted 04 May 2021 - 01:25 PM

Well said, I don’t normally get involved in this issue but to literally send something back because it is 0.96 instead of Joe’s 0.98 is unbelievable, I have read that before on some of these threads. Those posters actually thought they were getting short changed ! LOL !

I assumed that post was sarcasm.

I wouldn’t get worked up about it.

Tom in particular posts a lot of funny nonsense. Although this one wasn’t Tom. Allow people to have a sense of humor and don’t take them too seriously when they make ridiculous claims.

Scott
 

#60 vahe

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Posted 04 May 2021 - 01:35 PM

Well said, I don’t normally get involved in this issue but to literally send something back because it is 0.96 instead of Joe’s 0.98 is unbelievable, I have read that before on some of these threads. Those posters actually thought they were getting short changed !  LOL !

 

This is the prime reason why most high end scope makers no longer offer test data for their scopes. In fact they sell their products strictly based on their reputation.

.

Vahe


 

#61 Deadlake

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Posted 04 May 2021 - 02:05 PM

I assumed that post was sarcasm.

I wouldn’t get worked up about it.

Tom in particular posts a lot of funny nonsense. Although this one wasn’t Tom. Allow people to have a sense of humor and don’t take them too seriously when they make ridiculous claims.

Scott


I’ve heard these stories from a dealer, people sending scopes back because someone has posted on CN a higher Strehl report for same scope model.

I was in the situation where the lens cell went missing in the post. The replacement lens cell was a slightly less Strehl measurement but within the tolerance of the infereometer and I didn’t fancy waiting another six months for the next allocation to come along.

I think people are to hung up on Strehl and should look at PV and RMS as well.
 

#62 LDW47

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Posted 04 May 2021 - 02:18 PM

I assumed that post was sarcasm.

I wouldn’t get worked up about it.

Tom in particular posts a lot of funny nonsense. Although this one wasn’t Tom. Allow people to have a sense of humor and don’t take them too seriously when they make ridiculous claims.

Scott

I really don’t think you even understand the point of my post or you are quoting the wrong post ?


 

#63 LDW47

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Posted 04 May 2021 - 02:21 PM

I’ve heard these stories from a dealer, people sending scopes back because someone has posted on CN a higher Strehl report for same scope model.

I was in the situation where the lens cell went missing in the post. The replacement lens cell was a slightly less Strehl measurement but within the tolerance of the infereometer and I didn’t fancy waiting another six months for the next allocation to come along.

I think people are to hung up on Strehl and should look at PV and RMS as well.

Thats kind of what my post 35 was about !


 

#64 SeattleScott

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Posted 04 May 2021 - 04:41 PM

I really don’t think you even understand the point of my post or you are quoting the wrong post ?

I was referring back to the post about 98 Strehl being worlds better than 96, which I took as humorous satire, and it seemed like you were referencing that.

As for people returning a scope because it doesn’t meet a certain Strehl criteria, yeah I can believe that, although hopefully not because it was only 96 Strehl. Now if the Strehl is lower than the advertised minimum, that’s on the vendor. But returning a mass produced $1,000 Apo because it is only 92 and some other lucky person on CN boasts about getting a 96, well that’s just cherry picking and increases costs for all of us.

Scott
 

#65 GSBass

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Posted 04 May 2021 - 04:59 PM

I found this funny and true…. But it is a fun thing….I mean refractor  view are the holy grail of which other designs aspire to be… for this reason I give them a pass for their obsession

Strehl anxiety and optical quality obsession seems to be solely a disease of the refractor lovers community. I know it's true of me when I use my refractor. But the mirror scope folks seem to spend more time enjoying the night sky than worrying about optics and this is also true of me when I use my mirror scope:)


Edited by GSBass, 04 May 2021 - 04:59 PM.

 

#66 GSBass

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Posted 04 May 2021 - 05:06 PM

Btw…. It’s kinda why I think color correction has come to be the biggest factor…. Modern day optics seem to have solved the figure equation to certainly a good enough quality for most of us…… CA seems to be the biggest hurdle…. Seems to apply to cheap triplets and expensive doublets…. Often close to the same quality and success now days


 

#67 Joe1950

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Posted 04 May 2021 - 05:06 PM

GScope envy is a real issue. I do think some focus more on the mine vs. yours conflict than the actual use of whatever they have.   Especially true for the refractor group as noted by Nippon and GSBass in the above post.

 

I got into some heated topics in the past about scopes and brands and whatnot in the past, but I now avoid those really toxic discussions. They seem to go on and on with no answers because there aren’t answers when it comes to opinion.

 

I’m very happy with the scopes and accessories I have. They aren’t the upper echelon names, but they perform very well for me. I’ve never had the means to buy a premium name so I make do with what I have.

 

To answer the question of the OP. No, my opinion is that there is no observable difference in those levels of quality, even if accurate. Just my opinion.

 

 

Added: I must say, though, it is annoying when someone gives an opinion and mentions specific brands, especially if the lesser brand is one I happen to own. 

 

Someone compared a Baader Morpheus eyepiece to a like focal length Paradigm eyepiece, the latter making up most of my collection. The Paradigm/Agena EDs are very good eyepieces. Many users feel so. The Morpheus may be better, I don’t really know.

 

But often, the way things are worded, I believe the difference is exaggerated in the comparison. Just like with scopes. Some of the statements make the owners of the lesser product feel like they have a piece of junk compared to the better one. It’s like, Oh! What use is the item I have...

306AD4AE-83FD-421F-9970-F5C61C56C209.gif

 

So if I get into a comparison discussion, which I try not to, I tend to highlight the good points of the item or brand I am praising rather than trashing the other kind. Just the way I choose to approach things.

 

Plus, with things such as an eyepiece, the scope it’s used in makes a big difference in the perceived performance. 


Edited by Joe1950, 04 May 2021 - 05:29 PM.

 

#68 GSBass

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Posted 04 May 2021 - 05:10 PM

I think 99% of us agree with you….. 96% agree with you more :)

Scope envy is a real issue. I do think some focus more on the mine vs. yours conflict than the actual use of whatever they have.   Especially true for the refractor group as noted by Nippon and GSBass in the above post.

 

I got into some heated topics in the past about scopes and brands and whatnot in the past, but I now avoid those really toxic discussions. They seem to go on and on with no answers because there aren’t answers when it comes to opinion.

 

I’m very happy with the scopes and accessories I have. They aren’t the upper echelon names, but they perform very well for me. I’ve never had the means to buy a premium name so I make do with what I have.

 

To answer the question of the OP. No, my opinion is that there is no observable difference in those levels of quality, even if accurate. Just my opinion.


 

#69 LDW47

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Posted 04 May 2021 - 05:26 PM

I was referring back to the post about 98 Strehl being worlds better than 96, which I took as humorous satire, and it seemed like you were referencing that.

As for people returning a scope because it doesn’t meet a certain Strehl criteria, yeah I can believe that, although hopefully not because it was only 96 Strehl. Now if the Strehl is lower than the advertised minimum, that’s on the vendor. But returning a mass produced $1,000 Apo because it is only 92 and some other lucky person on CN boasts about getting a 96, well that’s just cherry picking and increases costs for all of us.

Scott

I didn’t say I read it very often but I read it on a post or two on a similar thread, not all that long ago ie within the last year where the Strehl didn’t meet the number they though it should so they either got a refund or an exchange because .......... ! I sure wasn’t talking mass produced anything. I don’t think I was referencing anything or anyone, can you give me the post # ? The reason, as I mentioned, is that I don’t normally get involved in this subject and all my achros have a 100% Strehl, lol !


 

#70 SeattleScott

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Posted 04 May 2021 - 05:38 PM

I didn’t say I read it very often but I read it on a post or two on a similar thread, not all that long ago ie within the last year where the Strehl didn’t meet the number they though it should so they either got a refund or an exchange because .......... ! I sure wasn’t talking mass produced anything. I don’t think I was referencing anything or anyone, can you give me the post # ? The reason, as I mentioned, is that I don’t normally get involved in this subject and all my achros have a 100% Strehl, lol !

I was just laying out hypothetical examples.

If someone buys a TEC and it is less than 95% then they probably have a basis for returning it. If it is a 100ED that is less than 95%, deal with it. Higher price should result in higher quality, generally speaking. But still, returning a high end scope because it is only 97 or something seems a little silly. Personally I haven’t heard of this but that doesn’t mean it hasn’t happened.

Scott
 

#71 GSBass

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Posted 04 May 2021 - 05:40 PM

One more thing :) no matter true or not i always cringe a little when I see people say…” but what color spectrum did they use”.  Perhaps the dive is a little too deep for me….. I do get it…..it just seems a little disingenuous, of course makers will put forth there best numbers even if the secondary numbers lag…. I think theoretically they are going to be close…. Probably impossible to say that green or blue is excellent but that red really sucks …. I’m not an optical engineer but guessing perfecting one color has the effect of bringing the others along for the ride


 

#72 LDW47

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Posted 04 May 2021 - 05:49 PM

I was just laying out hypothetical examples.

If someone buys a TEC and it is less than 95% then they probably have a basis for returning it. If it is a 100ED that is less than 95%, deal with it. Higher price should result in higher quality, generally speaking. But still, returning a high end scope because it is only 97 or something seems a little silly. Personally I haven’t heard of this but that doesn’t mean it hasn’t happened.

Scott

I will tell you one thing, I wouldn’t mention it if I hadn’t read it, I don’t operate like that and as well it really doesn’t matter to me because I never get involved in that nonsense ! That particular post(s) just stuck in my mind as a reminder as to why I don’t, lol !  My eyeballs wouldn’t be able to take it, lol !


 

#73 LDW47

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Posted 04 May 2021 - 05:50 PM

One more thing smile.gif no matter true or not i always cringe a little when I see people say…” but what color spectrum did they use”.  Perhaps the dive is a little too deep for me….. I do get it…..it just seems a little disingenuous, of course makers will put forth there best numbers even if the secondary numbers lag…. I think theoretically they are going to be close…. Probably impossible to say that green or blue is excellent but that red really sucks …. I’m not an optical engineer but guessing perfecting one color has the effect of bringing the others along for the ride

Why not unless ........ ?


 

#74 GSBass

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Posted 04 May 2021 - 06:09 PM

Random thought….. does not take much to destroy a scope, all it takes is a snazzy headline saying how bad it sucks and the 1500 reply’s of how great it is does not matter…. The cloudy night police should be a little more vigilant I think…. The example that comes to mind is the evoscope thread…. Thousands of happy campers but the thread remains the same…. Proven to be a major disappointment, simply false and misleading ….. not that I want one but it does matter when a headline hurts a vender imho


 

#75 LDW47

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Posted 04 May 2021 - 06:33 PM

I was referring back to the post about 98 Strehl being worlds better than 96, which I took as humorous satire, and it seemed like you were referencing that.

As for people returning a scope because it doesn’t meet a certain Strehl criteria, yeah I can believe that, although hopefully not because it was only 96 Strehl. Now if the Strehl is lower than the advertised minimum, that’s on the vendor. But returning a mass produced $1,000 Apo because it is only 92 and some other lucky person on CN boasts about getting a 96, well that’s just cherry picking and increases costs for all of us.

Scott

If you thought because I used the name Joe I was referring to a fellow astronomer, think twice, it was just a name I used to complete my post, it could have been Bill or Frank or ....... ! Have you never, in all your adult years, your learned years used that type of sentence description in a conversation ?? Really ?   PS:  Maybe I should have said ‘Mr. X’ is that better ?


Edited by LDW47, 04 May 2021 - 06:37 PM.

 


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