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Why do really expensive scopes sell and what attracts us to them ?


John
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2 hours ago, John said:

APM put the specs they use for their LZOS objectives in the public domain. I guess they were stringent back in 2005 but maybe not so much today ?

APMApo-Linsen-Spezifikationen.pdf 468.53 kB · 8 downloads

My priority has always been to try and get the best optical quality that I can afford. I've never been too fussy about focusers etc or even the quality of fit and finish, as long as the optical quality is there. With the more expensive scopes I would hope to get better quality in these departments as well.

Although not too fussy about focusers, even I can appreciate that the Feathertouch fitted to my TMB/LZOS 130 is something above and beyond anything else I've used though.

With a triplet refractor I think the mechanical design and precision of the objective cell is very important as well. Another area where the LZOS triplets seem extremely well executed. I'm sure that Tak and Astro Physics have great quality objective cells as well.

tmb3-jpg.202505

 

 

 

 

 

According to Markus lens design not changed since Thomas Black original design. 
And lens material, well we have measurements for that.

One thing I would state is that other manufacturers have been increasing there tolerances, e.g Stellarvue is now fabricated in house Strehl 0.99 lens whereas LZOS has not followed suite as would add at least an extra $1000 per lens. It’s not the lens material but figuring the lens.

We could also include the C-F correction for a scope.

Also the PV of a lens, if you have a high Strehl and a high PV which do you priorities, you want a smoother lens as well.

 

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6 minutes ago, Deadlake said:

Also the PV of a lens, if you have a high Strehl and a high PV which do you priorities, you want a smoother lens as well.

You can have a "high" PV and also a high Strehl if there only one or two little hills or valleys (you know what I mean). We should prioritize smoothness and Strehl IMHO. Btw a true 1/4 wave, .8 Strehl scope will show extremely good detail- I believe there are small but noticeable improvements up to .9 Strehl but not much after that.

In the real world the best test of optics (to me) is the ability of a scope to take high mag on lunar/planetary before breaking down and the best scopes are almost impossible to break down, of course this take super seeing. Also of course this is just my opinion.

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1 minute ago, vlaiv said:

That is great input.

Having that experience, do you think that current price difference between two scopes is justified?

Truthfully? No.

But let me qualify that.

1. I've never bought a really top end scope new..in the past I just didn't have the cash to do so, family commitments, mortgage etc etc.

Ironically, now that I maybe could afford to do so (crawling on hands and knees to my wife first!😂🤣), I don't feel the need to..if you buy used with care, you can get a scope that's been well looked after and that will last you for years to come, for much less than the new price.

2. I do think that Vixen loses out in the UK at least, because they are caught in between the top price, top reputation brands like Tak, TEC, Tele Vue, Lzos, AP etc and more mainstream brands such as Skywatcher, Celestron, Meade, Bresser, etc.

Also, they do offer "cheap" versions of some of their scopes, made in China, but not visibly better than the "authentic" Chinese made brands, and this kind of devalues their reputation in some people's minds..any marketing professional will tell you that you never "dilute" your main brand by confusing customers with a cheap brand carrying your main brands name. That's why Toyota's premium brand cars are branded Lexus, for example.

3. If I was interested in buying a top class refractor today, I would not buy new..I'd wait for someone to offer what I was looking for, used, and be patient. Even AP Starfire's come up for sale now and again!😊👍.

Dave

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21 minutes ago, F15Rules said:

Vixen has a reputation for excellent optics. I believe they are still the market leading brand in Japan. The two examples I had were superb visually. I had one of them for a while when I had also the Tak FS128, so was able to do a comparison..whilst the Tak was "better" in terms of light grasp and brighter images, I can't honestly say that the image quality (airy disk presentation, colour free in-focus, contrast, sharpness on axis and edge to edge etc was any better in the Tak. If a Vixen "ED128s" had been available, and of the same optical quality, I would have happily bought one.

Tak and Vixens scopes cost around the same in Japan, the price difference is on treasure island. 😃

One question around the focusing in the doublets you have used, does the FS128 keep the subject in focus other a greater range compared to the Vixen doublet? I find my LZOS triplet easier to focus as it’s focus range is greater then doublets I have used. e.g., on Jupiter I would have to adjust the focuser less with the LZOS compared to a doublet.

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13 minutes ago, jetstream said:

In the real world the best test of optics (to me) is the ability of a scope to take high mag on lunar/planetary before breaking down and the best scopes are almost impossible to break down, of course this take super seeing. Also of course this is just my opinion.

We can test a scope on an optical bench, however how the scope responds to environment is going to be hard to replicate and we’ve not even mentioned seeing conditions.

I’d suggest that’s the variation being reported…

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6 minutes ago, Deadlake said:

however how the scope responds to environment is going to be hard to replicate and we’ve not even mentioned seeing conditions.

If a scope has really performed, even once, it confirms its ability IMHO. Thing is, if seeing is superb for say a 120mm refractor it will also be superb for a 15" (in my case) so obviously I reach for the larger aperture, lower strehl and all than the 120mm.

My best scopes replicate their performance over and over again. They are not the "best of the best" but right up there.

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30 minutes ago, Deadlake said:

Tak and Vixens scopes cost around the same in Japan, the price difference is on treasure island. 😃

One question around the focusing in the doublets you have used, does the FS128 keep the subject in focus other a greater range compared to the Vixen doublet? I find my LZOS triplet easier to focus as it’s focus range is greater then doublets I have used. e.g., on Jupiter I would have to adjust the focuser less with the LZOS compared to a doublet.

I never noticed a significant difference in the "in and out" focuser range on either scope, but I haven't actually measured the exact travel either.

The scopes were F7.7 (Vixen) and F8.1 (Tak) so I would imagine they'd both have similar depth of focus?

I always found my long achromats had great depth of focus, and assumed that dual focusers came in with modern short focus (F7 or faster) as they could be difficult to get to snap focus without the micro focus capability.

I fitted an MEF3 focuser to my Tak and this did definitely make high power fine focus much easier.. but bear in mind that at 5" vs 4" and 1040mm vs 795mm focal length, the Tak can take significantly higher magnification than the Vixen.

The Vixen single speed focus on both examples I had were so smooth that I rarely used the dual speed facility on the one that had it fitted.

HTH,

Dave

 

Edited by F15Rules
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Strehl ratio can be misleading.  Would you prefer a 1mm objective with 99.9999 Strehl or 100mm objective or 300mm mirror with Strehl of 85.00. Just to make up some numbers.

It is a ratio of theoretical to actual performance but theoretical performance depend on aperture and other factors.

Regards  Andrew 

Edited by andrew s
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45 minutes ago, Deadlake said:

I find my LZOS triplet easier to focus as it’s focus range is greater then doublets I have used.

What do you mean by a triplet having a longer focus range? I’m aware of long focal ratio scopes being more tolerant to seeing because they have a longer focus range, but fast scopes like the LZOS tend to snap to focus ie they are either in or out of focus, no mistaking it.

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"Conclusion

Telescopes of equal aperture are affected the same by atmospheric turbulence, regardless of focal ratio. The error in the hypothesis is that it was assumed that the same atmospheric distortion will cause the same shift in the best focus position in the two telescopes, and this is not true. While the high f-number telescope does enjoy a greater depth of focus, unfortunately the shift in best focus caused by turbulence is also greater. In fact, the two are locked together; the instrument with four times greater depth of focus also has a four times greater linear shift of the best focus position."

https://www.fpi-protostar.com/bgreer/seeing.htm

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28 minutes ago, jetstream said:

"Conclusion

Telescopes of equal aperture are affected the same by atmospheric turbulence, regardless of focal ratio. The error in the hypothesis is that it was assumed that the same atmospheric distortion will cause the same shift in the best focus position in the two telescopes, and this is not true. While the high f-number telescope does enjoy a greater depth of focus, unfortunately the shift in best focus caused by turbulence is also greater. In fact, the two are locked together; the instrument with four times greater depth of focus also has a four times greater linear shift of the best focus position."

https://www.fpi-protostar.com/bgreer/seeing.htm

Thanks Gerry! Interesting.

So it is hogwash that slower scopes cope with seeing better? I’ve read it so often I assumed it to be true!

I certainly see no reason why an f6 triplet should have a greater focus range than a slower doublet, do you?

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I did a head to head between my 100mm f/13 Carton and a WO FLT98 for planetary observing and the greater depth of field of the Carton made a real difference on Jupiter for example as the entire disk was in sharp focus whereas with the FLT98 it wasn’t. The Carton was simply the better planetary scope. The FLT98 was however a better all rounder even though it was beaten for planetary. 

Edited by johninderby
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45 minutes ago, Stu said:

Thanks Gerry! Interesting.

So it is hogwash that slower scopes cope with seeing better? I’ve read it so often I assumed it to be true!

I certainly see no reason why an f6 triplet should have a greater focus range than a slower doublet, do you?

Sometimes I wonder about how much we read in forums is actually scientifically accurate, I mean we all read opinions then spread those to newcomers over years and years. There are some things which I always thought were absolute irrefutable facts until, someone explained why said "fact" it is not true. 

Edited by Sunshine
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15 minutes ago, Sunshine said:

There are some things which I always thought were absolute irrefutable facts until, someone explained why said "fact" it is not true. 

dk4.thumb.png.ac387efb3f8acd43be6af211546c6901.png

My experience so far in astronomy is either climbing up or falling down Mt. Stupid. Every day i learn something i did not know how little i understood of. Hearsay and myths are easy to circulate but facts are not so much, especially if the facts are difficult to understand and a convenient myth explains it in a simple (false) sentence.

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32 minutes ago, Sunshine said:

... I mean we all read opinions then spread those to newcomers over years and years. There are some things which I always thought were absolute irrefutable facts until, someone explained why said "fact" it is not true. 

I think that is an issue. Certain things do get repeated over and over without necessarily being re-tested. Every now and then some experienced and helpful person does post a "myth busting" piece which is great but many of these "facts" do seem to be like zombies - hard to kill off !

Also, some information that had some validity 20-30 years ago has been rendered obsolete / inaccurate by optical and technological developments over the intervening years. I'm sure those of us who have been around for a few years can all think of examples of that !

 

 

 

 

 

Edited by John
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1 hour ago, Stu said:

Thanks Gerry! Interesting.

So it is hogwash that slower scopes cope with seeing better? I’ve read it so often I assumed it to be true!

I certainly see no reason why an f6 triplet should have a greater focus range than a slower doublet, do you?

I think that focal length and focal ratio has little to do with visual astronomy as related to seeing and depth of focus. For imaging the depth of focus vs f ratio might be real...

As far as an f6 triplet having a greater focus range , yes its possible but nothing to do with the f ratio IMHO.

Edited by jetstream
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I find that often there is a measure of truth in most things that are stated. An example might be "aperture is king", which is true - until it isn't. And the reason it isn't, or rarely completely true, is that there are so many other variables that need to play their part to make the statement true. A Zeiss Abbe Orthoscopic, or a TMB Supermonocentric is the best eyepiece for planets, - that is until it's compared to a pair of cheap ortho's in a binoviewer. You need at least a 3" refractor or a 6" reflector to do any serious observing - that's plain wrong! A really expensive scope is better than a cheaper one - which may be true, or at least that's often the assumption, but it may equally as often be proved false.  Also, I can't remember a single instance where a fellow stargazer has blatantly lied so as to mislead, but instead found them all to be thoroughly decent, though a little bit overly enthusiastic at times, which may leave a newcomer to take their view as gospel.

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1 hour ago, Sunshine said:

Sometimes I wonder about how much we read in forums is actually scientifically accurate

One of the biggest myths is that OIII filters will not work with small apertures, it is simply not true. Another struggle many have or resist, sometimes vigorously is the concept of using exit pupil and not magnification. IMHO.

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One more myth as it was alluded to earlier. ie PV equates to about .8 Strehl, no necessarily so... IMHO

http://www.rfroyce.com/standards.htm

which one would you rather hav

"The answer is obvious. And so is the inadequacy of the peak to valley methodology as a measure of optical quality. It looks at only two points, the high and low, and ignores all that lies between. Important issues such as roughness are totally ignored while a very small high or low point are exaggerated totally out of proportion to their significance. A mirror showing a peak to valley value of lambda/2.5 (.4 wave) might in fact be an extremely good mirror with the vast majority of its surface at better than lambda/10 and very smooth. The reason that the peak to valley criterion is so popular is due to a combination of factors that have transpired over the years."

royce.jpg

Edited by jetstream
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2 hours ago, Sunshine said:

Sometimes I wonder about how much we read in forums is actually scientifically accurate, I mean we all read opinions then spread those to newcomers over years and years. There are some things which I always thought were absolute irrefutable facts until, someone explained why said "fact" it is not true. 

Trouble is that realization goes both ways. Even the new information can be just as bad as the original. If someone repeats something its exactly that. If they actually learned it themselves in the feild. It could be more reliable. But i stress could ? Depending on interpretation of whats learned

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1 hour ago, jetstream said:

I think that focal length and focal ratio has little to do with visual astronomy as related to seeing and depth of focus. For imaging the depth of focus vs f ratio might be real...

As far as an f6 triplet having a greater focus range , yes its possible but nothing to do with the f ratio IMHO.

If the depth of focus vs F ratio is real for imaging. Then it would also be real visually. A camera only sees what the eye would see. But is actually enhanced. Quite lost on that. Perhaps you didnt mean how i interpreted what you meant.  Can you explain what you mean by that please. 

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1 hour ago, mikeDnight said:

I find that often there is a measure of truth in most things that are stated. An example might be "aperture is king", which is true - until it isn't. And the reason it isn't, or rarely completely true, is that there are so many other variables that need to play their part to make the statement true. A Zeiss Abbe Orthoscopic, or a TMB Supermonocentric is the best eyepiece for planets, - that is until it's compared to a pair of cheap ortho's in a binoviewer. You need at least a 3" refractor or a 6" reflector to do any serious observing - that's plain wrong! A really expensive scope is better than a cheaper one - which may be true, or at least that's often the assumption, but it may equally as often be proved false.  Also, I can't remember a single instance where a fellow stargazer has blatantly lied so as to mislead, but instead found them all to be thoroughly decent, though a little bit overly enthusiastic at times, which may leave a newcomer to take their view as gospel.

I think there is a prime example where apeture is not always king. Air cells and imaging low targets. My small refractor copes better. it also cools quicker. and is less affected with the destructive problems of heat from the outset. In other words. it will perform quite well quite quickly. So yes i agree. These blanket statements need to be taken with the context they was intended for. Or can be very misleading 

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