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sva130t pixel peeping on astrobin

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#1 joelin

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Posted 10 July 2019 - 11:21 PM

So I've been pixel peeping the sva130t on astrobin to see how good it really is. I'll look at the large versions such as this: https://www.astrobin...6/0/?real=&mod= and this https://www.astrobin.com/full/392892/0/?real=&mod=

 

They honestly don't look so good near the corners....I think I expect a bit more from a premium scope and matched reducer correct?


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#2 Jerry Lodriguss

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Posted 10 July 2019 - 11:43 PM

I wrote a review of this scope for Sky & Tel in the Nov 2016 issue, you might want to look it up if you can find it.

 

Shooting full frame like those pix you linked to is hard on a lens.

 

If you want premium performance, get an Astro-Physics refractor.

 

And if you want premium performance on a full frame camera, get an AP refractor with a big focuser and the large format AP flattener/reducer.

 

You get what you pay for.

 

Jerry


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#3 joelin

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Posted 10 July 2019 - 11:48 PM

I wrote a review of this scope for Sky & Tel in the Nov 2016 issue, you might want to look it up if you can find it.

 

Shooting full frame like those pix you linked to is hard on a lens.

 

If you want premium performance, get an Astro-Physics refractor.

 

And if you want premium performance on a full frame camera, get an AP refractor with a big focuser and the large format AP flattener/reducer.

 

You get what you pay for.

 

Jerry

Yes I've seen your review and it said the stars in the corners were very good in a full frame sensor.

 

I'm surprised that the sva130t isn't considered premium performance and is a "get what you pay for" scope! 


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#4 PirateMike

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Posted 11 July 2019 - 12:11 AM

Well if I understand things properly, Stellarvue doesn't make telescopes, they just get them from China (or wherever), so calling them a telescope manufacturer is at the least very questionable. What they do is they specify the quality specifications that they will accept from those companies that actually do make telescopes.

 

So the scopes are not premium in my book, they are just the hand picked better performers of a mass produced model. One could purchase the same scope at a much lower price from somewhere else and get a scope just as good as a Stellarvue product. Of course, you could also get one of a lower quality.

 

One thing 

9of many things) that sets the premium telescopes manufacturers apart from the others is the quality of the glass, every type of glass has their own "quality tiers". For example, there is ok FPL-53, better FPL-53, good FPL-53 all the way up to the best FPL-53 (actually, I don't know the exact levels of quality for any one glass but my generalized point still hold true), the premium scope builders only use the best glass and leave the rest for the "others" and I can assure you that the telescopes that Stellarvue sells belongs in the group of "others".

 

I'm not "bashing" Stellarvue, they do sell a product with a gaurenteed level of quality, I'm just trying to explain how a telescope from a premium manufacturer and a Stellarvue telescope differ.

 

 

Miguel   8-)

 

.


Edited by PirateMike, 11 July 2019 - 01:01 AM.


#5 joelin

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Posted 11 July 2019 - 12:15 AM

Well if I understand things properly, Stellarvue doesn't make telescopes, they just get them from China. What they do is they specify the quality specifications that they will accept.

 

So the scopes are not premium in my book, they are just the hand picked better performers of a mass produced model. One could purchase the same scope at a much lower price from somewhere else and get a scope just as good as the Stellarvue products. Of course, you could also get one of lower quality.

 

The one thing that sets the premium telescopes apart from the others is the quality of the glass, every type of glass has their own "quality tiers". For example, there is ok FPL-53, better FPL-53, good FPL-53 all the way up to the best FPL-53 (actually, I don't know the exact levels of quality for any one glass but my generalized point still hold true), the premium scope builders only use the best glass and leave the rest for the "others" and I can assure you that the telescopes that Stellarvue sells belongs in the group of "others".

 

I'm not "bashing" Stellarvue, they do sell a product with a gaurenteed level of quality, I'm just trying to explain how a telescope from a premium manufacturer and a Stellarvue telescope differ.

 

 

Miguel   8-)

 

.

so from picking the cream of the crop they still can't get very good stars in the corners??


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#6 PirateMike

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Posted 11 July 2019 - 12:28 AM

Yes I've seen your review and it said the stars in the corners were very good in a full frame sensor.

 

I'm surprised that the sva130t isn't considered premium performance and is a "get what you pay for" scope! 

Well a "very good" rating is what the reviewer consider to be "very good". Note that Jerry didn't say "fantastic" or "the best there has ever been".

 

Stellarvue sold scope certainly are not premium scopes, they are just other companies scopes that have been tested to perform to a certain level.

 

 

Miguel   8-)

 

.


Edited by PirateMike, 11 July 2019 - 12:57 AM.


#7 PirateMike

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Posted 11 July 2019 - 12:39 AM

so from picking the cream of the crop they still can't get very good stars in the corners??

The best amateur telescope ever made is certainly capable of producing images with terrible stars in the corners if put in the hands of a "not so good" astrophotographer.

 

Nothing in AP is plug and play. In many cases a "top notch" astrophotographer can make a "just fine" telescope sing like a Diva until the sheep come home.

 

Astrophotography in an art, not a mechanical process. Give me 20 tubes of paint, a pallet and a blank canvas and I could paint you a pretty good painting of 20 different colored stick men. Give that same stuff to a certain Vincent VanGogh and I'm sure you would get something at least a little better. Heck, Vincent would only need three tubes of color to paint a masterpiece.

 

It's not the violin, it's the violin player.

 

 

f_0608.jpg

 

 

Miguel   8-)

 

.


Edited by PirateMike, 11 July 2019 - 01:03 AM.

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#8 PirateMike

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Posted 11 July 2019 - 01:04 AM

The secret (like in so many other aspects of life) is not to expect more from your tools... but to expect more from yourself!

 

 

Miguel   8-)

 

.


Edited by PirateMike, 11 July 2019 - 01:11 AM.


#9 PirateMike

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Posted 11 July 2019 - 01:31 AM

It's a triplet, right?  To get good stars at the corners you'll need the proper flattener, properly setup.  Many imagers do not have those two things done right.

And even if you have the proper flattener, setting it up properly will need a bit of finesse and quite possibly a good helping of patience.

 

You can't just slap the flattener on the end of the scope and boom... wonderful stars. You need to work to make them work together as good as the pair can.

 

Right Bob!  (and good morning to you Sir.)

 

 

Miguel   8-)

 

.


Edited by PirateMike, 11 July 2019 - 01:36 AM.


#10 Jerry Lodriguss

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Posted 11 July 2019 - 04:49 AM

I'm surprised that the sva130t isn't considered premium performance and is a "get what you pay for" scope! 

When you pay $30,000 for a Japanese car, you don't expect to get the quality and performance of a premium $60,000 Mercedes.

 

Likewise, there is a reason that the AP scopes cost twice as much as Stellarvue.

 

If the StellarVue scopes were as consistently just as good as AP scopes, and they sold for half the price, AP would go out of business. 

 

That's not to say you can't get very good performance in this price class, you just have to be lucky. That last 10 percent of performance is what costs you 90% of the price difference. Those who are discerning enough to know the difference, and can afford it, will happily pay for that excellence. 

 

You get what you pay for. You're not going to get perfection in this price-level scope, and it is unreasonable to expect it.

 

Jerry


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#11 whwang

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Posted 11 July 2019 - 07:02 AM

100% enlargement FF corner performance isn't something easy to get.  Quality of the optics is one thing.  Quality of the focuser and the entire tube assembly is another.

 

I have never owned an AP so I can't comment on that.  However, what I can tell you is that even TAK refractors can have a lot to complain about if your eyes are picky.  It's really hard to get perfect FF corners.


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#12 bmhjr

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Posted 11 July 2019 - 08:38 AM

With Stellarvue's new premium version of the 130 scope, they list the spec for the image circle.  And, even at the stated spec, there will still be some light fall off and more importantly distortion in the stars.  In what little I have learned over the few years I have been doing this, there is extreme importance for the flattener/reducer to match the scope as well as proper spacing etc.  There is a reason that flattener/reducers from the premium scope manufacturers cost $1000+ .   There are numerous threads here on CN about Stellarvue and reducers.

 

I have the SV80 and flattener and have come to accept distorted stars in the corners with my Full Frame DSLR.  Even though their Large Format flattener was sold as "fully corrected up to full frame".  That text was then later changed to "fully illuminate up to full frame".  And now there is no reference to full frame other than a 48mm T-Ring attachment.  wink.gif

 

SVX130T

Image Circle with 3.5" Focuser and .72X Reducer/Flattener: 40mm


Edited by bmhjr, 11 July 2019 - 08:55 AM.

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#13 PirateMike

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Posted 11 July 2019 - 09:45 PM

I have the SV80 and flattener and have come to accept distorted stars in the corners with my Full Frame DSLR.  Even though their Large Format flattener was sold as "fully corrected up to full frame".  That text was then later changed to "fully illuminate up to full frame".  And now there is no reference to full frame other than a 48mm T-Ring attachment.  wink.gif

As my dear father (rest his soul) would always tell me... "there are three things in life that are guaranteed"...

 

1. You will pay taxes.

 

2. You will die.

 

3. The salesman is lying.

 

 

Miguel   8-)

 

.


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#14 bmhjr

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Posted 11 July 2019 - 09:50 PM

I someday will moving up the ladder and getting a new scope, etc.

 

Fool me once, shame on you ...

 


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#15 joelin

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Posted 11 July 2019 - 11:15 PM

All of this sounds like Stellarvues aren't living up to the marketing and are subpar.

I'm quite surprised because most other posts on CN are more optimistic.

Also let's say the astrophotographer on astrobin was doing something wrong. What could that possibly be given the image that you see? His guiding and focus must be good since the stars in the center are sharp.

 

Could he have gotten his spacing wrong? I find that also really hard to believe. For one thing the reducer used comes ready for a 55mm backfocus which is perfect for the Nikon camera used and a T-ring. So I don't think its easy to get the back focus wrong unless he added something to the optical train.


Edited by joelin, 11 July 2019 - 11:38 PM.

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#16 whwang

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Posted 12 July 2019 - 12:16 AM

Although you said it’s hard for the user to make a mistake in spacing, I still find this kind of mistakes more common than what I expect. Many people simply do not know the importance of this and do all kinds of “creative” things to screw this up.

Another is flexure in the focuser. At least one of the two images you show has asymmetric star distortion in the four corners. That’s likely caused by focuser flexure. Part of this is really manufacture’s fault, but a careful user might be able to slightly reduce this problem (by imaging close to the zenith, applying enough but not too much tightening to the focuser lock, etc).

I suggest you to check as many as possible full resolution images taken by experienced astrophotographers, with other scopes of similar size but from different manufacturers if a large rang of price points. This should allow you to establish norm in this industry and the price you need to pay to get the results that are really good enough for you.
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#17 joelin

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Posted 12 July 2019 - 12:28 AM

Although you said it’s hard for the user to make a mistake in spacing, I still find this kind of mistakes more common than what I expect. Many people simply do not know the importance of this and do all kinds of “creative” things to screw this up.

Another is flexure in the focuser. At least one of the two images you show has asymmetric star distortion in the four corners. That’s likely caused by focuser flexure. Part of this is really manufacture’s fault, but a careful user might be able to slightly reduce this problem (by imaging close to the zenith, applying enough but not too much tightening to the focuser lock, etc).

I suggest you to check as many as possible full resolution images taken by experienced astrophotographers, with other scopes of similar size but from different manufacturers if a large rang of price points. This should allow you to establish norm in this industry and the price you need to pay to get the results that are really good enough for you.

and flexure could be a problem given that he was using a feather touch focuser? 


Edited by joelin, 12 July 2019 - 12:28 AM.


#18 Jerry Lodriguss

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Posted 12 July 2019 - 12:31 AM

Also let's say the astrophotographer on astrobin was doing something wrong. What could that possibly be given the image that you see? His guiding and focus must be good since the stars in the center are sharp.

 

Could he have gotten his spacing wrong? I find that also really hard to believe. For one thing the reducer used comes ready for a 55mm backfocus which is perfect for the Nikon camera used and a T-ring. So I don't think its easy to get the back focus wrong unless he added something to the optical train.

Well, StellarVue sent me the components knowing I was doing a review, so I assume they sent me the correct ones with the correct spacing.

 

It's not that complicated if you tell SV exactly what you plan on doing.

 

So, no. Spacing wasn't the issue with my tests (the stars in the corners of FF are not perfect).

 

Jerry



#19 whwang

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Posted 12 July 2019 - 12:35 AM

and flexure could be a problem given that he was using a feather touch focuser?


I have no idea who is using what focuser. I simply listed the possibilities. If you know more about a specific user and a specific scope, you can use your judgement and decide what would be the most likely cause of a problem.

#20 joelin

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Posted 12 July 2019 - 12:37 AM

Well, StellarVue sent me the components knowing I was doing a review, so I assume they sent me the correct ones with the correct spacing.

 

It's not that complicated if you tell SV exactly what you plan on doing.

 

So, no. Spacing wasn't the issue with my tests (the stars in the corners of FF are not perfect).

 

Jerry

so are you saying the stars in the corners of your FF camera when you did the test were not perfect? here https://www.cloudyni...arvue-sva-130t/ is your review but any the links to the originals which go to your site are gone now... the review you wrote said they were very good...just how good/bad did they actually look?

 

if you have a copy of the original photos that would be great too...


Edited by joelin, 12 July 2019 - 12:40 AM.


#21 joelin

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Posted 12 July 2019 - 12:39 AM

I have no idea who is using what focuser. I simply listed the possibilities. If you know more about a specific user and a specific scope, you can use your judgement and decide what would be the most likely cause of a problem.

the technical details of those photos hint at the focuser...the reducer is: Stellarvue SFFR.72-130-3FT-48 REDUCER/FLATTENER

 

the 3FT means a 3" feather touch focuser...it makes sense because Stellarvue offers the 3" feather touch focuser with the SVA130T 

 

so if they were using that focuser...I wouldn't expect flexure to be an issue



#22 whwang

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Posted 12 July 2019 - 01:09 AM

Then the asymmetric distortion could be caused by misalignment of lens elements.  There are many possibilities and the bottom line is it's really hard to get perfect stars in the FF corners.



#23 joelin

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Posted 12 July 2019 - 02:57 AM

Then the asymmetric distortion could be caused by misalignment of lens elements. There are many possibilities and the bottom line is it's really hard to get perfect stars in the FF corners.


Then it seems like Stellarvues failed to live up to their promise. Their website talks frequently about doing alignment and testing.

#24 whwang

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Posted 12 July 2019 - 04:19 AM

Below is not about Stellarvues specifically.  It's my general thought.  Unless a manufacture gives a quantitative statement (Strehl ratio, diameter of spot size, etc), all other qualitative statements (well corrected, flat field, etc) should all be taken as grains of salt.  For example, a well corrected (no matter how you define it) optics in the 90s on photographic film or on CCD with 20 um pixels may become totally inadequate in today's standard.  A well corrected optics for most of the casual observers can become unacceptable for very picky ones.  It's all relative.  Even if Stellarvues does promise something and even if they do indeed do their best in alignment/testing, there is no guarantee that every single scope from them can satisfy the most picky user.

 

Just move on and buy scopes from more reputable manufactures.  If you get enough evidence that Stellarvues cannot satisfy your need, there is no point trying to figure out what's wrong with them.  But if you really want to stay in the picky side of the user base, you may end up with being equally disappointed by other even more expansive scopes.  As I said earlier, perfect performance in FF corners is really hard to get.  At some point you may realize that it's your expectation that's not too realistic for today's technology.


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#25 joelin

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Posted 12 July 2019 - 12:10 PM

Below is not about Stellarvues specifically.  It's my general thought.  Unless a manufacture gives a quantitative statement (Strehl ratio, diameter of spot size, etc), all other qualitative statements (well corrected, flat field, etc) should all be taken as grains of salt.  For example, a well corrected (no matter how you define it) optics in the 90s on photographic film or on CCD with 20 um pixels may become totally inadequate in today's standard.  A well corrected optics for most of the casual observers can become unacceptable for very picky ones.  It's all relative.  Even if Stellarvues does promise something and even if they do indeed do their best in alignment/testing, there is no guarantee that every single scope from them can satisfy the most picky user.

 

Just move on and buy scopes from more reputable manufactures.  If you get enough evidence that Stellarvues cannot satisfy your need, there is no point trying to figure out what's wrong with them.  But if you really want to stay in the picky side of the user base, you may end up with being equally disappointed by other even more expansive scopes.  As I said earlier, perfect performance in FF corners is really hard to get.  At some point you may realize that it's your expectation that's not too realistic for today's technology.

In the case of the SVA130T, its guaranteed to be at least 0.95 strehl....does that say anything about the corners of a FF?


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