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sva130t pixel peeping on astrobin

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31 replies to this topic

#26 PirateMike

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Posted 12 July 2019 - 12:12 PM

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.

To be frank, I really don't think you should be making negative comments on one persons ability to produce,or not produce an image with a perfectly flat field, one that meets your criteria of how flat you think it should be. I would suggest that until you try and accomplish this very difficult, and possibly very expensive aspect of astro-imaging first, that you keep your comments in the realm of your own very limited to non-existent experience. Most of us here are not interested in what you think is the way that things should be, but more interested in learning how they actually are, and how to best deal with the shortcomings of non-professional astrophotography processes and it's equipment.

 

If you feel that the equipment (equipment that you never have used) is below your own lower limit of acceptability, then I suggest that you fork out the cash for the higher quality options as many of us have already done. No need to bash a company who has a lot of dedicated customers who appearently are very happy with their particular purchases. Maybe you should use your lack of knowledge and experience to design and build your own line up of telescopes, one with unparalleled quality, so that the rest of us can enjoy perfect optical quality at a very reasonable price.

 

Finally, get in the game or stop the negativity. We don't need a sideline "know it all" telling us how it should be. We are working and producing actual images in a world of reality.

 

 

Miguel   8-)


Edited by PirateMike, 12 July 2019 - 12:15 PM.


#27 PirateMike

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Posted 12 July 2019 - 12:14 PM

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?

no.



#28 whwang

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Posted 12 July 2019 - 12:18 PM

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?

Not at all.  It only applies to on-axis performance, unless Stellarvues specifically says it also applies to off-axis.



#29 joelin

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Posted 12 July 2019 - 01:58 PM

To be frank, I really don't think you should be making negative comments on one persons ability to produce,or not produce an image with a perfectly flat field, one that meets your criteria of how flat you think it should be. I would suggest that until you try and accomplish this very difficult, and possibly very expensive aspect of astro-imaging first, that you keep your comments in the realm of your own very limited to non-existent experience. Most of us here are not interested in what you think is the way that things should be, but more interested in learning how they actually are, and how to best deal with the shortcomings of non-professional astrophotography processes and it's equipment.

 

If you feel that the equipment (equipment that you never have used) is below your own lower limit of acceptability, then I suggest that you fork out the cash for the higher quality options as many of us have already done. No need to bash a company who has a lot of dedicated customers who appearently are very happy with their particular purchases. Maybe you should use your lack of knowledge and experience to design and build your own line up of telescopes, one with unparalleled quality, so that the rest of us can enjoy perfect optical quality at a very reasonable price.

 

Finally, get in the game or stop the negativity. We don't need a sideline "know it all" telling us how it should be. We are working and producing actual images in a world of reality.

 

 

Miguel   8-)

I wasn't making negative comments, I was merely responding to an earlier comment made by someone else about how getting a flat field is more so about the astrophotographers skill than equipment.

 

Then I said, what could have the astrophographer done? I inspected the astrobin images and the equipment list (assuming its correctly stated). The stars in the center were sharp indicating good focus and guiding. I was looking for more reasoned explanations for why the corners were they were they were. The focuser is also a feather touch 3" which I believe is of high quality so that eliminates the focuser. 

 

I never bashed the company at all. I read all over on CN about how Stellarvue is a brand with high quality and preimum telescopes and then many comments first page of this thread seems to give off the impression otherwise. 

 

I'm also getting a lot of conflicting information with Jerry's initial S&T review saying FF stars were very good in the corner and then some posts in this thread saying thats not a reasonable expectation.

 

I don't think getting emotional on this forum is necessary at all. All my comments in this thread have been objective, investigative and focused on evidence. 

 

Overall, I have no desire to bash anyone or any company. At the end of the day, I'm a bit tired of single telescope opinions. Theres just too many people who own a single cheap, midrange or expensive telescope and say this is awesome without truly comparing them side by side against something else under identical conditions. I just want some more objective information.  Where are the side by side comparisons of 1:1 crops of corners under identical conditions with different scopes? It seems that type of objectivity is elusive in this hobby. It's everywhere when it comes to other types of technology, including camera lenses and camera bodies, but not telescopes. 


Edited by joelin, 12 July 2019 - 02:09 PM.


#30 joelin

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Posted 12 July 2019 - 02:07 PM

Not at all.  It only applies to on-axis performance, unless Stellarvues specifically says it also applies to off-axis.

Then in the extreme case you might have that guaranteed very high performance but only within a very very tiny area on your sensor?...could be just an area of a single pixel...


Edited by joelin, 12 July 2019 - 02:08 PM.


#31 bobzeq25

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Posted 12 July 2019 - 07:24 PM

I wasn't making negative comments, I was merely responding to an earlier comment made by someone else about how getting a flat field is more so about the astrophotographers skill than equipment.

 

Then I said, what could have the astrophographer done? I inspected the astrobin images and the equipment list (assuming its correctly stated). The stars in the center were sharp indicating good focus and guiding. I was looking for more reasoned explanations for why the corners were they were they were. The focuser is also a feather touch 3" which I believe is of high quality so that eliminates the focuser. 

 

I never bashed the company at all. I read all over on CN about how Stellarvue is a brand with high quality and preimum telescopes and then many comments first page of this thread seems to give off the impression otherwise. 

 

I'm also getting a lot of conflicting information with Jerry's initial S&T review saying FF stars were very good in the corner and then some posts in this thread saying thats not a reasonable expectation.

 

I don't think getting emotional on this forum is necessary at all. All my comments in this thread have been objective, investigative and focused on evidence. 

 

Overall, I have no desire to bash anyone or any company. At the end of the day, I'm a bit tired of single telescope opinions. Theres just too many people who own a single cheap, midrange or expensive telescope and say this is awesome without truly comparing them side by side against something else under identical conditions. I just want some more objective information.  Where are the side by side comparisons of 1:1 crops of corners under identical conditions with different scopes? It seems that type of objectivity is elusive in this hobby. It's everywhere when it comes to other types of technology, including camera lenses and camera bodies, but not telescopes. 

Just too many variables.  It's not a conspiracy.

 

There's zero incentive for anyone to generate the data you want.  Too much time, too costly in other ways.

 

In the terrestrial world, it's far easier to generate that data, and there's a much larger market for it.  AP is _very_ different.

 

Think about it.  Would you want to do what's required to generate that data?  Why should anyone else want to?


Edited by bobzeq25, 12 July 2019 - 07:25 PM.

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#32 whwang

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Posted 12 July 2019 - 09:31 PM

Then in the extreme case you might have that guaranteed very high performance but only within a very very tiny area on your sensor?...could be just an area of a single pixel...

Arguments like this won't lead you anywhere.  I believe you should already know that field curvature and off-axis aberrations worsen the stars gradually from the field center.

 

There do exist many 100% corner crops of various optics, from lenses to scopes.  They just spread over many difference places, and not necessarily in the English-speaking side of the internet.  You have to look for them yourself.

 

This page can be also very useful:

https://www.telescope-optics.net

Also the book Telescope Optics published by Willmann-Bell.  They won't tell you about any specific brand of scopes.  But they can help you to build more realistic expectations on the off-axis performance of telescopes.

 

Good luck.


Edited by whwang, 12 July 2019 - 09:41 PM.



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