Alternative to Hyperstar

[Chris]

6 minutes ago, HiloDon said:

Had some clear skies last night and did a comparison of the Freestar and Hyperstar on my Evo 6 and Lodestar X2c.  All settings were the same.  M8 was the target.  If I tried to get better focus on the bright stars, the smaller dim stars would go out of focus.  

I'm someone can explain what's going on optically, but it's not good without Hyperstar.  First one is Freestar, then Hyperstar.

Thank you for doing this comparison  Freestar looks to be on the unusable side of things by the looks of it.

[AKB]

Well,that makes me feel better, since I have, indeed, just pressed the BUY button on a Hyperstar system for my C9.25.

 

[RobertI]

Thanks for posting your results Don. Those are pretty severe abberations, interesting to see what spherical abberation looks like though! Interesting phenomenon with the focussing too, would like to know why. Not sure I'll be trying funstar though. Thanks again for doing this.

[HiloDon]

I think this article explains things in simple terms.  The problem as stated by some earlier is an uncorrected spherical mirror.  It will cause spherical aberration equally across the entire field, even center stars.  That's why the Hyperstar lens is needed.

https://starizona.com/acb/basics/equip_optics101_spherical.aspx

[shirva]

Some pretty weird stars on the fun star,, more zoomed in compared to the hyperstar,, I wonder how the fun star image would has looked with less exposure time 

[HiloDon]

1 hour ago, shirva said:

Some pretty weird stars on the fun star,, more zoomed in compared to the hyperstar,, I wonder how the fun star image would has looked with less exposure time 

I do my focusing at five seconds.  It was just as bad.  The overly large stars are due to out of focus light from spherical aberration.  Exposure won't change that.

[Chris]

Shall we rename the Fun star to the Weird Star then?  

It's not as we all had hoped, but a worth while experiment and very interesting to see the effects of the very fast spherical mirror!

[Peter Drew]

Excessive sherical aberration IMO.   

[stash_old]

12 hours ago, HiloDon said:

I think this article explains things in simple terms.  The problem as stated by some earlier is an uncorrected spherical mirror.  It will cause spherical aberration equally across the entire field, even center stars.  That's why the Hyperstar lens is needed.

https://starizona.com/acb/basics/equip_optics101_spherical.aspx

Also this site http://hyperphysics.phy-astr.gsu.edu/hbase/ligcon.html#c1 

At least you tried. Where's an optician when you want one.

I notice on CN that there was also talk on why no competitive alternatives to Hyperstar are around - seems a guy at Starizona (who sell Hyperstar) owns the patent to the idea (Dont know if he bought it from Celestron Faster idea or his is different enough to be allowed a patent. 

I was once told by a good teacher  "don't be a sheep but always question what everyone assumes to be true even though 99/100 times they will be right and you will be ridiculed - the 1/100 will be worth it". 

Again Don thanks for the time you've spent on this subject.

 

[shirva]

6 hours ago, stash_old said:

Also this site http://hyperphysics.phy-astr.gsu.edu/hbase/ligcon.html#c1 

At least you tried. Where's an optician when you want one.

I notice on CN that there was also talk on why no competitive alternatives to Hyperstar are around - seems a guy at Starizona (who sell Hyperstar) owns the patent to the idea (Dont know if he bought it from Celestron Faster idea or his is different enough to be allowed a patent. 

I was once told by a good teacher  "don't be a sheep but always question what everyone assumes to be true even though 99/100 times they will be right and you will be ridiculed - the 1/100 will be worth it". 

Again Don thanks for the time you've spent on this subject.

 

Well said sir

[HiloDon]

Thanks, Stash.

One of the things I have noticed in this hobby is the lack of beta testing by the seller before the product is marketed.  Seems to be a common thing, especially with new cameras for EAA.  I enjoy the testing part of new astronomy equipment.  I try to be objective and identify the value and usefulness of a product, so others don't waste their money.  

There have been some ideas generated about Freestar that could make it work.  Nytecam has suggested an aperture mask that should, in theory reduce the SA significantly.  It's an easy thing to make, so I will try that next.  It won't be as fast, but it will have the wider FOV.  I'll report back.

Don

[alphatripleplus]

Don,

As I mentioned on CN, I am very grateful to see you doing the Hyperstar vs Freestar comparisons, as this exercise has been a real eye opener for me. It's great  that you enjoy the testing and are game to try and objectively test different people's suggestions with regard to the Freestar. I'm sure we are alll learning something useful from the exercise, and I'm hoping that in the future when others do camera comparisons, for example, they are just as objective as you are in this evaluation. Looking forward to seeing more results.

 

Errol

[elpajare]

Many thanks for your work, Chris.

[daslolo]

awesome test Don, thank you.

unacceptable for photo but maybe ok for visual, which requires other lenses to move the eyepiece off to the side

a guy on CN ran raytracing in OSLO and found an ok solution for about 60$: two meniscus

https://www.cloudynights.com/topic/599182-anyone-use-rev-imager-fun-star/?hl=%2Bmeniscus+%2Bfunstar#entry8320124