• Welcome to BirdForum, the internet's largest birding community with thousands of members from all over the world. The forums are dedicated to wild birds, birding, binoculars and equipment and all that goes with it.

    Please register for an account to take part in the discussions in the forum, post your pictures in the gallery and more.
ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Star Testing (1 Viewer)

If you can't decide whether the optics are under or over corrected you almost certainly don't have a problem. A real star test often shows a little softer rings outside focus from air turbulence somewhere in the atmosphere in front of the infinity focus point and correction also shifts with distance. Your images look too good to me to worry about.

Yes spotters can have pinched optics. Have you tried rotating your eye around the optical axis of the eyepiece while observing the oval shapes? That will tell you whether they originate in the scope or your own eye. If the oval rotates with your eye the astigmatism is coming from you. From your description this sounds like extremely mild astigmatism if it even is astigmatism.

Could be that you are now down to trying to decide whether your cherry scope is a good enough cherry. It might might be time to declare victory.

Henry
 
Hi Joker,

You need to do what Stanley Kubrick did. :)

Instead of renting lenses like everyone else, he bought ten of the finest lenses, tested them all and used the best of the ten for the movie with the second best as back up.

Unfortunately for Barry Lyndon he only had three of the Zeiss 50mm f/0.7 Planars so had less choice.

Only ten of these lenses were made with one remaining at Zeiss and most of the others used for photos of the back of the Moon taken with a modified Hassleblad.

If Saturn wasn't so low I'd expect to see Titan, Rhea, Dione, Tethys and Iapetus with the Swarovski STX 95.

I have seen Enceladus with a 150mm Maksutov from a town balcony.

At minus 10C one is likely to have temperature effects.

The large front elements could be affected by contraction.
It is possible the retaining ring could contract also, but I think it needs minus 30C or colder to be at risk of cracking an element.
The Kowa fluorite is probably more at risk.

One needs to be fully dressed with a scarf covering the mouth and nose.

Personally, I think the Swarovski you have is a keeper, but as I said, you could buy ten and maybe find a better one.

Regards,
B.
 
Last edited:
Hi,

yes, spotting scopes can have pinched optics, sometimes even only in cold conditions due to lenses sitting nice and snug at room temperature... a slight rattle is not sth to complain about with good optics...

As for the amount of SA - it's minuscule in the image you showed and you can really ignore it. At the level shown in your images, it might even have been introduced by the artificial star being a bit too close.. what was our distance btw?

Joachim
 
If you can't decide whether the optics are under or over corrected you almost certainly don't have a problem. A real star test often shows a little softer rings outside focus from air turbulence somewhere in the atmosphere in front of the infinity focus point and correction also shifts with distance. Your images look too good to me to worry about.

Yes spotters can have pinched optics. Have you tried rotating your eye around the optical axis of the eyepiece while observing the oval shapes? That will tell you whether they originate in the scope or your own eye. If the oval rotates with your eye the astigmatism is coming from you. From your description this sounds like extremely mild astigmatism if it even is astigmatism.

Could be that you are now down to trying to decide whether your cherry scope is a good enough cherry. It might might be time to declare victory.

Henry
Thank you, Henry. Probably a dumb question, but if the orientation of the oval shape changes from horizontal to vertical, even with my head in the same position but changing from inward defocus to outside of focus, would that not indicate that it is the scope? Sorry if that is a silly question.

Regardless, I will try what you suggested.

I do agree, though, that this scope is at minimum satisfactory, and probably above average. Color correction seems less than preferred, but good, all things considered. I really like it.
Hi Joker,

You need to do what Stanley Kubrick did. :)

Instead of renting lenses like everyone else, he bought ten of the finest lenses, tested them all and used the best of the ten for the movie with the second best as back up.

Unfortunately for Barry Lyndon he only had three of the Zeiss 50mm f/0.7 Planars so had less choice.

Only ten of these lenses were made with one remaining at Zeiss and most of the others used for photos of the back of the Moon taken with a modified Hassleblad.

If Saturn wasn't so low I'd expect to see Titan, Rhea, Dione, Tethys and Iapetus with the Swarovski STX 95.

I have seen Enceladus with a 150mm Maksutov from a town balcony.

At minus 10C one is likely to have temperature effects.

The large front elements could be affected by contraction.
It is possible the retaining ring could contract also, but I think it needs minus 30C or colder to be at risk of cracking an element.
The Kowa fluorite is probably more at risk.

One needs to be fully dressed with a scarf covering the mouth and nose.

Personally, I think the Swarovski you have is a keeper, but as I said, you could buy ten and maybe find a better one.

Regards,
B.
If only...I was made of money, I would not hesitate to try what you suggest. LOL. I know I am probably being overboard in this, but this amount of money is significant to me. I just want to be sure I am not going to end up with one of the "NON-cherry" examples. And, while I start to think I know what I am doing, in testing any of my optics, I just keep realizing how much I DON'T know.

So, if you are making fun of me, LOL, I agree with you. I am probably being paranoid. Also, I realize, at least I assume, that is all in good fun.

I appreciate your comment about the scope being a keeper. I am definitely agreeing with you at the moment. If there are serious issues, I am pretty certain that Swarovski would assist. Maybe, I am wrong, but that is what I am told. I very much like it. I really like Kowa too, but like the build, etc, better with Swarovski. I would have at least liked to have looked through the Harpia 95, but they were out. The 85 was very very nice. But, the digiscoping options with Swarovski, camera adapters, etc, made me go ahead with the Swarovski.
Hi,

yes, spotting scopes can have pinched optics, sometimes even only in cold conditions due to lenses sitting nice and snug at room temperature... a slight rattle is not sth to complain about with good optics...

As for the amount of SA - it's minuscule in the image you showed and you can really ignore it. At the level shown in your images, it might even have been introduced by the artificial star being a bit too close.. what was our distance btw?

Joachim

Thank you. There is definitely no rattle with this scope. I would expect to hear the same or similar rattle one would have with an air-spaced doublet refractor, is that correct?

Yes, I am sure that the Hubble star was too close. I used it indoors, so I was limited on distance, obviously. Distance was around 50 feet. I did the same test outdoors at 100+, and had similar results. The test with a real star the other night showed a more discernible set of rings on either side of focus. Neither was noticeably brighter on either side. The only real change I perceived was the fact that the fuzziness changed from inside to outside.

I REALLY appreciate the input on this star test. The last question for you guys, which again will be difficult to answer without actually looking through the scope, since my camera can introduce issues I am sure, is whether the color correction is ok. I think it is, but I see some fringing (Especially, around the Canada Goose's chest, which was at 70x and 40 yards away or so). I do not like it, but not sure it is worth risking something worse. I think the very very good outweighs the bad or mediocre here. Through the scope, things look great, in this area too, but I would prefer perfection...who doesn't.

Here are a few photos I took last night. Most of them were taken at 70x or close to it. I had to crop each of them to rid them of vignette. They were RAW images and finished with PS Express on my phone. It was thickly overcast, and 23 degrees F. So, higher ISO than preferred with a phone camera, but it is what it is.

Again, thank you for your input.
 

Attachments

  • PSX_20211207_173858.jpg
    PSX_20211207_173858.jpg
    3.3 MB · Views: 42
  • PSX_20211207_185701.jpg
    PSX_20211207_185701.jpg
    2.9 MB · Views: 41
  • PSX_20211207_193118.jpg
    PSX_20211207_193118.jpg
    2.9 MB · Views: 38
  • PSX_20211208_041506.jpg
    PSX_20211208_041506.jpg
    2.4 MB · Views: 40
Hi Joker,

The 90 degree shift in the ovals on opposite sides of focus happens whether the astigmatism is in the scope or your eye. Of course it could be in both so that the severity changes as you rotate your eye to positions that either tend to cancel or reinforce the scope’s astigmatism. At 120x your eye is not likely to show much astigmatism since the scope’s tiny exit pupil only covers a small part of the center of your eye’s lens.

Unfortunately you will just have to accept that the ATX does not correct longitudinal chromatic aberration is well as the Kowa Fluorite models and there is no significant sample variation for that aberration.
 
Hi Joker,

I am not making fun of you at all.

I am just pointing out the difficulty of finding a real cherry of any type of optic even from the best makers.

There are tolerances for everything. wedge, centration, figure etc.
There is no perfection.

I have seen and handled $1million lenses. They look glorious and are hand made.
They probably get as near to perfection as is possible.

Stanley Kubrick really understood lenses and I think always bought them and selected the best.
For him this was his way of working with attention to detail.

I have had a few nearly perfect optics, but there are very few.

Once I test an optic I then use it.
In reality the scopes I used were not the best, but the ones most suited to the observation.

I also found that short focus refractors were more sensitive to temperature effects than long focus refractors.
I suspect compact spotting scopes are even more sensitive to temperature than short focus doublets.

Regards,
B.
 
Hi,

regarding the star test, Henry has said what can be said without having a look ourselves.

The digiscoped images look good enough for sth shot at 70x and straight out of the camera/smartphone. Please keep in mind that any digiscoped stunners you see in the gallery here or elsewhere are:

a) usually taken at much lower magnification - usually 20-30x.

b) heavily postprocessed.

As for the CA, yes there is a little bit... in any scope... if you look hard enought... even in reflectors... then it's lateral CA from the EP...

Joachim
 
Why is SA so hard to correct in spotting scopes, or in other words; why does Swarovski do so well with ATX- models in that respect?

Good correction of SA has been well known fact for the ATX- models. As these pictures above regarding this sample, all ATX95 samples (total of 7) I have star tested also showed very similar inside/outside ring patterns. Some have had astigmatism, pinching or coma. With Kowa 883 and, as it seems, also with 99 model most of the samples have clear undercorrection of SA and of the samples I have seen, (4+2) even the best one was below what the worst ATX95 was.

This may be a silly question but I'm also wondering why the issue is allways (at least with all the samples I have seen) undercorrection; why isn't there also about equal amount of samples with overcorrection, if the desired outcome is somewhere between those?

Regards, Juhani
 
The lens designer or spotting scope designer has to make a choice as to which aberrations he or she wishes to correct.

With fast systems these choices are more selective.

Even before tolerances are considered it is likely that not all aberrations can be corrected.

That is why I prefer long focus doublet refractors or the occasional triplet long focus refractor. that I have used.
But these are from fixed locations.
I could not carry them in the field to watch birds.

For terrestrial use I used the 150mm Maksutov Cassegrain.
It was portable enough to carry in the car, but it was used in fixed locations usually by the seaside.

Are the Swarovski 115mm spotting scopes as well corrected as the Swarovski 95mm scopes or are they a step too far?

Regards,
B.
 
As to under or over correction.

In astro scopes temperatures dropping in the evening mean that some makers deliberately correct for temperature dropping rather than steady temperatures.

There is a well known case in New Zealand where the professional observatory scope of about 24 inch aperture charged for admission to visitors.

The superb telescope maker Graham Loftus, a friend of the fast motorcycle gentleman Burt Monro (World's fastest Indian), built a similar size Dobsonian in two days from scratch and put it in the car park near the observatory.
His scope gave much better images as it was corrected for falling temperatures.

His views were free, and the professional observatory then had few visitors.

Graham Loftus made hundreds of telescopes up to 36 inch aperture.

Regards,
B.
 
Last edited:
Hi Joker,

The 90 degree shift in the ovals on opposite sides of focus happens whether the astigmatism is in the scope or your eye. Of course it could be in both so that the severity changes as you rotate your eye to positions that either tend to cancel or reinforce the scope’s astigmatism. At 120x your eye is not likely to show much astigmatism since the scope’s tiny exit pupil only covers a small part of the center of your eye’s lens.

Unfortunately you will just have to accept that the ATX does not correct longitudinal chromatic aberration is well as the Kowa Fluorite models and there is no significant sample variation for that aberration.
Thank you, Henry. I appreciate your explanation.

I see your point about the CA.
 
Hi Joker,

I am not making fun of you at all.

I am just pointing out the difficulty of finding a real cherry of any type of optic even from the best makers.

There are tolerances for everything. wedge, centration, figure etc.
There is no perfection.

I have seen and handled $1million lenses. They look glorious and are hand made.
They probably get as near to perfection as is possible.

Stanley Kubrick really understood lenses and I think always bought them and selected the best.
For him this was his way of working with attention to detail.

I have had a few nearly perfect optics, but there are very few.

Once I test an optic I then use it.
In reality the scopes I used were not the best, but the ones most suited to the observation.

I also found that short focus refractors were more sensitive to temperature effects than long focus refractors.
I suspect compact spotting scopes are even more sensitive to temperature than short focus doublets.

Regards,
B.
Thanks, Binastro. Honestly, even if you were, it is deserved. LOL.

It really is difficult. And, me, being me, I have limited knowledge. Really, I think I have just enough knowledge to be suspicious of my optics, but not enough to confidently say either way about their "cherry-ness". So far, I think it holds up at 120x, so that is a plus. But, it is not as jaw-droppingly good as I would hope. But, then again, I am not sure any scope, spotter or otherwise, is that good. It probably is, but I am too ignorantly skeptical to realize it.

I am likely keeping this. The only thing I think the manufacturer might be able to do for me is to assess the possibility of pinched optics. I suspect, if anything, that this might be an issue.

I will probably use it every day. At least every day that my schedule allows, and as long as my shoulder(s) can hold up. Even as light as these scopes are, 5 miles with the fluid head, the tripod, and the scope on my shoulder, I can feel it at the end.
 
Hi,

regarding the star test, Henry has said what can be said without having a look ourselves.

The digiscoped images look good enough for sth shot at 70x and straight out of the camera/smartphone. Please keep in mind that any digiscoped stunners you see in the gallery here or elsewhere are:

a) usually taken at much lower magnification - usually 20-30x.

b) heavily postprocessed.

As for the CA, yes there is a little bit... in any scope... if you look hard enought... even in reflectors... then it's lateral CA from the EP...

Joachim
Good points, Joachim.

I definitely prefer to take photos at a lower magnification. I am sure that it would make a difference.

Also, the reality is, I probably should just get a camera if I expect better photos. A phone just doesn't really cut it.

Anyway, thank you all. It is much appreciated.
 
The lens designer or spotting scope designer has to make a choice as to which aberrations he or she wishes to correct.

With fast systems these choices are more selective.

Even before tolerances are considered it is likely that not all aberrations can be corrected.

That is why I prefer long focus doublet refractors or the occasional triplet long focus refractor. that I have used.
But these are from fixed locations.
I could not carry them in the field to watch birds.

For terrestrial use I used the 150mm Maksutov Cassegrain.
It was portable enough to carry in the car, but it was used in fixed locations usually by the seaside.

Are the Swarovski 115mm spotting scopes as well corrected as the Swarovski 95mm scopes or are they a step too far?

Regards,
B.
@Binastro
Is this what Mr. Christen was referring to with this statement:

“The dilemma for manufacturers then is, should we do our best to
produce smooth high contrast optics, or should we please the star
test crowd and do some hand aspherizing to get a more pleasing
out-of-focus star image? I can tell you that it is easy to do some
rough compensation with quick local polishing at several zones to get
more equal inside and outside star patterns, but the result will
almost certainly be a loss of contrast.”

Thanks,
Randy
 
Hi Randy,

No.

Roland Christen is I think referring to Apo triplet high quality astro refractors.
Here he says that the star testing fraternity have got it wrong.

He can reduce the quality of his scopes to satisfy their mistaken opinions regarding out of focus star images.

But I doubt that he would do this.

Regards,
B.
 
Hi Randy,

No.

Roland Christen is I think referring to Apo triplet high quality astro refractors.
Here he says that the star testing fraternity have got it wrong.

He can reduce the quality of his scopes to satisfy their mistaken opinions regarding out of focus star images.

But I doubt that he would do this.

Regards,
B.
@Binastro
Thank You, for your response and, please forgive another amateur question:
Do you think it would be possible for Mr. Christen to perform the “local polishing”, that he mentions, on a spotting scope to achieve a better star test or, does this only pertain to fast APO triplets?

Thanks,
Randy
 
@Binastro
Thank You, for your response and, please forgive another amateur question:
Do you think it would be possible for Mr. Christen to perform the “local polishing”, that he mentions, on a spotting scope to achieve a better star test or, does this only pertain to fast APO triplets?

Thanks,
Randy

Hi Randy,

Roland Christen is the head of Astro Physics, a legendary manufacturer of astro telescopes and mounts with a very long waiting list due to the hand aspherizing done by Roland to make his scopes perform best.

I am quite sure that he will not work on a spotting scope from another manufacturer. Even if he had time to do so, he probably would refuse to do sth. that degrades optical performance of the instrument in order to get a nicer star-test.
Because as Roland wrote, "...but the result will almost certainly be a loss of contrast.” And that is what we do not want.

Also working on already multicoated optics is quite problematic as the old coatings need to be polished off first - without altering the shape of the elements. Even if you found somebody to do it, you probably would not like the bill.

Joachim, who would save up and try to get an original AP stowaway 90/f5 if he really wanted the best of the best... it is also a worthy long term goal as these are kinda rare...
 
Hi Randy,

Roland Christen is the head of Astro Physics, a legendary manufacturer of astro telescopes and mounts with a very long waiting list due to the hand aspherizing done by Roland to make his scopes perform best.

I am quite sure that he will not work on a spotting scope from another manufacturer. Even if he had time to do so, he probably would refuse to do sth. that degrades optical performance of the instrument in order to get a nicer star-test.
Because as Roland wrote, "...but the result will almost certainly be a loss of contrast.” And that is what we do not want.

Also working on already multicoated optics is quite problematic as the old coatings need to be polished off first - without altering the shape of the elements. Even if you found somebody to do it, you probably would not like the bill.

Joachim, who would save up and try to get an original AP stowaway 90/f5 if he really wanted the best of the best... it is also a worthy long term goal as these are kinda rare...
@jring
Thank You, for your response.
I was only somewhat aware of who Mr. Christen was. The intent of my question was more technically motivated. I was interested to know if it was possible for someone like Mr. Christen to perform hand aspherizing on a spotting scope or, if there exists design differences that would only allow this to be done only on a astro triplet.
Or, if you removed the eyepiece from all of the following, what design differences would there be between a spotting scope, a astro doublet and a astro triplet (excluding correct image prisms)?

Thanks,
Randy
 
Last edited:
Any lens can be hand aspherized. Glenn LeDrew at Cloudy Nights described hand aspherizing the objectives of a cheap Bushnell binocular to improve their correction (at the cost of removing some of the AR coating).

For the last 20 years I've used one of Roland Christen's hand aspherized scopes for birding (92mm F/6.5 Stowaway). I would prefer a lighter waterproof scope for field use, but so far I haven't found one good enough to replace the Stowaway. My wife's Nikon Monarch 80ED actually comes close in terms of aberrations, but I want more aperture so the search goes on.

I expect Roland Christen's criticism of the star test cult's pissing contests in amateur astronomy applies to much more sensitive testing at very high magnifications which may reveal tiny (and perhaps misleading) differences in unfocused star images that we can't see at the exit pupils of 1.3-0.8mm we normally use for star testing spotting scopes. Using the Stowaway as a reference I've never yet seen a scope with substantial star test problems visible at around a 1mm exit pupil that did't also have image quality problems as a direct result.
 
Last edited:
Hi Randy,

It depends on the focal ratio, focal length and aperture.

My 100mm f/12 Pentax astro refractor, which was a Pentax demonstrator could easily be used on planets at 300x and tested well at 400x with no image breakdown.
This was a doublet, but I don't know if there was any hand aspherising.

My usual magnification was 200x.

I haven't seen a spotting scope this good.

The Ross 100mm f/15 uncoated triplet was essentially perfect. The most perfect refractor I had.

Rev. Dawes 6.5 inch approx long focus refractor was commonly used at 65x per inch of aperture, a bit over 400x on Jupiter, its moons and Mars.

An observatory 135mm f/16 refractor was essentially perfect.

I don't think that any consumer spotting scope is as good as these astro refractors at very high magnification.
What the spotting scopes provide is a wide field and compact size..

However, wide fields are obtainable with 2 inch fit and 3 inch fit eyepieces on long focus refractors, but the off axis performance might not be as good as on axis.

However, much of this nowadays is not so relevant as planetary observers use larger Newtonians and compound telescopes.

My 317mm Dall Kirkham certainly wasn't perfect but was used at up to 600x with no loss of image quality.

Horace Dall's 8 inch Maksutov Cassegrain at 400x through his attic window glass showed an image of Mars, which was quite unbelievable.

I have little time for owners of very high quality refractors, who never seem to present observations for publication, but brag about how very marvellous their telescopes are.

It is like the owner of a Leica I talked to, who had it dangling over his shoulder walking around town, but never semed to use it.

People love their Rolexes. I am very happy with a low price Timex that is still more accurate than Harrison's chronographs.

Regards,
B
 
Warning! This thread is more than 3 years ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.

Users who are viewing this thread

Back
Top