A beginner tries doing a star test (1 Viewer)

I recently purchased an Swarovski ATX95 spotting scope. Since I could not find one around here I did mail order and decided that I would try to verify myself if I thought I got a good example.

Now this is the first time that I have really tried doing this. I did not have a doubler or any magnifier to put on the scope but was really just looking to do confirmation testing and not trying to trouble shoot a questionable result.

My setup was using a small steel bearing set on a post about 35 yards away and shinning a 960 lumen cree led flashlight on it.

I was able to see clear rings on the inside focus and a little on the outside focus. I have attached some photo's that I took using a phone digiscope adapter and about 4x on the digital zoom. The view through the scope was a lot clearer than these pictures show.

Am I correct in saying that these seem to represent a decent sample? I know that perfect optics would have consistent inside and outside views, but that is unusual in a spotting scope correct?

I also have a Zen-Ray prime HD 20-60 spotting scope that I had side by side. The inside focus on that scope looked very much like the pictures that Henry Link posted from the "good" sample that has a impingement at about the 4:00 o'clock position, I could not get any decent pictures from that scope.

When I put them both on a USAF target I was able to resolve two additional elements on the ATX compared to the Zen-Ray both at 60x, when I bumped the ATX to 70x I was able to resolve two more elements.

So do these look like a good sample? It seems so to me and certainly has a much better view that the Zen-Ray.

The one thing that I have not cared for yet on the ATX is the hood which seems quite sticky and hard to move either in or out. I can't really move it with the scope case on. Maybe it frees up over time. As many have stated the zoom adjustment is fairly stiff and has a fair bit of turn, but I expect that.

Also if it looks like I'm doing anything wrong, please let me know. As I said I very new to all of this.

Thanks for your time and comments!

Scott

Hi Bob and welcome to BF.

It could be you have a good sample but are you able to redo the photos to show 6-7 rings (and adjust the exposure outside focus). Then it will be possible to see and say more.

Others with more experience than me will also be able to say more about any possible defects.

Hi Scott,
Welcome.

The scope seems to be well collimated.
LEDs are often blue rich and have a strange spectrum. So the photos may not show white light images.

Incidentally, very bright white LEDs are blue rich and harmful to humans and wildlife. They are being installed at incredible speed, without thought as to their long term damage.

With regard to visual testing, the main thing to consider is if your eyes have astigmatism. If at least one eye is free from astigmatism I would use that eye.
Also free from cataracts.

If your location has good Seeing, i.e. steady images I would look at Jupiter and its moons with both scopes and see how they actually perform.
The very best Seeing often occurs at 3 a.m. but Jupiter may be low then. Midnight should be good if temperatures are stable. I would leave the scope out for 20 minutes or more so it temperature stabilises.
One should look at high elevation targets, presumably the scopes have 45 degree angled eyepieces.
Unfortunately the magnifications are low. I would use about 150x to 200x to really test a good 95mmm scope.

Double stars are good tests.

The resolution on test charts relies also on your eyes.

Your scope is probably very good.
But, whether it is the best possible is difficult to say.
One would need to test several side by side.

Do you have an astronomy club locally, where someone could test it against very good refractors?

Hi Scott,

first of all, welcome to BF!

As dipped has noted one usually takes star test images with only a few rings visible. From your description and the images we see clear rings inside and some fuzzy disk outside which points to some degree of spherical undercorrection. A bit of undercorrectio quite common in refractors, my Kowa spotter has it too.

Also the inside image is not quite round which could be a sign of astigmatism. But since the outside image does not show a similar pattern with a 90 degree offset, it needs further investigation. It could also just be thermals. Did you leave the scope some time to cool down?

There is also quite a bit chromatic aberration visible, but this could also be due to excessive brightness of the artificial star and/or unequal white balance in both shots... my old Kowa certainly shows less even on a bright star like Sirius.

Joachim

First let me say thanks to everyone for your replies so far.

I tried to take some more pictures today but with no luck. It seems so very difficult to do to get these pictures!

While I can clearly see the rings when looking through the scope I can't seem to get them in a photo.

Of course I'm trying to learn how to use the digiscope adapter at the same time as trying to learn to start test. :^)

When looking at the rings they look to me to round, concentric and evenly spaced. But I do notice that playing with the phone can make it look oval or off centered.

Maybe I can try again when conditions are better here.

Thanks Again,
Scott

Hi Scott,
Maybe the phone camera is not perfectly aligned.
The second photo shows off centre flare outside the rings.

A simple double star for low magnification is Mizar in Ursa Major. This is usually easily be separated at 20x.

The double double star Epsilon Lyrae is a more serious test at 2.3 and 2.6 arcsecond separation.
But this might need 120x or more depending how good your eyesight is.
I don't know if 70x is enough to show the separate stars.

I suppose an astro eyepiece adapter is available for 1.25 inch barrel eyepieces.
Maybe 4mm or 5mm eyepieces. I would also get a 3mm eyepiece for high power.

Scott,

As others have said, it would be good to see images taken much closer to focus, with 3-8 rings visible either side of focus. That said, and knowing that photos tend to look much worse than what the eye sees, this looks very good. There's no signs of any serious problems, and to see rings this well defined also on the less defined side this far out of focus to me indicates that SA is not excessive. Problematic astigmatism would also make the ring patterns much more obviously oval. I also see no prism line in these photos.

Also your results with the bar target compared to the Zen Ray are better by enough of a margin to indicate a pretty good sample. Another indication is your rather obvious satisfaction with the image, which is evident in the way you write about it.

Kimmo

To echo other comments, this far in and out of focus, the rings are telling you more about alignment than quality of the figure or smoothness of the optics. Though I also agree that it's pretty obvious that nothing is terribly wrong.

In my experience star testing needs at least 35x/inch and 50x/inch is recommended. That would be magnification more like 150x-200x for your telescope, though of course it depends on your own acuity. Then there is the issue of interpreting star tests, which generally takes some practice and it helps to have a local guide. Suiter's Star Testing Astronomical Telescopes is a thorough and interesting book, but I still think it takes practice and guidance from someone who knows what they are seeing to do a proper diagnosis unless there is a very serious and obvious problem.

Given the design and intended use of this telescope, I would think that judging test patterns under a variety of light conditions might be more useful.

Alan