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Star test images, first attempt - how did I do? (3 Viewers)

4

4th_point

Well-known member
United States
I've tried star testing scopes for almost a year now, but only recently have I tried to take pictures. Anyway, if you would be willing to provide feedback on the quality of the images, or usefulness for identifying aberrations, I would appreciate it. My goal is to be able to capture good images from different scopes to share. I'm mostly interested in opinions of the images related to my technique, but would welcome comments on any sample defects that you see.

I used the following:

-digital camera
-spotting scope with EP @60x
-white LED + foil, with tiny hole
-indoors, across a few rooms (definitely some turbulent air)

I believe that the first two images below were out of focus away from the scope, towards infinity (inside of focus?). I did not alter the images in any way after capturing them with the camera.

Jason

ETA - I cropped the photos for easier viewing and so that they would show up in the post without having to open attachments.

DSC_0874 - Copy.jpg

DSC_0867 - Copy.jpg
 
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The next two images were from the same scope and setup but on the other side of focus, towards the scope (outside of focus?).

ETA - I cropped the photos for easier viewing and so that they would show up in the post without having to open attachments.

DSC_0879 - Copy.jpg

DSC_0878 - Copy.jpg
 
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I should mention that the camera captured various different pattern shapes, due to the air turbulence, so I took numerous photos and cherry picked ones that were representative of what I observed with my eyes. Just looking through the scope the patterns appeared static.

I mention that because the photos may show defects that might be my technique/setup and not the scope per se.
 
Here's another scope. Same setup as the previous, also at 60x.

This was out of focus towards infinity (inside of focus?).

DSC_0898 - Copy.jpg
 
Hi,

the images of the 2nd scope are quite useful and it seems to be a very good example.
The first set shows a little undercorrection and the rings are not concentric everywhere... which could be air currents or collimation problems.

As for technique, it gets better. less rings are good.

Joachim
 
Your technique looks fine. The closer you can get to the same number of rings on both sides of focus the better. 4-5 is good for Spherical Aberration, 2-3 for astigmatism. I'm curious about why you're experiencing air turbulence indoors? I have essentially none unless the heat or AC is on. Then a register in the floor about three feet from the 10m line of sight between the scope and the artificial star thoroughly ruins the image when it's blowing hot or cold air. The simple solution in my situation is just turning off the HVAC system.

What's the distance between the scope and star in your set-up? And what are the focal lengths and apertures of the two tested scopes?

Henry
 
Doorways create turbulence.

Unless the whole area is stabilised, perhaps at night.

Body heat also affects images.
I put an anorak on and a scarf around my mouth.

Heat from a kitchen is also troublesome.

Regards,
B.
 
henry link said:
Your technique looks fine. The closer you can get to the same number of rings on both sides of focus the better. 4-5 is good for Spherical Aberration, 2-3 for astigmatism.
Click to expand...
Thanks for checking out the photos, Henry. And the ring comments. They are helpful.

This test was only at ~45 feet but I sometimes can get ~70 feet with the right conditions. I have been experimenting with the size of the star (hole in foil) along with the distance too. I have noticed that some scopes appear to be under corrected at really close distances but seem fine at longer distances. A really small star seems to help with the closer distances but I am not sure why or that it applies to all scopes. Most of the scopes that I own have been tested numerous times at various distances just in case there is something amiss with a single test. I do have what I think is an excellent scope as a reference instrument that I use as well.

I don't know what the focal lengths are for the scopes. The first two are midsize scopes, but I have intentionally withheld details as I don't want to steer anybody one way or another regarding make/model based on my samples and technique. Eventually, I would like to share the star test and resolution results, along with subjective impressions. But I think that I should get a good handle on all that before posting such information.

I have several more scopes to test, and will post photos of those in this thread. And I'll probably retest scope #1. I'm not sure how interesting that is to anyone else, but I really like looking at star test photos!
 
Hello B.,

All three samples shown so far are midsize spotting scopes. Midsize to me is 60mm-ish. I also tested a compact (50mm-ish) and a fullsize (80mm-ish or more) but had problems with the air again. At least problems with the photos. Now that I think about it, maybe videos would be better for averaging.

Jason
 

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