24.05.2020 Testing-testing..

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I thought it might be interesting to test the result of camera zoom on image quality. Sadly it was the same, heavy overcast as yesterday. Moreover I placed my test subject in the shade of a tree.

The test piece was an A4, black and white, crisply printed, illustrated guide to plumbing fittings. At 24 meters [26.25 yards] from the target the telescope was placed on its tripod.

Visually, I could easily read every word, at all powers. Just as if I was standing right in front of the target.

Then I attached the camera. Minimum camera zoom [5mm] caused vignetting. The dark corners only disappeared with increasing camera zoom.

Medium camera zoom [10mm] provided excellent sharpness and fine black and white images. Full camera zoom [20mm] produced violet print at all powers instead of black. This means that I must zoom the camera and telescope carefully according to my needs. 

Then I went back out again and retested at my maximum clear baseline of 56 meters [61 yards.] Hedges intervene on potentially longer lines of sight. It was windy outside the shelter of the garden so I had to peg the target firmly to the tripod. This caused some creasing. Visually I could read the bolder text at 60x but it rapidly became too small to read at lower telescope powers. It wasn't possible to read the normal text at this distance at any telescope power.

See applied image labels above for details of camera and telescope combinations.
All images reduced from 4000x3000 to 1000x750. [Left click for enlargements.]

Telescope's nominal power.......................................27, 40, 50 & 60x.  

Effect of camera zoom at 5, 10, 17 and 20mm:  Ixus 117 sensor is 11mm.
Camera focal length /sensor diagonal.                                                                                                                                             

  5/11 Reduces the telescope power by 0.45x..........12, 18, 22 & 27x.

10/11 Reduces the power by 0.9x............................24, 36, 45 & 54x.

17/11 Amplifies the power by 1.5x............................40, 60, 75 & 90x.

20/11 amplifies the telescope power by 1.8..............49, 72, 90 &108x!

The Ixus117 does not give actual figures for zoom on the camera screen. Just a slider and guesswork. The actual focal length has to be read off the details later. Which are provided by image cataloguing software like Google's Picasa. Microsoft's OneDrive Photos shows the basic details. Google Photos the same, under Info.

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