29.05.2020 Vixen 90mm v Vortex Razor 85mm. Pt.1.

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Friday 29th 58F in bright sunshine. The following images were taken with my Lumix TZ7. Not through any telescope.

I still have some doubts about the true optical quality of the Vortex Razor 85mm. Yes, the view is impressively bright and sharp at 27x but it certainly gets softer with increasing power on the zoom.

So I set up my decades old, 90mm f/11 Vixen refractor alongside it on another tripod. As before, my target was the same, printed A4 instruction sheet with normal and bold black text and some drawings. Now looking crumpled after being caught by the wind.

I fitted a Baader 1.25" erecting diagonal to the Vixen to give them both the same correct left/right/erect view. The nearest useful power I had in 1.25" eyepieces for the 1000mm Vixen was a 20mm for 50x. I tried a no-name Chinese Plossl first and then settled on a secondhand, Meade 4000 series Plossl.

I set up both telescopes as closely together as possible and at exactly the same eyepiece height. Though I tried hard, I could not quite make a binocular out of the eyepieces. Because the telescopes got in each other's way. The Vortex was set to 50x on the zoom ring and this closely matched the Vixen. I was very careful to check the size of the A4 matched as seen through both instruments.

First I tried the target at 24 meters. Again, but it was too close to clearly separate them on image quality. So I put the target A4 on its own tripod outside the gate at 38 meters.  This is my longest sunlit line of sight while the telescopes remain inside the garden. I considered sunshine important to have good light [and some partial shade from a hedge] on the target.

The difference in the image colour was obvious as far as the normal, white duplicating paper of the target A4 was concerned. The Vortex was colder white with just a hint of violet. The Vixen rendered the white paper in a slightly warmer tone but still white.

I was surprised how the sun was already causing heat waves in the image. So that the text was not continuously sharp. It was slightly easier to read the bold text in the Vixen. Which, strangely, seemed less perturbed by the heat currents.

The Vixen is an old, Japanese made achromat. With absolutely no pretensions to being ED or APO. It has only a "middling" focal length rather than a classical F:15. So it is not as well corrected for false colour as instruments with longer focal lengths.

Vixen achromats have a good reputation but that is all. Mine is old and battered. Bought secondhand, years ago. I have no idea as to its true age. The objective is dusty inside and out with a small flake/chip from an accident caused during cleaning years ago.

My eventual, 38m target distance was well chosen to make reading the normal sized text really difficult.  It took real concentration to read the smaller text as it went in and out of focus in the warmth. In both 'scopes the text looked more like magenta than the target's normal, printed, jet black. The Vixen won on contrast and legibility.

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