31.05.2020 Vortex Razor 85mm and its exit pupils.

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The human eye has a pupil size depending on age and the brightness of the surroundings. In daylight that might be only 3mm. This sets a lower limit on the power of telescopes.  Go too low and most of the expensive, objective aperture is literally thrown away! Unless, of course, you increase the power to match the telescope's exit pupil to your own.

Elderly people have smaller pupils so greater aperture is a mixed blessing during daylight hours. The light passing through the telescope will also affect your pupil size.

So, is the huge eye lens of the Vortex simply a styling fetish to trap the unwary buyer? It seems that large eye lenses are more forgiving of poor eye alignment with the eyepiece. It avoids dark patches in the image [due to eye misalignment] and allows a larger field of view. So nothing to criticize there. Some "high end" binoculars have 24mm eye lenses.

How useful is that relatively large, 85mm aperture, to anybody but the very young 'scoping at dusk?

Aperture/Magnification = telescope exit pupil.

85/27x = 3mm, 85/40x = 2mm, 85/50x = 1.7mm, 85/60x = 1.4mm.

That looks fine. At the lowest power of 27x the telescope matches an average daylight human pupil. So the full aperture is still utilized.

The elderly buying 7x50 binoculars are wasting their time and money. Their pupil will never match the 7mm exit pupil even in the pitch black of a cave! 10x40 makes far more sense. Though some prefer 8x40 for the lower power simply to avoid the risk of shaky hands. Bino clamps are available to allow the binocular to be tripod or or monopod mounted for stability.

It is quite shocking how stabilizing a binocular will increase the detail which is visible. The detail is always there, but denied by one's inability to hold the binocular or telescope [image] perfectly still.

Try using a post or field gate for greater stability if one is nearby. The more distant a subject the steadier the binocular needs to be. The magnification acts like a huge optical lever. The longer the lever, the more the subject moves to the slightest shake of the hands!

Only at night, while looking at a dark sky with dim objects, will one need a larger exit pupil. Providing one is young enough to use it. The moon is bright though a telescope so the human eye pupil will not expand just because the sky is dark.

A wide angle eyepiece helps to give the impression that you are immersed in the view. Binoculars even more so. Smaller fields of view are more like looking at the view through a narrow tube.

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31.05.2020 Vortex Razor image quality.

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Sunday 31st. I was surprised, last night, when I was capturing stills and videos of the moon through the Vortex. Typically, for this time of year, the sky was still pale blue even though it was getting quite dark. The sun was well below the horizon by then but the sky hardly gets fully dark only a few, short weeks from the Longest Day.

My own view through the telescope of the Moon was actually quite pleasing for the very first time. Lots of lunar detail in the way of large and small craters. Though it lacked that "etched" look it really wasn't too bad at all. 

Usually, with an astro telescope, or binoculars of any quality, the detail is so mind blowing that you can't take it all in. It looks like that completely overblown, LG 4K OLED TV picture of a city at night. The deeper you look the more rewarding it becomes. Like fractal images which literally go on forever. Every crater has another crater inside the last. A visual Russian nested dolls situation, if you like. The Vortex Razor lacked that "special" quality. Which I find puzzling.

Despite the telescope and camera sitting on a rigid tripod in still conditions the images and videos still looked very washed out. As if light were leaking in from the sides. That had me thinking about possible causes:

The Razor's eye lens is huge in diameter. Could the moon and sky light be bouncing back and forth between my eye and the eye lens? Could the sky light be leaking in all around the sides of the huge lens ring? 

My Canon Ixus 117HS lens housing is absolutely ludicrously, chrome plated. Now imagine all that light flooding through the telescope and bursting out of the huge eye lens.

Where is it all going to go? It can't all be sucked in though the small camera lens like a black hole. So lots of light is going to be scattered back and forth between the huge eye lens and the chromed Ixus lens housing. 

The PS-100 system I eventually put together is light proof to the outside world. The nose of the camera lens is deliberately placed close to the telescope's eye lens. This is primarily to reduce vignetting. [Dark corners in the image.] I covered the open end of the Vortex eyepiece with the
camera switched on. There was no visible light leaking in anywhere.

The camera lens is hidden deep inside the huge adapter "cup" which fits over the Vortex rubber eyepiece ring. The picture shows the black packing strip I needed to match the two diameters. [57-61mm: Eyepiece and adapter ring.] The black, self adhesive strip must help to exclude external light.

The Moon's washed out appearance is a worry. It greatly reduces contrast. The huge eyepiece doesn't lend itself readily to conventional shielding with a "winged" light excluder.

My astro eyepieces did not suffer to the same extent while viewing the moon in broad daylight. They did not have the usual light excluders either. These eyepieces were roughly half the diameter of the Vortex. With the eye lenses sunken inside a tube.

The Vortex' is almost on the surface of the eye ring. This must increase its vulnerability. Though the outer rubber ring can be twisted up and down, to cater for spectacle wearers, it rarely stays still for long. The only way to keep it from rotating freely would be to tape it to the body! When raised, it must greatly improve light exclusion. Though not for the camera. Which demands the ring be fully lowered. The rubber ring has locking system but it is far too loose to be useful. There doesn't seem to be any means of adjustment when the outer rubber ring is removed.

I am going to try a black, felt ring to cover the Canon lens' shiny nose before I paint it matt black. Just to see if it stops multiple reflections between the shiny camera nose and eyepieces lenses. How I can do that for my own eye is another matter. Is my eye lit up by the  bright light exiting the huge eye lens and reflecting back and forth? It seems highly unlikely given the almost spherical shape of the human eye.

Or is it just the skylight leaking in all around my eye socket? That should be improved by gluing a black felt ring to the rubber ring around the Razor's eye lens. Even if it doesn't seal against skylight it will help to cut it down.

Or, I can easily experiment by covering my head with a black [shade] cloth while looking at the Moon in daylight.I added a crudely cut gasket of black rubber to reduce all risk of light intrusion.

Adjusting the camra back and forth on the telescope adapter produces some weird effects.

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