25 replies to this topic

[Merik]

Hello all,

 

This week i bought a pair of second hand Vixen 20x100 binoculars, see pictures below

I took some time to clean them and collimate the prisms

 

Then I tried to compare them to my Omegon Nightstar 20x80 last night. Both were on a tripod.

 

I see less cromatic aberration in the Vixen's but on Jupiter i could 'seperate' the moons (which were close to eachother) better on the Omegon 20x80

 

Also tested on fainter stars, but i couldn't notice any advantage of the Vixen 20x100 vs the Omegon 20x80, even while the Vixen should collect more light and thus see more fainter objects.

 

The manufacturer code is J-B251 J. Any info on this?

 

Thanks in advance

 

Greetings, Mark

 

[ihf]

Also tested on fainter stars, but i couldn't notice any advantage of the Vixen 20x100 vs the Omegon 20x80, even while the Vixen should collect more light and thus see more fainter objects.

Looking at the Pleiades in the big city (bortle 8) my Canon 18x50 and my APM 20x100 are reasonably close in how many stars they show. Except that the background in the Canon is stark black and the APM is dark blue due to the light pollution. At a dark site (bortle 2) both show a black sky background and the APM 20x100 more little stars everywhere.

 

I assume the same effect happens more subtly between your Omegon 80 and your Vixen 100. But maybe the Omegon is multi-coated and the Vixen seems from the pictures is not, then they might be pretty close to each other in light collection performance. You could take them outside on a sunny day and study the reflections of the sun in both objectives next to each other. The darker one lets more light through. At the end of the day there should still be a slight advantage to the Vixen, but maybe not enough to justify the extra size/weight.

[jrazz]

Bigger aperture gets you better contrast (all else being equal) but it can't make the image any brighter. To see fainter stars you really need more magnification.

[miniqtone]

Hi Mark! How did you find those fine binoculars?? Craigslist?

[Merik]

Thanks for the explanations. I will test them a little bit more

I bought them in the Netherlands, Europe

[Rutilus]

I've had a pair of these for the last 25 years. Vixen catalogue #1413.

The J-B251 code is Toho Opitcal Mfg.Co.Ltd Tokyo. My pair does not get

much use now, due to my bad back.

A few months ago I took them apart for a good clean. Went back togther

very easily and was able to adjust the prisms.

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[Terra Nova]

Bigger aperture gets you better contrast (all else being equal) but it can't make the image any brighter. To see fainter stars you really need more magnification.

This is not entirely correct. While equal exit pupils exhibit equal overall brightness, (exit pupil = aperture divided by magnification, hence 10x50 and 20x100 binoculars both have 5mm exit pupils of equal brigntness), the limiting magnitude of the dimmest star that can be seen by a particular optic is determined by the light gathering ability of the objective which is a function of the square of the aperture.

 

Comparing 80mm and 100mm objectives, the light gathering potential of the 100mm objective compared to the 80mm is (10² / 8² = 100/64 = 1.5625), ie the light gathering ability of the 100mm is one and a half times that of the 80mm. In terms of limiting magnitude, the dimmest star the 100mm objective can see is ~M12.5 whereas the limiting magnitude of the 80mm is ~M12. Since stellar magnitude is a logarithmic scale, that 0.5M difference makes a bigger difference than it seems, (the 12th magnitude star is 2.5x brighter than a 13 magnitude star). 

[Merik]

Great info, thanks
What is your opinion as a long time user of these binoculars?

While comparing with the Omegon 20x80, which is not so expensive, i mentioned that the stars look sharper like pinpoints in the Omegon

Maybe i have not found the perfect focus on the Vixen. The right eyepiece focus is completely turned clockwise till the end to show me a focused image. But i wonder if its completely in focus.. any tips on this matter? Is it possible to adjust the right eyepiece in a certain way?

I have not had that problem in any other bino's

Thanks

[pat in los angeles basin]

Are you nearsighted? Is there more correction needed in the right eye than the left eye? I'd try using the left eye on the right side  to see if it comes to focus . Then try the right eye on the left side and see if it comes to focus at approximately the same correction marking. It's possible in some binoculars to adjust the placement of the objective further back to compensate for such a correction but it's not a simple feat unless you have done it before and it affects collimation which adds to the complexity.  Pat

[Merik]

I am not nearsighted. If i try the left eye on right side and right eye on left side, i can come to a sharp image. For the right eye on left side i have to move  the focuswheel a  bit though.

 

But i am not sure about perfect focus. The focus range is quite broad. For example if i move the focuswheel or the individual focus on the right eyepiece, i still see sharp for quite a while. My eyes compensate i guess.

 

In general it is hard to find the sweet spot. Maybe i need more correction on the right eyepiece focus

[ihf]

Do you have access to a Bahtinov mask, which could help you achieve focus?

[Merik]

That is a great idea, thanks. I do not have it right now but i could buy it

Which size would i need to make it suit? Just a 100mm or closer to 120mm?

[ihf]

They work over a range of sizes. The main difference is how many slits there are, IIUC finer masks are for cameras, coarser for telescopes. Closer to 120mm. But if it can go smaller then it can be used by other binoculars like your 80mm or telescopes. I think you can always make one larger by adding a larger dark ring of paper around it, as long as you keep the mask reasonably centered. Maybe this one, but I think it ships from China? Or print one on foil or cut one out from paper.

Edited by ihf, 28 November 2022 - 01:40 PM.

[eyespy]

Hi Mark,

 

I have had a pair of these Deluxe 14x80’s made by Vixen since 1991 and they have performed admirably. If you have found a good pair then I doubt that you will regret it.

 

Doug…..

 

 

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Edited by eyespy, 29 November 2022 - 06:53 AM.

[Merik]

Great!

Today I received my bahtinov mask for the bino

Now i need to wait for clear skies!

 

To be continued..

[Merik]

I tested it with the bahtinov on Jupiter and that shows i can just barely get in focus. So that is not the problem i guess.

After that I went to look at Jupiter without the bahtinov and it shows some kind of reflection spikes around Jupiter, it is not just a perfectly round dot. Does that sound familiar with any of you?

The same on bright stars but less reflection spikes

[eyespy]

Hi Mark,

 

Sounds a bit strange. Photo or drawing of what you are seeing might help.  Reflection spikes ? Visible on both sides ? Do they rotate if you rotate the binoculars ?

 

Doug…..

[Merik]

Jupiter is like elongated and stars are not pinpoints

I couldn't take a picture but i tried to draw the effect on Jupiter

A bit exaggerated

 

 

 

 

[Rich V.]

Astigmatism can elongate the way planets appear.  It can be in the optics themselves or your eyes.  Definitely a cause of spiky looking planets.  Does the elongation of Jupiter that you see change orientation 90° on either side of best focus?

 

Years ago, I remember reading reports of 1990s vintage Vixen Japan binos being well built mechanically but having some variability of optical quality.  It sounds like your Omegons come to a finer, more detailed focus.

 

Rich

[Merik]

Thanks, i will test that.
Is there any solution for astigmatism?

Edited by Merik, 08 December 2022 - 03:11 AM.

[ihf]

Thanks, i will test that.
Is there any solution for astigmatism?

If it is in the instrument then there is no easy solution for astigmatism.

 

If it is in your eyes your optometrist may prescribe glasses. The Vixen may have enough eye relief to observe with glasses. Or use the cylinder part of the prescription from the optometrist to basically make glasses to fit the eyepieces. This often reduces they eye relief needed. Glass glasses work a bit better than polycarbonate/plastic ones.

 

I did experiment a bit with correcting eye astigmatism (-1.75) with contact lenses but that doesn't work well for me with 20x100 instruments. The exit pupil is too large for what the contacts provide for me.

 

Take a look at

https://www.televue...._page.asp?id=54

https://televue.com/...ht-astigmatism/

[eyespy]

Hi Mark,

 

Are you sure you were not looking at Saturn ? !! 

 

Doug…..

[Merik]

Lol, it was Jupiter! My drawings are not rings, they are some kind of spikes

 

Yesterday i had the opportunity to test again compared to the 20x80 omegon

 

With the Omegon 20x80 i was able to see a brown dust lane on Jupiter, which i was not able to see on the Vixen 20x100 because of the astigmatism

 

The astigmatism 'spikes' change when i go in and out of focus. Also they change when i rotate the bino

 

Also bright stars show a lot of spikes, like this: 

[ihf]

Do you see a cross in each eye, or a line in each eye that together forms a cross?

 

Sounds like the prisms or something intruding in the light path could be causing this. Look from the objectives for lines or corners.

[Merik]

Thanks, i will have to test that again.
When i look through the objectives, the prisms look good. They are not completely clean, some dust spots, but they are not damaged/scratched or anything