An Old Trick For My Binoculars

[Refractordude]

While making another three inch aperture mask for my 120mm f8 achromatic telescope, I thought I would make a pair for my 20x80 binoculars. This is the first time masking my binoculars. This evening's observation plan was originally all about Venus. I waited about two weeks for the weather to clear. So I was really excited to set things up and start observing. The smaller aperture mask that came with my telescope, and a moon filter gave me the best view of Venus. I enjoyed the tiny half moon looking dense clouds of Venus very much.

Looking at Venus with the binoculars showed a out of shape blob of colors. Adding the aperture masks showed the half moon shaped Venus with a little green flare. Diffidently an improvement with the 50mm aperture masks. I will make another pair at 40mm, and try them out Wednesday evening on Venus after work. Low magnitude brighter stars no longer showed a slightly out of focus look. Most of the the stars in Pleiades were tight. I never looked through a pair of ED apochromatic binoculars. If ED apochromatic binoculars are as good as my $125 20x80 binoculars with the 50mm aperture masks, they are diffidently worth it. Especially since they would have 30mm more aperture. Right click the images.

[Refractordude]

Forgot to mention that while using the 50m aperture masks on the binoculars. The moon was a lot sharper with just a very thin line of light green on one side, and very thin line of blue on the other side. The thin lines of blue and green were barley visible. Both lines would disappear if I looked at an angle.

[helicon]

Very interesting project with some good results.

Can't believe it but I have never had Papa John's pizza...

[aae0130]

Very interesting project with some good results.

Can't believe it but I have never had Papa John's pizza...

I had it once. Tastes like frozen pizza. However, being from New Jersey, I may be a pizza snob.

[j.gardavsky]

This is a very good experiment!

Masking down the aperture reduces the spherical aberration and spherochromatism due to the light rays, which experience a oblique incidence when far away from the optical axis of the achromatic doublet.
The spherical aberration and the spherochromatism increase both with the clear aperture diameter and with the speed of the refractor.
The green fringe you can still see, looks to me like a residual from the ordinary chromatic aberration

The 2/3 aperture masks seem to be a quite efficient rule of the thumb.

Thank you for sharing,
JG

[IvanM]

While making another three inch aperture mask for my 120mm f8 achromatic telescope, I thought I would make a pair for my 20x80 binoculars. This is the first time masking my binoculars. This evening's observation plan was originally all about Venus. I waited about two weeks for the weather to clear. So I was really excited to set things up and start observing. The smaller aperture mask that came with my telescope, and a moon filter gave me the best view of Venus. I enjoyed the tiny half moon looking dense clouds of Venus very much.

Looking at Venus with the binoculars showed a out of shape blob of colors. Adding the aperture masks showed the half moon shaped Venus with a little green flare. Diffidently an improvement with the 50mm aperture masks. I will make another pair at 40mm, and try them out Wednesday evening on Venus after work. Low magnitude brighter stars no longer showed a slightly out of focus look. Most of the the stars in Pleiades were tight. I never looked through a pair of ED apochromatic binoculars. If ED apochromatic binoculars are as good as my $125 20x80 binoculars with the 50mm aperture masks, they are diffidently worth it. Especially since they would have 30mm more aperture. Right click the images.

Hello

did you manage to do it for the binoculars? If you have a picture of it it would be amazing What does actually the aperture mask does for the binoculars? And how do you attach it to binos if you make it yourself?

[Refractordude]

While making another three inch aperture mask for my 120mm f8 achromatic telescope, I thought I would make a pair for my 20x80 binoculars. This is the first time masking my binoculars. This evening's observation plan was originally all about Venus. I waited about two weeks for the weather to clear. So I was really excited to set things up and start observing. The smaller aperture mask that came with my telescope, and a moon filter gave me the best view of Venus. I enjoyed the tiny half moon looking dense clouds of Venus very much.

Looking at Venus with the binoculars showed a out of shape blob of colors. Adding the aperture masks showed the half moon shaped Venus with a little green flare. Diffidently an improvement with the 50mm aperture masks. I will make another pair at 40mm, and try them out Wednesday evening on Venus after work. Low magnitude brighter stars no longer showed a slightly out of focus look. Most of the the stars in Pleiades were tight. I never looked through a pair of ED apochromatic binoculars. If ED apochromatic binoculars are as good as my $125 20x80 binoculars with the 50mm aperture masks, they are diffidently worth it. Especially since they would have 30mm more aperture. Right click the images.

Hello

did you manage to do it for the binoculars? If you have a picture of it it would be amazing What does actually the aperture mask does for the binoculars? And how do you attach it to binos if you make it yourself?

The aperture mask increases the focal ratio. The higher the focal ratio the better the image with achromatic scopes/binoculars. I got the idea from this website https://10minuteastronomy.wordpress.com ... refractor/ For example my scope is a 1000mm long f8 with 120mm of aperture. I use a 3"/76.2mm aperture mask that turns my scope into a f13 with 76.2 mm of aperture. Divide 1000mm by 76.3 and you get 13. I would bet that my 3" masked aperture does the same/equal good job on the moon as a 3 inch triplet refractor. I get absolutely no false color. The website I have listed does a better job at explaining this technique.

The first post has the images of the masks. I just snug fit them onto the front of the lenses.

[IvanM]

Whew, it's quite a mathematics for me I tried to calculate mine 10x50s binoculars f.

If I understood corectly, I measured the lenght from eyepiece lens to objective lens (excluding the rubber piece around it). It is 145mm for each "tube".
I divide it by 50mm objective lense size and the result is f2.9

Then I made aperture mask with 20mm whole in the middle. Then i divide 145mm by 20mm and the result is f7.25mm with the mask on.

I tried it while watching the super moon tonight The difference was a bit less bright picture and slightly more detailed picture, but nothing spectacularly better. I guess it works better on the bigger telescopes and binoculars, but please feel free to correct me.

Thank you for the advice

[DeanD]

Whew, it's quite a mathematics for me I tried to calculate mine 10x50s binoculars f.

If I understood corectly, I measured the lenght from eyepiece lens to objective lens (excluding the rubber piece around it). It is 145mm for each "tube".
I divide it by 50mm objective lense size and the result is f2.9

Then I made aperture mask with 20mm whole in the middle. Then i divide 145mm by 20mm and the result is f7.25mm with the mask on.

I tried it while watching the super moon tonight The difference was a bit less bright picture and slightly more detailed picture, but nothing spectacularly better. I guess it works better on the bigger telescopes and binoculars, but please feel free to correct me.

Thank you for the advice

Hi Ivan.

You have the right general idea, but binoculars have prisms inside which lengthen the light path. Also, the focal length of the objective lens is from the lens to the point (actually a plane) where it brings the light into focus from infinity. The eyepiece then focuses on this point. So unless you know the focal length of the eyepiece and the thicknesses of the prisms it is pretty much impossible to measure the over-all focal length in binoculars without unscrewing the front lens and measuring it independently to the rest of the binocular. Most binoculars are probably around f5-f6.

Also, if you want to put an aperture mask on 50mm binoculars, I would suggest nothing smaller than around 35mm (around 2/3 of the aperture as JG suggested); otherwise the image is too dim as you noticed, and the actual resolution is a lot less.

Happy viewing!

Dean

[John Baars]

Yes, it is a very old trick. First seen in the seventeenth century and applied by telescope-makers of those days. Christiaan Huygens, the discoverer of Saturn's moon (Titan) used several 60-65 mm diameter single lenses, stopped down to less than 40 mm. (2/3)
As a boy I used a 60 mm F1000 mm eyeglass lens in a cardboard tube , stopped it down to even 20 mm , and "discovered" the rings of Saturn with it.

[IvanM]

Thanks everyone