ED82, any chart to test if the optics are a good sample? (1 Viewer)

[birdwatcheryes]

Been thinking about this for awhile. Has anyone come up with a test chart to test lets say the 75x DS fixed eyepiece and the 30x DS eyepiece to determine if the sharpness is on the higher or lower side of the scale as I've read here often about sample variation?

 

[wllmspd]

You can find resolution charts online, you could print one out and then nail it to a suitable spot far enough away for testing. You’d need to do some sums to work out what you’re expecting, so you only resolve a few of the features.

Peter

 

[birdwatcheryes]

I have one of those charts that I use for my binoculars but is there any benchmark as to what I should be resolving at around 100 yards at 30x and 75x?

Right now the only benchmark I have is that my friend lives over 1/2 mile away and told me to spot his house and tell him what I see, so I did that last night and told him I see he has his tv on and gave him a play by play report about a hockey game I saw in progress That was with my fixed 75x DS eyepiece. Could easily read the numbers on the players shirts as well.

I just did a google map calculation and the house is exactly 0.435 miles away or .7 km, so I was a little off.

 

[wllmspd]

You are looking at at how close the scope can come to the Rayleigh criterion theoretical resolution. The eyepiece will likely affect it and a higher power will help you resolve finer detail that will help determine how fine detail the scope can. Some people assess binoculars by adding multiplier lenses to provide more magnification to be able to see details fine enough to check performance.
A quick google check provides the smallest expected physical size resolved as 1.22x wavelength x distance / aperture.

Doing the maths for an 80mm scope and your friends house and assuming green light 500nanometer wavelength, gives around 0.5mm, so plenty good enough to watch TV as you did.

Peter

 

[birdwatcheryes]

Thanks Peter, I'll do some reading about the RCTR that you mentioned to understand and test my scope.

 

[wllmspd]

Apologies, but of finger error on the calculator, should be 5.5mm…. Power of 10 out… thanks to those who noticed!

Peter

 

[birdwatcheryes]

You can find resolution charts online, you could print one out and then nail it to a suitable spot far enough away for testing. You’d need to do some sums to work out what you’re expecting, so you only resolve a few of the features.

Peter

The chart below is the one I've been using for all my binoculars. I'm thinking of setting it 100 yds away first to test the 30x and 75x eyepieces of the ED82 and then keep moving it further maybe 50 yards at a time until I can't resolve the vertical lines top and bottom at the ends. That should give me an idea I think.

 

[Hermann]

Do a star test. You'll find descriptions of how to do it here on the forum.

Hermann