Home Forums Hunting & Shooting Hunting Optics Engineer in physics, master's degree in OPTICS INFO

This is what info an old hunting friend told me so I'll pass it on. Some or many of you may know this already.

Lens quality is discovered by viewing distant images of say pine trees. Don't let your eye go to the center of the lens but look at the clarity of the perimeter of the lens. Set the unit on a tripod so it's not jumping around with your hand. If it's a variable power, change the power and see if anything in clarity changes at the outer edges. Your eye normally goes to the lens center and most scopes do OK here.

Last weekend my friend and I were visiting and I asked him about scopes. Last year I'd read an article in a hook and bullet magazine that rated optics and the gist was that for the money, the Brunton 18x38x50 was a good buy. So I went to Sportsman Warehouse and laid down $500 +/- for what I thought was a good spotting scope (on sale BTW).

Well, it's OK but I wish I could have had a chance to do my own test as the Brunton is NOT very clear at the edges. Understand, I'm not the pro here but I wish I'd asked my friend before buying a spotting scope.

For what it's worth he said the greatest advances in optics have been in the lens coatings lately. What he does is put his new scope at room temperature into the freezer. I haven't done that with the Brunton but I wonder how different that is than taking a scope from a warm tent in the wilderness and putting it in a saddle bag and going for a horse trip up a mountain at zero dergees. Anyone ever thought of doing this ?? <img src="/ubbthreads/images/graemlins/confused.gif" alt="" />

Well, the lack of replies tells me this guy is all wet.?? I'm not the 'horse's mouth' here but I thought it would be some oats to chew on. Evidently NOT....interesting..... <img src="/ubbthreads/images/graemlins/confused.gif" alt="" />

I don't think he's all wet. He measues clarity pretty much the same way i do. I haven't tried the warm to cold thing, but apparently its a way to figure out of the scope is fogproof.
I have a Burris spotter and I can't see 22 calibre holes past 200 yards because it's not clear enough past 30 power.

If you want to check the resolution on a scope or binocular, the easiest way is to use a chart like this:

http://www.sinepatterns.com/images/USAF---XL-target.gif

As you get farther from the images, at some point the bars blend together and you can't distinguish the vertical pattern from the horizontal. The image just looks like a grey square.

I don't understand what you are testing for by throwing a scope in a freezer. To see if it gets cold??

Freezing or cooking that Brunton won't help it a bit. Next time your friend should read these and other webpages and not the factory write ups. Bruntons are ok, if you want to spend a lot of money for a mid range product.

As far as edge distortions, that is only one parameter I look at for optics, and not a real important one. I like high contrast, great low light views, depth of field and field of view. If my binos or scope have some edge distortion, and they have a great center (80%), then the edge distortion can be lived with. This is far better than having a in-focus flat field (no edge distortion), and not being able to much around sunrise, sunset. I have noticed that when I am doing serious glassing, I do not look through the edges much at all, I look primarily through the center.

http://www.betterviewdesired.com/Test.html

scroll down about halfway to

Resolution and general optical quality:

for objective ways to compare optical quality.

--Mike

To All,
I read and digested your input. Had my eyes checked recently and for an 'oldster', they're great. Love those contacts though. <img src="/ubbthreads/images/graemlins/grin.gif" alt="" /> Sure, light gathering and field of view are the main considerations along with clarity. I hunt with optics rather than travelling through the country whenever possible. Saves gobs of time provided the country is suitable.

The freezer issue IS to test them for sealing. The bit about travelling in airplanes was new to me AND for sure my binocs will be better taken care of. Thanks for your thoughts. <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />

Idahochukar,

Another good optics review can be checked out at: http://www.holgermerlitz.de/dialyt10x40.html

Good Luck

for me the edge clarity is very important. That was my biggest dissapointment on the Leice 10x40 geovids. Other guys rave about them. I say that the most experienced glassers use a method that is learned from practice and it is that you put the optics on a steady rest and move your eyes around the FOV instead of moving the optics. In this manner you can pick out movement much better. This is why guys living and hunting the desert talk a lot about edge clarity, because they usually are glassing farther.

Evaluate not only the performance at the edges in normal lighting, but the performance under low light conditions. Under bright lights, your eye's pupil contracts to mask out excess light. It just so happens that the light masked off comes from the edges of the optics, so in bright light, you're only evaluating the quality of the central portions of the optics (as well as overall correction of abberations for the optical design), even at the edge of the field of view.

Andy

I use my binos in the mountains watching across ravines/canyons for deer. I also try not to move my whole head too much, and try to section the mountain up, and check each section as well as I can. If a section is away from the center, I will move my head slightly. I am too lazy to pack in a tripod for a better view. I rarely take hard long looks near the edge, as it causes me too much eye strain. I use the edges for observing movement (hopefully). That said, have a real flat field in any optics is nicer and less disruptive than having slight edge distortion. I will still take a better low light bino with slight edge distortion over a lesser low light binow with a better flat field effect.

I just put up a newspaper at different distances and then set the scope up and see which one will let me read the papers at the greatest distance. It is a good test for late in the day or early morn and you will find out how good a scope is really quickly. Read clear to the edges of the paper. I'm sure there are more "scientific" test but give it a try.

I have done something similar to using the newspapers. And it is an excellent quick way to do scope comparison without getting at all technical.

At higher powers one must be careful about windy conditions, or sunny days where ground heating obscures relative resolution, and such.