Author Topic: A.O. focus (Read 941 times)

Lee D. · « **on:** August 28, 2003, 12:34:57 PM »

Can anyone explain why the focus is so critical on A.O. scopes? A regular 3X9 stays in focus from about 30 yards out but with the AO you have to focus about every 10 yards until you get to about 100.
Also, is there any good reason to not us a .22 scope on a high power rifle? I know that they are normally set for about a 50yd. parralax as opposed to about 150 for high power, but most of the shooting I do is under 100yds. I am short one high power scope right now and have a spare 3X9X42 .22 scope.

Dave in WV · « **Reply #1 on:** August 28, 2003, 01:25:21 PM »

Lee, I have a Leupold compact EER 3x9 and it stays in focus through out the different distances. I do have to keep the parallax setting close to the right distance. A .22 scope is not normally beefed up for heavy recoil but most are set up to take forward recoil from air rifles. A normal centerfire scope won't take the forward recoil. Dave

TheOpticZone · « **Reply #2 on:** August 28, 2003, 03:43:46 PM »

Rifle scope with out an Adjustable Objective usually have the parallex set for 100-150 yards, depending on brand. These scopes that are basically used for mid-range big game hunting. Scopes with Adjustable Objectives are usually for long distance shooting and/or varmint type hunting. With a scope without an AO, the close you get to the object the harder it is to focus on the target. That is why a AO usually starts are 10-20 yards, for those close up shots and has high yards at the other end of the spectrum. Allowing the shooter to focus on the target at many different distance, with just a turn of the AO. Same thing with longer distances, the farther you are away, the harder it is to focus on the object. Also, a typical rimfire scope the parallex is set for a closer distance, 60-80 yards. Due to the limited distance a rimfire is fired, the smaller parallex helps eliminate the focus problems.

P.S. After reading the question again, I guess I was doing a lot of babbling! :oops:

JimInNJ · « **Reply #3 on:** August 29, 2003, 06:11:11 AM »

I think that another way of asking your question would be "Why can't I just set my AO scope at 100 or 150yds and get the same depth of focus that I get with a non adjustable scope?"

If you were comparing two scopes of the same power and the same objective size you would get the same results. But AO scopes are usually more powerful and have larger objectives. The higher the magnification or the larger the lens the more critical the focus will be. It is a law of physics. And it is why they put the AO feature on the bigger scopes.

- Jim

Zachary · « **Reply #4 on:** August 29, 2003, 08:47:57 AM »

Lee,

Don't put a .22LR scope on a high power rifle - it won't take the recoil.

Scopes with magnification usually over 12x need AOs because of the parallax problem. Have you ever seen a 6x-24x without an AO? I never have.

The only problem with an AO scope (which I own several) is that if it is set at, say, 100 yards, and a deer shows up at, say, 200 yards, you better adjust the AO to 200 yards because otherwise the deer won't be in focus. You hardly ever have to worry about that problem with a regular 3x-9x.

Zachary

Lee D. · « **Reply #5 on:** September 02, 2003, 03:46:42 AM »

I am more concerned with short range focus-- 30 to 80 yards. 4X12 is not that much different than 3X9 so I don't understand why the focus is so different. I could still shoot a deer at 50 if the scope was a little out of focus but I was just wondering if a 4 to 12 could be made that wasn't as sensitive or is the focus problem more related to the fact that it is a AO setup? I haven't ried one of the 3X9 AO scopes yet.

Graybeard · « **Reply #6 on:** September 02, 2003, 04:12:46 AM »

Lee I do fully understand and share your concerns. I can't explain the whys of it but what you have observed is exactly correct.

If you have an adjustable objective feature on your scope you really MUST use it. It has a serious adverse affect on your ability to clearly see to shoot otherwise.

My work around is that I just refuse to use any scope with an adjustable objective for big game hunting. Varmints and targets yes but nothing else. That doesn't answer your question but bottom line is you aren't going to get around it. Either accept it or change to a scope without the AO feature as I have.

GB

Lee D. · « **Reply #7 on:** September 02, 2003, 04:29:13 AM »

Greybeard,
That is what I thought but I hoped someone could explain or come up with some alternate. I do a lot of precision squirrel hunting and the focus probem is a pain and causes me to miss opportunities. When shooting between 20 and 80 yards I have to change focus to much. I have a new 3X9 to try and it may have enough magnification to work. With a 4X12 or a 6X18 I can get a nice precise aim if I can get focused in time.
I load 6 shells and when they are gone I am done hunting. Whether I have none or the limit. It makes for an interesting hunt and keeps me from taking any risky shots. I always shoot either thru. the ribs or the front shoulders, head shots only if the game is looking either directly at me or directly away.

Zachary · « **Reply #8 on:** September 02, 2003, 01:03:12 PM »

Quote from: Lee D.

I haven't ried one of the 3X9 AO scopes yet.

Lee,

I don't think that I have ever seen a 3x-9x WITH an AO. Conversely, (with the exception of a Nightforce NXS scope in 5.5x-22x-56mm - of which I own one) I don't think that I have seen something like 6x-24x withOUT an AO.

Zachary

Dave in WV · « **Reply #9 on:** September 02, 2003, 02:37:10 PM »

Lee, maybe a 3x9 or 2.5x10 with a European type quick focus instead of an AO is what you need. You could mark the focus ring on say 30 yds and 100yds. Someone with experience with this type of focus may know if this would work. Dave

Lee D. · « **Reply #10 on:** September 02, 2003, 04:01:18 PM »

I'm not sure which company but I recently looked at airgun/rimfire scopes that were 3X9 with AO.
The focus ring is not the same as the A.O. adjustment. I may have been confusing by using the word "focus". The focus on most scopes is something you adjust when you first set the scope up and then only have to change it if your eyes change significantly. The A.O. also focuses the lens system but it corrects the paralax to the desired range also. Last year my prescription changed and I had to re focus all my scopes.
Also I used to be able to help people focus their scopes, now my eyes are no where near correct for most other people. I run a sight in weekend at our club and it is amazing how many people try to sight in a scope that is so fuzzy they can hardly see the target and don't even realize something is wrong.
My original question really should have been---Is the reason that A.O. scopes are so sensitive to focusing for clarity because that is how the paralax is adjusted precisely for range? If that is the reason I would give up some precision on paralax for a longer depth of field in the focus.

Dave in WV · « **Reply #11 on:** September 02, 2003, 04:20:44 PM »

Lee, I feel your pain because two years ago I went through the same thing. Something I noticed about a month ago is one pair of my glasses aren't worth a hoot with my scopes and the other are great. The pair that aren't clear have glass lens' and the good pair polycarbonate lens'. I don't know if that is the problem or a poor grind. The good news is I discovered my dot sight wasn't broken. Bad news was my eyes were. :eek: Have you thought about contacts for hunting? I know guys that wear them for hunting. No rain/snow/fogging problems and they can see better. I work in a high dust inviroment and won't consider them. Dave

Graybeard · « **Reply #12 on:** September 02, 2003, 05:30:57 PM »

My squirrel rifles wear Leupold Compact 3-9 AO Extended Focus Range scopes on them. Around the house here for shooting in the back yard I keep the AO set at a bit over 25 yards as that's about my average shot. When hunting I set it to 50 most of the time. Seldom have to adjust it for squirrel hunting that way.

I shoot head shots only. It don't count if it has a hole outside the head among the folks I've hunted with.

GB

Lee D. · « **Reply #13 on:** September 24, 2003, 01:33:43 PM »

http://www.charm.net/~kmarsh/scope.html
I went to this site and looked under his adjusting parralax heading. Yesterday I went out and bought a cheap scope($29.99) to try this with. I took the tasco 3X9X40 which had about 2 inches of parralax at 20 yards and adjusted it to nearly none. However, the focus was only good from about 18 to 30 yards (very approximate). With a little more adjusting I settled for about .25" of parralax and a decent focus out past 50 yards. So this scope will now be a fairly function rimfire scope. Very interesting now I want to get ahold of a Bushnell 3X9X40 with a circle-X reticule and try to do the same thing.