Home Forums Hunting & Shooting Hunting Optics Focusing a scope from Leupold Tech.

Thanks for the info Ed.

Rob

taz4570,

Sounds to me like you are an uncorrected hyperope that simply can't accomodate enough to compensate for your hyperopia anymore. You are adjusting the focus to "correct" your refractive error using the scope, instead of hanging some specs on your nose to do the same thing all the time.

to all,

I have posted this in the past, and will now again. You may be capable of reading a Snellen eye chart (developed in the 1800's) to the 20/20 line and still have a refractive error i.e. spectacle lenses could "correct" your vision. I see patients every week that can rattle off 20/40 lines on a snellen chart and have at the DMV for years, but in the office I test their vision at 20/100 or worse. 20/40 = unrestricted driver's license, 20/100= restricted to day light only and 25 miles from home.
Because of this, you can adjust the focus of your scope, bino etc to allow the right amount of convergent or divergent light to be emitted to correct that error and see more clearly through the optic. Spectacle lenses bend light to correct refractive error in the exact same manner.

Great info Doc, thanks. While we have your ear, if you like to shoot really vicious kickers, is PRK safer than LASIK as far as not having it detach again? I guess the thought of LASIK scares me more from a durability standpoint.

Thanks for the knowedgable post. So many factors must be considered in optics. I changed to Zeiss lens in my glasses & my night vision was improved. I am including this info when I teach scope mounting/zeroing/focusing seminars. This was great information.

I'll have to check, but I swear one of my scopes does appear to reduce the magnification when focused. Could be the Bushnell Banner on my 10-22 or an old B&L from the B-I-L's win70.

Anyhow, I picked up a Nikon 4-16x42 for a simple budget scope on a new varmint rig. It too needs to have the focus bottomed out for me to see the crosshairs clearly.

Interested to hear Doc's reply on this also, I had PRK 3 years ago. After reading the info I though PRK would be better for me since there's no chance of detachment. I read that PRK was the only thing the military would allow for fighter pilots but then I read that they had changed that and now allow LASIK.

In the end the decision was taken out of my hands as PRK was recommended for my particular situation. The healing process certainly was longer but I'm very happy with the results. My eyes sometimes get a little dry at the end of the day, especially while in front of a TV, I keep some drops handy but other than that I test at 20-15.

Had to get used to reading glasses and can't see a rear leaf sight worth a sh*t so I have all reciever sights and scopes now.

in theory PRK is safer concerning retinal detachment, but it really depends on which model for the RD you subscribe too. The most common belief about retinal detachment(RD) post-op refractive surgery is based on the thinning of the cornea. By thinning it to reshape and correct near sightedness, internal forces (pressure) pushes forward with less resistance from corneal tissue (since there is less there). This pressure shift forward allows the vitreous (a gel like substance keeping the eye round) to move forward and reduces its back pressure on retinal tissue. This allows all kinds of crap to happen to the retinal tissue. All this time the vitreous is also degenerating because of age and collapsing inwardly pulling, sometimes rigorously at its attachment points on the retina, which can lead to a tearing of the retina and then fluid seeping into the tear and under the retinal tissue, hydrollically lifting it and cauusing the RD.

So in theory, because of the less traumatic PRK requiring less thinning this scenario is less likely to occur versus LASIK were flap depth is not an exact science and chances of making things a little thinner are greater. Practically speaking it really depends more on the amount of tissue removed. An average cornea is.555 mm thick (555 microns). An average of 15 microns of tissue (I like to use 18 as a safty fudge factor) must be burned off to correct for -1.00 Diopter of myopia. The higher myopia the more tissue and thinner, so more dangerous for RD. PRK requires scraping off epithelium and doing a surface ablation (flattening) versus LASIK with a flap cutting and ablation of the stromal bed. Because the flap thickness can't be exactly controlled then this procedure causes axtra thinning.

An example Joe wants LASIK, he has 550 micron cornea and is a -6.00D myope. Joe needs the laser to evaporate 90 microns of tissue. The surgeon shoots for a 160 micron flap, and must keep 250 microns in the stromal bed or he will perforate. So 560 minus 160 is 400 then minus 90 is 310 microns in the bed, Joe is a go for LASIK. If Joe had a cornea 440 microns minus 160 = 280 in the bed. This allows only 30 microns to be removed so Joe can have 2.00D of correction and is left as -4.00D. Since there is no flap to contend with in PRK the factor of 160 is greatly reduced (usually to 50 for safety. Now the 440 cornea-50=390-90 for sx=300 and thin cornea Joe can have PRK but not LASIK.

In the end, big boomers can cause retinal trauma leading to detachmnet no matter what and it seems to be a bit of a crap shoot.

ED

ED, thanks greatly for the information.

Rob

I had interlace lasik surgery back on Nov 14 / 07. Vision was
20/20 the very nxt day. Latest eye test shows that I am 20/10.
I wish I would have done this years ago. Now if they could only have a procedure to cure macro degeneration (I think that's what it is called). The age thing where as you get older, the cheaters come out to enable you to read the fine print. I still do experience dryness but only occasionly when tired or after many hours in fromt of the computer.

Thanks ED, that's great information.

gube,


the age thing is presbyopia, due to inflexability in the crystaline lens inside the eye. Macular degeneration is a blinding affliction in which photoreceptive nerves in the central vision area die off and you end up with a huge blind spot in your central vision. There are surgeries for presbyopia, the most effective you can't have because you have had LASIK. This is implantation of a multifocal intraocular lens after a lens extraction procedure. Another uses an implantable contact lens like apparatus for one eye. and yet another uses scleral expansion bands (think breathe right strips) implanted into the white part of the eye 360 degrees around.

The computer is bad because by human nature you are staring at it with out blinking. Get an artificial tear called Soothe. It has an oil emoliant that will blur vision for 2 minutes or so, but then bulks up the outer oil layer of the tears and keeps them from evaporating as quickly.

ED