Changing a telescopic sights minimum focus distance

[ovenpaa]

Having started shooting LSR I have noticed finding a 'scopes that work on higher magnification and focus at the required 20 yards are very few and far between. So this morning I experimented with a Hawke 3-9x40 that would not go beyond 3.bowl magnification and focus on a target at the end of workshop. (10 metres) Assuming the 'scope was going to be sacrificial I stated with the objective end. Unscrewed the short shroud and the objective lens component could now be screwed in or out. I opted for out to increase the focal length and around 5,0mm got me focused at 10m and 9X magnification. Next job is try this at 20 yards and see if it got the job done and try it at 50 yards as that is the other length I am signed up to compete at this year.

So, has anyone tried this before and if so any views on such a modification? Right now I am working on a fifty quid ish 'scope. If I am happy I may try this on something a bit more up market as I would like around 16x magnification

[kennyc]

used to be a common mod back when a lot of scopes came parralaxed for 100yds, from memory you screw in/out the objective lens until the target has no sideways movement as seen through the scope while you move your head back and forth. due to their gas fill I would be loath to do it with a more expensive scope, but for cheap scopes it should be fine. Although there ara a lot of AO cheap scopes around now so not sure if its worth it except as an exercise in curiosity.

[strangesam]

An AO or SF scope which you can adjust the Parallax/Focus down to 10-15m is the best bet.

Hawke make a lot fairly cheaply.

[ovenpaa]

AO and SF? I assume SF is side focus but...

I must admit to being more used to Austrian or German glass :)

[strangesam]

Adjustable Objective - can adjust the parallax focus by twisting the objective lens

Side Focus - can adjust the parallax focus with a turret on the side


Both will then allow further adjustment of focus with the eyepiece.


With high magnifications especially, the parallax error at 20m, with a standard scope set for 100yds or 100m can be significant, especially for things like LWS or Benchrest.


The Hawke Frontier 30 SF series are very nice if you want to start with Teutonic glass prices.

[kennyc]

AO and SF? I assume SF is side focus but...

I must admit to being more used to Austrian or German glass :)

you are shooting at 10m bottle glasss will work

[ovenpaa]

20 yards!

Some are shooting at 24X magnification in LSR which does seem quite extreme. I will see how I get on with 9X next week.

[1066]

I find anything above about 10x to be counter productive with LSR. The points lost are not the ability to see the target, it's all about holding the thing still while you pull the trigger. Quartering the slightly fuzzy blob up in the sights would work just well if the rest is good.

Higher mag, crystal clear scopes tend to make you hang on too long looking for the PERFECT shot. Just think how much magnification a top class 10m air rifle shooter uses - none, and their scores would translate to a possible every card on the PL14's

[strangesam]

Personally I use somewhere in the range of 4-6x for prone LWR, My scope can go up to 15x but my scores are noticeably better at the lower magnification.

I can see 24x for benchrest, but x15 just wobbles everywhere unsupported.

[Cookisan]

I know of people that adjusted the objective lens position as you have said, to allow closer focusing (7 to 9yds?) when I did Field Target many moons ago. I think it was in the days before scope manufactures catered specifically for the FT shooters requirements. I see now that you can get S&B PMII's with reduced magnification for the HFT crowd. Talking to a bloke last weekend about FT, and he said it's not unheard of to see March scopes these days. I digress!

I vaguely remember Leupold did an adapter to allow for close targets, it looked like a glorified objective lens cap but deeper with a hole drilled in the centre. Somebody told me it worked on the same principal as a pin hole camera?? I have also seen diy jobs which allegedly worked. I assume the hole size would have been fairly critical, start small and open out?

All pretty vague as a lot of red wine has been consumed in the interim period!