general question - regards front element and rear iris.

[Jackothepiglet]

Hi all, new to this sport, even thought I have been air gunning for many years.

Recently I have inheratated a Diana Original 75 so decided to give it a go. It was low on power and the orignal seals were falling apart so sent it off to be serviced. Just got it back from being serviced, new seals, internal clean etc.and it shoots like a dream. I have decided to change the rear dioptre for an adjustable iris (gehmann 510) as I was getting the cobweb effect from the original. By setting the iris to 1.3 to 1.4 I now get a clear view ( no cobweb effect), Someone did say to me if I alter the rear iris I need to change the front element, is this true?

The rifle came with a front element ( polycarbonate it think) with a 3.2mm hole. Any suggestions as to what I need to change it to, if I need to do it at all. The rifle is zeroed for 20yards ( inch group). I do have a range of metal elements as well.

Is there a list of settings for example, rear iris size to front element size.

thanks for taking the time to read this and any help considered.

regards

Jack

[Tim S]

Jack,

No, you don't normally need to change the front element if you alter the rear aperture. An adjustable rear iris lens you control the light to suit the range conditions.

The front element really depends on your target and sight radius (the distance between front and rear sights); a larger target (in proportion to the range) or a longer sight radius need a larger element. You want a good gap between the target and the foresight ring, enough to contain any wobble in your aim. 3.2mm would be really small for the ISSF 10 metre target, partly because that's mostly shot standing. But 3.2mm might be OK on the same target at 20 yards from a bench because your aim is steadier (the target would be tiny mind you).

[Jackothepiglet]

thanks Tim.