The mono frome lense holder that fits to the rear of your sight strikes me as perhaps being better than shooting glasses, as you set them up sqaure on to the sights and Bobs your uncle.
I wear glasses and with them you do have to make sure they are square on to the sights, they can move, so you have to keep an eye on them, (excuse pun).
Definately get a diopter, I love mine.

Grumpy may be able to help here, but I've seen them.

For indoors there is no probs with using either or even both if you want to, as far as I know.
There are nifty little holders available for securing a lens to the rear sights ( some people used to fit a small lens in the old rubber cups which whould slip over the rear sight) and I think there are moves afoot to allow them outdoors for ISSF type matches
Diopters are not allowed for ISSF type matches and you should (need to) get TSNZ aproval to use them for other outdoor matches
You see you are not supposed to have any sort of optical aids for OD shooting with the exception of corrective lenses worn by the shooter and I guess by fitting a lens in a holder attached to the rear sights and then fitting a diopter you can effectively make yourself a telescopice sight (optical aid?) Even a lens in a holder fixed with the rear sight and adjusted in combination with the apeture of the rear sight can technically be adjusted to give a telescopic sight effect

Hi Environs, are you still looking for shooting frames, I have a set of Knobloks with an approx 38mm lense holder that I no longer need due to upgrading to the rear sight mounted holder, (they are great). I will be at conference in Ch Ch end Oct and can pass to someone if you wish. If you are interested, pm me and we can discuss.

Hi Grumpy here are the current rules, the bold underlined bits are the ones that lead me to beleive I carnt use 2 fixed lenses.
4.3 SIGHTS
4.3.1 Any form of ‘open’ or ‘aperture’ sight, fixed or adjustable, is permitted.
4.3.2 Foresight elements of plastic or metal, iris foresights and all neutral dioptre light filters, are permitted.
4.3.3 No magnifying combination of lenses is permitted, except that one lens not exceeding 0.5 dioptre (1.5
magnification) may be fitted to [b]either the front or the rear sight. In specific cases a dispensation may be granted.[/b]
Refer to Rule 7, Clause 7.5.
4.3.4 Corrective glasses or contact lenses may be worn alone, or in addition to, any lens used as specified in Clause
4.3.3.
4.3.5 A blinder may be attached to the rifle or the rear sight.
4.3.6 Telescopic or electronic sights, including light emitting devices, are prohibited.
&
7.5 Any competitor suffering from defective eyesight and whose condition the provisions of Rule 4.3 cannot rectify
may apply for dispensation to use additional optical aids.

So Grumpy are what you are saying I could have 2 fixed lens but it would be under Rule 7.5? Your help would be appriciated.
Environs

The operative words here are magnifying lens and corrective lens and magnifying combination
The lens that you would put on the front sight is a diopter of no more than .5 dioptors (.5 magnification)
The lens that you want to put on the rear sight would be a corrective lens. The fact that it is fixed to the rear sight instead of being fixed in a frame worn by the shooter dosen't change what it is as for as indoor rules are concerned and to the best of my knowledge is allowed. However, if the lens at the rear sight was a magnifying lens then, when set and focused correctly, effectively becomes a telescopic sight or in the words of the rules "magnifying combination" and is not allowed.
I have seen a number of shooters use a mounting system for a corrective lens fixed to the rear sight including TSNZ Executive Members.
Corrective lenses as their name suggests correct visual problems such as astigmatism and short or long sightedness of the shooters aiming eye and do not magnify to any sgnificant degree.
Some say that using a corrective lens in conjuction with a diopter can actually cause the shooter problems but again I have seen shooters including myself using such a combination and have seen 100.10s shot with that combination.
To further explain; the outdoor rules specifically prohibit attaching the corrective lense to the rear sight in rule 4.4.4 "Correcting lenses must not be attached to the rifle. The shooter may wear correcting glasses". Such a rule is not presently included in the indoor rules
No dispensation should be required for indoors, of course if you were to shoot outdoors then you would have to get dispensation to have lens in the front sight and not use it for ISSF type matches, BTW you could always contact the TSNZ Secretary and ask for clarification.
Hope this helps

I use a .3 diopter and went from 4.2 to 5.1 nomanally

I only have short barrel and no bloop tube, from memory only 600mm site radius. If I had 5.1 I would be able to the edge of all the surrounding targets.
Environs

Think from memory my sight radius about 750mm