scope objective lenses

[Viney75]

Hello all,
my question what do people prefer in regards to objective lenses sizes for f class?
I see golden eagle and NF comp have 50mm objectives is this so the view will be more refined ?
Verses a 60mm or 56mm lenses ,or maybe helps cutting out mirage?
thanks for any help

[AlanF]

Viney,

The only advantage I am aware of for a larger objective lens is greater light gathering ability i.e. a brighter target image. By my calculations a 60mm objective will gather about 44% more light than a 50mm. Particularly for older eyes, this is significant. BUT, you could get the same image brightness increase by slightly reducing the magnification on a variable power scope e.g. from 30X to 25X. If I don't have this quite right, then Peter Smith is our resident expert on optics, so hopefully he will confirm or otherwise.

[UL1700]

This is something I have been thinking about also as our March 8-80 with its 56mm lens pretty much permanently has its modifier disk fitted as to my eye it helps the white lines stand out on the black target face. This then makes me wonder why it has a 56mm lens! On another note, March say to fit it infront of the objective lenses yet I see many of them fitted at the end if the shade tube. I have tried both and can't see much difference!

[pjifl]

If you can improve the definition by stopping down the objective lens, this tells you that the design is less sophisticated. But don't blame the scope maker - read on. Best position is for the stop to be close to the lens with high magnification small field of view optical instruments like a riflescope. Also, in a well designed riflescope, a long shade tube should be unnecessary. BUT These are all relative and we pay for them. But people are now willing to pay more and more these days. This plays havoc with the even playing field concept at affordable prices.

The most crucial aspect of the objective is its F:NO. Just like a camera lens. Lens aberrations sky rocket with smaller F:NO objectives. Also, with smaller F:NO objectives, (i.e. shorter but wider), the scope can have a wider elevation range in a certain size tube. It is just so much easier for the scope maker to design a maximum resolution wide apparent field with a larger F:NO (longer, narrower) aperture scope. So keeping aperture diameter to a minimum is always better in this respect. WIDER objective gives a BRIGHTER IMAGE. BUT THEN THE WEIGHT OF THE RIFLESCOPE IS SIGNIFICANTLY HEAVIER, AND TO ACHIEVE BEST ABERRATION CONTROL THE DESIGN MUST BE MORE COMPLEX AND MORE EXPENSIVE. Weight of the glass in an objective (and eyepiece) goes up as the cube of the diameter and can become very significant. The subsequent zoom and erector lens system also becomes more complex with shorter and wider objectives. On top of this, unless the manufacturer complies with popular shooters demands - even if they are unrealistic as they usually are - they will go out of business. Another aspect of riflescope design that has changed recently is the trend for significantly wider apparent field of view as seen by the eye. To achieve this, many top brand modern military riflescopes now have much reduced eye relief. This allows smaller diameter eyepieces to be used saving a LOT of weight. This is now possible because of the general adoption of muzzle brakes. Amazing what drives what these days.

None of this really answers the original question. Sorry about that, but maybe it helps show that the design philosophy of a riflescope is one huge compromise. In reality, it will usually be used in a limiting atmosphere to make matters worse.

Personally, I do not think the view of scintillation (Shooter's mirage) is favored by either type of design. The best and brightest image is the main determining factor, and you pay in terms of cash, weight, loss of elevation range and compactness. Special glasses help but are often exaggerated by advertisers. It has always been so in optical instruments and always will be. Tiny amounts of colour (chromatic aberration) tends to offend some more than others and much comes down to your personal aiming technique.

Peter Smith.