Why Use Different Size and Magnification Scopes

[rottenshot]

I know the difference between say 40mm and 50mm is it lets more light in and I also get 12x's mag shows distant objects up more than 3x's magnification but you often see people using say for arguments sake a Simmons Whitetail Classic 1.5-5 x 20 .... what are the advantages and when would you use something like that???

I get there's obviously a weight saving but the 20mm surely makes it harder to see through and why would you want less magnification rather than more???

My Hawke Airmax 3-9 x 40 I can focus clearly down to 10 meters and I wouldn't have thought I'm going to be getting any closer to rats or anything than that before they scarper so I'm probably missing the point but I can't see why you'd want a lower magnification and narrower tube apart from a possible weight saving???

[junglie]

You've obviously not looked through your scope alongside a little whitetail at the same mag setting in low light at dawn or dusk. I can get another 20mins to half an hours shooting with the whitetails compared to my hawkes. The only scope I have that matches them is a german pecar that was probably 3 times their price new. Oh & the weight saving & compact size are advantages too! Forgot to add the simmons is a wide angle scope so the feild of view is bigger than the hawkes at same mag setting too. If only they made them with mildots & ir reticules.....

[Gwylan]

It depends what you want to use the scope for. It's true that a small objective scope will let less light in, but the low magnification of the Simmonds you mention can give just as bright an image as a higher mag scope with a larger objective. In other words, brightness will depend on how much the light available is "spread out" by the magnification. (Quality of glass, accuracy of polishing and coatings will affect things as well.) Smaller lenses are cheaper to make, so can be of better quality, they also give more depth of field, so focussing/parallax adjustments are not necessary. I bought my first 4X40 scope in 1972, it's sharper and brighter than my Big Nikko FT scope..!

Gus

[bullbarrel]

At any magnification the smaller objective should give a larger depth of field.

This means if hunting, or especially HFT, the target is likely to be in focus from 5-40 metres so you don't (or can't) adjust the focus.

[p.sharp]

You could have a 200mm objective lense, the light still has to travel down the same 1" tube, and the human eye can only deal with a small diameter (7mm iirc) of light anyway. Smaller, higher quality lenses will always be better than 50+mm mid price range lenses.

[rottenshot]

Thanks for the response everyone, a quick question as a by product does magnification generally affect your depth of field irrespective of what scope you're using ie lower mag better depth of field???

I can't find one of these for sale anywhere so I'm guessing they've been discontinued and you're just lucky if you manage to find a 2nd hand one, does anyone how much were thy when they were new and are there other "good" alternatives that don't an arm and 2 legs??

[bullbarrel]

Thanks for the response everyone, a quick question as a by product does magnification generally affect your depth of field irrespective of what scope you're using ie lower mag better depth of field???

Yes. And from memory I think its non linear.

[Fluffybuck]

As mentioned in another post above: low-magnification scopes don't need such large objective lenses to gather the light.
The smaller the objective lens, the closer/lower the scope can be mounted to the barrel, meaning the point-blank-range can be brought in closer, meaning reduced need for hold-over at very close range.
The lower magnification of small scopes also gives a wider field of view which makes it easier to track a target at close range - rats don't stay still for long.

I've bounced around the generalised simplification for 12ftlb airgun hunting that roughly 1x mag for every 5yd distance to target seems about right, and 7mm of objective lens diameter for every multiple of magnification.