Upper end of spotting scope use?

[Ruskin]

Looking for some perspectives. I have an old Bausch and Lomb spotting scope ( more like a telescope) that is 20x60. When you dial it up to 60 it's real grainy. Granted its old and probably not the best glass. Last yr trying to count points on an elk at 1000 yards was real difficult but I did it. The bull helped by standing still in great light for a long time.

So my question is are the upper ends of magnification on a 15x45 or 20x60 useable? Can a buy a vortex 15x45 and expect clarity at 45? What about at 60? Or do you need to buy a 60 to get a good usable picture at 45+?

Thanks for the info.

 

[Beastmode]

As long as mirage isn't a factor my 16-48 razor stays clear @ 48x. It isn't as clear as 16x but is extremely impressive for a $1k spotter. I do see a downfall at low light on high power but that is expected.

 

[luke moffat]

I have read that folks often say you can't use much beyond 45X of a 65mm scope. I found that wasn't much the case with my 65mm Swaro when dialed up 60X. Yes occasionally I couldn't gain much above even 30X at times due to wind or mirage, but i would say this was the exception rather than the rule and I'll dial up to max power as often as I can. Really my scope usually sits at the lowest setting for finding the target and then dial it up to max setting right away unless the atmospheric conditions don't allow for it.

These days I use a Zeiss Diascope with 75X zoom on the high end and find I sitll am able to take advantage of the extra zoom more often than not. I like to have as much zoom as possible. Its kinda like having a pack that is huge vs. one that is just as big as you need it. You can always compress the pack down to take up the extra space, or dial the zoom down on a high power zoom spotter, but you can't expand a smaller pack bigger or turn up past 45-50X on a spotter than won't go above it.

Of course a lot of this is relative as a 60X on a Vortex Nomad isn't going to give you near the resolution or details as 50X on a Swaro 65mm spotter. But I think you get what I am getting at if you are comparing apples to apples in glass quality I prefer to have as much zoom as possible.

 

[Jon Pynch]

i use my 65mm swaro on 60x all the time in cooler weather, and love it! when mirage kicks up really bad it doesn't matter if you're at 30x or 60x it just doesn't work real great. can't speak to the vortex as I haven't used them

 

[Buffy]

Limits of resolution

I saw an article in Western Optics Hunter magazine once that showed a calculation for your max resolution based on your objective size. I don't remember it exactly but I know on my 60x scope it came out to about 32x. Sometimes the full 40x zoom seems to help discern certain features but normally I can't see much better on 40x than at 32x or so. Maybe it's just on my leoupy gold ring spotter.

 

[Buster]

Take in to consideration your hunting grounds. A lot of distortion can come from heat waves. Relatively flat ground makes glassing conditions tougher. I grew up in the prairies, and anything above 30x was very tough to use on most days because temperature differences between the ground and the air create distortion. On the prairies, ground level tends to be very close to line of sight, which results in more distortion. Once I moved to the mountains and started glassing across valleys (situations where line of sight does not follow closely to ground level), I found that I was able to use higher zoom ranges more frequently. Just something to consider.

 

[Matt Cashell]

This is a good discussion. The "formula" for best optical performance by objective size is just somebody's opinion that a 2mm exit pupil (30x for a 60mm scope, 40x for an 80mm scope) provides the performance they like the best. This is of course just their opinion, and not a fact about optics in general.

The "heat distortion" Buster refers to is the atmospheric disturbance provided by heating or cooling air moving, especially near the ground, as he mentions. This is the number one factor that hinders long distance, high magnification spotting scope images, in my experience.

In optics discussions terms, distortion more appropriately describes an optics tendencies to bend straight lines across the field, and this is usually in pincushion or barrel forms.

All of the quality spotters should show their greatest resolution at the highest magnifications. That is to say as you increase magnification, you should see more detail, as long as the atmosphere is stable enough to allow for it.

If you have good viewing conditions (or are viewing an object close to you) and you see more detail at a lower magnification, then there is either a problem with the spotting scope design (likely the eyepiece) or a problem with that particular scope.

Some people feel like their spotter isn't as "clear" at high powers, even when it is showing more resolution (detail). What they are seeing is a dimmer image, because as you increase magnification, the exit pupil shrinks. With some spotters at high magnification the exit pupil shrinks to nearly 1mm.

Conversely as the exit pupil expands, the image gets brighter, and you make use of more light, leading to the impression of a "clearer" image, although technically you aren't seeing more fine detail.

 

[Mad Mountain Mike]

^^^^^^ Thanks for the good info Bitterroot Bulls. That really clears up a lot of questions about spotters.( no pun intended ). ^^^^^^

 

[parshal]

So my question is are the upper ends of magnification on a 15x45 or 20x60 useable? Can a buy a vortex 15x45 and expect clarity at 45? What about at 60? Or do you need to buy a 60 to get a good usable picture at 45+?

Take a look at my Swarovski thread in the Digiscoping forum. I've posted pictures from both 65mm and 95mm objective lenses at full power at 1000 yards and 9.5 miles. Although there is some mirage at the longer range the pictures show very usable images at full power. I can't comment what the Vortex looks like at full power.

 

[russ_outdoors]

Like others above, I've found 60x to be very helpful on my 65mm Swaro and use it frequently. Most of my hunting/spotting is done at altitude (8-11,000') early and late in the day.