Scope light gathering

[theLBC]

Thanks for the reply. That is interesting and impressive. I guess that (at least partially) explains why those premium variable scopes cost what they do.

After reading your post, I went back to the Meopta site to see if I could find some specifications that would make more sense of this. Something that then occurred to me: I think I was looking at the wrong specifications. I was previously comparing the Daylight Transmission and Twilight Transmission values for these two scopes, which are identical between the two models I was comparing.

After giving it a little more thought, it seems like these values only tell part of the story. These transmission specifications seem to describe the "efficiency" of the glass; what percentage of the light entering the scope will make it to your eye. But, these values do not describe image brightness (in absolute terms) because they don't tell how much light initially enters the scope. By this, I mean, there could be two scopes with the same transmission specifications but different objective diameters that should have different light gathering characteristics.

It sounds like this is where Twilight Factor might come into play. As I read, Twilight Factor is the square root of (Objective Diameter * Magnification). Something about this value doesn't make sense to me. It certainly sounds like a larger Twilight Factor should be better since a larger Objective Diameter leads to a larger Twilight Factor. But why would higher Magnification make for a better Twilight Factor?

My intuitions tell me, if I wanted to make an image appear more bright at night, I would turn down the Magnification on the scope.... My logic here is that lower Magnifications have larger Field of View so, lower Magnifications would capture light over a larger field, sending more total light to my eye. I must be missing something here.

As I am imagining it, there should be some specification that is essentially the Objective Diameter multiplied by a Transmission factor. Or, even better, if they would simply state the light intensity of the image in the scope at some predefined ambient light level (and perhaps distance). This would seem to characterize the light gathering of a given design. (If any scope manufacturers steal this idea, you definitely—at a minimum—owe me a kick ass scope!)

If anyone wants to clarify any of this, I would be interested to hear.

Thanks,
Nick

the way i understand it is twilight factors is more of a "potential" value based on size of the objective and magnification power (because it is about seeing detail). so all scopes with the same power and objective size will be the same.

relative brightness is sort of the opposite, where low magnification will give a higher value (lower power mean larger exit pupil size).

what this means to me is that these values aren't really effective at "comparing" scopes of the same specifications.

 

[lennyk]

I have just received an alpha 6 4.5-27 50

this thing is noticeably brighter than my more expensive sidewinder at comparative magnification, what gives ?

 

[boscoebrea]

Let me see the light.....well if only a larger bell or bigger body was needed we would all be saving a lot of money....but the truth is quality takes a lot of steps and the coating that are used on lenses is very important........so many different things coming together .........

Simply ,say no to bigger is better.....and take the time to study this interesting subject,optics...or just buy the best you can afford.....

A lot of good information posted above.

Brighter is not always better,for one I want resolution,to be able to see the blades of grass and not just the grass.

Resolution to be able to see .177 pellets holes at over 200 or more yards.....

You can have both and you need brightness to have great resolution......