Scope used at max power

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Ghys_T3LSS

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Good morning,

I am curious about one thing. It is probably a scientific evidence that the more you zoom in, the less permissive is the eye vs tube placement if I can say... for example my 3-9 scope. I can move my head left and right a lot when at 3, but the sweet spot at 9 is very small.

Now... I thought this was a common issue with cheap to medium priced scopes, but I also experience the same with my 6-24 Engage. My comfortable setting is around 20 with that 24 scope... with my Redfield, it is around 15-16 for a 18!scope...

Tricky question... is it only a question of being more patient and have a better technique...??? I would like to use the bdc/mil dot, but I need to be at max power...

Other option is to move to a FFP...

Additional question: what is your best choice of scope around 6-700$, for 4-5-600yds shooting...? Exposed turrets, good tracking...

Thanks!
 
If youre using the reticle, FFP is a good choice....if youre dialing SFP is a good choice.

Leupold CDS is a good option VX3i...:)
 
Maybe what you are asking has to do with some physics of the scope? Take the diameter of the Objective lens in mm; divide by the magnification, The result is the size of the "focused image" that will fall onto your eye's retina. So a 20 mm 2.5 power scope - 20/2.5 = 8mm. Younger people have an iris in their eye that can open much wider than old folks. Rough idea might be 7.5 mm when you are in your 20's; 5 mm or less when you are in your 60's. Major reason why "old guys" like more lighting when reading or doing fine work - their iris can no longer open as wide to let in light - hence need more intense lighting. So the scope - that one is probably brighter than anyone's eye can actually use. So go to typical 3-9x40. At 3 power, have a 40/3= 13.33 mm "beam" to hit your retina - pretty forgiving. Same scope at 9 power - 40/9= 4.44 gotta have that pretty much centered to get it all onto the retina. Go higher - 40 mm front lens, 24 power scope = 1.66, so now getting pretty fussy to get that exactly onto the "sweet spot" - will also appear dimmer for most everyone, compared to that 2.5 power. Coatings and quality of the glass definitely affect the len's light transmission - block some colours, enhance others - so "good" scopes and "poorer" scopes even though same magnification range. Without electronic enhancement, all glass will reduce the amount of light passing through to some level - 80%, 90%, 99% getting through - do not know of any 100% glass??
 
So, if I understand correctly, let’s say I am comfortable with a 50mm objective when zoomed at 18, and plan to use mil dots or bdc, then I should not look for more magnification...

Or I find a FFP and use the dots at whatever magnification I am.
 
If you are "comfortable" with 50 mm and 18 power, then the focused image you are getting is about 2.77 mm diameter, and you sound like that works. So more magnification gets a smaller width of "focused image"; larger objective would get a larger "focused image".

Not certain I can follow about First Focal Plane focusing though - The diameter of the image that you can see is not going to change, whether focused or not. The effect is a result of the physical diameter of the Objective lens in the scope, and the magnification. I have a 100 mm diameter objective spotting scope / telescope - I will get that same 2.77 mm diameter image at about 36 power. Although mounted on a good heavy tripod with gear drive aligning knobs, for my eyes, it is virtually unusable at 60 power - 1.66 mm output, the slightest movement of my head and I loose that image - which is the same as 24 power through a 40 mm objective lens - the very tiny "sweet spot" that you mentioned in your first post.
 
What I mean is If the image I got from a 50mm / 18x is the smallest I am comfortable with, then If I get a 20 or 24 x 50, and want to use the dots, and have the correct holdover, then it needs to be a FFP (if I don’t use it at full power). (Only option to use the dots at 18x, on a 24 scope would be FFP...)
 
You will have similar relief issues with ffp. It's 90% technique; if your eye isn't in the same spot, for every shot, your accuracy will suffer, even with unlimited eye relief.
 
OP - I did not realize that scopes needed to be at maximum power for the mil dots to be accurate - I knew they had to be set at a specific power - often that "ranging power" is a different colour number on the magnification ring, but did not know that at least some scopes had to be a maximum magnification.

So, if the size of the output is your issue, then you can do the math. Sounds like you are "comfortable" with 2.77 mm? So if 40 mm objective, that is about 14.4 power. With 42 mm objective = 15.2 power 50 mm = 18 power 56 mm = 20.2 power In your first post you said the "sweet spot" on your 3-9 scope set at 9 was very small - you did not mention the objective size - if 32 mm, then 3.6 mm output; if 40 mm, then 4.4mm output. So even a 50mm at 18 power is going to be smaller than what you referred to as a "very small" sweet spot.
 
If you set your eye relief at mid range power setting you will average out over power spectrum
 
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