Update on spotting scope recommendations

[BFMIN]

Maybe this will help.

This is INTERNAL to the scope & so doesn't include things like water vapor in the 200 yds of air, mirage caused by temperature variations & so on.

BUT.
It is an absolute for "how small a thing can I see at what distance".

Telescopes are graded in "arc seconds".
That's 1/60th of a minute of angle. Which is (roughly) 1" @ 100 yds.
That's 2" @ 200 yds, divided by 60 to convert back to seconds from minutes.
So its 0.03" recurring, for a .22 diameter hole (approximately to keep the math simple).
There's a rule of optics that says you need 1" of open aperture per 20X of magnification. Open aperture is front (objective) lens diameter minus any obstruction (like a front mirror).
So to get your .22" hole visible you need the magnification to bring the 0.03 Arc Second target into the operating range of the telescope.

So.
look up the resolution.
figure out the magnification to bring it into the resolving power of the scope & divide by 20.
THAT is the Open Aperture of the scope defined.

Let me promise you this a 90mm (3.5") aint even close to making it!
A quick guess & a bit of basic math says you MUST have a minimum of an 8" objective mirror, but a 10" would be better, to get that kind of magnification & resolution.
An 8" runs about $1050~ 1600, without erecting prisms & eyepieces!
a 10" is much more at $2200~ 3050.

 

[atblis]

I have a Razor gen 1 as well as others. 100 yards, 22 caliber holes are no problem. 200 yards, generally observable. 300 yards, is where it gets tricky. Shots in the black can be hard to spot. Shoot and see type targets make it much easier. Thing is, once you get to 300 yards and further, conditions really matter and even the best spotting scope won't help you. A little mirage, some shadows, etc. etc.

I've used a Viper HD and it seems on par with the Gen 1 Razor.

 

[atblis]

Maybe this will help.

This is INTERNAL to the scope & so doesn't include things like water vapor in the 200 yds of air, mirage caused by temperature variations & so on.

BUT.
It is an absolute for "how small a thing can I see at what distance".

Telescopes are graded in "arc seconds".
That's 1/60th of a minute of angle. Which is (roughly) 1" @ 100 yds.
That's 2" @ 200 yds, divided by 60 to convert back to seconds from minutes.
So its 0.03" recurring, for a .22 diameter hole (approximately to keep the math simple).
There's a rule of optics that says you need 1" of open aperture per 20X of magnification. Open aperture is front (objective) lens diameter minus any obstruction (like a front mirror).
So to get your .22" hole visible you need the magnification to bring the 0.03 Arc Second target into the operating range of the telescope.

So.
look up the resolution.
figure out the magnification to bring it into the resolving power of the scope & divide by 20.
THAT is the Open Aperture of the scope defined.

Let me promise you this a 90mm (3.5") aint even close to making it!
A quick guess & a bit of basic math says you MUST have a minimum of an 8" objective mirror, but a 10" would be better, to get that kind of magnification & resolution.
An 8" runs about $1050~ 1600, without erecting prisms & eyepieces!
a 10" is much more at $2200~ 3050.

Yeah, so how is it I can 22 caliber holes at 200 yards with my 80mm objective? I think you're trying to apply the diffraction limit. Astronomy is a bit different of a problem so while valid some of the limits and associated rules of thumb aren't actually applicable to the problem at hand. Contrast seems to be what limits observing bullet holes on paper in my experience.

 

[Speedluvn]

I have a Razor gen 1 as well as others. 100 yards, 22 caliber holes are no problem. 200 yards, generally observable. 300 yards, is where it gets tricky. Shots in the black can be hard to spot. Shoot and see type targets make it much easier. Thing is, once you get to 300 yards and further, conditions really matter and even the best spotting scope won't help you. A little mirage, some shadows, etc. etc.

I've used a Viper HD and it seems on par with the Gen 1 Razor.

Maybe this will help.

This is INTERNAL to the scope & so doesn't include things like water vapor in the 200 yds of air, mirage caused by temperature variations & so on.

BUT.
It is an absolute for "how small a thing can I see at what distance".

Telescopes are graded in "arc seconds".
That's 1/60th of a minute of angle. Which is (roughly) 1" @ 100 yds.
That's 2" @ 200 yds, divided by 60 to convert back to seconds from minutes.
So its 0.03" recurring, for a .22 diameter hole (approximately to keep the math simple).
There's a rule of optics that says you need 1" of open aperture per 20X of magnification. Open aperture is front (objective) lens diameter minus any obstruction (like a front mirror).
So to get your .22" hole visible you need the magnification to bring the 0.03 Arc Second target into the operating range of the telescope.

So.
look up the resolution.
figure out the magnification to bring it into the resolving power of the scope & divide by 20.
THAT is the Open Aperture of the scope defined.

Let me promise you this a 90mm (3.5") aint even close to making it!
A quick guess & a bit of basic math says you MUST have a minimum of an 8" objective mirror, but a 10" would be better, to get that kind of magnification & resolution.
An 8" runs about $1050~ 1600, without erecting prisms & eyepieces!
a 10" is much more at $2200~ 3050.

Yeah, so how is it I can 22 caliber holes at 200 yards with my 80mm objective? I think you're trying to apply the diffraction limit. Astronomy is a bit different of a problem so while valid some of the limits and associated rules of thumb aren't actually applicable to the problem at hand. Contrast seems to be what limits observing bullet holes on paper in my experience.

This type of discussion, after my needing to process it, is what I was hoping to achieve. I appreciate this discussion. You guys have introduced things that I may or may not have previously considered.

Please continue!

 

[BFMIN]

I think you're trying to apply the diffraction limit.

Not at all I'm applying several decades of using various spotting scopes on rifle ranges.
I'm talking about "Optical Resolution" as in How many black/white line pairs per millimeter can the optic actually record at a given distance (angle subtended). 80 is considered the border between Good & Poor.
Look at it this way, if the scope can't see (resolve) the "target" all the contrast in the world won't help.
Yes good contrast does help too, but if it is blurry you've lost actual resolution (sharpness).

PRACTICAL use, not airy-fairy theory.

Scope makers are (in)famous for wildly exaggerated claims of "power", it is not possible to get "400X POWAH"! (whatever that is), from a 3 1/2" objective, no matter how well made it is.
Sure you can screw a short focal length eyepiece into a 1,000mm objective & "Get 400X", but its degraded fuzzy & poorly defined BEFORE you add atmospherics to the blurry mess.

I use a 4 1/2" scope of good quality at at about 27X mag. because I want SHARPNESS, actual resolution in lines per mm, not so much power its soup. It will resolve a .30 caliber bullet hole on a suitable background in good clear conditions out to 300 yds. (just). If I crank up the power by switching to a shorter eyepiece its bigger, but not as well defined.
So my bullet hole roughly 1.36 X bigger than your .223 is going to get lost in the murk if you crank up to make it the same apparent size.
Look at it another way.
Your "target" (the bullet hole) is roughly 2/3 the diameter of mine so to get the same image resolving power you can either limit the range to 2/3 the distance I'm using, OR increase the magnification by 1.36 WITHOUT ANY DEGRADATION of image quality. That means a bigger (6.5X) front lens, enabling 36X mag with retained image quality.

 

[atblis]

https://en.wikipedia.org/wiki/Diffraction-limited_system
Read this. Please.

 

[Pinecone]

I've used a Viper HD and it seems on par with the Gen 1 Razor.

Hmm, I have run my Gen 1 Razor side by side with a Viper HD, and there was NO comparison.

The Viper HD is a nice spotting scope. But even the Gen 1 Razor is much better.