Scope Depth of Field?

[Gnome of the Woods]

Just a quick question on the amount of depth of field different type of scopes produce. I have a Simmons 6.5-20 x 44 Mag and just roughly pacing it out the depth of field is about 20 Yards. Will a fixed mag scope produce a greater depth of field or is it just a case of the better the scope the more depth of field is produced. I am assuming that depth of field in scope terms is the same as the photographic use of the term i.e.The distance between the near and far focus points.

Thanks,
Paul

[steven]

Just a quick question on the amount of depth of field different type of scopes produce. I have a Simmons 6.5-20 x 44 Mag and just roughly pacing it out the depth of field is about 20 Yards.


am assuming that depth of field in scope terms is the same as the photographic use of the term i.e.The distance between the near and far focus points.

Thanks,
Paul

What Mag did you measure at? It's going to decrease with increased Mag.
Second bit... spot on.

[Gnome of the Woods]

Sorry I measured it at 10x as this appears to be the optimum for HFT. All advice welcome.

Paul

[Darren Petts]

It'll vary scope to scope even of the same type and is dependant on a great many factors. As a rule the smaller the objective the greater the depth. I have two Burris 8-32 that have vastly different depths of field. On 8x one's over 30 yds and the others under 20. Ironically both rangefind on 32x just as well as each other. A 10x40 Bushnell I had fell somewhere between the two but nearer to the better one.

[steven]

As Darren has just pointed out, the greatest influence is the diameter of the objective lens.
For HFT I find it rather useful to get blurring at <15 yrds and the same at >40 yrds; helps greatly with range estimation.

[Gwylan]

Depth of field is controlled by aperture(fixed) and focal length, which depends on the mag setting. This is why a 10X40 is a good compromise for HFT, where most things are sharp from about 40ish to 15ish, depending where you set the parallax.

Gus

[Dead_eye]

I belive this is why simmons (i think) brought out that scope with the oval lense- wider than it is high- So you can lock onto a second target quicker at higher mags rather than getting "lost" in the grass lolol

[Murphy]

it was tasco not simmons

[damascus]

Interesting comments on depth of field guys,

I have a Bushnell Elite 3200 10x 40 Tactical Scope that I need re-parallaxing, but am undecided what to set it to.

I have been contemplating HFT use, but my main forte is target shooting and bunny bashing. My back garden is 25yards deep with a 15yards minimum. This is where I do most of my shooting. I try not to exceed 35-40yards with the bunnies.

I too have a Simmons 44Mag 6.5-20x. I have carried out comparisons where I have preset this to fixed distances at 10x mag, but it seems to have quite a narrow depth of focus. This could be giving me a false impression.

Any suggestions on parallax distance settings for the 3200?

Are special tools available to adjust the front objectives?

Thanks.

[Gwylan]

To reset the Bushnell, you just need to unscrew the front ring, you might need a strap wrench like a "Baby Boa,", or you can make do with a leather belt, and pliers. Set out targets, or newsprint at 15, 35 and 45 yards. Adjust the parallax so that 15 and 45 yds are just "fuzzy." This helps with rangefinding for HFT.
You will now have a small gap between the ring and tube. This can be covered with a Butler Creek. Some people put a big O-ring in the gap.

Gus

[damascus]

Hi Gwylan,

What happens to the dry nitrogen gas filling when you do this, does it not require to be done by a specialist who can replace the gas?

I am not quite following this gap business - where does this gap actually appear. Are you saying that the lens ring is unscrewed so far forward that it sticks out of the housing, or have I got the wrong end of the stick? Please explain.

Regards

[Gwylan]

No Problem....! If you look at the top of the front bell, you'll see a join filled with a spacer ring with "Bushnell" on it. This is nothing to do with any slotted locking ring on the inside of the lens housing. (some other scopes need to be adjusted this way, but not the 10X40). You only need to unscrew about 3/4 to 1 turn, so you won't lose any nitrogen. The bit you unscrew is the ring in front of the thin "Bushnell" ring, which forms the front of the scope. This will now have a small gap between it and the spacer ring.
Some people strech a big O-ring, (like a rubber band) over the front, then it "pings" into the gap, keeping the rain out. (you might need 2 O-rings.)
If you use Butler Creek, or similar flip-up covers, you don't need the O-ring.
It's a very easy job, but you've done the right thing in making sure you are clear about what to do. (I hope you are now...! )
HTH
Gus

[damascus]

Ah I see! Now I understand why you might need an 'O' ring. I had no idea it was that easy to do. I had expected to have to unscrew the slotted ring at the very front of the lens. I could not understand how you could do that without loosening the lens/losing nitrogen. I had assumed that it must be under spring tension.

Opticswarehouse were wanting to charge me &#163;35 for the privilege of unscrewing the front of my scope

Thank you so much for the imformation. You have been a great help.

Regards

[Ridge Walker]

Just a quick question on the amount of depth of field different type of scopes produce. I have a Simmons 6.5-20 x 44 Mag and just roughly pacing it out the depth of field is about 20 Yards. Will a fixed mag scope produce a greater depth of field or is it just a case of the better the scope the more depth of field is produced. I am assuming that depth of field in scope terms is the same as the photographic use of the term i.e.The distance between the near and far focus points.

Thanks,
Paul

It's nothing to do with the quality of the scope ect. Its all to do with the mag. Higher the magnification less depth of field. That's why anything under 32 mag is not very good at range finding, The distance between 45yds & 55yds varies. It's more inportant especialy if you are shooting FT.
Yes it's the same as in photography.

[TheShootist]

This will now have a small gap between it and the spacer ring. Some people strech a big O-ring, (like a rubber band) over the front, then it "pings" into the gap, keeping the rain out. (you might need 2 O-rings.)
HTH
Gus

Certainly wont need two O rings, one is often too thick. You'll need a single small O ring about 15mm diameter and stretch it over the end bell and into the slot. Stretched that far it will be thin enough (be prepared to snap one or two stretching them that much!)

Opticswarehouse were wanting to charge me £35 for the privilege of unscrewing the front of my scope

Regards

The reason people use the O ring method is that the inner threaded lens carrier on the 10x40 has a locking agent on it making it nigh on impossible to seperate the end ring. So the O ring method lets you move the two together. Opticswarehouse charge £35 because they do it properly and seperate the two components and adjust the inner threaded carrier before replacing the end ring and leaves no gap to be filled and no O ring.

It's nothing to do with the quality of the scope ect. Its all to do with the mag. Higher the magnification less depth of field. That's why anything under 32 mag is not very good at range finding, The distance between 45yds & 55yds varies. It's more inportant especialy if you are shooting FT.
Yes it's the same as in photography.

Mag and object lens size (apature in photography... you stop down for more depth of field). So smaller lens will give you better depth of field and conversly a larger 50mm plus lens gives smaller depth of the field... So high mag and big lens is the way to go for FT... Moderate mag and smaller lenses for HFT


Regards
Tony