Rifle Scopes Photo/Video Geek Question

[LoneWolfUSMC]

Ok boys and girls, put your thinking caps on and check my math.

Assuming a full frame sensor (35mm film) equivalent, it is pretty well accepted that a 50mm lense best approximates the focal length (zoom) of the human eye.

So theoretically I would need a 500mm lense to approximate what we see through a 10x optic and 1000mm for a 20 optic.

Where am I going with this? I am looking at a new video rig to be able to record long range video. It's a DSLR with a crop body (1.6x) and the ability to digitally zoom 10x and retain full HD. I have an EXTREMELY good 70-200mm lens. With a 1.6x crop factor this brings the lens up to 320mm equivalent and the digital zoom would max it out at the equivalent of 3200mm on a full frame DSLR. Even if the 10x digital zoom cancels out the 1.6x crop (which I am betting it will) that leaves me with a system that will give me approximate the same view in full HD that a 40x spotting scope without having to resort to adapters, brackets and all that nonsense.

 

[fdkay]

Re: Photo/Video Geek Question

John, you make my head hurt!

Have you tried any of the photo forums?

 

[hk dave]

Re: Photo/Video Geek Question

The 1.6x factor doesn't really bring a 200mm lens up to 320mm... but rather it "crops" down the image. A true 320mm lens would have different focus fall off, resolution, as well as perspective.

But say it's for looking at a 1 dimensional thing like a target, it would work just fine.

As for digital zoom... that is also "cropping". There is no actual "zoom" going on. It's just the camera cropping down and using the center of the sensor. You lose massive resolution when you do that.

So imagine you're running 1080p video or 1920x1080... if you digital zoom in 10x, you're essentially running 192x108 video.

 

[LoneWolfUSMC]

Re: Photo/Video Geek Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: hk dave</div><div class="ubbcode-body">
As for digital zoom... that is also "cropping". There is no actual "zoom" going on. It's just the camera cropping down and using the center of the sensor. You lose massive resolution when you do that.

So imagine you're running 1080p video or 1920x1080... if you digital zoom in 10x, you're essentially running 192x108 video. </div></div>

Normally I would agree with you, beacuse that is how most "digital zooms" work. However the Canon EOS T3i uses a MUCH larger sensor than is needed for digital video. It's one of the only cameras that I know of that has "movie crop" instead of a real "digital zoom" what it does is instead of dropping pixels to make a multi-megapixel image into a 1080p image it just uses the center pixels from the sensor. Effectively this crops the image. No it isn't real "zoom" like an optical zoom, but it also does not loose any digital resolution. The limit is the resolution of the lens you attach. In the case of Canon "L" glass that rivals what is on 99.9% of rifle scopes that is a pretty wide limit.

I started thinking about this because I very frequently shoot a still, then crop in very tight when I use it in a video. The image still looks amazingly sharp. The same process occurs with the "movie crop mode" it just occurs in camera. While the camera's processor isn't powerful enough to deal with all of the data coming off the sensor at 24fps, it is powerful enough to just take the center pixels which is exactly what I would see if I just cropped a full resolution jpeg to 1080.

I wish my EOS 60D did this now, but it doesn't. Since I need a second HDSLR now, I am thinking the T3i may allow me some stunning long range video using the glass I have now. It's way cheaper than trying to hang an 800mm zoom on my 60D.

 

[LoneWolfUSMC]

Re: Photo/Video Geek Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fdkay</div><div class="ubbcode-body">
Have you tried any of the photo forums? </div></div>

I would have the opposite problem with photo forums. They don't think in 10x, 20x, etc. It's all in focal length (50mm, 80mm, 200mm, etc). They don't directly translate, but for the purpose at hand I think it may be close enough. With what I am trying to accomplish I don't really care about bokeh, DOF, etc. I just want to be able to capture mirage and splash at a distance.

The "other" way is to just jack a digital video camera into a spotter, but the results are often less than cinematic.

 

[dcjs]

Re: Photo/Video Geek Question

John,

you're right that translating focal length to "magnification" as we know it in telescopes (binoculars, spotters, rifle scopes) is difficult, and approximating 50mm focal length on 35mm format to "1x" magnification doesn't really work for this purpose since the output size and viewing distance of the reslulting image is unknown. The correctly calculated photographic magnification, which is the relation between the object size and the image size on the image plane, would be ridiculously small for larger distances.

If you want to know how your view through the camera with a lens of a certain focal length looks compared to a spotting or rifle scope, it is best to compare the <span style="font-style: italic">viewing angle</span> (angular measurement like mrad or MOA!).

Assuming you are using the center 1920x1080 pixel portion of the EOS T3i, we first need to know how big that senor area is. That particular camera has a pixel pitch of ~4.3µm (sensor width in mm divided by the corresponding number of pixels of the long side of the image), so we're looking at an area of ~8.26x4.64 mm².

Now we need to put those numbers for the width and height plus the 200mm focal length into this online widget that spits out the result way faster than I could even remember where to look up how to calculate this, and we get the corresponding <span style="font-style: italic">angular</span> field of view (the result is in degrees and minutes).

Given the widescreen video format, I think the height of the image is what really matters, which is 1°20' or 80 MOA in this case. Now you just need to look up what optic has an 80 MOA/24 mrad FOV. In a riflescope with it's comparatively small FOV, this would be about 15-16x magnification. In a spotting scope with it's larger FOV, it would be equal to less magnification of course.

Anyway, if I have managed to explain my way of thinking, you'll be able to run the numbers for different focal lengths etc. and see for yourself what is equal/similar to what. If my explanation was too convoluted or you have any other questions, feel free to ask.

 

[LoneWolfUSMC]

Re: Photo/Video Geek Question

Thanks for the input David!

 

[hk dave]

Re: Photo/Video Geek Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: LoneWolfUSMC</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: hk dave</div><div class="ubbcode-body">
As for digital zoom... that is also "cropping". There is no actual "zoom" going on. It's just the camera cropping down and using the center of the sensor. You lose massive resolution when you do that.

So imagine you're running 1080p video or 1920x1080... if you digital zoom in 10x, you're essentially running 192x108 video. </div></div>

Normally I would agree with you, beacuse that is how most "digital zooms" work. However the Canon EOS T3i uses a MUCH larger sensor than is needed for digital video. It's one of the only cameras that I know of that has "movie crop" instead of a real "digital zoom" what it does is instead of dropping pixels to make a multi-megapixel image into a 1080p image it just uses the center pixels from the sensor. Effectively this crops the image. No it isn't real "zoom" like an optical zoom, but it also does not loose any digital resolution. The limit is the resolution of the lens you attach. In the case of Canon "L" glass that rivals what is on 99.9% of rifle scopes that is a pretty wide limit.

I started thinking about this because I very frequently shoot a still, then crop in very tight when I use it in a video. The image still looks amazingly sharp. The same process occurs with the "movie crop mode" it just occurs in camera. While the camera's processor isn't powerful enough to deal with all of the data coming off the sensor at 24fps, it is powerful enough to just take the center pixels which is exactly what I would see if I just cropped a full resolution jpeg to 1080.

I wish my EOS 60D did this now, but it doesn't. Since I need a second HDSLR now, I am thinking the T3i may allow me some stunning long range video using the glass I have now. It's way cheaper than trying to hang an 800mm zoom on my 60D.</div></div>

If the camera does indeed not lose resolution during "digital zoom" then that might be the ticket.

The things I said still apply though when digital zooming or 1.6x cropping when it comes to focus falloff, lens resolution limits and perspective.

 

[Lowlight]

Re: Photo/Video Geek Question

Get the IWitness adapter, find an iPhone 4 or 4s and hook it to a good spotter and you'll get great 1080p video.

I have some images and video I will post this week. It's good.

Go to Phil Bloom and he shows some footage and the crop factor. He uses a Canon and D800 and you can see the distortion.

Getting useable video at distance with consumer, and prosumer cameras is tough unless you rent a couple of those $10k lenses. Even a super 35 chipset. We filmed a lot of the SH DVD with a super 35mm. Even with a $15k lens you aren't gonna get what you want.

Putting a camera down range is better.

 

[hk dave]

Re: Photo/Video Geek Question

I agree with Frank... best thing to do is put the camera down range.

When you're video taping things from that far... the image is so compressed in focus that it loses all sense of depth anyhow... unless of course that's what you're trying for.

 

[_Windrider_]

Re: Photo/Video Geek Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: LoneWolfUSMC</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: hk dave</div><div class="ubbcode-body">
As for digital zoom... that is also "cropping". There is no actual "zoom" going on. It's just the camera cropping down and using the center of the sensor. You lose massive resolution when you do that.

So imagine you're running 1080p video or 1920x1080... if you digital zoom in 10x, you're essentially running 192x108 video. </div></div>

Normally I would agree with you, beacuse that is how most "digital zooms" work. However the Canon EOS T3i uses a MUCH larger sensor than is needed for digital video. It's one of the only cameras that I know of that has "movie crop" instead of a real "digital zoom" what it does is instead of dropping pixels to make a multi-megapixel image into a 1080p image it just uses the center pixels from the sensor. Effectively this crops the image. No it isn't real "zoom" like an optical zoom, but it also does not loose any digital resolution. The limit is the resolution of the lens you attach. In the case of Canon "L" glass that rivals what is on 99.9% of rifle scopes that is a pretty wide limit.

I started thinking about this because I very frequently shoot a still, then crop in very tight when I use it in a video. The image still looks amazingly sharp. The same process occurs with the "movie crop mode" it just occurs in camera. While the camera's processor isn't powerful enough to deal with all of the data coming off the sensor at 24fps, it is powerful enough to just take the center pixels which is exactly what I would see if I just cropped a full resolution jpeg to 1080.

I wish my EOS 60D did this now, but it doesn't. Since I need a second HDSLR now, I am thinking the T3i may allow me some stunning long range video using the glass I have now. It's way cheaper than trying to hang an 800mm zoom on my 60D. </div></div>

I have a Celestron Telescope that with the right adapter becomes a 1300mm lens. I wonder if that would work? Not that it helps you but it made me curious.

 

[Lowlight]

Re: Photo/Video Geek Question

Reading this again,

It doesn't just work via the sensor crop, you have to consider the sensor bit depth. Your stills are different from video because the depth is higher. Those DSLR are doing two thing, primilary stills get the focus. The video part is secondary.

Going to a cheaper sensor with a low video resolution won't give you better images down range because of the crop factor. Think of it more as height and width and not length. It might have a 12 bit still sensor and an 8 bit video one. So the crop on the still will out perform the video cropped at the same place.

My AF-100 is a micro 4/3rd and had crop factor over the Sony F3 we used, and I have a Nikon mount to use my Nikkor still lenses. You increase the mm on the lense but the Sony we used was still better resolution. It's about the depth and range, can you pull the pixels upfront without blowing them out.

There is a reason they don't do long shots from far away and put secondary cameras out. Even the 4k stuff is not for pulling in as far as you are asking it work.

 

[Ring]

Re: Photo/Video Geek Question

you are better off buying a HD camcorder with a 40+ to 70 X Optical Zoom..

many on ebay for under 200$...

 

[Lowlight]

Re: Photo/Video Geek Question

I think he wants a DSLR for the "look" it has, the shallow depth of field,

I am pretty sure he is not interested in a camcorder.

And digital zooms in the field blow out, and are not great, especially if there is anything in the air. They shake bad in the wind, and generally speaking just don't perform well. Especially at $200, nothing in that range looks good.

Then after, you are stepping on it to get it uploaded so you lose some there, and they don't look good at all, cheap camcorders are just that, cheap.

 

[Lowlight]

Re: Photo/Video Geek Question

Here are the two cameras we used and I would not attempt to shoot the video at targets downrange.

F3

We even used a crop feature in post that tightened in the shot, and still that far away, not right.

These lenses are like $15k, you can see just how big the 35mm and 50mm was, the 85mm we used was a tank.

My camera was the AF-100 which allowed me to use my Nikkor 70-200m, as well I have some longer lenses and still even with a crop factor, not happening.

 

[LoneWolfUSMC]

Re: Photo/Video Geek Question

You bring up good points.

I need another DSLR for a "B" camera so I may end up picking up the T3i just to see. Worst comes to worst, I will just stick it downrange behind a steel plate.