add on vs. scopeless

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reindeer
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add on vs. scopeless

Post by reindeer » 29 Sep 2014, 13:02

Why is it that a scopeless NV seems (is??) much brighter with added IR than an add on? This is the impression I get after watching various youtube videos on the subjet.
Is this because the complicated multiple lens system in a riflescope allows less light go through than a typical camera lens as used in most scopless builds?
Is this also true for high end scope brands with transmissions > 90%?
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some bloke
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Re: add on vs. scopeless

Post by some bloke » 29 Sep 2014, 13:17

Yup. - plus Light loss increases with magnification because the scope exit pupil gets smaller so it illuminates less area of your eye - or the camera sensor' However it remains the best option for longer range NV shooting.

Scopeless/dedicated really scores for air and rimfire ranges with light shy quarry because it can use less light. Most of the scopeless videos I see use more light than they need, which is seen as whiteout mostly around the centre of the image or below.

I'm not going to try to explain the exit pupil - read here lol:

http://www.singularsci.com/Accessories2.htm
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Re: add on vs. scopeless

Post by reindeer » 29 Sep 2014, 13:57

Thank you for our explanation. I have one more question though.
I use the 16 mm lens that comes standard with the Sure 24 add on package. I don't know the F-stop of this lens.
Is there really much to gain by using a 16 mm F 1.4 megapixel lens instead?
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Re: add on vs. scopeless

Post by Snapper » 29 Sep 2014, 14:12

I think it depends on different factors - scope size, quality, lens coatings etc, as my add on is better than my scopeless. Scopes generally don't have many elements (lenses) and a simple board lens may only have 2. Unlike the lens on my scopleless which is an f1.8 zoom which may have 7 to 10 elements, the lens on my add-on is a simple f1.2 lens so not only is it roughly a stop faster it also has fewer elements.

I am getting a new (well, second-hand) 75 mm f1.2 lens tomorrow so I will be able to do a like-for-like comparison between the two setups.

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Re: add on vs. scopeless

Post by Jirka » 29 Sep 2014, 14:31

some bloke wrote:Yup. - plus Light loss increases with magnification because the scope exit pupil gets smaller so it illuminates less area of your eye - or the camera sensor' However it remains the best option for longer range NV shooting.
If the scope lets thru the same amount of light regardless of magnification (does it?), then to me the opposite would seem true - the smaller the exit pupil and the area illuminated, the higher the light intensity. So not all sensor pixels would be lit, but those that would, would receive more light.

As for light transmission in scope vs lens - I do not see any significant difference in the number of lens elements in add-on vs scopeless. My Nikko Stirling scope 3-9 x 40 uses 6 or 7 elements in 5 groups - plus one or two in the camera lens. My Nikkor 50/1.4 lens uses 8 lenses in 7 groups, 85/1.8 has 9 elements in 9 groups and my guess is that Cosmicar 75/1.4 will not be far behind.

I suspect, that the main difference in infrared light transmission is in the quality of optical coatings. In my scopeless spotter, a relatively cheap Honeywell 5-50/1.6 CCTV lens performs better than the above mentioned Nikkor 50/1.4 and even my add-on setup (NS 3-9x40 + E700 with 16 mm lens) is slightly more sensitive.

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Re: add on vs. scopeless

Post by some bloke » 29 Sep 2014, 18:07

Jirka wrote:
some bloke wrote:Yup. - plus Light loss increases with magnification because the scope exit pupil gets smaller so it illuminates less area of your eye - or the camera sensor' However it remains the best option for longer range NV shooting.
If the scope lets thru the same amount of light regardless of magnification (does it?), then to me the opposite would seem true - the smaller the exit pupil and the area illuminated, the higher the light intensity. So not all sensor pixels would be lit, but those that would, would receive more light.

As for light transmission in scope vs lens - I do not see any significant difference in the number of lens elements in add-on vs scopeless. My Nikko Stirling scope 3-9 x 40 uses 6 or 7 elements in 5 groups - plus one or two in the camera lens. My Nikkor 50/1.4 lens uses 8 lenses in 7 groups, 85/1.8 has 9 elements in 9 groups and my guess is that Cosmicar 75/1.4 will not be far behind.

I suspect, that the main difference in infrared light transmission is in the quality of optical coatings. In my scopeless spotter, a relatively cheap Honeywell 5-50/1.6 CCTV lens performs better than the above mentioned Nikkor 50/1.4 and even my add-on setup (NS 3-9x40 + E700 with 16 mm lens) is slightly more sensitive.
I don't know if the same amount of light gets through at all mags - I have no means of doing that. :angel:
I suspect that day scopes pass less light because of the much smaller lenses in the erector tube before the image gets to the exit pupil.

What I do know is if you check out what you can see on an average night through your day scoped rear add-on rig without using IR, then remove your rig and look about you will see a stack more.

If you were to spend the same amount on a quality lens to go in front of the camera as you'd spend on a dayscope you will be a very very happy chappy with what you can view without giving away your presence at rimfire ranges, and far beyond for spotting only.

Here's a quick vid I did soon after I spotted the potential (Pun intended) Its a street light lit area, so not as shockingly different as if it's done in the country side.

I'm sure the image quality would become worse if I raise the scope mag. I guess I could do that if anyone wants me to.
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Re: add on vs. scopeless

Post by Jirka » 29 Sep 2014, 19:11

some bloke wrote: If you were to spend the same amount on a quality lens to go in front of the camera as you'd spend on a dayscope you will be a very very happy chappy with what you can view without giving away your presence at rimfire ranges, and far beyond for spotting only.
I have a lens, which costs about 8 times as much as my Bushnell Elite 6500 and I have access to some even more expensive glass, so I will give it a try :-)

And one more observation: we are all talking about lenses in terms of f-stop and about scopes in terms of % of light transmission. Is that not completely wrong? If a scope gathers noticeably less light, then it is only logical, that less light reaches the sensor and it does not matter whether only 90 or 95 % of the light gathered by the objective gets thru.

To me it seems it would make more sense to consider f-stop or speed of the scope rather than how many % of gathered light it can transfer. So if I have a scope whose objective is 50 mm in diameter and its focal length is 125 mm, then the total amount of light delivered by the scope should be comparable with a f/2.5 lens - less than half of what what f/1.4 lens on scopeless can deliver. If however, the scope used a „shorter“ objective lens, its speed or f-number would be lower. Is that not the true reason why some people get different results when comparing add-on vs scopeless?
I'm sure the image quality would become worse if I raise the scope mag. I guess I could do that if anyone wants me to.
Yes, my experience is the same. But I thought it was because I was unable to focus the scope precisely on high magnification in infrared light.

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Re: add on vs. scopeless

Post by some bloke » 30 Sep 2014, 04:20

Add-on Vs scopeless is still very much a horses for courses affair, sort of long range Vs short range.

We have probably all seen the murky edged high scope mag videos with only the centre part of the screen lit up. I think that is mostly due to the small exit pupil but may also be aggravated by the increasing tightness of IR beams to penetrate long distances.

Just as scopeless is making no/low IR gains at moderate range, larger illuminator lenses are reaching further out to make gains for scoped NV too. I rather think that more can be got when brighter larger emitters evolve to give a larger beam at current outer ranges without sacrificing brightness so the mag doesn't need to be cranked up as much.

If I were a long range scoped shooter I think I would be trying scopes with a larger objective to create a larger exit pupil. I think some are trying such a 'beast' already, but why do ocular lenses have to be so small? :think:

I realise that the latter parts of what I wrote may appear to conflict with my low light preferences, but bear in mind some people used to have tea plate size lightforce reflector lamps on their rifles, and longer range shooting doesn't need to be anywhere near as covert because hunters smell and sound doesn't generally reach those distances.

I also have a bug in my brain that reflectors still have gains to make from LED's:
There are vehicle type LED 'bulbs' with LED's fitted to the sides of a square stem?... I've got enough debts with what I do so I'll let someone else take that idea further for scoped rigs. :D
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Re: add on vs. scopeless

Post by snoopy » 30 Sep 2014, 18:46

Jirka wrote:
some bloke wrote: If you were to spend the same amount on a quality lens to go in front of the camera as you'd spend on a dayscope you will be a very very happy chappy with what you can view without giving away your presence at rimfire ranges, and far beyond for spotting only.
I have a lens, which costs about 8 times as much as my Bushnell Elite 6500 and I have access to some even more expensive glass, so I will give it a try :-)

And one more observation: we are all talking about lenses in terms of f-stop and about scopes in terms of % of light transmission. Is that not completely wrong? If a scope gathers noticeably less light, then it is only logical, that less light reaches the sensor and it does not matter whether only 90 or 95 % of the light gathered by the objective gets thru.

To me it seems it would make more sense to consider f-stop or speed of the scope rather than how many % of gathered light it can transfer. So if I have a scope whose objective is 50 mm in diameter and its focal length is 125 mm, then the total amount of light delivered by the scope should be comparable with a f/2.5 lens - less than half of what what f/1.4 lens on scopeless can deliver. If however, the scope used a „shorter“ objective lens, its speed or f-number would be lower. Is that not the true reason why some people get different results when comparing add-on vs scopeless?
I'm sure the image quality would become worse if I raise the scope mag. I guess I could do that if anyone wants me to.
Yes, my experience is the same. But I thought it was because I was unable to focus the scope precisely on high magnification in infrared light.
95% of 0.01 lux is quite a lot more than 90.
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Re: add on vs. scopeless

Post by Jirka » 30 Sep 2014, 20:07

0,0095 lux and 0,009 lux is almost no difference. If you just use f/1.8 lens instead of f/1.2, you lose 50 % of light and you have to try hard or have side-by-side comparison to spot the difference.

As I wrote, we cannot just operate with %. The total amount of light available to sensor is an absolute value and it can be increased it by increasing the area from which the light is collected. This is the reason astronomic telescopes have enormous objective lenses (or mirrors). If you collect twice as much light (by using one-stop faster lens for example), and then lose 30 % of it inside the optics, you are still better off than with less light collected and only 5 % loss.

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