Subscriber Discussion

Need A 100mm+ Lens For A 1.3MP Camera - Recommendations?

I got a case where I need to look at a hole of 20x20cm at a distance of 12m and according to the lovely calculators I'm in need of roughly around 100mm+ lens. It says I actually need a 216mm lens, but I recon that with a 100mm I already have enough detail, but more is always better.

I have this scarey feeling I might need a motorised lens, and the prices on them ain't pretty.

Perhaps any of you know any lenses that could fit this case ? The closest I could find was a Fuijinon 8-80mm.

How about a C-Mount 2x extender with a 75mm lens?

Does anyone know if extenders degrade the image of megapixel rated lenses?

If they don't, your best bet is either the Computar TEC-V7X or, if that's too expensive, the Kowa LMVZ990-IR.

You could also stick an SLR lens on the camera, but I don't properly understand how to calculate the field of view on those lenses, so I'm going to let someone else advise you on which lenses would be appropriate.

The question isn't if but how much the image quality will be degraded by an extender. I would hope it to be less than a 2x digital zoom... Keep in mind though that extenders steal about a full stop of light and limit the usable imager size.

Also found this one in the list of the usual suspects: Tamron 13VG20100AS

There is this lesser known manufacturer who has a broad lineup of fix focal length lenses for CCTV and machine vision: VS Technology, they offer lenses with up to 100m focal length in various qualitiy grades (SD - Multi MP).

Got another trick up my sleeve, although this one borders on cheating: You can use a camera with a 1/4" Full HD imager and crop it to 1.3 MP. The pixels and accordingly the field of view are about 1.7 times smaller, making it look like you are using a 1.7 times longer focal length. This will give you a smaller field of view, but not necessarily more resolution.

SLR lenses usually state their "true" focal length and thus behave like a CCTV lens with some crazy mount. However, if the lens is made for smaller sensors (eg. Canon EF-S, Nikon DX) they sometimes state a "Full-Frame equivalent" focal length. This one already takes the crop factor from above into acount, so divide by the crop factor to get to the true focal length.

Excellent, thanks!

Although I thought that Tamron wasn't megapixel rated? That's why I didn't mention it.

Just found that Tamron in our lab, sitting right next to a Senko ADL MHV12x1016D. A quick subjective test turned out that the Tamron is at least on par with the Senko, even without the megapixel rating. I guess that some manufacturers are just more generous with their megapixel labeling than others. While the Tamron is rated for 1/3" imagers, the Senko is made for a 1/2" sensor, so they probably account for the bigger pixels. On the other hand the Senko is IR corrected, which usually comes at the cost of some image quality in the visible region but keeps the performance up at night. If you don't need the IR correction the uncorrected version might still beat the Tamron.

I would give megapixel ratings for CCTV lenses the same credibility as lux ratings for cameras - never trust the datasheet, if possible see for yourself. On that note: IPVM, please do more lens tests! (That's what I'm here for, anyway)

Good to know!

A website with which I happen to be familiar sells that lens for less than $130. Combine it with a $60 extender, and it's really your cheapest option.

Computar Ganz has some great C mount lenses that are magapixel rated with fixed focal lengths. They are rated for 1/2" and 2/3" sensors but we have used them on 1/3" cameras with great results. For that application I would consider using the 50mm fixed lens with the 2x adapter. We buy that lens from ADI for about $100.00 Can't remember what the doubler costs.

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Have you considered making the camera a 2MP, so then you need less zoom for pixel density you're looking for?

There was another thread on here for long range fixed and vairfocal lenses. Hopefully someone turns up with the link.

We have the computar 75mm megapixel lens and the 1.5 x extender sitting on a shelf as we were going to use it for a particular installation that never happened. M7528-MP and EXC1.5

One downside I can see about the 75 mm lens is the f-stop is 2.8 whereas the 50mm M5018-MP2 is only f1.8 so there's a lot more light available with the lesser focal length. Of course the extender will also reduce the light too so there's that to consider. To be honest we have not used the extender yet so I have yet to see just how much it reduces the light and image quality.

I think I just might play around with the 75mm lens and extender we have and see what it's like!

Thank you all for the suggestions. For the time being I'm trying out 2X extenders.

Since I'm looking into a hole of a large cannister where they hold liquid steel, lack of light is the last thing I have to worry about.