lense info required

[sodagar 0]

Hi,

I have a c-mount camera HR , and i have lences of F1.2 or F2.0 4mm standard from different manufacturers , so which lense either F1.2 4mm , or F2.0 4mm will give the best image results and what will be the diffrence.

And one more thing i have experiance that a standard fixed lense works more better in day and night as compared to auto iris lenses (VD,DD).Why is that so?

[Cooperman 0]

Your question initially relates to the maximum aperture of the lens and so should (in theory) provide an indication as to the light gathering capability of each optic; i.e. smaller number = bigger aperture = more light passing through.

 

So whereas you might expect that the f1.2 lens will work much better in low light conditions than an f2, in practice, the quality of the glass components (known as elements), the lens coatings and the basic optical design, will affect the eventual quality of the image.

 

Before I forget, you need to check that the lenses (particularly the f1.2) are 'C' mount so that they will work on your C mount camera. If they are 'CS' mount, they will screw on to the camera, but you won't be able to focus an image.

 

As regards auto iris lenses, in general terms, the graduated 'ND' neutral density filter which is fitted into an auto iris lens, serves to not only degrade the image, but also force the aperture to a wider setting, which in itself reduces the optical performance of the lens.

 

That's really a rather brief answer, so if you want me to bore you senseless with an even more detailed explanation, you only have to ask!!

 

BTW sodagar, welcome to the forum

[Thomas 0]

Isn't the T-Factor a better indicator?

[Cooperman 0]

It certainly should be Thomas, but .... how many lens manufacturers can you think of that use the 'T' factor to express their products light gathering capabilities.

 

In an ideal world, it would be very useful if all companies used a standardised measure, but as they don't, we're really stuck with a well proven concept - which is very roughly, don't accept as accurate anything that is written down on a specification sheet, until you've had a chance to prove it for yourself

[Thomas 0]

Oh that part is a given in any industry. I think Fujinon will list the T-Factor on the spec sheet itself. But they don't list it on the package or model number, so it would be useless without the spec sheet.