Century Precision Optics - 10mm -> 6mm FocusFocus Adaptor
Posted 16 January 2013 - 04:49 PM
When using an adaptor, 10mm to 6mm, is there a specific method or chart to follow when attempting focus. Is there any difference in depth or light loss to factor in. Although the lens is refocused to a different size, im worries that the focus will be slightly off if i simply follow the 6mm charting ratio's and such. Best,
Posted 16 January 2013 - 05:28 PM
Posted 16 January 2013 - 06:37 PM
Funny how topics come in little clusters - in one of the black-lagic threads we were discussing how with adaptors when you go wider you actually get more light - as in a light-gain factor - it makes sense to me thinking that you're sucking more 'image' into the same area, so the density per area, per time is greater = more exposure.
Mind you, I don't know what I don't know about optics so I'm looking forward to learning.
Posted 16 January 2013 - 08:23 PM
Posted 16 January 2013 - 08:37 PM
The Speed Booster thing goes at the back of a lens and condenses the image circle, so that the same amount of light fills a smaller area, hence increasing the speed. It doesn't create a wider angle of view than the original lens had, it just allows the same angle of view on a smaller imaging area, effectively reducing the lens focal length.
Posted 16 January 2013 - 09:02 PM
The additional glass actually adds more reflective surfaces and refraction so that you lose some light.
Yep that's a given - but besides the point (but I know you know that I know that we know that )
I'm hitting a conceptual block - too many variables for my cache.
When you say 'they gather a wider view yes' I see a big evenly illuminated erm, 'void' (infinitely even and 'white' in all aspects for the sake of discussion) - ok, so standard optic gathers 1 'light unit' and presents it across the imaging sensor which has a unit area - the ratio between light and area is '1' (flux if you will). Now double your angle of view, the sensor now 'sees' 4 times the original viewable area of that infinitely even white ether - where does all this light go ? I see it hitting the same sensor - what I'm not understanding is why it isn't 4 times denser when it gets there - same sensor area, but it's 'collecting' area is 4 times bigger. The thing I'm not factoring in is the effective aperture - need to draw some diagrams but I'm stuck here with no dang pen.
Posted 21 January 2013 - 08:11 PM
I've also just completed a test, and the result with only the 10 mm lens, and then the 6 mm lens did not have much difference in light loss (at least not by a stop, anyway). So, it would appear that focus would now be my main question - and if you factor in Chris' comment of 'sucking more into a lens', perhaps the lens remains at it's base lens focus (in this case 10 mm) and as an addition, the frame is provided a wider angle. So, given that the 10 mm lens contains the preferred depth of field, adding a 6mm adaptor will offer more viewing to the scene. Seems like a bonus to me...