# Sensor sizes, where do the imperial sizes like 2/3″ or 4/3″ come from?

Video sensor size measurement originates from the first tube cameras where the size designation would have related to the outside diameter of the glass tube. The area of the face of the tube used to create the actual image would have been much smaller, typically about 2/3rds of the tubes outside diameter. So a 1″ tube would give a 2/3″ diameter active area, within which you would have a 4:3 frame with a 16mm diagonal.

An old 2/3″ Tube camera would have had a 4:3 active area of about 8.8mm x 6.6mm giving an 11mm diagonal. This 4:3 11mm diagonal is the size now used to denote a modern 2/3″ sensor. A 1/2″ sensor has a 8mm diagonal and a 1″ sensor a 16mm diagonal.

Yes, it’s confusing, but the same 2/3″ lenses as designed for tube cameras in the 1950’s can still be used today on a modern 2/3″ video camera and will give the same field of view today as they did back then. So the sizes have stuck, even though they have little relationship with the physical size of a modern sensor. A modern 2/3″ sensor is nowhere near 2/3 of an inch across the diagonal.

This is why some manufacturers are now using the term “1 inch type”, as this is the active area that would be the equivalent to the active area of an old 1″ diameter Vidicon/Saticon/Plumbicon Tube from the 1950’s.

For comparison:

1/3″ = 6mm diag.
1/2″ = 8mm
2/3″ = 11mm
1″ = 16mm
4/3″ = 22mm

A camera with a Super35mm sensor would be the equivalent of approx 35-40mm
APS-C would be approx 30mm

# Playing with lenses: 2/3″ Broadcast lens on PMW-F3.

OK folks. I wanted to see just how well a 2/3″ broadcast lens would work on an F3, but don’t have \$5.5k to fork out on one of the Abel adapters. So with a bit of head scratching, a few, lowish cost lens purchases and a few hours in the workshop I cobbled together my own adapter. At first I tried a 2x magnifier but this didn’t quite give me full sensor coverage and was soft out in the corners. With a little more work I took the magnification up to 2.5x and I have clean corners. I’m really pleased with the performance, although one lens element needs changing for a higher quality element to combat some softness when the iris is fully open.

My old Canon J16x8 f1.8 becomes a 24 to 320mm f4(ish) par-focal lens which is actually quite handy. Next step is to make up a power cable for the lens so I can use the zoom servo.

I’m considering trying to find a manufacturer that can make these up for me properly, the converter should cost a lot less than \$5.5k

# Playing with lenses: 2/3″ Broadcast lens on PMW-F3.

OK folks. I wanted to see just how well a 2/3″ broadcast lens would work on an F3, but don’t have \$5.5k to fork out on one of the Abel adapters. So with a bit of head scratching, a few, lowish cost lens purchases and a few hours in the workshop I cobbled together my own adapter. At first I tried a 2x magnifier but this didn’t quite give me full sensor coverage and was soft out in the corners. With a little more work I took the magnification up to 2.5x and I have clean corners. I’m really pleased with the performance, although one lens element needs changing for a higher quality element to combat some softness when the iris is fully open.

My old Canon J16x8 f1.8 becomes a 24 to 320mm f4(ish) par-focal lens which is actually quite handy. Next step is to make up a power cable for the lens so I can use the zoom servo.

I’m considering trying to find a manufacturer that can make these up for me properly, the converter should cost a lot less than \$5.5k

# Can you use a 2/3″ Zoom on a 35mm camera??

Can you use a 2/3″ B4 broadcast zoom on a 35mm camera. Well yesterday I would have said “no”, but having seen this video on the AbelCine web site, now I’m not so sure. UPDATE: OK Should have read the specs…. it’s only suitable for smaller sensors as it has a 22mm image circle, the F3 has a 27mm diagonal. It’s still a viable option for the AF100 however.

http://blog.abelcine.com/2011/02/11/using-23-lenses-on-the-panasonic-af100/

The HDx2 adapter magnifies the image to fill a 35mm sensor, doubling the focal length at the same time. This is very intriguing as 35mm zooms are few and far between and very expensive. There is a 2 stop light loss (well if you expand the image 2 times that’s what happens) but most broadcast zooms are pretty fast lenses to start with. I can’t help but think that the pictures might be a little soft, but if you already have decent 2/3″ glass then the \$5,500 for the adapter might make a lot of sense. Anyone out there with experience of one of these? I’d love to know how it performs.

# Can you use a 2/3″ Zoom on a 35mm camera??

Can you use a 2/3″ B4 broadcast zoom on a 35mm camera. Well yesterday I would have said “no”, but having seen this video on the AbelCine web site, now I’m not so sure. UPDATE: OK Should have read the specs…. it’s only suitable for smaller sensors as it has a 22mm image circle, the F3 has a 27mm diagonal. It’s still a viable option for the AF100 however.

http://blog.abelcine.com/2011/02/11/using-23-lenses-on-the-panasonic-af100/

The HDx2 adapter magnifies the image to fill a 35mm sensor, doubling the focal length at the same time. This is very intriguing as 35mm zooms are few and far between and very expensive. There is a 2 stop light loss (well if you expand the image 2 times that’s what happens) but most broadcast zooms are pretty fast lenses to start with. I can’t help but think that the pictures might be a little soft, but if you already have decent 2/3″ glass then the \$5,500 for the adapter might make a lot of sense. Anyone out there with experience of one of these? I’d love to know how it performs.

# Low Cost 2/3? HD Lenses.

OK, here’s my take on the situation.

If money is no problem then the safest bet is to purchase a good quality HD lens, expect to spend at least £8k.

If you budget is restricted then the situation is much less clear. There are now several low cost 2/3? HD lenses designed for cameras such as the Panasonic HPX500. In my opinion these lenses are just not worth the money. They might be cheap (£4k ish) but the one’s I’ve played with have been pretty grim, suffering from lots of CA and soft corners.

If your on a tight budget the best thing you can do is take your camera to a good dealer and go through their second hand lenses, trying them on the camera. Check for resolution (use a chart), corner softness, CA and contrast. I did this and ended up with a Canon 16x8x2 IF lens. I found that lenses with lower zoom ratios tended to be better than those with higher ratios. I’m really pleased with my lens and when compared to the latest HD equivalents I can not tell the difference in real world use. It certainly outperforms all the budget HD lenses I’ve tried.

One interesting thing that I have discovered in my research into this subject is that Contrast is what makes the biggest difference in lens performance, not simply resolution as one might expect. Visually the next thing you notice is CA. This is a tough one as when you increase the resolution or sharpness of a lens you also tend to increase the CA.

Until lens manufacturers start to release MTF curves for their lenses the only thing we have as buyers to go on is the advertising blurb. It’s easy for a manufacturer to claim improved performance or new glass or other technology, but without accurate MTF curves it’s all pretty meaningless. You would only need the tiniest resolution improvement to be able to claim that you new HD lens range is sharper than your SD range, it could just be a fraction of a percent difference.