HM 700 and 2/3 lens

[Calvin Bellows]

Hi everyone. I am looking at getting a 2/3 lens for my HM 700. The reason being is I am going to be shooting a stage and would like to have a longer lens without buying a big box lens. I know I'll need an adapter ring. Is there anything else I should consider/be aware of when doing this? I have found some used SD lenses on ebay would these work? The final output will be web and dvd. Also the reason for not wanting to get the 2x piece is that is takes 2 stops of light which we all know is important to have with these 1/3 cameras. Thanks for your help.

Fujinon A18x7.6 BDERM M48 2/3" 18X Lens B4 2x Extender - eBay (item 370488651193 end time Mar-30-11 01:31:04 PDT)

Canon J21aX7.8 B4 IRS SX12 Broadcast Lens GREAT Cond! - eBay (item 220752083583 end time Mar-16-11 15:34:03 PDT)

[Calvin Bellows]

No takers? Can anyone suggest somewhere I can post this on DVinfo or suggest another site I can look.

[Joachim Claus]

Calvin,
just a few remarks with lenses designed for SD. The optical transfer charachteristics for HD are more stringent than those for SD. Top quality HD-lenses take care of the higher resolution and have adaquate optical charachteristics. With an SD-lens in front of an HD-camera you will probably loose some resolution (lines per inch) and you will also find a higher degree of chromatic abberation. This is all due to the higher resolution of the CCD/CMOS chip. With SD-chips small chromatic abberations are not visible, while with HD-chips they are.

Nevertheless, a good 2/3 SD-lens may provide better results than the usual cheap HD-lenses supplied with the camcorder. There is one advantage of using a 2/3'' in front of a 1/3'' camera, that is the CCD/CMOS chip of the camera only uses the middle portion of the lens' optical footprint and abberations which usually increase with objects at the edges are invisible. I use a good quality Canon YH19x6,7IRS 1I2'' lens from my old GY-DV500 with my HM700 with excellent results. I compare it with my high quality Fujinon HTS 18x4,2BRM, and I cannot detect any chromatic abberation with the Canon but some with the Fujinon at the edges, while I observe some loss of sharpness with the Canon.

Joachim

[George Kilroy]

I'd be interested in doing this as well for similar reasons as Calvin.
Can you tell me where I'd get the adaptor I'd need to use a Fujinon S20x6.4BRM.

[Mike Kujbida]

JVC lists two different adapters, the ACM-12 for 1/2" lenses ($740.00 at B&H) and the ACM-17 for 2/3" lenses ($1,353.00 at B&H)

JVC Professional Accessories page

[Calvin Bellows]

Thanks a lot Joachim. I never thought about the CA but it sees to be minimal since it will use the centre of the lens. Also since it uses the middle of the lens is there still lines lost? Is this noticeable? If it is could you point me to an example. Thanks.

[Peter DeArmond]

A JVC document discussed using legacy 1/2 and 2/3 inch SD lenses with the HM700. The document was used as part of a marketing campaign to TV stations -- basically, to show they how they could save money with JVC. You can find it online here:

http://pro.jvc.com/pro/pr/2009/nab/2009ProHDReport.pdf

Start at page 45 for the information on using SD lenses. Very interesting.

[Joachim Claus]

Originally Posted by George Kilroy

I'd be interested in doing this as well for similar reasons as Calvin.
Can you tell me where I'd get the adaptor I'd need to use a Fujinon S20x6.4BRM.

The S20x6.4BRM is a 1/2'' lens- So you would need JVC's 1/2'' adapter.
Joachim

[Joachim Claus]

Originally Posted by Calvin Bellows

Thanks a lot Joachim. I never thought about the CA but it sees to be minimal since it will use the centre of the lens. Also since it uses the middle of the lens is there still lines lost? Is this noticeable? If it is could you point me to an example. Thanks.

Calvin,
the loss of resolution performance only appears with SD-lenses when used for HD-cameras. With SD, the optical transfer performance of the lens is calculated taking into account the SD-format with 720 x 576 (PAL) pixels, i.e., if the lens is designed for 2/3'', the sensor has a format of 12.8 x 9.6 mm (4:3 format). The optical resolution needs to be about 28 linepairs/mm to allow 720 horizontel pixels.

If you consider a 2/3'' lens designed for HD (1920x1080 with 16:9 format), the sensor format is 13,8 x 7,8 mm. To achieve the horizontal resolution (1920 pixels) the lens needs to achieve 70 linepairs per mm.

The resolution with a 1/3'' sensor would require a lens with a resolution of 140 linepairs per mm, because the sensor size is half of the 2/3'' sensor (6.9 x 3.9 mm), and you still want to get 1920 horizontal pixels (or 960 linepairs over the sensor's horizontal 6.9 mm.

If you consider the two extremes SD 2/3'' and HD 1/3'' sensor sizes, you can easily recognize, that the lens designed for the SD-case will not provide the full resolution with the HD-case.

Example:
Assuming, the SD-lens is well designed and has an optical resolution of 60 linepairs per mm (which is double the number needed for SD), you will get a resolution of 828 linepairs with a 2/3'' HD-sensor, and 414 linepairs with a 1/3'' sensor. From this example you can see, that you will achieve 86% of the horizontal resolution with 2/3'' sensors, and only 43% of the horizontal resolution with 1/3'' sensors.

This is just a theoretical discussion of the subject. But it shows the physical limitations of video lenses designed for a specific sensor size. By the end of the day, you cannot avoid to make test shots using a Siemens star and then consider the achieved results.

Joachim

[Joachim Claus]

I have to correct my previous message, as I accidently used wrong sizes for 2/3'' and 1/3'' sensors. The correct values for the lenses footprints are 11mm diameter for the 2/3'' and 6mm diameter for the1/3''. This results in sensor formats of 8.8 x 6.6mm (SD 4:3 format) or 9.6 x 5.4mm (HD 16:9 format) for the 2/3'' case and 5.23 x 2.94mm (HD 16:9 format) for the 1/3'' case.

Taking these values into my calculation results in the following:

The loss of resolution performance only appears with SD-lenses when used for HD-cameras. With SD, the optical transfer performance of the lens is calculated taking into account the SD-format with 720 x 576 (PAL) pixels, i.e., if the lens is designed for 2/3'', the sensor has a format of 8.8 x 6.6 mm (4:3 format). The optical resolution needs to be about 41 linepairs/mm to allow 720 horizontel pixels.

If you consider a 2/3'' lens designed for HD (1920x1080 with 16:9 format), the sensor format is 9.6 x 5.4 mm. To achieve the horizontal resolution (1920 pixels) the lens needs to achieve 100 linepairs per mm.

The resolution with a 1/3'' sensor would require a lens with a resolution of 184 linepairs per mm, because the sensor size is about half of the 2/3'' sensor (5.23 x 2.94 mm), and you still want to get 1920 horizontal pixels (or 960 linepairs over the sensor's horizontal 5.23 mm.

If you consider the two extremes SD 2/3'' and HD 1/3'' sensor sizes, you can easily recognize, that the lens designed for the SD-case will not provide the full resolution with the HD-case.

Example:
Assuming, the SD-lens is well designed and has an optical resolution of 80 linepairs per mm (which is double the number needed for SD), you will get a resolution of 768 linepairs with a 2/3'' HD-sensor, and 418 linepairs with a 1/3'' sensor. From this example you can see, that you will achieve 80% of the horizontal resolution with 2/3'' sensors, and only 44% of the horizontal resolution with 1/3'' sensors.

This is just a theoretical discussion of the subject. But it shows the physical limitations of video lenses designed for a specific sensor size. By the end of the day, you cannot avoid to make test shots using a Siemens star and then consider the achieved results.

Joachim

[Joachim Claus]

I made some test shots with a Siemens Star with two lenses:
1. Fujinon HTs18x4.2BRM designed for 1/3'' cameras,
2. Canon YH19x6.7IRS which has an extender with factor 2 and is designed for 1/2'' cameras.

The results and description can be found in an album under my profile.

Joachim

[Calvin Bellows]

Joachim

Thanks for your hard work and good explanations of all of this. Way over my head but after reading your posts and seeing your pics I think I have a good handle on it. I love it when I can learn new stuff. I'm going to get a lens and try it out for myself and see how it goes. Thanks again.

[Joachim Claus]

You are welcome Calvin. I had a lot of fun doing the test shots, and I also learned more about my two lenses.
Joachim

[Calvin Bellows]

So what lens do you like to use more...your SD or HD one.

[Joachim Claus]

In most cases I use the Fujinon HTs18x4.2, because is has a much wider angle of view. My 1/2'' Canon YH19x6.7 is mainly used for sport shots, where I love the large zoom factor, especially when switching the extender on.
Joachim