November 21st, 2011, 01:39 PM
Forgive my ignorance here, but I am thinking of investing in a DOF adapter. I have been offered an SGPro for a decent price, however the chap who is selling it says that the achromat is for the EX-1. Are achromats specific for each camera? I have a JVC HM700 - can anyone offer help in explaining what I need to purchase in order to make it compatible with my camera.
Thanks in advance
November 25th, 2011, 09:09 PM
The Sony PMW-EX1 and EX3 use 1/2" sensors and a custom Fujinon zoom for the camera type. The image footprint of the lens is a very very close fit to the size of the image sensor. I recall there were reported a few instances of the steadyshot function causing a vignette, which I recall was an exceptional event dealt with under normal warranties.
The peculiar optical characteristics of this lens/sensor combination offerd unique challenges to the 35mm adaptor manufacturers. A normal achromatic dioptre use for relay would throw a relayed image which would not be in uniform focus across the frame. The special achromats were made to solve this issue.
You may therefore find that on a "normal" camera, there may not be sharp relay focus across the whole frame. I can't speak for Wayne's adaptor as I have not used it but the optical rules for all adaptors are fairly close.
I found that with the EX1 special achromat on a Letus Extreme, it worked fine on a Sony Z1 with the Sony's own lens iris in the sweet zone of about f4-f6.3. The Z1 is a 1/3" sensor camera.
The JVC HM700 is I understand, a 1/3" sensor camera. The JVC GY-HD100 family of cameras also offered some unique challenges when relay was directed through this camera's own detachable Fujinon lens. My recall is that placement of the achromat on the front of the Fujinon lens itself was the best solution. This style of lens is not internally focussed. The front of the lens focus barrel moves forward and turns as closer focus is sought therefore the physical distance between the front element of the camera lens and the 35mm adaptor changes.
I think Ted Ramasola used Wayne Kinney's achromat on his medium format adaptors for his JVC HD250 so an email to him via dvinfo.net might be helpful to you. I found that I needed to mount my own AGUS35 styled adaptor to the fixed 72mm filter mount on the front of the Fujinon lens but also to support the adaptor with bridgeplate and rails as the fixture on front of the Fujinon lens is not intended to carry weight.
My personal preference would be to give Wayne Kinney an email to see if he still has stock of the standard achromat suited to your camera/adaptor combination and whether he has tested for the HM700. As you would be aware, 35mm groundglass relay adaptors are a declining market now that HD capable 35mm DSLRs have been turned loose into the marketplace. Ongoing development by adaptor manufacturers for newer camera types may not now be financially sustainable for them.
If the price is very, very good I'd say go with it. It would be possible to make it work but might require some modification which may be beyond your do-it-yourself abilities. There are Century Optics achromats which can be made to work with the JVC HD*** camera family optical path but changes to the spacing between camcorder and adaptor likely would be needed. The combined camera/adaptor/lens/mattebox may become an awkardly long appliance.