New HV30 owner with DIY lens adapter

[Dick Mays]

Others might be interested in building lens adapters, so I thought I'd post my experience. The need to LIGHT the subject is clear, but I was surprised the HV30 could focus so closely that an macro lens wasn't needed.

Not quite the results I wanted as there is more of a hot spot in the center. Any pointers on how to minimize this will be appreciated.

http://www.youtube.com/watch?v=tUak2qZbCMo&fmt=18

[Chris Barcellos]

Hey Dick great one.....

That hot spot you are dealing is what you have to actually zoom inside of. While the HV20 gets pretty close, you still have to deal with some vignetting.

If you go here, you will see one design using a vibrating screen. And they reference some places to get $ 7 achromats. I use a Cinevate achromat that normally goes on Brevis.

http://www.jetsetmodels.info/news.htm

I am attaching some pics of two spinning adapters I've made. I've also experimented with one of the Jetset vibrating screens, and made my own wax ground glass screens.

In the pics, the one with the almuminum cage is first one I fashioned, made from a Radio Shack project box. But it was bulky, like yours. So I am working on a second one using 3 inch sewer pipe fitting, lids from caschew cans, motor from a CD player, and the disk from Redrock I used them on both projects. They have a DIY plan kit for $50.00 which gives a starting place, and provide on disk. You can buy extras for $25.00. That disk is smaller than a CD, so you can make thing a bit smaller.


I had gone to vibrating screens, but I am trying to get back to spinners because Letus and the others seem to be rolling back that way. I think a lot of it has to do with CMOS chip rolling shutter issues, thought no one really talks about it. With my vibrating system, I have occasionally seen footage act like a bowl of jello.

[Chris Barcellos]

Dick:

Pic below are of rig I currently shoot with HV20, with a Letus 35a modded with the Cinevate achromat. It seems to be a bit better than Letus's original acrhomat. L
Once I get the smaller spinner perfect, I will try to phase out the 35a. I shoot it upside down so footage flip isn't required. However, I did order a flip module from Letus, so that will change design of rig.

[Dick Mays]

Chris,

You are the one that got me interested in this in the first place. I believe you posted some video of your daughters facing a window and then turning on cue.

I see that it is a slippery slope when you start down the path of wanting a different look that what the camera provides. Now I need to budget for a small video display, better tripod mount, achromat. Etc. Not that I know what that is.

Does the achromat lens reduce the vignetting effect?

Thanks.

[Chris Barcellos]

Dick:

Essentially, the achromat is a closeup lens. In the early days, people were using closeup lenses, but there was a lot of loss of edge sharpness, so these achromat got used. I am not real sharp on optics, and diopters, etc., so I settled on getting the Cinevate one cause I figured if it worked for Brevis, it should work for this. I see on line there are 72mm ones you can get from India, for $ 115.00, but I haven't tried those. There are other sizes two.

The achromat essentially allows you to focus closer. What you showed in your initial posted film was image that was degraded and vignetting at the edges. With an achromat, you can focus while zooming inside that degraded area. You will also have to experiment with the ideal distance of putting the camera away from the ground glass, to get it right on.

My early Letus35a also had a condensor on it, designed to reduce vignetting or edge fall off, but most self builders are relying primarily on the achromat. It is a bit of give and take. With the condenser in, I felt general sharpness was affected.

The reason I stay with the 72 mm is that it can be fit to anything smaller, and will actually work on 82mm for the HVX too. On top of that, with the HV20, I figure, while I don't need that large of a achromat, I'm thinking have a larger sweet spot to work with.

The cheap achromats referred to in the link I gave you actually work pretty well for what they cost, though, they lose a little on the edges. They won't work on the big cameras, but for the HV30 should do okay.

I think this was film you were referring too:

http://www.youtube.com/watch?v=d1UDU1DpEPc

Forgive the aspect ratio issue, as I had learned YouTube only did 4:3 at that time.

[Lee Wilson]

Originally Posted by Chris Barcellos

With my vibrating system, I have occasionally seen footage act like a bowl of jello.

Yep ! Test footgae with JelloFX™ from the rolling shutter + vibration motor.

It appears on all this footage, but is at it's most apparent on scenes with obvious geometry / hard edges:

http://www.vimeo.com/1382835
http://www.vimeo.com/1383747

It can look very much like heat haze.

[Chris Barcellos]

Lee: My experience is that if you vibrate at slower rates, this effect won't happen as much. I discovered this because in my Letus35a, I had a motor lead break, so I replaced it with another motor. It ran a lot faster, and it seemed like it was causing not only noise, but rolling shutter issues to the extreme. I later fixed one of the Letus FEs for a friend, and in process I discovered they had surface mount resistor on the leads. They are so tiny I never saw them-- to small for me, with my gear to solder back on. I just got a handfull of regular in line resistors from Frys, and discovered that a 33 ohm worked about right. Since I put that in my line, I have a pretty stable picture, and the vibrations reduced, and the noise is reduced too ! With the JagPro, I would try to slow it down a bit.

[Lee Wilson]

Cheers for the tip Chris, I will try just that.