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Old September 20th, 2006, 12:34 PM   #1
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DVX100B and achromats

Hey guys!

Right now I'm trying to get a decent image with my DVX100B, a homemade adapter and two 58mm Canon 250D´s (with a stepring), but when I zoom in on the groundglass, I noticed the corners gets soft. When I zoom out everything is sharp and dandy.

Does anyone know why this happends?

Any help appriciated!
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Old September 20th, 2006, 01:58 PM   #2
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Do the corners get soft or do they darken a bit? Not sure why they would get soft. The 250D's use two elements, so they should be pretty good edge to edge. It could be that you're zooming in too far because the 250D's aren't strong enough. Maybe...
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Old September 20th, 2006, 03:25 PM   #3
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Hey Mike!

I've uploaded some footage so you can see for yourself! :)

http://martin.cmplete.com/adapter/

Compare the two pictures. Look at the green LED on the screen, it gets kinda distorted in the corner. I've managed to minimize the effect, but I want to know if I can get rid of it complete.

The funny thing is that I can get the corners into focus but that makes the rest of image out of focus. Whats up with that?

Anyone here with a DVX100B with better results than this? Please share :)
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Old September 20th, 2006, 03:32 PM   #4
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Interesting. Rather interesting. I've got a DVX100A, so I'm in a similar boat.

Seems like you're getting a hotspot in the middle there. Are you using a condenser of any sort? That may be part of it, but I doubt it. Edge blur is usually caused by the macros (or achromats in this case). Could be the stacking that's causing the problem. I've seen that happen with cheap macros, but the 250D's are achromats. Hmmm...hope someone else jumps in. I'm inclined to think it's the achromats. How far are you zooming in the DVX and what's your MF at?
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Old September 20th, 2006, 04:00 PM   #5
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Yes, I'm using one condenser (+12) close to the GG. I tried two but that gave me too much chromatic abberation. But the hotspot isn't that bad, it's just that it's more prominent in lowlight. :)


Yeah, stacking macros is not very recommended, i know. I thought I could get away with it by using good achromats, but apparently not :)

My zoom is 77 and my focus is 23.

What kinda setup do you have, Mike? What achromat are you using?
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Old September 21st, 2006, 12:10 AM   #6
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Two stacked achromats may well cause you problems, in combination with having the stepdown arrangement.

Does the stepdown ring place the achromat furthur forward of the camera? Some I have seen add as much as 4mm.

I think you may find that if you offer the achromat up to the camera hand-held without the step ring and get as close as you can to the camcorder lens without scratching it, you may get a small improvement as your zoom-through will lose a little of the edge abberation.

A single higher power achromat may be the only real solution.

7+ and nearly full zoom with the DVX100 (a?) gets you about 22mm x 16mm or slightly larger off a GG at about 120mm?

This was only with a handheld offering of my complete erecting AGUS35 for PD150 up to a DVX100 with a stepped down 58mm +7.

My stepdown ring does not place the achromat any furthur forward.

There was no condenser in the path.

The DVX100 (a?) was a nice image.
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Old September 21st, 2006, 12:34 AM   #7
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Guys, i'm confused here! I tought that dvx100b(and later models like hvx etc) have so small minimum focusing distance that You don't have to use any condenser. What i missed here??
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Old September 21st, 2006, 06:51 AM   #8
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Frank, the condenser is required to even out light distribution to (or from) the GG. The macro is another issue. Martin, pmail me on your achromat issues. I may be able to help you out :-)
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Old September 21st, 2006, 07:00 AM   #9
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Bob!

I am actually using three steprings, so that gives me about 1 cm distance between the DVX lens and macros, so I tried without the steprings, holding the achromats close to the lens, but I got the same soft corners. bummer :(

Well, a strong, single achromat might be the only way. It´s too bad I can't find any of these here in Sweden.

Frank!

I'm not really following you. Sure, the DVX has a great macrofunction, but that doesn´t mean you don't need a condenser? Perhaps you meant achromat ? Well, I can't really get that close to the GG. I have to zoom in, and when I do that without an achromat, it gets all blurry, and I can't focus on the GG! Am I making sense? :)
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Old September 21st, 2006, 08:43 AM   #10
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Quote:
Originally Posted by Dennis Wood
... condenser is required to even out light distribution to (or from) the GG...
and
Quote:
Originally Posted by Martin Lindstedt
Well, I can't really get that close to the GG
That is why most of sample footage seems always to me much with larger FL as lens given FL. You guys use actually smaler area than 24x36?
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Old September 21st, 2006, 09:37 AM   #11
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Martin, I think that using that strong of a condenser along with the stacked achromats may be the problem. Is the condenser placed next to the GG with the flat side against the GG? If that is the case then it's probably the achromats. If it is reversed (with the flat side NOT against the GG) I'd probably blame the condenser. +12 is pretty powerful, and assuming that it's a PCX lens that may be the trouble. Hmm...don't you love all the problems these things create? =)
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Old September 21st, 2006, 12:16 PM   #12
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Martin.

Email Dennis. As I understand things,

Achromatic dioptre - essential.
Condenser lens (es) - optional.
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Old September 22nd, 2006, 06:06 AM   #13
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Frank!

No, I'm using the entire 36x24 frame.


Mike!

My condenser is very close to the GG indeed, and the flat side facing it. I just tried without it, but no, the soft corners are still there.

"don't you love all the problems these things create? =)"

Haha, I hear you! Sometimes I just wish I could forget all about these technical stuff, and just go out and shoot something instead. That´s what really matters in the end. :)

Bob!

I've emailed Dennis. :)
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Old September 22nd, 2006, 07:53 AM   #14
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Quote:
Originally Posted by Martin Lindstedt
No, I'm using the entire 36x24 frame.
Why condenser if DVX100B can zoom given 24x36 frame?
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Old September 22nd, 2006, 08:19 AM   #15
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Frank,

The condenser lens is for eliminating the hotspot/vignetting only and sits againsts or very close to the GG. It's the macro/achromat that helps with zooming in and focusing. They have 2 different roles.
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