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Old January 15th, 2008, 12:40 AM   #1
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A Cheapper Achromat?

http://www.thecinecity.com/product.p...cat=258&page=1
could this possibly be the answer to my prayers for finally being able to afford the redrock? or is it just a cruel joke ment to tease me! lol please tell. thanks =D
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Old January 15th, 2008, 08:20 AM   #2
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The old saying comes into play here.... You get what you pay for!
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Old January 15th, 2008, 08:43 AM   #3
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This lens is not necessarily bad. It is even better if it is glass and not polycarbonate.

I have seen some polycarbonate optical products that have changed shape over time so I am not a huge fan of them.

My main concern is not knowing or being able to read from the website what power dioptre it is. Without this knowing you are really on a guesswork ride to maybe success, maybe a good way of using the sun to light the barbecue if it is not a success.

Rule of thumb :-

Non-flip adaptor 7+ to 10+ with 10+ beginning to introduce edges softness issues in some designs, to keep length of adaptor manageable.

Flip adaptor 3+ to 7+ to allow distance in the optical path for the foldback prism or mirror path to fit between GG and front of lens and still be able to focus sharply on GG.

Last edited by Bob Hart; January 15th, 2008 at 08:44 AM. Reason: error
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Old January 15th, 2008, 09:47 AM   #4
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I've been using a plain old +10 close-up on my redrock.
It cost me $20 dollars off B&H used.
The only problem I have is a bit of vignetting from the apature and just shoot accordingly and crop.
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Old January 15th, 2008, 02:15 PM   #5
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Samuel, so instead of buying the like 400 achromat from redrock, you can just buy something from bh? can i have a link or something please =D
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Old January 15th, 2008, 11:07 PM   #6
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If this lens is the Hoya 10+ or an unbranded equivalent, you may find it unsatisfactory depending on what camcorder type you use. The exit pupil diameter is too small to use on some camcorders without vignetting or soft edges or corners.

You can as suggested, crop out the vignette in post but then, you have a smaller view of the groundglass itself and consequent magnification of the texture, the proportional resolution loss associated with rescaling this image and the resolution losses arising from the digital effects process itself.

For $20 it is an easy tryout but most who have been playing with adaptors for a while, have tucked their heads into the doorway of this dead-end, backed out and moved on. (This population includes Redrock who started off as enthusiasts refining Agus Casse's original).

Redrock, SGPro, Brevis and Letus, which have their origins in the dvinfo community, sought alternative sources or placed custom orders for achromatic dioptres.

The suitable on-shelf lenses were fairly costly and not available in the higher powers needed for non-flip adaptors at the wider diameters required for initially the Panasonic HVX100 and subequent HDV cameras.

Last edited by Bob Hart; January 15th, 2008 at 11:11 PM. Reason: error
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Old January 16th, 2008, 12:09 AM   #7
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i mean i dont know if this is the same thing, but on my photographs i love using vignetta, i mean its kinda my style, but i dont know if its the same thing for video. does anyone have a screen shot of somethign with one of these adaptors?
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Old January 16th, 2008, 01:50 AM   #8
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Phil Bloom who posts on the Letus forums has previously for some clips, deliberately chosen the vignette effect of groundglass adaptors as a creative tool by not zooming in quite far enough to eliminate it.

You may find his clips or links to them here

www.philipbloom.co.uk

It is more desirable to have the choice rather than have to live within it by cropping in post.


(Whilst not normally given to adding oneliners on end of messages I could not let this one roll by without giving it a helping kick down the hill - I put myself in the frame for this comment - "The twins of genius and insanity were with him but genius did not like what it saw and went back."

Last edited by Bob Hart; January 16th, 2008 at 03:01 AM. Reason: error
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Old January 16th, 2008, 02:03 AM   #9
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Bob is totally right about what he is saying.

I do most of my work for the web and so the loss in resolution and all is acceptable to me. Ground glass texturing hasn't been a big problem with the M2 since it spins fast (more of an f-stop issue there). The local noise produced by the camera image sensor is however there in less than perfect lighting and if scaled will cause issues.

I will say, as I'm gearing up to go to HD, that I will probably be sucking it up and just spending the $400 dollars.

What I'm doing is down right unacceptable for the larger hvx or a1 type cameras unless you want dv resolution out of an hd camera or need a purposed filter to create the vignetting and soft edges. I'd just do it in post though.

This is a good example of why you might want to stay clear of this direction
Attached Thumbnails
A Cheapper Achromat?-showing-vignetting.jpg  
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Old January 16th, 2008, 02:06 AM   #10
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I bought my achromat from Cinevate for about $250.00, and use it doubled with the Letus 35a achromat to get better zoom incapability to eliminate vignetting on my FX1 and HV20 with that adapter. I also use with my self builth Redrock based spinner and a 5inch tube to give me a good image on it.

I saw a similar achromat on Ebay for $120.00. Never know what you are going to get there, though.
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Old January 16th, 2008, 02:31 AM   #11
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Samuel.

What you have there is not so much of a vignette as not being zoomed in close enough on the groundglass because you have picked up the outer edge of the disk, edge of lens rim or macro tube in bottom of frame.

I'm guessing the achromat is a 3+ if you are zoomed in all the way but as you suggest it is a 10+ something else is obviously going on. There seems to be no vignette from insufficient exit pupil diameter.

How long is the distance between front of achromat and groundglass?

Is the achromat mounted directly to the camcorder filter mount or very close to the front element of the camcorder's own lens? If that edge is the frame of the achromat and not the disk edge, then there seems to be a vertical offset because the centre of groundglass projected image is not centred to the optical centre axis of the achromat, which is itself not centred on the camcorder optical centre axis. This is a circumstance which is really really hostile to image sharpness.

Can you zoom in closer or position the achromat closer to the groundglass to be able to frame inside the bright part of the groundglass image.

If you can zoom in closer, do you lose ability for close focus at the "close" end of the camcorder lens focus or at the infinity end or is it pretty much centre in the camcorder's focal range?

Seems like you are not realising the best potential of the M2 at present which is a pity because properly set up it is a great adaptor. There's two feature movies, one in significant theatrical release in the US, originated on the M2 so you definitely have room to move here even by fine tuning what you already have.

Conservatively, I think I could get you another 50 TV lines of resolution just by fine tuning those two adjustments, achromat-camcorder lens optical axis centricity and position of achromat relative to the front lens element of the camcorder, closer = better so long as they do NOT touch glass and get scratched.

Loren. You'll find Phil Bloom's vignette effects on the JVC HD 250 Brevis page on the 35mm Shootout article he has there.

Last edited by Bob Hart; January 16th, 2008 at 03:03 AM. Reason: error
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Old January 16th, 2008, 03:04 AM   #12
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@bob

I'm using an older Panasonic dvc20. The issue I have is that I can focus on an image (with the camera alone) to about 2 cm from the lens. The camera probably wouldn't need any glass between the adapter except that the M2 is a big box and the camera has a bit of protrusion past the lens itself with the zoom controls and hand grip, so they can't get close enough to each other.
This causes me to have to zoom in, but then I lose focus. That's why I got the macro and I just took B&H's word that it was a +10, maybe it's not.

The M2 has that IMHO dumb reverse threading coming out of the camera side of the adapter and haven't bothered to to get a male-male ring to get them screwed into each other yet. I was going to get another generic macro and a reversing ring or whatever those male to male filter rings are called and see if it worked or not. I never lost a job from not having the M2 before so it's been mostly a toy for now.

What you see is from the aperture and will get better or worse at different stops. So maybe it isn't getting close enough to the GG. I just assumed it was that exit pupil phenomenon you mentioned.

The image was from some of my first shots when I had it all rigged up on wood and has since been fixed to be properly aligned, although not connected.

I really just wanted to play with one when I bought it, because to do it right, it seems you have to spend $2000-$3000 after lenses and mounts and matte boxes and monitors and on and on.
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Old January 16th, 2008, 03:21 AM   #13
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Samuel.


Wood is good even if sometimes ugly. Doesn't do much for the pose value on location but if results alone count -- .

The accessories are the icing on the cake for practical utility in an intense production environment where you need things to work predictably and fast.

You can get equally good images with much less, even just using a sharp f1.8 50mm on front of the M2 and no other lenses.

When you get the achromat centred and mounted to the threads, the distance from camcorder to achromat closed up, the correct distance achromat to groundglass for focus through the achromat established to be as close to infinity as you can get it but still leaving trim room for final focus - sharp on about 15 metres should be fine, you may find yourself a lot happier.

Sit on an aperture of f2.8 on a f1.8 50mm SLR lens, as close to f5.6 on the Panasonic as you can get with ND filters or none depending on available light, 1/50th or 1/60th sec shutter.
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Old January 16th, 2008, 04:47 AM   #14
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Bob

I found that you can use just about anything for building camera gear as long as you paint it black: wood, metal, plastic, anything. Your right, results are the supreme decision maker.

Now I use a 50mm f1.4 on f2-2.8 and just close the aperture as much as possible on the camera, so ends up about the same as you saying.

This camera is gonna retire soon. His twin brother had an imager go bad and I'm not up to sending it out for repair when I'm already going to buy a few new cameras in the next month or two.

To stay on topic though, I'm gonna see if $50 might make it work just for kicks
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Old January 16th, 2008, 11:10 AM   #15
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Just a thought on cheaper achromats. I've been off the adapter scene for a long time, but when I made a few I often used the achromats out of binoculars. You can get a good pair of binocs with a 10x or 12x magnification for $50. Only problem is that most of the lenses are coated with either a red or green tint and it messes with the colors. If you can find non-coated optics it's not a bad way to go. Is it the best way? No, obviously you can find even better quality glass. But it's a good place to start, especially if you don't have a lot to spend.
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