The Letus Extreme "smear"

[Jamon Lewis]

Originally Posted by Coco Bermudez

I already built my own LetUs Extreme for my HD100...work beautifully. And I am not talking about adding the adapter to the end of the fujinon lens. I was able to get a adapter to connect nikon prime to the HD-100 body and then attach the Extreme to it...works like a champ!

EXTREME - NIKON PRIME - JVC

Really? I'd like to know more about that...

[Bob Hart]

Les Bosher JVC to Nikon lens adaptor >> Nikon prime lens (35mm or 50mm) >> close-up lens or achromatic dioptre >> the hard bit you make your self - new bridging tube between back of Letus and front of Nikon.

NOTE: This is a theoretical "means", not a verfied and tested "end" result.

[Steve Brady]

Originally Posted by Bob Hart

The means of the achieving those solutions is likely to have been a new groundglass with a finer texture and greater transmissiveness.

The piper to be paid is that beyond a certain point, the finer the grade of the groundglass texture, the more pass-through of aerial image occurs.

It manifests at its worst when the soft background contains bright sharply defined highlights such as white barked tree branches in late afternoon or pinshines off motorcars etc..

Choice of groundglass texture is all a balancing act.

From what I see in Phil Bloom's grabs, sharp highlights are coming through the groundglass.

The downer is choices will have to be made to avoid bright pinpoint highlights in background.

The upside is that footage from this groundglass will intercut much better with direct-to-camera footage.

Lens choices may not make much difference.

I'm no expert, but shouldn't it be the case that if the camcorder's aperture is wide open, then the aerial image will be out of focus anyway? Perhaps these undiffused pinpoint highlights could be eradicated by opening up the camcorder's aperture and using an ND filter?

[Bob Hart]

I am no optical expert, just someone who sometimes gets a few cogent thoughts together and discovers a particular experiment works.

The use of a wider camcorder aperture makes sense and may account somewhat for the inconsistent manifestation of this artifact and that it is much less apparent in controlled artificial lighting environments. In those, everything is often opened wide to suck in every available skerrick of light which might account for this anomaly.

My personal preference is to try to stay within the camcorder's optical sweet spot in regard to aperture, mainly to stay in the sharpness zone, but also to avoid reported diffraction artifacts attributed to very tight camcorder aperture settings and small format CCDs. Your comment gives me cause to re-examine my preferences.

With the existing LETUS35 direct relay models, this is also somewhat mandatory as the Minolta relay lens sharpness tends to go off when it is fully wide-open. If Quyen is going with a custom relay lens for the new "Extreme" things could get interesting.

I can't speak for the Brevis, SGPro or Redrock M2 as I have not played with them.

The P+S Technik Mini35 direct relay version for JVC HD100, does not seem to care what you do to it. The relay lens is apparently sharp all the way to wide-open, which is likely why you pay premium price for the product.

Aerial image has not passed through in any work that I have observed on it thus far. The same best practice rules apply relating to flare and light levels at the groundglass.

According to P+S Technik's Tino Liberatore, who demonstrated their products here earlier this year, the grade of groundglass they use is as fine as it can be taken without producing passthrough and a lot of work was done in arriving at the ideal grade. (my paraphrase recollection of his discourse).

With alternative adaptors and homebuilds with finer groundglass textures, a long setback arrangement with a lower power dioptre might work better in this regard than a short setback arrangement with higher power as the camcorder's own inherent depth of field will be shallower from being zoomed furthur in or at maximum. This might account for P+S Technik's use of a long arrangement besides the optical benefits relating to edge-to-edge sharpness.

The use of ND filters before the groundglass is consistent with best practice to limit internal reflection and flare in the groundglass in any event.

[Coco Bermudez]

Originally Posted by Bob Hart

Minolta relay lens

Pardon my ignorance...but how does a relay lens differs from a regular lens?
I've googled it but I quite don't get it.

When building my own Letus Extreme version for the HD100 i had copied the idea by looking at a picture of the current Letus version for the HD100. I saw there was a lens attached to the camera body and that was in turn attached to the Letus. After searching for the perfect lens...i found a nikon that would allow me to focus on the Letus Extreme. The picture is perfect and sharp...still i dont understand the concept of the Relay Lens.

[Bob Hart]

In basic terms, it doesn't. All you are doing with relay is taking a picture of another picture. However there are desirable minimum performances required from it.

The term "relay" is applied to the optics which lie between the groundglass in the case of a 35mm adaptor or the display tube in night vision.

In "lens-in-camera" style video cameras, the "relay" lens becomes the combination of the camcorder's inbuilt lens and (if neccessary), the close-up lens which goes on front to enable closer focus.

In detachable lens style cameras the "relay" lens may be a dedicated lens to replace the standard lens and good for nothing else than close focus, perfect image without barrel or pincushion distortion and preferably equal sharpness throughout its aperture range. If an adaptor builder chooses to use the existing standard camcorder lens plus a close-up lens on front, this combination becomes the "relay".

Ideally, a dedicated lens will also be small to avoid the combination of camcorder and adaptor becoming too unwieldy.

SLR camera lenses in the range approx 35mm to 50mm can be used to "relay" the image from the groundglass to a detachable lens style camcorder imager. Most will require an added close-up lens on front or forward offset to enable "macro" focus, so there is little advantage to this approach except for cost.

The LETUS35 uses a 50mm Minolta SLR camera lens. P+S Technik use a dedicated lens which previous references here suggest is made for them by Schneider-Kreuznach.

For home builders, the 55mm f3.5 Micro-Nikkor might work for them without any close-up lens on front straight off the Les Bosher adaptor or may require a minimal forward offset.

The low light performance would be less than ideal.

Off-topic, the Micro-Nikkor f3.5 55mm apparently was used in microlithography for scaling of the microprocessor designs from human workable drawing sizes down to the real-world size of the chips in the early days of R&D, another reference from this site.

[Coco Bermudez]

Originally Posted by Bob Hart

In basic terms, it doesn't. All you are doing with relay is taking a picture of another picture. However there are desirable minimum performances required from it.

The term "relay" is applied to the optics which lie between the groundglass in the case of a 35mm adaptor or the display tube in night vision.

In "lens-in-camera" style video cameras, the "relay" lens becomes the combination of the camcorder's inbuilt lens and (if neccessary), the close-up lens which goes on front to enable closer focus.

In detachable lens style cameras the "relay" lens may be a dedicated lens to replace the standard lens and good for nothing else than close focus, perfect image without barrel or pincushion distortion and preferably equal sharpness throughout its aperture range. If an adaptor builder chooses to use the existing standard camcorder lens plus a close-up lens on front, this combination becomes the "relay".

Ideally, a dedicated lens will also be small to avoid the combination of camcorder and adaptor becoming too unwieldy.

SLR camera lenses in the range approx 35mm to 50mm can be used to "relay" the image from the groundglass to a detachable lens style camcorder imager. Most will require an added close-up lens on front or forward offset to enable "macro" focus, so there is little advantage to this approach except for cost.

The LETUS35 uses a 50mm Minolta SLR camera lens. P+S Technik use a dedicated lens which previous references here suggest is made for them by Schneider-Kreuznach.

For home builders, the 55mm f3.5 Micro-Nikkor might work for them without any close-up lens on front straight off the Les Bosher adaptor or may require a minimal forward offset.

The low light performance would be less than ideal.

Off-topic, the Micro-Nikkor f3.5 55mm apparently was used in microlithography for scaling of the microprocessor designs from human workable drawing sizes down to the real-world size of the chips in the early days of R&D, another reference from this site.

thanks for the response...you da man. Upon close inspection, my lens in between the letus extreme and the JVC is a Nikon with Macro..I remeber that all other lenses I tried did not work. All that extra telephoto that I was getting, did not allow me to properly focus on the ground glass...go figure

[Bob Hart]

Coco.

If you have a chance, could you shoot a test chart and post a frame grab, also provide the model of Nikon lens. This would be a good help for home-builders seeking direct relay to the JVC HD100 style and Canon XL style camcorder families.

If this approach is viable, the stills lens vendors and ebay may become confounded by another sudden demand for a particular lens type.

[Coco Bermudez]

Originally Posted by Bob Hart

Coco.

If you have a chance, could you shoot a test chart and post a frame grab, also provide the model of Nikon lens. This would be a good help for home-builders seeking direct relay to the JVC HD100 style and Canon XL style camcorder families.

If this approach is viable, the stills lens vendors and ebay may become confounded by another sudden demand for a particular lens type.

I will gladly do it....but....where do i download a test chart. Do i have to use certain lights, wattage, what distance from the chart should I shoot. Any paramaters I should keep in mind? Any type of lens in front of the LetUs Extreme?

[Bob Hart]

Coco.


A few of us here have used the EIA 1959 chart.

Here is a web address which gives some info on charts. It linked to a high quality copy of the EIA 1959 chart which can be downloaded as a .pdf and printed.

http://www.bealecorner.com/trv900/respat/

Use the standard 50mm lens. The chart should frame vertically at about 1M to 1.2M, which is about 39" to about 47" approximately. There will be a missing piece on the sides because this chart is a 4:3 chart.

Whatever light you can put on it which does not force you into more than about 3db video gain should be okay. Position the lights in traditional key-fill or crosskeys so that no shine comes back off the chart. Otherwise take it outside and clothespeg it to a chairback.

Try to make sure it is square-on to the camera lens otherwise there will be soft areas.

[Brandon Freeman]

Phil, just curious, when you shot the initial footage that revealed the smear, did you have the camera iris closed tightly, or did you stop down with an internal ND filter? Check this thread out here, and give me your thoughts.

http://www.dvinfo.net/conf/showthrea...=112518&page=2

Being a soon to be Letus owner, I'm following this with great interest!

[S. Abdul Jamal]

Originally Posted by Coco Bermudez

I already built my own LetUs Extreme for my HD100...work beautifully. And I am not talking about adding the adapter to the end of the fujinon lens. I was able to get a adapter to connect nikon prime to the HD-100 body and then attach the Extreme to it...works like a champ!

EXTREME - NIKON PRIME - JVC

which adapter are you using to mount the nikon lens to the jvc body ?

which nikon prime lens work the best ?

any magnification issue ?

do you have any footage to post ?

thanks

[Phil Bloom]

Originally Posted by Brandon Freeman

Phil, just curious, when you shot the initial footage that revealed the smear, did you have the camera iris closed tightly, or did you stop down with an internal ND filter? Check this thread out here, and give me your thoughts.

http://www.dvinfo.net/conf/showthrea...=112518&page=2

Being a soon to be Letus owner, I'm following this with great interest!

can't remember. But not experienced it since