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Old February 17th, 2008, 06:34 PM   #1
Join Date: Dec 2006
Location: Central Coast - NSW, Australia
Posts: 1,364
long lens on the LEX

I'm shooting some surfing footage and I'm thinking about getting a longer lens.

I have the XH-A1 and could just get a Raynox or I can get a longer canon lens for the LEX. Is there any disadvantage in using a longer zoom lens (say 500, 800) with a higher F stop with the LEX.

I'm not thinking about DOF in this situation - Just looking at the most economical way to get closer to the board rider without getting my feet wet.
Cheers - Paul M.
www.relivetheday.com.au : www.perbenyik.com
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Old February 17th, 2008, 07:56 PM   #2
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You may find that using the Letus35 for long lenses will work against you due to the wider 35mm format, meaning a longer lens needed for the same field-of-view for the camera.

Refractive lenses of tighter aperture than f5.6 may cause fixed pattern artifacts. With the older Letus35 this was an issue with some lenses as wide as f3.5 but I understand the new Extreme has addressed that.

On the larger than standard movie frame groundglass area that some versions of the Letus35 and other adaptors use, you may encounter dark corners with long lenses. You may however also see that with the XH-A1 and the Raynox.

You may find flare from the overbright foam is more controllable with the Letus if you use a piece or more of ND filter gel in the space behind the lens inside the Letus lens mount.

You may find longer than 500mm becomes uncontrollable for aquiring and tracking your moving subject unless you pair two cameras on the one tripod, one to use as a sighting aid and for wide shot cutaways when you momentarily lose your moving subject.

Alternatively you can make a simple ring-sight and fasten it to left of your camera eyepiece centred on your left eye position. Harmonise this to the centre of the viewfinder view and with practice you'll find you can home in pretty quick.

In coastal environments wind buffet at good viewpoints can be a problem as I am sure you already know.

With the Letus or other groundglass adaptor, the choice of long lens options is greater. Best if they can be as wide an aperture as you can find them. I have even stuck a 1084mm f10.5 MTO on to see what would happen. Shake becomes a real problem.

http://www.dvinfo.net/media/hart/agusmto3.JPG The dark right margin is a prism misalignment, not the lens.

I even tried it with a doubler on to see what would happen - not much - ridiculous really - too blurry over long distances due to atmospheric haze except on really cold crisp clear days.

The mirror telephotos are interesting. They seem to lose a bit of rez compared to a refracting lens but the tighter fixed aperture does not seem to aggravate the groundglass artifact on my home-made. How the Letus will fare I cannot estimate.

The Mini35 does not artifact with a 500mm f8 Nikon mirror in daylight conditions so the new Letus may be fine.

Mirror telephotos create an interesting effect on out-of-focus pinpoint highlights. These become donuts.

If you can borrow or hire a Sigma f4-f6.3 50mm-500mm zoom, give it a try. The zoom Sigmas of this style need some protection from sand and dust as they breathe, quite literally, in and out through the lens mount with zoom movements and there is an exposed sliding joint. I've linked this clip to death recently so it may be boring, however here is is again.


This was shot with the Sigma on an AGUS35 which has close to the same groundglass area as the Letus. The whole rig took a hard knock whilst I was carrying it and the alignment was off. You will see a little of the edge of the groundglass disk. The groundglass finish near the disk rim is inconsistent so there is an observable artifact if you look for it when the Sigma is at f6.3 zoomed right in.

If there is an artifact with the Letus, zoomed right in will be where it becomes apparent. Surf shots with lots of brightness and contrast, textures and motion may mask artifacts if they turn up.

Last edited by Bob Hart; February 17th, 2008 at 08:18 PM. Reason: added URL
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Old February 18th, 2008, 04:56 AM   #3
Join Date: Dec 2006
Location: Central Coast - NSW, Australia
Posts: 1,364
..... Wow - thanks Bob. We'll have to start calling you the Oracle.

I was wondering about those mirror telephoto's. I know a couple of photographers and I'll hit them up for a lend of a few lenses to see what the results are.

From what you say it's certainly worth trying.
Cheers - Paul M.
www.relivetheday.com.au : www.perbenyik.com
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