Stopping down slightly for shaper images

B

benandaim

Well-known member
Hi,

I was wondering if you should always stop down a lens slightly rather than shoot with it wide open if you'd like the sharpest possible image?

eg. With a 50mm 1.4 or 1.8 should you stop down to 2.8? & i'd like to know if the HVX lens should be stopped down slightly when focused on the GG rather than wide open for maximum sharpness.

Regards,

Ben :)
 
Most people agree that stopping the HVX lens down to 4.0 or higher is a good practice. Be sure your HVX focus is PERFECT, cause it will make a much bigger impact than the iris setting. If you are using a rotating disk style adapter, make sure your runout (disk wobble) is as perfect as you can make it as well. Check it often, especially after whip pans as gyroscopic forces can pull the disk out of alignment.

As far as the 35mm lens that's up to your artistic goals. You almost always loose sharpness at the edges first, but that's usually not so important as the action rarely takes place on the edges of the screen.

Most HVX + 35mm adapter users are pretty excited about the 200A because it's improvements will make using an adapter easier. You will be able to get the same image brightness with one of the two lenses stopped down an additional 1/2 stop (or with less lighting).

Bob
 
You can also get a sharper image by using a faster shutter speed. If I want it to be really sharp I use 130-degree or faster.


Marco
 
The image also gets sharper when your camera iris is stopped down in the range of 2.8~6.8. 5.6 the sweet spot.

I think the optimal conditions for an adapter setup would b 5.6 on the taking lens and 5.6 on the camera. It would be an interesting small test to see: whether stopping down the camera iris exhibits sharper results in a limited situation or the taking lens.

My guess is that stopping down the camera first optimizes sharpness and then the taking lens since the primary image (ground glass projection to camera lens) suffers before secondary (taking lens to ground glass). Thoughts?
 
Most still photography lenses normally have their sweet-spot at around f5.6-f8. Of course you can't stop down this much when shooting inside, but just about every lens get sharper the more you stop down until diffraction kicks in. Diffraction normally comes in at around f11.
 
Thanks Guys, I figured this might be the case but just wanted to verify.

Kholi your theory is what i had based my thoughts around.

Cheers,

Ben
 
From my own tests I would tend to agree with Kholi that i would first want to get my video camera down to 2.8 because the achromat is probably working the hardest - then close down the 35mm lens, but really that depends on the adapter the video camera and the specific 35mm lens. All the adapters seem to have better corner to corner sharpness then they did even 6 months ago so I wouldn't want to guess. Look on your own monitor .

Lenny Levy
 
Quotes from a post I made earlier this year, that discuss this:

"I'll go ahead and be the nerd in the room...

A lot of this talk about optimal f/stops has a lot to do with longitudinal chromatic aberration.

Basically, in a nut shell, not all the wavelengths of light passing threw the lens are focused on the same plane at very wide open f/stops. By increasing your depth of field via a tighter f/stop, you can increase your sharpness.

It looks sharper because more of the light is actually focused on the focal plane.
Typically, the green channel is spot on no mater what f/stop, and that makes some sense. It's the most important channel. It's always the cleanest, so a lower quality lens better make sure that channel is always performing spot on.

Look carefully at some footage shot wide open with high contrast edges. I guarantee you will see some hazy colored edges. If you isolate the red and blue channels, they will be badly out of focus. You see the colored edges because of LATERAL chromatic aberration. Thats a bit different. The different wavelengths of light are basically not lined up perfectly. You can compensate for it in post if you know how, and I do personally."

"Lateral CA is strictly mis alignment, and it can happen at any f/stop or focal length, though my personal studies with the DVX Leica lens have shown that it shifts around depending on what focal length you are on. I'm not sure about where its perfect just yet.

Longitudinal is strictly out of focus channels (to be more technical, not all wavelengths of light clearly focused on the focal plane). By stopping down, you can help negate this effect."

The above statements also apply to the SLR lens on your adapter, in a nutshell, a really sharp image via an adapter means killer light loss (due to the stopping down needed on BOTH lenses). The adapter must truly be custom made for a specific camera with great care taken to correct any issues with longitudinal CA in the host camera lens, via the achromat lens. This would allow you to shoot with wider apertures on the host camera, and maintain sharpness, in all three channels.

Honestly, I have not seen a single acrhomat do this properly yet, at least not for my DVX100....

Hope that helps,

NERD OUT!
 
This is precisely why we strongly encourage Brevis users with CF1le or CF1 in their adapters to dial in a few stops on their 35mm lens. We don't see a full stop of loss from the entire system to the camera until the 35mm lens is at f5.6 or so. There was a huge debate ongoing over the light loss linearity of 35mm adapters, which pretty much stopped when we shot a technical video demonstrating that one stop on the 35mm lens does not necessarily translate into 1 stop of light loss to the lens adapter. In other words, dialing in f4 is strongly recommended on the 35mm lens (assuming you're using CF1 or CF1Le), as total light loss to the video camera is still under 1 stop total.

The stock camera lens is where the hit is the greatest because one stop there is really 50% light lost. On the Undertow production currently shooting, the DP refuses to shoot with the HVX200 lens at less than f5.6. That's a lot of light, but the payoff in terms of the increase in sharpness at the corners we've seen at near 100 lines. Our $1500 Nikon 17-35mm zoom lens on the other hand is quite sharp at f2.8...which is wide open for this lens. I'd go as far as saying that the single biggest factor in edge sharpness (assuming the adapter is properly designed and configured), is the f stop setting of the video camera in use!

If you truly want edge to edge sharpness, you must baseline your camera first, then the 35mm lenses that you're planning on using. Scott (AC on Undertow) spent 3 days in our studio testing our Lomo lenses and the HVX200. He was thorough to the point of identifying a .125mm difference in collimation between our 80 and 50mm lenses. In other words, he's tweaking our micro-collimation turn 1/8 of a turn when using the 50mm Lomo so his focus marks match. Somewhere down the line we'll send this 50mm lens off so that it matches the others in the set. We're learning more and more that our micro-collimation capability is very critical to proper alignment and sharpness of the SLR or cinema lenses being used. I'd offer up this list, in order of importance, in terms of the Brevis MP.1 flip and what I think is critical to get sharp footage edge to edge:

1. Backfocus (camera to imaging element correct, and adjusted/checked all the time!)
2. 35mm lens properly collimated to adapter.
3. Oscillation tuning (that's why we use an onboard microprocessor)
4. Video camera f-stop setting.
5. 35mm lens camera f stop setting.

Methodically testing with your lenses, these tips in mind, and a decent chart will pay huge dividends in your footage! Our video university is our attempt to educate our shooters in improving their results, and certainly we're committed to raising the general level of understanding :-) Here's the corner of EX1 frame grabs (1080 24p HQ) at 200% showing the difference between f5.6 and f8. This DSC labs back focus chart tests up to 1600 TV LPPH. Note that we didn't test the EX1 lens wide open here, but you get the idea:



Verbal/Cerebral dump, off...
 
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Dennis,

I love the advances you've made in adjustments. I've a few questions. Is your current achromat optimized for both the EX and HVX for edge to edge? Or must I buy a separate achromat for each. Do you offer a kit that includes rings for both? How easy is the GG centering adjustment? This is an issue wit my past and current set-ups, making edge to edge fall off lopsided. What's the return policy - say I wasn't satisfied with the E2E.

Also how do the Lomos measure up against the Nikon 17-35mm?
Were you able to come up with an acceptable focus pulling method with the Nikon with its short draw?
re: EX tests pics. Is that 5.6 and 8 on the EX's lens or the 35mm lens?

My last question has nothing to do with sharpness - but have you made improvements in sealing the GG from dust? That was the main reason I unloaded my last Brevis. If this is too off topic, PM me.

As you may guess, I'm in the market for another adaptor that has easy collimation.
Tim
 
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Tim, our achromat is optimized assuming the video camera has a flat field of focus at close focus distances. The EX1 is the only camera of all the ones we've ever tested that suffers the distorted focus field issue to an obvious degree, and it cannot be fixed with an achromat. The other solutons just use a stronger achromat to mask the issue...something we're not doing. Our fix is not released yet, but we're in final confidence testing of our optical correction for the EX1.

The AC on Undertow is pulling focus just fine with the Nikons, using a combination of our 100mm diameter solid focus rings, and the Chroziel DV flavour folow focus ( the $1500 one). This FF is a beast with the Lomos as it requires 3 full rotatons for a complete rack on the 80mm. This however works to its advantage on the Nikon resulting in a complete rotation of the FF for a full rack on the 17-35mm. We're working on gear setups for our own FF to accomodate both situations. The Nikons are sharper edge to edge than the Lomos by a large margin, but breath much more during racks. That said, "Undertow" has four veteran film makers on the crew and every one of them prefers the organic feel of the Russian glass.

On the EX1, that's the bare lens we were testing. The sweet spot at f8 is a bit of a nightmare for adapter use as it means you must accept a lot of edge softness if you want to use this camera wide open.

Dust is always an issue with any adapter, but like everything else, we've been working on it. The important thing is that the adapter can easily be cleaned, and the imaging elements are removable, and washable if required.
 
Washable. Spin / Rinse cycle or hand wash?
re: lomos. "Organic" feel in the mechanics or the look?

re: FFocus. I have the same FF. Are you using the large or small gear? I bought it with the small and it takes a few turns to move it. I only use that for my real tight focus draws (50mm 1.4 and 35mm 1.4) Otherwise, I use the big gear.

re: EX fix. So if I get what you're saying. Some fixes just use a stronger magnifying glass so to speak. What is the alternative optical design?
If I buy the new and improved Bvis now? Will I be able to get the EX fix later with a user discount?

Sorry bout all the questions, but I'm on the verge of purchasing an EX and am always looking for something better in the adaptor world.

Thanks,

Tim
 
No spin, just a finger + soap and running water followed by a compressed air dry.

The EX1 solution is a modular thing, added later in a fashion similar to our interchangeable imaging elements. It is designed to be quickly removed if using any other camera other than the EX1.

The Chroziel FF is using the .8 pitch gear..and I believe there's only one spec'd for it. It's approx 30mm in diameter.

The Lomo organic reference is specifically to the look. The image is sharp but the bokeh has a certain quality to it. No one can quite put their finger on what it is...but everyone agrees they like it. Breathing on the 28, 50 and 80 is extremely low.
 
Actually Chrozsiel make two diameters for their FF. Small (model number 206-15) and a large (#206-12). Both are .8. The small one comes in handy for those tight draws.

Also, where can you find lomos. Rare bird these days.
 
they're becoming a hot commodity sadly. There was a set here on DVXuser going for 800 and now they're going for 3200. I'm gonna have a set next week and planning to just do a comparison of my own in aesthetic regards against a set of Zeiss standard speeds and Zeiss Contax.

I suspect that they wont be as sharp but "different". They also have a reputation of warming the image up noticably.
 
the set that went for $800 was all normal speed lenses without gear ring . i paid $1750 for the 75mm t1.6 and the 50mm t1.5 and find another high speed set of 4 oversea which i paid little over $3000 .
the 18mm and 22mm high speed are rare i've only seen the 22mm high speed for sale once on ebay and the set went for little over 4k .
 
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I'm confused. If the iris is wide open, it means you don't have a lot of light. How would stopping it down (reducing the light?) do anything but cause gain to kick in?
 
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