Century .75x filter vignettes on EX1

[Max Allen]

Hello everybody,

Wondering if anyone has had success in finding a clear and pola filter to fit the Century .75x converter (0HD-75CV-EX3) that will not vignette? The converter is being used with the EX1.

What happen was the 2 filters below were purchased based on the 102mm front thread specification of the converter on Schneider's site, http://www.schneideroptics.com/Ecomm...=1474&IID=6766 and both vignette, which is not good. So now stuck with these filters.

Schneider 102mm True-pol non-rotating 68-013002
Schneider 102mm clear slim MTD coated 68-120021

Thanks in advance.

[Dave Morrison]

I'm surprised that YOU'RE surprised! Any time you start stacking filters, you're begging for trouble. Even thin-mount filters are pushing the limits when you put them on any WA attachment. I doubt I could put much of anything on my Century .6x

[Tom Hardwick]

Might be better to get a 77 mm polarisor, that way it would work with and without the wide-angle converter. They might swap them out for you.

[Max Allen]

Thanks for your thoughts guys.

Originally Posted by Dave Morrison

I'm surprised that YOU'RE surprised! Any time you start stacking filters, you're begging for trouble. Even thin-mount filters are pushing the limits when you put them on any WA attachment. I doubt I could put much of anything on my Century .6x

Hi Doug, how great it would be if those two filters could be stacked on the Century .75x! The bad vignetting happens with just one filter mounted, even the slim. I guess I could have been more specific.

Trouble is I've found no other 102mm filter by any manufacturer. As the wide angle is highly susceptible to dust and grime in ENG work, the use of a clear filter, at minimum, would be helpful to protect a $1000 unit; especially with this converter being a full zoom through which lets you have it on more often and longer through a shoot.

If no filter is suitable my immediate thought would be why Schneider/Century built this converter with front threads? Also, a hood for this converter is needed to counter flare and glare. In my opinion wide angles should come with a hood for ENG; again, especially when you have a zoom-through.

I've been a fan of Schneider products for a long time so I like to see them put out good products.

Originally Posted by Tom Hardwick

Might be better to get a 77 mm polarisor, that way it would work with and without the wide-angle converter. They might swap them out for you.

Hey Tom, the Century .75x mates with a bayonet mount onto the EX-1. This allows nothing to be on the EX-1 lens when mounting the wide angle adapter so I don't see how you could use a 77mm pola with the wide angle, unless I understood you wrong.

[Tom Hardwick]

Ah - a bayonet mount, so that's why you went for 102 mm filters. Now I understand.

But wide-angle converters don't have filter threads, they have hood threads - that's what you should look on them as. When you're working at focal lengths down in the 4 mm region the depth of field is huge, and any imperfection on your front element shows up in against the light shots as horrible bits and bobs.

Modern multi-coatings are really tough and I have no fear of cleaning mine (with care, mind you) any time and any where. I certainly wouldn't use filters over wide converters - they add two more air to glass surfaces with all the problems this brings.

tom.

[Max Allen]

That's interesting, I haven't come across a wide angle hood that threads on instead of clamping on. Can anyone provide a link to this accessory?

I've used the HVX200 version of the Century and 16x9 WA converters without protection filters plenty of times amidst dirt, rain and flying paint! With more than one lens cloth at the ready so when one became ready I'd switch to a clean one... so I know what you mean there. Still, even with a scratch resistant coating, risking getting a few grains of sand between your cloth and lens when wiping can be significant. Not a prospect I'm that comfortable with. Often, it's also not that easy to erase all the smudges off a lens quickly and with few strokes when you're wiping the grime off for the 5th time on a shoot, rather than, say, switch to a backup clear filter and clean the dirty one later. The filter surfaces are faster and easier to clean as well vs. lens surfaces. The flatness of the filter surface I think contributes to this vs. the convex surface of the lens and probably the different coating which makes the cloth glide easier than on the lens surface. A clear filter let's me take my mind off watching out for the surface too and push the lens into high risk areas more liberally.

Not to transgress, but I have to disagree with you on DOF. In principle, a short focal length doesn't automatically equal high DOF. Lighting is as much a contributor. True, less pronounced on smaller sensors. DOF is not as immediately perceivable on a wide angle of view vs. a narrow one so there is this misconception that a WA adapter/converter automatically equals high DOF. I could create quite narrow DOF on a 30k 5mm wide angle broadcast lens if light levels are low enough.

Originally Posted by Tom Hardwick

I certainly wouldn't use filters over wide converters - they add two more air to glass surfaces with all the problems this brings.

tom.

"Problems"... shall I assume you're referring to additional surface area for debris accumulation, reflections or both?

[Tom Hardwick]

Originally Posted by Max Allen

In principle, a short focal length doesn't automatically equal high DOF... so there is this misconception that a WA adapter/converter automatically equals high DOF. I could create quite narrow DOF on a 30k 5mm wide angle broadcast lens if light levels are low enough.

Of course sensor size has a lot to do with it. A pinhole camera made using aluminium foil and my DSLR body gives about 19 mm focal length and almost infinite dof. Conversely the minute ¼" chips on my old TRV900 meant getting differential focus was difficult whatever the aperture and focal lengths used.

But you're using a 0.75x converter on tiny ½" EX1 chips and unless you're working pretty close and very wide, oodles of dof will come as standard.

Yes, each piece of glass placed in front of your front element adds flare as well as two more air to glass surfaces, meaning two more surfaces to keep clean.

tom.

[Max Allen]

Thanks for the reply Tom.

With a clear filter once on, ideally not coming off the lens, how do you have additional surfaces to get dirty once you clean the space between filter and lens. If you need to mount something directly to the lens, OK, that's a couple of bursts of a Giottos at most.

You would be hard pressed to detect flare added inherently by mounting a quality clear filter on a lens. If you can actually see this I'd really love to see a frame grab. By way of pure physics your statement could be true in that reflections will be created from the filter's rear surface, although imperceptible to humans. I'm not referring to polygonal or circular flare. That to me is a purely subjective call. I'm referring to uniform flare.

I can visualize 2/3" DOF better than smaller sensors but let's take the EX1. With the .75x on, if your subject is 2 to 3 feet from the lens against a background stretching to 'infinity' at full wide with the lens fully open, the background will blur, ergo shallow DOF. Take the focus plane to infinity and your foreground will not be sharp. Even in fisheye there can be shallow DOF. Of course of a different type than the lens adapters everyone is now accustomed to. As long as you can get the lens full open, there is decrease in DOF albeit hard to see by eye with a smaller sensor. Blow it up on on a 20 foot screen and it will be easier.

[Tom Hardwick]

I follow your every word Max, and understand your references to veiling and diaphragm flare.

Some years ago I too believed that a 'fitted when new and never removed' MC UV would cause no picture degradation. Of course it never did with my 35 mm camera, but wide-angle on that meant a huge 24 mm focal length, whereas now to get that fov I need to shoot at a minuscule 3 mm.

I had two VX2000s a few years ago. One lens had a lovely Hoya HMC UV fitted, the other was nude. I could demonstrate the picture degradation caused by the filter to anyone who cared to witness it, though it took careful placement aimed into a bright light.

A lot of this was due to the loss of hood efficiency. With a bayonet-on hood, each filter you add reduces the hood's effective length of course, meaning that even with its excellent shadow-mask hood the filtered VX2k was at a big disadvantage.

Since that time I've avoided using filters on cameras with tiny chips. If Sony thought that adding a plane-parallel piece of glass to the front of their 14 element zoom would in any way improve the image quality, it would be there. Zeiss T* MC is tough and can easily withstand repeated (careful) cleaning I find.

tom.

[Max Allen]

Well if we want to manipulate lighting of course any filter will increase susceptibility to flare as the multiplied refractions of adding glass will do. All other things being equal, without changing a shot or lighting, a UV/MRC filter is not going to cause fogging flare of a measurably visual amount is my point. I see what you mean with decreasing hood length when that becomes a more often occurring problem. Personally if I see that when I move the camera outside of ENG I'll use the eyebrow or throw a flag on a stand or a number of other things before I remove the filter but agreed every situation can be different with the combination of chip size, lens, focal length and so on.

I don't have enough experience with the VX2000 having only used it once but my confidence in Sony camera design has been reduced at least with the totally unacceptable EX IR problem, vignetting on the first run and other issues that just shouldn't be when you put out a camera, and that from the Cine-Alta section of the company no less. I can deal with most small format camera trade-offs but some things are just not workable. Good black reproduction is elementary. Let me stop before going too off topic.