VX2100 filter position

[John Jay]

The flat glass plate on the front on the lens assembly is about 10mm in front of where the real lens starts and is itself about 8mm behind the filter thread plane. In practice therefore and in round terms the nearest you can arrange a filter is 20mm from the real lens.

As it is a design point replicated in say the FX/Z series, I wonder if anyone can share their thoughts on why this is optically desirable. I know for example matte boxes can push filters out to this distance on professional B4 mount lenses. Most theories suggest as close to the lens as possible but I suspect the reason is more to do with vignetting.


Could it be that this distance is chosen to avoid reflections even with coated filters?

[Tom Hardwick]

What you're describing is the Sony VAP OIS, John. In front of the 12x zoom sits these two sheets of glass, the front one of which is curved. I'm guessing that although it looks like a lens it is in fact a plane parallel sheet of glass. Between these two elements sits the fluid that forms the wedge of the stabilising prism.

I agree with you about filters and converter lenses and so on ~ they're being held too far away from the zoom's genuine front element, and as such need to be spotlessly clean to avoid shadowing the chip with foreign objects when small apertures are used.

The FX1 uses the TRV900's OIS though, where internal vibrating elements move to take out the camera shake. It's a better idea than the VAP for a lot of reasons, and appears to work just as well.

So you want to filter your VX/PD? Get a 52 mm filter, take it out of its mount and attach the glass directly to the 'Sony lens' info plate. Then accessories can use the existing camera's filter threads and be that much closer to the chips.

tom.

[John Jay]

Tom,
Sony describes the flat glass plate as RING ASSY, GLASS ORNAMENTAL see here

http://62.6.248.8/PF/POV041130/98762...views/lens.PDF

the VAP is further back behing the glass ornamental



I'm still wondering why the standoff distance though - love to know what that design philosophy is all about.

[Tom Hardwick]

We're talking VX/PD, right John? If you go into the menu and toggle the SSSS on and off while looking at your front element, you'll see that the front element remains fixed while the next element (the one with the horizontal plastic masking) floats around to counteract your camera shake.

If you look in good light you can actually see the VAP bellows compressing and expanding between these two elements. So there doesn't seem to be any 'unnecessary' glass in the lens' lineup. And they're all beautifully coated on my two cameras.

tom.

[John Jay]

if you have seen the exploded lens assembly linked to earlier then yes we're talking about the same static piece of coated flat glass.

However the coating is less efficient at low incident angles of light and the reason for the filter standoff I suspect is to prevent low incident light refracting and reflecting through the flat glass ornamental where the coating is least efficient. Some lens attachments can cause low incident light to form which may lead to problems


btw the male thread of a 49mm filter fits snugly in the groove around the glass ornamental.

[Tom Hardwick]

But a 49 mm filter stops you using the Sony 58 mm thread, right? Which is why I suggest using the glass alone, without the filter ring. That way you can have your 58 mm w'angle converter as close to the chips as possible.

The front element of the VX/PD isn't flat - it's quite noticeably convex John, which makes me suspicious of these exploded views that show the VAP as two plane parallel, flat pieces of glass. I've just been to check the camera right now. Convex, parallel glass is backed by flat, parallel glass is followed by zoom's front element.

tom.

[John Jay]

I stand corrected the ornamental of the VX is convex as you say, its the FX1 which is flat - too wicked and lazy to check

In any case and howsoever the 52/49 filter could be mounted, the question on my mind is that if a broadband super multi coated filter was fitted would it result in much better low incident light performance?

Phrased another way - does adding another superior coated filter give a net improved result?

[Tom Hardwick]

"does adding another superior coated filter give a net improved result?"

Never. Remenber this, and repeat after me: Filters add nothing; they only take away.

They take away colours or reflections or light. They also take away a little bit of sharpness as the best filter in the world isn't truely plane parallel or truely clean. They also spoil the flare control, offer more surfaces for dust and fingerprints and move converter lenses away from the front element.

Just maybe if you had a camera with a completely uncoated front element adding a S-HMC Hoya would let you go out in the sunshine.

BTW, I've no idea why the marketing boys are calling it an ornamental element. The VAP OIS is as close to real magic as you or I will get, so there's nothing 'ornamental' about it. It's a very necessary piece of glass in the VX/PD's optical lineup.

tom.

[John Jay]

Tom Hardwick > Remenber this, and repeat after me: Filters add nothing; they only take away.

OK, I believe you, so what filter do I need to take away reflections only in the blue channel and where best should it be placed?

[Tom Hardwick]

No idea, sorry.

[John Jay]

thanks for your time Tom