Meniscus lens in 300-600mm prime teles

[JohnRay]

[ QUOTE ]
Doug_Kerr wrote:

It's important to note that (as I understand it now), the addition of the meniscus lens does not reduce ghosting that would be present with no protective element at all in front of the lens ..... So it is in fact an expensive - and bad-side-effect-free - protective glass.

[/ QUOTE ]

Understood. They've elected to protect the expensive front element and have found a way to make the best of the situation.

I shoot in a lot of harsh conditions (or maybe I'm just not careful enough) and I am constantly wiping stuff off the front of my lens. In some rush situations I just used my tee-shirt. For this reason all of my lenses have UV filters, and I will remove them for certain shots/lighting conditions.

It would be nice to have filter available that could be left on more, or most, of the the time.


[ QUOTE ]
You also wrote:
Quote:

only a lens of zero thickness can have the same spherical radius on both sides.

That is not so. It is quite possible to have a very thick meniscus lens with precisely the same radius of curvature on both sides. I think you may have meant to say something a little different.

[/ QUOTE ]

Oops! You are correct. I meant to infer that only a lens of zero thickness could be the same thickness throughout its surface and have the same spherical radius on both sides. In other words, no such lens exists.

[david_place]

where does one get the Lens Work books ?

can't seem to locate on Amazon under "lens works" _

dp

[JohnRay]

Take a look here:

http://www.bhphotovideo.com/bnh/cont...u=12218&is=REG

BTW, it's Lens Work. I've seen several peopls search for works in the past without success...

[ChuckWestfall]

>>1) While I will assume one of the reasons for this element is to protect the far more expensive front element behind it, can I assume the reduction in ghosting is such that it's more advantageous optically to have it than not. By this I mean, was the meniscus lens selected as part of the initial optical design to help eliminate ghosting and any physical protection properties was just an added benefit, or was the decision to protect the front element first and foremost in the design and the selection of the meniscus shape was chosen to make the best of the situation? ie, kind of like having a screw-on meniscus UV filter.<<

The front element in question here is primarily a protective filter that is fully gasketed and sealed to enhance the moisture resistance of the lens. It is a meniscus lens rather than a flat filter in order to eliminate ghosting with digital SLRs. By the way, the only lenses that have this feature are:

EF300mm f/2.8L IS USM
EF400mm f/2.8L IS USM
EF400mm f/4 DO IS USM
EF500mm f/4L IS USM
EF600mm f/4L IS USM

>>2) Does it block UV?<<

All conventional optical glasses are opaque to UV wavelengths below 300nm. Other than this, the front filter has no special anti-UV properties. However, it is multi-coated to preserve the color balance of the lens.

>>3) Is this element the same thickness throughout its entire surface, or is it a concavo-convex or convexo-concave shape?<<

It is convex on the front and concave on the rear, but the radius of curvature is so low that it's hard to see.

>>4) Has anyone ever had one of these meniscus elements replaced, and if so, how much does/did it cost.<<

It varies according to the lens, but the range is approximately $150 to $250.

5) What is the purpose of the other apparently flat element in these lenses near the lens mount. Is it just for protection? A UV filter? Is it flat? Is it yet another meniscus element to offset optical characteristics of the first meniscus element<<

It's simply the 52mm drop-in filter, and it's totally flat. The IS super-telephotos referenced above are supplied with a gealtin filter holder that incorporates a multi-coated clear glass filter as part of its construction. We also offer a drop-in 52mm screw-in filter holder and a drop-in 52mm adjustable circular polarizer as optional accessories for these lenses.

[JohnRay]

Thanks Chuck, that's just what I needed.

I'm want to get a 300mm f/2.8 in the near future, and hopefully the 500mm f/4 sometime later. I just wanted to know what I was getting myself into, plus I was curious...

[ChuckWestfall]

Hi, John:

I'm glad the information was useful. After I wrote my reply, Canon USA's Factory Service Center supplied the current pricing for replacement of the protective filters for the IS super-telephoto lenses. They said that the labor fee could vary as shown in the list below depending on the overall condition of the lens. Also, CPS members would receive a 20% discount off these prices.

PROTECTIVE FILTER PARTS PRICING

EF300/2.8L IS $140.57
EF400/2.8L IS $315.15
EF500/4.0L IS $261.60
EF600/4.0L IS $366.25


LABOR FEES

STANDARD $168.00
MAJOR $299.00
EXTENSIVE $600.00