Filter clearance on APO Summicron-M 90mm ASPH

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On July 05, 2001 there was a thread posted here by Jeff Stuart concerning the clearance of a polarizing filter when used on a APO Summicron-M 90mm ASPH lens. The front element on this lens as you may know is quite rounded and projects forward in it's center almost level with the threaded end of the lens barrel.

Having read this and needing a UV filter for protection on my new APO 90 (lot's of pumice dust in my area), I purchased a Heliopan filter of the 'slim line' type (the only one I could get). After nervously screwing in this filter with the utmost care, as I didn't know whether it was going to meet the clearance required, I am pleased to say it does not touch the glass, at least as far as I can tell.

To reiterate the question asked by Jeff, does anyone know why the warning that comes in the instruction booklet only applies to polarizing filters, as I would of thought the warning would apply to all filters?

-- Sam Smith (Ruy_Lopez@hotmail.com), July 19, 2001

Answers

I can't answer your question, but I use a B+W UV on my 90 SAA, and haven't had any problems.

-- David Page (pagedt@attglobal.net), July 19, 2001.

The reason there is a warning is because the Leica E55 polarising filter will contact the lens element. Leica provides clearances so you can check other filters as well. As long as the glass is not recessed in the filter ring (below the threads) it will be fine.

Cheers

-- John Collier (jbcollier@powersurfr.com), July 19, 2001.


Per the generous suggestions from others I bought the Heliopan E55 linear pol. filter for my 90mm APO and it mounts without any problems. It is a tall filter, the rotating glass is recessed a shade more than 3mm from the base (9.7mm overall). I see no evidence of vignetting with the filter, not that you'd expect any with this lens.

I don't know whether to take Leica's 2.8mm minimum literally. It appears from my measurements the front element coincides with the innermost filter thread. As John Collier suggests, even 1mm clearance would seem to be enough, 2 would be plenty and 2.8 is overkill. But then why is Leica putting me though this? I don't get it.

There are few filters more than 2mm deep. All the Hoyas I've measured (CP, UV, 81A) are 2mm or less. For some reason people don't want me sticking my ruler into their B+W's, so I can't say for sure, but they look to be about 2mm also.

I'm looking for an 81A for the 90. Based on everything to date, I think I'll spring for the B+W. If you hear a scream from the direction of Florida you'll know it didn't work.

Cheers, Jeff

-- Jeff Stuart (jstuart1@tampabay.rr.com), July 20, 2001.


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