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What causes the rangefinder patch to flare?

Introduction

Sometimes when you are using your M in a brightly lit place and are trying to focus on something in the shadows, the rangefinder patch can experience a "white-out", making focusing impossible. Bug? Feature? What's going on?

Unfortunately, until the advent of the Leica MP in 2003, this is a known problem and is inherent in the optical design of M rangefinder mechanisms. Consensus amongst users is that it is slightly worse with the 0.85 high magnification M6 finders, and not so bad in older cameras like the M2 or M4. Furthermore, older users claim that their M3s never flare!

Still unclear or maybe even in denial about RF patch flare? Read this May 2003 description of all the different types of VF flare at <LUG - v24/msg12085.html> by John Collier.

Flare pathology

The main reason for the intermittent white-out appears to be that rangefinder optics changed some time during Leica M4-2 production. But what was the exact change?…

Rob Schneider supplies one explanation:

The rangefinder/viewfinder on the M6TTL .72 is the same as on the M6 "Classic". It's also the same as on the M4-P and, apparently, the later runs of the M4-2. A condenser lens was removed from the frame masking mechanism, making the framelines and RF patch slightly brighter and contrastier (compare any M6 to any well-maintained M2 or M4 and you'll notice the difference. Not dramatic, but there.). The mechanism was redesigned ostensibly to allow the meter LED's to be piped through. But there were also construction issues involved. The condenser lens was cemented in place and the cement was some oddball gunk (technical term) that required application at specific temperatures. Was cost involved? Despite the local nay sayers, bet on it. One other benefit of the lack of the little condenser lens: if you ever get dust or a hair in the masking mechanism, it won't be magnified so that it looks like a giant snake!

Precisely when the changeover took place was commented upon by Stephen Gandy in Jan 2002:

The change in the M4-2 finder somewhere in mid production, ie finder implication by the removal of a few small condensers, was brought to my attention by another Lugger, confirmed by a famous Leica trained repair tech who does not care to be quoted, and finally confirmed to me by Mr. Horst Braun, while he headed the repair department at Solms.
 
As a result, I personally take the story of M4-2 finder changes about midway thru production as fact, and believe the changes went a long way toward creating occasional RF patch flare in the later M4-2 and succeeding cameras.

In March 2002 Dr Alexander Kraus added the following:

Recently, I found an interesting posting in the Leica customer forum, where someone stated that the reason for the whiteout of the rangefinder patch would be the switch from a flat mirror (for brightline illumination) to a parabolic one. The latter one would give siginifcantly brighter frames, however under certain light conditions, the light would be focussed directly on the rangefinder hole of the frame mask mechanism.
 
This sounded very reasonable to me and so I decided ton ask Leica directly whether above explanation is correct. Yesterday, I received an email from Mr. von Gyimes from Leica. He wrote: (in German, translated into English)
 
It is correct that the rangefinder (patch) flare problem is caused by the parabolic mirror. Under certain light conditions (110° to the light source) the rangefinder patch can become bright white and unusable.
 
This problem was significantly reduced by introducing a second reflective surface in the M7 and M6 TTL, but it was not yet possible to eliminate it completely.
 
However, we are working on a solution and we are confident that it will be introduced at the Photokina 2002. The coated viewfinder windows of the M7 enhance the contrast of the viewfinder image visibly. In fall 2002 it will be possible to upgrade Leica M6/M6TTL cameras with these windows.

In April 2003 Erwin Puts created a RF Flare page on his www-site where he concludes that of all the M cameras only the Leica M3 is truly flare-free owing to its more linear RF design. Although this seems reasonable he does not address the common observation noted by many M2 and M4 users that their cameras also do not suffer from any RF flare either(!)

Well, I can confirm from my own experience that Mr Puts is right when it comes to the M3 VF patch. After months of using a 1964 M3, I have not seen its focus patch flare once!

MP viewfinder "flare-fix" upgrade

After a year of promises and wishful thinking, in September 2003 Leica finally began offering a VF "MP flare-fix upgrade" for older Ms for @ $US 280.

According to Gerry Smith at Kindermann (Canada) & Leica NJ, the upgrade does not replace your entire VF mechanism, it merely replaces the frame mask sub-assembly with a new one which has a MP condenser lens built in.

See these Sept 2003 discussion links:

  1. <Photo.net: #00605p>
  2. <Photo.net: #00610s>

So why not just swap over the entire RF/VF assembly? Because it would cost much more than $280, and also because there are intractable problems with aligning different viewfinder display electronics in the M6, M6TTL and M7.

As you can imagine there is (still) quite a demand for this upgrade. So expect long (4+ weeks) delays.

Cheaper alternatives?

In April 2004 Ben Shapiro and Jim Arnold reported that DAG will do the MP flare-fix for $US 150 plus P&H - which is almost half the price charged by Leica NJ.

(In case you are wondering, according to Mr Shapiro, DAG uses exactly the same MP finder upgrade kit as Leica NJ.)

FWIW, in May 2004 Chen Dayuan put up a (now defunct "Geocities") web page which showed the parts in the RF upgrade kit. It appeared from his photographs that there are only two: a mask and small condenser lens.

Free upgrade under warranty?

You bought a M7 or M6TTL and it's still under Passport warranty. Can you have the RF retro-fit done for free?

Yes and no, it depends on which country you live in.

USA

Leica NJ will NOT do the refit under warranty. This is company policy and everyone has to pay for the finder update, regardless of how recently they bought the camera. Fair? Unfair? Conspiracy?…. Contact Leica NJ to discuss.

Europe / Asia

Internationally however you may be able to get the flare-fix done under warranty(!) In August 2004 Elaine Ashton sent me the following note:

I received an email from Leica service today and they indicated that the flare fix for the M7 is free of charge, but the M6 is €232 Euro. They didn't enquire what country I reside in so it may be independent of country or warranty. [P]erhaps Leica has recently changed their policy for the M7 owners? I'm certainly happy to find that the repair is free and thought that you might like to know about it.
 
I emailed the service center in Solms as I'm actually living in Finland and it's closer, but the camera [a Leica M7] was purchased in the US.
 
The service person didn't ask about country or warranty at all, so it may be worth asking the NJ people what the deal is. There's a PDF form you have to download and fill-out but, aside from that, it seems fairly straightforward.

Freebie flare workarounds

Okay, so other than doing a veiwfinder retro-fit, what can you do about RF flare now?

Shield the central finder

An easy fix is to shield the central finder illumination panel (the almost square serrated, frosted glass window immediately above the lens) with your hand, this will cut down the light flooding into the RF chamber and (hopefully) kill the flare.

Reposition your eye

Another trick is to reposition your eye when looking through the finder until you find an angle where the flare is not so bad. If you have time then two-steps-to-the-side, focus, then two-steps-back also works.

Rotate the camera

Another technique, again if you have time, is to turn the camera 90°, focus, and then rotate it back. You don't have to rotate the camera the full 90°, even a slight roll of a few degrees will most often be enough.

All these techniques are easy to remember and cost nothing. For those who want a more permanent "fix", try any of the following…

Add-on flare solutions

Konermann's "The Shade"

An ingenious solution is to use a small lattice-like filter to dim the illumination panel - this appears to be what Lutz Konermann when he designed his The Shade accessory. How does it work? Lutz sent me this note:

The Shade is not exactly a polarizing filter. It still acts grid-like, but on a much rougher scale. Rather think of it as of a venetian blind, which keeps off light coming from any greater than a given angle - in this case around 45 degrees to the upper left (as much as to the less crucial lower right) frame corner.

Sounds great but big caveat - as he notes on his www site, "The Shade" can dim the rangefinder patch and framelines a fair bit, making low light use awkward. Nevertheless, at only $US 10, how can you lose?

The easiest way to buy a "Shade" is online via the following www site:

<leicagoodies.com/shade.html>

Black rectangular mask

Alternatively, in February 2001 Robert G. Stevens mentioned this handy (and cheap) tip:

Put a little piece of black tape in the middle of the frame line illumination window. Make the piece of tape about the size the range finder patch appears in the viewfinder. The frame lines will be slightly less bright, but it cures a lot of the problem.

Instead of using a tape, a more permanent (but still easily removable) alternative is to paint a small black rectangle onto the centre of the serrated illumination window, using Liquid Electrical Tape. This won't look so damn cheesy, and can still be scraped off (with a drop of nail varnish remover) at a later date. This is unlike black paint, which can be difficult to remove without leaving scratch marks or a black stain on the frosted perspex.

Frosted Scotch tape

Maybe you have heard that frosted Scotch tape over the rangefinder illumination window will work. Frankly… it doesn't. After reading about this solution in a Leica mailing list, I tried it out on my M6 TTL (0.85). It didn't work — no effect.

This is not surprising if you think about it, as the tape does not cut down light transmission, nor does it "shape" the incoming light like Lutz's "Shade" (noted above) or "3M Light Control Film" (noted below).

Yellow Post-It™ note

In May 2004 Kelvin Lau sent me the following (ultra cheap) tip:

One cheap & reversible way of increasing your M6 rangefinder patch contrast is by cutting out a sheet of paper from a Post-It note, with the adhesive on it, to place over the frameline window. I have used a yellow piece. It cuts the framline brightness by around 50% but the rangefinder patch will seem more contrasty in some situations. It will however still flare with backlighting etc.
 
Give it a try - it won't cost anything if you steal it from someone's desk from work!

White cross mask

In May 2002 Charles Barcellona suggested the following:

I have some of that low tack white framers tape. Its the cloth backed stuff, consistency of duck tape, but with no silvery stuff - it's pure white, and almost, but not quite opaque. I cut two strips, one about 1/4 inch wide, and one about 5/16 inch wide (experiment with the width).
 
The thinner strip goes horizontally across the light gathering frame, the thicker one goes vertically. The effect is to cut out about 1/3 of the frame vertically and horizontally, with a totally dark center. Bingo! Frame lines are just a wee bit dimmer, but the patch seems to be quite nearly totally flare free. I can now leave my eye a bit off center and focus easily in strong sidelight or strong overhead light (especially against dark subjects).

3M Light Control Film

For those who find the above tips a little rough, Bob Parsons recommended the following more elegant solution:

For a number of months I've used 3M Light Control Film over the frame line illumination window to reduce rangefinder flare. If the Konermann "Shade" is a similar material, then the answer is, it does help. It's disadvantage is the brightness of the frame lines is reduced.
 
It's quite expensive but Edmund Optics sell a 2 x 3 inch sample strip - stock number NT52-390 - for $9.60:

 
<edmundoptics.com/…/productid=1976>
 
I ordered on the US site and the UK based York office telephoned me to confirm the order.
 
I tried the 0, 18 and 30 degree materials with different orientations on the camera's illumination window. I found the 0° film with an acceptance angle of 60° to work the best. Part number NT52-390.
 
You need to orientate the film over the window so that the louvres are vertical allowing a ± 30° horizontal acceptance angle. I left the protective covering films on the strip until after I had cut several rectangles out with scissors. You can also cut it to size by scribing and bending the film to snap it. I attached the light control film to the camera using two very narrow strips of double sided adhesive tape down each side of the window.
 
3M light control film is a fairly new material (developed for security screens and LCD displays etc.) I'm curious to know if Leica have ever considered using this material inside the viewfinder. There also several types of lens films for LCD displays manufactured by 3M which look as if they might be a useful tool in optical design.

White-out witch-hunt?

So how big a problem is rangefinder flare anyway?

Depends on how fussy you are. Some Wetzlar Snobs whinge and whinge about how awful the flare is and how much better things were back in the 1950s with their perfect two-stroke M3s. Others live with it and remark that it only happens very rarely, under known circumstances, and can be easily worked around.

A note about possible broken links

This FAQ has over 900 external links. Over time it is inevitable some of them will break. If you are bothered by this, see this detailed topic elsewhere in the FAQ.

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