Minolta CLC metering and filters?

Hi, I have an XE-7 and I've been playing around with filters. Unfortunately everything taken with red or orange ended up too dark. It didn't seem to matter whether I was using a preset or automatic lens.

My fear is the CLC meter doesn't understand anything besides UV and and yellow filters. I'm not sure how to compensate for each, so I thought maybe someone on here has experience?

Interesting Problem

I don't use the XE-7, but I do shoot the Minolta SRT 102s and 101s with CLC metering, and have never run into this little problem before. I am going to have to go out and do some work with my Red 29 and Red 25 filters to see what effect they may have.

I would expect them to reduce the amount of light to a certain amount, thus the rationale behind filter factors on rangefinders, but I would expect Minolta's TTL metering to account for the reduced light coming through the lens.

Were you using color film or black and white? How much of a reduction do you estimate may have occurred? Is it a couple of stops? Also, what brand filters are you using?

I was using Efke 50. The CLC sort of meters two things at once and is pre-programmed to take a certain spot inbetween them or something.

I thought the same thing as you, The reduction is complicated because It looks like upwards of two stops, but some highlights are blown out. Perhaps it is more the film, I just found this

(there was a url link here which no longer exists)

Next time yellow or orange... I just figured filters where best for it because it responds poorly to being overexposed, compared to most films (so I've been told, I get underexposures with it, if anything). I actually thought I had two oranges but I had two red for awhile!

My filters are a total mix of brands (I got them all for $5 a piece or less at a rummage sale, at a local camera place). I'm trying to use a UV with my lenses that are not MD's, or my Olympus newer ones, because they seem to have issues with flare.

Although I must say the one shot I did pointing right at the sun tucked in a bunch of clouds looks freaking awesome with the heavy red filter. (I think it is a 25)

The spectral sensitivity of TTL sensors don't respond to filters the same as film. Most systems don't.
There's a nice chart in the Simmons book regarding filter factors.
CLC is a system where the top and bottom sections of the negative is given different weight. Ie top biased toward more exposure to build density and bottom to reduce it.

This book? http://www.amazon.com/National-Geographic-Photography-Field-Guide/dp/0792268784

I'm trying to avoid putting filters on after metering. If I can just figure out how to meter with one on, I'll be fine.

CLC is only a system whereby the camera gives more weight to the lower part (in landscape orientation) than to the upper part.
If you use it in portrait mode, CLC will weight more the left or right side (depending on how you rotate the camera, having the shutter release down or up) which makes no sense but in general did not make the situation worse.

It basically was a method to have a higher percentage of well exposed images from an unexperienced and unaware photographer who would underexpose images with a great portion of sky in them, especially when the foreground is in shade. When used vertically the bright sky would be "evenly" spread in both upper and lower portion of the image and so the CLC system would, at least, not worsen the measurement in respect to an ordinary cell disposition.

For the experienced and "aware" photographer it was just another complication, you have to "second guess" what the camera is trying to do to help you. Basically it's a primitive form of "matrix metering": the illusion that if the photographer is stupid, the camera can be intelligent in his stead.

Regarding mistakes with red filters, that camera very likely has a CdS light meter. CdS doesn't have a linear response to light of various colours. If the subject is more or less neutral, it works fine. If the subject is markedly blue, or red, it will give you a wrong measurement. If you put a coloured filter in front of a TTL light meter with a CdS cells you force it to work in a region of the spectrum where its response it's not accurate.

The remedy is to note the compensation factor, to measure light without filter, and to screw it on the lens after that by compensating the exposure.

SBC cells and GaSP cells were more linear in response and were less affected by this phenomenon, and so could be used with better results with filters in front of the lens, but I think they made their appearance on the market later (late seventies). Selenium cells are also, IIRC, quite linear in response. The problem is one of the things that made CdS light meters disappear. The other is the "memory effect" which is a nuisance as well.

Fabrizio

Fabrizio, I have to disagree a little with you in your description of the CLC metering system.

The two CdS cells utilized are not "weighted" in any way - simply averaged. The electrical schematic of the SRT-101 shows no components which could do anything but average the output of the cells - they are on the same circuit. Both cells carry the same part number, so they are identical in output.

The owners manual of the XE-7 states that the coverage of the cells overlaps.

When looking through the viewfinder of either camera at a single light source, it appears that the area of coverage indicated by the meter needle is oval-shaped, falls off equally top-to-bottom and I couldn't detect any fall-off when the light source was positioned halfway between where the light reading falls off top-to-bottom. The area is, of course, somewhat bigger than a traditional truly center-weighted meter covers, but not huge. I pointed both cameras out the window at a distinct sky/horizon scene and then turned them upside-down and the meter readings were the same. I've never noticed any issues holding the cameras vertically, as for a portrait - no side-to-side weirdness.

I have used these cameras extensively, also the XD which has a distinctly spot-type (silicon) meter and have never had to "second guess" the metering on any of them, at least as far as how the CLC system vs. a single sensor system reacts to a scene. Consideration has to be given to the fact that the older cameras do have the limitations of the CdS technology, as you correctly state. The CLC system spreads the metering area out vertically a little more than center-weighted systems - as you say, an early form of matrix metering, which I use almost exclusively when using my DSLR.

Mike

Would the XD11 be an example of a camera that doesn't get affected by the filters?

metwr without the filter and then, apply the filter factor. metering through filters confuses the meter's spectral sensitivity.

I think you need to experiment a bit to see how the meter responds with and without the filter.

E.g. a red filter normally needs an extra three stops of exposure. If your meter only asks for an extra two stops then you know that you need to compensate by an extra stop. You can do this by setting the compensation dial to +1 stop.

After a bit of experimentation you should know how much compensation you need to add for each filter.

It's not a perfect system and could still be fooled in some situations but I think it will get you closer to what you want. i.e. a simple method of working out exposure without constantly removing and replacing the filter.


Steve.

upnorthcyclist said:

Fabrizio, I have to disagree a little with you in your description of the CLC metering system.

The two CdS cells utilized are not "weighted" in any way - simply averaged. The electrical schematic of the SRT-101 shows no components which could do anything but average the output of the cells - they are on the same circuit. Both cells carry the same part number, so they are identical in output.

Click to expand...

Probably Minolta used the CLC acronym in different cameras for different electrical schemes.

Found this old conversation:
http://photo.net/sony-minolta-slr-system-forum/005WeU

It seems that CLC meant, at some stage, some bottom-weighted measurement and, at some other stage, a circuit which gave more weight to the dark part of the frame if there is a great difference between the two. I found somewhere both versions on the net. In any case I don't deem likely the final effect (see below) of the circuit is simply to average the two cells as this wouldn't have warranted an "acronym", marketing being marketing but Minolta being Minolta as well

I don't see any advantage, either theoretical or practical, in having two averaged cells rather than one cell in high contrast situations.

I also read somewhere that there were CLC cameras which had 3 cells, two toward the lower part of the frame and 1 toward the upper part, and by averaging them a bias was given to the lower part.

Frankly, I have no idea how to read electric schemes so in no way I am implying you are wrong regarding the specific scheme you are reading, I'm just saying that CLC was used for different schemes but there always was the intent to help the photographer in "high contrast" situations.

The two cells might be "averaged" but oriented in a different way so that one is given more "bias" because it weights more in the final result.
E.g. if the lower cell reads the lower 33% of the frame and the upper cell reads the upper 66% of the frame (with a certain degree of necessary overlapping) and you average them the lower third of the frame will account, in the final result, more than each of the other two thirds of the frame. The electrical scheme will suggest there is a simple "averaging" but in fact there is a bias toward the lower portion of the frame.

Fabrizio

See how memory works. I remembered where I read the description of the CLC system. That's an old almanac, Annuario Fotografico 1982, which I still have. In the description of the Minolta SrT100x it says that the camera has 3 cells: two point with prevalence to the lower part of the frame (the "grass"), one points with prevalence to the upper part of the frame (the "sky"). In normal outdoor situations in landscape orientation the "sky" will weight less on the final measurement than the "grass". (I presume the three values are averaged).

The comments are written by Maurizio Capobussi who is always very informed and precise, but, as said, it is likely that CLC of the SrT100x was different than CLC of other cameras.

Fabrizio

From what I remember, there are two (or three) light dependent resistors. The brighter the light, the lower resistance.

They are connected in series so that if one LDR is subject to bright light, its resistance drops to a low value so only the one metering mid tones has a significant effect on the series resistance and hence the exposure. In theory, and hopefully in practice, it means that the meter should not be fooled by a bright sky.

My distant memory seems to recall that two were used, arranged so it still worked with the camera rotated by ninety degrees.


Steve.

I guess I got a little defensive about my much-beloved Minoltas - I've been shooting with an SRT-102 since, well, forever. My point was that my CLC bodies meter just fine, especially considering all are 30+ years old. These days I shoot transparencies exclusively which are pretty fussy exposure-wise, and don't have issues with weird metering. Perhaps earlier in the SRT line the metering was as Fabrizio described - who knows. I didn't mean to sound strident - I should master the use of emoticons ;-)

Mike

The most likely problem is that the glue that bonds the meter cell glass blocks to the prism is cracked and yellowed. If one is more so than the other your meter readings will be off. To get an idea of what I am referring to check this page. http://www.colynsfotografs.com/srt.html

This problem is common with the srT's and XE-7 models..but is easily fixed on the srT's but you'll have to have it done by a repairman with the XE-7 since adjustments are electrical instead of mechanical...

My meter is as accurate as my friends little digital fujipix. Plus all my other photos that came out where good. Just the red confuses it too much, and Efke responds poorly to it. I think for Yellow giving it just a hair more exposure is wise (not even a stop).

My fear is the CLC meter doesn't understand anything besides UV and and yellow filters. I'm not sure how to compensate for each, so I thought maybe someone on here has experience?

Click to expand...

I've used the srT's since they came out in the 60's and have never had metering issues with any filter..

The CLC meter is nothing more than 2 CDS cells arranged to meter different areas but giving priority to the center..

Field said:

My meter is as accurate as my friends little digital fujipix. Plus all my other photos that came out where good. Just the red confuses it too much, and Efke responds poorly to it. I think for Yellow giving it just a hair more exposure is wise (not even a stop).

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What brand of filters are you using? Some off brand filters use non-optical dyes which do not filter the color spectrum properly...filters should also be made from optical glass..

Based on experience I still lean toward yellowed/cracked glue bonding the cell glass blocks to the prism. When this condition exists you can still get acceptable results without a filter but adding a dark filter such as the red filter will then cause issues..

I have several Marumi filters, vivitars, Hoya, and some others. There may be some that could be offbrand like promaster. I feel some what certain I didn't really grab anything that seemed all that uncommon, but I'll check when I'm home.

leicarfcam said:

Based on experience I still lean toward yellowed/cracked glue bonding the cell glass blocks to the prism. When this condition exists you can still get acceptable results without a filter but adding a dark filter such as the red filter will then cause issues..

Click to expand...

Wouldn't this cause over-exposure though?


Steve.

Steve Smith said:

Wouldn't this cause over-exposure though?


Steve.

Click to expand...

It would depend on whether the user was using a 625a battery or another of the proper voltage..

Some srT's have been converted to use the 625a battery which is a mistake because of the small window of accuracy you'll get with it..

Unlike mercury or silver oxide batteries, alkaline batteries start to lose voltage as you use it therefore meter accuracy will over expose and under expose depending on how much voltage remains..

The best method is to convert the camera to use silver oxide batteries..