Pentax digital spotmeter: differences with Minolta Spotmeter F

[jhorvat]

I have been using Minolta Spotmeter F for years. While the spotmeter worked great and consistently, I was eyeing the Pentax spotmeter due to its dial exposure calculator. With Minolta, I had to push too many buttons to get the required shutter speed. Minolta only works in time priority mode and I use aperture priority for B&W landscapes. Well, I finally got the Pentax digital spotmeter and would like to share my first impressions and ask a couple of questions..

When first comparing the two, I noticed that the Pentax viewfinder is about 1 stop dimmer than Minolta. This came as a surprise, since the lens diameter seems to be the same as for Minolta and the magnification is less than for Minolta. I also noticed that the spot circle is much easier to see in Spotmeter F: it gets dark with bright background and somehow it shines when there is a dark background. With Pentax, it is difficult to see the circle with background at EV 5 or less.... I read many forums before buying the Pentax, but no one mentioned this issue, I wonder would there be variations between the Pentax digital spotmeters (serial number on my is 117752 and it is zone VI modified)?

Second observation is that the Pentax reads about 1 EV less than Minolta. Using a spotmeter on a digital camera, the reading was the same as for Minolta. Now I wonder would this be due to zone VI modification, plus better glare handling of multicoated Pentax spotmeter? I made a hole on white cardboard and put it in front of shoe-box that had black wrapping paper inside. Measuring the reading of the hole and comparing it to the reading on the white cardboard, I got about 3 stops less on the hole with Minolta and about 3.5-4 stops less with Pentax (the white board gave ~ EV 17). Both of them gave too high EV, but Pentax less so (reading off the wrapping paper from behind the white paper gave about EV 9).

My third observation was that Pentax drained the battery much more than expected. I was using 6V silver oxide battery, which was supposed to hold 6.1 V for long time. However after only a few hours of playing with the spotmeter, the voltage dropped to 5.7 V (the temperature was about 15 C). I went to measure the current drain of the battery: it was 18 mA when measuring with lid on the lens and about 23 mA with lid removed from the lens. Without metering, the current was zero. I gather there may be a problem with my spotmeter, draining too much of the current. This current would correspond to effective circuitry resistance of 300 Ohms, way too low....In comparison, Minolta spotmeter drained only about 0.2-0.3 mA (on 1.5V battery). I wonder if anyone else had a similar experience with Pentax spotmeter??

Overall, the Pentax spotmeter is nicer to handle than the Spotmeter F, even though it is difficult to locate the spot circle in dim light. Pentax feels better in hands and is less fiddly to use. However, the battery drain is a concern... I suspect a battery may have leaked in the past, living a conductive path inside the meter.

[Jim Noel]

If the meter you have was altered by Zone VI, the readings may be different than that of other meters. Also, I would suspect the Minolta and the digital camera of being skewed toward Zone Vi rather than V nore than I would the Pentax. Mine does not drain the battery fast. I change it every year whether I need to or not.

[vinny]

If you read up on the pentax you'll find that the meter can read outside the spot circle area in some cases. Not sure what causes it but I've owned three of them before my current model and the first two were off by quite a bit. This can be fixed with proper calibration. Check your meter reading at the edge of a bright/dark edge like a corner of a building in full sun.
The minolta is brighter, I do miss that.

[Adrian Pybus]

Funny, I've had exactly the opposite experience and don't use my Minolta spot anymore.


If you read up on the pentax you'll find that the meter can read outside the spot circle area in some cases. Not sure what causes it but I've owned three of them before my current model and the first two were off by quite a bit. This can be fixed with proper calibration. Check your meter reading at the edge of a bright/dark edge like a corner of a building in full sun.
The minolta is brighter, I do miss that.

[Brian Ellis]

The Spotmeter F was my first spot meter. I thought it was a fine meter for someone who wanted and used all of its features. But I just wanted a spot meter for zone system purposes, i.e. to give me read-outs in EVs and convert them to zones. All the other features the Minolta had and all the things it did were unimportant to me and they just got in the way. So I sold it and bought a Pentax which does only one thing but does that one thing quickly, easily, and accurately. I didn't have any of the issues with it that you mention, particularly not the battery problem.

[Drew Wiley]

I've had about four Pentax digital spotmeters and one Minolta F. They all read exactly the
same, but the Pentax is a lot quicker and more spontaneous to use. I recalibrate them
about once a decade (one particular meter is simply kept in the lab unused, just to check the others, and as a reserve if I ever need it).

[jhorvat]

Hi vinny,
Both meters seem to measure pretty much within the circle, I was scanninng the "hole on the shoe box" :). My Pentax actually has two concentric circles in the center... In the Pentax manual they do mention that the spotmeter is likely to give lower readings than the spotmeters from other brands, because of improved way they deal with internal reflections. I wouldn't expect this to amount for 1 stop difference, though. Anyway, when I got my Minolta, I re-calibrated it to my previous meter (Gossen Lunasix F) and that calibration just happened to coincide with the reading of my Olympus spotmeter at the time. The calibration does not bother me too much, I can easily re-adjust the zone sticker to account for the discrepancy.
Thanks, Joseph

[jhorvat]

If the meter you have was altered by Zone VI, the readings may be different than that of other meters. Also, I would suspect the Minolta and the digital camera of being skewed toward Zone Vi rather than V nore than I would the Pentax. Mine does not drain the battery fast. I change it every year whether I need to or not.

This is a good point, Jim,
If the zone VI calibration puts the "mid-grey", whatever that might be, on zone VI, it effectively increases the exposure by one stop, as compared to the meters centered to zone V. That is exactly what I am getting...
Joseph

[jhorvat]

I just found at: http://www.largeformatphotography.info/forum/archive/index.php/t-42707.html
that Eric Woodbury estimates the battery drain of 10-20 mA for Pentax digital spotmeter. With 20 mA drain and say 140 mAh capacity, this would translate to about 7 working hours per battery. Funny, my Minolta spotmeter drains about 100 times less current with 1.5V battery. However, when turning the light on in Minolta's viewfinder, the current jumps to about 10 mA. This makes me thinking, Pentax uses different (bright) LED's in its viewfinder, with which there is no need for a separate light source in low light conditions. This may translate into a higher battery consumption. I guess it is possible that over a year, we only use the spotmeter for less than 7 hours in total.
However, this all begs another question. There was plenty of talk in the forums on the need for a battery with very flat discharge curve (i.e. constant voltage) for Pentax spotmetrs. That's why silver oxide batteries are recommended as best. The problem being, they seem to have flat discharge curve only at low currents, less than 1 mA. I am using Black Diamond brand silver oxide cell and voltage dropped quickly from about 6.3 V to 5.7 V. It recovered overnight to 5.85 V, to drop again to 5.61 V after use. The temperatures are between 10 and 15 C. I wonder how low it will go after a few months' use. So far, I don't see any difference in reading due to the voltage drop, as compared to Spotmeter F (i.e. the difference remains at 1 stop).
Did anyone measure the voltage of silver oxide cells in their Pentax spotmeters through a year of use?
The guy that sold me the spotmeter has another one and he will measure the current drain on his spotmeter tomorrow, will keep you posted.
Joseph

[Drew Wiley]

I seem to need a new battery in the Pentax about every six years, and I use it all the time.
I prefer silver oxide batteries, but don't know how that dovetails into all the "what if" math,
which sounds like BS to me anyway. As a matter of common sense, I carry a spare battery in my kit, but the original one in the meter seems to last so long that once I fetch the replacement, it is past its official expiration date anyway! In extreme cold, like winter
snow camping, I put the meter in the sleeping bag with me at nite to keep the batter warm, or else remove the battery and put it in a pocket. Otherwise, I don't have any issues with either silver oxide or alkaline batteries, and not reading discrepancies either.

[jhorvat]

Well, it seems the seller has some problems in measuring the current consumption of the second Pentax spotmeter, so I doubt I will get that information.

In the meantime, I found something interesting on web:

1) The silver oxide batteries produced by different manufacturers have different discharge characteristics (see attached file). The Pentax spotmeter (as measured on mine) uses about 20 mA of current. With that drain, the battery voltage for some silver oxide batteries can drop to 5.6V within 1 hour of continuous use. Similar happens with 2.5mA of continuous use, just later. The voltage then drops very slowly to 5.2V. The voltage on batteries I use dropped to 5.7V in less than 1 hour of (intermittent) use.

However, another manufacturer lists data according to which the batteries keep their voltage above 6 V until discharged (last figure in the attached file, data given for 2 mA of continuous use). This makes me conclude that it is best to buy the batteries made by a manufacturer that specializes in photo equipment (or the one that publicly releases the data on their batteries).
This said, I didn't notice any difference in the reading of my Pentax spotmeter as the battery voltage was dropping to the current 5.7V, as compared to the reading of Minolta F.

2.) There are difference between the Pentax and Minolta spotmeters that should obviously result in different current consumption. Minolta used Liquid Crystal Display (LCD), while Pentax uses a display that contains elements reminiscent of Light Emitting Diodes (LED). The LCD-type displays consume much less power (no light is emitted by LCD's) than the LED-based ones. This also means that the Pentax spotmeter does not need an additional light to illuminate its display when used in low-light conditions. Minolta, on the other hand, does require a small light bulb in these conditions: with light turned on, Minolta consumes about 10mA of current.

I think this settles it all, I should have realized this long time ago: the current drain I measure on my spotmeter must be its normal consumption. Additionally, the difference in the readings between Pentax and Minolta spotmeters of 1 EV seems to be due to a different calibration standard that was used years ago for some of Pentax spotmeters (as discussed on some of the threads on this site). My solution is to rate the film 1 EI faster.

[dmmartindale]

However, this all begs another question. There was plenty of talk in the forums on the need for a battery with very flat discharge curve (i.e. constant voltage) for Pentax spotmetrs.

How much does the reading change with battery voltage? Pentax specifies an alkaline battery (537) as well as silver oxide (544), so they must believe that both provide sufficient accuracy within the range of voltages high enough for the meter to avoid shutting itself down. The silver oxide battery will provide more readings before it reaches the shutdown point (it has a higher capacity to begin with, and keeps the voltage higher longer than an alkaline) but it will eventually drop to the cutoff voltage too.


I am using Black Diamond brand silver oxide cell and voltage dropped quickly from about 6.3 V to 5.7 V. It recovered overnight to 5.85 V, to drop again to 5.61 V after use. The temperatures are between 10 and 15 C. I wonder how low it will go after a few months' use. So far, I don't see any difference in reading due to the voltage drop, as compared to Spotmeter F (i.e. the difference remains at 1 stop).


Just a side note: that Black Diamond battery is suspect. Black Diamond is a sports equipment manufacturer, not a battery manufacturer. They sell that 6 V battery for use in a tiny headlamp that they sell (I have one). The battery is labelled "silver oxide" on the package, but it was amazingly inexpensive for silver oxide. I took one of them apart (you can just peel off the outer metal sleeve with a pair of pliers) and found four LR44 (alkaline) cells inside, not four SR44. Many people do not know the difference between LR44 (A76, L1154) and SR44 (357), since both will fit the same equipment. With 4LR44 and 4SR44 (what the Pentax takes), you can't even see the markings on the individual cells, so you can't check for yourself.

The Pentax should still work with the Black Diamond battery, but it probably is alkaline, not silver oxide.

Comparing the Pentax against your Minolta is a good idea. As long as the difference between them is constant, it is unlikely that the calibration of either meter has drifted.

- Dave

PS: Yes, I know this thread is nearly a decade old. But the information is still useful, and still accessible to people (like myself) who only found it now. I don't expect the person who posted the original question to check back and read my comment; but I expect it may someday be useful to someone else - perhaps a decade from now.

[CedarMesaPhoto]

I got a Spotmeter M to use as a smaller field meter in addition to my Pentax. They read exactly the same. I hate all that calculator stuff on the Minolta, though. I printed the numbers from the Pentax dial on a mailing label and stuck it on the Minolta. Now I just read direct EV at ASA 100 and my chart gives me the numbers corrected for myself film speed I use. Makes it as simple as the Pentax.

Sent from my XT1080 using Tapatalk

[CedarMesaPhoto]

I like the Minolta because it fits in my TLR bag where the analog Pentax does not. I couldn't believe all that dreadful electronic calculator stuff when I got it, so quickly figured out how to make it be simple to use in the field with my EV sticker.

Sent from my XT1080 using Tapatalk

[Drew Wiley]

The condition of the battery won't affect the reading per se, but whether it reads at all. When a battery starts getting weak, sometimes the LED will get dim and
give you a clue. But when the battery is just too cold or outright expired, you don't get any reading at all. The electronics in the meter assure that if there is a
reading, it will be correct regardless. Meters can drift over time and need recalibration; but that is a different issue and incremental. Alkaline versus silver oxide
is irrelevant to this discussion. Buy good batteries, not private-label ones, because they're generally cheapos. I hesitate to say anything about Black Diamond
because of personal connections that have nothing to do with equipment per se, except that sometimes a freebie test sample of some tent or gadget might be along for the trip too.

[dmmartindale]

I got a Spotmeter M to use as a smaller field meter in addition to my Pentax. They read exactly the same. I hate all that calculator stuff on the Minolta, though. I printed the numbers from the Pentax dial on a mailing label and stuck it on the Minolta. Now I just read direct EV at ASA 100 and my chart gives me the numbers corrected for myself film speed I use. Makes it as simple as the Pentax.


Yes, I like the simpler calculator on the Pentax. The "Highlight" reading button on the Minolta just subtracts a fixed offset (2 1/3 stops?) from the reading, on the assumption that a highlight is that much brighter than mid-grey. Setting the Pentax meter reading opposite IRE 10 on the TV scale does exactly the same thing. The Minolta "Shadow" reading button just adds a (different) fixed offset (2 2/3 stops?) to the EV - exactly the same result as setting the Pentax reading opposite IRE 1 on the TV scale. If you read both the shadows and highlights, you can see where the two readings fall simultaneously on the Pentax's calculator, and if the range is too large, you can decide which one to favour.

With the Minolta, you have to do some of the comparison math in your head, and you can have it display either EV or F/#, but you can't see both simultaneously. The Pentax lets you see the range of EVs in the image, and the set of shutter speed/f-number combinations, all at once in a natural way. This is one place where the simple mechanical slide rule (Pentax) still beats the electronic calculator (Minolta).

- Dave

[Drew Wiley]

I've owned a Minolta too. It was a little more compact than the Pentax, but read identically over the full range. I think the dial on the Pentax is more intuitive to read, though at my age I often need reading glasses or a magnifying glass. And I've heard that Pentax meters are more solidly built internally.