Minolta IV F Light Meter Reflected Light Disk

DonF · Oct 11, 2017

I recently purchased a used Minolta IV F flash light meter. Although in great condition, the 40 degree reflect light meter disk that replaces the incident light dome is missing. I know there is a contact in the sensor head that is engaged by the dome to adjust the meter compensation. As the reflected light disk is simply a piece of flat plastic with a hole the size of the sensor, is there any reason it must be used? In other words, does the basic reflected light disk engage any contact, or is the meter operating as though no contact is engaged?

Kenko makes a nearly identical model meter (the KFM-1100). I have heard that the KFM400 reflected light disk accessory will work in the Minolta IV F. Does anyone have any experience with using the KFM400 in the Minolta or any other relevant information.

Thanks and best regards,

Don

chriscrawfordphoto · Oct 11, 2017

The disk has a hole that limits the angle of view of the meter in reflected light mode. It also pushes down that button on the meter's accessory mount (its a button not an electrical contact). The button tells the meter that the reflected light attachment is mounted and adjusts the meter's readings for it.

The KFM-400 reflected attachment should work. The original Minolta one is common on ebay.

DonF · Oct 11, 2017

Thanks, Chris. It sounds like I need the disk both to control the aperture/angle an to perform some kind of internal adjustment to the meter calibration.

Adorama sells the KFM400 for 23.90 USD, a crazy price but still cheaper than the Ebay Minolta OEM prices I saw. Maybe I'll hold out for the spot meter attachment.

Best,

Don

wiltw · Oct 11, 2017

Failure to use the reflected light reading attach 1) causes the meter to misread the measured light because the protruding pin on the face of the light meter head is not depressed, 2) may have some affect on the limiting of light striking the sensor reflected from the scene in the about-45 degree angle of view. Readings without the pin depressed properly are totally wrong!

DonF · Oct 16, 2017

Thanks for all the info! The meter arrived in almost unused and mint condition. However, it was missing the reflected mode disk.

There is a pin and a contact beneath the incident light dome diffuser. I believe various combinations of pressure set the internal compensation for the disk, the 10 degree spot attachment, and the 5 degree spot attachment. Depressing combinations of the contacts manually alters the ambient display by various amounts.

I found a 10 degree spot attachment at KEH for 27.00 USD. It's in a bit rough shape cosmetically, but the optics and mechanical connection work fine. Nice that the compensation is automatic, although I think the absolute EV range is reduced with the attachment connected.

Best regards,

Don

wiltw · Oct 17, 2017

chriscrawfordphoto said:
The KFM-400 reflected attachment should work. The original Minolta one is common on ebay.

The KFM-400 is based upon the design of the later Minolta Autometer Vf. I had purchased a new Autometer IVf and a (optional) reflected light attachment for it for many years earlier, and when I found a price I could not pass up I purchased an Autometer Vf meter.
During the time I had both meters, I tried out the reflected light attachment and the 5 degree spotmeter attachment from the Autometer IVf on my new Vf, and discovered that the sensing of the reflected light attachment was not compatible and it did not meter properly.
The Autometer Vf was indeed compatible with the 5 degree spotmeter for the IVf. So when I sold off the IVf, I included the reflected light disk with the IVf meter, but kept the spotmeter attachment.
While I used the flat diffuser and spotmeter with the IVf alot for my shooting, I had actually never ever used the reflected light disk, and so nothing was 'lost' to me via the meter upgrade and the incompatibility of the reflected disk.

DonF · Oct 17, 2017

wiltw said:
The KFM-400 is based upon the design of the later Minolta Autometer Vf. I had purchased a new Autometer IVf and a (optional) reflected light attachment for it for many years earlier, and when I found a price I could not pass up I purchased an Autometer Vf meter.
During the time I had both meters, I tried out the reflected light attachment and the 5 degree spotmeter attachment from the Autometer IVf on my new Vf, and discovered that the sensing of the reflected light attachment was not compatible and it did not meter properly.
The Autometer Vf was indeed compatible with the 5 degree spotmeter for the IVf. So when I sold off the IVf, I included the reflected light disk with the IVf meter, but kept the spotmeter attachment.
While I used the flat diffuser and spotmeter with the IVf alot for my shooting, I had actually never ever used the reflected light disk, and so nothing was 'lost' to me via the meter upgrade and the incompatibility of the reflected disk.

Did you ever try the "10 Degree Viewfinder II" attachment on the VF?

That's interesting. I looked at the IVF and VF manuals. While specific accessory part numbers aren't shown, the spot meter attachments for both are listed as "Viewfinder 10 degree II" and "Viewfinder 5 Degree". I believe these refer to the bayonet-style attachments. There appears to be an earlier pre-IVF version of both spot attachments that use a knurled screw-in connection.

The 40 degree reflected disk for the VF isn't illustrated, but indicates one was sold. Unusual that the spot meters would work between meter models, but not the cheapie disk.

I wonder if there might be an issue with dirty contacts inside the sensor head on your VF. There is a YouTube video that shows a procedure to "calibrate" an inaccurate meter by using a dollar bill edge to clean the contact. Perhaps one of the contacts not used by the 5 degree spot attachment was dirty or intermittent.

I haven't seen any Minolta reflected reading attachment design updates since the bayonet-style Viewfinders.

Regards,

Don

DonF · Oct 17, 2017

This thread has some interesting info on attachment compatibility for the Minolta meters:

https://www.rangefinderforum.com/forums/showthread.php?p=2754214

Don

wiltw · Oct 17, 2017

DonF said:
Did you ever try the "10 Degree Viewfinder II" attachment on the VF?

That's interesting. I looked at the IVF and VF manuals. While specific accessory part numbers aren't shown, the spot meter attachments for both are listed as "Viewfinder 10 degree II" and "Viewfinder 5 Degree". I believe these refer to the bayonet-style attachments. There appears to be an earlier pre-IVF version of both spot attachments that use a knurled screw-in connection.

The 40 degree reflected disk for the VF isn't illustrated, but indicates one was sold. Unusual that the spot meters would work between meter models, but not the cheapie disk.

I wonder if there might be an issue with dirty contacts inside the sensor head on your VF. There is a YouTube video that shows a procedure to "calibrate" an inaccurate meter by using a dollar bill edge to clean the contact. Perhaps one of the contacts not used by the 5 degree spot attachment was dirty or intermittent.

I haven't seen any Minolta reflected reading attachment design updates since the bayonet-style Viewfinders.

Regards,

Don

The Autometer IVf reflected disk controls the actuating pin (in vs. out) which is clearly visible on the face of the Autometer IVf meter head. This was a source of unreliability, in the pin being pushed in but the electrical circuit not being made, causing erroneous readings. I myself had to send in my Autometer IVf for repairs by Minolta for that issue.
On the Autometer Vf, the pin is replaced by a pair of electrical contacts at the 12 o'clock position rather than employing mechanical deflection of a pin to make contact. The Autometer Vf reflected disk bridges those two contacts when it is mounted, which fully accounts for what the IVf reflected disk does not work on the Vf meter. So the Autometer Vf reflected light attachment-II was offered for it.
The bearing surface of the 5 degree spotmeter attachment (which allows the pin to protrude on the flat disk), is like the flat disk attachment, and NOT like the Autometer IVf reflected attachment. As I never purchased a 10 degree attachment, I never tested it on the Vf. Minolta never officially supported the Spot 10 as an accessory for the Autometer Vf.

DonF · Oct 19, 2017

I received my bargain-grade spot meter adapter (looks in A+ condition to me) from KEH for my “new” Minolta IVf flash meter. I decided to test the accuracy of the adapter by comparing the incident reading of the light falling on the subject with the dome diffuser to the reflected reading of an 18% gray card with the adapter. Light meters are supposed to be calibrated so that the reflected mode reading gives a correct exposure if the average light reflected from the scene is 18%. I used modeling lamps from two of our studio flashes. The readings were within 0.1 f/stop of one another. Pretty good for a 25 year old meter!

bernard_L · Oct 19, 2017

DonF said:
Light meters are supposed to be calibrated so that the reflected mode reading gives a correct exposure if the average light reflected from the scene is 18%.

Do you know you are opening a can of worms? I'll walk to a safe distance. Anyway, your experimental result shows that your Minolta meter gives consistent readings based on 18%...

jtk · Mar 29, 2018

I've only known that meter in studio situations, mine and others... the critical standard has been Ektachrome tests from the intended lab (now mostly vanished)....or, if not critical, Polaroids (also vanished).

wiltw · Mar 29, 2018

DonF said:
Did you ever try the "10 Degree Viewfinder II" attachment on the VF?

I didn't come back to this thread until 6 months later, so sorry for lack of response to the question until now. I just tested Minolta Autometer Vf with 5 degree spot attachment, and the reading was within 0.1EV (f/2 + 0.2) of the incident reading (f/2 + 0.1)

bernard_L said:
Do you know you are opening a can of worms?

...stepping around the worms (fully knowing about 18% vs. 12.5% discussions of the past, and understanding the theory, but not consistently being able to substantiate the theory in practical testing over the years)
As you said, Bernard, "your experimental result shows that your Minolta meter gives consistent readings based on 18%..."

wiltw · Mar 29, 2018

DonF said:
I recently purchased a used Minolta IV F flash light meter. Although in great condition, the 40 degree reflect light meter disk that replaces the incident light dome is missing.
Don

Are you still looking for a 40 degree reflect light disk for your Autometer IVf (since you already have a spotmeter attachment for it)?

DonF · Mar 29, 2018

wiltw said:
Are you still looking for a 40 degree reflect light disk for your Autometer IVf (since you already have a spotmeter attachment for it)?

I concluded that the 40 degree disk was not too useful. The 10 degree spot meter attachment has been working very well, though. The field of view defined by the circle in the viewfinder seems to match the actual coverage well.

Don

Chan Tran · Mar 29, 2018

If you buy the disk used be aware of the fact that the disk made for old meter (Autometer II and flashmeter II) do not push the button and thus the meter reading is off by 2.7EV.

Minolta IV F Light Meter Reflected Light Disk

Privacy & Transparency

Privacy & Transparency