Rolleiflex meter diffuser - are new ones decorative only or actually functional/reliable?

[Colin O]

I have a Rolleiflex 3.5F with a working meter. Well, I'm not sure it's accurate, but it reacts to light at least. I did used to rely on it, and got mostly fine results, but have been using a modern handheld meter instead for a couple of years now.

Still, I find it to be slow and cumbersome to use the handheld meter, especially when I'm taking someone's portrait - they're generally not comfortable posing for as long as I need to meter and focus. So, I'm considering trying to speed up the process by reverting to the built-in meter again.

Comparing the built-in meter's readings to my Gossen Digisix, the Rollei's meter seems to overestimate the light levels, suggesting settings that would lead to slightly underexposed photos. I'm considering buying a meter diffuser, which I never got with my camera, to see if that might help the meter to make more "conservative" readings.

I'm searching around on eBay and all I can find are aftermarket diffusers. Some appear to be 3D-printed by, I guess, "one-man operations". What I'm wondering though is if the plastic in these diffusers should transmit a specific amount of light? I mean, if someone just knocks together a diffuser on their 3D printer, who's to say that the diffuser doesn't block too much light, and consequently cause the meter to suggest settings that would overexpose the photos, right? I want the diffuser to be functional, not just decorative.

For example, here are three I've considered...

https://www.ebay.co.uk/itm/124352777457

https://www.ebay.co.uk/itm/134325099064

https://www.ebay.co.uk/itm/285173162216

 

[SCL]

Weren't those diffusers used to convert the reading from reflective metering to incident light metering? If you're uncertain about the accuracy of the underlying meter in your camera, adding a diffuser to get an incident light reading won't improve the situation. Either continue to use a handheld meter, or apply a corrective factor to the camera's meter readings, or switch to using Sunny 16 exposure guidelines.

[Niels - NHSN]

The diffuser changes the lightmeter from reflected metering to incident metering.

It will not make the meter faster to operate - quite the opposite.

Take a look at this old (poorly formatted) thread which explains how awkward the use-case is: 

 

I'd suggest that you focus on modifying your process to speed up the procedure.

A modern lightmeter such as a Sekonic L-308 will take a direct reading (incident or reflected, whatever you prefer) and you can transfer the reading directly to to camera without fumbling with turning discs on the meter.

All can be done while you are having a conversation with your subject to hold the focus and ease the potential tension of the situation - and you only have to focus and compose behind the camera.