Sinar F2 Sensitometer

Hello

Off the back off @reneboehmer great plotting app work, I was wondering whats the easiest repeatable sensitometer I can build. I don't currently have the space for an enlarger so thats out. What I do have however is a F2 with a spare rear standard.
So I could use the Intrepid Enlarger via graflok attachment and attach it to the front of the camera pointing at the film plane. Then my stouffer step wedge and film goes in the other rear standard as normal.

Pros
- Everything is aligned for me already
- Repeatable
- Can be set up whenever required
- Light source controllable ( Ive asked Intrepid whats the shortest exposure time their unit does), dimmable and can also move it further back down the rail easily
- Can do it in daylight
- Even light source across film plane

Cons
- Expensive, I have everything bar the unit and its £300
- Although they say its calibrated it probably uses the LEDs with a blue spike in the spectrum and not the new swanky more full spectrum ones


Anything else Im missing?, I enjoy the methodical process of film speed testing and know I could just as well go and take real photos and probably get close enough

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acrobatic_citron said:

Although they say its calibrated it probably uses the LEDs with a blue spike in the spectrum

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If you're referring to the intrepid enlarger light source, this uses RGB Leds and not full spectrum white. Whether this is a problem and how to deal with it is a complex question in itself. It's above my pay grade to work that out, as it involves figuring out how the spectral characteristics of the LEDs mesh with the sensitivity of the Sinar probe and how this relates to film spectral sensitivity, and how all that in turn maps onto ISO standards for film speed. I can't really help you with that except suggesting it's probably an easier option to use a daylight balanced white light source, or alternatively a full spectrum tungsten source.

Ah, didn't see the RGB part, thanks, if someone could make a graflok diffused daylight balanced light source that would be swell

You could start by sourcing a generic daylight-balanced white LED, mount that at some distance from the Graflok back and put a milky white plexiglass diffusor panel in the Graflok mount. Put the LED on a timer (Arduino + simple MOSFET switch etc.), optionally add some scrims between light source and diffusor panel if exposures turn out too short. This is not too complicated and quite affordable to build.

Plenty of sensitometers on eBay.

ic-racer said:

Plenty of sensitometers on eBay.

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4x5 ones? ( I have all the 4x5 gear already including step wedge) Are they not all blue/green light? Also I live in the UK and we are not as spoilt for choice in gear over the pond

koraks said:

You could start by sourcing a generic daylight-balanced white LED, mount that at some distance from the Graflok back and put a milky white plexiglass diffusor panel in the Graflok mount. Put the LED on a timer (Arduino + simple MOSFET switch etc.), optionally add some scrims between light source and diffusor panel if exposures turn out too short. This is not too complicated and quite affordable to build.

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Yeah might look at the Sunlike LEDS and build something from those, thanks

acrobatic_citron said:

4x5 ones?

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Doesn't have to be 4x5 though. You can snip a strip from a sheet.

acrobatic_citron said:

Also I live in the UK and we are not as spoilt for choice in gear over the pond

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That's a different matter; I just checked and here on mainland Europe there's not a whole lot going on w.r.t. sensitometers. I see one being listed in Poland; that seems reasonable, although its correct functioning (let alone calibration) is unknown.

koraks said:

You could start by sourcing a generic daylight-balanced white LED, mount that at some distance from the Graflok back and put a milky white plexiglass diffusor panel in the Graflok mount. Put the LED on a timer (Arduino + simple MOSFET switch etc.), optionally add some scrims between light source and diffusor panel if exposures turn out too short. This is not too complicated and quite affordable to build.

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In your experience how many LEDS do you think it would take? Would 1 suffice to cover the whole film, Ive some experience with Arduino. I don't want to be buying the strips that need 12-24v

Depends on the LED power, distance to diffusor (so the size you need to illuminate evenly), diffusor density, desired exposure time - and probably a few more factors.

acrobatic_citron said:

I don't want to be buying the strips that need 12-24v

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Why not?

koraks said:

Depends on the LED power, distance to diffusor (so the size you need to illuminate evenly), diffusor density, desired exposure time - and probably a few more factors.


Why not?

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An irrational fear of wiring that much voltage to my arduino, trusting the power supplies etc. Us Brits don't even have sockets in bathrooms remember

There are many instructions and diagrams outlining how to hook up something to an Arduino. LEDs in particular. I'd start by looking for a suitable light source and take it from there.

Great, thank you for the help

No worries, feel free to reach out if you have parts in mind and have specific questions.