A question about 35mm film cassette

[Jack Tu]

有谁知道35mm胶片暗盒一侧的绒布厚度是多少？防止光线进入所需的最小厚度是多少？

 

[Nicholas Lindan]

Translation of the question from Chinese:

Does anyone know how thick the velvet is on one side of a 35mm film cassette? What is the minimum thickness required to prevent light from entering?​

My answer: it depends on the design of the rest of the cassette, the type of light trap material, the light piping characteristics of the film, etc., etc. - or - for those who simply must have an answer: 1.2370mm to 1.2375mm.

 

[Jack Tu]

问题的中文翻译：

有谁知道 35 毫米胶片暗盒一侧的绒布有多厚？防止光线进入所需的最小厚度是多少？​

我的答案：这取决于暗盒其余部分的设计、光阱材料的类型、胶片的光管道特性等等 - 或者 - 对于那些必须有答案的人：1.2370mm到1.2375毫米。

这包括底座的厚度吗？

 

[Jack Tu]

Translation of the question from Chinese:

Does anyone know how thick the velvet is on one side of a 35mm film cassette? What is the minimum thickness required to prevent light from entering?​

My answer: it depends on the design of the rest of the cassette, the type of light trap material, the light piping characteristics of the film, etc., etc. - or - for those who simply must have an answer: 1.2370mm to 1.2375mm.

Does this include the thickness of the base?

 

[neilt3]

Does this include the thickness of the base?

It's like Nicholas said , it depends.
Read his post again ;

it depends on the design of the rest of the cassette, the type of light trap material, the light piping characteristics of the film, etc.

So it depends largely on the size of the gap on your cassette and the thickness of the film used .
So if you've got some cassettes whose felt needs replacing , you need to measure that , or if you've 3d printed your own , you need to measure the gap .
Then measure the thickness of the film your using .
The light trap should be just touching where it meets to exclude light , assuming the material is soft enough for the film to pass between without scratching.
So it also depends on the material used . If it's too dense , you might have to leave a clearence gap and make sure you never wind the film fully in or unload your camera in the light .

In other words , you need to measure up yourself and work it out for yourself as there are too many variables for anyone to answer the question for you .

Only you can answer how big a gap you have to fill in your cassette.

 

[neilt3]

Are you repairing some old ones or making some new ones from scratch ?

 

[Jack Tu]

Are you repairing some old ones or making some new ones from scratch ?

I plan to mass-produce a full line of cassettes

 

[Jack Tu]

It's like Nicholas said , it depends.
Read his post again ;





So it depends largely on the size of the gap on your cassette and the thickness of the film used .
So if you've got some cassettes whose felt needs replacing , you need to measure that , or if you've 3d printed your own , you need to measure the gap .
Then measure the thickness of the film your using .
The light trap should be just touching where it meets to exclude light , assuming the material is soft enough for the film to pass between without scratching.
So it also depends on the material used . If it's too dense , you might have to leave a clearence gap and make sure you never wind the film fully in or unload your camera in the light .

In other words , you need to measure up yourself and work it out for yourself as there are too many variables for anyone to answer the question for you .

Only you can answer how big a gap you have to fill in your cassette.

I measured the cassettes of Ilford and Kodak. When containing base, the flocking thickness is 1.75mm-1.90mm.

 

[neilt3]

I plan to mass-produce a full line of cassettes

Excellent. I look forward to seeing your final product.
Just make sure you thoroughly lest them in strong light with a variety of emulsions .
Injection moulded ?

I measured the cassettes of Ilford and Kodak. When containing base, the flocking thickness is 1.75mm-1.90mm.

You have your answer .

You'll be using the correct thickness to suit your cassette, and you make your cassette to suit what is readily available light seal material to obtain , rather than having a firm custom produce for you .

 

[MattKing]

Just make sure you thoroughly lest them in strong light with a variety of emulsions .

Including both acetate based and polyester based films.
We look forward to seeing the results!

 

[Don_ih]

If the film base is clear, it will pipe light, no matter how much of what flocking is used in the cassette. The flocking has to block light when the film is sticking out and when the film has been rewound - those are the conditions to be tested, preferably with a fast film on a base that won't light-pipe.

 

[MattKing]

If the film base is clear, it will pipe light, no matter how much of what flocking is used in the cassette. The flocking has to block light when the film is sticking out and when the film has been rewound - those are the conditions to be tested, preferably with a fast film on a base that won't light-pipe.

When compared to acetate based films, polyester based films often are of a slightly different thickness, and have slightly different physical/mechanical characteristics. I would check any cassette lip material with both.

 

[Don_ih]

When compared to acetate based films, polyester based films often are of a slightly different thickness, and have slightly different physical/mechanical characteristics. I would check any cassette lip material with both.

If the cassette doesn't leak light when the film is rewound, and the velvet conforms to the edges of some sample of film and so doesn't leak in that instance, there's not much left to worry about. The thickest 35mm film is not objectively much thicker than the thinnest.

At any rate, you can't test for light-tightness using a film that easily pipes light.

 

[Ivo Stunga]

Have Aviphot 80 (Adox HR-50/Scala 50, Rollei Retro 80S and RPX25) or Adox CHS 100 II (PET), or Fomapan R 100 (clear triacetate) for this test.

Aviphot 80 base will be quite a lot thinner than CHS 100 II base which has thickest PET base I've encountered.

Aviphot being IR sensitive will give opportunity to test cassettes to this spectrum too.