Contax 645 Vacuum back--does it make audible noise?

[jeffrey_steinberg]

I have had my Contax 645 since 1999 and I love it. I finally decided

to buy the vacuum 220 film holder.

 

Dumb question: Can you hear the vacuum working? I was thinking I

would hear something but I don't hear a damn thing. How do I know its

working (other than waiting to see if I can tell from negative sharpness).

 

I wasn't expecting a hoovermatic-type sound but something.

[gary_yeowell]

Jeffrey,

When I purchased my 220 vacuum inserts I wondered the same thing, how do I know they are working as they are indeed silent and a quick call to my Contax rep confirmed this to be so. However when I received my first rolls back I knew they were working and for the first time was stunned by the results, focus consistantly bang on with wide apertures, which had not been the case before!

[william_yu]

No you can not hear anything from the vacuum back, but it is working.

[frdchang]

doesn't the vacuum back work using piezo ceramics vibrating rather than an actual fan sucking air?

 

if so, perhaps the frequency or amplitude of the noise is lower than our threshold of hearing.

[jeffrey_steinberg]

Cermaics make sense--it looks like it and Contax was built by Kyrocera which is a major supplier and innovator in cermaics for industrial applications. If memory serves, the shaft the Contax AX used to move the film cage around (it was AF with MF lenses) used a ceramic core).

 

I hear vacuum and think "whoosh"

[colin_elliott]

Audible difference? No

Visual difference? Absolutely!!

[david_chilvers]

Jeff

 

I suppose Contax wouldn`t have made the back if 1. it wasn`t needed 2. it didn`t make things better but I had one and after careful scanning I really couldn`t see the change(using glass carrier on 8000.)

[louis_brak]

The back works by having a diaphragm pull back, at the time of exposure, creating a vacuum at the pressure plate which is made of a ceramic material, for flatness, with small holes in it through which the air can escape. It is normally silent though I have sometimes heard a slight sound during longer exposures (the vacuum back is deactivated at exposures longer than, I think, around somewhere between 1/2 to 2 sec as the vacuum would not be stable for that long).

 

I have often wondered whether the vacuum back could degrade sharpness by creating slight film movement as the film is pulled towards the pressure plate from the vacuum. I have never seen actual tests showing sharpness improvement from using the vacuum back. I use it and have never had an unsharp picture with the setup, however, I have had strikingly sharp pictures without the vac back also (I use 220 film mostly-which may be flatter). Only on one roll of 120 film have I ever noticed unsharp images that I attributed to film flatness issues not using the vac back (the vac back only takes 220 film).

 

Does anyone know of an objective test that was ever done on the vacuum back regarding sharpness?