Contax 645 film flatness

[gary_yeowell]

I have now been through three different cameras, 2 used and the

latest new and am still experiencing film flatness issues. Without

changing focus and in a sequence of exposures of the same shot I can

get one image that is sharp and the next that is off and this

happens regardless of the amount of time between exposures. The 120

macro at long distances seems worse effected followed by the 80 and

not really noticeable with the 35 which I find odd as I thought

depth of focus as opposed to depth of field was greater with longer

lenses and should help with film flatness. It's driving me mad and

is spoiling the otherwise fantastic performance of this system and

today in desperation I ordered a vacuum insert in a last ditch

effort to solve the problem. I tend to use the lenses a lot around

the f2.8-f8 region where focus issues are revealed very clearly and

also use my Hasselblad in the same way without any problems. Has

anyone had similar experiences and do vacuum insert users think it

makes any difference? Your thoughts would be appreciated.

[ulrich_ploedereder]

Hello Gary,

 

I've also observed film flatness issues but only when the film remains in the magazine for a couple of days between the shots. Since that time I use film type 220 whenever I can. I own one magazine with standard insert and another one with the vacuum insert. And it does make a difference! But I think the main improvement is the usage of 220 film type vs. 120, a vacuum magazin adds yet another (IMHO) smaller effect.

 

Regards

 

Uli

[hendrik]

Hi,

 

I would bet the 220 vacuum will solve your problems.

 

You don't mention your preferred subject matter. This is obviously important since you need critical focus.

 

I have never had any film flatness problems, maybe I'm not as critical as I should be - my clients do not seem to be unhappy.

 

Hope you come right.

[william_yu]

Generally I use 220 film instead of the 120. I have both the normal insert and the vacuum insert. On the light table, I have not noticed any film flatness problem from both inserts. But I usually shoot landscape, with aperture of f 11 or smaller. 220 film probably will give you most of the improvement you can get.

[peter_langfelder]

Gary, depth of focus (or depth of field at the film plane) depends in theory only on the aperture, long and short lenses should be equivalent in this regard. However, the 35mm on a 645 must be much longer than its focal length suggests (to clear the mirror), so it may have more depth of field at the film plane than a normal (or telephoto) lens design. If you're mathematically inclined: the depth of field at the film plane depends on the angle of the cone in which focused rays arrive from the lens; this angle would depend only on the aperture for a normal lens design, but the angle is probably narrower (larger depth of focus) for a retro-focus wideangle that sits further away from the film plane.

[l_a_k_h_i_n_d_e_r]

Pardon me, but if your subsequent photos are not sharp regardless of

time between exposures, why would be the first one be sharp? Hypothetically, you could shoot a complete roll in 1 minute, and get only the first one sharp? That is a strange problem!

[gary_yeowell]

I did not say the first one was sharp and the rest not, the plane of sharp focus shifts which can only be film flatness, and my point regarding the amount of time between exposures was made to counter the film curl and roller issue.

[vijay_nebhrajani]

<i>the plane of sharp focus shifts which can only be film flatness</i><p>

 

Or some issue with the autofocus. I'd suggest you repeat your experiments with the AF off (if it is not already so). Focus on something and fire off eight shots. Wait a day, repeat with the remaining eight on the same roll. If shots 1-8 are OK, the ninth shot has a shifted plane of focus but 10 through 16 are OK, you probably have reverse curl issues but that is a known problem. If the plane of focus is still "jumpy", this definitely puts suspicion on the cameras ability to hold the film flat.

[juan_mateos_hernandez1]

I used to have a Contax 645 and among some other isssues I found this one: film flatness.

I thought the vacuum insert would do the difference but it didnt. I had the same problems

you, Gary, were talking about. Even with f/8 I found that the same scene was on focus on

one shot and out of it in the very next shot. So I decided to sell camera and lenses. I

bought a Hassy 503 cw and never looked back. No problems of films flatness at any

aperture.

Hope this helps