Front-focus problem EOS 30 & EF-100/2

[koraks]

I'm still quite fond of the EOS30 and that's the camera I use 99% of the time when shooting 35mm. Some time ago I got a 2nd hand Canon EF100 f/2 which I've been using off and on. But I've got a focus problem: this combination of body + lens seems to exhibit a significant front focus issue. In other words, if I focus on something on the horizon (effectively infinity) the negative shows the focus to be some distance closer than the actual point of focus. This happens with autofocus as well as careful manual focusing.

I have so far not noticed anything like this on this camera with other lenses - but I have to say I always use a 50mm or even shorter lenses, and nothing longer than that.

So I did the (in my mind) logical thing, which was to put the camera with lens mounted on a tripod, focus on a point on the horizon, open the back, put a piece of ground glass exactly in the film plane and flip up the mirror (which is awkward with an EOS 30, but it can be done). Well, what do you think? The image on the film-plane ground glass matches perfectly with the image in the viewfinder. Mind you, I've used this approach successfully to calibrate the rangefinder on some 35mm cameras as well as the mirror on a medium format Mamiya, so I'm not taking a stab in the dark.

The obvious cause could be a problem with film flatness, but the camera is pretty much like new from the inside, the pressure plate is firm and presses like a motherf*** (it does its job just fine it seems). I never noticed a problem with other lenses, but like I said, they're shorter and shorter lenses tend to be somewhat less iffy when it comes to precise focus - or put differently, focus problems with shorter lenses are just a little less obvious most of the time. Still, haven't had any. Just with this EF100/2.

I'm stumped. Can anyone enlighten me on the focusing system of the EOS 30 and any possible wear of mirror catchers etc? Has anyone ever experienced this same issue by any chance?

Obviously I tried googling several times, but the results are horribly diluted by the masses of digital pixel peepers worrying about focus issues with their digital gear (not saying those aren't legitimate, but it does make finding information on film bodies specifically harder).

 

[Anon Ymous]

Well, well, well, I also have an EOS 30 that I dearly love. Even eye focusing works for me! The camera really is in excellent condition, with hardly any signs of use. I noticed some soft images with this camera and initially attributed them to user error. This softness was more pronounced when using my EF 100mm f/2,8 macro. This didn't surprise me that much, because my slightest movement at very close focusing distances could ruin the shot anyway. But progressively it became rather clear that there's a front focusing problem. When taking the photograph, the picture in the viewfinder looks perfectly focused. After becoming suspicious, I noticed that some front focusing cases have also occured with my 50mm f/1,8 STM as well, although they're not as frequent, nor severe, for obvious reasons. I also thought that a focus - recompose approach that I occasionally take could explain some cases, but even manually choosing the right focusing point and not recomposing at all didn't help. When using the same lenses with my 6D, the focusing problems never occur. I haven't tried checking what the film sees compared to the image in the viewfinder. What's even more frustrating is the fact that it's quite erratic. It has a tendency to front focus, but it won't always happen. I tried some shots on a tripod with the central focus point on a test target at about a 45° angle. It produced varying degrees of front focusing and even some cases of correct focusing. This thing is really puzzling...

 

[koraks]

Umph, sounds like we're in the same boat. Except that it occurs pretty consistently with my EOS30/100 combination. In fact, the other day I shot some frames and decided to shoot some doubles in which I deliberately shifted the focus a bit beyond the actual focus point. Those came out pretty much dead-on. But it's not a workable compromise.

I guess I'll have to dust off the other EOS30 I've got lying around. I haven't used it in a while since it sometimes doesn't play nice when loading film; fails to recognize that film has been put in and you have to take the battery out, sometimes repeatedly, before it resets itself. But maybe it can shed some light on this focusing issue. While I'm at it I'll probably have to try the same lens on the EOS 1 and the 50E I have - but boy, do I hate these little A-B testing games.

So...maybe the EOS30 isn't the perfect body after all? I always thought it was. It's light-weight, quiet, has the important functions and nearly no unnecessary ones, seems to be fairly reliable (cough - mostly), isn't too hungry on batteries, autofocus is fairly fast if you need it. OK, it doesn't have mirror lockup (I think?), but with a tiny mirror that's damped so well I never missed it. Somebody should make more of these.

 

[Anon Ymous]

@koraks You said you did a focus test with a focus point somewhere on the horizon, which means you focused far. You didn't notice a problem when checking what the film sees, but have you tried focusing somewhere near the closest focusing distance? If anything, it should reveal any focusing errors better than when focusing far away.

 

[koraks]

When checking against a film plane ground glass I always do a double check at (near) infinite and 1-1.5m distance. Neither showed a deviation between pentaprism ground glass and film plane ground glass.

Physical inspection shows nothing odd with the film plane and back plate. The only issue I can imagine now is a problem with the main mirror angle. However in that scenario autofocus should still be accurate if I'm not mistaken. I did notice a minimal amount of play on the main mirror if I press lightly on it, but the other eos30 I checked showed the same.

So I'm really clutching at straws here. In the meantime I did find this: http://goriz.disca.upv.es/personal/autofocus.html it is relevant for the eos 30 as well but only applies to autofocus as the adjustment screw is for the auxiliary mirror only it seems.

 

[koraks]

Well, I ran some tests with 2x EOS30 bodies and 1x EOS50 and the 100/2 mounted on each of these. Set up a slanted focus chart at about minimum focus distance (ca. 90cm). Autofocused as well as manually focused on the center of the chart and exposed onto actual film. Developed, printed, analyzed. Found no significant focus deviation in any of these 3 cases.
I also tested both EOS30 bodies with a 50/1.4 and in both instances I found a significant front-focus problem. Autofocus and manual focus aligned perfectly with each other, but the film plane image (as recorded on film) showed front-focus.

Since the 100mm consistently seems to give accurate results, at least in this test setup, I figure it can't really be a problem with the cameras. Why the 50/1.4 gives me problems is unclear to me, but I suspect...user error. I.e. I'm not good enough at judging correct focus on the ground glass. Doesn't help that these cameras don't have a split image focusing aid and an alternative focus screen is kind of difficult/expensive to get. I guess I'll have to practice more!?

 

[Anon Ymous]

Hmmm, so you're basically having an erratic behavior which mirrors my experience. The same lens may have front focus issues at some point, then perform flawlessly. And this is more obvious with longer lenses, for the obvious reasons. I too had front focusing problems with my 50mm f/1,8 STM, but definitely much rarer than when using the 100mm f/2,8 macro. I'm seriously wondering if the tolerance of the AF system is just too wide in what it considers to be in focus. The same lenses, when used with my 6D perform far better. And this is a huge let down...

 

[Anon Ymous]

Hey @koraks it's been a while... I noticed something odd with my EOS 30 the other day. There seems to be a bump at the back of the secondary mirror of my camera as seen in these two shots:

I suppose that's the cause of my problems, perhaps yours could have something similar?

 

[koraks]

I just checked: no bump. This would also be inconsistent with the evidence that the problem is NOT there with the 100/2, but it DOES occur with the 50/1.4 If the problem were associated with the mirror, it would occur with both lenses (and likely even more pronouncedly with the 100mm). Additionally, it doesn't really fit well with the fact that there was perfect alignment between the autofocus and manual focus. The bump on the AF mirror would likely create problems with AF, but not with MF.