Focusing Consumer vs Pro SLR's

[tunalegs]

I must say I'm a bit baffled by this attitude. Having your camera set up properly, so that what is in focus on the ground glass/focus screen, is also what is in focus on the film in the camera, is really basic. From testing the few consumer cameras I have at my disposal, I found the accuracy of the above statement to be off, whereas the pro level cameras I have at my disposal, were spot on.

You need to start with your piece of mechanical equipment, have that spot on, then make sure to limit camera shake and other variables. But if your mechanical equipment is not spot on, then even if you control all other variables, you will still not get properly in focus pictures.

My test method is to shoot focus charts on Tri-X film with a 50mm f1.2 lens (set at f1.2), process, scan with a Nikon 9000, and look at the scan at 100%, and I have no problem seeing the difference.

But as I said before, if you're happy with the focusing of your consumer SLR, great, more power to you.

Best,
-Tim

It's not that I don't think proper collimation is critical. Just that for the vast majority of users, the vast majority of the time, the miniscule difference between the best pro SLR and the average consumer SLR, is negligible, if even detectible in the final print.

So what I am interested in seeing is the results. (edit: post above made while I was writing.)

 

[Timmyjoe]

I don't consider the difference minuscule or negligible, and I can definitely detect the difference in a final print, or even in an on screen image, but everybody is different.

Best,
-Tim

 

[David Hughes]

No, I haven't. Well, except for rangefinders (a technically different matter). The original poster was talking about misaligned ground glass.

written on the road

Hi,

I was thinking of an SLR when I typed that. The one in question appeared to be in focus due, of course, to the screen telling me it was. But the prints were not quite focussed.

The same lenses used on the back-up body (to keep the thing used and not rusting away) were in focus on the screen and were in focus as confirmed by the prints. Isn't the difference between focus on the screen and focus on the film what this is about?

EDIT The lens in question being a newish f/1.4 that had cost me a lot of my hard earned cash. It was a great disappointment until I saw some shots from the back-up body and realised it was the posh body at fault.

Regards, David

PS (EDIT) I agree with tunalegs above, the typical user with the typical 4 x 6 isn't going to notice anything. Alas, my local lab tell me most people want those little prints these days.

 

[Godfrey]

Not fair, Godfrey. The OP talked about adjustments of 0.101mm and 0.190mm, which is in your tolerance ballpark. ...

If the variability is .127mm, making adjustments of .100 to .190 mm is useless.

I see the difference in the pictures from the collimated A-1, but that doesn't prove anything general about the difference between consumer grade vs pro SLR cameras. It simply indicates that this particular A-1's calibration was off. Repeat that test a few hundred times with F1n and A-1 bodies, and then there's some objective evidence that the lower price bodies have a calibration problem.

G

 

[Timmyjoe]

Found the same when comparing a Nikon F3HP and a Nikon FM2N. Small sample, sure, but consistent.

YMMV.

"Isn't the difference between focus on the screen and focus on the film what this is about?"

That's exactly what I started the thread to discuss.

Best,
-Tim

 

[Ranchu]

The tolerances of the film*position in the film gate of a 35mm pro SLR camera vary by as much as .005" (0.127mm). Trying to collimate focusing screen to image plane position more accurately than that is a waste of time.

The film plane is not flat anyway, it's slightly convex, because there has to be room for the film to move in the format gate; the required free space means that the film bends a little. (Yes, I know about vacuum pressure plates and clamping pressure plates ... I only know of one pro-grade 35mm DSLR that was produced with that feature, the rest are technical, specialist, and industrial cameras.)

Film position doesn't vary that much on the pressure plate (prove it?), and the film is not 'convex'. It curves at the top and bottom, and then is flat on the pressure plate, unless the camera is badly designed.

 

[Godfrey]

Film position doesn't vary that much on the pressure plate (prove it?), and the film is not 'convex'. It curves at the top and bottom, and then is flat on the pressure plate, unless the camera is badly designed.

Read "Camera Techonology, the Dark Side of the Lens" by Norman Goldberg

Film thickness varies depending on base and emulsion type, so the amount of clearance required in the film channels has to be enough to allow the thickest film to pass without binding, scratching, or scuffing. This poses some challenges to try to keep the film as flat as possible and keep the focusing plane stable.

Compared to the flatness of a digital sensor, the imaging surface of film is almost a bowl. ;-)

To Timmyjoe: I have worked with *many* Nikon F and FM/FE series film SLRs from 1969 to the present, probably three dozen in all. I have NEVER seen such extreme focusing plane-film plane miscalibration in any of them. My FM/FM2n/FE2 bodies all produced extraordinarily sharp results that were exactly the same as my F/F2/F3 cameras.

Saying that you have seen differences in two pairs of cameras is not statistically viable to generalize from. Any individual camera can certainly be out of calibration.

G

 

[Ranchu]

It's not a bowl. Take the lens off, open he shutter and look at a light reflecting off the film. The problem with digital sensors is that they apparently can't be placed accurately and consistently enough. Otherwise all dslrs would work for manual focus out of the box. I've had six, and none did.

 

[Sarcophilus Harrisii]

Tim,
If you don't mind me asking, please, what type of auto collimator do you use and approximately how much do they cost?
I'd love one myself but they appear both hard to find and expensive when you do.
Cheers,
Brett

 

[Sarcophilus Harrisii]

And thanks for posting this information. It's a subject I am always looking to increase my understanding of.
Cheers
Brett

 

[Timmyjoe]

G,

The two consumer cameras I tested in comparison to the two pro cameras, were both off. Never said anything about statistically how many consumer cameras were off. I would highly doubt your statement about all your previous cameras being spot on. And if you hadn't tested them with something like a 50mm f1.2 lens set at f1.2, you probably wouldn't have noticed if they were off or not. The work I do with my film cameras requires me to shoot in low light without flash, so I am shooting wide open with 50 and 85mm f1.2 & f1.4 lenses quite a bit. Bringing the focus screen into spec on the consumer cameras has allowed me to use them alongside my pro bodies, and not to worry about focus issues.

One of the reasons you use a collimator to inspect the flange focal distance is that it reads off the front surface of the film, no matter what the film thickness is.

Best,
-Tim

 

[Timmyjoe]

Brett,

My auto collimator is really old, it is the one I used when I serviced Arriflex motion picture cameras and lenses. It was made by a guy named Richter, he ran a company that made these specifically for the motion picture industry. He died a decade or so ago, and I'm not sure they are available anymore. Sorry.

Best,
-Tim

 

[Sarcophilus Harrisii]

Thanks Tim. It's also problematic for me here in Australia, because of the freight costs involved.
Cheers
Brett

 

[Sarcophilus Harrisii]

You've consistently referred to shimming the focus screen to correct viewfinder inaccuracies Tim. Some SLRs provide for viewfinder adjustment by altering the stop position of the reflex mirror. Eg. Exaktas.

Do you have any observations to make about the advantages/disadvantages or, accuracy, of these two different methods of setting viewfinder focus? I have in the past pondered the effect that altering the angle of the mirror would have on accuracy across the viewfinder.
Cheers,
Brett

 

[tunalegs]

You've consistently referred to shimming the focus screen to correct viewfinder inaccuracies Tim. Some SLRs provide for viewfinder adjustment by altering the stop position of the reflex mirror. Eg. Exaktas.

Do you have any observations to make about the advantages/disadvantages or, accuracy, of these two different methods of setting viewfinder focus? I have in the past pondered the effect that altering the angle of the mirror would have on accuracy across the viewfinder.
Cheers,
Brett

Adjusting the mirror will effect the position of the image in the viewfinder relative to the image on the film plane. Ie. what's in the viewfinder will move up or down depending on the position of the mirror, but the image at the film plane will remain centered, presuming the lens mount is centered correctly.

 

[Sarcophilus Harrisii]

Adjusting the mirror will effect the position of the image in the viewfinder relative to the image on the film plane. Ie. what's in the viewfinder will move up or down depending on the position of the mirror, but the image at the film plane will remain centered, presuming the lens mount is centered correctly.

Thanks, I was aware of that but it is a good point to make. Like you, I've done some photography with SLRs that do not feature automatic mirror return Eg. Exaktas and my various Contaflexes. So I've observed the image "sliding" across the focus screen as the mirror descends, something one can't really do with more modern SLRs that have instant return mirrors. I suppose I was wondering whether, assuming proper execution of both adjustment procedures, one had a theoretical or practical accuracy advantage over the other?

The point that comes to mind is that if the SLR involved has 100% viewfinder coverage, adjusting the focus screen might seem preferable so there is better inclusion of the image recorded on the film at the viewfinder edges. With most SLRs offering less than 100% coverage perhaps setting the mirror is not an issue with those, as any clipping of the edges would perhaps be less than that omitted by the viewfinder coverage anyway?
Cheers,
Brett

 

[Godfrey]

G,

The two consumer cameras I tested in comparison to the two pro cameras, were both off. Never said anything about statistically how many consumer cameras were off. I would highly doubt your statement about all your previous cameras being spot on. And if you hadn't tested them with something like a 50mm f1.2 lens set at f1.2, you probably wouldn't have noticed if they were off or not. The work I do with my film cameras requires me to shoot in low light without flash, so I am shooting wide open with 50 and 85mm f1.2 & f1.4 lenses quite a bit. Bringing the focus screen into spec on the consumer cameras has allowed me to use them alongside my pro bodies, and not to worry about focus issues.

One of the reasons you use a collimator to inspect the flange focal distance is that it reads off the front surface of the film, no matter what the film thickness is.

Best,
-Tim

I guess you know all about me, Tim. I guess the 50/1.2, 85/1.8, and 35/1.4 have never been used wide open in the thirty years I've owned them.

Nonsense. It's a waste of time listening to you explain how there must be something wrong with everyone's cameras because they don't spend a ridiculous amount of time worrying about collimating for best calibration.

Unless you use a tripod with sandbags and spend time to critically focus each and every exposure, and NEVER shoot an exposure hand-held, all your collimating and search for perfection in the focusing system is just so much wasted time.

Yes, if a camera is out of tolerances, you won't get spot on focus. It's not a common problem, unless you're doing scientific or forensic data gathering, or industrial photography where every little bit is critical to success... Which you would never do wide open with an ultra-fast 50 or 85 mm lens.

Enough. Enjoy your camera collimating hobby.

G

 

[Ranchu]

"The truth will set you free, but first it will piss you off."

-Gloria Steinem

 

[Timmyjoe]

Godfrey, when you've gone through the ARRI factory training, are certified to service $50,000 motion picture cameras and collimate $20,000 motion picture camera lenses, why don't you come back and we'll have an intelligent discussion. Until then, enjoy your photo hobby and let's hope your pictures stay close to "in-focus", because you obviously find that "good-enough".

Best,
-Tim

 

[tunalegs]

Whoa. I didn't expect to tone to turn all apug like that...

Let's not make this personal folks. Nor is there any need to snub anybody's standards. There are plenty of people on this forum to who zone focus, and even shoot from the hip. Not my thing, but I wouldn't dump on people for it. I've also seen some people take photos with a Holga (also not my type of camera) better than most people here can manage with the latest and greatest cameras. People do what works for them, and if the results are what they wanted, there's nothing wrong with that.

What is "perfect" (or "good enough") only needs to meet the needs and wants of whoever is defining perfect. Pretending otherwise is silly. To me it seems needless to have a super precise camera, if you're just going to go out and hand hold the camera anyway. But it won't make the photos any worse either way. So if that makes whoever happy, happy, they can do that.