FD lens depth-of-field preview subtlety

Theo Sulphate · Apr 4, 2019

While checking for depth of field on my Canon EF recently, I noticed the aperture wasn't closing fully. Thinking for a moment, I cocked the shutter, tried again, and all was good.

So I learned that for the EF and AE-1P the shutter must be cocked before the DOF lever will close the aperture (*). In fact, the AE-1P manual states that if you try to check DOF when the shutter is not cocked, the lens aperture will close down to whatever previous aperture was used. Anyone making that mistake might not be aware of what has happened.

I haven't checked my F-1N yet to see if the same is true, although the manual does not mention having to cock the shutter.

You might be wondering why I'd be checking DOF when the shutter was uncocked - well, I'd just changed lenses and I wanted to check the swiftness of the aperture blades as they operate to ensure they weren't sluggish. On anything other than the vexatiously designed complex FD lenses, it's easy to test unmounted lenses.

(*) same is true of SRT-101 and its lenses.

AgX · Apr 4, 2019

This can drive you into madness. The lens stops down fine when off, but turns crazy when mounted...

The issue is the aperture simulator/control. Do not ask how long it took me to find out... I realized that the issue only appeared when playing with a FD camera. But not in regular use; when the shutter is cocked after each exposure.

Theo Sulphate · Apr 4, 2019

My friend, a professional camera repairman, once showed me how to test aperture operations on an unmounted FD lens, but I forgot. It's such a complex mount, with so many levers and pins.

Nikon and Pentax is trivial in comparison.

AgX · Apr 4, 2019

Checking off-camera operation of a brech-lock lens is dead simple, you should find out yourself without help. Checking a new-model lens is a bit tricky.

benjiboy · Apr 11, 2019

I just checked my EF with a FDn 35m.f2.8 lens set at f16, and it stops do if cocked or not. I'll try it with my breech lock 35mm f2 lens in a minute. I checked it with the breechlock lens and that as you say it only stops down if the shutter is cocked, so it appears it only happens with the old breechlock optics. I hope this sets your mind at rest Theo.

AgX · Apr 11, 2019

I do not see what the mount type has to do with it. I got that issue with a new-FD lens. On AE-1.

benjiboy · Apr 11, 2019

AgX said:
I do not see what the mount type has to do with it. I got that issue with a new-FD lens. On AE-1.

Neither do AgX I, I'm just describing what happened when I tested them.

benjiboy · Apr 12, 2019

I don't have an A series Canon camera but I tried the experiment with both a breechlock and new type FD lens both on a Canon New F1 and an F1n and found they both stopped down if the shutter was cocked or not.

AgX · Apr 12, 2019

Issue is that they will not stop down throughout all the range.
I would have to look up my notes or posts on this issue, but it drove me crazy.

But again, it would only happen when playing around with the cameras. In typical daily habit of cocking immediately after each exposure there should not be any problem.

Theo Sulphate · Apr 16, 2019

benjiboy said:
... I just checked my EF ... with the breechlock lens and that as you say it only stops down if the shutter is cocked, so it appears it only happens with the old breechlock optics. I hope this sets your mind at rest Theo.

Thank you, Ben. It's strange that for the EF the shutter needs to be cocked, whereas for the FTb and F-1N such cocking is not necessary - nor is it necessary for FDn lenses.

The discrepancy between FD and FDn for this function makes no sense to me.

Anyway, I have been enjoying my Canon EF immensely. As for the F-1N ... what a well-designed, well-built camera that is! I'm tempted to say it's the best 35mm SLR ever, but I realize "best" is a very subjective thing.

AgX · Apr 16, 2019

As I wrote above, I had experienced the issue with an New-FD lens.

The culprit is the working of the camera's aperture simulator.

benjiboy · Apr 17, 2019

Theo Sulphate said:
Thank you, Ben. It's strange that for the EF the shutter needs to be cocked, whereas for the FTb and F-1N such cocking is not necessary - nor is it necessary for FDn lenses.

The discrepancy between FD and FDn for this function makes no sense to me.

Anyway, I have been enjoying my Canon EF immensely. As for the F-1N ... what a well-designed, well-built camera that is! I'm tempted to say it's the best 35mm SLR ever, but I realize "best" is a very subjective thing.

I love my EF it's great for street shooting on auto I just use 400 I.S.O. film and with my FD 35mm lens set at about ten feet and the shutter set at 1/250sec I can just point and shoot.
I agree with you entirely about Canon F1N (I have three of them) their only drawback to me as I'm getting old is that with their build quality is the fact that they are heavy, and I can't carry two bodies. any more.
P.S I just noticed this is my 10,001st post

ronnies · Apr 17, 2019

I seem to recall that the A-1 also needed the shutter cocked before you could use the DoF preview.

Ronnie

CMoore · Apr 17, 2019

I must not know how to use that feature (in any camera)
The image is so dark and so small, i could never see the value of it.
Anyway.....is the problem, of the OP, something that is unique to Canon.?
Was it done that way fro some purpose, or just an unintended consequence of the Canon design.?
Thank You

AgX · Apr 17, 2019

Seemingly the result of the way the camera operates that aperture simulator/control lever.
There would be no user-benefit from such design. And as said, in typical daily use the error will not happen.

Stopping down is a useful feature. As long as subject luminance is sufficient to evalute DOF. In former times stopping down was even necessary for metering and screens were even dimmer.
It is not actually intended for focusing (leaving something as focus-shift aside...).

I would not use a SLR without DOF-feature for training.

CMoore · Apr 17, 2019

I suppose i will simply need to spend some more time trying it.
You are one of many that speaks highly of the DOF feature.
Maybe my biggest problem has been my choice of focus screens, with that split image that goes 1/2 dark below f/5.6

So, looking down a typical street with cars and buildings.....you can see a difference between f/8 and f/11.?
That is to say, you can see what parts of the composition will fall to f/8 but will still be "good" at f/11.?
Thank You

Theo Sulphate · Apr 17, 2019

I used to scoff at DOF preview, thinking it was too imprecise to show me what would be in focus on a print (...and a print of what size?).

However, by giving the matter more attention, I've come to use it and depend on it. A bright viewing screen does help. Ok, the difference between f/8 and f/11 might border on being undetectable, but it depends on the subject. If I photograph flowering buds, stopping down with DOF preview will show me how many fine details in the stamens and petals I'll get and how sharp they might be.

abruzzi · Apr 18, 2019

It’s harder to use at smaller apertures, obviously because it gets pretty dark, but I find it pretty useful at larger apertures to see which aperture gets me the amount of blur I want in the background.

benjiboy · Apr 18, 2019

CMoore said:
I suppose i will simply need to spend some more time trying it.
You are one of many that speaks highly of the DOF feature.
Maybe my biggest problem has been my choice of focus screens, with that split image that goes 1/2 dark below f/5.6

So, looking down a typical street with cars and buildings.....you can see a difference between f/8 and f/11.?
That is to say, you can see what parts of the composition will fall to f/8 but will still be "good" at f/11.?
Thank You

The double echelette split image " B " screens" FN for the New Canon F1 eliminates darkening of the split image even when slow lenses are used they are available in spot, partial and average configurations.

FD lens depth-of-field preview subtlety

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