Camera & Mirror

I don't think that has anything to do with what "depth of field" means. The presence of the (flat) mirror changes neither the focal length nor the depth of field.

That's what I was thinking & have pursued the design in that way but the 'depth of field' issue kept bothering me.

The only difference that I see is that the image will be a mirror image.

Then you will have to be careful about saying such things as "the left-handed burglar..."

Correct & I'm not sure at this stage which way the customer expects to see the image so I've made the camera mounting reversible.

Most software can easily reverse the image. An easy solution to avoid confusion is to have some obvious non-symmetrical object (e.g. text) in the image field.

In this case the image will be from random protons & neutrons. The only reason for having the mirror is that the neutrons will probably pass straight through the whole assembly & could damage the CCD sensor.

Shouldn't make any difference to zip, except maybe how the camera measures distance to an object to focus? Will it try to focus on the surface of the mirror? My experience with auto focus is it will ficus on anything other than the object you want... they just don't want to focus on a bow limb held up dead centre of frame... instead it focuses on a bloody flowerbed 25' away.

It tickles me that the face recognition will pick up on Sophie's cat face

Del

Auto focus is a pain in our applications so we always use manual.

I gave you a second GA for a good catch and explanation of DOF.

I think he meant focal distance, which his analysis as to the plane or field of focus will be the same as it would for the same distance without the mirror.

Depth of field as I understand it is the distance from the nearest object in reasonable focus to the furthest object. I was concerned that the lens would have to focus over distance 'D' in my sketch but I'm convinced now that this is not the case.

Beat me to it. Yes a mirror as used in Newtonian telescopes is required for the reasons you elucidate. A GA from me. A prism from an old reflex camera would work as well. I once used a cover slip ( used for microscope slides ) as a beam splitter to light the object and simultaneously view it. Viewing it at 90deg whilst lighting it perpendicularly. It worked because the glass was so thin.

Jim

Yes, I'm using 1st surface, once built the mirror will be sealed & protected. The reason for all this was in post #10, our customer is looking at protons & neutrons. The neutrons have enough energy to pass straight through our detector & would probably damage a CCD sensor in direct line.

Then you must be shielding the camera with poly or something similar?

If the Neutron flux is high enough to damage the CCD, then, eventually, it will activate the mirror and surrounding bits and the radiation from the activated components will interfere with proper CCD operation in any event. Or is this a short-term use?

The customer will not give us full details, (not unusual) so we don't know the frequency of the neutrons but you are right, long term use will activate other components. It may be that these parts will have to be replaced at some point.

One detail you should insist upon, any returns for repair must be first surveyed for radiation activation and contamination at the customer's expense before being shipped anywhere.

That's a standard part of our conditions, we don't accept anything back without a contamination statement.

Not quite the same but you have the function right. Most of our devices have input & output optics with the output one having having a coating of phosphor. This particular device has no input optic but will be bolted onto a vacuum chamber of some sort in which the protons & neutrons are generated. The protons will cause the phosphor to scintillate & the CCD camera will read the scintillations. Unfortunately I don't know the function of all this, the customer is a research institute & are not sharing the details of their research with us, some do, some don't.

I suspect you should have drawn your expected DOF between x2 and y2. But it doesn't matter anyway as it is O.K.

Jim

Depth of field is a function of the camera, the F-stop. The larger the "hole", the shorter the depth of field (less is shown to be in focus). With a smaller hole, the greater the distance shown "in" focus.

As far as I am aware, a normal flat mirror will not change the depth of field.

Having a good light sensitive (years ago "film") camera allows a photographer more leeway with using depth of field to his or her advantage, or not.

An insensitive camera has fewer possibilities, especially when light is low.....

On (older) cameras, there is sometimes a ring to adjust focus and it also shows the depth of field with regard to the aperture chosen....maybe high level cameras of today have it also, I never noticed....

Obviously in a camera, the f.stop and the shutter speed work together to allow a specific "volume" or "amount" of light through, that the film or the photo element need to produce a correctly lit picture....

With video or movies, you have less leeway with timing, sometimes none and the whole exposure is controlled by the f.stop and depth of field is affected by the amount of light or not on the subject.....you are stuck with the timing, so to say....

Here is a reasonable article on the subject:-

Achieve-Depth-of-Field-in-Photography

I feel that its easier to understand the phenomena in still photography first, before applying it to video or movies.....

I hope this helps.