Raynox and SR

I've recently acquired a Raynox DCR-250 macro adapter for those times when I only want to carry one lens around and don't expect to take macro, but just in case something pops up... Anyway, trying it out for the first time today (with the 55-300mm), it dawned on me that I had no idea what to do about shake reduction. The camera (K3) didn't know that the Raynox was attached so would have been doing whatever it does for the 55-300mm. However, that surely isn't appropriate with the Raynox. So... what should I do if using the Raynox (hand held of course)?

Steve

Interesting question, and not my area of expertise.

A bit of googling shows that a close-up adapter increases magnification, allows a closer working distance, and decreases the lens's FL

I guess therefore if the lens is set to 300mm, and so is the SR, you may have over-compensation from the SR , depending on of course shutter speed and how steady you hold the camera.

I would suggest you do some experimentation at various manual settings for SR (at and below the FL used), as well as OFF

I would be interested to see your findings.

I've just bought one of these, using it on my 100WR. Never gave SR a 2nd thought till now. But so far I've had some pretty sharp images. I'll do some with the SR off next time out.

How would a close-up add-on lens change a lens's focal length?

The SR does not "see" anything through the lens, it senses camera movement and compensates. I believe the only thing it needs to know is the focal length, which it gets from the lens itself (when using a lens that communicates with the camera). The focus distance makes no difference to the way that SR works, whether it's within the lens's normal capabilities or using an add-on lens or macro tubes.

Using a reverse-adapter for close-up might be different as I think it would be a different focal length, but that's another matter.

The focal length of the lens isn't changed, of course, but the camera now has two lenses in sequence and thus SR needs to take into account the focal length of the two lenses in combination. It's the same as wearing glasses or contact lenses - the focal length of the eye isn't right, adding the extra lens brings the focal length of the combination to the correct value.

I've found a closeup filter calculator on the Extreme Macro website link. Give it the focal length of the main lens and the dipotre (1/f) of the add-on lens and it calculates (among other things) the focal length of a lens that is equivalent to the combination.

Steve

Adding any elements or distance between existing lens and focal plane can certainly change a lenses FL. The latter is defined as "the distance between the optical centre of a lens and the capture medium (film or sensor).

What surprised me is that adding a close-up lens (magnifier) actually decreases the FL. I would have thought the opposite, but am not experienced enough in optics to know.

That definition of a FL is only true if the image is actually in focus. The way I think about it is to imagine a beam of parallel light rays entering the lens. When the beam leaves the other end of the lens it is converging to a point of focus behind the lens (it's what I used to do as a child with a bright sun, magnifying glass and combustible paper :twisted. The focal length is the distance between the optical centre of the lens and the point of focus. It's a property of the lens and exisits whether of not there is a capture medium behind the lens.


The add-on lens on its own also brings a beam of parallel rays to a focus. So when the main lens is put behind the add-on, the beam is already converging when it enters the main lens. Add the convergence from the main lens to the already converging beam and the point at which it converges to a point of focus behind the main lens is closer to the rear of that lens than in the absence of the add-on lens. Thus, the focal length of the combination is less than that of the main lens on its own. I'm pretty sure that the mathematical formulae for this sort of thing was covered in A-level physics, but that was a looooong while ago !

Steve

I don't see how extension can change a lenses focal length as I believe focal length is defined as the point where infinity is brought to a focus.

Close up lenses have to decrease the focal length to work. The distance a lens has to be from the sensor is a function of focal length, to focus closer the distance is increased. (for thin lenses it's calculated using 1/f=1/i+1/s where f is focal length, i is image distance & s is subject distance)
The lens is set to hold the optics at the right distance to focus at distant objects, to focus closer either the lens has to move further out or the focal length must be reduced,

I'm sure it was, fortunately I've played with it enough to remember diopters are additive.
Simply change the lenses focal length into diopters add the close up lenses diopter (+8 for the DCR250, or +4.8 for tha DCR150) then convert back to focal length.
As mentioned upthread diopter is 1/focal length but the focal length must be in meters

A 250mm lens has a diopter of +4, add the DCR250 & the combination is +12, which gives 0.083333m or 83mm
at 100mm the lenses diopter is +10, giving 45.5mm combined with the DCR250

It's also useful to realise the furthest you can focus with a close up filter is determined by it's diopter (calculate it's focal length & that's your answer) This is one of the reasons I prefer the weaker DCR150. It typically gives quite enough magnification on a 300mm lens & the added working distance is always helpful.