is this common in porro prisms?

[matt green]

in the last couple of days i have noticed a small amount of resistance when focusing from near focus to infinity on my opticron imagic porro prisms.it's not much and does'nt detract from the view but it's a little more noticable in warm weather.in short the focus wheel runs easiar in one direction than the other.just wondered if any other porro user's get the same thing.i presume a pair of roof prisms would not suffer from this because of the internal focusing mechanism?.i dont really want to send them for an unneccasory service as i dont have a spare back up pair.any advice.matt

[richt]

in the last couple of days i have noticed a small amount of resistance when focusing from near focus to infinity on my opticron imagic porro prisms.it's not much and does'nt detract from the view but it's a little more noticable in warm weather.in short the focus wheel runs easiar in one direction than the other.just wondered if any other porro user's get the same thing.i presume a pair of roof prisms would not suffer from this because of the internal focusing mechanism?.i dont really want to send them for an unneccasory service as i dont have a spare back up pair.any advice.matt

Hi Matt
Interesting post
I too notice with my Zeiss 10 x 50 MC Jenoptem porros that on warm days the focus wheel runs a little easier generally
Also there is a distinct "default focus position" which the bins slot into (possibly wear or due to my average view distance being similair) again this is more noticeable on the warmer days
Of course these are quite old (87-88 i think according to serial no) and DDR built so the focus mechanism is more primitive and perhaps not as advanced as Opticron variants
I suspect porro's focussing travel/resistance will always be a little more prone to temperature than the totally internal sealed roof types
In general terms probably the better models should suffer less fluctuation if the engineering/build quality is relative
There is the argument that as long as a focus mechanism is a "sealed unit" it should last a "lifetime" and perform with complete consistence but i have already experienced even in my relatively short birding involvement several focus movement quirks in both cheap and expensive porro and roof bins which makes me wonder
However i can say, that based on recent useage and without brand promoting my Nikon 10 x 42 SE's have tended to be very consistent and i have only really noticed a slight increase in focus resistance when out at Bempton Cliffs in mid winter
(and it was bloody cold then !!) i think my entire body had resistance to movement never mind the bins !!!
Wouldnt have thought the service is necessary just yet unless there is a definite increase or frequency in the problem

Regards
Rich

[mcdowella]

I have one Swift 820 which has never been smooth, and another (well, the ED version) which has always been smooth. In the Swift, I put it down to a slightly duff sample. I do know somebody who has a pair of Ace Avian roof prism binoculars they are very happy with, except that now they squeak slightly on focusing - so I guess roofs can have their troubles too.

[rezMole]

My girlfriend has the imagic porros and i've noticed it too - i suspect it's oil "squeaking" - well that's what it sounds like. I wouldn't worry about it. My Nikon sporters (roofs) seem to have a slight "stick" at certain places. As i said, it's probably due to lubrication.

[dipped]

Just a thought, but you are using the bins in a horizontal position rather than vertical. If it was vertical, focussing the bridge up against gravity might increase the resistance slightly. There may also be "O" rings inside the eyepiece tubes affecting things.

[RAH]

Just want to mention that there are porro binocs that have "internal" focusing - e.g. most of the Pentax porros do not move externally when you focus, even on the non-waterproof models. At least in the case of all the Pentax porros I've tried, their focusing is accurate, with no difference going in or out. Don't know if this is a function of the internal focusing or if they are just well-made.