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Paul Kay

Member Since 27 Nov 2003
Offline Last Active May 14 2015 12:15 PM

Posts I've Made

In Topic: Seacam Silver Housing outfit - Canon 5D Mk1

10 April 2015 - 11:11 AM


In Topic: Second thoughts about vacuum systems

28 March 2015 - 07:36 AM

is the force that'll move the o rings not just the pressure difference?

Exerting a force by sucking the 'O' ring inwards from decreased internal pressure when the exterior is subject to air pressure may not be the same as increasing liquid pressure applied from the exterior - I say might, I'm not sure what if any the difference is. Also you would need to take into account the physical 'pre-load' on the 'O' ring due to the housing fastening system. As I said it intrigues me. Sounds simple, but is it?

In Topic: Second thoughts about vacuum systems

28 March 2015 - 12:31 AM

And IMHO the camera shop owner is completely wrong! It does not make any difference if you pull from inside the housing (= apply a vacuum) or push from outside (= apply water pressure). So the idea that the o-rings are "sucked in" is nonsense. And nonsense especially if you think about the relatively small degree of vacuum you apply with your pump.

I wouldn't be so sure. This idea intrigues me and I don't have an answer, but sucking an 'O' ring into place might well result in the 'O' ring seating differently than pressure pushing it into place will - the forces at work may well be being applied in different ways. Clearly this doesn't cause problems most of the time, but that said, in my experience the vast, vast majority of floods are usually down to very obvious reasons (and more often than not simple user error I'm afraid!). And many floods are caused by rushing which would probably mean ignoring the vacuuming step anyway. Whilst I suppose I could fit a vacuum system and have thought about doing so, I've always shied away from doing so as I've always thought that good pre-dive preparation doesn't need yet another step - its time consuming enough as it is. Depending where it enters 6-12ml of seawater could do a lot of damage so it makes sense to see a vacuum system as a pre-dive check only as far as I can see from what has been said. Interesting thread.

In Topic: Rolleimarin Info wanted

27 February 2015 - 01:52 AM

Thanks for all the info. The 'interface units' are missing, BUT.....


Having had a really good look at this housing I am now of the opinion that it has actually never been used! I still can't open it as the main seal is well stuck down due, I suspect, to it having been unopened for many years - it needs easing and will eventually open I'm sure. Condition though is fabulous - it is immaculate and very close to being in 'mint' condition. Which leaves me in a bit of a quandry. If it had been used I might just have modified a cheap TLR to get it running, but its in 'collectable' condition and to use it would inevitably change this. So I suspect that I will sell it on - it really deserves to be appreciated as a piece of history in its current condition rather than anything else - even though I think equipment should be used really. In a way its a pity but I'm not a collector but rather a user. And FWIW its and early housing I think - it not to hand to quote the s/n but sound early.

In Topic: Canon 5dS and 5DR

11 February 2015 - 04:43 AM

Am curiois as to when the resolving power of the L series lenses is impacted/overcome by pixel density.

It is and isn't! More sampling (pixels) will provide more data which may be tonal or resolution. The interaction between the lens and pixel density is complex and you will find numerous internet discussions, arguments and a great deal of misinformation and lack of knowledge stated in defence of various apparently strongly held views.


I suspect that we already have cameras and lenses capable of results beyond those needed for the vast majority of images which are taken. When needed, today's highest MPixel cameras and 'best' lenses are extraordinarily capable - if used appropriately. 50MPixel cameras will no doubt yield measurably 'better' images, but whether the images will be obviously, visually better or simply marginally better will be an interesting question. For myself I see little point in going much beyond 25MPixels simply because I don't need to for the vast majority of images I take. [Its a bit like driving a car capable of higher speeds than legal and/or roads allow. An interesting talking point, but unless you are going to race them on a track, somewhat irrelevant in general usage terms.]