Polorised?

[Mr Noble]

Whats the difference between a linier and a circ?

Just been hunting in the attic and have found a load of cokin filters of the P variety including an ND4 gradual and 160 coef. + 1 2/3 Pola on the cokin website itself it says that the P160 is a liniar one, not a circular.

Thanks.

Greg

[simpo two]

I'll leave the tecchy bit to Philbrettguy, but in summary you're only supposed to use Circular (CP) ones with AF cameras, as the other kind can cause focusing problems I hear.

[Mr Noble]

Ahh, well thats wiped the grin off my face.

More money to spend! Am I right in saying that all good camera bags should have a Circ Poloriser, ND filters and a grad grey in them?

Any other ideas?

Greg

[simpo two]

Mr Noble said:

More money to spend! Am I right in saying that all good camera bags should have a Circ Poloriser, ND filters and a grad grey in them?

Not grad grey but grad ND (to even out the contrast difference of bright sky and dark foregound). However bracketing and compositing is more precise, at the expense of time.

I hardly ever use my CP. If I want more saturated colours I use PS. One thing PS can't do is reduce glare/reflections, but a CP's success at that is very dependent on the angles. It's certainly not a cure-all IMHO.

One gadget I do use is a Giotto Rocket air blower - very good for getting dust off sensors and lenses.

[GetCarter]

simpo two said:

Not grad grey but grad ND

er... last time I looked these were the same. (Cokin seem to agree... the ND filters are all called grad grey 1, 2 etc). Or am I missing something?

I'd agree re the poloriser - only really useful these days for looking through water - PS will do it all post prod.

[simpo two]

GetCarter said:

er... last time I looked these were the same.

All ND filters look grey but not all greys are NDs - 'grey' is not necessarily colour-neutral. Mind you, in these days of digital WB, it probably doesn't make much difference

[trackdemon]

simpo two said:

I hardly ever use my CP.

Blimey! I almost always use mine, but then again I shoot cars mostly, which have lots of reflective sufaces......

[ledaig]

A circular polarizing filter is a linear polarizing filter followed by a quarter-wave plate set at 45 degrees to the axis of polarization. Whilst I have a reasonable idea of what is going on with this concept, explaining it is another matter entirely.

After passing through the polarizing portion of the filter, the light now effectively has two components traveling towards the quarter wave plate. The purpose of the quarter wave plate is to delay light traveling in one direction by a quarter of a wavelength, whilst light traveling in the other direction is unaffected. This shifts the phase of the (light) components in relation to each other, this is where the term ‘circularly polarized’ enters the equation as although the light is ‘polarized’, it is now out of step so to speak in different directions.
If linear polarized light is allowed to enter a DLSR for example, it can badly affect the metering system as it will not see a true representation of what will strike the sensor as the light will be bounced off the mirror, the angle of which will affect the amount of linear polarized light reflected. This can also affect the auto-focus in much the same way.


I will now run for cover as someone will be along shortly who actually knows what they are talking about

[beano500]

I'll also leave the deep techie stuff for another day, but just out of interest you may care to know that I managed to buy the wrong one earlier this year.

Anyway, I've tried out the LINEAR polariser on AF and it "appears" to focus and meter quite happily.

After several discussions and some surfing, apparently sometimes the combo will work, sometimes it won't. Anyway, I use filters only sparingly (and against most of the advise you lot will give me ) so I'm not going to rush out and buy another 72mm filter just for the mo.

[Mr Noble]

Think I will risk my already owner liners one then. It is amazing just looking through it at a stormy sky or my computer screen.

If its just the AF that may be affected and I only use it occasionally and normally on landscape stuff then I think it will do the job just fine.

I take on board that all other filters (bar ND's) can be done in PS once I learn how!

Good to know as otherwise I would have been lugging round 15 different filters.

I have an ND4 so am going to but another ND8 which will really slow water and clouds down in daylight etc and give me a huge DOF when needed.

Guess I just need the following in bag.

holder

62mm ring

67mm ring

ND4

ND8

Pola.

Thanks

[beano500]

Mr Noble said:

... a huge DOF ...

Unless I've completely misunderstood***, I think you mean minimum DoF?






***which has about as high a probability as me missing out on the lottery again......

[Mr Noble]

might have helped my point then if I knew what I was talking about.

I can never remember which way around it is.



[off to get camera again, to take one shot at f2.8 and another at f45 to remember which way round it is!!]

Greg

[GetCarter]

I have that trouble with overdraft limits.

[beano500]

I find it easy to get confused between negative numbers and imaginary numbers, whether it's the bank account or the F-stop. I blame the standard of my "A-level" Maffs Edjucayshun.....

[Mr Noble]

Just been playing a bit more. Sure there is a fault with my D70 or 18-70 lens. But its far more likely with me.

How do you get the shots I see on here of say a desk (one of the threads yesterday) where the focus is on x and 20mm behind and 20mm infront is all blurred.

I have been trying this with my lens and at 18mm there is really no difference between a shot I took of my office at 1/60th f3.5 and the same shot at f28 10 secs (on tripod)

I have tried it at 50mm and 70mm where there is a little more dof at the smaller f numbers but nothing like the shots I have seen on here.


Just ordered the Scott Kelby CS book, but I wonder if I should have ordered the "simple photography for loosers" book too! I did GCSE pohtog and can't remember a thing!

Help please boys.

Greg

[beano500]

Mr Noble said:

I did GCSE pohtog and ...I should have dun Inglish insted

I did Photog at O-level, must have been different


I think you'll find that (with a digital sensor) a wideangle gives you a fair amount of DOF at whatever F.

Get in real close, you will see a difference. Go to the 70mm end.

Do you have a DoF preview button/option?

[simpo two]

Mr Noble said:

Think I will risk my already owner liners one then.

What, you own a ship as well?

Mr Noble said:

How do you get the shots I see on here of say a desk (one of the threads yesterday) where the focus is on x and 20mm behind and 20mm infront is all blurred. I have been trying this with my lens and at 18mm there is really no difference between a shot I took of my office at 1/60th f3.5 and the same shot at f28 10 secs (on tripod) I have tried it at 50mm and 70mm where there is a little more dof at the smaller f numbers but nothing like the shots I have seen on here.

Panic not, DOF depends on magification as well as aperture. The wider you go (ie 18mm) the more DOF you get - ie more is sharp. The 18-70 is only averagely fast so the DOF difference is relatively small.

The super-shallow DOF shots (this is getting ridiculous!) that you've seen here are either taken with a much larger aperture, eg f1.8, or a long lens, or both - neither of which the 18-70 can emulate.

Another way is to go macro, where DOF virtually disappears due to the magnication. This was taken at 60mm and f5.6, but it's the mag that does it:



>> Edited by simpo two on Friday 2nd December 15:33

[GetCarter]

Mr Noble said:

I did GCSE pohtog and ...I should have dun Inglish insted

Off topic: I dun Maths O level and my Easter report simply said: "I haven't seen him yet"

It was the only time a teacher made me laugh in 14 years.

[beano500]

My desktop now, 45mm lens DX-size sensor (D70 Nikkie)

F8 - augmented stylish by camera shake:





Versus F2.8

[Mr Noble]

fanks 4 da replis.

fink I unda stand it naw!


Sorry about my speed typing!! I never look up to check it you see............


I thought it would be something to do with my lens not being fast enough. I guess the difference between f3.5 and f1.4 say is actually huge. I have a canon 50mm f1.2 under my bad on an AE1 body that takes lovely shots but sadly may never get used again!


Right, so to get those shallow dof shots I really need to get me the Nik 60mm macro or the 105mm one.

Nearly did a few months ago but spent money on a car crash instead. :doh:



Thanks for the help.

Greg