Polarising Filters

[Alpha1653]

Good afternoon all,

I'm new to this Forum after having bought my first DSLR at Christmas so hello everyone! Early results are a long way off perfect but I'm happy with them so far.

However, I've hit a bit of an impasse: I'm trying to use a Camlink polarising filter to make my outdoor shots really stand out but for some reason the filter is confusing the hell out of my camera. Without the filter, the shots are well focussed and pin sharp. However, with the filter they blur massively. Am I doing something wrong??

I've already confirmed that it is a circular not linear polarising filter. The camera's a Sony A57 with the kit 18-55, a Minolta 55-105 AF and a Minolta 100-300 lenses. All lenses have either a Camlink UV filter or a Hoya Skylight 1B filter as protection if that makes any difference.

Thanks in advance!

[Alpha1653]

Following the above post, I've been playing around with the camera and lenses. It turns out the polarising filter works with the Sony kit lense but not the older Minolta lenses.

Does anyone have any idea why?

[donoreo]

Until I read the second post I thought it was just that you were doing it hand held and getting camera shake. The filter will drop about 2 stops of light so the shutter speed will be longer.

However it could still be similar. What f/ number are you shooting at and what shutter speed in your tests for the lenses?

[jet_kit]

That's a bit of a puzzle.
There's no reason why a filter should work on one lens and not on another. It's all about light, there's no physical changes taking place.
CPLs can be a bit tricky to start with. First off, as my Canadian chum says, you'll lose 2 stops of light through it, but the on-board meter should take care of that for exposure. However, remember that the autofocus relies on light (and plenty of it) to react. It may be that when the filter's fitted the AF is taking a little longer to lock in and you're pressing the shutter too soon.
Second. You need to understand what you're trying to do with the filter. If you want the clouds to stand out against a dark blue sky, your best results will be when the sun is at 90 degrees to your lens. The closer the sun is to 0 degrees the less the overall effect will be.
The next useful feature of the CPL is to cut through reflections. Sometimes we want good reflections in water etc, and sometimes we don't - that's where the CPL comes in and you need to rotate it for maximum effect, both in the sky and water/window etc.
Lastly, if you have a CPL fitted then a UV or Skylight is just another two air/glass surfaces which will not enhance you images. Take 'em off.

[Alpha1653]

Thanks for the replies guys. It really is a bit of a quandary as, like you say Chris, surely a CPL just limits the amount of light reaching the sensor. I don't think it's a case of pressing the shutter release too soon though as the autofocus indicates that the shot is in focus even though it looks blurred. Ref the autofocus, without the CPL, the autofocus is just as quick and accurate on the older lenses as it is with the kit lense. It's all very strange!

I will take a few more sample shots tomorrow with all factors being equal and post them for comparison. I'll be sure to remove the UV/Skylights as well. Just to reiterate, it just affects the older Minolta lenses, not the Sony 18-55 kit lense.

I'll take it into my local shop this week to see if they can shed any light on the matter (no pun intended!).

[wave01]

hi i dont know what type of camlink you have but looking at the price i would suggest you try another make like hoya pro1.

[Alpha1653]

I took my camera, lenses and CPL into my local shop for the guys to have a look at it. They had never come across it before so played around with it for about 45 minutes, trying different combinations and cracking out a few other CPLs both cheap and expensive. Long story short, the filters work well when all the kit is modern but through in a 25 year old Minolta lense and it all goes blurry. The only thing they could suggest was that it's an incompatibility issue between old and new kit.

Thanks for your help and suggestions - I'm going to find a Minolta/Sony forum somewhere and see if anyone knows anything. I will report back if I find anything interesting.

[donoreo]

That is odd. I think it is great for Sony owners to be able to use old Minolta lenses, but that is annoying with the CPL.

[Alpha1653]

To be honest, although it's annoying I'm not that worried as the CPL works really well with the 18-55mm kit lense so should be ok for most of the landscape shots I'll be using the CPL for. The Minoltas are 55-105 and 100-300 so less likely to require the CPL. It's still strange though.