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Circular Polariser seems to give focus problems with EM-1 + 75-300mk2

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brian1208
brian1208 e2 Member 1110366 forum postsbrian1208 vcard United Kingdom12 Constructive Critique Points
27 Apr 2014 - 6:04 AM

I spent a few hours getting 2000+ shots of ZapCats in action yesterday using my EM-1 + 75-300mk2. As there was a lot of sand and salt spray + quite strong sun I started out using my Hoya circular polariser but after a while (and around 1000 +/- shots) I got the impression that I was getting a lot of OOF images (isn't it difficult to check the image quality on the LCD in bright sun!).

Switching to my Hoya Pro 1 UV filter I found that the incident of OOF images dropped significantly (confirmed when I reviewed the images at home - CP filter = 20-30% sharp, UV filter = 60+ % sharp)

Both filters and the lens were meticulously cleaned before I started and I made my best efforts to keep them clean in action (although was an awful lot of muck in the air)

Has anyone else experienced this effect?

(the camera and lens were given a good clean in fresh water when I got home Smile )

Last Modified By brian1208 at 27 Apr 2014 - 6:05 AM
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LesJD
LesJD  2148 forum posts Wales
27 Apr 2014 - 6:29 AM

OOF or blurred by the shakes ? You're sacrificing around two stops of light with a polariser attached. Shooting with 750-300 on m/43 is akin to shooting 150-600 full frame so you'll need to make sure you take this into account when choosing your shutter speed.

brian1208
brian1208 e2 Member 1110366 forum postsbrian1208 vcard United Kingdom12 Constructive Critique Points
27 Apr 2014 - 6:43 AM

thanks Les, not the shakes, should have said, shooting off the monopod with 1/1000th to 1/1600th sec in both cases (adjusted ISO to keep shutter speed and aperture the same) and it was across the focal range from 75mm to 300mm

LesJD
LesJD  2148 forum posts Wales
27 Apr 2014 - 7:00 AM

Your welcome. That's me stumped then now you've cleared that up. Smile Maybe you should try the polariser/lens combo on a static subject to see if the polariser is causing the AF to malfunction ?

Last Modified By LesJD at 27 Apr 2014 - 7:00 AM
brian1208
brian1208 e2 Member 1110366 forum postsbrian1208 vcard United Kingdom12 Constructive Critique Points
27 Apr 2014 - 7:02 AM

Thanks for trying Les, that's a good idea, I'll give it a go Smile

Paul Morgan
Paul Morgan e2 Member 1315626 forum postsPaul Morgan vcard England6 Constructive Critique Points
27 Apr 2014 - 7:02 AM

Both filters and the lens were meticulously cleaned before I started and I made my best efforts to keep them clean in action

The answer is that its probably better to just use one filter in front of the lens then Brian, each filter added increases the risk of some flare and this can effect focus.

I don`t believe it was due to your polariser.

Last Modified By Paul Morgan at 27 Apr 2014 - 7:07 AM
brian1208
brian1208 e2 Member 1110366 forum postsbrian1208 vcard United Kingdom12 Constructive Critique Points
27 Apr 2014 - 7:15 AM

Thanks Paul, but only one was in use at a time, as here :

"I started out using my Hoya circular polariser"

"Switching to my Hoya Pro 1 UV filter"

Paul Morgan
Paul Morgan e2 Member 1315626 forum postsPaul Morgan vcard England6 Constructive Critique Points
27 Apr 2014 - 7:18 AM

Could it simply be miss focusing due to all that spray though.

brian1208
brian1208 e2 Member 1110366 forum postsbrian1208 vcard United Kingdom12 Constructive Critique Points
27 Apr 2014 - 7:28 AM

Its possible Paul, although there was no change in conditions, if anything the spray and wind blown muck on the filter was even worse once I had switched to the UV.

Don't forget, we are talking about 1000+ shots with each filter so the variability of conditions will be averaged out (it was bright and sunny throughout)

rogerfry
rogerfry e2 Member 9509 forum postsrogerfry vcard United Kingdom
27 Apr 2014 - 8:13 AM

I can't offer any explanation Brian, but I had a similar situation with a Sigma circular polariser and Canon 100-400 on a 7D a few years ago.....it was fine at 100, but at 400 it was hunting frantically but wouldn't focus. The Sigma worked perfectly on a 70-200, and a Hoya filter worked perfectly on the 100-400......it just seemed to be that the Sigma and the 100-400 didn't like each other!

Coast
Coast Critique Team 61337 forum postsCoast vcard United Kingdom292 Constructive Critique Points
27 Apr 2014 - 9:24 AM


Quote: I can't offer any explanation Brian, but I had a similar situation with a Sigma circular polariser and Canon 100-400 on a 7D a few years ago.....it was fine at 100, but at 400 it was hunting frantically but wouldn't focus. The Sigma worked perfectly on a 70-200, and a Hoya filter worked perfectly on the 100-400......it just seemed to be that the Sigma and the 100-400 didn't like each other!

At the 400mm end of the Canon lens you are at f5.6. With the Polariser typically cutting the light down by two stops you are effectively at f11. The Canon autofocus on the 7D will not be able to operate with such little light.

My guess in Brian's case is much the same. The polariser just cutting the light down too much for the autofocus to operate effectively. It would certainly slow it down.

Regards
Paul

LesJD
LesJD  2148 forum posts Wales
27 Apr 2014 - 9:42 AM


Quote: I can't offer any explanation Brian, but I had a similar situation with a Sigma circular polariser and Canon 100-400 on a 7D a few years ago.....it was fine at 100, but at 400 it was hunting frantically but wouldn't focus. The Sigma worked perfectly on a 70-200, and a Hoya filter worked perfectly on the 100-400......it just seemed to be that the Sigma and the 100-400 didn't like each other!

At the 400mm end of the Canon lens you are at f5.6. With the Polariser typically cutting the light down by two stops you are effectively at f11. The Canon autofocus on the 7D will not be able to operate with such little light.

My guess in Brian's case is much the same. The polariser just cutting the light down too much for the autofocus to operate effectively. It would certainly slow it down.

Regards
Paul

That only applies when a TC is attached so your logic is flawed because the effective aperture stays the same with the polarizer attached,only the shutter speed is affected. By your reasoning the lens would only AF properly in the brightest of lighting but that's not the case is it ?

Last Modified By LesJD at 27 Apr 2014 - 9:45 AM
brian1208
brian1208 e2 Member 1110366 forum postsbrian1208 vcard United Kingdom12 Constructive Critique Points
27 Apr 2014 - 10:20 AM

I tried a shot through the car windscreen when we were parked up on the coast this morning and had similar focusing issues which resolved themselves as soon as I shot in the open.

I'm beginning to wonder if its a reflection issue with the CP filter being a double "glass" and the UV a single?

My solution is simple, I won't bother with the CP filter when shooting action in future but keep it for static shots of landscapes, flowers and the like Smile

keithh
keithh e2 Member 1023181 forum postskeithh vcard Wallis and Futuna33 Constructive Critique Points
27 Apr 2014 - 10:32 AM

Although it was a drop in, the last thing I'd ever have fitted to the 300mm Canon was a polariser. Nightmare when photographing sports. Even tennis players and they moved slower than a speed boat.

MichaelMelb_AU
27 Apr 2014 - 10:33 AM


Quote: OOF or blurred by the shakes ? You're sacrificing around two stops of light with a polariser attached. Shooting with 750-300 on m/43 is akin to shooting 150-600 full frame so you'll need to make sure you take this into account when choosing your shutter speed.

Close enough, but not quite. This may have to do not with the speed of the shutter but with the speed of focusing system - which also drops when light gets dimmer. For this reason camera gets considerable focusing lag, and focuses on a subject where it was some short time ago - which, with use of very fast shutter speeds and open aperture, leads not to a motion blur but true out of focus image.

Initial cause is the same though - light loss due to filter density.

Last Modified By MichaelMelb_AU at 27 Apr 2014 - 10:33 AM

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