[Squier]

Focus wide open and stop down after

[Canada_Rockies]

Focus wide open and stop down after

No, that's not the problem. The problem is that split and micro prisms darken with slow lenses. I often shoot my 400 with a converter on the back giving either f/8 or f/9.5 wide open, and this will black out one side of the prism causing a metering error. Split and micro prisms don't like anything from f/5.6 up, pretty well.

[Squier]

yeah, i may come across this phenomenon when i use my Tamron 350mm with the Tammy flat field converter 2x, because the TC actually converts the stops by 2, to f8, so you cant use the original f4.5 by mistake.

If i want to use the Tamron 350 with a 2x TC, i'll have to use my Panagor 2x. I'll then be able to focus at f4.5, then stop to f8 and shoot

I'll adapt to this when my Focusing.com screen arrives

[Voodoo Daddy]

Hi I'm relitivley new here, I just stumbled across an article the other day that explained the difference between circular and flat pretty well. Here it is - A Circular Polarizer Doesn't Doesn't Have to be Round, and Vice Versa - Photo Tips @ Earthbound Light

[Canada_Rockies]

yeah, i may come across this phenomenon when i use my Tamron 350mm with the Tammy flat field converter 2x, because the TC actually converts the stops by 2, to f8, so you cant use the original f4.5 by mistake.

If i want to use the Tamron 350 with a 2x TC, i'll have to use my Panagor 2x. I'll then be able to focus at f4.5, then stop to f8 and shoot

I'll adapt to this when my Focusing.com screen arrives

No 2x converter on a f/4 lens will give you anything other than f/8 while focusing. Guaranteed. That's what they do. 300/4 becomes 600/8.

[Squier]

What i mean is, if i used a regular ole 2x TC like my panagor TC, i could still set the stop to f4.5 on my Tamron 350, ignoring the the fact that i had fitted the TC. I wouldnt get any pictures at f4.5 , but i could focus, THEN stop down and shoot.

With the Tamron TC, i cant do this. It has its own aperture ring, and when fitting to the lens, re-arranges the 2 F stops to F8 from F4.5

Are you saying if i used just a generic 2X TC, i couldnt focus @ F4.5 , then stop down to F8 ?

[Canada_Rockies]

What i mean is, if i used a regular ole 2x TC like my panagor TC, i could still set the stop to f4.5 on my Tamron 350, ignoring the the fact that i had fitted the TC. I wouldnt get any pictures at f4.5 , but i could focus, THEN stop down and shoot.

With the Tamron TC, i cant do this. It has its own aperture ring, and when fitting to the lens, re-arranges the 2 F stops to F8 from F4.5

Are you saying if i used just a generic 2X TC, i couldnt focus @ F4.5 , then stop down to F8 ?

Yes you can, but you won't be focusing at f/4.5, you will be focusing at f/9. The number of the ring is 4.5, but the f/stop seen at the focusing screen is f/9, with all the problems that causes with split image and microprism focusing screen blackouts. The meter may not see f/9 if half the prism is blacked out. This is not unique to DSLR owners - it is for any camera. That's why I prefer a plain matte screen. I don't like all that junk in my field of view.

[Squier]

Nicely explained - thanks CR.

I may have trouble with the new screen then. But only with my longest tele if the 2X TC is mounted, or my 90mm macro f2.8 which i generally use at f5.6 or smaller - sometimes f11 /f16

[Digitalis]

one difference I have noticed between circular and linear polarisers is that the linear type are a half stop faster than the circular ones.

[TER-OR]

I'm confused now. Does the orientation affect a circular polarizer? When using a polarizing filter years ago, I would rotate it to get the brightest picture. I presumed this was a linear polarizer. Does a circular polarizer negate the need to rotate, or will I still need to do so - if this is the case, then my choice of lenses would be different. If I plan to use a lens hood on a lens which has a rotating front element, the need to rotate the polarizer makes it a serious pain.

[Canada_Rockies]

I'm confused now. Does the orientation affect a circular polarizer? When using a polarizing filter years ago, I would rotate it to get the brightest picture. I presumed this was a linear polarizer. Does a circular polarizer negate the need to rotate, or will I still need to do so - if this is the case, then my choice of lenses would be different. If I plan to use a lens hood on a lens which has a rotating front element, the need to rotate the polarizer makes it a serious pain.

The circular polarizer consists of a linear polarizer with an extra element between the filter and the camera that "circularizes" the output so that it is not seen as polarized in the camera. It still has a variable effect depending on its orientation, just like the linear polarizer.

In short, if you have a lens with a rotating front element, the polarizer will be a pain, circular or not. The circular polarizer is alleged to alleviate possible problems in the AF system and/or metering system. I think the only Pentax that has metering problems is the LX which meters from the reflection from the film surface behind the mirror. All the Pentax AF systems (even the ME-F, to the best of my knowledge) used a half silvered area on the mirror to divert some light to the AF module in the floor of the mirror chamber, and would be subject to this apparently rare occurrence.

The problem is the beam splitter in the mirror - a half silvered area - that will at certain times act like a polarizer, and filter out some of the light coming from the linear polarizer. It appears to be something that does not happen very often. The orientation of the filtered light has to be just right, and many people have happily used the linear polarizers without problems.

If Mr. Pentax suggests I would be better off with a circular polarizer, that's what I buy despite the extra money I pay out.

[TER-OR]

Thanks for clearing that up.

I'll certainly use a polarizer on the 16-45 when using it outdoors (once the lens arrives). I may experiment with the Tamron lens, too, though the rotation probably makes the polarizer use too problematic with a lens hood. Perhaps one or the other.

[Squier]

I would imagine ( could be wrong here though ) that Mr Pentax maybe advising a CPL over a Linear because they expect owners to be using AF metering / Lenses.

If one were using all manual lenses and / or MF, i guess that it wouldnt be a problem on which type of polarizer, apart from front rotating lenses of course

[Canada_Rockies]

I would imagine ( could be wrong here though ) that Mr Pentax maybe advising a CPL over a Linear because they expect owners to be using AF metering / Lenses.

If one were using all manual lenses and / or MF, i guess that it wouldnt be a problem on which type of polarizer, apart from front rotating lenses of course

They are probably being overly cautious (but then, so am I ) but this seems to be the case. If one is using MF lenses and the green hexagon to assist in detecting focus, the problem could arise. That would give even more ammunition to the "Pentax is no good because ... " crowd.

Those of us who, on occasion, use Snap-In-Focus (or Catch-In-Focus) would be a bit upset if as we were taking the portrait of a butterfly with the image of Her Majesty Queen Elizabeth II on its wings, and the camera refused to fire. There goes our profit from sales to the National Inquirer.

[Squier]

I would buy 2nd hand / used, and that way one doesnt lose too much ( if anything at all ) on the price if it doesnt suit.

Means hanging around waiting for one to turn up though - always a pain