Heavy vignetting on Pentax LX with wide lenses?

Norkusa · Apr 11, 2015

Just scored a beautiful Pentax LX body the other day for only $15. Put some fresh batteries & TriX in it and everything seems to be working smoothly. Was shooting with a 50mm f/1.4 at first and then switched to the SMC 28mm f/2.8. Right away I noticed some heavy, dark vignetting around the corners of the frame. Almost to the point where I had problems seeing anything outside the center of the frame while shooting indoors.

I attached a non-Pentax 28mm l had and was experiencing the same heavy vignetting with that lens too. Didn't have this problem with the 50mm though. It sounds like LX's came installed with split-prisim focusing screens and the screen inside this one is matte. Maybe the vignetting has something to do with that?

dynachrome · Apr 11, 2015

I have a 28/2.8 SMC Pentax-M. It does not cause darkening of the edges of the frame when I put it on a K1000, KM, KX, K2 or any other Pentax K mount body. Even on an LX the overall brightness with a 28/2.8 will be loser than with a 50/1.4. Are the aperture mechanisms of your two 28mm lenses working properly? Which focusing screen is in the LX? Do you wear eyeglasses? Are you keeping your eye centered when you look through the finder? Do your 28mm lenses have filters and/or lens hoods attached to them? An LX in good condition for only $15 is quite a find even for people used to seeing low film camera prices.

Hatchetman · Apr 11, 2015

Filters?

Dan Daniel · Apr 11, 2015

http://www.bdimitrov.de/kmp/misc/focus/screens/

http://www.mir.com.my/rb/photography/hardwares/classics/pentaxlx/screens/index.htm

Any chance you have the SE-25 screen? Meant for 300mm or longer lenses. I assume that the cutting of the fresnels is tuned for pretty direct light so the angled light from a 28 throws it off?

pentaxuser · Apr 11, 2015

In the U.K. any $15 Pentax LX "fell off the back of a lorry, guv" as we say. I don't believe it is your 28mm lens. I have one for a Pentax MZ7 and it is fine. It is the same lens for the whole Pentax range.

Are you sure that the 50 is completely OK on this LX. It just seems strange that the 50 is OK which rules out a problem with the LX but which seems to have a problem with another 28 as well?

Something not adding up here

pentaxuser

Jeff Bradford · Apr 11, 2015

If the replaced viewfinder has the wrong magnification factor, it could show you an area wider than the image circle. Who knows what the previous owner put in there? Check your negatives to be sure.

Les Sarile · Apr 11, 2015

Wow, that's a great score!

I just verified my M 28mm f2.8 on my LX, KX & MX and there is no heavy vignette on any of the three. Like Dan suggests, perhaps a more appropriate screen.

summicron1 · Apr 11, 2015

are you certain that the lens is really fully open on that body? Stopping down would make it a lot darker.

Norkusa · Apr 11, 2015

Thank you everyone for the replies! I just put the 50mm back on the LX and there's definitely *no* vignetting with it and everything looks clear & bright. And I've found a third 28mm lens in my collection to test and that one also has the same vignetting problems. So it's definitely not my lenses as someone already pointed out. I've checked to make sure that all the lenses were fully opened too.

The vignetting is so dark, you can actually see the grain in the matte screen. I'm not sure which screen is installed in my LX, but it looks like it's either the SA-21, SA-23, or SA-26. Does not look like a SE-25 like Dan suggested, but the SA-26 sounds similar....maybe that's what I have installed in the LX?

pentaxuser · Apr 11, 2015

What counts: Is the vignetting on the negative? Can changing screens make any difference to the negative?

Yes, it might be off-putting to see vignetting on the screen but if it has no effect on the negative then you can at least work with the 28mm lens while working out what the cause is.

pentaxuser

GRHazelton · Apr 11, 2015

Very peculiar. I've used my LX with the Pentax 28mm, and also a Vivitar 19mm with no vignetting. Well, the 19mm has a little fall-off, common with superwide lenses. Nor have I experienced any vignetting with any of the viewfinders I have for it. I can't see how a plain matte screen could cause the problem.

GRHazelton · Apr 11, 2015

pentaxuser said:
What counts: Is the vignetting on the negative? Can changing screens make any difference to the negative?

Yes, it might be off-putting to see vignetting on the screen but if it has no effect on the negative then you can at least work with the 28mm lens while working out what the cause is.

pentaxuser

I can't see how the screen could affect the negative.

Norkusa · Apr 11, 2015

Sure, it doesn't affect the negative but it definitely makes it harder for me to shoot indoors since the viewfinder is so dark.

I'm shopping around for a new screen (trying to find the standard SC-21 split-microprisim) and hopefully that will fix things. If not, I guess I'll just stick to using 50mm and greater on the LX.

benjiboy · Apr 11, 2015

I suspect that the problem is that something inside the lens is out of place either due to impact damage or a ham fisted attempted repair on some body's kitchen table.

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AllanD · Apr 12, 2015

Is the vignetting occurring in all four corners? If it is just at the bottom of the frame it could be that the mirror rest position is wrong, or the mirror is sticking and is not fully down. The 28 may be showing the problem more than the normal lens because it natuarally has more light fall-off at the edges.

lxdude · Apr 12, 2015

Norkusa said:
Thank you everyone for the replies! I just put the 50mm back on the LX and there's definitely *no* vignetting with it and everything looks clear & bright. And I've found a third 28mm lens in my collection to test and that one also has the same vignetting problems. So it's definitely not my lenses as someone already pointed out. I've checked to make sure that all the lenses were fully opened too.

The vignetting is so dark, you can actually see the grain in the matte screen. I'm not sure which screen is installed in my LX, but it looks like it's either the SA-21, SA-23, or SA-26. Does not look like a SE-25 like Dan suggested, but the SA-26 sounds similar....maybe that's what I have installed in the LX?

If you remove the screen, you will see what it is on the tab.

lxdude · Apr 12, 2015

Norkusa said:
Thank you everyone for the replies! I just put the 50mm back on the LX and there's definitely *no* vignetting with it and everything looks clear & bright. And I've found a third 28mm lens in my collection to test and that one also has the same vignetting problems. So it's definitely not my lenses as someone already pointed out. I've checked to make sure that all the lenses were fully opened too.

The vignetting is so dark, you can actually see the grain in the matte screen. I'm not sure which screen is installed in my LX, but it looks like it's either the SA-21, SA-23, or SA-26. Does not look like a SE-25 like Dan suggested, but the SA-26 sounds similar....maybe that's what I have installed in the LX?

It is likely the screen.
If you remove the screen, you will see what it is on the tab.

Xmas · Apr 12, 2015

Removing the screen is as likely to damage as not if your ham fisted.
If it is a plain screen it will be dark with some finders eBay a replacement ebay your current one after wards you may be in pocket.

Norkusa · Apr 12, 2015

AllanD said:
Is the vignetting occurring in all four corners? If it is just at the bottom of the frame it could be that the mirror rest position is wrong, or the mirror is sticking and is not fully down. The 28 may be showing the problem more than the normal lens because it natuarally has more light fall-off at the edges.

Yes, the vignetting is occurring in all four corners. I'm convinced that it's a problem with the screen now. I've been trying to track down a replacement at a good price but most I see available are the ones for use with 300mm lenses & greater.

PentaxBronica · Apr 12, 2015

I would definitely suspect the mirror rest position. Can you get infinity focus with the wide angle lenses?

The mirror rests on rubber pads which turn into goo with age, if they've deteriorated or fallen off then the mirror will end up at the wrong angle.

At that price I would suggest a CLA. Yes it'll cost you a lot more than the camera but you'll end up with a clean, fully functional LX for about the going rate of a "functional, but no service history" example.

As for screens, as I understand it you can use the screens intended for the MX in an LX with no problems. Might make it easier to hunt for a new one if you're convinced that's the cause.

Les Sarile · Apr 12, 2015

Norkusa said:
Sure, it doesn't affect the negative but it definitely makes it harder for me to shoot indoors since the viewfinder is so dark.

I'm shopping around for a new screen (trying to find the standard SC-21 split-microprisim) and hopefully that will fix things. If not, I guess I'll just stick to using 50mm and greater on the LX.

That would be ironic since the Pentax LX's meter is particularly handy for dark settings that would require a very bright finder to focus with. I don't know where in the world you are but Eric is known to be the Pentax guru if it comes down to it -> [url]http://pentaxs.com/index.html[/URL]

Norkusa · Apr 13, 2015

PentaxBronica said:
I would definitely suspect the mirror rest position. Can you get infinity focus with the wide angle lenses?

The mirror rests on rubber pads which turn into goo with age, if they've deteriorated or fallen off then the mirror will end up at the wrong angle.

I can get infinity focus with the wide lenses. Mirror seems to be resting fine. I notice the the vignetting gets worse if I move my eye off-center in the viewfinder. If I'm looking directly down the center though, it isn't as bad but still noticable.

I'm going to shop around for another screen, if that doesn't fix it, I'll give Eric at Pentaxs a buzz and see what he has to say about it.

Les Sarile · Apr 13, 2015

I don't know if it affects the issue you are seeing but what finder do you have and did you already adjust the diopter?

MattKing · Apr 13, 2015

Could this be caused by a problem in the prism?

Heavy vignetting on Pentax LX with wide lenses?

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