[Finn]

I've given up trying to use variable-aperture zooms with a katzeye split image focusing screen because the light meter freaks out toward the long end and severely underexposes. The viewfinder also goes dark, presumably due to the smaller max aperture.

Does anyone else have this issue, and is there a workaround (other than investing in a constant-aperture zoom)?

Can someone give me a technical explanation for what is going on? Why does this not happen with a 35mm camera with a split image screen?

[Lowell Goudge]

I think it does depending upon the aperture range.

Split images for me have always been an issue at F5.6 unless you are really careful about your allignment on the split image.

As for an explanation, it is an optical thing, I knew it once but forgot over time.

it is really not a question of variable aperture but of a small aperture.

Note that as AF came into play, and focusing aids disappeared in favor of a clear central section of the viewfinder, many variable aperture zooms evolved to having maximum apertures of F6.3 because that was the realistic working limit of AF. Sure there were faster ones but cheap ones went to the limit of AF pretty quick.

Note a variable aperture F2.8-F4 should work just fine.

[stevebrot]

A little more information might help.

• What lens are you using?
• How are you determining exposure?
• If an "A" contact lens, is the aperture ring in the "A" position?
• If not an "A" contact lens, are you familiar with the general issues related to stopped-down metering (the only metering available with non-A lenses)?

I own the Katzeye with Optibrite and previously owned the non-Optibrite version. Both meter essentially as well as the stock screen with "A" contact lenses. That is not saying much though since all three screen pretty much suck for stopped-down metering at wider apertures (gross underexposure). That being said, it is unlikely that your screen is at fault. That wretched behavior is a feature of the metering system and is actually addressed in the owner's manual.

As for the viewfinder going dark...that is what you would expect with a variable aperture lens and a proper focusing screen. For example, the 18-55/3.5-5.6 passes less than half as much light at 55mm as it does at 18mm.

Steve

[Raptorman]

Shoot manual?

[Finn]

Hmm...maybe I should have been clearer. This happens with any variable-aperture zoom, but right now the only one I have is an old Promaster one with an A setting. I've had the same issue with the kit lens and FA 28-90 as well. I understand that there is less light coming in at longer focal lengths (= smaller aperture), but why wouldn't this happen with the original focusing screen? Why wouldn't it happen with a split image screen in a 35mm camera?

Really this isn't much of an issue. I mostly stick to fast primes, so I was really just curious about it.

I've got my eye on a DA* 16-50 as my next big purchase, so hopefully in the future this will all be a moot point.

[stevebrot]

Hmm...maybe I should have been clearer. This happens with any variable-aperture zoom, but right now the only one I have is an old Promaster one with an A setting. I've had the same issue with the kit lens and FA 28-90 as well. I understand that there is less light coming in at longer focal lengths (= smaller aperture), but why wouldn't this happen with the original focusing screen? Why wouldn't it happen with a split image screen in a 35mm camera?

Really this isn't much of an issue. I mostly stick to fast primes, so I was really just curious about it.

I've got my eye on a DA* 16-50 as my next big purchase, so hopefully in the future this will all be a moot point.

You should not have any exposure problems with your Promaster as long as the aperture ring is on the "A" setting. If you are and your other lenses meter properly, there is a problem with the lens.

Steve

[Lowell Goudge]

it is in the desing of the split image. the origonal focusing screen gets darker when you zoom but you fail to notice the change in lighting along with the change in image.

It's just that the split image is very sensitive to a specific light level

[Raptorman]

well that still shouldn't make the light meter freak out...thats part of Katz eye's marketing is that their focusing screen doesn't affect the light metering of the camera.

[little laker]

Although I never had a katzeye screen when I shot with Pentax digital I noticed the same thing to a point while shooting with Zooms. That's the main reason why I started shooting full manual.

I can use the same (although modified) lenses on my Sigma SD14, and it's always consistent.
The same thing while shooting with my Pentax film camera.

I don't know if Pentax changed anything major on their Digital metering system, or if they're just more sensitive to exposure than film and my Sigma.

[Recercare]

A little more information might help.

I own the Katzeye with Optibrite and previously owned the non-Optibrite version. Both meter essentially as well as the stock screen with "A" contact lenses. That is not saying much though since all three screen pretty much suck for stopped-down metering at wider apertures (gross underexposure). That being said, it is unlikely that your screen is at fault. That wretched behavior is a feature of the metering system and is actually addressed in the owner's manual.
Steve

Just a quick question. Was the optibrite worth the money ?
I am using primes only (F2.0-3.5).

Kind regards
.lars

[RichardS]

I had similar problems 30 years ago with manual everything (apart from the coupled light meter). My Nikkormat FT3 with the 50mm f1.4 gave no problems. With a 200mm prime (f2.8?), no problems. With my Vivitar 100-300mm f5, I had problems with one half and sometimes both halves of the split image going black. When I moved my eye socket as little, I could get both halves working. I'm sure it has something to do with the smaller maximum aperture and not necessarily the amount of light being let through. The light is very bright here.

Richard.

[Lowell Goudge]

Raptorman metering is affected for spot metering only. on the K10D and K20D with Manual Aperture lenses the average metering is actually improved

Recercare except for my 300 and 400mm, all my primes are faster than F2.8 it is well worth it, especially with wide angle where it is difficult to be accurate on focusing due to the big depth of field with these lenses

[JohnBee]

Just a quick question. Was the optibrite worth the money ?
I am using primes only (F2.0-3.5).

Kind regards
.lars

Yes.

I'd also like to add that adding a plit prism to a camera most often comes in commitment to manual shooting. That is to say its best viewed as an either or scenario.

ie: we dedicated our K200D as a manual shooter with katzeye and use out K20D as an AF rig.

If however, I wanted the best of both worlds, then I wouldn't bother with a split prism as the camera AF indicator(red blink + beep) can do a pretty good job of nailing focus on it's own.

[ovim]

I had a Vivitar Series 1 2.8-4/70-210 zoom which underexposed at longer FL when used in A position. If I used manual aperture and metered with the green button exposures were correct (or better anyway).

I never figured out why it did that, could it be that when the body "saw" the aperture to be 2.8 it was actually 4 and when taking a pic it closed the aperture too much?

[Recercare]

Recercare except for my 300 and 400mm, all my primes are faster than F2.8 it is well worth it, especially with wide angle where it is difficult to be accurate on focusing due to the big depth of field with these lenses

Yes.

I'd also like to add that adding a plit prism to a camera most often comes in commitment to manual shooting. That is to say its best viewed as an either or scenario.

ie: we dedicated our K200D as a manual shooter with katzeye and use out K20D as an AF rig.

If however, I wanted the best of both worlds, then I wouldn't bother with a split prism as the camera AF indicator(red blink + beep) can do a pretty good job of nailing focus on it's own.

Thanks, I have 6 SMC-M lenses and 2 DA Ltd lenses. Why is the split prism a disadvantage for AF lenses?
Kind regards
.lars