[5teve]

Hi Guys

I have fitted the split prism focus screen from Jinfinance and have taken it out for a play yesterday.

I had the Sigma 18-50 lens attached and noticed the prism being very dark some pictures turned out ok, but some were massively over exposed. Any particular reason for this? it seems to work ok with the auto chinon 50mm f1.7 i have ok (apart from the usual exposure dramas for manual lens's)

has anyone else seen this with modern lens's used with split prisms?

Thanks

Steve

[Jewelltrail]

I bought my split prism from "jinfinance" too. I have now used it with well over 20 lenses--it is an awesome tool--no complaints. This, coupled with the KPS eyepiece, makes manual focus a joy.

My exposure difficulties are no greater or lesser when compared with the original, Pentax screen. The prism should not be dark, unless you are viewing with it @ f5.6 or smaller. On a modern lens, there should be no issues with a dark screen unless the max aperture is 5.6 or smaller.

[Douglas_of_Sweden]

I second Jewelltrail's observations. I have the same screen in my K20D. Works fine with all my lenses wihtout exposure problems. The prism gets dark and hard to use on my old Tokina 400/5.6, but is bright enough on all other lenses I've used.

You know, on film bodies with interchangeable screens one was usually recommended to go over to a microprism on longer lenses. So probably one should have more than one screen for a DSLR also.

[5teve]

well i have been to the zoo today and it seems to be an issue with varying apertures, i cannot put my finger on what is causing it tho... some over expose other under (under i can understand with a hugely bright background behind the subject!)

as an example i have attached 2 photos, both taken with the sigma 18-50 3.5-5.6 that i was just carrying around it seems to be this lens that suffers a fair bit..

anyway.... pictures...


Model: PENTAX K20D
ISO: 100
Exposure: 1/60 sec
Aperture: 5.6
Focal Length: 50mm



Model: PENTAX K20D
ISO: 200
Exposure: 1/20 sec
Aperture: 8.0
Focal Length: 50mm


im sure its operator error as its such a learning curve from my old camera which was vey much point and shoot... but the prism is most definitely blacking out with both of my sigma's on not badly... just maybe enough to cause over exposure..

Thanks

Steve

[pedrojoper]

Try to avoid spot metering, so it won't meter exclusively on the split center, which is the part going dark at smaller apertures (at f5.6 the center is probably darker than it should...).

[5teve]

i had to actually resort to spot metering at the zoo to get it right... but the above examples as most of mine are, are evaluation, not even centre weighted!

i have read tho that spot doesnt work well on the splits...

Thanks

Steve

[SOldBear]

I've tried 2 split prism focusing screens, one from jinfinance and another from shoot-ing. The results are very similar.

- Exposures with M lenses are generally correct at larger apertures until 1:4, then progressively overexposed. This is not better nor worse than the stock focusing screen of the K10D (LI-80).

- With lens with max. aperture of 1:4.5 or smaller, the center micro prism becomes very distracting. It's difficult to see the center red LED.

- At aperture of 1:5.6 or smaller, half of the split prism darkens and thus can't be relied on for focusing.

So IMHO, the split prism screen is great for metering and focusing at large apertures (say, 1:3.5 or greater). Its usefulness decreases sharply at small apertures.

That plus the problem of overexposure at smaller apertures always annoy me.

So when I found an LL-60 screen, I swapped the split prism screen out. I've done it twice for both of my K10D bodies. On one of the K10D, I have the Pentax 0-ME3 eyecup. I'm not yet sure if I buy one for the other K10D.

Now I have to rely more on my eye and the focus confirmation. But at least the problem of incorrect exposure is fixed with the LL-60 screen.

Note: I always use center-weighted metering.