split focus screen and exposure - again!

**5teve** · 05-10-2009, 01:28 AM

Hi Guys

Me again and still having exposure issues. but a bit more quanitified this time... but only a bit

Just been out playing with my vivitar 70-150 f3.8 and the auto chinon 50mm f1.7

the vivitar works lovely apart from a bit soft at f3.8 above that it starts over exposing badly (im in M mode using the green button k20d) but in a graduated way. i know this is a known problem with the standard screen but this is with the jinfinance one.

the auto chinon under exposes at f1.7 is about right at f4 but then starts over exposing hugely again after that..

my theory? - all M lenses default the camera to centre weighted metering so the blacking out of the prism caused it to over expose.

im still trying to work out why it does it on my sigma lenses tho... so i'll start experimenting with a focus / exposure test shortly!

Any more ideas or thoughts on my theories?

Thanks

Steve

res3567 · 05-10-2009, 02:50 AM

Originally posted by 5teve

Hi Guys

Me again and still having exposure issues. but a bit more quanitified this time... but only a bit

Just been out playing with my vivitar 70-150 f3.8 and the auto chinon 50mm f1.7

the vivitar works lovely apart from a bit soft at f3.8 above that it starts over exposing badly (im in M mode using the green button k20d) but in a graduated way. i know this is a known problem with the standard screen but this is with the jinfinance one.

the auto chinon under exposes at f1.7 is about right at f4 but then starts over exposing hugely again after that..

my theory? - all M lenses default the camera to centre weighted metering so the blacking out of the prism caused it to over expose.

im still trying to work out why it does it on my sigma lenses tho... so i'll start experimenting with a focus / exposure test shortly!

Any more ideas or thoughts on my theories?

Thanks

Steve

Just got mine( not from jinfinance, but from another Chinese store) and am experiencing the same thing as well in early tests.

I will try all of my MF lenses and get back with you!

**5teve** · 05-10-2009, 03:19 AM

Originally posted by res3567

Just got mine( not from jinfinance, but from another Chinese store) and am experiencing the same thing as well in early tests.

I will try all of my MF lenses and get back with you!

Thanks! will be interesting to hear....

another question... does your centre focus point also end up in the middle of split prism? i have just noticed mine is sitting to the left and down from centre (focus point) meaning the split prism isnt lined up in the frame or.. isnt machined correctly...

can anyone comment? mine is the jinfinance one..

thanks

Steve

res3567 · 05-10-2009, 03:23 AM

Originally posted by 5teve

Thanks! will be interesting to hear....

another question... does your centre focus point also end up in the middle of split prism? i have just noticed mine is sitting to the left and down from centre (focus point) meaning the split prism isnt lined up in the frame or.. isnt machined correctly...

can anyone comment? mine is the jinfinance one..

thanks

Steve

Mine looks like it is down a slightly to the right. It is below the line in the split prism.

**5teve** · 05-10-2009, 04:44 AM

hmm seems common then... oh well!

right been doing some testing on the 50mm...

dark at 1.7 lightening to f4 then darkening slightly until f16 which it gets wrong and used same shutter as f11 set it to next shutter and its still dark but not bad.

under controlled lighting and subject its not a million miles away... still not great.. but doesnt vary like it does in real use.

will get back with some more shortly!

Steve

**cupic** · 05-10-2009, 04:51 AM

Originally posted by res3567

Just got mine( not from jinfinance, but from another Chinese store) and am experiencing the same thing as well in early tests.

I will try all of my MF lenses and get back with you!

I did buy one from Jinfinance(Had a better word of mouth) so it will be interesting to compare

cheers

**5teve** · 05-10-2009, 05:45 AM

ok tried a few thing...

pictures can be found here..

Picasa Web Albums - Rachael & Steve - test of metering

filename is the description of mode etc. click more info on right for details

all apart from the TAV were done using M mode and the green button. interesting results on all lenses!

lenses tested are

50mm auto chinon f1.7
70-150mm f3.8 vivitar set to close focus 70mm
70-300mm f4-5.6 sigma dg set to 70mm but had to move tripod back as it would focus.

see what you think... and see if you can work out what is happening. also if you can try the same... i'd be interested.

results basically say for non A lenses exposure is all over the place using the jinfinance screen!

thanks

Steve

stevebrot · 05-10-2009, 09:36 AM

5teve,
You can expect that stop-down metering on your non-A lenses will still be flaky with your 3rd-party screen. Each screen is a little different in this respect, but none give linear results in an exposure series. Sorry...

Steve

P.S. I used the word "none" above...someone will probably pop into this thread and correct me and suggest the Pentax LL-60 or LF-60 screens for the *ist D. While these are reputed to offer correct exposure with stop-down metering, they do not offer any focus aids. There is also some question as to whether regular (open-aperture) metering is affected with these screens.

OregonJim · 05-10-2009, 09:36 AM

Originally posted by 5teve

another question... does your centre focus point also end up in the middle of split prism? i have just noticed mine is sitting to the left and down from centre (focus point) meaning the split prism isnt lined up in the frame or.. isnt machined correctly...

can anyone comment? mine is the jinfinance one..

I have two of the jinfinance screens. One in *ist DL, the other in K200D. Both have the center focus point smack dab in the middle of the prism. These are the diagonal split prisms, if that makes a difference. Neither camera seems to have any of the metering issues with M lenses that are common in the K10/K20. I haven't done extensive testing, though, as I normally use a handheld meter for exposure anyway...

stevebrot · 05-10-2009, 10:56 AM

Originally posted by OregonJim

I have two of the jinfinance screens. One in *ist DL, the other in K200D. Both have the center focus point smack dab in the middle of the prism. These are the diagonal split prisms, if that makes a difference. Neither camera seems to have any of the metering issues with M lenses that are common in the K10/K20. I haven't done extensive testing, though, as I normally use a handheld meter for exposure anyway...

Your experience agrees with other reports on this forum. Stop-down metering on the *istD series and the penta-mirror models seem to be accurate. The K10D and K20D have a different metering system that apparently applies some mathematical "splines" to the meter reading dependent on aperture information supplied by the lens. With non-A lenses, this information is absent and the meter fails over into some sort of default mode that results in non-linearity at both wide and narrower apertures.

I have noted other curiosities as well that include:

1/2 stop difference for infinity vs. close focus with some lenses
Fall off in meter sensitivity at about EV1.5

The second issue is particularly pertinent to stop-down metering in dim light. Values below EV2 at the sensor are relatively common when the lens is stopped down to any extent. The manual indicates linearity to EV0, but perhaps that is not quite true?

Steve

05-10-2009, 01:28 AM	#1
5teve Site Supporter	split focus screen and exposure - again! Hi Guys Me again and still having exposure issues. but a bit more quanitified this time... but only a bit Just been out playing with my vivitar 70-150 f3.8 and the auto chinon 50mm f1.7 the vivitar works lovely apart from a bit soft at f3.8 above that it starts over exposing badly (im in M mode using the green button k20d) but in a graduated way. i know this is a known problem with the standard screen but this is with the jinfinance one. the auto chinon under exposes at f1.7 is about right at f4 but then starts over exposing hugely again after that.. my theory? - all M lenses default the camera to centre weighted metering so the blacking out of the prism caused it to over expose. im still trying to work out why it does it on my sigma lenses tho... so i'll start experimenting with a focus / exposure test shortly! Any more ideas or thoughts on my theories? Thanks Steve

05-10-2009, 10:56 AM	#10
stevebrot Pentaxian	Originally posted by OregonJim I have two of the jinfinance screens. One in ist DL, the other in K200D. Both have the center focus point smack dab in the middle of the prism. These are the diagonal split prisms, if that makes a difference. Neither camera seems to have any of the metering issues with M lenses that are common in the K10/K20. I haven't done extensive testing, though, as I normally use a handheld meter for exposure anyway... Your experience agrees with other reports on this forum. Stop-down metering on the istD series and the penta-mirror models seem to be accurate. The K10D and K20D have a different metering system that apparently applies some mathematical "splines" to the meter reading dependent on aperture information supplied by the lens. With non-A lenses, this information is absent and the meter fails over into some sort of default mode that results in non-linearity at both wide and narrower apertures. I have noted other curiosities as well that include: 1/2 stop difference for infinity vs. close focus with some lenses Fall off in meter sensitivity at about EV1.5 The second issue is particularly pertinent to stop-down metering in dim light. Values below EV2 at the sensor are relatively common when the lens is stopped down to any extent. The manual indicates linearity to EV0, but perhaps that is not quite true? Steve

Thread Tools	Search this Thread
Show Printable Version E-mail to a Friend	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Split screen focus...	jess	Pentax Camera and Field Accessories	164	09-03-2010 10:32 AM
k-x split focus screen from a ks super	vasili	Pentax Camera and Field Accessories	5	01-31-2010 04:47 PM
Problem with split focus screen.	mstolt	Pentax Camera and Field Accessories	16	06-28-2009 03:33 PM
Quick Question: Pentax KM screen replaceable with split-focus screen?	vinzer	Pentax Film SLR Discussion	2	01-06-2009 12:21 AM
K10, split-screen, LF80 & LL60 : Focus and exposure accuracy	dlacouture	Pentax DSLR Discussion	24	11-18-2008 05:20 AM

05-10-2009, 02:50 AM	#2
res3567 Veteran Member	Originally posted by 5teve Hi Guys Me again and still having exposure issues. but a bit more quanitified this time... but only a bit Just been out playing with my vivitar 70-150 f3.8 and the auto chinon 50mm f1.7 the vivitar works lovely apart from a bit soft at f3.8 above that it starts over exposing badly (im in M mode using the green button k20d) but in a graduated way. i know this is a known problem with the standard screen but this is with the jinfinance one. the auto chinon under exposes at f1.7 is about right at f4 but then starts over exposing hugely again after that.. my theory? - all M lenses default the camera to centre weighted metering so the blacking out of the prism caused it to over expose. im still trying to work out why it does it on my sigma lenses tho... so i'll start experimenting with a focus / exposure test shortly! Any more ideas or thoughts on my theories? Thanks Steve Just got mine( not from jinfinance, but from another Chinese store) and am experiencing the same thing as well in early tests. I will try all of my MF lenses and get back with you!

05-10-2009, 03:19 AM	#3
5teve Site Supporter	Originally posted by res3567 Just got mine( not from jinfinance, but from another Chinese store) and am experiencing the same thing as well in early tests. I will try all of my MF lenses and get back with you! Thanks! will be interesting to hear.... another question... does your centre focus point also end up in the middle of split prism? i have just noticed mine is sitting to the left and down from centre (focus point) meaning the split prism isnt lined up in the frame or.. isnt machined correctly... can anyone comment? mine is the jinfinance one.. thanks Steve

05-10-2009, 03:23 AM	#4
res3567 Veteran Member	Originally posted by 5teve Thanks! will be interesting to hear.... another question... does your centre focus point also end up in the middle of split prism? i have just noticed mine is sitting to the left and down from centre (focus point) meaning the split prism isnt lined up in the frame or.. isnt machined correctly... can anyone comment? mine is the jinfinance one.. thanks Steve Mine looks like it is down a slightly to the right. It is below the line in the split prism.

05-10-2009, 04:44 AM	#5
5teve Site Supporter	hmm seems common then... oh well! right been doing some testing on the 50mm... dark at 1.7 lightening to f4 then darkening slightly until f16 which it gets wrong and used same shutter as f11 set it to next shutter and its still dark but not bad. under controlled lighting and subject its not a million miles away... still not great.. but doesnt vary like it does in real use. will get back with some more shortly! Steve

05-10-2009, 04:51 AM	#6
cupic Site Supporter	Originally posted by res3567 Just got mine( not from jinfinance, but from another Chinese store) and am experiencing the same thing as well in early tests. I will try all of my MF lenses and get back with you! I did buy one from Jinfinance(Had a better word of mouth) so it will be interesting to compare cheers

05-10-2009, 05:45 AM	#7
5teve Site Supporter	ok tried a few thing... pictures can be found here.. Picasa Web Albums - Rachael & Steve - test of metering filename is the description of mode etc. click more info on right for details all apart from the TAV were done using M mode and the green button. interesting results on all lenses! lenses tested are 50mm auto chinon f1.7 70-150mm f3.8 vivitar set to close focus 70mm 70-300mm f4-5.6 sigma dg set to 70mm but had to move tripod back as it would focus. see what you think... and see if you can work out what is happening. also if you can try the same... i'd be interested. results basically say for non A lenses exposure is all over the place using the jinfinance screen! thanks Steve

05-10-2009, 09:36 AM	#8
stevebrot Pentaxian	5teve, You can expect that stop-down metering on your non-A lenses will still be flaky with your 3rd-party screen. Each screen is a little different in this respect, but none give linear results in an exposure series. Sorry... Steve P.S. I used the word "none" above...someone will probably pop into this thread and correct me and suggest the Pentax LL-60 or LF-60 screens for the *ist D. While these are reputed to offer correct exposure with stop-down metering, they do not offer any focus aids. There is also some question as to whether regular (open-aperture) metering is affected with these screens.

05-10-2009, 09:36 AM	#9
OregonJim Veteran Member	Originally posted by 5teve another question... does your centre focus point also end up in the middle of split prism? i have just noticed mine is sitting to the left and down from centre (focus point) meaning the split prism isnt lined up in the frame or.. isnt machined correctly... can anyone comment? mine is the jinfinance one.. I have two of the jinfinance screens. One in *ist DL, the other in K200D. Both have the center focus point smack dab in the middle of the prism. These are the diagonal split prisms, if that makes a difference. Neither camera seems to have any of the metering issues with M lenses that are common in the K10/K20. I haven't done extensive testing, though, as I normally use a handheld meter for exposure anyway...