Win a Pentax Limited Lens: Raffle Now Live!

**pentagor** · 01-15-2008, 12:29 PM

Today, I received my Pentax M 50/1.7 lense, which I bought on ebay. It is in pretty good condition.

But I have some problems with focus. It seems to me, that the lense is having a front focus issues. I tested it from a close distance at F/1.7 and by my opinion the front focus is about 2cm or about 1 inch. Is this possible or am I just that bad in manual focusing?
Below is one test pic, with apperture F/2 and 1/15s at ISO 400. This one is pretty sharp, but I would rather notshow you the rest.

This one is way off: (I was focusing candy in the middle)

So please tell me, is it really so hard to manual focus?

And another question: How do you guys keep track of EXIF data on manual lenses?

Fritz · 01-15-2008, 12:51 PM

Are you using the green focus confirmation light as your indicator that the picture is in focus? Mine also had a slight front focus issue when relying on the focus confirmation light, which was more pronounced with low f stops and low light. A split prism focus screen helped me to be more accurate with my manual focus.

As far as EXIF, the camera will ask for the focal length when you turn it on. The only thing it will not record with the M lens is the f stop.

Finn · 01-15-2008, 01:03 PM

Great lens! I use it all the time on my K100D. It is indeed difficult to focus accurately at wide apertures, and I find the green indicator light to be kind of imprecise. I had a split prism focusing screen in my camera for a while, but I decided to go back to the regular screen because the prism caused wacky metering problems on M lenses. My advice when using wide apertures is to shoot lots of pictures -- some of them are bound to come out, right?

**pentagor** · 01-15-2008, 01:03 PM

@Fritz: Yes, most of the time, I use green focus confirmation light. That's exactly what is happening to me. Can you tell me, what this is: A split prism focus screen?

@Finn: Thanks.

tux08902 · 01-15-2008, 02:35 PM

That lens is absolutely amazing. I enjoy using it a lot, but I'm thinking of replacing mine with the A 50/1.7, if I can get a good deal on it because of the additional features of the K10D all A series lenses are compatible with.

Fritz · 01-15-2008, 02:36 PM

The split prism focus screen uses two half circles that move as you focus the lens. The lens is in focus when the two half circles are lined up with each other to make a full circle.

Here is a link that has some pictures of how to install a split prism screen into your k100d. It was a common type of screen to have on the older manual focus cameras. It's what I learned with on my old ME Super. And though the screen on the k100d is not as big as my ME Super was, the split prism still helps a bunch IMHO. I have not had the exposure problems that some people have had(as finn mentioned). I purchased a chinese made e-bay screen from the seller "jinfinance". It has worked well for me. Another popular model is the "Katz eye" focus screen, but it's quite a bit more money.

The split prism screen does mess up spot metering, but as long as I'm using matrix, or center weighted metering I have not had a problem.

ftpaddict · 01-15-2008, 02:49 PM

Although focusing screens help quite a bit, on my manual cameras; I've never felt the need for one on any DSLR I've used to date. In fact, if I had the ability to choose, I'd go for the screen on the K10D, rather than the one on my Praktica.

Fritz · 01-15-2008, 03:12 PM

I agree that the screen that comes from the factory is nice clear and bright. And in many ways better then a split prism screen. Especially if you mostly use auto focus lenses.

I only have 2 auto focus lenses, and 7 manual focus lenses(which I primarily use). I had found the focus indicator in my camera to be inaccurate, which ended up with almost all my low f stop shots being out of focus. So I got the split prism screen, and at least I could focus accurately with that. I know there are techniques with manual focusing matte screens, but my hit miss ratio was still not acceptable.

I did recalibrate my focus indicator to match my split prism screen. So now even my focus indicator light results in accurate focusing. So I guess I could go back to my matte screen.

Who knows, I may.....

**pentagor** · 01-16-2008, 11:38 AM

Wow you guys are really great help!!! Thanks a lot!

truonganh · 01-17-2008, 08:27 PM

ok i see a general trend on the bright lens. I have AF-50mmf1.4 and M-50f1.7. I think when you test for it at low light, there is a tendency to front-focus on a test chart. When retested at bright light (well lit indoor window) or flash, focus is very good. (I always test it at the biggest possible f-stop) I think it has to do with visual perception when the light is low.

fastoys2nv · 01-17-2008, 09:08 PM

here are a couple of test shots from my K100D ( camera was replaced tonight by Henrys ) and my M-50mm f1.7. Focus was on the center can at f1.7. The cans are spaced about 8 inches apart. Focus was on the center can with the indicator on.

Fritz · 01-17-2008, 10:13 PM

Wow.

Do all your lenses do that, or just the 50mm f1.7?

**pentagor** · 01-18-2008, 02:36 AM

But this is back focus as I see. I have issues with front focus.

creampuff · 01-18-2008, 04:12 AM

LOL, how can there be front focus or back focus when you are focusing manually?

As has been mentioned, the red AF focus indicator is merely a guide to where the camera senses the focus point. The area covered is a little bigger than the red square. The green focus confirmation light is only a guide. If you're using manual focusing, get the diopter correction dialled in to your eyesight first but you still need to USE YOUR EYES. Why fault the camera when the whole point of manual focusing is to trust your eyes.

I have never felt the need to change to a split image rangefinder or microprism focusing screen but I can vouch the O-M5E3 eyepiece magnifier helps a lot when focusing manually.

**pentagor** · 01-18-2008, 04:19 AM

Originally posted by creampuff

LOL, how can there be front focus or back focus when you are focusing manually?

As has been mentioned, the red AF focus indicator is merely a guide to where the camera senses the focus point. The area covered is a little bigger than the red square. The green focus confirmation light is only a guide. If you're using manual focusing, get the diopter correction dialled in to your eyesight first but you still need to USE YOUR EYES. Why fault the camera when the whole point of manual focusing is to trust your eyes.

I have never felt the need to change to a split image rangefinder or microprism focusing screen but I can vouch the O-M5E3 eyepiece magnifier helps a lot when focusing manually.

Sorry creampuff, but I don't agree with you. After your first post, I beleived you, but then I tried to trust my eyes and nothing changed. Still frontfocus. Don't tell me to adjust my eyes or get diopter correction fixed, 'cause I did all that too.
And since I'm not the only one, one question for you: Do you own a 50/1.7 M lense?

01-15-2008, 12:29 PM	#1
pentagor Site Supporter Join Date: Dec 2007 Location: Ljubljana, Slovenia Posts: 495	Got my 50/1.7 Pentax Today, I received my Pentax M 50/1.7 lense, which I bought on ebay. It is in pretty good condition. But I have some problems with focus. It seems to me, that the lense is having a front focus issues. I tested it from a close distance at F/1.7 and by my opinion the front focus is about 2cm or about 1 inch. Is this possible or am I just that bad in manual focusing? Below is one test pic, with apperture F/2 and 1/15s at ISO 400. This one is pretty sharp, but I would rather notshow you the rest. This one is way off: (I was focusing candy in the middle) So please tell me, is it really so hard to manual focus? And another question: How do you guys keep track of EXIF data on manual lenses?

01-15-2008, 12:51 PM	#2
Fritz Veteran Member Join Date: Jun 2007 Location: Tillamook, OR Posts: 1,222	Are you using the green focus confirmation light as your indicator that the picture is in focus? Mine also had a slight front focus issue when relying on the focus confirmation light, which was more pronounced with low f stops and low light. A split prism focus screen helped me to be more accurate with my manual focus. As far as EXIF, the camera will ask for the focal length when you turn it on. The only thing it will not record with the M lens is the f stop.

01-15-2008, 01:03 PM	#3
Finn Veteran Member Join Date: Feb 2007 Location: Phoenix Photos: Gallery Posts: 1,056	Great lens! I use it all the time on my K100D. It is indeed difficult to focus accurately at wide apertures, and I find the green indicator light to be kind of imprecise. I had a split prism focusing screen in my camera for a while, but I decided to go back to the regular screen because the prism caused wacky metering problems on M lenses. My advice when using wide apertures is to shoot lots of pictures -- some of them are bound to come out, right?

01-15-2008, 02:35 PM	#5
tux08902 Inactive Account Join Date: Nov 2007 Location: North Brunswick, NJ Posts: 473	That lens is absolutely amazing. I enjoy using it a lot, but I'm thinking of replacing mine with the A 50/1.7, if I can get a good deal on it because of the additional features of the K10D all A series lenses are compatible with.

01-15-2008, 02:36 PM	#6
Fritz Veteran Member Join Date: Jun 2007 Location: Tillamook, OR Posts: 1,222	The split prism focus screen uses two half circles that move as you focus the lens. The lens is in focus when the two half circles are lined up with each other to make a full circle. Here is a link that has some pictures of how to install a split prism screen into your k100d. It was a common type of screen to have on the older manual focus cameras. It's what I learned with on my old ME Super. And though the screen on the k100d is not as big as my ME Super was, the split prism still helps a bunch IMHO. I have not had the exposure problems that some people have had(as finn mentioned). I purchased a chinese made e-bay screen from the seller "jinfinance". It has worked well for me. Another popular model is the "Katz eye" focus screen, but it's quite a bit more money. The split prism screen does mess up spot metering, but as long as I'm using matrix, or center weighted metering I have not had a problem.

01-15-2008, 02:49 PM	#7
ftpaddict Veteran Member Join Date: Jan 2008 Location: Yurp Photos: Gallery Posts: 4,666	Although focusing screens help quite a bit, on my manual cameras; I've never felt the need for one on any DSLR I've used to date. In fact, if I had the ability to choose, I'd go for the screen on the K10D, rather than the one on my Praktica.

01-15-2008, 03:12 PM	#8
Fritz Veteran Member Join Date: Jun 2007 Location: Tillamook, OR Posts: 1,222	I agree that the screen that comes from the factory is nice clear and bright. And in many ways better then a split prism screen. Especially if you mostly use auto focus lenses. I only have 2 auto focus lenses, and 7 manual focus lenses(which I primarily use). I had found the focus indicator in my camera to be inaccurate, which ended up with almost all my low f stop shots being out of focus. So I got the split prism screen, and at least I could focus accurately with that. I know there are techniques with manual focusing matte screens, but my hit miss ratio was still not acceptable. I did recalibrate my focus indicator to match my split prism screen. So now even my focus indicator light results in accurate focusing. So I guess I could go back to my matte screen. Who knows, I may.....

01-16-2008, 11:38 AM	#9
pentagor Site Supporter Join Date: Dec 2007 Location: Ljubljana, Slovenia Posts: 495 Original Poster	Wow you guys are really great help!!! Thanks a lot!

01-17-2008, 08:27 PM	#10
truonganh Senior Member Join Date: Nov 2007 Location: Bay area, CA Photos: Gallery Posts: 194	ok i see a general trend on the bright lens. I have AF-50mmf1.4 and M-50f1.7. I think when you test for it at low light, there is a tendency to front-focus on a test chart. When retested at bright light (well lit indoor window) or flash, focus is very good. (I always test it at the biggest possible f-stop) I think it has to do with visual perception when the light is low.

01-17-2008, 09:08 PM	#11
fastoys2nv Senior Member Join Date: Oct 2007 Location: GTA Ontario Canada (Tottenham Area) Posts: 138	here are a couple of test shots from my K100D ( camera was replaced tonight by Henrys ) and my M-50mm f1.7. Focus was on the center can at f1.7. The cans are spaced about 8 inches apart. Focus was on the center can with the indicator on.

01-17-2008, 10:13 PM	#12
Fritz Veteran Member Join Date: Jun 2007 Location: Tillamook, OR Posts: 1,222	Wow. Do all your lenses do that, or just the 50mm f1.7?

01-18-2008, 02:36 AM	#13
pentagor Site Supporter Join Date: Dec 2007 Location: Ljubljana, Slovenia Posts: 495 Original Poster	But this is back focus as I see. I have issues with front focus.

01-18-2008, 04:12 AM	#14
creampuff Veteran Member Join Date: May 2007 Location: Singapore Photos: Gallery Posts: 3,953	LOL, how can there be front focus or back focus when you are focusing manually? As has been mentioned, the red AF focus indicator is merely a guide to where the camera senses the focus point. The area covered is a little bigger than the red square. The green focus confirmation light is only a guide. If you're using manual focusing, get the diopter correction dialled in to your eyesight first but you still need to USE YOUR EYES. Why fault the camera when the whole point of manual focusing is to trust your eyes. I have never felt the need to change to a split image rangefinder or microprism focusing screen but I can vouch the O-M5E3 eyepiece magnifier helps a lot when focusing manually.

01-18-2008, 04:19 AM	#15
pentagor Site Supporter Join Date: Dec 2007 Location: Ljubljana, Slovenia Posts: 495 Original Poster	Originally posted by creampuff LOL, how can there be front focus or back focus when you are focusing manually? As has been mentioned, the red AF focus indicator is merely a guide to where the camera senses the focus point. The area covered is a little bigger than the red square. The green focus confirmation light is only a guide. If you're using manual focusing, get the diopter correction dialled in to your eyesight first but you still need to USE YOUR EYES. Why fault the camera when the whole point of manual focusing is to trust your eyes. I have never felt the need to change to a split image rangefinder or microprism focusing screen but I can vouch the O-M5E3 eyepiece magnifier helps a lot when focusing manually. Sorry creampuff, but I don't agree with you. After your first post, I beleived you, but then I tried to trust my eyes and nothing changed. Still frontfocus. Don't tell me to adjust my eyes or get diopter correction fixed, 'cause I did all that too. And since I'm not the only one, one question for you: Do you own a 50/1.7 M lense?

Got my 50/1.7 Pentax

Win a Pentax Limited Lens: Raffle Now Live!