Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
01-15-2008, 12:29 PM   #1
Veteran Member
pentagor's Avatar

Join Date: Dec 2007
Location: Ljubljana, Slovenia
Photos: Gallery
Posts: 473
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
Veteran Member
Fritz's Avatar

Join Date: Jun 2007
Location: Tillamook, OR
Posts: 1,168
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
Veteran Member
Finn's Avatar

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, 01:03 PM   #4
Veteran Member
pentagor's Avatar

Join Date: Dec 2007
Location: Ljubljana, Slovenia
Photos: Gallery
Posts: 473
Original Poster
@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.

01-15-2008, 02:35 PM   #5
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
Veteran Member
Fritz's Avatar

Join Date: Jun 2007
Location: Tillamook, OR
Posts: 1,168
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
Veteran Member
ftpaddict's Avatar

Join Date: Jan 2008
Location: Yurp
Photos: Gallery
Posts: 4,669
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
Veteran Member
Fritz's Avatar

Join Date: Jun 2007
Location: Tillamook, OR
Posts: 1,168
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
Veteran Member
pentagor's Avatar

Join Date: Dec 2007
Location: Ljubljana, Slovenia
Photos: Gallery
Posts: 473
Original Poster
Wow you guys are really great help!!! Thanks a lot!
01-17-2008, 08:27 PM   #10
Senior Member




Join Date: Nov 2007
Location: Bay area, CA
Photos: Gallery
Posts: 192
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
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
Veteran Member
Fritz's Avatar

Join Date: Jun 2007
Location: Tillamook, OR
Posts: 1,168
Wow. Do all your lenses do that, or just the 50mm f1.7?
01-18-2008, 02:36 AM   #13
Veteran Member
pentagor's Avatar

Join Date: Dec 2007
Location: Ljubljana, Slovenia
Photos: Gallery
Posts: 473
Original Poster
But this is back focus as I see. I have issues with front focus.
01-18-2008, 04:12 AM   #14
Veteran Member
creampuff's Avatar

Join Date: May 2007
Location: Singapore
Photos: Gallery
Posts: 3,955
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
Veteran Member
pentagor's Avatar

Join Date: Dec 2007
Location: Ljubljana, Slovenia
Photos: Gallery
Posts: 473
Original Poster
QuoteOriginally posted by creampuff Quote
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?
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
focus, front, k-mount, lense, pentax, pentax lens, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search



All times are GMT -7. The time now is 05:54 PM. | See also: NikonForums.com, part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top