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09-17-2015, 01:33 AM   #1
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DSLR, manual focusing and myopia

I've had my first DSLR [ a K-S2] for a few months now, and as my last serious camera was a Super-A I've had a lot to learn, and I've been tackling it slowly attempting to learn one thing at a time. I'm now at the point where I want to use my old manual Pentax prime f50 1.4 lens from the Super-A instead of the standard lens that came with the K-S2. Obviously auto-focus is not going to work with the old lens. I'm having a bit of trouble with the focusing, with several shots apparently focused in not quite the right place, especially using f2 and faster. I've read that manual focus with DSLR screens can be a bit tricky, but I'm wondering if my -2 short sight is adding to the problem. I usually peer into the viewfinder with my specs on but not always. I can see all the indicators in the viewfinder nice and sharply either way.

So the question is - is it possible that when I focus with my specs off I am using the camera to compensate for my poor distance eyesight, so when the subject looks in focus to me, it's not in focus to the camera sensor?

09-17-2015, 02:08 AM   #2
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Did you adjust the diopter?
09-17-2015, 02:20 AM   #3
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My eyesight is not as good as it used to be. I am using the autofocus leds, to show when I have got it right. Remember, they still indicate focus even when you are focusing manually.
09-17-2015, 02:24 AM   #4
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Be aware that the only focus point indicator that will work with the manual lens is the centre one, so if you're using that for reference then you'd need to use a sort of focus then recompose technique.

Regarding the differences between what the eyes see and the sensor, then I believe there is the 'dioptre correction' adjustment on the viewfinder housing, as mentioned by photolady ..... a small wheel adjuster.I haven't needed it myself yet, but others will no doubt give details on the correct techniques to adjust it.

09-17-2015, 08:14 AM   #5
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Some lenses are harder to focus than others, and it definitely takes practice. I found a macro lens was the easiest for me to focus, and that's what I practice on. The one lens I've never managed to focus correctly on a consistent basis is the K24 f2.8 - too bad because it's a lovely lens. And yes, I will use the center point indicator and re-frame if I can't obviously see the focus - perhaps that's why I have issues with the K24 - the focus is rarely obvious and perhaps the camera doesn't focus accurately with it.

You can also try using live view, too - I find sometimes it's easier to use it and zoom in if I'm using a tripod (especially if I'm also using macro rails).

One of the things I've found is that just because you can see the indicators clearly doesn't mean that your subject is going to be in focus. While you are looking through a scene through a glass reflected in a mirror, the scene isn't really at the same plane as the indicators. I figured that out when I was taking pictures of scenes reflected in a muddy puddle with a longer lens. The puddle was relatively close and I could get the surface of the puddle and grass around it in focus or the reflected scene, but not both at the same time with a relatively large aperture. I think the camera is more or less the same thing - I wear bifocals and while I can see the scene clearly with my distance correction, I can't see the indicators as well. I can't manage without my glasses at all as the dioper adjustment doesn't compensate enough for my eye's deviation. If the dioper adjustment can compensate for your eyes without your glasses, then you can use it instead of your glasses.
09-17-2015, 09:12 AM   #6
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Photolady - I have tried adjusting the diopter. Its a sort of sliding affair. I didn't want to use it as it's not especially easy to re-locate it in its centre position afterwards, which I need to when I have my specs on, and when the camera is used by other people who have better eyesight than me.

mtngal - I think you're saying yes, don't confuse sharpness of the viewfinder indicators with an ability to focus your subject.

I have been using the little centre red square, and it could be my lack of practice but it does seem to take a while to light up. Also I've been shooting my pets close-up (with the camera!) and they don't stay still while I turn turn turn the ring...

So I think the general advice is (1) keep your specs on, (2) practice, practice, practice, preferably on subjects that don't run around, (3) use the leds and find out about liveview + zooming and (4) if all else fails get the better eyes to do it for you!
09-17-2015, 09:38 AM   #7
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QuoteOriginally posted by LarfinGiraffe Quote
I have tried adjusting the diopter. Its a sort of sliding affair. I didn't want to use it as it's not especially easy to re-locate it in its centre position afterwards, which I need to when I have my specs on, and when the camera is used by other people who have better eyesight than me.
Center? Either their eyesight isn't that good, or you're being really mean to them. On every Pentax DSLR I've owned, the default position for the diopter slider was all the way to the right. I felt very old the day that I had to give in and move it two clicks to the left on all my cameras (and add a pair of reading glasses to my travel kit).

While I usually turn off all sounds on my cameras, for manual focusing, I turn the focus confirm chirp back on, so that I have an additional cue.
09-17-2015, 11:11 AM   #8
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I don't think the red lights in the viewfinder are useful for accurate manual focusing judgment . As said earlier, only the centre point works anyway. The key camera indicator that the AF sensors think something's in focus is the green hexagon focus confirmation along the bottom of the viewfinder.

09-17-2015, 11:26 AM   #9
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Hhhmmm, interesting, THoog, perhaps this is a clue to where I'm going wrong. The user manual appears to show a plus sign on the left hand side of the slider, and a minus on the right. I cannot see anything on the actual slider on the camera, and there's no explanation as to what the plus means anyway. With specs off if I slide to the left, all the indicators go very fuzzy, and to the right is sharp. With specs on its clearer in the middle. My prescription is -1.75ish. There's no click-stops on the slider.

I think I'll take your tip about listening for the chirp. Also I need to do a little more research on the red-square-in-viewfinder vs hexagon-indicator-light. Should they both be lit for in-focus?
Sorry about the questions being so basic. I am but at the start of a long journey...

---------- Post added 09-17-15 at 07:27 PM ----------

thanks mcgregni, I think our posts crossed in the ether!
09-17-2015, 11:59 AM   #10
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I haven't handled a K-S2 - as the newest design, the diopter adjustment might be different (I would be surprised, 'tho). My K-S1 has very slight clicks on the slider.

A lot of folks confuse the red square with the hexagon - the red square should only indicate which focus point is in use. The green hex confirms focus. The good news is you have experience with manual focusing. Growing up with manual focus cameras has helped me in a lot of situations where AF just didn't work.
09-17-2015, 01:27 PM   #11
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My ever-so-slightly out of focus rat, my first attempt at focusing up real close with the Pentax-A f1.4 at f2 1/60th iso 800 auto exposure.
I love this lens, it may well replace the standard permanently, so I will persevere with the manual focusing techniques. Thanks everyone for your helpful suggestions.

09-17-2015, 01:55 PM   #12
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With a -10.50/-10.25 diopter I cannot use the viewfinder without eyeglasses but I still need to adjust the diopter. This is how I do it. With an AF lens with focus point set at center AF focus on a high contrast subject - like a page of text or other sharply defined pattern. Adjust the diopter for sharpest image in viewfinder. My K10D has click stops on the diopter adjustment slider.

MF training: After setting the diopter as above use AF to get focus confirmation and lock on a variety of subjects. Study and train your "eye" to recognize what in-focus subjects look like on the focus screen. Switch to MF and without turning on the meter and focus check with the half press focus manually the best you can using only the image in the viewfinder. Then check by turning on the meter. With enough practice you'll find that you get a satisfying focus confirmation chirp and green symbol almost every time. You can use a MF lens for this stage. Adjusting the diopter is crucial.

Many people will switch to a split-image focus screen but there are other drawbacks to this as it can affect the viewfinder metering.
09-17-2015, 02:16 PM   #13
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QuoteOriginally posted by LarfinGiraffe Quote
So the question is - is it possible that when I focus with my specs off I am using the camera to compensate for my poor distance eyesight, so when the subject looks in focus to me, it's not in focus to the camera sensor?
I don't think this can be the case. If it's out of focus to the sensor, and thus out of focus on the screen, your eye is not then going to be able to focus it. At best what you see will be as poorly focussed as the screen is, at worst a lot worse than that. Your eye can't compensate.
09-17-2015, 03:28 PM   #14
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I only scanned through this thread, so I truly apologize if it has been mentioned, or ruled out.
Have you tried the focus peaking option using the display on the K-S2?
09-17-2015, 04:57 PM   #15
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You can search for second-hand SMC Correction Lens Adapter M in -2 (eBay or KEH). That device slips over the frame of the VF exit pupil and will help correct for your myopia, allowing you to shoot without your eyeglasses.

I believe most camera viewfinders are intentionally set to a -1 diopter. You should then need to add -.75 to make the internal indicators an accurate correction for your prescription (if I understand the mechanics correctly), but that won't make the focusing screen properly corrected.

My prescription right eye is -1.25 so with a slight shift of the diopter adjustment (wheel on the K-3, slider on the K10D) I can shoot without eyeglasses. For fast lenses (set wider than f/2.8) it is often better for me to use focus peaking since the zone of critical focus is so thin. I brace by pushing the camera away from my body putting light tension on the strap.

Last edited by monochrome; 09-17-2015 at 05:03 PM.
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