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Changing focusing screen: worth the hassle? [Pentax K-50]

Discussion in 'General Equipment Chat & Advice' started by CPRobertson, Oct 29, 2018.

  1. CPRobertson

    CPRobertson Active Member

    Good morning folks!

    I found myself acquiring a 300mm manual lens yesterday for a pittance - £5 at a local forum (the old-fashioned kind of forum - where people gather in real life - mostly to sell stuff :p)

    Anyway! I like the lens a lot - but focusing is slow!

    My camera is a Pentax K-50 - (my first DSLR ::hugs camera-bag::) - which I believe allows for changing the focusing screens (it is listed in the manual as "interchangeable natural-bright-matte III focusing screen)

    I have a few questions - as I would like to add a split focus screen but obviously wanted to do my research!

    1) Am I correct in thinking that adding a focus screen with a 45° split image focus not going to affect AF when using regular KAF2-compatible lenses?

    2) How much is the optical image quality going to be affected? I would assume this depends on the quality of the screen I receive/purchase?

    3) Is AE going to be affected? I have read that a darkening of the optical image is to be expected - buty does this carry across to the AE metering?

    4) Finally, how difficult is it to change the focus screen? I am an electrical engineer who takes things apart a lot after all! But taking apart cameras, I happen to know from past experience, is... a little finicky.... It looks like it's just a matter of disconnecting the retainer lever and it pops out - BUT, again, I like doing my research :)

    Many thanks in anticipation!
    Done_rundleCams likes this.
  2. PeteRob

    PeteRob Well-Known Member

    I don't know but I'll guess. Personally I'd not bother. With a 300 F4 or so a split image focus may not be any better than using the existing finder. I'd suggest to practice a bit rather than risk messing the camera up for the sake of a £5 "bargain". Mirrorless cameras are generally better suited to using old lenses.

    1) the AF sensors are usually under the mirror (which is part silvered) so changing the focus screen shoukdn't affect the AF but the AF information is usually overlaid on the focus screen so you may lose focus confirmation in the view finder.
    2) focus screen doesn't affect image quality, unless you can't focus with it. That's down to the lens
    3) I have no idea. The meter is usually in the prism housing so very possibly.
    4) if it is a changeable screen it should be clipped in. Whether you need a special tool to release the clips or just a pair of tweezers I am not sure, but it'll likely be a bit fiddly.
    Done_rundleCams and CPRobertson like this.
  3. CPRobertson

    CPRobertson Active Member

    I've been reading more into it - especially regard 3: apparently it usually drops the AE by 1/3-to-1 stops, but that can easily be counteracted using the AE-adjust in the opposite direction.

    That's good news on the AF! Not sure I like the idea of losing the AF indicators though - when you combine that with the changes in AE metering, I think that's enough of a reason not to get a split prism - too many issues and not enough benefits. If I want to go properly manual I'll just buy an old 38mm film camera. 32mm... 38mm... oh dear lord I can't remember the size of old film :S

    On the other hand, I'm strongly considering a grid-overlay focus screen like the ML-60 (the pentax-original part) I can pick one up for £25 and I think I'd get use from it (and being an original part, it definitely fits and won't mess with the various sensors).

    The fiddly-ness I can deal with! I've taken apart worse (and got most of things back together again in working condition! ;))

    Would anybody advise against me getting and installing an ML-60 for a total price of £27.50?
  4. nimbus

    nimbus Well-Known Member

    I tend to agree this is not really worth the bother. Presumably the lens can be focused using the green focus confirm that will operate with an AF lens, it will be a bit slower than a split image, but many DSLRs have poorer viewfinders in brightness terms that older film SLRs. Really fast focusing will only be achieved with an AF lens, I would be wary of taking the camera apart to change the screen.
  5. spinno

    spinno Well-Known Member

    Can you source a suitable screen?
  6. Chester AP

    Chester AP Well-Known Member

    I have a K-5, which was the top of the range model when released, and looked carefully in the user guide to see if the focus screen can be changed as it could on their film SLRs. There is no entry about about this.

    But the ever-useful PentaxForums website has something about it:


    This website is also very useful for information about old lenses if you are buying secondhand.
  7. nimbus

    nimbus Well-Known Member

    A further point, spilt-image focusing screens tend to work better with relatively fast lenses, if you lens is f5.6, which for an old 300mm is quite likely, you may find such a screen is not really satisfactory, they tend to black up on one side of the split.
  8. CPRobertson

    CPRobertson Active Member

    Yup! That lens is a 4.5-5.6 lens - another mark against a split prism focusing screen!

    That's what I've been doing so far. My other manual lens (Miranda DA 28-70mm F3.5-4.8) works well with the focus confirm - especially when paired with the Catch-in Focus on the camera (hold the shutter release down and it fires when in-focus :D

    For some reason, the fully manual lens (the barest K-mount you can get: not a single contact on there) doesn't allow the catch-in focus to operate (it just takes a photo) - not sure what's up with that, but I can work with it in full manual! It's currently my longest focal point lens, but it's only a 300mm lens: and I have an full AF 50-200mm lens in my kit anyway - so I can manage without it! I did buy it on a whim after all!

    The focus-confirm can be a bit slow at times - but I'm getting better at eyeballing it - practice-practice-practice!

    Changing the focus screen on this camera should be fairly simple - had a look inside it yesterday and it's just a case of squeezing the retaining clip and the focus screen pops out - grab it by the handling tab (with supplied plastic tweezers) and it just lifts out: replacement is the same but in reverse.

    Katzeyes (used to make aftermarket split prism focusing screens) have a step-by-step guide for my particular camera family (these cameras all use the same focus screen mount and other brands of cameras have focus screens that can fit in it too - sometimes they require shimming as they are a different thickness, but they still fit in the mount! I love interoperability like that!)

    No Pentax OEM sellers of split prism lenses - but there are plenty of other genuine pentax (and other brands) of focus screen available.

    I'm personally interested in the ML-60 screen: I've purchased one for £25 (+£2.50 P&P) from Bristol Cameras - no word on if it's a genuine part, but I don't see why it wouldn't be since the genuine parts are still available! If it's not genuine I'll send it back and try again elsewhere.

    I think the split prism would be useful if I only had manual lenses - but as my manual lenses are "just for a bit of fun" and I have three perfectly good AF lenses (F1.8 50mm prime, 18-55mm and a 50-200mm tele) it's just not worth the

    I do however feel the ML-60 will be worth it! I keep finding myself looking through the viewfinder and saying "dang, wish I had some gridlines!" - yes I know you can just eyeball it/picture it in your head (that's what I've been doing up until now, after all!) - and the default focus screen AF-grid does pretty much line up with the rule-of-thirds grid - but it'd be nice just to drop things onto the intersection - for the sake of what should be a 2-minute job to install it, well worth it in my opinion (note; other people may not find it useful! This is solely for me - I cannot speak for any other photographer!)

    ANYWAY! Quick question - while browsing the available genuine pentax focus screens, I was rather curious about the simple graduated crosshair screens like the MI-60 - I was just curious - what is the purpose of such a crosshair?
    Can't say I've came across any rule-of-thumbs for composition that directly involve it! Rule of thirds, golden ratio, diagonals, etc, sure! But never graduated crosshairs! Am I just a noob/greenhorn or is it some niche composition rule that I've never came across - or just a convenience feature for the existing rule of thirds/golden ratio?
  9. Roger Hicks

    Roger Hicks Well-Known Member

    I don't think it's for composition: more for scaling and centring.


  10. CPRobertson

    CPRobertson Active Member

    Huh, is that it? Fair enough! I thought the larger graduations might correspond 1/4 gridlines - looking back over it they don't quite line up though!
  11. Benchista

    Benchista Which Tyler

    Crosshair screens were primarily for macro work, but also were useful for precise focus with long lenses (and fairly static subjects!). They allow precision focus via a parallax system, and also an assessment of image size. I keep meaning to try one on some camera or other...

    I always thought I liked split image screens, then found that I actually preferred microprisms on their own.

    I do like gridded screens, I find them very useful to keep horizons level and as an instant reminder for composition.
  12. CPRobertson

    CPRobertson Active Member

    It's a pity it's not easier to change out the focus screens (and it's a pity they aren't cheaper! - but hey, 'dem's the breaks!) - it would be great fun to experiment more with (all sorts of focus screens I mean - from split-image to various different grids and reticles).

    I'm actually surprised I've never seen a customisable overlay for the live screen views and electronic viewfinders; it wouldn't even be terribly difficult to do programming-wise!

    Now I'm a bit confused - what do you mean when you say "microprisms on their own"? Are you meaning a focus screen with no reticle markings and just a split prism, or is there another split prism I've never seen before!?

    My bridge camera (Fujifilm HS-10) had a grid overlay on it's electronic viewfinder - I didn't turn it off very often at all! I've found that since getting the DLSR which only has the AF brackets on it that I've returned a little to my old habit of centering my subject - I mean, I can train myself out of it - but I like the convenience of having the grid overlay! As you said, instant reminder - and now that you mention it, it is useful for lining up the horizon (and vertical lines too) - I wasn't actually conscious I was doing that - it just sort of happened!

    I'll update you all once the focus screen arrives - might as well do a miniblog of the whole process of changing the screen over so folk who have never done it before can get an idea of what's involved (surprisingly little, from my reading! :O)
  13. PeteRob

    PeteRob Well-Known Member

    It was usual to have a compound focussing screen - plain around the outside. A split prism in the centre and around it an annular micro prism that would scintillate if not in focus. I always found this easier than the split prism which would often just turn black.
  14. CPRobertson

    CPRobertson Active Member

    Ah! That sounds pretty useful actually - one day I'm going to buy an SLR and do some "manual" photography - though to be fair, I do have plans to experiment and put an electronic sensor in one as well... I'm thinking a full-frame sensor tied to an FPGA with a battery pack will be able to fit neatly in the space where the film used to go: and of course, being a module, it can be added and removed without damaging the camera itself. FPGAs are not my strong point though... so that's definitely a project for another day/month/year ;)

    The local antique shop has a table and a box full of old cameras - I'll need to drop by at some point - there might be some bargains mixed up in there - maybe even some rare kit. He had a camera obscura and a couple of large format cameras as well - wonder how much he wanted for them...! :p

    Anyhoo - thanks for the info :p
  15. Benchista

    Benchista Which Tyler

    Yes indeed. But some screens were just split image, or just microprism, and as you say, I always found microrpisms easier especially with slightly slower lenses.
  16. PeteRob

    PeteRob Well-Known Member

    If it could be done it would have been! There are digital backs for some medium format cameras but I'd think even 10 year old ones would be still a bit on the pricy side. For an up-to-date one think £25k. Camera extra.
  17. Done_rundleCams

    Done_rundleCams AP Forum Ambassador to Canada

    Hi CPR,

    I have a K-50 -- not my first DSLR, but, my latest of several Pentax DSLR's ;) and I have owned a PhotoSniper 300/4.5 (thread mount Russian lens) for, at least, 12-15 years and have used it over the years with most, if not all, of my Pentax DSLR's and film cameras :).

    To your query, I have not changed any focussing screens on my cameras when using any older manual focus tele's :). Here are some example of using
    my K-50 and K-r with the aforementioned PhotoSniper lens ...

    I was, also, gifted a Takumar 400/5.6 (thread mount) lens last summer which I have used with my K-50, but, the photos are on a flash drive which
    is at film processing lab so, if necessary, I can provide some of those images :). BTW, the image of the moon shows both the full-image and the cropped
    image just in case you were wondering ;)

    Jan14-18-AP-Sun-IMGP5121 copy.jpg Jan14-18-AP-Sun-IMGP5120 copy.jpg Jan14-18-AP-Sun-IMGP5113 copy.jpg Jan14-18-AP-Sun-IMGP5110 copy.jpg Jan30-18-AP-Tues-JRSP4213 copy2.jpg Jan30-18-AP-Tues-JRSP4213 copy.jpg

    As for the cost of changing the screen, wow, that seems pretty reasonable and from the Pentax Forums, here is the link
    to K-50's focussing screens available from the Taiwanese supplier:


    Cheers and, regardless of focussing screens, continued good shooting :D

    CPRobertson likes this.
  18. CPRobertson

    CPRobertson Active Member

    @Done_rundleCams - Thanks for the pics!

    I'm starting to get a little more used to working the manual - but, particularly with my larger 300mm lens it's a bit touchy trying to get it pin sharp.

    I can't seem to get the catch-in focus to work with the 300mm lens - are you able to get that working with your screw-in lenses? I assumed it was because my 300mm lens was entirely manual (no pins to give aperture info) - not sure if I'm doing something wrong since catch-in focus works with my small manual lens but allows me to take pictures with no lens (or the 300mm lens) attached and out of focus!? Might need to query the pentax forums about that one!


    Back on topic!

    Got the ML-50 focusing screen in today - fitted in about a minute... got dust, refitted in about two minutes... repeated that process five times until I was happy about not having dust on it o_O

    BUT now it's working great - can't wait to take it out and give it a burl! It's less obtrusive than I feared it might be - and had I given it a blow before installing it, it would have been a two-minute job (instead of ::gasp:: a ten-minute job!) - so one doesn't have to fear changing out their focusing screens in future (though, as mentioned above, the split-prism and multi-prism focus screens can interfere with AE metering! Just be aware of the downsides of adding manual focusing screens in!)
    Done_rundleCams likes this.
  19. PeteRob

    PeteRob Well-Known Member

    The lens is probably not fast enough, especially if you are using it stopped down. AF systems, which, like metering, operate at full aperture, perform better the wider the aperture. So a 300 mm F2.8 will generally autofocus faster * than a 300 F4 than a 300 F5.6. Early cameras used to give up at F8 and even top of the range would AF only with the centre point.

    *there are other factors too - the AF motors are beefed up.
    Done_rundleCams likes this.
  20. Done_rundleCams

    Done_rundleCams AP Forum Ambassador to Canada

    Looking forward to seeing some pics with your bigboy lens, CPR :)



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