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12-31-2016, 08:14 AM   #1
alain Gillot
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focusing screen

on a pentax istD S [ 6.1 MP ] LIKE NEW , the focusing screen sucks , i use this camera with T mount tele lenses [ birds ] it work great in automatic function , but focusing is difficult due to the poor quality on the screen . can this be replace with a smooth one .the existing one is made with circular grooves . a 800mm lens f11 is toucy on the focusing .thank you .

12-31-2016, 09:04 AM   #2
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Hello Alain.
There is quite a lot of discussion re focusing aids and screens on the forum - see reviews- accessories and use the search. I use VF magnifiers: a Tenpa 1.36x and a recently acquired pentax teleview-M which is 2x. I have also previously tried a Vf screen from a derelict ME super with a split prism. All these can be beneficial. However when push comes to shove, using the magnified liveview function on those cameras which have it tends to be the best resort when the focus gets indeterminate eg with slow TP's. In fact focus at f11 800mm is likely to be really difficult with any optical VF set up. I find mirrorless cameras with a good hi def evf + a strong magnification do better in those circumstances.
12-31-2016, 02:09 PM   #3
MJL
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I owned an istD S for a long time and I don't remember the focusing screen is user replaceable. The AF sytem on that camera simply cannot cope with any dim light (e.g. dusk to dawn outdoor) situation. It was extremly hard for me to manually focus any slow (<f/6.3) long telephoto lens (>500mm) even with Katzeye screen in a K-5.
12-31-2016, 04:16 PM   #4
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QuoteOriginally posted by MJL Quote
I don't remember the focusing screen is user replaceable
According to the PF reviews on this camera, the focusing screen is exchangeable.

Listed under Viewfinder/LCD screen items.

01-01-2017, 03:02 PM   #5
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QuoteOriginally posted by alain Gillot Quote
on a pentax istD S [ 6.1 MP ] LIKE NEW , the focusing screen sucks , i use this camera with T mount tele lenses [ birds ] it work great in automatic function , but focusing is difficult due to the poor quality on the screen . can this be replace with a smooth one .the existing one is made with circular grooves . a 800mm lens f11 is toucy on the focusing .thank you .
The circular grooves you refer to are the ridges of the screen's Fresnel lens. They serve to improve screen brightness and are not an indication of poor quality or design. Almost all modern screens use some form of Fresnel lens. The Fresnel "lines" are generally not visible when using faster lenses typical of general shooting but become very obvious at narrower apertures. Replacement screens do exist that do not have a Fresnel, but those will be quite dim with your lens. Screens are available that have split-image and microprism focus aides, but neither will work well at apertures narrower than about f/5.6-f/8. I would normally suggest using the focus confirmation feature of your camera, but it too is essentially inoperative at apertures narrower than about f/8.


Steve

Last edited by stevebrot; 01-01-2017 at 03:13 PM.
01-01-2017, 11:52 PM   #6
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QuoteOriginally posted by Sliver-Surfer Quote
iF you are handy I have a video where I make a screen out of a Canon EE-s for my k5 because pentax doesn't have a suitable screen for fast manual lenses. Just scan your original screen to use as a template or measure it with a digital caliper
Focus Screen EE s to Pentax K5 or whatever part 1 - YouTube
Good idea, except that the OP is wanting to use a VERY slow (f/11) lens. The S-type Canon screen is impossibly dark at those apertures. I believe that the Canon literature specifies lenses in the range f/1.8 to f/2.8 for Super Precision Matte (S-type) screens.


Steve

Last edited by stevebrot; 01-01-2017 at 11:59 PM.
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