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Forum: Pentax K-3 11-02-2016, 02:09 PM  
K-3 needs +10 AF-Adjust for DA35/2.4 ???
Posted By m42man
Replies: 14
Views: 842
Thanks for the reassurance folks. And it's nice to know that I'll probably be able to fine-tune (if necessary) the popular third-party lenses too. Isn't phase-detect AF a black art though!

I am aware of focus-shift, but I must say, I'm assuming it'll usually be quite small. And as for decentred lens elements, most of my (very-consumer grade) zooms have this to some degree or other (I've even got a vintage Cosinon nifty-fifty which seems to suffer from it!).
Forum: Pentax K-3 11-02-2016, 01:12 PM  
K-3 needs +10 AF-Adjust for DA35/2.4 ???
Posted By m42man
Replies: 14
Views: 842
Thanks for the replies, guys. Maybe it's not too uncommon to need such a large AF adjustment. I wonder if the K3 is less tolerant of lens variations than, say the K-50 etc. etc.?

Yes, I must say, after noticing the somewhat OOF centre with the 18-55, I was thinking about AF accuracy. At least the AF error was in the right direction! (It sharpened towards the edges at the expense of the centre.)

Regarding test setup, this was nothing special - about 15 feet and f2.8 for AF setup/tests with a small target, and 220 feet and f5.6 for general across-frame sharpness evaluation. Nothing too scientific at this stage I'm afraid.

Assuming this is fairly normal behaviour, then I'm not really concerned, but am I right in assuming you can't assign AF adjustments to third-party lenses on an individual basis?
Forum: Pentax K-3 11-02-2016, 12:23 PM  
K-3 needs +10 AF-Adjust for DA35/2.4 ???
Posted By m42man
Replies: 14
Views: 842
Hi,

I decided to buy a used K-3 after my K-50 got the dreaded lurgy.

Testing with a DA 18-55, I was intrigued to find that, at the wider zoom settings, sharpness increased somewhat as you moved away from the centre of the frame (several apertures). Focusing problem?

So, I thought I'd try my DA 35/2.4, on a distant subject. Wall-to wall blur (at f5.6)! Alarmed, I tried Live View (and manual focus), and all was OK. I then experimented with AF microadjust, and found that sharpness was achieved by setting + 8, 9 or 10. Taking repeated shots, the focus mechanism seemed to remain in a set position until I hit +8, when it shifted audibly - and I achieved sharpness.

This doesn't bode well for third-party lenses, or zoom lenses in general, I suppose. (Though I did briefly try a couple of known-quantity zoom lenses, and all seemed pretty much OK).

Is this normal behaviour (I've never had this kind of problem before)? I can post images, but I can say that the blur before microadjusting was gross, when viewed at 100%.
Forum: Pentax SLR Lens Discussion 10-27-2016, 12:05 AM  
K-series vs M-series image quality-wise?
Posted By m42man
Replies: 20
Views: 1,496
I don't think you can generalise. Some M lenses are optically the same (in terms of elements and groups), so you'd expect similar performance (the M's are more modern, so may have slight improvements, but against that they're smaller and slightly more "plasticky" - though still beautifully made).

Some M lenses either have no K counterpart, or have a completely different optical formula. An example of the latter would be the 135/3.5, where the K has 4 elements in 4 groups (like preceding Takumars - the later ones, that is), the M has 5 elements in 5 groups. The reason would seem to be that the M was made much smaller - though IQ may possibly have suffered slightly in the process.
Forum: Pentax K-30 & K-50 10-21-2016, 10:40 PM  
Pulled out my K-30 today for the first time in about a year... NO APERTURE CONTROL?!
Posted By m42man
Replies: 42
Views: 3,542
Mine did exactly the same after one tenth the number of shutter actuations. It seems that the thing to avoid is to leave the camera unused for longish periods. Use it daily and I'll bet the problem never happens.

You don't have to restrict use to manual-focus lenses (someone mentioned M and K). There are plenty of (legacy and current) F and FA autofocus lenses out there - the important thing is that you need a lens with an APERTURE RING, and these do indeed have aperture rings. (There's also a fair number of third-party autofocus lenses with aperture rings.) You then use the Green Button for stop-down metering in M mode.

Trouble is, you won't find a decent "legacy" wide-angle lens. My suggestion would be to butcher your kit lens so that it limits stop-down to a reasonable aperture (wide-open would be easiest to implement). The 18-55 is pretty good at the 18mm end (though edges benefit from a touch of stopping-down). I have yet to implement such a scheme myself though...
Forum: Pentax SLR Lens Discussion 10-12-2016, 12:11 AM  
Which focal lenght to enter?
Posted By m42man
Replies: 6
Views: 665
I have to do this from time to time (don't know why):

"If you want a compromise focal length, use the following:

2*min*max/(min+max)

This will equalise the amount of shake reduction at both ends of the zoom range. So, for a 35-105, set 50mm for the closest approximation.

Best SR results are obviously when you set the focal length to the value which you input to the camera. But don't make the mistake of inputting, say, 105mm and then forgetting and operating at the 35mm end. Because you'll end up magnifying the shake-induced blur. The other way round is fine though (i.e. telling the camera it's a 35 and operating at 105mm) - it's just that you won't get optimum shake reduction."
Forum: Pentax K-30 & K-50 10-12-2016, 12:03 AM  
Manual focus zoom lens Focal length setting
Posted By m42man
Replies: 11
Views: 2,873
If you want a compromise focal length, use the following:

2*min*max/(min+max)

This will equalise the amount of shake reduction at both ends of the zoom range. So, for an 80-200, set 120mm for the closest approximation.

Best SR results are obviously when you set the focal length to the value which you input to the camera. But don't make the mistake of inputting, say, 200mm and then forgetting and operating at the 80mm end. Because you'll end up magnifying the shake-induced blur. The other way round is fine though (i.e. telling the camera it's a 75 or 80 and operating at 200mm) - it's just that you won't get optimum shake reduction.
Forum: Pentax K-30 & K-50 10-11-2016, 11:52 PM  
Survey with shutter count and aperture block or shutter failure.
Posted By m42man
Replies: 256
Views: 27,340
Very much my experience. Mine has only a few hundred actuations, made mostly a couple of years ago, then a gap of about a year. Aperture control found to be kaput (all shots stopped down to minimum aperture).

I think the conclusion is, if you want to keep the camera working as it should, use it regularly.
Forum: Pentax SLR Lens Discussion 09-18-2016, 11:54 AM  
Top 5 K-1 Lenses (full frame only) at the Flea Mariet
Posted By m42man
Replies: 48
Views: 3,331
Don't be silly, you've just spent 1800 on a K1, get a seriously decent walk-around autofocus zoom lens called the Pentax HD PENTAX-D FA 28-105mm F3.5-5.6 ED DC WR for 550. Or less, if it's part of the deal.
Forum: Pentax K-30 & K-50 08-17-2016, 02:27 AM  
Split prism focusing screens?
Posted By m42man
Replies: 35
Views: 4,885
Are you sure about the f4 bit? I'd assume the screen on my K-m would be about f4, but the screen on the K-50 is SO much better. I suppose the fact that it's a pentaprism viewfinder probably helps too though...
Forum: Pentax K-30 & K-50 08-14-2016, 12:42 PM  
Split prism focusing screens?
Posted By m42man
Replies: 35
Views: 4,885
You may have a point there - the wider lenses are a pain to focus manually. Whether doing it by eye, or by using the green hexagon, the wider lenses are difficult. It may well be that a split-prism is the way to go in these situations (or else you have to use stopped-down hyperfocal - or other - techniques).
Forum: Pentax K-30 & K-50 08-14-2016, 12:21 PM  
Split prism focusing screens?
Posted By m42man
Replies: 35
Views: 4,885
Split prisms are a waste of time, IMHO. They're not accurate enough. The standard K-50 screen is really good at manual focusing. Why would you want to go to the bother (and expense) of replacing it with something that needs an awful lot of setting up (re-shimming etc.)?
Forum: Pentax K-30 & K-50 08-14-2016, 12:16 PM  
Survey with shutter count and aperture block or shutter failure.
Posted By m42man
Replies: 256
Views: 27,340
Plus the viewfinder/focusing-screen of the K-30/K-50 is particularly good, making manual focus a viable option - even nowadays, with millions of pixels and pixel-peeping. Still a bit of a bummer though...
Forum: Pentax K-30 & K-50 08-13-2016, 01:24 PM  
Survey with shutter count and aperture block or shutter failure.
Posted By m42man
Replies: 256
Views: 27,340
After that experience, why are you now sure your next camera will be a Pentax? I love Pentax, but after my experience with the K-50 - similar to yours, it seems - there's no way I'd be buying another until I was satisfied they'd cured the problem. And that means OWNING UP TO IT.
Forum: Pentax K-30 & K-50 08-11-2016, 11:13 AM  
Survey with shutter count and aperture block or shutter failure.
Posted By m42man
Replies: 256
Views: 27,340
Haven't been following the story in the greatest of detail, but my K-50 has aperture failure after 2 years and very few actuations. But is this linked to future shutter failure?

If so, that is much much worse, as the camera will then be a total write-off.
Forum: Pentax K-30 & K-50 08-09-2016, 11:05 AM  
Survey with shutter count and aperture block or shutter failure.
Posted By m42man
Replies: 256
Views: 27,340
Quite so. I bought my K-50 a couple of years ago, haven't used it much, and lo and behold it's now unusable. In fact, if I'd used it a lot more, I think I'd have been luckier (judging by comments here).

Actually, with any luck, it's not going to be unusable, as it still seems to work with lenses which have an aperture ring (using M-mode and the green button). How long that situation will exist remains to be seen.

Just as well I'm a less keen photographer nowadays. Just wish I hadn't recommended it to others.

Not at all happy with Pentax.
Forum: Pentax SLR Lens Discussion 08-01-2016, 11:17 PM  
Manual focus "normal" zoom
Posted By m42man
Replies: 21
Views: 1,569
Ta!

I think that someone was me, and the formula was 2*min*max/(min+max). So you're just right with you're settings.

Just to repeat a warning for everyone: if you input more than 2x the actual focal length, you will magnify any effects of shake.
Forum: Pentax SLR Lens Discussion 08-01-2016, 11:58 AM  
Manual focus confirmation question
Posted By m42man
Replies: 17
Views: 1,554
My experience is that it is FL which determines whether or not focus confirmation works accurately. 50mm lenses, unlike other FLs, are perfectly focused when you get the green hexagon. 28mm lenses give an unusably vague indication, and longer lenses (e.g. 135mm) give a sharp confirmation, but are way "off".

You can actually use CiF with the 50mm lens: with a fairly static subject, rotate the focus ring slowly, and the camera will fire when accurate focus is reached.

I suppose it's just possible that aperture may have something to do with it, but my gut feeling is that it doesn't.
Forum: Pentax SLR Lens Discussion 08-01-2016, 11:44 AM  
Manual focus "normal" zoom
Posted By m42man
Replies: 21
Views: 1,569
Definitely a big drawback. Be careful with your FL guess though, as if you enter a value much higher than the actual value you risk amplifying your shake.

Either enter the shortest focal length - which is totally safe, and SR will be at full strength when shooting at the wide end - or you can use a simple formula. I'll definitely be accused of boring everyone if I reiterate it, but, don't worry, the answer is the same for all your lenses: 100mm.

Agree about the 75-150 though - I've had one from new and it's certainly sharp enough.

(By the way, it's been a long time - hello again everyone!)
Forum: Pentax SLR Lens Discussion 02-17-2015, 01:48 AM  
Tamron, Asahi, CZJ? Which is the best?
Posted By m42man
Replies: 21
Views: 1,843
By the way, I rather doubt the CZJ "Prakticar" lens is actually Pentax K fit - as a bayonet, it's surely going to be Praktica Bayonet (though I may be wrong). I doubt it's even East-German made (a lot of CZJ lenses were badged Japanese).

I don't think this lens should be confused with the M42 CZJ MC Sonnar 135/3.5 - which is a "proper" East-German lens, and which is optically great (probably beats just about anything), though isn't as well made as a Japanese lens (particularly an M42 Takumar).
Forum: Pentax SLR Lens Discussion 01-04-2015, 11:26 PM  
Ring numbers meaning of Pentax-A 50mm lens
Posted By m42man
Replies: 17
Views: 2,063
Be aware that the dof rings on vintage lenses assume a very small print size (I seem to remember 7"x5"), and a "normal" sort of viewing distance. Usually, nowadays, we'll be thinking about much bigger displayed image size. This will have a large effect on dof, since the out-of-focus blur will appear much larger (and therefore the plane of "in-focus" will shrink).

So, the dof scale on the lens will be far too optimistic. In practice, especially on an APS-c camera, this means using a VERY conservative aperture value when using the scale (e.g. 4 stops wider than actual aperture). For more info, look here:

A Flexible Depth of Field Calculator

And be sure to click on "show advanced".
Forum: Pentax SLR Lens Discussion 01-02-2015, 11:43 PM  
SMC Pentax A 50: 1.4 vs 1.7
Posted By m42man
Replies: 11
Views: 1,504
Here's what you need:

Nifty 50 Shootout : ERPhotoReview

You'll see that the 50/1.4 outperforms just abut everything, as far as resolution is concerned. Also, I do recall that it has a very good reputation for soft bokeh.
Forum: Pentax SLR Lens Discussion 12-31-2014, 12:14 AM  
M Prime Lenses on a K-3
Posted By m42man
Replies: 10
Views: 1,357
The (A) 50/1.4 does very well in this shootout:

Nifty 50 Shootout : ERPhotoReview

Not sharp wide open, but stop it down and it's pretty amazing. Also, it has a reputation for nice soft bokeh (the nicest of all the Pentax/Takumar 50/55's, second only to the 50/1.2 - which of course is also the sharpest, rarest and most valuable).
Forum: Pentax SLR Lens Discussion 12-28-2014, 12:33 PM  
Pentax-A f4 or Vivitar Series 1 70-210 2.8-4
Posted By m42man
Replies: 27
Views: 2,510
I didn't read about it, I derived it. Done to death? Only because some people seem to suspend analytical thinking, in favour of hearsay. I suspect you did the following (using a 70-210 as an example): you tried a few shots at 210mm actual, with a 70mm set value. Well, you'll get a 30% improvement in shake-induced blur, but how would you notice (unless you'd taken 100 shots)? Then you'll have tried a set value of 210mm with a set value of 70mm. So you get 2x shake magnification (which is exactly what I'm warning against), and you conclude that it's all useless.

It's actually quite easy to explain. Take a lens of focal length 100mm. Shake causes image to move by 1mm across the sensor plane:

SR off: sensor sees 1mm movement: 1mm of blur.
SR on, FL value set to 50mm: sensor moves 0.5mm: a net 0.5mm of blur
SR on: FL value set to 100mm: sensor moves 1.0mm: a net zero blur
SR on, FL value set to 150mm: sensor moves 1.5mm: a net 0.5mm of blur
SR on, FL value set to 200mm: sensor moves 2.0mm: a net 1.0mm of blur (same as SR-off)
SR on, FL value set to 300mm: sensor moves 3.0mm: a net 2.0mm of blur (2x blur of SR-off)

I have posted several times on this very issue, but I'm not sure I can be bothered to exhume them - and you're only going to embarrass yourself.

Try the formula. You might like it. But don't expect miracles: SR is extremely effective when FL is matched. You'll get only a relatively small improvement at the extremes of the zoom lens - but still worthwhile, and a lot better than turning SR off. But of course, you've given up an Pentax cameras anyway.

A word to the OP: why are you considering a vintage 70-210? They're mount-threateningly heavy, and expensive too (because the Vivitars are cult items). What's wrong with a Pentax M75-150 - much smaller/lighter, easily as sharp, much cheaper and you'll suffer less from a focal length mismatch.
Forum: Pentax SLR Lens Discussion 12-28-2014, 02:04 AM  
Pentax-A f4 or Vivitar Series 1 70-210 2.8-4
Posted By m42man
Replies: 27
Views: 2,510
Sorry, you've been misinformed. Provided you don't set your value greater than 2x the actual focal length, you're always better with SR switched on.
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