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Forum: Pentax DSLR Discussion 1 Day Ago  
K-50 pictures are black when taken through viewfinder, but not in live view - help
Posted By m42man
Replies: 51
Views: 4,614
Yes - that's why Manual mode with the green button for stop-down metering works (i.e. the official method).

But try using Av mode with a healthy K-50 (or any other Pentax DSLR), with a K-mount lens, using the aperture ring, and you'll find that the lens doesn't stop down. All shots are wide-open.

The peculiarity is that a K-50 with aperture block failure behaves the way that it does.
Forum: Pentax DSLR Discussion 2 Days Ago  
K-50 pictures are black when taken through viewfinder, but not in live view - help
Posted By m42man
Replies: 51
Views: 4,614
What is happening is that the camera meters with lens wide-open, just like Av mode with a normal camera. The difference is that, in normal operation, the camera will know the aperture that will be used for taking the shot, so can calculate the correct shutter speed for taking the shot. When you take a shot with an afflicted camera, you're using the aperture ring - only you know what the target aperture is. So, you calculate the difference between wide-open and stopped down target aperture - and, in general, you can't do that accurately with a variable-aperture zoom (and in any case, you'd be having to change Compensation as you change zoom setting - inconvenient at best).
Forum: Pentax DSLR Discussion 3 Days Ago  
K-50 pictures are black when taken through viewfinder, but not in live view - help
Posted By m42man
Replies: 51
Views: 4,614
Well, you have 5 stops to play with, so up to f11 for an f2 lens, f16 for an f2.8 lens, f22 for an f4 lens, etc. I think the biggest drawback is when you are using a variable-aperture zoom...
Forum: Pentax DSLR Discussion 6 Days Ago  
K-50 pictures are black when taken through viewfinder, but not in live view - help
Posted By m42man
Replies: 51
Views: 4,614
A strange quirk seems to be that, with an afflicted K-50, you can set Av mode, with Aperture Ring Enabled, and the camera will stop the lens down to the aperture set by the aperture-ring when the shutter is fired. This is not the behaviour you get with a healthy camera.

This is very handy, but as far as metering is concerned, the camera has no knowledge of the set aperture, so assumes the same aperture as when metering was done - i.e., wide-open. So, in order to get the correct exposure, you need to use exposure compensation. For example, if you're using an f2 lens set to f4, you need to set +2EV compensation. Works a treat, and exposure is accurate, as this apes normal operation (unlike stopped-down metering with the green button).
Forum: Pentax SLR Lens Discussion 10-10-2020, 04:29 AM  
Recommended Filter
Posted By m42man
Replies: 31
Views: 1,255
I think a protection filter gives you peace of mind. Plus, I defy anyone to be able to pixel-peep any difference between an excellent lens with and without an excellent filter - or a DA50-200 with and without a good filter.

Exception would be night-time shots with bright lights, when flare may well be a problem. Just remove the filter.
Forum: Pentax SLR Lens Discussion 10-04-2020, 05:49 AM  
Used Lenses Advice.
Posted By m42man
Replies: 14
Views: 802
Do make use of the lens user reviews on this site, also this:

Check Lens Compatibility with Your Pentax Camera
Forum: Pentax SLR Lens Discussion 09-29-2020, 10:44 PM  
Recommended Filter
Posted By m42man
Replies: 31
Views: 1,255
I think this is overkill - a lesser (multicoated) Hoya or Marumi would be appropriate for the DA50-200.

Remember to choose the vendor with care.
Forum: Pentax SLR Lens Discussion 09-28-2020, 11:19 PM  
Recommended Filter
Posted By m42man
Replies: 31
Views: 1,255
I'd certainly recommend a decent filter for protection. The trick with that lens is to avoid spending a fortune, whilst still getting something which won't visibly degrade the image.

Here's a fairly old, but still relevant, filter test:

UV filters test - Introduction - LensTip.com

Note especially the flare performance.

I can personally recommend Hoya and Marumi. B+W are very well thought of, but too expensive. By the way, do note that filters are a prime target for counterfeiters, so buy from a reputable dealer!
Forum: Pentax SLR Lens Discussion 09-23-2020, 02:25 AM  
Lens filters
Posted By m42man
Replies: 19
Views: 903
There are good filters and bad filters. I remember a thread on this forum from a few years ago, in which a UV filter was shown to significantly degrade sharpness. However, this was a suspect brand anyway. For a comparison of much more reputable brands, look here:

UV filters test - Introduction - LensTip.com

Amongst other aspects, note the difference between levels of coating, as regards flare. Also note that filters are a major attraction for counterfeiters - be very careful who you buy from...

For an idea of how much degradation can occur when you stack a load of random filters:

Lens Rentals | Blog
Forum: Pentax K-30 & K-50 09-16-2020, 01:21 AM  
Market for aperture issue K-50?
Posted By m42man
Replies: 19
Views: 1,002
That's interesting. I think I've had similar feedback in the past. It's my preferred method, unless using a variable-aperture zoom.

As to Live View, I can't remember trying it, but, yes, that makes sense.

Thanks for the feedback. :)
Forum: Pentax K-30 & K-50 09-12-2020, 03:47 AM  
Market for aperture issue K-50?
Posted By m42man
Replies: 19
Views: 1,002
As I've mentioned before, my afflicted K-50 allows use of Av mode with K-mount lenses which have aperture rings. It shouldn't do, but it does. Would be nice to know if others find similar. You have to use Ev compensation to compensate for the fact that the camera assumes the lens is always set wide open. So, for an f2 lens set to f4, use +2Ev compensation.

This ends up with much more accurate exposures (because you are metering wide-open, as opposed to stopped-down). Plus, you can shoot away just as you would with a healthy camera. Not quite so convenient if you want to keep changing aperture though - or if you're using a variable-aperture zoom (most of the autofocus ones are).
Forum: Pentax K-30 & K-50 08-06-2020, 12:34 PM  
trying to help a friend diagnose his K-50 problem
Posted By m42man
Replies: 12
Views: 868
If you decide to fix yourself (with a white solenoid, one hopes) be careful of very high voltages (used for the flash). They are potentially lethal.

Alternatively, the camera could be reserved for lenses with an aperture ring. You need to set the "Enable Aperture ring" feature to On, set the camera to Manual exposure, and use the green button to meter the scene before you take the photo (more details are available on these forums).

Alternatively, with aperture ring enabled, you might try Av mode, set your preferred aperture, and use Exposure Compensation to get correct exposure. This seems to work well with cameras afflicted by the solenoid failure (for some reason) - and give better results than using the above (and usually prescribed) Manual mode and green-button method.

What you need to do is compare your set aperture to the aperture of the lens when wide open. Then set Exposure Compensation to match - for example, with an f2 lens, and your set aperture at f4, you would set the Exposure Compensation to +2EV. Then snap away as you want.
Forum: Pentax SLR Lens Discussion 07-26-2020, 12:05 PM  
135 3.5 Variants
Posted By m42man
Replies: 9
Views: 797
I have a version 1 (5 elements/4 groups) and a later Super-Multi-Coated one (4 elements). The former is soft (could be a bad example, for whatever reason). The S-M-C one is very sharp, even wide-open. Both are beautifully made and a joy to focus (even despite my having non-ideal vision).
Forum: Pentax SLR Lens Discussion 07-06-2020, 11:51 PM  
Portrait Lens Length
Posted By m42man
Replies: 39
Views: 2,407
Here's a good guide to portraiture focal length (on a full-frame camera):

Untitled Document

I think this demonstrates why 70mm provides the best perspective for head-and-shoulders portraits (if the subject doesn't mind the lack of social distancing!).
Forum: Pentax SLR Lens Discussion 07-03-2020, 12:29 PM  
Setting the aperture on the 135mm f/2.5 bayonet
Posted By m42man
Replies: 12
Views: 740
I've recently revised my opinion of this lens. It's pretty sharp (stop it down just a bit), though slightly low on contrast, and has a cool colour cast Like most Pentax lenses from that era. Like it a lot (I owned it from new).
Forum: Pentax SLR Lens Discussion 06-28-2020, 11:36 AM  
Portrait Lens Length
Posted By m42man
Replies: 39
Views: 2,407
It's all down to perspective. You need to be 3 or 4 feet away from the subject for the best rendition - that's regardless of format and regardless of how much of the subject you want to include in the shot. Of course, if you end up with a lens with too wide an angle of view, there may be lens distortion issues (nothing to do with perspective "distortion"), but for head/shoulders down to half-body shots you're OK.
Forum: Pentax SLR Lens Discussion 04-26-2020, 11:47 PM  
catch in focus with laowa 15mm
Posted By m42man
Replies: 27
Views: 946
15mm is pretty wide-angle, even on aps-c. My experience with CiF is that it only works (and works well) consistently with lenses of approximately 50mm and up.

I find that even a 28mm lens will trigger focus over a wide range of actual focus distance. So it's no surprise to me to hear of the sort of difficulties you're having with a 15mm lens.

Try CiF with a much longer lens - 50mm, for example. This should at least prove that you're following the correct procedure.
Forum: Pentax SLR Lens Discussion 10-10-2019, 04:04 AM  
Why persist in using legacy manual lenses
Posted By m42man
Replies: 156
Views: 9,582
I'd be a bit careful with distance and DOF markings on a vintage lens. Distance marks are approximate only, and DOF markings are intended for full-frame film cameras with much lower resolution than modern DSLRs. Plus, when mounted on a crop-frame camera, there is less DOF anyway.

So, in general, be very conservative when using lens markings.
Forum: Pentax K-30 & K-50 09-26-2019, 03:01 AM  
K-50, Aperture Ring and Av Mode
Posted By m42man
Replies: 31
Views: 2,828
Still unclear to me.

Does your K-30 with broken solenoid stop down a lens with aperture set by its ring in Av mode a) with firmware 1.00 and b) with firmware 1.06?
Forum: Pentax K-30 & K-50 09-25-2019, 10:57 AM  
K-50, Aperture Ring and Av Mode
Posted By m42man
Replies: 31
Views: 2,828
Ah! So - just to clarify - a firmware update to 1.06 returns the K30/K50 (K500?) to business as usual?

Very interesting (I can imagine there will be some users with that firmware who will want to return it to an earlier version).

Thanks for the info!
Forum: Pentax SLR Lens Discussion 09-16-2019, 10:29 PM  
Vintage Zoom Lenses and Input Focal Length
Posted By m42man
Replies: 3
Views: 674
Yep, it's over-correcting by 50%, so you'd still be getting 2x blur reduction. And, when you zoom in at 100mm, it under-corrects, but you still get get 4x reduction. Whereas, if you had input the shortest FL, at 100mm, you would get only 2x reduction.

You only really need to worry if it over-corrects by more than 100% (in other words, more than 2x the input focal length), in which case you end up with more blur than you would have had with SR switched off.
Forum: Pentax SLR Lens Discussion 09-16-2019, 06:54 AM  
Vintage Zoom Lenses and Input Focal Length
Posted By m42man
Replies: 3
Views: 674
Just a comparison of the two methods:

For a lens with a zoom ratio of 2x, method 1 yields 3x blur reduction at each end, method 2 yields 2x blur reduction at the short end and 4x reduction at the long end.

For a lens with a zoom ratio of 3x, method 1 yields 2x blur reduction at each end, method 2 yields zero blur reduction at the short end and 3x reduction at the long end.

Somewhere between the two methods may be best compromise - though obviously it's best if you can match FL for every shot.
Forum: Pentax SLR Lens Discussion 09-16-2019, 04:47 AM  
Vintage Zoom Lenses and Input Focal Length
Posted By m42man
Replies: 3
Views: 674
Most will be aware that you need to tell the camera the focal length of the lens you are using, if the camera hasn't actually been told the value by the lens itself (i.e. so those vintage manual focus lenses). And that this due to need for the SR mechanism to correctly counter blur caused by camera shake.

Obviously a problem for zoom lenses, unless you want to be constantly changing the value to match the focal length you choose for taking a shot.

Some may remember I came up with a formula a few years ago, for the choice of best "compromise" value - as follows:

FL = 2*min*max/(min+max) (where min and max are the extremes of the lens in question).

This was to equalise the amount of blur reduction you get at the extremes of the zoom range.

HOWEVER, since you need more blur reduction at the long end, it might be better to equalise the actual amount of blur you get for a given amount of camera shake.

So, a new formula that does this - surprisingly it comes out as (min+max)/2, i.e. the average of the focal length extremes. This works well for lenses with zoom ratios up to 3x. Above that, you would actually get blur magnification when zoomed-out. In fact, for a 3x zoom fully zoomed-out, you would end up with the SR mechanism applying twice the amount of blur, but in the opposite direction (so a net blur equal to that you get without SR).

As an example, for a 28-70 zoom (a zoom ratio of 2.5x), the first formula yields a figure of 40mm, the new one a figure of 49mm.

As always, it's as well to remind that an FL entered which is more than 2x the actual shooting FL, will result in more blur than you would get with SR turned off.
Forum: Pentax K-30 & K-50 09-10-2019, 02:30 AM  
K-50, Aperture Ring and Av Mode
Posted By m42man
Replies: 31
Views: 2,828
Well, equally, you can set an aperture (perhaps to maximise sharpness) and then shoot away without needing to remember to use the green button before each shot (assuming lighting is varying).

But why do you say the metering might not be right? Metering is carried out wide open, just like a normal camera, and the appropriate shutter speed set according to the chosen shooting aperture, just like a normal camera. Exposure compensation is effectively just the same as the camera actually knowing the (relative) aperture (whether for a vintage SLR via a non-crippled K-mount linkage, or by the user selecting an aperture using a thumbwheel).

So you'd expect the same exposure accuracy as you get for a lens in normal use.

Stop-down metering sounds like it would be immune to exposure errors due to the actual aperture being inaccurately implemented by the lens, but in my experience this seems to be outweighed by errors presumably induced by the metering system coping badly with varying apertures.

Anyway, it's nice to have the choice. I'd suggest users try both methods and compare results for themselves.
Forum: Pentax K-30 & K-50 09-08-2019, 10:30 PM  
K-50, Aperture Ring and Av Mode
Posted By m42man
Replies: 31
Views: 2,828
Ah, so that seems to confirm the "happy coincidence" model.

So, if you're unlucky enough to get aperture block failure, you get the benefit of an arguably superior option when using a legacy lens.

Sounds fair enough to me!
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