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Forum: Pentax SLR Lens Discussion 04-27-2019, 07:20 AM  
Decentered DFA*50?
Posted By Dan
Replies: 28
Views: 1,352
Yes your lens looks decentered, but it is not a severe case and so I doubt that they will consider it a defect. You cannot rely on a manufacturer's warranty to address decentering issues. If you want to avoid the problem then you need to test each lens you buy while it is still within the return window, and then return any lens that is not up to your expectations. Of course this also means that you need to restrict your purchases to sellers that have a good return policy. When I see a seller adopt a "no returns" policy I run the other way.

As for the price of the lens, it doesn't matter how much a lens costs, some copies will suffer from decentering. I used to shoot Nikon gear, and even very expensive lenses had about a 50-percent failure rate in my decentering tests (a bit worse for zooms, a bit better for primes). In my experience Pentax is no better, with the exception of the "DA limited" lenses which seem to have a lower rate of decentering. This may be due to their relatively simple design, or maybe my sample size simply isn't large enough. In any case, you need to test a lens thoroughly when you first receive it if you want to avoid unpleasant surprises down the road. It doesn't pay for manufacturers to sell only well-centered lenses. It would be very costly, and most buyers don't seem to care.

Dan
Forum: Pentax SLR Lens Discussion 04-15-2019, 05:46 AM  
Samyang 20mm f/1.8 - did I expect too much ?
Posted By Dan
Replies: 18
Views: 1,294
It looks to me like you have a good copy. As you note, the lens seems well centered. The corners look decent for f/1.8, particularly for a 20mm lens. They will look even better if you adjust for lateral chromatic aberration. This is quite easy to do when processing a raw image, and it can make a big difference with wide angle lenses. Even the f/5.6 shot shows extreme CA along the edges. The edges will improve dramatically with better processing of the raw image.

As for the "stretching" in the corners, that type of distortion is just a fact of life with a rectilinear wide angle. You can avoid it by using a fish-eye lens, but that will then introduce another type of distortion. Pick your poison.

Dan
Forum: Pentax SLR Lens Discussion 03-26-2019, 07:18 AM  
What's the highest rated lens you own according to PF?
Posted By Dan
Replies: 111
Views: 4,597
These are my highest-rated lenses:

RATING - LENS

10 - Voigtlander APO-Lanthar 125/2.5
10 - Voigtlander APO-Lanthar 180/4
9.92 - Voigtlander APO-Lanthar 90/3.5
9.89 - Pentax-F* 300/4.5

They are all significantly better than lenses that I have in the 9-9.5 range, particularly in terms of various aberrations. It seems like the rating scale is overly compressed at the high end. Or perhaps the problem is that that too much weight is given to sharpness alone. A really great lens is not just super sharp, it has minimal aberrations. Of course this is much easier to achieve with longer lenses. My most-used lenses are all wide-angle lenses that do not rate as highly. It's hard to make a wide angle lens that's a "10".

Dan
Forum: Pentax Price Watch 11-29-2018, 09:28 AM  
Rokinon lenses - 20% off on Amazon
Posted By Dan
Replies: 1
Views: 492
Good catch. Thanks! The only issue is that the discount only applies to sales by Amazon itself (as expected), Amazon is out of stock on some of these lenses (in both variants), and there is a 1-3 month wait for the lenses that they don't have in stock. I was hoping to pick up a 20mm, but no such luck. I did manage to get a 14mm for $199 net, plus tax. Not a bad deal. Hopefully I'll get a good copy--fingers crossed!
Forum: Pentax Price Watch 11-20-2018, 06:06 AM  
Pentax K-1 - $1496 + grip + freebies - lowest price to date!
Posted By Dan
Replies: 36
Views: 11,501
The deal is still available via Amazon (click on the link above). As of this morning they still have 20 units available.
Forum: Pentax Price Watch 10-29-2018, 04:00 PM  
Pentax K-1 - $1496 + grip + freebies - lowest price to date!
Posted By Dan
Replies: 36
Views: 11,501
Unless by "anytime soon" you mean 24 hours. :) The deal was off during all of 10/28, but it's back today, 10/29. Apparently the first round failed to clear all of the inventory, so Pentax re-authorized the deal. These things are difficult to predict.
Forum: Pentax Price Watch 10-27-2018, 09:34 PM  
Pentax K-1 - $1496 + grip + freebies - lowest price to date!
Posted By Dan
Replies: 36
Views: 11,501
You were right about that! The deal ended at midnight at both Adorama and B&H. It's still on at Amazon, but it's not yet midnight on the west coast.
Forum: Lens Clubs 10-18-2018, 12:48 PM  
The M Club!
Posted By Dan
Replies: 7,254
Views: 1,073,377
Very impressive job with the stitching. The image must be very impressive at full resolution. The sky and water both create some challenges for seamless stitching. What software did you use?

By the way, I see that you are in Espoo, which gives me an opportunity to use the few words of Finnish that I have learned: Suomi on kaunis maa! (Sorry if I botched that.)

Dan
Forum: Homepage & Official Pentax News 10-17-2018, 09:17 AM  
D FA* 50mm F1.4 Review Posted
Posted By Dan
Replies: 4
Views: 403
Thanks for this fair and comprehensive review. It was an interesting read. I was expecting the lens to be roughly on par with the Sigma Art, but based on this test (and other tests) the Pentax lens is clearly superior.
Forum: Non-Pentax Cameras: Canon, Nikon, etc. 09-29-2018, 08:06 AM  
Micro Four Thirds and Panasonic FF
Posted By Dan
Replies: 27
Views: 1,214
Micro Four Thirds will be around a long time. The format has a major advantage in terms of LENS size (and lens choice). There are many terrific yet TINY lenses for the format. In some of these discussions there's too much emphasis on body size. Mirrorless FF bodies may be of modest size, but it's a challenge to design a lens that can provide sharp corners when combining a large sensor with a short register distance. The angles are extreme. The resulting lenses are huge, eliminating most of the weight advantage of a smallish body. When dealing with a short register distance it's much easier to get sharp corners when the sensor is relatively small. There are some superb MFT lenses that are almost unbelievably tiny, even by APS-C standards. You can put together a really compact kit. It's all about the lenses!

In addition, recent improvements in sensor technology and noise handling have reduced the drawbacks to the smaller MFT sensors. To see this, look at the output from the new 20-megapixel sensors in the Panasonic G9 and GX9. The image quality is as good as (or better than) what you could get from APS-C not that long ago. Of course the newer APS-C sensors are better still, but the difference is not large enough to matter for many applications.

The MFT format will continue to serve a couple of important niches. First, some people prefer a small and lightweight system, and don't need the very best output. MFT offers the smallest overall kit with a decent sensor size. Second, some FF (and MF) shooters who do have a need for the very best output also have a MFT system because sometimes they want to travel light, and in some cases MFT output is good enough. This second group doesn't view MFT as a substitute for FF, but rather as a very useful complement. Because of these two markets, and because of the terrific lens selection, MFT isn't going away anytime soon.

Dan
Forum: Non-Pentax Cameras: Canon, Nikon, etc. 09-26-2018, 08:53 PM  
Fuji XT-3 anyone???
Posted By Dan
Replies: 31
Views: 2,587
I think that Fuji screwed the pooch on this one. After putting IBS in the X-H1 (yipee!) they decided to leave it out of the XT-3. So no, I'm not thinking of getting one. Maybe the XT-4?
Forum: Pentax News and Rumors 09-25-2018, 09:19 AM  
Ricoh GR III
Posted By Dan
Replies: 730
Views: 61,748
I'm not sure that I understand this comment. The new Panasonic series competes in a completely different market, and serves a different use case. As impressive as it is, the new Panasonic will not fit in a shirt pocket (even without a 28mm lens attached). Indeed, I would not be surprised if some people who buy one of the new FF cameras also buy (or already own) a tiny pocketable camera. The one is not a substitute for the other.

Dan
Forum: Pentax News and Rumors 09-25-2018, 09:07 AM  
Ricoh GR III
Posted By Dan
Replies: 730
Views: 61,748
This looks great to me. I was hoping for shake reduction, but wasn't sure if it was possible without making the camera larger. It turns out that they manged to add shake reduction while making the camera smaller. This also allows for dust removal. Well done, Ricoh! The thing that is great about the GR series is its TINY size, combined with an APS-C sensor, and an excellent lens. I am also a fan of the 18mm focal length ("28mm-equivalent"), since that's my most-used field of view. And now they have added SR and a modern sensor.

What competing camera has an APS-C sensor, such a small a body, shake reduction, and a "28mm-equivalent" field of view? None that I know of. The GRIII stands alone.

Very exciting!
Forum: Pentax SLR Lens Discussion 08-26-2018, 10:16 PM  
Lens flare of DA*55 Vs FA50 macro
Posted By Dan
Replies: 9
Views: 697
That's an interesting comparison. Thanks for posting.

In my experience a faster lens will be more prone to flare, ceteris paribus. The coatings are not all that much better on the 55, so I would expect the 50 macro to have better flare performance in a situation like this. If you are going to shoot scenes with bright lights at f/8 or f/11 in most cases you will be better off with a slower lens (assuming that it's a good lens, which certainly is the case with the FA macro). The DA*55, on the other hand, would have a big advantage at f/1.8-f/2.8. :-)

Sometimes it's better to have less glass between the image and the sensor.

Dan
Forum: Pentax News and Rumors 06-07-2018, 03:12 PM  
DFA*50/1.4 first review
Posted By Dan
Replies: 325
Views: 24,203
Of course the lens is sharp. But what really amazes me is the bokeh, which is outstanding. I didn't think that I would be interested in this lens, but after seeing those images I will definitely have to rethink things. It looks like it was worth the wait!
Forum: Welcomes and Introductions 05-10-2018, 11:23 AM  
why shoot with Pentax?
Posted By Dan
Replies: 33
Views: 1,560
That's an outstanding summary. You have stated succinctly the many benefits of the Pentax system. You have also noted fairly the drawbacks with regard to video, autofocus, and service. For me, the advantages far outweigh the disadvantages, but it really depends on the user's priorities. Your summary should help the OP make an informed decision.

Dan
Forum: Photographic Industry and Professionals 04-01-2018, 06:18 AM  
Ricoh wont listen to us pros anymore!
Posted By Dan
Replies: 54
Views: 6,139
You got me too, even though I logged on this morning thinking that there would be some April Fools jokes on the forum. That's a testament to how well it was done. As is so often the case, the photo really sold it. My first thoughts were simply "Det var synd!" and "Lykke til!" :o

It's nice to know that you will be hanging around for a while.
Forum: Lens Sample Photo Archive 02-18-2018, 07:02 PM  
SMC Pentax 50mm F4 Macro
Posted By Dan
Replies: 5
Views: 1,630
Wow! I love the rendering of that lens. Great bokeh. It looks like I will have to get one for myself. :-) Very nice images, BTW. You have a good eye for closeups.
Forum: Pentax SLR Lens Discussion 04-04-2017, 07:21 AM  
Corner Sharpness: Tamron 17-50 @17mm
Posted By Dan
Replies: 6
Views: 774
I wrote my response before you posted your update saying that the problem was with the lower left corner. I edited my response accordingly. This does seem to be a de-centering problem with your copy, but I doubt that Tamron will fix it. Of course it doesn't hurt to try, since it is still under warranty.

It's always a good idea to test lenses for decentering when you first get them so that they can be returned as defective during the return period. It is very rare for a manufacturer to fix a decentering problem under warranty. This is a very common flaw. I've had to return about half of the lenses I've purchased due to severe decentering. The problem seems worse among zooms. I've had the best luck with the Pentax limiteds.

Dan
Forum: Pentax SLR Lens Discussion 04-04-2017, 07:09 AM  
Corner Sharpness: Tamron 17-50 @17mm
Posted By Dan
Replies: 6
Views: 774
The Tamron 17-50 suffers from extreme field curvature at 17mm. Here is a summary of the problem from the Photozone review:

"Unfortunately the lens has a less than desirable characteristic - at 17mm it suffers from very strong field curvature which can render the outer corners out-of-focus." source: Tamron AF 17-50mm f/2.8 SP XR Di II LD Aspherical [IF] (Nikon) - Review / Test Report - Analysis

I believe that this is what you are experiencing. When the center is sharp the corners are out of focus. In short, it is a design flaw, not a problem with your specific copy of the lens. There's nothing they can do to fix it, other than redesigning the lens.

Dan

Edit: Since you now say that the problem is worse in the lower left corner, the problem is probably exacerbated by de-centering. The decentering is, of course, a problem with your copy, but it's very likely that Tamron will claim that it is "within specs".
Forum: Pentax Price Watch 11-25-2016, 08:37 AM  
Black Friday SD Card Deals!
Posted By Dan
Replies: 5
Views: 1,242
It is the "Video Class" of the card. It signifies that the card can record at a minimum of 30 MB/s, which is adequate for 4K video.

I hope this helps,

Dan
Forum: Pentax DSLR Discussion 11-16-2016, 11:17 AM  
The Great JPEG Shootout! (Canon, Nikon, Sony, Fuji, iPhone, Pentax, Olympus, Panasoni
Posted By Dan
Replies: 90
Views: 8,824
In my experience, Pentax JPEGs are really quite bad. In the test they used the K-70. While I haven't tried that camera, I do have its predecessor, the K-S2. The K-S2 JPEGs are so bad that I quit shooting RAW+JPEG. I found that I could never use the JPEGs, and so they were just a waste of card space. Maybe I would have been happier with the quality if I just shot JPEG and wasn't able to compare them to the results I was getting from the RAW files.
Forum: Pentax K-1 11-03-2016, 10:50 AM  
So I broke down...
Posted By Dan
Replies: 15
Views: 1,728
Where did you get that price on the K-1? Those look like B&H product codes, but I'm seeing $1,946.95 everywhere I look, including B&H.
Forum: General Photography 10-07-2016, 02:14 PM  
Check your hue ability - TEST
Posted By Dan
Replies: 53
Views: 3,102
I scored a zero, but I cheated. I have a good monitor. :)
Forum: Pentax K-70 08-30-2016, 07:04 AM  
Red CA, a problem?
Posted By Dan
Replies: 9
Views: 879
I agree that it's very obvious. But it only affects the brushes in the upper left corner of the image. If you examine the same style brushes in the lower right part of the image the nasty fringing is gone, even though the lighting and reflections are very similar. This suggests that it is not a sensor problem, but rather a problem with lens. The lens elements are not perfectly centered. This can affect not just sharpness, but fringing as well.

Why does this not show up with the K3-II? Two possibilities come to mind. First, as others have mentioned, it could be that they used different copies of the lens. Another possibility is that the same lens was focused slightly differently in the two tests. Even very small differences in focusing can affect fringing.

As someone who has done a lot of my own lens testing, I can tell you that it is an extremely difficult thing to do. Small changes in the setup can have noticeable effects on the results. Moreover, modern sensors have such high resolution that they can reveal small flaws in lens assembly and small differences in focus.

Dan
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