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Forum: Sold Items 04-28-2020, 07:30 PM  
For Sale - Sold: Pentax HD FA* 50mm f/1.4 SDM AW Lens
Posted By JBox
Replies: 13
Views: 2,426
PM sent.
Forum: Pentax SLR Lens Discussion 03-11-2020, 03:39 PM  
Using the DFA* 50 f1.4 on the LX
Posted By JBox
Replies: 19
Views: 1,240
Thanks everyone for your comments!


For the reasons others have mentioned already, I can basically guarantee that the Z-1/Z-1p will not be able to control the electronic aperture of the DFA* 50. However, I don't know what to expect otherwise in terms of functionality with that combo. I don't see a reason why it wouldn't at least allow taking a picture, unless the Z-1/Z-1p gets some kind of unexpected info back from the lens and decides it cannot work with it. The reason why the LX is easier to understand is that it has no electrical communication with any lenses, so it is intuitive what will or will not work. Probably the only way to know the level of functionality of that combo is to directly test it. I would guess that AF will not work, you would need to put the camera in aperture-priority, and you would need to select f 1.4. The reason for this is that the Z-1/Z-1p will think it can stop the lens down, but it actually can't. Thus, if it is in any exposure mode besides manual or aperture-priority, you will likely end-up with a wildly incorrect exposure.


I didn't think to mention that. You are correct that the dark corners are from the slide frames, not vignetting.


I was forgetting about this aspect of the LX. My assumption was that, because I was getting correct exposures, the opening on the DFA* 50's mount was in the correct place to indicate wide-open. However, if it was the case that the off-the-film metering was correcting for error indicated by the lens, my assumption could be incorrect. Testing would be needed on another aperture-priority-only body that has more standard metering, such as the ME Super.


Not many tests are done with newer lenses on older bodies. There is a lot of potential there. I am also not sure that this compatibility was unintentional. They could have just as easily had the opening for the aperture indicator signal stopped-all-the-way-down as is the case with all other DFA lenses without aperture rings.
Forum: Pentax SLR Lens Discussion 03-11-2020, 10:31 AM  
Using the DFA* 50 f1.4 on the LX
Posted By JBox
Replies: 19
Views: 1,240
I am always interested in Pentax camera body and lens compatibility. Shortly after the announcement of the DFA* 50, I began to suspect that, it might work better on manual-aperture and aperture-priority-only film bodies than existing FAJ, DA, and DFA lenses that do not have aperture rings. This is due to reasons related to the new electronic aperture, which I will go into later. I rented a copy of the DFA* 50 to find-out how/if it would work on the LX specifically. I found that it actually works well, with the one major limitation that the only available aperture is the max of 1.4. Manual focus works as expected and aperture-priority auto-exposure also works. Again, it is aperture-priority in the sense that the aperture is fixed at 1.4. Below I will discuss why this works and why it works better than previous DFA lenses, as well as show some example pictures taken with the DFA* 50 and LX combo.

(I should note that I did this test quite some time ago, which is why it is summer in the pictures. I didn't post this at first because I was not thrilled with my scans. I recently looked at them again and thought they were not bad.)



Let's first discuss the technical aspects of the test, and try to understand if the situation might be better than previous DFA lenses. All previous K-mount lenses that are set to the A aperture setting or have no aperture ring will stop all the way down to the smallest aperture when the diaphragm actuator lever is let-out completely by the body. Aperture-priority-only film bodies can only let the diaphragm actuator lever out completely. Thus, a standard DA or DFA lens such as the DFA 28-105 (which has no aperture ring) will only be able to be used at the smallest aperture on such a body. In the case of the electronic aperture of the DFA* 50, there is no diaphragm actuator lever on the lens, so the attempts of the body to let-out the diaphragm actuator lever will do nothing. Further, no power is applied to the lens, and the default aperture with no power is open. The net result is that the aperture remains all the way open at all times. Thus, we are able to conclude that on an aperture-priority-only film body, the only available aperture on a standard DFA lens such as the 28-105 will be the smallest aperture, while the only available aperture on the DFA* 50 will be the largest aperture. While both are severe limitations, having only the largest aperture available is arguably a much more usable situation than having only the smallest aperture available. This is the key compatibility difference between the DFA* 50 and previous DFA lenses without aperture rings.

The remaining questions are: will the body know that the lens is wide-open and will auto-exposure work? This is where examining the mount of the DFA* 50 will tell us something:



On the left is the DFA* 50, and on the right is the FA* 28-70. The locations circled are approximately where the body expects the aperture ring coupler to be when the lens is wide-open. On the FA* there is an aperture range that the lens can indicate to the body (because it has an aperture ring). On the DFA* we see that there is an opening only at the wide-open end of the range. Thus, it seems that the DFA* will indicate to an aperture ring coupler enabled body that it is only wide-open all of the time. And this is what we want! I suspect that this opening's function is two-fold: to indicate that the aperture is wide-open, and to prevent damaging a body with an aperture ring coupler when such a lens is attached. If there were no opening in this location, attaching the DFA* 50 to the LX or other aperture ring coupler enabled body would bend the aperture ring coupler into the body.

Another picture of the aperture indication opening on the DFA* 50:




Finally as promised, here are some example pictures taken with the DFA* 50 on the LX. All are on Fujichrome Provia 100F. Exposure in general seemed reasonable with this combo. I used negative exposure bias for many of the pictures. This was for the look I was going for rather than correcting a technical issue. I punched-up the contrast on some of the scans, but I think it is still clear that some interesting results can be found even with the fixed aperture. The overcast day lent itself well to the wide-open aperture. If trying this on a sunny day, you would need an ND set and/or a polarizer.













I hope you found this investigation interesting!
Forum: Sold Items 05-29-2019, 05:24 AM  
For Sale - Sold: SMC Pentax-FA 20-35mm F4 AL
Posted By JBox
Replies: 2
Views: 810
PM sent.
Forum: Pentax SLR Lens Discussion 08-09-2018, 09:23 AM  
Comparing DFA* 50mm with 50mm f2.8 MACRO
Posted By JBox
Replies: 35
Views: 3,817
@dofmaster
Just a point of clarification: Which 50mm f2.8 MACRO are you testing? I assume that it is one of the F, FA, or DFA?
Forum: Sold Items 03-26-2018, 09:20 AM  
For Sale - Sold: FA 24~90/3.5~4.5 AL [IF] Like New NIB/NOS
Posted By JBox
Replies: 4
Views: 694
PM sent.
Forum: Pentax News and Rumors 02-22-2018, 03:11 PM  
The official presentation (Ricoh) of the Pentax Mark II
Posted By JBox
Replies: 331
Views: 35,720
Indeed:
Forum: Pentax News and Rumors 02-22-2018, 11:42 AM  
DFA*50 1.4 coming
Posted By JBox
Replies: 3,156
Views: 308,360
I will re-post this since it has gone largely unnoticed. It appears that the DFA* 50 was used for some of the sample images for the K-1 II:
Forum: Pentax News and Rumors 02-21-2018, 07:03 PM  
DFA*50 1.4 coming
Posted By JBox
Replies: 3,156
Views: 308,360
Go to the page here for K-1 II sample images. The last few images claim to have used the lens "HD PENTAX-D FA*50mmF1.4 SDM AW". Below it says: "The lens used is Beta version, and the name is tentative."
Forum: Pentax News and Rumors 02-21-2018, 04:37 PM  
Ricoh announces an upgrade service for current PENTAX K-1 consumers
Posted By JBox
Replies: 258
Views: 23,187
This upgrade option is probably one of the more interesting things about this K-1 II release. Does anyone know if other camera makers have done a hardware upgrade like this before?

I wonder if they will transfer the camera specific info such as serial number, shutter count, manufacture date, etc. to the new main board?
Forum: Pentax SLR Lens Discussion 01-18-2018, 07:28 PM  
A new kind of lens oddity?
Posted By JBox
Replies: 3
Views: 918
The duplicated marks you see in the head-on shot are reflections. In that picture I believe that the inner most marks are the direct view and the outer marks are their reflections.

I guess it could be blackening. Regardless of what exactly it is, it seems to beg the question about whether the lens is been worked-on in the past. The lens has some wear, but I don't see any direct evidence that it has been disassembled. I have also wondered if the glue/sealant/blackening could have worked itself out of where it is supposed to be due to temperature extremes?
Forum: Pentax SLR Lens Discussion 01-18-2018, 06:01 PM  
A new kind of lens oddity?
Posted By JBox
Replies: 3
Views: 918
I just received an FA 20-35 that I bought, and I noticed something right away that I have not seen before or heard about as a type of issue. There seems to be some glue or sealant around the inside of the front element that is not evenly applied. This can be seen by looking from the front, but mainly by looking at the front element from an angle. There are also a few spots of the substance that are not connected to the bead around the edge. See pictures below. Has anyone seen this kind of thing before? I am not sure that it is even a problem. I have not taken many test shots yet. I am mainly wondering if it is indicative of some larger issue. :(

Thanks for any insights.




Forum: Pentax K-1 12-12-2017, 03:04 PM  
White dots in images taken indoors at exposures 1/25 through 1/10 sec. at f/2.8
Posted By JBox
Replies: 50
Views: 4,019
Would you be able to post your raw test images that you have so far? I would like to compare them to my tests. I had my K-1 calibrated by Precision last year for the white dot issue. I saw improvement over its initial performance, but lately I have been hearing things that are making me think it is still not on par with the best performing K-1's. :(


I would be interested to see longer test images as well. :)
Forum: Pentax K-1 09-07-2017, 05:41 AM  
K-1 white dot issue. ?
Posted By JBox
Replies: 516
Views: 49,939
I would very much appreciate it if you could. I think it would be very helpful for @awscreo and I to have your test images to compare to our tests.
Forum: Pentax K-1 09-06-2017, 07:34 AM  
K-1 white dot issue. ?
Posted By JBox
Replies: 516
Views: 49,939
I got around to doing some test images last night. I did a sequence of 3 at ISO800, then 2 at ISO100, and finally another at ISO800. I did a map pixels between the two ISO100 images. That removed some of the obvious hot pixels, but not any of the noise that we are concerned with. See the sequence here. A number of the images are mostly light because clouds kept moving through. My K-1 was reporting a few degrees higher temp, but they all still look pretty bad by comparison. I have not done any LE stuff since I had it calibrated around a year ago. I guess ignorance is bliss after all. :(

@MJKoski
Would it be possible for you to post 4 minute ISO100 and ISO800 examples from your second K-1? It would be really good to get some kind of baseline in this thread.
Forum: Pentax K-1 09-01-2017, 03:04 PM  
K-1 white dot issue. ?
Posted By JBox
Replies: 516
Views: 49,939
It would also be useful to know if shadow or highlight correction were on for the test image.

If I have time this weekend, I will try to get some similar images to use for comparing.
Forum: Pentax K-1 09-01-2017, 12:55 PM  
K-1 white dot issue. ?
Posted By JBox
Replies: 516
Views: 49,939
Yes. See my posts here and here. One of the post-calibration dark-frames from my camera was also used in @MJKoski's comparison image in this tread.

However, looking back in this thread, it seems that your K-1 compared favorably to all others including mine post-calibration. Thus, I am not sure how much improvement you can expect to see. I am not sure how to compare to the image you just posted since it doesn't have the exposure info metadata. I can maybe do a dark-frame with mine if you can provide the exposure info for it. I would need at least ISO and exposure time.
Forum: Pentax SLR Lens Discussion 07-18-2017, 03:47 PM  
FA* 85 f1.4
Posted By JBox
Replies: 21
Views: 1,941
+1 for the A* 85.

1. I do not own the FA* 85.
2. I have not owned it.
3. For 85mm, I thought about the A* first and ended-up getting that.
4/5. Now that I have the A*, I have not really given much thought to the FA*. The A* meets all my needs in the 85mm department.
Forum: Sold Items 05-18-2017, 09:59 AM  
For Sale - Sold: SMC K 28mm f/2.0 28/2 [Zeiss 'Distagon'/'Hollywood'] [w/ optional dedicated hood]
Posted By JBox
Replies: 14
Views: 2,382
First of all, PM sent.

Secondly, from the linked info, it seems that the most recent Zeiss ZK/ZF2/ZE versions of the 28/2 would fall under the diagram labeled "Zeiss-Cosina Distagon 28/2". Is that correct?
Forum: Sold Items 03-18-2017, 03:57 PM  
Wanted - Acquired: Pentax A* 85 f1.4
Posted By JBox
Replies: 4
Views: 441
Manish is having second thoughts about parting with his, so I am looking again. Please let me know if you have one!
Forum: Sold Items 03-16-2017, 09:58 AM  
Wanted - Acquired: Pentax A* 85 f1.4
Posted By JBox
Replies: 4
Views: 441
Looking for a good condition A* 85 f1.4, preferably with the original MH-RA hood included. Must be fully functional and optics must be in very good condition with no scratches or haze. I am willing to consider a number of external/cosmetic conditions. I will pay up to $1100 USD (depending on the condition) and buy from anywhere, but seller must be able to ship to Michigan, USA. If you've got one you are willing to part with, please let me know!

Jeff
Forum: Troubleshooting and Beginner Help 12-10-2016, 12:01 PM  
Formal process to suggest product and/or firmware update ideas?
Posted By JBox
Replies: 3
Views: 774
Great! I, and no doubt others, will be sending our ideas your way!
Forum: Troubleshooting and Beginner Help 12-09-2016, 06:15 AM  
Formal process to suggest product and/or firmware update ideas?
Posted By JBox
Replies: 3
Views: 774
As you may have noticed, there are very many product and/or firmware update ideas for Ricoh Imaging / Pentax on PentaxForums. Does Ricoh have plans to create a formal process to gather these ideas from customers? At the moment, there is an informal process where members of the PentaxForums staff will present some ideas from the forums to Ricoh reps at industry shows. It would be great to see a process that would allow more ideas to be presented and considered by the Ricoh Imaging / Pentax team.

Thank you for your consideration.
Forum: Pentax K-1 11-23-2016, 09:01 PM  
K-1 white dot issue. ?
Posted By JBox
Replies: 516
Views: 49,939
I just went back and found that I have not posted an ISO 100 dark-frame here (I had assumed it was one of the initial ones I had posed). Is that one of awscreo's dark-frames?
Forum: Pentax K-1 11-23-2016, 10:24 AM  
K-1 white dot issue. ?
Posted By JBox
Replies: 516
Views: 49,939
Just an FYI, that ISO 100 dark-frame is from before my K-1 was recalibrated, so it is likely there is even less noise at ISO 100 now. I can do another ISO 100 dark-frame if you are interested, but I will probably not be able to before next week.
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