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Forum: Sold Items 02-26-2021, 11:45 AM  
For Sale - Sold: Promaster 100/3.5 Macro
Posted By JBox
Replies: 7
Views: 1,276
PM sent for F 35-70.
Forum: Pentax News and Rumors 01-12-2021, 09:11 PM  
Guangzhou | K-3 Mark III preview meeting
Posted By JBox
Replies: 264
Views: 32,603
A 3D printed mock-up of the A* 85 f1.4 and its hood?
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: 2,037
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: 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: 2,037
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 News and Rumors 02-21-2018, 07:03 PM  
DFA*50 1.4 coming
Posted By JBox
Replies: 3,156
Views: 351,207
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: 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: 944
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 DSLR Discussion 06-04-2016, 06:35 AM  
Firmware wish list - stop down metering in shutter release in M mode
Posted By JBox
Replies: 16
Views: 2,096
I am one of those who has suggested this before (but not the first). My idea was to implement it as a new exposure mode that would be a hybrid between M and Av. See my post here documenting it for the K-1, although it could be any recent Pentax DSLR. The new exposure mode would be enabled with a new option for custom function "Using Aperture Ring". This would allow the new Av-like functionality with K/M lenses while not changing any of the existing exposure modes, and allowing use the current way of doing things.

I believe Adam has discussed this idea with one of the Pentax reps at WPPI, and they gave some odd objections that I don't fully understand. I think if we bring it to their attention again, it might go better if we emphasize that it is basically a user interface change that does not change the underlying camera functionality. Maybe that would help? :confused:
Forum: Pentax K-1 & K-1 II 05-20-2016, 03:31 PM  
Pentax K-1 new firmware suggestions
Posted By JBox
Replies: 144
Views: 15,272
One thing I didn't notice at first is that the K-1 is missing the underexposure highlighting in instant review and playback. On the K-5, we had an option called "Bright/Dark Area" instead of "Highlight Alert" on the K-1. Both over and under exposed areas would flash in red and yellow respectively when "Bright/Dark Area" was active. Looking at the online manuals, it appears that "Highlight Alert" had already replaced "Bright/Dark Area" on the K-3.

I wonder why they removed just the underexposure highlighting. Does anyone know? In any case, underexposure highlighting was a good feature that I used, and it would be nice to see it come back in a firmware update.
Forum: Pentax Full Frame 04-30-2016, 01:43 PM  
Pentax K1 delivered! Pictures with lenses.
Posted By JBox
Replies: 33
Views: 22,219
The K lens looks amazing on it! :) Of course, I prefer the K/M lens styling over any of the others so far. It almost seems like the grips on the top knobs are in a somewhat K/M style.
Forum: Pentax K-1 & K-1 II 02-18-2016, 11:18 AM  
"Crippled" mount or not?
Posted By JBox
Replies: 32
Views: 4,478
Not only is it not in the pictures, but every unofficial and official spec sheet has plainly stated that nothing has changed from the K-3 with respect to K/M lenses.


And we can expect this to continue as long as it is missing for the very simple reason that the lack of it will continue to cause inconvenience (however minor) and a desire to have it back. I also think there is a qualitative difference between the "feature" request of the aperture linkage and other feature requests. I, and I suspect others, see the lack of the aperture linkage as a deficiency to be fixed rather than a new feature. Thus, it is different from 4K video for example, which is a new thing that will require significant new R&D to develop. Further, I don't see anything wrong with highlighting a continuing issue. I could see a concrete statement from Pentax one way or the other resolving it. I personally haven't heard such a statement from them.


Who told you this? Or is this just inference from the interviews over the years? I am not trying to put you on the spot here. I am just looking for that concrete statement.


I am still not convinced by the "lack of space" reason. I think this is likely the superficial reason, but that they could overcome the challenge if they really wanted to. I think the real reason is one that has been mentioned many times on this forum, which is a perceived lack of interest in the uncrippled K-mount. I personally am not convinced that the interest group is as small as people on this forum think. We may be a very small minority on these forums, but there is a world outside of PF. :lol: An interesting note here is that, in the last few days before the release, a few new or low post users (not unlike myself) posted to ask about uncrippling specifically. Just because they don't have a loud voice here doesn't mean they aren't interested.


I have thought about this as well and would like to see it on the K-1. It likely doesn't have it now, but if there is enough interest, maybe it can be added in an update?


I think what has disappointed me most is that there was a lot of talk in the K-1 teasers and now on the K-1 "Special Site" about the Pentax legacy and history and all that, but none of this talk appears to have translated into actual product changes. It is all marketing fluff. The facts of the matter are that there have been no "old" lens compatibility features introduced since at least the K-7. (Maybe even further back? I am not very familiar the pre K-7 DSLRs.) Sure, the full-frame format itself can be seen as an "old" lens compatibility feature, but it is not only that.
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