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03-25-2013, 09:04 PM   #1
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is this a K mount?

Sorry for the noob question but I've never held a K mount lense before, and surprisingly I cant even find a good pic on google.

It would help me out so much if you guys can tell me what mount this is, thanks!



03-25-2013, 09:21 PM   #2
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Yes it is.

Many good illustrations here:
K-Mount Evolution, Features and Operation

and photos of various mounts here:
http://rick_oleson.tripod.com/index-99.html
03-25-2013, 09:36 PM   #3
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Thank you so much!
03-26-2013, 03:49 AM   #4
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Sorry to intervene. I do have the same issue. I bought an old Sigma 28mm mini-wide lens and its mount is shown below. When I use it on my K-r, the pictures are lacking of contrast and sharpness on almost all f-stops. Some suggested that, I've to remove the flange, but I don't know what's flange and what to remove and what to file. Any advice will be highly appreciated.
Thanks,


Last edited by vass; 09-09-2014 at 09:35 PM.
03-26-2013, 04:51 AM   #5
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The flange in question is the black tab on the left seen most clearly in the second photo. On third party lenses these are sometimes too long and prevent the lens from being locked in place or interfering the diaphragm stop down lever on the camera.

However it looks to me as though the diaphragm stop down lever on the lens has been filed down. Canon users will often mangle this part as it can strike the mirror or other parts in Canon DSLRs. It may be too short to reach the lever in the camera.

This lens does not appear to have an "A" setting on it. You probably need to enable the use of aperture ring in your setup and use stop-down metering. Does it stop down when you make an exposure?

https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...k-x-k-7-a.html

If this doesn't work:

When mounting the lens does it turn far enough that the locking pin engages? If it doesn't the flange may be the problem.

If the lens locks in place is the aperture always fully closed? If so the lever is probably too short. If this is the case you'll have to repair the lever somehow.

Last edited by Not a Number; 03-26-2013 at 04:56 AM.
03-26-2013, 07:57 AM   #6
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I saw an eBay add of something that for sure isn't a k-mount and for sure aint a PENTAX Rear Converter-A 2X-S. I hope no one buy that "2X-S".

http://www.ebay.co.uk/itm/ASAHI-PENTAX-Rear-Converter-A-2X-S-Made-in-Japan-/...E:B:SS:GB:1123
03-26-2013, 01:19 PM   #7
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QuoteOriginally posted by vass Quote
When I use it on my K-r, the pictures are lacking of contrast and sharpness on almost all f-stops. Some suggested that, I've to remove the flange, but I don't know what's flange and what to remove and what to file. Any advice will be highly appreciated.
If you are able to mount and shoot, you don't have a flange problem.

Ummmm...in addition, there is nothing on the mount that would or could create a soft image. If your Sigma is not delivering as expected, you might want to try a hood. You might also want to give it a good look-see for fungus.

Steve
03-26-2013, 01:21 PM   #8
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QuoteOriginally posted by siamthai Quote
I saw an eBay add of something that for sure isn't a k-mount and for sure aint a PENTAX Rear Converter-A 2X-S. I hope no one buy that "2X-S".

ASAHI PENTAX Rear Converter-A 2X-S Made in Japan 027075028906 | eBay
But its been tested! Works fine


Steve

03-26-2013, 01:33 PM   #9
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Thanks very much for the quick reply. I can mount the perfectly on the camera and I can see the stop-down working fine. I didn't find any locking issues when I mount it. I'll have to check for the Aperture closes while mounting the lens. I'll update it soon.
03-26-2013, 01:37 PM   #10
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QuoteOriginally posted by stevebrot Quote
If you are able to mount and shoot, you don't have a flange problem.

Ummmm...in addition, there is nothing on the mount that would or could create a soft image. If your Sigma is not delivering as expected, you might want to try a hood. You might also want to give it a good look-see for fungus.

Steve
I tried with the hood also but no effect of it. The lenses are bright and clear. Also, I've checked it with a 2X tele, again no use. If I turn to above f8, I could notice slight contrast increment.
Thanks
03-26-2013, 02:15 PM   #11
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OK, I'm prepelxed... can you post a couple of examples?
03-26-2013, 04:15 PM   #12
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QuoteOriginally posted by titrisol Quote
OK, I'm prepelxed... can you post a couple of examples?
The first 3 pictures taken with f4,f5.6 and f8 respectively with Pentax M50mm, f1.7 lens. Next 3 pictures are taken with Sigma 28mm(aforesaid lens) with the same f-stops as Sigma lens.
Thanks

Last edited by vass; 09-09-2014 at 09:35 PM.
03-26-2013, 06:00 PM   #13
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According to the EXIF data all the photos except the second one (shot with the Pentax lens) have a shutter speed of 1/160th of a second. The photo in question shows a shutter speed of 1/125.

All the photos except the third photo shot with the Pentax show an ISO of 100. The third photo shows an ISO of 200.

The net effect is that there is only a 1/3 stop difference between the 2nd and 3rd photos.

If you keep the ISO and shutter speed constant the first set of photos shot with the Pentax lens should look like those shot with the SIgma.

What settings are you using on your camera? And how are you metering the shots?
03-26-2013, 07:24 PM   #14
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I did a quick eye ball of the six shots and don't know that the Sigma did that poorly.

Lens comparisons between different focal lengths are a bit tricky. It is usually best to provide equivalent magnification which means that the shorter lens needs to be closer to the subject. (I generally use 20x the focal length.) Doing so introduces the issue of different perspective, so it is usually best to choose a flat, highly detailed, high contrast subject (a sheet of classified newspaper ads often works just fine.) Then you can compare apples with apples.

It is possible to shoot from the same distance and crop, but then you are asking a lot more from the shorter lens.

FWIW, it might have been good to start a new thread regarding the performance of your Sigma. There are several users on the forum who are fans of your lens and who might be willing to offer their insight as to how high your expectations should be.


Steve

Last edited by stevebrot; 03-26-2013 at 07:30 PM.
03-26-2013, 07:27 PM   #15
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QuoteOriginally posted by Not a Number Quote
According to the EXIF data all the photos except the second one (shot with the Pentax lens) have a shutter speed of 1/160th of a second. The photo in question shows a shutter speed of 1/125.

All the photos except the third photo shot with the Pentax show an ISO of 100. The third photo shows an ISO of 200.

The net effect is that there is only a 1/3 stop difference between the 2nd and 3rd photos.

If you keep the ISO and shutter speed constant the first set of photos shot with the Pentax lens should look like those shot with the SIgma.

What settings are you using on your camera? And how are you metering the shots?
I don't know that the vass' first comment above is concerned about the difference in exposure. There has been a flurry of posts in the last few weeks from users who are concerned that their vintage 28mm lenses do not perform (sharpness and contrast) at the same level as their Pentax fast 50s. This is another of those.


Steve
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