exposure control and manual lens

mns · 09-16-2013, 11:51 AM

i just received a Pentax M lens 50mm f1.7 manual
However when i start my k01 the LCD shows this message : input focal length with a highlighted number that could be changed between 8 to 800
I am expecting that it should be 50
Am I right and what dose this number mean ?
another question : what to do other than to experiment in order to get the correct exposure ?
Thanks

Not a Number · 09-16-2013, 12:02 PM

You are correct - the number entered should be equal or less than the focal length of the lens. This is for the Shake Reduction. If you turn off SR, it will not ask you for the focal length. Zooms depend on the range you typically will be using.

Please refer to the following threads. They should answer all your questions. And welcome to the joys of using legacy lenses on you Pentax Digital Camera.

https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...k-x-k-7-a.html
https://www.pentaxforums.com/forums/pentax-dslr-camera-articles/100260-manual...ic-lenses.html

PS: Be sure Auto ISO is not selected.

PiDicus Rex · 09-18-2013, 10:29 PM

Not just for SR - It also gets recorded in to the image and video meta-data.

My personal use rule, so I can tell which lens I used when editing, is to set primes with their correct number, and zooms with the wide-end number.
So my 24 and 50 primes are entered as 24 and 50, my 28-70 zoom as 28, and the 70-200 as 70.
My two AF zooms tell the camera which lens they are, so no input needed.

prime.partisan · 09-19-2013, 12:08 PM

For my Sigma 50mm macro, I usually put in 75 and it seems to work better that way. But I haven't done any real testing, so it might just be placebo/my imagination.

mns · 09-19-2013, 12:30 PM

Originally posted by Not a Number

You are correct - the number entered should be equal or less than the focal length of the lens. This is for the Shake Reduction. If you turn off SR, it will not ask you for the focal length. Zooms depend on the range you typically will be using.

Please refer to the following threads. They should answer all your questions. And welcome to the joys of using legacy lenses on you Pentax Digital Camera.

https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...k-x-k-7-a.html
https://www.pentaxforums.com/forums/pentax-dslr-camera-articles/100260-manual...ic-lenses.html

PS: Be sure Auto ISO is not selected.

a friend told me that number should be 75 as this number reflects the actual focal length on DX sensor !!?
50 should be OK for FX cams.

Not a Number · 09-19-2013, 04:33 PM

No, it should be the physical (actual) focal length of the lens.What you set the camera is going use to make calculations for moving the sensor. Draw two circles one 50mm the other 75mm in diameter. Take a 5 degree slice from the center of each. The length of the arc or chord of the 75mm circle on the same 5 degree slice is longer. So if set to 75mm with a 50mm lens the sensor would move more than it actually has to for this type of movement.

mns · 09-20-2013, 06:15 AM

Originally posted by Not a Number

No, it should be the physical (actual) focal length of the lens.What you set the camera is going use to make calculations for moving the sensor. Draw two circles one 50mm the other 75mm in diameter. Take a 5 degree slice from the center of each. The length of the arc or chord of the 75mm circle on the same 5 degree slice is longer. So if set to 75mm with a 50mm lens the sensor would move more than it actually has to for this type of movement.

Thanks a lot

09-16-2013, 11:51 AM	#1
mns New Member Join Date: Aug 2013 Posts: 23	exposure control and manual lens i just received a Pentax M lens 50mm f1.7 manual However when i start my k01 the LCD shows this message : input focal length with a highlighted number that could be changed between 8 to 800 I am expecting that it should be 50 Am I right and what dose this number mean ? another question : what to do other than to experiment in order to get the correct exposure ? Thanks

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Curious about High-Speed Sync and Manual Flash Exposure	akhawar	Flashes, Lighting, and Studio	9	08-23-2012 12:29 AM
Manual lens and exposure	HoBykoYan	Pentax K-5 & K-5 II	7	05-03-2012 07:56 AM
K-7 exposure and manual lenses, better then K10D?	KungPOW	Pentax DSLR Discussion	10	04-04-2012 04:15 AM
Remote control and exposure bracketing	Heron1	Troubleshooting and Beginner Help	10	07-10-2011 06:10 PM
Filters and manual exposure	Kitty	Troubleshooting and Beginner Help	7	01-21-2011 10:38 AM

09-16-2013, 12:02 PM	#2
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 10,526	You are correct - the number entered should be equal or less than the focal length of the lens. This is for the Shake Reduction. If you turn off SR, it will not ask you for the focal length. Zooms depend on the range you typically will be using. Please refer to the following threads. They should answer all your questions. And welcome to the joys of using legacy lenses on you Pentax Digital Camera. https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...k-x-k-7-a.html https://www.pentaxforums.com/forums/pentax-dslr-camera-articles/100260-manual...ic-lenses.html PS: Be sure Auto ISO is not selected.

09-18-2013, 10:29 PM	#3
PiDicus Rex Veteran Member Join Date: May 2013 Location: Melbourne, Australia Posts: 1,381	Not just for SR - It also gets recorded in to the image and video meta-data. My personal use rule, so I can tell which lens I used when editing, is to set primes with their correct number, and zooms with the wide-end number. So my 24 and 50 primes are entered as 24 and 50, my 28-70 zoom as 28, and the 70-200 as 70. My two AF zooms tell the camera which lens they are, so no input needed.

09-19-2013, 12:08 PM	#4
prime.partisan Senior Member Join Date: Jun 2013 Posts: 198	For my Sigma 50mm macro, I usually put in 75 and it seems to work better that way. But I haven't done any real testing, so it might just be placebo/my imagination.

09-19-2013, 12:30 PM	#5
mns New Member Join Date: Aug 2013 Posts: 23 Original Poster	Originally posted by Not a Number You are correct - the number entered should be equal or less than the focal length of the lens. This is for the Shake Reduction. If you turn off SR, it will not ask you for the focal length. Zooms depend on the range you typically will be using. Please refer to the following threads. They should answer all your questions. And welcome to the joys of using legacy lenses on you Pentax Digital Camera. https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...k-x-k-7-a.html https://www.pentaxforums.com/forums/pentax-dslr-camera-articles/100260-manual...ic-lenses.html PS: Be sure Auto ISO is not selected. a friend told me that number should be 75 as this number reflects the actual focal length on DX sensor !!? 50 should be OK for FX cams.

09-19-2013, 04:33 PM	#6
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 10,526	No, it should be the physical (actual) focal length of the lens.What you set the camera is going use to make calculations for moving the sensor. Draw two circles one 50mm the other 75mm in diameter. Take a 5 degree slice from the center of each. The length of the arc or chord of the 75mm circle on the same 5 degree slice is longer. So if set to 75mm with a 50mm lens the sensor would move more than it actually has to for this type of movement.

09-20-2013, 06:15 AM	#7
mns New Member Join Date: Aug 2013 Posts: 23 Original Poster	Originally posted by Not a Number No, it should be the physical (actual) focal length of the lens.What you set the camera is going use to make calculations for moving the sensor. Draw two circles one 50mm the other 75mm in diameter. Take a 5 degree slice from the center of each. The length of the arc or chord of the 75mm circle on the same 5 degree slice is longer. So if set to 75mm with a 50mm lens the sensor would move more than it actually has to for this type of movement. Thanks a lot