Auto F stop vs Manual F Stop adjustment on Zoom Lense

tommies · 12-29-2022, 05:52 AM

Good afternoon, I'm new to the forum.
I have Pentax K100D and using a Sigma DG 70-300mm 1:2-56 Zoom lense. Been using it for some time and still battle to use the Apperture setting on the lense between A and pre define setting. When non- Auto, gives me a error message on the camera "AV" and cannot use the camera. What am I doing wrong or how do I use manual aperture setting on the lense with the K100D camera

steephill · 12-29-2022, 06:31 AM

There is nothing to be gained and a lot to lose from manually setting the aperture on the lens. Just leave it on A and set it from the camera body. If you must try it you need to enable the use of the aperture ring from the menu system. After that you can set the aperture on the lens but will be restricted to manual exposure mode only.

Useful video here https://www.pentaxforums.com/articles/tutorial-videos/how-to-use-manual-lene...tax-dslrs.html

jgnfld · 12-29-2022, 07:13 AM

Welcome from Newfoundland. You live in a photography paradise!

In the future I might suggest you'll get better replies if you post specific questions like this in the "Troubleshooting and Beginner Help" area here Troubleshooting and Beginner Help - PentaxForums.com

Happy shooting.

OrchidJulie · 12-29-2022, 01:18 PM

Originally posted by jgnfld

Welcome from Newfoundland. You live in a photography paradise!

In the future I might suggest you'll get better replies if you post specific questions like this in the "Troubleshooting and Beginner Help" area here Troubleshooting and Beginner Help - PentaxForums.com

Happy shooting.

That's such a good idea, I'm moving the thread there...

**Lowell Goudge** · 12-30-2022, 06:15 AM

You need to go into the special functions and select use aperture ring.

The camera will then work, but there is no metering. To activate the metering, you need to put the camera into manual (M mode) and press the green button to have the camera set the suited to match aperture, or use the Depth of field preview to see the exposure in terms of +/- Fstops for the shutter and aperture you have set.

However as steephill has indicated there is nothing to be gained by using manual aperture

**mikesbike** · 12-30-2022, 07:59 PM

In fact, as steephill says, you lose important functions. For starters, gone is matrix (multi-segment) metering, and then your aperture will not hold to true setting when less than wide-open as it would when on the "A" position and setting aperture via the camera's on-body control. Being a variable-aperture lens, this will constantly change as you zoom to various focal lengths if using the aperture ring to set aperture! Then you'll have to constantly use the green button to re-set the shutter speed to compensate- what a pain!

tommies · 01-03-2023, 01:37 AM

Thank you for everyone who has responded to my post. I feel more comfortable now to just use "A" .
Seeing forward to be part of the forum

12-29-2022, 05:52 AM	#1
tommies New Member Join Date: Dec 2022 Posts: 2	Auto F stop vs Manual F Stop adjustment on Zoom Lense Good afternoon, I'm new to the forum. I have Pentax K100D and using a Sigma DG 70-300mm 1:2-56 Zoom lense. Been using it for some time and still battle to use the Apperture setting on the lense between A and pre define setting. When non- Auto, gives me a error message on the camera "AV" and cannot use the camera. What am I doing wrong or how do I use manual aperture setting on the lense with the K100D camera

12-29-2022, 06:31 AM	#2
steephill Pentaxian Join Date: Nov 2018 Photos: Gallery Posts: 585	There is nothing to be gained and a lot to lose from manually setting the aperture on the lens. Just leave it on A and set it from the camera body. If you must try it you need to enable the use of the aperture ring from the menu system. After that you can set the aperture on the lens but will be restricted to manual exposure mode only. Useful video here https://www.pentaxforums.com/articles/tutorial-videos/how-to-use-manual-lene...tax-dslrs.html Last edited by steephill; 12-29-2022 at 06:36 AM.

01-03-2023, 01:37 AM	#7
tommies New Member Join Date: Dec 2022 Posts: 2 Original Poster	Feedback Thank you for everyone who has responded to my post. I feel more comfortable now to just use "A" . Seeing forward to be part of the forum

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12-29-2022, 07:13 AM	#3
jgnfld Moderator Loyal Site Supporter Join Date: Feb 2015 Location: Avalon Peninsula, Newfoundland Photos: Gallery \| Albums Posts: 1,789	Welcome from Newfoundland. You live in a photography paradise! In the future I might suggest you'll get better replies if you post specific questions like this in the "Troubleshooting and Beginner Help" area here Troubleshooting and Beginner Help - PentaxForums.com Happy shooting.

12-29-2022, 01:18 PM	#4
OrchidJulie Moderator Loyal Site Supporter Join Date: Jun 2012 Location: Magic City Photos: Gallery \| Albums Posts: 6,932	Originally posted by jgnfld Welcome from Newfoundland. You live in a photography paradise! In the future I might suggest you'll get better replies if you post specific questions like this in the "Troubleshooting and Beginner Help" area here Troubleshooting and Beginner Help - PentaxForums.com Happy shooting. That's such a good idea, I'm moving the thread there...

12-30-2022, 06:15 AM	#5
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,887	You need to go into the special functions and select use aperture ring. The camera will then work, but there is no metering. To activate the metering, you need to put the camera into manual (M mode) and press the green button to have the camera set the suited to match aperture, or use the Depth of field preview to see the exposure in terms of +/- Fstops for the shutter and aperture you have set. However as steephill has indicated there is nothing to be gained by using manual aperture

12-30-2022, 07:59 PM	#6
mikesbike Site Supporter Join Date: Dec 2016 Location: Southeastern Michigan Posts: 4,549	In fact, as steephill says, you lose important functions. For starters, gone is matrix (multi-segment) metering, and then your aperture will not hold to true setting when less than wide-open as it would when on the "A" position and setting aperture via the camera's on-body control. Being a variable-aperture lens, this will constantly change as you zoom to various focal lengths if using the aperture ring to set aperture! Then you'll have to constantly use the green button to re-set the shutter speed to compensate- what a pain!