K-1 AF accuracy with FA lenses

Class A · 05-15-2016, 12:43 AM

Originally posted by scopedude

It's meant to be a practical way to test the lens.

Sure.

The method I proposed takes a bit more time but is rather practical as well.

Originally posted by scopedude

There is a grid in K1's viewfinder that would really help.

Using the grid for alignment is a nice idea.

However, you are then relying on the fact that the grid has been aligned with 100% precision. Imagine a slight slant and then you'd not be aligning your camera correctly. Viewfinder elements are typically not calibrated with utmost precision because they have no impact on the final image.

Therefore, I'd be cautious with this approach.

Also, you'd want it to apply in portrait mode as well. Otherwise you might be missing out on some vertical degradation.

Originally posted by scopedude

Pentax people came to my office with 2 K1s and 2 28-105s, and some other lenses so I had to decide which one to take home.

How nice of them.

Originally posted by scopedude

I've been doing it for years after getting less than ideal samples (many of them) from Canon and Zeiss ZE/ZF.

Sure.

I always check my lenses as well. No matter the manufacturer, there are always subpar copies. Recently a shop assistant tried to tell me otherwise ("Does not not happen anymore these days...") trying to explain why I wouldn't be able to return a lens that I found to be wanting. Guess what, I didn't buy the lens there.

scopedude · 05-15-2016, 03:10 AM

Well, that is my method for testing the lens in a short time, at least I know which one to take (more or less) - but it's certainly helpful to buy in a store that is willing to be 'flexible'. I have good relationships with the distributors here, so I'm getting the first K1 - and it will be launched later this month. They also left some 'goodies' for me to try.

Anyway, I just tested the 28-105 again today, so far so good. It's a very good lens, at 28mm WO the corners are already reasonably sharp, and at f/8 (throughout the range) I have no complaints

MadMathMind · 05-15-2016, 12:47 PM

All of my FA lenses needed an adjustment of -5 to -8 according to Lens Align. At close focus, except the FA43, this seems to be correct. Need to test it more.

One thing though: I have a permanent +0.7EV compensation dialed in. This seems to be correct as I don't get overexposed images. Camera is badly underexposing with all the FA lenses.

stevebrot · 05-15-2016, 03:31 PM

Originally posted by MadMathMind

Camera is badly underexposing with all the FA lenses.

That is strange. Did you add a comment on the "issues" page?

Steve

kp0c · 05-15-2016, 04:19 PM

Originally posted by MadMathMind

All of my FA lenses needed an adjustment of -5 to -8 according to Lens Align. At close focus, except the FA43, this seems to be correct. Need to test it more.

One thing though: I have a permanent +0.7EV compensation dialed in. This seems to be correct as I don't get overexposed images. Camera is badly underexposing with all the FA lenses.

By badly, do you mean 0.7 stop? Or is the 0.7+ adjustment just to get nearer "proper" (per the histogram) exposure?
Because less than a stop would probably be "conservative" metering rather than "badly underxposed" metering imo.

MadMathMind · 05-15-2016, 06:08 PM

Originally posted by kp0c

By badly, do you mean 0.7 stop? Or is the 0.7+ adjustment just to get nearer "proper" (per the histogram) exposure?
Because less than a stop would probably be "conservative" metering rather than "badly underxposed" metering imo.

They are the same, no? Each stop is 1EV, so a +0.7 exposure compensation value is equivalent to the camera underexposing by 2/3s of a stop.

And the +0.7 isn't a "perfect exposure" by any means as I still boost it in post when I apply contrast, etc. Still, I'd expect better metering out of the 86k sensor than my 77 segment K-5IIs.

It's also possible that there's something wrong with my unit. I do most of my shooting in manual mode anyway with flashes and an external meter so it's not the end of the world, but surprisingly and a bit annoying.

6BQ5 · 05-16-2016, 06:24 AM

What software are you using to process your images? It could be the software is not reading the image data correctly and lowering the exposure by approximately -1. So, you compensate for this by adding +0.7 to your exposure in the camera?

MadMathMind · 05-16-2016, 09:21 PM

Originally posted by 6BQ5

What software are you using to process your images? It could be the software is not reading the image data correctly and lowering the exposure by approximately -1. So, you compensate for this by adding +0.7 to your exposure in the camera?

Lightroom.

But I shoot RAW+JPEG (mostly for preview purposes). Without the +0.7EV, the in-camera JPEGs come out way too dark.

I do find I have to compensate with additional exposure (+0.5 or less usually) in processing after contrast is added, but that makes sense because I add a lot and that usually darkens the image by a small amount.

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05-15-2016, 12:43 AM	#16
Class A Pentaxian Join Date: Aug 2008 Location: Wellington, New Zealand Posts: 11,251	Originally posted by scopedude It's meant to be a practical way to test the lens. Sure. The method I proposed takes a bit more time but is rather practical as well. Originally posted by scopedude There is a grid in K1's viewfinder that would really help. Using the grid for alignment is a nice idea. However, you are then relying on the fact that the grid has been aligned with 100% precision. Imagine a slight slant and then you'd not be aligning your camera correctly. Viewfinder elements are typically not calibrated with utmost precision because they have no impact on the final image. Therefore, I'd be cautious with this approach. Also, you'd want it to apply in portrait mode as well. Otherwise you might be missing out on some vertical degradation. Originally posted by scopedude Pentax people came to my office with 2 K1s and 2 28-105s, and some other lenses so I had to decide which one to take home. How nice of them. Originally posted by scopedude I've been doing it for years after getting less than ideal samples (many of them) from Canon and Zeiss ZE/ZF. Sure. I always check my lenses as well. No matter the manufacturer, there are always subpar copies. Recently a shop assistant tried to tell me otherwise ("Does not not happen anymore these days...") trying to explain why I wouldn't be able to return a lens that I found to be wanting. Guess what, I didn't buy the lens there.

05-15-2016, 03:10 AM	#17
scopedude Junior Member Join Date: Apr 2013 Posts: 43 Original Poster	Well, that is my method for testing the lens in a short time, at least I know which one to take (more or less) - but it's certainly helpful to buy in a store that is willing to be 'flexible'. I have good relationships with the distributors here, so I'm getting the first K1 - and it will be launched later this month. They also left some 'goodies' for me to try. Anyway, I just tested the 28-105 again today, so far so good. It's a very good lens, at 28mm WO the corners are already reasonably sharp, and at f/8 (throughout the range) I have no complaints

05-15-2016, 03:31 PM	#19
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by MadMathMind Camera is badly underexposing with all the FA lenses. That is strange. Did you add a comment on the "issues" page? Steve

05-15-2016, 04:19 PM	#20
kp0c Veteran Member Join Date: Jan 2010 Location: Montreal Photos: Gallery Posts: 761	Originally posted by MadMathMind All of my FA lenses needed an adjustment of -5 to -8 according to Lens Align. At close focus, except the FA43, this seems to be correct. Need to test it more. One thing though: I have a permanent +0.7EV compensation dialed in. This seems to be correct as I don't get overexposed images. Camera is badly underexposing with all the FA lenses. By badly, do you mean 0.7 stop? Or is the 0.7+ adjustment just to get nearer "proper" (per the histogram) exposure? Because less than a stop would probably be "conservative" metering rather than "badly underxposed" metering imo.

05-15-2016, 06:08 PM	#21
MadMathMind Veteran Member Join Date: Dec 2013 Location: Houston, TX Photos: Gallery Posts: 1,717	Originally posted by kp0c By badly, do you mean 0.7 stop? Or is the 0.7+ adjustment just to get nearer "proper" (per the histogram) exposure? Because less than a stop would probably be "conservative" metering rather than "badly underxposed" metering imo. They are the same, no? Each stop is 1EV, so a +0.7 exposure compensation value is equivalent to the camera underexposing by 2/3s of a stop. And the +0.7 isn't a "perfect exposure" by any means as I still boost it in post when I apply contrast, etc. Still, I'd expect better metering out of the 86k sensor than my 77 segment K-5IIs. It's also possible that there's something wrong with my unit. I do most of my shooting in manual mode anyway with flashes and an external meter so it's not the end of the world, but surprisingly and a bit annoying.

05-16-2016, 06:24 AM	#22
6BQ5 Veteran Member Join Date: Jun 2013 Location: Nevada, USA Photos: Albums Posts: 3,348	What software are you using to process your images? It could be the software is not reading the image data correctly and lowering the exposure by approximately -1. So, you compensate for this by adding +0.7 to your exposure in the camera?

05-16-2016, 09:21 PM	#23
MadMathMind Veteran Member Join Date: Dec 2013 Location: Houston, TX Photos: Gallery Posts: 1,717	Originally posted by 6BQ5 What software are you using to process your images? It could be the software is not reading the image data correctly and lowering the exposure by approximately -1. So, you compensate for this by adding +0.7 to your exposure in the camera? Lightroom. But I shoot RAW+JPEG (mostly for preview purposes). Without the +0.7EV, the in-camera JPEGs come out way too dark. I do find I have to compensate with additional exposure (+0.5 or less usually) in processing after contrast is added, but that makes sense because I add a lot and that usually darkens the image by a small amount.