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05-04-2018, 07:25 PM   #1
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Manual lens - is auto ISO possible with manual shutter speed ?

I have been trying a few of my lenses with my new K-1 II. One of them is a t-mount Rokinon 800mm mirror lens. Not the sharpest lens, I know. And very tough to focus. I wanted to use high shutter speeds with it. I set the auto ISO in the camera from 100 - 819,200 .

It looks like the only mode on the camera that will let me set shutter speed is "M". But ISO is also fully manual in this mode. I'm not able to get auto-ISO to work.
What I would like is to set the shutter speed, and get the camera to set the required ISO for me. Is it possible, and if so how ?
Obviously, the camera cannot set aperture since the lens is manual and has no contacts.

I would think some type of auto-exposure for ISO would be possible, since in full "auto" mode (green mode), the camera is able to compute shutter speed and ISO automatically.
Am I missing something ?


Last edited by madbrain; 05-04-2018 at 08:06 PM.
05-04-2018, 07:33 PM   #2
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Have you tried TAv mode?
05-04-2018, 08:00 PM   #3
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QuoteOriginally posted by MrMojo Quote
Have you tried TAv mode?
Yes. TAv as well as Tv and P modes won't allow the shutter speed to be changed with this lens. The camera just says it's in aperture priority mode.

Last edited by madbrain; 05-04-2018 at 08:06 PM.
05-04-2018, 08:53 PM   #4
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If you set the camera to Av mode you control shutter speed indirectly by adjusting ISO (and exposure compensation).

I believe that is the closest to Tv or TAv mode you will get with a lens like this.

05-05-2018, 03:11 AM   #5
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QuoteOriginally posted by Fogel70 Quote
If you set the camera to Av mode you control shutter speed indirectly by adjusting ISO (and exposure compensation).
Thanks, that works ! But it's certainly not intuitive.

And this is really more like Sv mode. Except Sv mode doesn't actually work either with such lenses - and still turns into aperture priority
So, you have to hold the ISO button and the dial to change ISO value. Or assign the third dial to ISO and use it for that.
It just seems odd that neither of the two main dials (aperture or shutter speed) do anything at all in any of the auto modes. I can certainly understand why the aperture dial can't operate, but the shutter speed dial should work, at least when ISO is set to auto.

Just had to check on my older K-30, and actually it doesn't allow setting shutter speed either with this lens, not even in M mode. Only ISO can be set, and then shutter speed gets computed as a function of it.

Last edited by madbrain; 05-05-2018 at 03:18 AM.
05-05-2018, 06:13 AM   #6
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This is one of the small peeves of many Pentax owners. After years of dealing with these kinds of workarounds, I ended up buying a used Sony A7R for my sizable collection of old Pentax lenses. It has the same sensor as my K1. With an inexpensive adapter, you get all the modes which a manual lens with aperture set on the lens can support plus TTL flash. You donít get auto aperture, but with live view, you donít need it as often. It is a nice addition to my Pentax bodies, and the best choice for my SMC Pentax K 500mm/4.5, a fast and sharp old lens which has preset aperture anyway.
05-05-2018, 08:26 AM   #7
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QuoteOriginally posted by madbrain Quote
... It just seems odd that neither of the two main dials (aperture or shutter speed) do anything at all in any of the auto modes. I can certainly understand why the aperture dial can't operate, but the shutter speed dial should work, at least when ISO is set to auto. ...
Command dials can be tasked to perform different functions and the functions chosen can vary by exposure mode.

Custom Functions menu can be used to select the functions command dials control. In Av, the front dial can be set to control either ISO or Exp Compensation. You can make the front dial control aperture and put ISO on the rear dial. Tv mode can be set up differently than Av mode. In Av mode, you may want the second dial to control Exp Comp but in Tv mode you might want the second dial to control ISO. Whatever.

If this is helpful to you, I recommend going through all the menu items to see what is in there. :^)
05-05-2018, 09:42 AM   #8
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I don't know if this helps or even applies to your issue but you can set the ISO using the top control dial which makes adjusting it a lot easier and puts it on an independent dial. Just select ISO with the top selection dial, and then the adjustment knob will allow you to quickly adjust ISO while controlling shutter speed with the rear dial.

Not auto ISO but it saves a lot of mode changing to get to ISO adjustment.

05-06-2018, 12:34 AM   #9
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QuoteOriginally posted by Bob 256 Quote
I don't know if this helps or even applies to your issue but you can set the ISO using the top control dial which makes adjusting it a lot easier and puts it on an independent dial. Just select ISO with the top selection dial, and then the adjustment knob will allow you to quickly adjust ISO while controlling shutter speed with the rear dial.

Not auto ISO but it saves a lot of mode changing to get to ISO adjustment.
Yes, it is helpful to me, but I had already figured that part out and mentioned it in my previous post.
05-08-2018, 03:28 AM   #10
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QuoteOriginally posted by madbrain Quote
Thanks, that works ! But it's certainly not intuitive.
Just had to check on my older K-30, and actually it doesn't allow setting shutter speed either with this lens, not even in M mode. Only ISO can be set, and then shutter speed gets computed as a function of it.
Not sure what I was doing friday but earlier today I tried again on the K-30 and M mode behaved identically with the K-1 II - ie. could set both shutter sped and ISO manually.
05-08-2018, 07:16 AM   #11
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QuoteOriginally posted by madbrain Quote
Not sure what I was doing friday but earlier today I tried again on the K-30 and M mode behaved identically with the K-1 II - ie. could set both shutter sped and ISO manually.
You might have enabled auto-ISO i M-mode (if that is possible on K-30), then the camera switch into TAv-mode.
But TAv-mode is not supported with an all manual lens, so the camera switch to Av-mode, where you cannot change shutter speed.
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