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06-07-2018, 05:22 PM   #1
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Irix 15 mm - using hyper focal guides on the lens

I bought the IRIX blackstone 15 mm and it arrived today. I bought it for a trip to Venice this fall. I am nervous about it being manual focus and missing an amazing shot because I didn't get the focus right. Getting old is no fun! The eyes aren't what they used to be.

I have seen comments about setting the focus to infinity and using hyper focal distance to keep things sharp. I can't seem to find a good explanation of how to do this.

I want to love this lens because of the price and the ability to add filters easily. I don't want to spend the $1300 on the Pentax 15-30 mm.

Any help would be greatly appreciated!

06-07-2018, 07:15 PM   #2
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Congratulations. I own this lens and I love it to bits, it's phenomenal.



As for a hyperfocal explanation, let's look at a picture of the lens:



Starting at the bayonet and moving forward, we see the tacky "neutrino noating" branding, and then some markings of interest: first, the depth of field scale, then the distance scale with markings in metres and feet.

The numbers on the depth of field scale,
16 11 8 | 8 11 16,
correspond to aperture settings; at f/8, everything between the two 8s will be in focus. The central | is the focus mark proper.

In the photo, focus is set to infinity - the infinity mark () on the focus ring lines up with the central focus mark on the depth of field scale.

To focus the lens hyperfocally for f/8, we will turn the focus ring until the infinity mark lines up with the right 8 on the depth of field scale. The left 8 will now be somewhere near 2 metres on the distance scale. Now, everything beyond a couple of metres should be in focus, at least in the centre of the image.



Hyperfocal focusing is not an exact science since different people have different opinions on what constitutes acceptable sharpness. You have lots of time to familiarise yourself with the lens and determine if you "agree" with the depth of field scale; I don't think there's anything to be nervous about!

By the way, there's an Irix thread in the lens club forum which may be of interest to you.
06-07-2018, 07:23 PM   #3
dms
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A minor additional comment--if using a APSC sensor the settings to use are for 1 stop more open, so if lens is at f/8, use the marking for f/5.6.
06-07-2018, 09:06 PM   #4
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Nicely described above, and I agree I love this lens.

Irix also has a tutorial page:
Hyperfocal Distance, the DOF Scale and the Hyperfocal Scale Irix USA

06-07-2018, 09:29 PM   #5
dms
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QuoteOriginally posted by riseform Quote
Nicely described above, and I agree I love this lens.

Irix also has a tutorial page:
Hyperfocal Distance, the DOF Scale and the Hyperfocal Scale – Irix USA
Except the lens markings on their tutorial are wrong!

It shows f/11 hyperfocal distance is about 8 feet. The correct value is about 2 feet per DOF master site (online calculator)--for 35 mm film--which is what the lens markings should be as it is FF lens.

As a check my Pentax 16 mm (FF) fish eye has it as about 2.5 feet for f/11.

BTW I checked the Irix page and they do say it is the 15 mm lens--so very odd? And looking at the photo of the lens above--it certainly does not look like what Irix shows in their tutorial. Someone could look at their lens and say if it is wrong or not.

Last edited by dms; 06-07-2018 at 09:42 PM.
06-08-2018, 05:29 AM   #6
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QuoteOriginally posted by Docbot Quote
I bought the IRIX blackstone 15 mm and it arrived today. I bought it for a trip to Venice this fall. I am nervous about it being manual focus and missing an amazing shot because I didn't get the focus right. Getting old is no fun! The eyes aren't what they used to be.

I have seen comments about setting the focus to infinity and using hyper focal distance to keep things sharp. I can't seem to find a good explanation of how to do this.

I want to love this lens because of the price and the ability to add filters easily. I don't want to spend the $1300 on the Pentax 15-30 mm.

Any help would be greatly appreciated!
What camera are you using? It isn't using hyper focal distance but my K-1 indicates a manual focus lens is in focus when the little green light (seen using the view finder) illuminates as focus is adjusted. I've found it to be reliable. Using live view focus peaking with image magnification also works well. I have the same problem with aging eyes and need all the help I can get. I don't have any any other Pentax models so don't know if any of this applies to other than the K-1.
06-10-2018, 12:12 PM   #7
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I using a K-1. I tried the green dot focus indicator!! Thanks for that tip. I forgot that indicator was even there.
I am still working on the hyper focal and infinity focusing.

I know some people have had to reset the infinity focus on the lens. I am reallllllllly hoping I don't have to do that.
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