FD > PK Adapter, digital results blurry

[Michiel]

Hi guys,

I have a confusing issue. I am happy with my Pentax K-x dslr and kit lens. However, I have these really nice Canon FD lenses just lying around (love-hate relationship with my Canon A-1) and thought I would really like to use the 50mm 1.4 on my Pentax.

So I bought a good quality adapter from Amazon (http://www.amazon.com/gp/product/B0095OODVO/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1), stuck it on my Pentax, bolted in the Canon FD lens and after adjusting the camera to overexpose a few stops it works!

But at apertures wider than 2.8 the results become incredibly blurry... And shooting wide open is of course why I wanted to use the lens.

And here's what I don't understand: I'm looking through the same lens, right? It looks just fine! Clear and sharp as heck. Why is the sensor recording such a blurry picture?? I can't wrap my head around it. Experimented with mis-focusing on purpose, but that isn't what's causing it. Does anyone know what's going wrong?

Thanks!

Edit: I think the correct term for the issue is "blooming" of highlights.

 

[jpfisher]

Focus screens in modern digital cameras aren't really able to show you anything better than f/2.8. Can you accurately manually focus with any native PK lenses? Are you listening for the in-focus confirmation beep from the camera, or relying only on what you're seeing in the viewfinder?

 

[John Cox]

The problem is that the mirror is meant for a different base length (not the screen). Because of this the focus will be off on everything that you focus using the viewfinder. Use Live View and that should help things.

 

[Michiel]

Well, the problem is the same if I use the viewfinder or life view.

The problem isn't actually that the image is out of focus, when I have focused what I think is correctly, the result is actually in focus. It's just that everything bright is very blurry. Truly it looks like I'm taking correctly focused pictures through a lens that has vaseline on it!

Attached is an example. As you can see from the letters on the icons, the lens is in focus.

Thanks for your help, guys.

 

[ruby.monkey]

I doubt that the compensating lens in that adapter is going to do anything but harm image quality.

 

[Michiel]

What makes this so strange to me is the difference between what I see with my eye through the lens, and what the sensor records.

Is my eye receiving what the sensor sees and is my brain correcting without me noticing, or is the sensor receiving what I see, but recording it wrong?

I'm guessing it's the first option: The alterations to the light made by the adapter are not having any effect on how I see it, but they are confusing or inappropriate for the sensor.

In that case my adapter is worthless, though. I was hoping there was a fix. Bummer..

 

[Sid836]

Try this:
1. Stop down the lens to f/4 or more.
2. Focus
3. Open it up
4. Shoot.

Does that still provide you with blurry images?

 

[Michiel]

Thanks for the suggestion, Nikos72! I've tried it, unfortunately no difference. The pictures at f/2.8, 4, 8 etc. look fine, but when I open up the aperture to 2 or wider without touching the focusing ring the same problem persists. It's worst at 1.4, still noticeable at 2, and gone at 2.8.

After reading a lot more about adapters, I think the correct term for the issue is "blooming" of highlights.

If my girlfriend didn't prefer digital pictures, I'd throw this thing in the trash and use my Yashica GSN...

 

[raid]

I use an FD mount Vivitar 90-180 on my EP-2, and also fast lenses, such as the 50/1.2, and the results are very sharp.