Luminous Landscape Forum

Equipment & Techniques => Medium Format / Film / Digital Backs – and Large Sensor Photography => Topic started by: Jason Denning on October 13, 2009, 12:27:03 pm

Title: Mamiya 645 80mm F1.9 blooming
Post by: Jason Denning on October 13, 2009, 12:27:03 pm

Hi All,

I've had the f1.9 lens for a while, but only had the digital back for a few months and have noticed what looks a bit like blooming when the lens is wide open, it almost looks like it's got a soften effect on it. When I stop down just one stop this disapears, so wondering if it's an issue of too much light reflecting from the sensor back to the lens and back again that I read somewhere.

The lens also only recently got a scratch on the rear element, could this be the problem?

Does onyone else have this lens and seen this issue on a digital back? I am yet to test it wil film, but will do as soon as I get time to process it.

Thanks

Jason

Title: Mamiya 645 80mm F1.9 blooming
Post by: Jack Flesher on October 13, 2009, 01:32:42 pm

Can you post an example pic?  I have the lens, and it is soft outside the central 1/2 of the frame wide open.  It is also lower contrast than the AF 80's at all apertures, though both resolution and contrast increase as you stop down.  The blooming you are seeing may be lateral CA -- this lens does exhibit some.  Next, what back and raw converter are you using?  Some backs can exhibit purple fringing artifacts with certain raw converters, like Phase backs with LR or ACR.

Title: Mamiya 645 80mm F1.9 blooming
Post by: Jason Denning on October 14, 2009, 03:18:44 pm

Hi Jack, attached are examples, the first is with the lens at f1.9 so wide epon, the second is stopped down to f2.8, it looks like a soft glow.
Both are 100% crops, so no other artefacts are present, never seen the purple fringing that was mentioned.

Thanks

Jason
[attachment=17197:80mm_f1.9.jpg]
[attachment=17198:80mm_f2.8.jpg]

Quote from: Jack Flesher

Can you post an example pic?  I have the lens, and it is soft outside the central 1/2 of the frame wide open.  It is also lower contrast than the AF 80's at all apertures, though both resolution and contrast increase as you stop down.  The blooming you are seeing may be lateral CA -- this lens does exhibit some.  Next, what back and raw converter are you using?  Some backs can exhibit purple fringing artifacts with certain raw converters, like Phase backs with LR or ACR.

Title: Mamiya 645 80mm F1.9 blooming
Post by: ced on October 15, 2009, 09:35:16 am

Does not look like blooming but with that light coming in at the bottom left corner it is more likely flare, the file looks too like the camera had some vibration.
Were you using a lens hood?

Title: Mamiya 645 80mm F1.9 blooming
Post by: Jack Flesher on October 15, 2009, 11:20:22 am

My guess is flare and lens softness combined, not blooming.  Have you inspected the inner surfaces of the lens elements closely?  I ask because the few lenses I have owned that showed that much variation at wide open apertures had a lot of internal dust or fungus...  Try shining a light at an angle through the rear element while looking through the front at the inner elements -- I suspect you might see a lot of crud or haze.