Bad copy of this lens?

Started 4 days ago | Discussions thread
W5JCK
W5JCK Senior Member • Posts: 2,902
Re: Bad copy of this lens?

DavidWright2010 wrote:

W5JCK wrote:

None of the stars look the way they should. No nice points of light. I suspect you didn't get the focus nailed down. But there are likely some lens issues too, especially wide open at f/1.4. The Samyang/Rokinon lenses are fairly inexpensive and often require stopping down to f/2 or f/2.8 to get the best sharpness, but they usually look a lot better than your images do.

Do you have an example?

Be sure to focus first on brighter stars then switch to the faint stars to fine tune the focus. As you mentioned, faint stars will disappear if the focus is too soft. Make the faint stars as small of a point of light as you can.

I did that. The faint stars basically disappear from the view screen with the smallest change I make in the focusing ring.

In the center of the image, the faintest stars are 2 x 2 pixels at the full rez output (6000 x 4000), as shown in this 400% enlargement:

But on either one side or the other, I see even the dim stars sitting in a little bubble:

I also tried 'walking' thru the best focus point by moving the focus the width of the infinity mark on the lens (about 1 mm). The image was worse as I moved away in either direction.

I'll try again tonight.

David

Here is a couple of images from my Sony a7 with Rokinon 24mm lens. I didn't zoom in as I don't like pixel peeking, but you can see that the stars are not sitting inside bubbles. These images were shot wide open at f/1.4, 8 sec, ISO 3200. If I stop it dow to f/2.8 it is much sharper.

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Best Regards,
Jack
Website: http://w5jck.com/nightscapes-gallery.html
Flickr: https://www.flickr.com/photos/jackswinden
Sony RX100M3, a6000, and a7

 W5JCK's gear list:W5JCK's gear list
Sony RX100 III Sony Alpha a7 Sony a6000 Canon EF 400mm f/5.6L USM Sony E 50mm F1.8 OSS +13 more
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