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06-17-2014, 04:35 AM   #1
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Focus issue with Rokinon 1.4/24mm and K-5IIs

Hi All,

A friend of mine bought me a Rokinon 1.4/24mm in the US (as recommended in How-To: Picking a Great Lens for Milky Way Photography). Brought it home and wanted to try it on my K-5IIs but I can't focus. Whatever I try, it is never really sharp.

See samples attached (1:1 screenshots of the PEF as seen in Lightroom.

Do I have a broken lens or is that likely me being clumsy? Or am I expecting too much?

Cheers,
Jan

Attached Images
   
06-17-2014, 06:21 AM   #2
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Uhhh, broken lens, broken lens!!
I would get it exchanged right away...
06-17-2014, 06:43 AM   #3
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QuoteOriginally posted by GabrielFFontes Quote
Uhhh, broken lens, broken lens!!
I would get it exchanged right away...
Thanks mate.

Unfortunately, that'll be difficult... I live in Europe.

*sigh*
06-17-2014, 11:19 AM   #4
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It can be really tough to focus manually on the night sky. Blowing it up in live view might help. If your shots are still blurry, then there's probably something wrong with the lens, though.


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06-17-2014, 11:27 AM   #5
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QuoteOriginally posted by Adam Quote
It can be really tough to focus manually on the night sky. Blowing it up in live view might help. If your shots are still blurry, then there's probably something wrong with the lens, though.
Thanks Adam.

I know it's hard, even with blown up live view. That's why I also tried it in daylight and I tried to "focus bracket" a bit.

I used to do it quite a lot 15 years ago, but then I guess my eyes were better back then. I would totally blame my own incompetence if I hadn't been able to focus properly with other lenses (e.g. a Pentax 50mm/1.4) on this body lately.
06-20-2014, 04:26 PM   #6
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QuoteOriginally posted by jexner Quote
Thanks Adam.

I know it's hard, even with blown up live view. That's why I also tried it in daylight and I tried to "focus bracket" a bit.

I used to do it quite a lot 15 years ago, but then I guess my eyes were better back then. I would totally blame my own incompetence if I hadn't been able to focus properly with other lenses (e.g. a Pentax 50mm/1.4) on this body lately.
That second shot really shows that the lens is broken...you can see the lens go in and out of focus without being sharp.
I hope you can get it sorted out...let us know
Cheers
06-21-2014, 02:49 PM   #7
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QuoteOriginally posted by GabrielFFontes Quote
That second shot really shows that the lens is broken...you can see the lens go in and out of focus without being sharp.
I hope you can get it sorted out...let us know
Cheers
I had an email exchange with Rokinon and they told me to send it in (to the US, of course), which I will do next week.

We'll see how it goes.

Thanks for all the help!
06-22-2014, 05:42 AM   #8
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Hey, welcome!
I wish those photos had exif data, so we could see what shutter speed and settings you used.
The problem is that with photo 1) you might have focused wrong. The distance scales on Samyang/Rokinon lenses are often miscalibrated, so the infinity sign might not be true infinity.
photo 2) the photo seems dark, so I guess you used a long exposure / slow shutter speed, which might introduce blur.

Anyway:
To test sharpness, place the camera on a sturdy tripod, in good daylight, use 2 sec timer and ISO 100, manually focus the lens to around nearest focus, and place a piece of newspaper at 45 degrees to it in front of the lens, where the focus should be. Set camera to Av mode and take photos at lowest f-stop and f8. Feel free to use exposure compensation to make the photo brighter. Is the text in the newspaper sharp anywhere? Is one half of the frame blurred but not the other? Is the DoF diagonal, bent? This is how you can diagnose the lens a little better.

Also, make sure the lens is set to "A" on the aperture ring (you have to push a little button to slide it into A). When you focus, try using the viewfinder, and also try with Live view (and focus peaking with digital zoom). Finally, you can try Catch in focus. Manual focus lenses like the Samyang lenses are difficult to focus on modern digital cameras, but there are tools to help you with that.
This is what you can try doing before you send the lens back. Samyang does have quality control problems, though. I had to exchange my 14mm f2.8, and the second copy isn't perfect, either.

06-23-2014, 08:40 AM   #9
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QuoteOriginally posted by Na Horuk Quote
Hey, welcome!
I wish those photos had exif data, so we could see what shutter speed and settings you used.
The problem is that with photo 1) you might have focused wrong. The distance scales on Samyang/Rokinon lenses are often miscalibrated, so the infinity sign might not be true infinity.
photo 2) the photo seems dark, so I guess you used a long exposure / slow shutter speed, which might introduce blur.

Anyway:
To test sharpness, place the camera on a sturdy tripod, in good daylight, use 2 sec timer and ISO 100, manually focus the lens to around nearest focus, and place a piece of newspaper at 45 degrees to it in front of the lens, where the focus should be. Set camera to Av mode and take photos at lowest f-stop and f8. Feel free to use exposure compensation to make the photo brighter. Is the text in the newspaper sharp anywhere? Is one half of the frame blurred but not the other? Is the DoF diagonal, bent? This is how you can diagnose the lens a little better.

Also, make sure the lens is set to "A" on the aperture ring (you have to push a little button to slide it into A). When you focus, try using the viewfinder, and also try with Live view (and focus peaking with digital zoom). Finally, you can try Catch in focus. Manual focus lenses like the Samyang lenses are difficult to focus on modern digital cameras, but there are tools to help you with that.
This is what you can try doing before you send the lens back. Samyang does have quality control problems, though. I had to exchange my 14mm f2.8, and the second copy isn't perfect, either.
Thanks for the tips!

I've retaken the image(s) as you said, see attached.

Can I put links here to the original PEF files? If so http://www.jan-exner.de/images/IMPP4764.PEF (f1.4) and http://www.jan-exner.de/images/IMPP4766.PEF (f8).

What do you think?
Attached Images
View Picture EXIF
PENTAX K-5 II s  Photo 
View Picture EXIF
PENTAX K-5 II s  Photo 
View Picture EXIF
Nexus 5  Photo 
06-24-2014, 10:24 AM   #10
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Here's a review of the lens which shows that it isn't an f/1.4 lens, but actually much closer to an f/1.8: Samyang 24 mm f/1.4 ED AS UMC review - Introduction - Lenstip.com

On photozone.de, their MTF charts shows a 10-20% reduction in resolution between f/8 and f/1.4. The images you've posted appear to have a much greater discrepancy between f/8 and f/1.4 than just 10-20%. Here's the link: Samyang 24mm f/1.4 ED AS UMC (EOS) - Full Format Review - Analysis

In any event, the image taken at f/8 looks fine, while the image at f/1.4 is excessively soft IMO.
06-28-2014, 12:01 AM   #11
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QuoteOriginally posted by FrankC Quote
Here's a review of the lens which shows that it isn't an f/1.4 lens, but actually much closer to an f/1.8: Samyang 24 mm f/1.4 ED AS UMC review - Introduction - Lenstip.com

On photozone.de, their MTF charts shows a 10-20% reduction in resolution between f/8 and f/1.4. The images you've posted appear to have a much greater discrepancy between f/8 and f/1.4 than just 10-20%. Here's the link: Samyang 24mm f/1.4 ED AS UMC (EOS) - Full Format Review - Analysis

In any event, the image taken at f/8 looks fine, while the image at f/1.4 is excessively soft IMO.
Danke Frank, that's what I thought as well.

I had read the article about f/1.4 vs f/1.8. I guess even at f/1.8 this lens still captures more light than most others.
06-28-2014, 04:30 AM   #12
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Well its for your to decide if the top photo is acceptable as the "maximum potential" or not. I think the f8 one looks about right, but the f1.4 might be a bit soft (seems almost like a glaze over it? are you using a filter? are the front and back elements of the lens clean?). On the other hand, since you shoot raw, you can post process that photo and make it quite a bit sharper and more contrasty.
At least now you have a reference for when you get the lens exchanged, so you can see if it is just like this one or better.
Just keep in mind that the stunning photos you see taken with Samyang lenses are often heavily post processed, so they might build up wrong expectations
06-28-2014, 04:13 PM   #13
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QuoteOriginally posted by Na Horuk Quote
Well its for your to decide if the top photo is acceptable as the "maximum potential" or not. I think the f8 one looks about right, but the f1.4 might be a bit soft (seems almost like a glaze over it? are you using a filter? are the front and back elements of the lens clean?). On the other hand, since you shoot raw, you can post process that photo and make it quite a bit sharper and more contrasty.
At least now you have a reference for when you get the lens exchanged, so you can see if it is just like this one or better.
Just keep in mind that the stunning photos you see taken with Samyang lenses are often heavily post processed, so they might build up wrong expectations
Hiya,

The lens is clean, yes.

I don't think I expect too much. As you can see in the first picture I posted, there is definitely a problem around point light sources (stars), and if you compare that with the images on How to Pick a Lens for Milky Way Photography – Lonely Speck (which I believe is NOT heavily edited), mine really doesn't compare at all.

Let's see what Rokinon say and do. I'll report back once I know.

Thanks everyone!
Jan
08-10-2014, 03:03 PM   #14
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So...

I returned the lens to Rokinon in NY. They checked it and said it was indeed a defect. So they sent me a new one at that seems to be a lot better.

I am not yet fully convinced of the new lens, but even if it is not perfect, I won't do an exchange again. Boy, this was expensive... Two times shipping, plus the Swiss took duties and tax when the new lens came back.

Europeans: buying stuff in the US is a gamble. Sometimes you win, sometimes you lose.
12-08-2014, 12:20 PM   #15
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It IS better

Some time later, and I can say that the replacement lens they sent me is clearly a lot better than the original one.

I compared with some older pictures taken with a K10D and a SMC 1.4/50 and 1.7/50. They beat the Rokinon in the centre but not in the corners.

So I guess I need to run more tests with actual stars.
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