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08-27-2015, 09:51 AM   #1
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How to find perfect infinity focus (Rokinon 14mm)?

I have been shooting milky way and night skies for a few months now and the most difficult thing is finding infinity focus. I look at live view while zooming in all the way (I think 10x is the maximum on K3) to see if the stars are in focus. During my first few outings, I found that the stars looked (or seemed to look) most sharp/in focus when the focus ring was turned all the way till the end beyond the infinity mark. That was easy to remember as I had to turn the ring till the end (till it stops) beyond infinity to get stars in focus. It was easy to do it even in pick dark. But I noticed that stars in all my photos still looked a little out of focus when I started to post process them on my desktop like the image below. I chalked it up to lens limitation and kept shooting the same way.



Couple of weeks ago I was trying to capture milky way at Ancient Bristlecone Pine Forest and I guess I did not turn my lens all the way to the end beyond infinity (It was below freezing and I could hardly feel my fingers). That image came out to be a lot more sharper than all my previous milky way images (link below). That is when i realized that turning it all the way to the end is not truly infinity focus.... but I based that on live view.

https://www.pentaxforums.com/forums/12-post-your-photos/302522-night-ancient-beings.html

So, is looking at magnified live view not the right way for determining infinity focus? What is the best way to exactly figure out the point at which starts are the sharpest? Next time I will probably try shoot same image by rotating the focus ring to different points and then check the focus on my desktop screen to figure out which position has the sharpest stars.... but that still does not give me a way to determine and remember the exact point at which the lens is at infinity focus. Ideally I would like to mark the point on my lens (with a pen?) so I don't have to experiment every time I am out in the dark.

Thanks.

08-27-2015, 09:59 AM   #2
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The best thing to do is calibrate your lens for infinity -- they all seem to need it (the Samyang 14/2.8s), although I wonder if there is any variation in different temperatures. Magnified view should work as well, but if you are just the tiniest bit off (especially if you go beyond where true infinity actually is on the lens) you'll lose sharpness -- it is tough.

Calibrate the focus ring of the Samyang 14mm F2.8 | DSLR Astrophotography
08-27-2015, 10:05 AM   #3
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QuoteOriginally posted by uday029 Quote

So, is looking at magnified live view not the right way for determining infinity focus? What is the best way to exactly figure out the point at which starts are the sharpest? Next time I will probably try shoot same image by rotating the focus ring to different points and then check the focus on my desktop screen to figure out which position has the sharpest stars.... but that still does not give me a way to determine and remember the exact point at which the lens is at infinity focus. Ideally I would like to mark the point on my lens (with a pen?) so I don't have to experiment every time I am out in the dark.

Thanks.
NOPE.....shoot images and compare on computer. That's how I did it and then calibrated my lens. Rotating slightly and checking and rechecking is the only way. Live View ISNT going to help much if at all.
08-27-2015, 12:00 PM   #4
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Be careful with how you calibrate, as there is both field curvature issues and focus shift between aperture settings (not as much as the huge shift on the 8mm), so you might achieve infinity for one particular situation and then find out that you can't get there at other times. The factory has set the calibration where it is for a reason - and often on UWA lenses you will go past for most situations. Best to use live view to find the focus point when shooting static options, and avoid home calibration which voids the warranty.

---------- Post added 08-27-2015 at 02:10 PM ----------

QuoteOriginally posted by uday029 Quote
I have been shooting milky way and night skies for a few months now and the most difficult thing is finding infinity focus. I look at live view while zooming in all the way (I think 10x is the maximum on K3) to see if the stars are in focus. During my first few outings, I found that the stars looked (or seemed to look) most sharp/in focus when the focus ring was turned all the way till the end beyond the infinity mark. That was easy to remember as I had to turn the ring till the end (till it stops) beyond infinity to get stars in focus. It was easy to do it even in pick dark. But I noticed that stars in all my photos still looked a little out of focus when I started to post process them on my desktop like the image below. I chalked it up to lens limitation and kept shooting the same way.



Couple of weeks ago I was trying to capture milky way at Ancient Bristlecone Pine Forest and I guess I did not turn my lens all the way to the end beyond infinity (It was below freezing and I could hardly feel my fingers). That image came out to be a lot more sharper than all my previous milky way images (link below). That is when i realized that turning it all the way to the end is not truly infinity focus.... but I based that on live view.

https://www.pentaxforums.com/forums/12-post-your-photos/302522-night-ancient-beings.html

So, is looking at magnified live view not the right way for determining infinity focus? What is the best way to exactly figure out the point at which starts are the sharpest? Next time I will probably try shoot same image by rotating the focus ring to different points and then check the focus on my desktop screen to figure out which position has the sharpest stars.... but that still does not give me a way to determine and remember the exact point at which the lens is at infinity focus. Ideally I would like to mark the point on my lens (with a pen?) so I don't have to experiment every time I am out in the dark.

Thanks.
Most of what I am seeing here in terms of degradation has little to do with the focusing per se - and calibration would have absolutely no effect (but could actually increase degradation if done poorly). It appears that there is a bit of vibration (especially apparent toward the top), the image is significantly overexposed, and I'm guessing that there are thermal radiation issues related to the difference in the air temperature and the equipment (especially the lens itself). Astrophotography is difficult in weather extremes. Reading more on the topic might help you identify why you haven't been as successful as hoped.

08-27-2015, 12:15 PM   #5
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trying to focus on stars by themselves is almost impossible. We need an object that is closer, and has more detail, light and shadow.

the closest thing we have to true infinity is the sun. This is the standard that is used to measure the focal length of your lens. But you should not point your camera directly at the sun. And never look at the sun through your viewfinder. Alternatively, the moon is the next closest object that we can focus on safely. If you have sharp focus on the moon, All the stars should be in good focus. The difference in the actual position of the lens is microscopic. a quarter moon works best for this purpose. You can see lots of detail, and very little glare. a full moon can work, but you have to look at the very edge to see the detail, and ignore the central portion. once you have the moon in focus, you can take note of where the infinity mark is.

Last edited by promacjoe; 08-27-2015 at 12:24 PM.
08-27-2015, 12:33 PM   #6
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do you have focus peaking on? that extra white halo may be throwing off your ability to judge the size of the stars when zoomed in.
08-27-2015, 12:42 PM   #7
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QuoteOriginally posted by Dlanor Sekao Quote
NOPE.....shoot images and compare on computer. That's how I did it and then calibrated my lens. Rotating slightly and checking and rechecking is the only way. Live View ISNT going to help much if at all.
that's what i had to do with this lens on the k10d... it was a royal pia, but when i finally hit it, the entire picture kinda popped... that's when i noticed that it was decentered, which i was able to confirm on the a7r a week later... returned the lens for a refund.

the hassle of setting accurate infinity hard stops was one of the things that pushed me into mirrorless, because with a good evf camera, hard stops on lenses are an obsolete concept, you can get accurate infinity focus wherever you want, including the stars.
08-27-2015, 01:28 PM   #8
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Ive helped calibrate 4 Samyang 14mm lenses (mine or Friends). ALL were far from even being close to infinity on the hard stop and benefited greatly from HOME calibration. Its a pain , but when its over You will have new respect for this lens !

08-27-2015, 04:43 PM   #9
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QuoteOriginally posted by ScooterMaxi Jim Quote
Be careful with how you calibrate, as there is both field curvature issues and focus shift between aperture settings (not as much as the huge shift on the 8mm), so you might achieve infinity for one particular situation and then find out that you can't get there at other times. The factory has set the calibration where it is for a reason - and often on UWA lenses you will go past for most situations.
The Samyang's are notoriously wrong, random really. They are not set for any reason -- they are usually no where near correct. Luckily they are quite easy to adjust.
08-27-2015, 04:50 PM   #10
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QuoteOriginally posted by vonBaloney Quote
The Samyang's are notoriously wrong, random really. They are not set for any reason -- they are usually no where near correct. Luckily they are quite easy to adjust.
+1 on that. However when we calibrated them the distance scale is pretty much spot on and works as it should. And that is nice !
Also for what its worth...... the 14mm seems to be sharpest at f5.6+ so that's where I did all my calibration at.

Last edited by Dlanor Sekao; 08-27-2015 at 04:56 PM.
08-28-2015, 09:18 AM   #11
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QuoteOriginally posted by vonBaloney Quote
The Samyang's are notoriously wrong, random really. They are not set for any reason -- they are usually no where near correct. Luckily they are quite easy to adjust.
Is this based on "notoriety," or have you done any actual testing and thorough research into it?

In the case of the 8mm - the exotic lens that has created most of the controversy - the reports of the extent of beyond-infinity focus at wide open were absolutely consistent at a point midway between 0.7 meter and 1 meter; everyone who bothered to do the measurement came up with the same result. This odd consistency prompted me to do proper testing - and I found that the focus shift goes to close alignment with the barrel distance at around f/11. So, if you recalibrate to f/3.5 (which is quite soft and should not be used), you will not reach infinity at f/11 - or even at f/8 where the lens is absolutely sharpest from corner-to-corner. I tested sharpness and shifting extensively.

Keep in mind that these are internal focus lenses. Even if the re-calibration was needed, you aren't in any way making the lens sharper with the reworking. You just gain about an inch on the close focus side - which most likely you'll never use.

Given the excellent build and design of the Samyang (Rokinon, Bower, Vivitar, etc.) lenses, as well as so few reports of decentering or other manufacturing defects, do you really believe the company would let the supposed "problem" continue over so many years?

When I bought the 14mm, I didn't even bother with measuring the "problem." It is pretty clear that leaving the lens alone makes the most sense, as it outperforms any other UWA option in Pentax mount for overall sharpness (although it is large, and the colors aren't typical Pentax). By the way, the Samyang 85mm lens also has a well-documented aperture focus shift issue despite its otherwise excellent IQ. It seems that this is the Samyang engineering philosophy to emphasize ultimate sharpness and dismiss the significance of focus shift in order to reach an economical price point.
08-28-2015, 10:03 AM   #12
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QuoteOriginally posted by ScooterMaxi Jim Quote
Is this based on "notoriety," or have you done any actual testing and thorough research into it?
Well, I have one (the 14/2.8), and it badly needed it. After adjustment, it is much easier to use and of course it is nice to have the distance scale have some relation to reality. We're talking a large adjustment on the dial -- like an inch. It is well beyond focus-shift range.

QuoteQuote:
In the case of the 8mm - the exotic lens that has created most of the controversy
We're talking about the 14mm, not the 8mm, and the 14mm is in-fact notorious for both the distance scale being completely wrong and for decentering. I have observed both on the 4 copies I've had.

QuoteQuote:
Keep in mind that these are internal focus lenses. Even if the re-calibration was needed, you aren't in any way making the lens sharper with the reworking. You just gain about an inch on the close focus side - which most likely you'll never use.
Speak for yourself -- I use it for "wide-angle macro"(ish) at the minimum distance.

QuoteQuote:
Given the excellent build and design of the Samyang (Rokinon, Bower, Vivitar, etc.) lenses, as well as so few reports of decentering or other manufacturing defects, do you really believe the company would let the supposed "problem" continue over so many years?
Not sure what you're talking about as there have been a ton of reports of decentering with the 14mm. I went through a total of 4 copies to find a good one. 2 were obviously decentered with blurry edges and heavy CA, and the other two were better, but still one was noticeably superior to the other. This not a phantom or uncommon issue by any means -- they are truly all over the place. Apparently the decentering is also fairly easy to correct, but since I was buying them new I felt it better just to exchange than trying to self-repair. Still I did calibrate the ring once I had a copy I was happy with -- it only takes a few minutes really.

QuoteQuote:
When I bought the 14mm, I didn't even bother with measuring the "problem." It is pretty clear that leaving the lens alone makes the most sense...
Glad you got a good copy right off the bat. Not everyone has had the same experience...
08-28-2015, 11:16 AM   #13
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Just to be clear for the sake of the OP, none of this discussion regarding calibration has anything to do with the softness, blur and aberrations seen in the photo posted. Be careful of this red herring as a potential solution to the problem posted.

The complexities of UWA are a real challenge, and extreme issues with not only focus shift but field curvature are nearly unavoidable (especially so in economical designs).

Frankly, a one-inch shift in close focusing on a 14mm lens (especially one that needs to stop down to f/4 to perform at its best) is barely perceptible. However, an f/8 shot with the same lens that cannot quite reach infinity is a real problem.

I wonder how many home engineers have gone straight ahead with recalibration just a day or two after getting the lens, and just happened to discover that their sloppy work resulted in a "manufacturing defect" allowing them to return the item. Perhaps some of them even tried this two or three times, taking greater care each time until they finally got what they wanted (a lens that focuses at infinity at f/2.8, but doesn't quite get there when stopped down). I suppose that could happen, and Samyang would get all the blame. Not that one person did this, but possibly some returns got shuffled back out the door of the retailer.

By the way, I'd be curious to know why anyone would feel like they should go all the way to a fourth copy rather than seek a refund for an inferior product. Possibly it isn't such a bad item to be going through so many hassles.
08-28-2015, 11:48 AM   #14
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What ISO are you shooting at? That picture is incredibly noisy.

Almost seems like detail loss from very high ISOs probably mixed with atmospheric haze.
08-28-2015, 12:02 PM - 1 Like   #15
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QuoteOriginally posted by ScooterMaxi Jim Quote
Frankly, a one-inch shift in close focusing on a 14mm lens (especially one that needs to stop down to f/4 to perform at its best) is barely perceptible. However, an f/8 shot with the same lens that cannot quite reach infinity is a real problem.
Being able to find infinity is also helpful. And at minimum distance shooting small objects, an inch makes a big difference in how big in the frame it will appear.

QuoteQuote:
I wonder how many home engineers have gone straight ahead with recalibration just a day or two after getting the lens, and just happened to discover that their sloppy work resulted in a "manufacturing defect" allowing them to return the item.
An extreme minority, if any. Especially since it is so easy to try again and get it right -- you're just adjusting the infinity stop, if it is in the wrong place, you just move it again. Not much that can go wrong or be sloppy. If you mean try to adjust the decentering yourself, that would be an even smaller number, but presumably only made up of people that had done that sort of thing before. And even if they did return it, it deserved returning or they wouldn't have been trying to fix it in the first place. So I think this happened approximately zero times.

QuoteQuote:
Perhaps some of them even tried this two or three times, taking greater care each time until they finally got what they wanted (a lens that focuses at infinity at f/2.8, but doesn't quite get there when stopped down). I suppose that could happen, and Samyang would get all the blame. Not that one person did this, but possibly some returns got shuffled back out the door of the retailer.
So this extreme minority (that I would reasonably estimate to be actually none) would also have to be returning to a dishonest retailer who re-sells defective returns that are supposed to be sent back to the manufacturer. That's a pretty tortured and unlikely scenario to account for the number of reports of these problems, or even a single report.

QuoteQuote:
By the way, I'd be curious to know why anyone would feel like they should go all the way to a fourth copy rather than seek a refund for an inferior product. Possibly it isn't such a bad item to be going through so many hassles.
And I'm curious to know why someone would feel it was so important for them to be right that they seek to imply that other's experiences are not really happening. And who said it was a bad item? But the reason was of course I wanted a good copy. The reviews are all glowing about how sharp it is and how little CA, but they also warn that you must get a good copy because decentering is common. Plus what actually happened is that I bought the first one mainly because it was on sale with an incredible deal (<$200 at the time when they were selling for >$300), and I tested it, but not enough (the center was good), and then ended up not using it. (Really I wanted a good wide-angle that was full-frame capable for the future, but I also have the Sigma 8-16 so I tend to use that, and I was in the middle of a cross-country move about that time as well.) Anyway, I eventually got it out again, but past the return period when I discovered some of the edges weren't so great. So sent it back as a warranty exchange as my only option other than trying to adjust elements myself. (I couldn't sell it to someone else in good conscience.) Exchange copy was worse than the first one, sent it back again. And then while I was waiting for that, there was another good sale on it so I bought another one just to increase my odds. I really wanted a good one! And so then they both arrived and I had two to compare side-by-side -- both were much better than the first two, and so I kept the one and returned the other. And then lately I've been doing this close-up wide-angle stuff, and it is good for that...
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