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Old 03-02-2019, 09:56 AM
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xelasnave
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Nikon 50 mm lens focus problem.

I purchased a Nikkor lens? AF 50mm f/1.8D.
Gave it a short run last night but I noticed that I had to take it out to infinity such it would go no further...lookinh in the camera display focus looked good ...however when trying to process I now notice that I have little doughnuts for stars...it seems like I need more in travel although I will check again that maybe I went too far...assuming the worst I am thinkng that maybe by adding a "protective" filter (as you do with a camera...I think they call the uv filters but the idea is merely to put a glass barrier in front of your lens) in the hope that I get a better focus...what do you think?
Alex
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Old 03-02-2019, 10:08 AM
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The other thing this lens seems only to work at f5 I think it was..in any event although there is a range to 2.8 I cant use them... I need d a trip back to the he shop as maybe I am missing something but it sure seems limited to the one.

The intervalometer works great so I may try some wid field with my 70/200 lens now that I can run it past 30 second conds...
And I am lucky...
I set things running doing 3 minute captures with a 30 second interval. ..all good I thought come back in an hour...after about thirty minutes I thought better check the battery...went out black as...fortunately only the one previous capture was blacked out...but I thought tidy up and give up for the night...well I had only just put my ne silver cover on the gear and it rains..massive down pour...
If I had been slack and had a cuppa before tidy up I think most everything could have been ruined.
Still most disappointed to see dougnuts as the captures looked real good.
Alex
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Old 03-02-2019, 10:12 AM
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You can see the settings I hope.
Alex
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Old 03-02-2019, 10:23 AM
JA
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Quote:
Originally Posted by xelasnave View Post
I purchased a Nikkor lens? AF 50mm f/1.8D.
Gave it a short run last night but I noticed that I had to take it out to infinity such it would go no further...lookinh in the camera display focus looked good ...however when trying to process I now notice that I have little doughnuts for stars...it seems like I need more in travel although I will check again that maybe I went too far...assuming the worst I am thinkng that maybe by adding a "protective" filter (as you do with a camera...I think they call the uv filters but the idea is merely to put a glass barrier in front of your lens) in the hope that I get a better focus...what do you think?
Alex
Hi Alex,

I would try to assess the manual versus autofocus accuracy (out of curiosity/for comaprison, that is if your camera can can drive a Nikon AF lens - It depends on camera model) in daylight and then take it form there first. You may have been on one side or the other of perfect focus. Did you use Liveview for focus check at its maximum magnification? And then, did you see both sides of perfect focus trying to detect for the smallest possible dot (star) size? Who know - perhaps the focus was a little off, if not using maximum magnification.

Best
JA
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Old 03-02-2019, 11:53 AM
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Hi JA
I will try all of that but I have nothing to focus on as there is mist here☺.
I used the live view and everything seemed perfect ... I will do some test shots if it clears.
Thanks for all your help.
Alex
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Old 04-02-2019, 11:43 AM
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live view doesn't have enough resolution to accurately tell if in good focus especially with a 50mm lens.

infinity markers on lenses are NOT the infinity point, just an indicator of which direction you need to turn the focus ring. The end stop on lenses is actually beyond the infinity focus point. this gives you the chance to tweak back and forth and see for yourself where the ideal focus is. Live view was made for dummies and this is a camera dont forget, its design is meant for an eye to the viewfinder to see through the lens TTL. They are not designed with live view in mind as primary view, just because its there don't assume it is.

Also Live view is Never Live, the sensor has to capture what is sees, the processor has to process and then the screen has to display it. All these parts take time to do their thing so as you adjust focus it can take maybe half a second for the screen to catch up and display the change. But most people dont understand any of this and so dont pause when adjusting just keep moving the focus instead.

the donut is the artifact that shows you went beyond the focus point of the lens. You should only ever use live view for composition as its useless for fine focus. You can use it to display and zoom in on a test photo as this is more accurate, live view is a preview not a captured photo. do a series of fine adjustments and view close each test to find the sweet spot. Then maybe use a sharpie to mark on your lens where the spot really is.

Once you do this keep that as a reference sample and set camera to spot focus and pick any bright star to spot focus on, easy to do using any lens. and take test shots again, some cameras have back/front focus adjusters in their menu to fine tune a lens' focus on that body. some also let you configure camera buttons . for example my nikon d800e I have tuned and tested and configured it to have a convenience constant focus button for me and remove focus from the shutter button completely. I know my autofocus does as good a job as my eye did manually focusing which I cant do after my stroke. So I just point to a bright star and hold the button down a few seconds for it to setlle and get good "infinite focus" then I can just point to where I want, use live view to composite and use remote to take the shots.

Donut images are not entirely useless, you can still process as normal and then halve the image size at the end to close the stars down to dots again instead of donuts for a usable shot. and it'll still be a resolution you probably would've killed for a few years ago.

A uv filter is just another layer of glass, so you'll lose photons and it does zero for focus. you should check your lens attaches to the camera firmly. there should be zero hint of a wobble there but if you've bent the connectors even a fraction of a millimetre your focusing will be screwed because the lens to sensor (focal plane) distance is now altered.
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Old 07-02-2019, 03:53 PM
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AG Hybrid (Adrian)
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Can always use the moon as a focus target. Take note of the settings then apply it to stars on a darker sky maybe?
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Old 07-02-2019, 05:19 PM
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DeWynter (ILYA)
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Alexander,

I had (still have) two same lenses from different years (the first one with only 6 digits serial number ). I used these lenses for nearly 13 years. While I really loved them for landscape photography (very sharp, no distortion, awesome beautiful sun rays around spot lights at f11) they are not good for astrophoto. This lens has really bad coma towards the edges at f1.8 - f2.8. Plus general focusing issues at open aperture because of discrete focusing system (cannot be stopped at any chosen point but only at some points) inside (not the case for landscape photo at closed aperture, but real issue with astrophoto) and backlash. This lens has a "screwdriver"-type focusing driver which is not very accurate anyway. Coupling with discrete focusing this becomes a real issue. At some point both my lenses broke because of plastic gear inside.

I spent fair bit of time looking for non-expensive alternative and ended up with Tamron SP 45/1.8. This is absolutely fantastic lens for astrophoto - no coma at wide open, very sharp, and not so expensive.

So if you want to use it for landscape photography - keep it. At f8 and smaller it's a fantastic lens that costs only $150, produces images with better quality than from lenses for $1000.
If you want to do astrophoto with it - better to change it to something else.

Regards,
Ilya
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