pcardinal42 Posted March 16, 2019 Share Posted March 16, 2019 How do you tell if you have a bad lens? I have a Sony A7 II and am using a 50mm 1.8. I was just trying to take a shot of Orion, all manual settings and I tried multiple f stops from 1.8 - 3.5, ISO from 400 - 1600, exposure times no greater than 10" - 2", and using live view to focus on a bright star and get it as sharp as possible. All the stars in the picture look like they have wings. I am shooting from a tripod and it was a little windy last night so maybe that is what it is. I'm trying to get some pics uploaded but having trouble. Any tips or suggestions are helpful. Link to comment Share on other sites More sharing options...
Louis D Posted March 16, 2019 Share Posted March 16, 2019 Stars toward the edge will have wings if the lens suffers from astigmatism. The size of the wings should decrease with increasing f-stop. By f/8, they should be gone, though this might only be possible to test with an artificial star. Stars on axis (in the central region) should be pinpoint or close to it with just about any decent lens. I would try photographing a flashlight (torch) reflection off of a dark ball bearing about 30 feet away. Try it centered and near the edge at varying f-stops while tripod mounted. This should allow you to characterize the aberrations of your lens. p.s., Is that a B-1 bomber in your avatar photo? Link to comment Share on other sites More sharing options...
pcardinal42 Posted March 16, 2019 Author Share Posted March 16, 2019 1 hour ago, Louis D said: Stars toward the edge will have wings if the lens suffers from astigmatism. The size of the wings should decrease with increasing f-stop. By f/8, they should be gone, though this might only be possible to test with an artificial star. Stars on axis (in the central region) should be pinpoint or close to it with just about any decent lens. I would try photographing a flashlight (torch) reflection off of a dark ball bearing about 30 feet away. Try it centered and near the edge at varying f-stops while tripod mounted. This should allow you to characterize the aberrations of your lens. p.s., Is that a B-1 bomber in your avatar photo? Thanks for the quick reply. The stars in the entire field were all jacked up but I'll try your recommendation. Yes they are, I used to work on them and they are one of my favorite aircraft. Link to comment Share on other sites More sharing options...
Sunshine Posted March 16, 2019 Share Posted March 16, 2019 Oh the b1 is a beautiful aircraft, ominous looking and commanding. Link to comment Share on other sites More sharing options...
alacant Posted March 16, 2019 Share Posted March 16, 2019 5 hours ago, pcardinal42 said: stars in the entire field were all jacked up Hi. If it's not the wind, try taking the exposure from your phone rather than touching the camera physically. It maybe vibration as you started the shot. HTH Link to comment Share on other sites More sharing options...
pcardinal42 Posted March 16, 2019 Author Share Posted March 16, 2019 1 hour ago, alacant said: Hi. If it's not the wind, try taking the exposure from your phone rather than touching the camera physically. It maybe vibration as you started the shot. HTH Guess I should've mentioned that I use a 2" delay for the shutter. So whatever vibrations should have rested but I have set up the remote settings for my phone for the next time. Link to comment Share on other sites More sharing options...
pcardinal42 Posted March 16, 2019 Author Share Posted March 16, 2019 1 hour ago, alacant said: Hi. If it's not the wind, try taking the exposure from your phone rather than touching the camera physically. It maybe vibration as you started the shot. HTH Guess I should've mentioned that I use a 2" delay for the shutter. So whatever vibrations should have rested but I have set up the remote settings for my phone for the next time. Link to comment Share on other sites More sharing options...
Stub Mandrel Posted March 16, 2019 Share Posted March 16, 2019 They all look like vibration, how stiff is your tripod? Link to comment Share on other sites More sharing options...
pcardinal42 Posted March 16, 2019 Author Share Posted March 16, 2019 7 minutes ago, Stub Mandrel said: They all look like vibration, how stiff is your tripod? It is this one https://www.amazon.com/gp/product/B005KP473Q/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1 I didn't splurge on it so maybe I need to do my usual buy once cry once Link to comment Share on other sites More sharing options...
Louis D Posted March 16, 2019 Share Posted March 16, 2019 Those all look like normal star trails to me. Today's high megapixel cameras pick up star trails more easily than the low resolution sensors the star trailing rules were written for. Link to comment Share on other sites More sharing options...
Mognet Posted March 16, 2019 Share Posted March 16, 2019 The star shapes in the third image suggest camera movement. Next time try hanging something from the hook on the bottom of the tripod and not extending the centre rod. More weight and a lower centre of gravity will make it more stable, even if it's a cheap tripod. And a 10 second delay will be more than enough to allow any vibrations from pressing the shutter release to damp down. Using a remote release is even better. Another thing is to try not to move around too much while the image is being taken as vibrations through soil can sometimes affect it too Once you've tried that, take images in different directions from the same spot and look at how the lines move. If they are reasonably consistant across the image, but vary from image to image then it's likely to be star trails Link to comment Share on other sites More sharing options...
Stub Mandrel Posted March 16, 2019 Share Posted March 16, 2019 1 hour ago, pcardinal42 said: It is this one https://www.amazon.com/gp/product/B005KP473Q/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1 I didn't splurge on it so maybe I need to do my usual buy once cry once Looks the same as my Hama tripod, but nearly twice the price - and still good value! Not as solid as would be ideal, but I've had good results for long exposure looking for meteors, but of course that's getting star trailing as part of the package. I have found that it's best not to raise the centre pillar to get good results, also you can stick a carrier bag with a few kg of 'stuff' on the hook which will help stabilise it a lot. Link to comment Share on other sites More sharing options...
Louis D Posted March 17, 2019 Share Posted March 17, 2019 I thought about it after my star trails post and came up with a way to prove or disprove my theory. Take exposures at 1s, 2s, 4s, and 8s and see if the star trails double in length with each doubling of exposure time. Link to comment Share on other sites More sharing options...
pcardinal42 Posted March 19, 2019 Author Share Posted March 19, 2019 I had a night of no wind, weighed down the center of my tripod, and used the app on my phone to take the pictures. 28 lights and darks, F1.8, 10", ISO 400, and stacked in sequator. The raws were much more stable. I appreciate all the advice. Link to comment Share on other sites More sharing options...
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