User talk:Slaunger/Archives/2012/11
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Quantum dots 630 nm pumped with green laser 01.jpg
You said:
Challenging to review, and I have not been in a laser lab for many years, but the detail level is dissapoiting. Then I noticed the aperture f/18(!) For the 500d you begin to be diffraction limited for apertures smaller than f/7.6, and I think you may have degraded the image quality by choosing such a small aperture. Have you tried a larger aperture?
I am wondering where did you get this information about f/7.6 aperture (I think it is related more to the lens than to the camera)? If you are right, than with EF-S 18-135mm f/3.5-5.6 at 135mm I have only four (!) stops of exposure to adjust by means of diaphragm. Isn't it too little? Why is it like this? Then when should I use values from f/7.6 to f/32, which are available?
Regarding the photo - yes, I can try to shoot it again some time. Thank you for your review --Ximeg (talk) 22:58, 15 November 2012 (UTC)
- Hi Ximeg,
- I found the f/7.6 info at www.the-digital-picture.com the Difrraction Limited Aperture (DLA) column in the table there. I am not an expert in this and I would not have dared claim that it was a visible issue at, say f/13. I do think it depends on the lens as well. So the f/7.6 is just an indication of an aperture may diffraction begins to have an impact. But the loss of detail due to diffraction competes with depth-of-field considerations. Thus if you are after a deep DOF because you have several object placed at widely different distances that you want to have in focus, you have to use a smaller aperture as otherwise the blurring due to a too large aperture is much worse than the blurring due to difrraction. So at smaller apertures it is a compromise between the DOF and the difrraction blur. I think these tradeoff concerns makes sense down to about f/20. For even smaller apertures I think the main reason for having those is for cases where you have a lot of light and you want a long exposure time, say if you want to show the motion blur of some objects as not those of static objects - and then live with the diffraction issues. If you reshoot at a larger aperture and get the same kind of quality (I presime you used a tripod or similar), I am proven wrong... --Slaunger (talk) 07:57, 16 November 2012 (UTC)
- Thank you for your response and for pointing to the useful website. According to the images published on the-digital-picture.com this effect really takes place... I am just wondering that usually people recommend to close the aperture when doing the landscape photography, and nobody cares about the diffraction effects! As for me, a long time ago I noticed the strong decrease of quality after, say, f/22. --Ximeg (talk) 10:07, 16 November 2012 (UTC)
- Yes, it is not easy to make strict rules of thumb for this. One indication I have is this FPC nomination I once made for a photo done at f/20, where it was noted in the review that some of the lack of detail in the photo was probably due to a too small aperture. But again, the exact limit, where this gets severe, depends on the type of photo you are trying to take, the sensor, and lens and it may be that I am wrong that f/18 is actually the root cause of the lack of detail in your particular photo. Are you sure there was no vibration of the camera during the 8 sec exposure? --Slaunger (talk) 12:18, 16 November 2012 (UTC)
- Well, I don't remember exactly, but I suppose that I had no tripod at that moment and used standard optomechanics to quicly somehow fix the camera to the optical table. This photo was not intended to be perfect - just to capture some fluorescence and show it to my boss. But I find the idea quite nice, and I think that it is worth to be retaken, isn't it? --Ximeg (talk) 19:56, 16 November 2012 (UTC)
- Indeed, the idea is nice and worthy of a reshoot. There are many great photo oppurtunities in a laser lab - it is a great way to illustrate topics within physics in an interesting and eye-catching manner. --Slaunger (talk) 08:04, 17 November 2012 (UTC)
- Well, I don't remember exactly, but I suppose that I had no tripod at that moment and used standard optomechanics to quicly somehow fix the camera to the optical table. This photo was not intended to be perfect - just to capture some fluorescence and show it to my boss. But I find the idea quite nice, and I think that it is worth to be retaken, isn't it? --Ximeg (talk) 19:56, 16 November 2012 (UTC)
- Yes, it is not easy to make strict rules of thumb for this. One indication I have is this FPC nomination I once made for a photo done at f/20, where it was noted in the review that some of the lack of detail in the photo was probably due to a too small aperture. But again, the exact limit, where this gets severe, depends on the type of photo you are trying to take, the sensor, and lens and it may be that I am wrong that f/18 is actually the root cause of the lack of detail in your particular photo. Are you sure there was no vibration of the camera during the 8 sec exposure? --Slaunger (talk) 12:18, 16 November 2012 (UTC)
- Thank you for your response and for pointing to the useful website. According to the images published on the-digital-picture.com this effect really takes place... I am just wondering that usually people recommend to close the aperture when doing the landscape photography, and nobody cares about the diffraction effects! As for me, a long time ago I noticed the strong decrease of quality after, say, f/22. --Ximeg (talk) 10:07, 16 November 2012 (UTC)
Signature needed
You forgot to put your signature at Commons:Featured_picture_candidates/Image:Berg_Hohenstaufen.jpg. :) JKadavoor Jee 15:21, 18 November 2012 (UTC)
Don't kill the gulls !
- Of course not ! The birds are a recurring problem on the QI page : do we have to clone them out or not ? There's no rule, I think. I noticed them on your picture but I wasn't sure... And, in fact, they're so small and so far, compared to the other ones ! Let's respect wild life... when it's not too wild ! -- Best regards. --JLPC (talk) 20:59, 19 November 2012 (UTC)
Hello Slaunger,
I've reviewed the alternative file and my vote remained same. I overlooked the nomination that it has an alternative file. Thank you fore notifying. Regards, JDP90 (talk) 17:47, 25 November 2012 (UTC)
Hello, can you by any chance give a look at this bot work request? Thanks, Nemo 10:40, 26 November 2012 (UTC)