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Issue : How can I evaluate my cameras performance synthetically?
Scenario : Bought a Nikon D3100 an year back. Photos looked good enough. The camera fell, zoom lens effected. But works. Cleaned lens using soap, water etc. Carefully. Now photos look much worse.
How do I know if Photos are really bad? Is there a tool?
Sample Photo
Now (Bad) Photo in Picasa
Original (Good) Photo in Picasa
Please help me realize whether my camera has gone bad. Can you tell your personal opinion also?
What lens was it? Do you have other lenses to test?
I'll start off by saying that the "good" one does look a little sharper than the "bad" one, but I'm not sure of settings or lens type. And as Matt said, there are many variables.
If you have another lens, try to test it out at similar focal lengths.
If not, ensure that the lens is cleaned properly. Soap can leave residue and result in 'Days of our Lives' images. (Frosty & soft. Sometimes this is intended and people actually make the lens smudgy). Use cleaning alcohol. Acetone diluted to water, 50/50 is fine. (This can sometimes be contentious as people will say it will ruin and remove the coating, but this won't. I know of a solvent called X55 which works really well and doesn't need diluting.)
Make sure VR is turned OFF and reset the camera through the user menu. Use a tripod or stable surface and move the lens to Wide. Because the sample you gave are reasonably wide, do this on a sunny day, outside. Take a shot at open aperture, then one at f16 (depending on lens, open aperture maybe over exposed).
Then zoom to Tele and do the same. One at open, one at f16.
If they look different, then it shouldn't be a problem. If they both look the same then there could be a problem. It's really hard tell as you might be more familiar with the lens than myself but these simple tests could help.
You might find that the problem is only at wide.
If you're still unsure, take it in for a service/inspection.
Let us know how it goes.
Trying another lens is the best way to test if the lens or the camera is the problem. As far as a drop goes, lenses are the most fragile component. They are likely to either break outright or have minor alignment issues after a fall. The upside is that a decent lens can have the alignment adjusted, but the bad news is that it requires specialized equipment to do properly, so it'll require sending the lens in to be serviced if there are issues.
The camera itself is much more likely to break outright or work fine. The sensor could be knocked lose, but that would be pretty obvious from skewed images, screens could break, but again, that would be obvious since it simply wouldn't work. The biggest danger to solid state electronics from a drop is that connections break and then they simply wouldn't work outright.
As for using soap on the lens, that was a big mistake. You never want to use anything that will leave a residue or be abrasive on optical glass and soap does both. Always use clean, dry, microfiber cleaning cloths and bulb air dusters (the ones where you squeeze the bulb to blow air out) when cleaning lenses in order to avoid damage. If you absolutely must use liquid to get something off, distilled water is best as it will evaporate cleanly and not leave minerals or residue behind. Always be as gentle as possible to avoid scratching or damaging the coatings on the lens which will have a permanent and potentially significant impact on image quality.
If the camera is hurt from the fall it will have features not working at all. it wont degrade the quality - it will stop taking pictures at all, or stop AFing. Your focus screen could be knocked out of place, which could affect AF and your ability to evaluate if the AF was right.
Now, first dropping, and then cleaning a lens with soap can seriously affect your contrast, proneness to flares, and sharpness.
