When should I use the "Bad Focus" button?

Frequently Asked Questions

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When should I use the "Bad Focus" button?

Post by bmendez »

Q: When should I use the "Bad Focus" button?

A: The focus for each movie is determined by an automated microscope that is scanning the aerogel. Sometimes, because of the uneven surface, it has difficulty determining where the surface is and does not focus properly.

The ideal focus situation would be such that the surface is in focus near the middle to upper third of the focus range. Such as in tutorial page 1 (http://anfield.ssl.berkeley.edu:8000/ss ... e_number=1).

Particle tracks will only be visible starting at the surface (not above it) and will remain in focus below the surface. So it is necessary to be able to focus to a reasonable depth below the surface of the aerogel.

If you find a movie where the focus is too high and the surface never comes into focus, then click "Bad Focus." Example: tutorial page 9 (http://anfield.ssl.berkeley.edu:8000/ss ... e_number=9).

If you find a movie where the focus just barely makes it to the surface but does not go far enough below to be able to tell if there is a track or not, then click "Bad Focus." Example: http://stardustathome.ssl.berkeley.edu/ ... e_id=46210

Sometimes the surface is very tilted, but it is still possible to see every part of the field of view below the surface. Click "No Track" or on a track if you happen to see one in the field of view. Example: tutorial page 7 (http://anfield.ssl.berkeley.edu:8000/ss ... e_number=7)

Other times it is so sloped that you cannot get all of the field below the surface. In these cases, click "Bad Focus." Example: tutorial page 8 (http://anfield.ssl.berkeley.edu:8000/ss ... e_number=8)

Occasionally, people come across a movie that has more than one field of view mixed in. As described in the FAQ about this (http://stardustathome.ssl.berkeley.edu/ ... .php?t=469), this is really only a problem if the split happens near the middle of the focus range and prevents you from determining if there is a track or not. If it does prevent you from making a clear determination, then click "Bad Focus." Otherwise click as normal.

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Post by geckzilla »

This really helps. I think I decided my threshold for "Bad Focus" was less than 5 frames of below surface visible.

Occassionally there are also movies which seem to be way too deep too though. One such example is this:
http://stardustathome.ssl.berkeley.edu/ ... e_id=44529

There happen to be a few bogeys there but I just linked it because I have it saved because of them. There are a lot more that don't have anything on them.

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Post by TimStrange »

Thank you for addressing this issue. I think there are two more situations that need to be addressed regarding bad focus:

1. The surface looked like it was just about to come into focus at the top of the slider, which means the entire focal range is within the gel. If it really looks close (just about to come into focus), I've been accepted these as valid and not clicking "Bad Focus"

2. No distinguishing features to be able to tell when the surface is coming into focus. I've been clicking "Bad Focus" on these since I have no idea where the focal range is falling.

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Just below surface

Post by fjgiie »

Hi Tim,

Sounds like to me you know what you are doing. First find out if you are above or below the surface. If just below like you said, look for tracks.
You can also tell that you never quite get down to the surface. This is bad focus.

Now, something to get me in trouble:
If I am a good bit below the surface and know it, I judge the movie.
Another "IF" On the side ways focus where one half is below and the other half is above or unknown. If you see a track, click it. I have been judging movies where there are only 2 or 3 frames below the surface. And boy when there are many surface spots, you have to look at all of them. Hope you keep your %'s up ! Keep on searching


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Post by somepoint »

Hello, I'm new to the forum, but am also getting frustrated with focus movies with the surface too near the bottom, and thinking about all the tracks I might be missing below where I can see!

A suggestion - is there any way you could get people to click on the focus bar to show where the surface of the sample is for each movie, and record the result? This way you will end up with a record of how deep each focus movie goes, and an easy way to go back and decide which to scan again if in future you think you need to look deeper than many of the focus movies go?

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Increasing number of bad focus or bad focus range movies

Post by SG22 »

Is it just me and I hit a large batch of focus movies that have a bad focus range or is there some kind of problem?

Lately it's as if there are more movies with a bad focus range. For the last 30 minutes or so I believe about half of what I viewed had a bad focus range.

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Two minds thinking alike

Post by Bizyfe123 »

I am glad to read what TimStrange wrote. Thank you TimStrange. I have been doing that also, and was wondering if anyone else was. I also have set my own personal level of how shallow I will accept to look for tracks. My personal is right about the down arrow of the focus bars, which is about 6-7 bars of depth focus.

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Post by Wolter »

This thread: http://stardustathome.ssl.berkeley.edu/ ... .php?t=124 describes some of the issues encountered during the processing of an aerogel tile. As you see each tile contains out of focus movies. Processing of the movies is done in batches where one batch contains a complete tile. Only when the number of out of focus movies is to high the entire tile is re-done. When the number is limited, the tile is processed and the movies are presented to the VM. So with a tile which is on the edge of being re-scanned the number of bad focus movies presented can be relative high. Also, due to the random nature of movies being presented to you you can get a large number of bad focus movies in a row.
Just dusting... Image

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Calibration Movies

Post by itzac »

It might be helpful to add Bad Focus calibration movies. They wouldn't need to be scored, just let the user know if they judged right. It could help users to get a more practical sense of what they should or shouldn't try to judge.

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Focus Bars Disappearing

Post by Senator »

I have been having a problem with a number of movies where I am getting a short focus tool. About only half of the focus bars on the right are appearing. The above surface and below surface bars are simply not there.

I tried reloading the page and bringing my curser above and below the focus bars that are showing, no luck. I have been reporting them as bad focus. Can some one explain why this problem is happening?

Thanks 8)

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completely featureless field of view

Post by mmolvray »

I've been having the same difficulty as Tim, above. Some movies don't have a single speck of surface dust or any irregularity. At the actual microscope, you'd know when you were at the surface, but on a monitor, I have no way of being sure whether I'm looking at a truly featureless, in-focus surface, or one where the focus is so far away that nothing shows up.

I've been marking these 'bad focus' but what they really are is 'I haven't got a clue!' What's the preferred way to handle this situation?

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Post by Nikita »

Yes, these are bad focus movies. They could very well be very clean images, but since there are no reference points, we need to have them checked to be sure that there wasn't a problem scanning them.
Good job and Dust On!
From dust we come

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Post by Howie »

Hi All,

And especially the mods and Team...
And NO pointing a finger at anyone!
About Focus???

After all this time I would think that taking pics of the gel would produce better movie quality after all this experience, not to judge, but, in my opinion, there are too, too, many bad focus movies!!!

I rough guess, about 90%!!!
It seems by now I would be seeing some clearer movies and less bad focus?


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Post by DustBuster »

Hi Howie.

I remember this before as well. Remember that each movie covers much less than a freckle, and any imperfection as big as a quarter will result in many movies that are out of focus. There is a process in use that keeps these to a minimum, but nothing's perfect. It seems you just got a lucky batch. Bad Focus reports are just as important as any other in relaying information.. keep up the good work!

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Post by Bram »

Hi Dustbuster,
Just for the record, I must have been swamped by the same lucky batch.
Apres moi la deluge? :wink:

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