Cleaned Low Pass Filter

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augusthouse
Posts: 1195
Joined: Sat Sep 16, 2006 1:39 am
Location: New South Wales Australia

Cleaned Low Pass Filter

Post by augusthouse »

Just cleaned my low pass filter for the first time.

Set my camera to f22 and under room lights photographed a piece of white paper that I was moving in front of the camera and exposed for 1.5 secs.

Is this what it should look like?

Image

Giottos Rocket Blower worked well, until I had a closer look at f32 on the Micro Nikkor. The 'welded' dust was scary (I didn't keep the 'before' image). :evil:

I purchased my D100 S/H so I don't know if the sensor filter was ever cleaned, and with all my playing around with bellows and lenses it's no wonder there was dust.

Looks like mission accomplished to me; but as I said this was my first time. :twisted:

Photoshop file here here

Craig
To use a classic quote from 'Antz' - "I almost know exactly what I'm doing!"

rjlittlefield
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Post by rjlittlefield »

I'd be a lot more convinced if your image was not pure white (255,255,255).

Since it is, I'm thinking "bloomed and blown", in which case small spots of dust will just disappear.

Crank your exposure down to a light/middle gray, and see what it looks like then.

--Rik

augusthouse
Posts: 1195
Joined: Sat Sep 16, 2006 1:39 am
Location: New South Wales Australia

Post by augusthouse »

Thanks for the tip Rik.

Yep, there is still a few still on there.
I count 21. They are easier to detect if I apply auto contrast or auto colour in Photoshop and then use the zoom tool.

*Later note: I'll give it another go with Sensor Swab and then Dust-Aid tomorrow. :twisted:

All these images were shot in jpeg - 'fine' which might explain some 'noise'.

This one, same proceedure: 1/5th of a second.

Image


This one at 1/2 second.

Image


Craig
To use a classic quote from 'Antz' - "I almost know exactly what I'm doing!"

rjlittlefield
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Post by rjlittlefield »

Only 21, eh? That's not bad for a camera that was awful and only got cleaned once.

The remaining dust is not very obvious either. In the images you've posted, I can only see a couple of them by naked eye, at coordinates [479,505] and [575,73]. By pulling your image into Photoshop and doing the auto-contrast trick I can see about half the rest. Using levels adjust instead of auto-contrast also calls attention to a couple of hot pixels, at [778,264] and [783,454]. Hot pixels become worse with longer exposures. My camera has one that gets pretty ferocious around 1 second.

It would be an interesting experiment to compare images shot raw and JPEG under these conditions. The big difference I see with my camera (Canon 300D) is in color rendition in the shadows. Shooting the same scene in raw and JPEG, then level-adjusting to bring out shadow detail, the camera's JPEG will have very obvious color streaking in what should be smooth dark areas. It would be a mistake to blame the JPEG format for this, however. Converting the raw image in Photoshop, then having Photoshop save it as JPEG, produces a JPEG image that is the same size as the camera's but does not develop color streaks when level-adjusted. Apparently the problem is that the camera's raw conversion and/or JPEG compressor is not nearly as good as Photoshop's. Another difference is that in raw the hot pixel is exactly one pixel, where with JPEG the defect tends to spread to a few neighboring pixels.

Oh, BTW, one more trick... Image defects like dust and posterization become much easier to see if you grab the window with your mouse and move it slowly around the screen. This separates image features from dust and streaks on the screen.

--Rik

augusthouse
Posts: 1195
Joined: Sat Sep 16, 2006 1:39 am
Location: New South Wales Australia

Post by augusthouse »

Thanks Rik,
I'll look into doing the JPEG v RAW comparison.

In regard to cleaning the low pass filter; it's a bit like digging a hole in dry sand - just as much goes in as comes off. The 'welded' dust appears to be off, but under such close scrutiny I sometimes wonder if I have achieved much. Is such close scrutiny necessary??

I was trialing Sensor Swab - Eclipse and Dust-Aid - both ludicrously priced.

*Later Note: So the trick is to ditch the expensive Sensor Swabs and use a MicroTools SensorWand in combination with the Pec*Pads and the Eclipse solution that is compatible with your DSLR.

More info at the link below. There are a number of pages attached to this site. The most important ones are Methods and also Precautions. Look for menu top-right.

http://www.cleaningdigitalcameras.com/index.html

Craig
Last edited by augusthouse on Sun Mar 30, 2008 12:11 am, edited 3 times in total.
To use a classic quote from 'Antz' - "I almost know exactly what I'm doing!"

rjlittlefield
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Post by rjlittlefield »

augusthouse wrote:Is such close scrutiny necessary??
In my personal opinion, no.

Dust happens.

I've even had dust spots appear suddenly part way through a stack. (See http://www.photomacrography.net/forum/v ... php?t=4461, last paragraph of the first posting.)

I do have one of those fancy cleaning kits with Eclipse and Pec*Pads , and I'm glad that I do, but the fact is I don't use it very often -- maybe twice a year. The rest of the time, I just use an air blower.

Yeah, my images straight from the camera usually have a little dust in them. In most cases, if the spots are easy to see, they're also easy to touch out. And the problem is hugely less than what I used to get with printing from film, where dust spots were both obvious and difficult to retouch. So maybe it's a feature of my upbringing, but I find that dust is a small problem compared with all the others I wrestle with.

--Rik

augusthouse
Posts: 1195
Joined: Sat Sep 16, 2006 1:39 am
Location: New South Wales Australia

Post by augusthouse »

Just thinking...

A fixed lens camera doesn't have that much of a problem with dust. A DSLR does because of its ability to allow for interchangeable lenses. The low pass filter is set back just infont of the sensor.

Has any company ever attempted to make a DSLR that has a 'seal' made of similar material to a low pass filter that forms a shallow recessed 'cup' just behind the lens fitting that shields the inner body of the DSLR and affectively seals it from outside contaminants without effecting image data reaching the sensor or interferring with the changing of lenses?

Or a type of shallow extension ring with an optical glass insert (removable, cleanable and replaceable) like a filter - that still enables AF functions and to which the lenses are connected, again affectively sealing the inner mechanisms from external contaminants?

I think that's worth exploring.

Craig
To use a classic quote from 'Antz' - "I almost know exactly what I'm doing!"

augusthouse
Posts: 1195
Joined: Sat Sep 16, 2006 1:39 am
Location: New South Wales Australia

Post by augusthouse »

Something like this with the inclusion of AF connects; but without correctional optics.

Image

Craig
To use a classic quote from 'Antz' - "I almost know exactly what I'm doing!"

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