mattchase

I currently have a wireless pinhole camera that does a decent job, but I notice it often is either too bright or too dark in it's exposure. I can turn the brightness up or down on my capture software, but that doesn't really solve the problem as I would have to do this constantly while flying (I'm not that good!). The picture is pretty good when the exposure is right, and I'm sure that part of the problem is that I am in the desert where my ground is very light in color causing some of the exposure problems.

But I also wonder if the pinhole lens is part of the problem. Would you guys say that a normal lens camera is more tolerant to wide exposure latitudes in a scene and picks the correct exposure more often? Or do you think I would have the same problems even then? I know you can do this with a real video camera, but are there any micro cameras that you can set the exposure manually preflight, so that it doesn't change while in the air?

Or maybe I should just move!

Thanks

Troglotech

The problem is not with the lens but with the sensor itself, I would guess that you are using one of the CMOS cameras that are prevalent in the market at the moment. This model of CMOS sensor (usually an Omnivision device) has quite poor dynamic range which means that if you have an area of the picture that is well illuminated (like the sky) the rest of the picture becomes under-exposed and dark. This is due to the underlying structure of the sensor and it's inability to cope with high light levels.

Most CCD cameras, on the other hand, can readily accept a high illumination level in half the picture and still provide a well-exposed picture in the other half. This is because the device has a good dynamic range and can accept the high level of illumination without 'throwing away' the charge accumulated in the less-exposed portion.

The CMOS cameras also have another limitation which is the number of different 'shutter speeds' (i.e. the number of different charge-accumulation periods per frame) available. Quite often, in bright sunlight, the sensor will reach a point where only the fastest 'shutter speeds' are acceptable, at the fastest shutter speed the picture is too dark, and on the next lower 'shutter speed' the camera is over-exposed. This is the bane of CMOS cameras on bright days where the whole video is spoilt by being too dark, the only way around this is to use an ND filter in front of the lens (ND 1 works well). Without the filter the best pictures can be obtained by pointing the camera downwards so that the sky takes up a very small proportion of the overall picture.

However, you should get a better picture with a standard lens rather than the pinhole types. The pinhole lenses tend to have poor resolution around the edge of the picture. What you will find though, is that standard lenses will not fit most CMOS cameras that are supplied with pinhole lenses. This is because the 'back focal distance' of the pinhole lenses are very short (as small as 2mm) wheras the standard lenses are usually much longer. This means that by the time you have screwed in a standard lens the camera is well out of focus and screwing the lens further in only makes it worse!

mattchase

Thanks for the info, I figured it had something to do with my camera. I do believe it is a CMOS sensor, so will make sure my next kit is CCD.

Joe Bennett

Troglotech,

Can't really lay full blame on the type of sensor, CCD or CMOS. Many of the high end digital cameras today actually do use a CMOS sensor. Example would be the Canon EOS 20D which is an 8.2 megapixel digital SLR camera. ISO's on this range from 100 to 1600, and even up to 3200 on its extended modes. Top shutter speed is 1/8000 second too. The main reason that low end CMOS sensors have less dynamic range is that they are scanned differently than CCD sensors are. They are also used more in cheaper cameras because they actually are much cheaper to manufacture. Just wanted to point this out. Good info though Trog, and thanks..............Later............

Joe

Troglotech

No problem Dark Overlord!

I am actually reffering to the type of CMOS sensor fitted to the very abundant pin-hole cameras that are currently in the wireless market. I've designed three commercial cameras that are built around the Omnivision CMOS sensor (OV7910), for exactly the same reason as the wireless camera manufacturers do...they are cheap and all the processing is done on-chip....i.e. you stick 5V, a crystal and a few capacitors on one and you get composite video out the other end! For those reasons they are brilliant. They take very little current (25mA) and are very small 19mm x 19mm.

That said, they do have their limitations, unlike a CCD sensor, the Omnivision CMOS sensor has a transistor per charge well (wheras the CCD sensors have a bulk substrate where the charge is sheparded by electrodes) and this limits two things, the active 'light collecting' area and the ability to store bulk charge....hence the limitations in dynamic range.

You are absolutely right when you mention that it is wrong to say that this is true for all CMOS sensors....it patently isn't. In fact, I would go as far to say that in the photographic field (non-streaming video) the CMOS sensor is well ahead on points. There will certainly be a point where CMOS is the way to go for video, they have already managed to manufacture single pixels that are full-colour spectrum (i.e. each pixel gives a full colour output). However, the CMOS sensors used in high-end photographic equipment are not the same as those used in wireless video. All post-processing in photographic cameras is done off-chip just as in a CCD sensor, the only difference is that the output is digital rather than the analogue output from CCD's. This allows high-end CMOS sensors to have almost the same bulk-charge carrying ability as the CCD's and following on from that....the same dynamic range

All that said, the OV7910 has a lot going for it...here is a comparison, the bits on the left constitute a CCD camera including processing into analogue video via a DSP, the bit on the right is a complete CMOS camera including lighting and video buffering!

Joe Bennett

Trog,

Thanks! I appreciate the added info you have posted. Too many people, it seems, just go by the "party line" regarding CCD vers. CMOS without actually knowing the facts. I do use both types myself, as I am sure many others do to. I just hope that someday soon, even though we are such a small portion of the marketplace, a manufacturer will see the benefit to producing a camera system that is niche designed for our AP type of usage.We can only hope I guess. Again, thanks for taking the time to discuss the differences. Later..............

Joe

Troglotech

My pleasure Dark (may I call you Dark, Overlord).....!

And a camera made for AP? How about a 5-hour duration LiPo camera with 4 channel outputs?
Yes....that's the whole camera and transmitter....I just Velcro it to whatever I'm flying!
Oh.....and it weighs 1 ounce!

Jetset

My Feedback: (2)

Trog,
What's the info on that sweet little camera unit???
Myles

Troglotech

Yes, it IS a sweet little thing that's for sure. It's a standard CMOS pinhole camera but fitted with an elongated body with a LiPo battery and charge circuit built-in. It's also got audio. I bought a hand-held receiver at the same time that matches the four output frequencies which also has a LiPo and charger circuit with a built-in LCD unit. Both the camera and receiver came with wall chargers, the camera lasts 5 hours on a charge and the receiver 2.5 hours....fortunately the receiver came with two LiPo's so it lasts as long as the camera.

I was getting fed up of lugging all the usual stuff around, batteries, chargers, inverters, monitors and all the hassle that went with it so I saw this and bought it! Now everything is battery operated including the video recorder. I stick a couple of strips of Velcro to the side of the plane (Challenger at the moment) and have a strip on the sides of the camera, this means I can angle the camera wherever I like which I couldn't do with the 'battery and camera' Ebay purchase I had before. It makes a change to look backwards and see yourself throwing the plane at the start of the video....and it's interesting to watch the Elevons doing their stuff.

I must point out though, this is strictly a fun setup and in no way compares to the great stuff that can be bought from BWAV and others, but it was reasonably cheap and really suits the Challenger and the other RTF planes as it comes....well...ready to fly! It means I can fly at lunchtime and record what I'm doing at the same time (the LCD picture on the recorder shows a Bristol retail park from a lunchtime flight). I now seem to spend my time while I'm driving around thinking about what the scenery would look like from the air...and seeing if there is somewhere to launch and retrieve the plane as it's always ready in the trunk of the car. It also means I can stick some Velcro on my buddies plane and check out his flying!

The only thing I would change is the aerial used in the receiver....it's a bit too feeble, being a simple short wire similar to the one on the camera (I just love to take things apart). My next plan is to fit a whip aerial on the side of the case to get the distance back up to around the distance I got with the 'Ebay' receiver. The LCD is just big enough to remotely fly the plane (I usually stick the receiver on a post or wall) but I prefer the LCD on the video recorder as it's a little bit bigger.

All in all I'm pleased I came across this setup, it really suits my type of flying (lazy RTF stuff), and it's great fun watching those crashes over and over again!

beldraak

That is an awesome camera, where did you find it?

Troglotech

I found him via an Ebay ad for something completely different! (isn't that the normal way)....
He has now started a website that specialises in RTF wireless cameras:

http://www.wirelesscamerashop.com/
[email protected]

I'm not sure that he sells that cameras on their own but it's worth a go......

Jstanzak

The camera and recievers can also be found at www.microwireless.net

Troglotech

I know I have posted this elsewhere....but, here is a very short sample of video taken from this little camera:

[link=http://www.meeknet.co.uk/Hedge_hopping.wmv]Short wirelesscamerashop clip ~3MB[/link]

This was recorded on a small PVR (SD card type), I get better resolution (and bigger files) using the PV 390