Is a Webcam Better than a DSLR for Astrophotography?

[Cranfieldstar]

Hi,
Recently started with astronomy with a basic 5 inch reflector, not motorised but interesting initial explorations. Subsequently became interested in trying to take pictures of the moon, saturn and then onto Jupiter. Found through utube that you can modify cheap webcams and in combination with registax etc and a £12 HP HD 2200 webcam managed an image of Jupiter with a little band detail on it. After much debating coughed up £300 for a canon 1100 DSLR and have replaced webcam with the camera body only on t-piece with the same barlow used with webcam , I think initially assuming I would be able to get better image detail, but I think I have fallen foul of the relative CMOS sizes in the two cameras. ie although the camera is 12MP, the sensor size is 22x14 mm approx compared with the cheap webcam which is lower pixels but on a much smaller sensor maybe 3 x 2mm . Consequently even if I use a better barlow than I have at present (2x), the final image will always be better from the webcam I believe because the Jupiter image is activating more pixels in the webcam than the camera. Am I correct?
(I accept the DSLR is good for wide view long exposures, so not completely waste wasted £300).

 

[russ_watters]

Welcome to PF!

If it is planets that you want to take pictures of, then the only modification you need to make to a webcam is to remove the lens and attach an eyepiece socket adapter.

Webcams are superior to DSLRs for imaging planets because they easily produce video clips, directly on your computer, with potentially thousands of individual, raw images that Registax can utilize to build a single high quality image.

Image scale, however, can be corrected by changing the Barlow. The thing is, the optical resolution of a planetary image captured by an amateur telescope is pretty small, so you don't need to (and it is better not to) span too many pixels. The actual image of Jupiter only needs to be about 100 pixels across. And the fewer pixels you span, the brighter the image can be.

 

[chemisttree]

You need to get exact measurements to be sure but yes, the camera with the smallest individual pixel elements will give you the best digital resolution. Webcam can be better than the DSLR because you can capture many images over a very short time and reduce noise post processing with Registax. That's a little more difficult with the DSLR.

 

[Drakkith]

The are of the sensor that the image falls on doesn't really matter. The number of pixels the image falls on is far more important. I say this because small pixels are generally better than larger pixels for getting small details on bright objects such as planets. As Russ and Chemistree said above, the number of exposures you can get can have a great effect on the final image quality.

 

[Cranfieldstar]

Cheers for all replies.
I think basically the webcam pixels individual areas are approximately half the size of the DSLR, but will perservere with the DSLR, because it took three nights with the webcam to get the brightness and contrast settings set so that I could make out some detail in the video image which then subsequently developed a better stacked image. Only shot one video so far of Jupiter with the DSLR. The DSLR (canon EOS) I have can be controlled from the computer, so its video does store directly if necessary. Just have to sort out conversion from mov to avi to load into registax, or if anyone knows is there a software which will just break the mov file down into a batch of stills I can load into registax.

 

[russ_watters]

Can the DSLR send uncompressed video? For stacking, compression has a huge impact on quality. I use a DMK camera, which is basically a specialized for astrophotography webcam and as the resolution is increased, framerate drops due to bandwidth limitations.

 

[Cranfieldstar]

Hi Russ,

Unfortunately, I don't have any control over the camera video output. Its either set to 25 or 30 fps. So far I save the video on the camera and then transfer across once back in the warm as I've not ventured out with laptop attached to the new DSLR. The camera does have a live view option which allows objets to be enlarged 10x on the camera screen so sharper focusing can be achieved and maybe better contrast setting before shooting the video which will hopefully give a better success rate.
Also because I just modified a standard webcam, the webcam only has the option of 25 to30fps control(I think).
Have seen that you can get specialised webcams eg (celestron nexstar) which I think allow you to set the frame rate to lower levels which I had read can improve the eventual stacked image.

CRanfieldstar

 

[sophiecentaur]

It can't be a matter of superior performance by a cheap and nasty webcam (even the noise performance will be poor compared with a good camera sensor). It must just be the way the optics, with no modification, are presenting a more compatible image to the Webcam.
Anyone with a good telescope and DSLR has already spent loads of money. They should be able to bring themselves to get hold of the appropriate optics that will get the best out of the two. Can it be more than just a matter of looking at the real image that the telescope is producing with a lens with the appropriate focal length that will 'fill' the field of the DSLR array?
A Webcam lens will be only about 4mm (?), which gives it an advantage but you can get DSLR lenses down to 14mm focal length for not a lot and 10mm for a bit more money.
It wouldn't need to be top quality, I think. But, for a couple of hundred quid (possibly a bit more, on reflection but what the hell), a suitable OEM could be found for all the good camera makes. You would then have most of your 16MPx or whatever, to play with - perhaps enough to show up all the inadequacies of your objective lens - you can't win.

Have I missed some 'clincher' factor that still gives the webcam an advantage?

 

[Drakkith]

If the webcam has pixels half the size of the dslr, then perhaps its getting better resolution if the optics allow? Also, are you shooting at prime focus? IE you don't have an eyepiece between the imager and the telescope.

 

[sophiecentaur]

I was amazed to see just how cheap these Barlow lenses are on the net. That is compared with 1.4X and 2X teleconverters for camera lenses. Why is this? I should have thought that IQ was just as important in astronomy as in normal photography.

Also, on this thread, people seem to be making the same old mistake of confusing the pitch of the sensor pixels with the quality of picture obtainable from a camera. Is there a difference in the astronomy context as well? A 'sucked acid drop' in place of a lens will never give good IQ and I know there are some ghastly webcams about - claiming HD resolution.

I recently looked at some not-cheap birding telescopes and was staggered at the absolute rubbish image quality you get for your money. Consequently, I decided not to bother and to stick with my binos. However, I did subsequently buy a Kenko Lenscope which I can mount on my high quality Pentax tele lens and the results are stunning, with good contrast and low CA. I can't believe that telescope users screw a different set of eyes on when they move from telescoping and photographing. What's up? CAn someone put me right, here?

 

[Cranfieldstar]

Hi Sophie, and Drakkith,
Am shooting with a 2x barlow in but no eyepiece which I think is prime focus in both webcam and dslr case. I removed the lens from the webcam as suggested by other sources, and just use a tpiece and ring to hold the dslr body on the scope..
So if there is a way I can get the fully focused image of Jupiter falling across all the whole sensor of the dslr then that would be ideal I suppose. At present the size of the image falling on the sensors must be about 1/30 of the webcam sensor and 1/500th of the dslr sensor, but as both are recording in HD which is about 950,000 pixels, the webcam image is 30000 pixels and the dslr image 1800 pixels.

 

[Chronos]

The pixel density of a decent dslr is so much better than your typical webcam, the only explanation for getting a dramatic result must be magnification and stacking.

 

[Drakkith]

Hi Sophie, and Drakkith,
Am shooting with a 2x barlow in but no eyepiece which I think is prime focus in both webcam and dslr case. I removed the lens from the webcam as suggested by other sources, and just use a tpiece and ring to hold the dslr body on the scope..

Yes, that is prime focus. You are putting the sensor at the focal point of the objective itself.

So if there is a way I can get the fully focused image of Jupiter falling across all the whole sensor of the dslr then that would be ideal I suppose.

You'd have to use a more powerful barlow lens. However I doubt this would do any good. Your telescope being only 5 inches in diameter, you are probably pretty close to hitting your resolution limit anyways, and further magnification won't have any affect. A magnified blurry image is still a blurry image. The only way around this is a telescope with a larger diameter aperture.

At present the size of the image falling on the sensors must be about 1/30 of the webcam sensor and 1/500th of the dslr sensor, but as both are recording in HD which is about 950,000 pixels, the webcam image is 30000 pixels and the dslr image 1800 pixels.

Have you tried taking a normal picture with the DSLR? It' sensor has FAR more resolution than the 1080x720 that the video option records in. I think it may be compressing the video and losing data and resolution in the process.

I tried looking up the specs to the webcam, but couldn't find any details on the sensor size or pixel size. The DSLR has 5.2 micron size pixels, and I could believe the webcam having smaller pixels, leading to a higher resolution. Note by resolution I don't mean the NUMBER of pixels which is usually the case. I mean the image will appear larger on the webcam and MAY capture more detail. For example, an image of Jupiter, when focused through your telescope onto the focal plane, will appear a certain size. If you have a sensor with smaller pixels, which I think someone called higher pixel density, you have the capability of seeing more detail since more pixels will be under the image. It isn't guaranteed that you will get better detail, since as I explained you may be running into the limits of your optics.

 

[russ_watters]

It can't be a matter of superior performance by a cheap and nasty webcam (even the noise performance will be poor compared with a good camera sensor). It must just be the way the optics, with no modification, are presenting a more compatible image to the Webcam.

It isn't superior performance, it is more about features and the particular strengths and weaknesses get flipped due to the unique requirements of the task.

A DSLR can record HD video, but it is compressed. A webcam is lower resolution because it has to transmit the video in realtime and typically uncompressed. In this context, realtime transmission and lack of compression is much more important than resolution.

Anyone with a good telescope and DSLR has already spent loads of money. They should be able to bring themselves to get hold of the appropriate optics that will get the best out of the two.

I've seen hundreds of people's examples of quality amateur photos of planets. I've never seen one do it with a DSLR. I'm not saying they don't exist, I'm just saying it isn't the norm. Few people even attempt it because once they learn about how the photography is done, they realize a DSLR isn't well suited to the task.

A Webcam lens will be only about 4mm (?), which gives it an advantage but you can get DSLR lenses down to 14mm focal length for not a lot and 10mm for a bit more money.

Astrophotography cameras doe not have their own lenses: they have telescopes.

Have I missed some 'clincher' factor that still gives the webcam an advantage?

In short: low resolution and the ability to transmit raw (uncompressed) video in realtime.

 

[russ_watters]

I was amazed to see just how cheap these Barlow lenses are on the net. That is compared with 1.4X and 2X teleconverters for camera lenses. Why is this? I should have thought that IQ was just as important in astronomy as in normal photography.

A teleconverter is a complete optical system whereas a Barlow is not.

A 'sucked acid drop' in place of a lens will never give good IQ...

This is your main mistake: not understanding the optics you're dealing with. Webcam astrophotographers do not use stock lenses on their cameras, they use telescopes. Step 1 in converting any camera to an astrocam is to remove the lens!

I recently looked at some not-cheap birding telescopes and was staggered at the absolute rubbish image quality you get for your money. Consequently, I decided not to bother and to stick with my binos. However, I did subsequently buy a Kenko Lenscope which I can mount on my high quality Pentax tele lens and the results are stunning, with good contrast and low CA. I can't believe that telescope users screw a different set of eyes on when they move from telescoping and photographing. What's up? CAn someone put me right, here?

I'm not sure what you mean there. Good telescope optics are of exquisite quality and they are expensive. How much money are you talking here? Note, though, that mirrors are cheaper than lenses...

 

[russ_watters]

So if there is a way I can get the fully focused image of Jupiter falling across all the whole sensor of the dslr then that would be ideal I suppose.

You don't need or want that. The optical resolution of your imaging system is nowhere close to high enough for that to be helpful and if you do it, the image brightness will be uselessly low.

At present the size of the image falling on the sensors must be about 1/30 of the webcam sensor and 1/500th of the dslr sensor, but as both are recording in HD which is about 950,000 pixels, the webcam image is 30000 pixels and the dslr image 1800 pixels.

Use the native resolution. For the DSLR to have a resolution that low, it would need to group pixels together with software and you don't want that. You are much better off shooting the native resolution and cropping the result. For the webcam, if its native resolution is lower, it will upscale with software, which is even worse.

 

[russ_watters]

The pixel density of a decent dslr is so much better than your typical webcam, the only explanation for getting a dramatic result must be magnification and stacking.

And realtime uncompressed transmission of the images. The high pixel density (total resolution) is not a benefit here. At best, it just gets in the way by making it difficult to use the images.

I can't overemphasize how big of a problem too much resolution can be: I start with TEN GIGABYTES of data to get one photo of Jupiter, which takes an hour to whittle down. Why would I want fifty more gigabytes of blackness?

People tend to be shocked at just how low the resolution is on astrocams. My planetary camera is .77 MP and my deep-sky camera is 1.4MP. The deep-sky is a touch on the low side, but the planetary is perfect.

One thing to remember about non-dedicated astrocams is they all have filter matrices on them that make the effective resolution about 1/3 of what is advertised.

I use the 1024x768 version of this camera: http://www.optcorp.com/ProductList.aspx?uid=319-320-1214-1285
Note how the framerate drops as the resolution increases...

 

[russ_watters]

Also: Jupiter is 40 arcsec across and the best amateur telescopes have a resolution of about 0.1 arcsec. So you really don't need Jupiter to span more than about 400 pixels.

 

[sophiecentaur]

A teleconverter is a complete optical system whereas a Barlow is not. This is your main mistake: not understanding the optics you're dealing with. Webcam astrophotographers do not use stock lenses on their cameras, they use telescopes. Step 1 in converting any camera to an astrocam is to remove the lens!
I'm not sure what you mean there. Good telescope optics are of exquisite quality and they are expensive. How much money are you talking here? Note, though, that mirrors are cheaper than lenses...

Thanks for that info (and the other posts). What you say makes a lot of sense; every field of study has its own wrinkles and you are setting me straight.
The birding telescopes I was looking at were less than £1k but not much less. I appreciate that birders are likely to be far less techie than astronomers so they may just not be so fussy - things like weatherproofing being possibly more important for (foul weather) birding than (essentially fair weather) astronomy.

I need to re-think my ideas about using cameras with telescopes. I was clearly 'raving' to suggest that the camera lens would replace an eyepiece as you are looking at a virtual image in an eyepiece and you need to project a real image with a camera. (though, why not use an eyepiece and then photograph what you would 'see'? I guess that would involve more glass in the way - not a good idea when contrast and low flare are seriously important in astronomy. However, I don't actually understand why the best solution appears to be just to use the native resolution. I think I understand what that means - just projecting the image from the objective (+barlow) onto the sensor?. Surely it must be possible to improve on final quality by processing images where the samples (pixels) are more dense (i.e. using more of the image array). I appreciate that the flux arriving at each pixel would be less but the processing would take care of that.

 

[sophiecentaur]

@russ
I looked at the web page with the CCD arrays and they are more like the sort of price I'd expect to pay for serious imaging. More than your average webcam!
So you astronomers really do have to be stinky rich, as with all serious pastimes! I pour all my money down a boat-shaped hole instead.

 

[russ_watters]

Well... Skill is important. There are guys using normal webcams who have gotten better results than me.

Native resolution is 1 pixel on the ccd = 1 pixel on the screen. You don't want the camera intepolating because it can mess up the data.

 

[Cranfieldstar]

Cheers Russ, But when you say span 400 pixels, do you mean an area of 20 x 20 pixels, or do you mean a linear dimension of 400 pixels, so Jupiter actually falls over an area of approx 400 x400 pixels (160,000 pixels).

 

[russ_watters]

400x400

 

[sophiecentaur]

Also: Jupiter is 40 arcsec across and the best amateur telescopes have a resolution of about 0.1 arcsec. So you really don't need Jupiter to span more than about 400 pixels.

Cheers Russ, But when you say span 400 pixels, do you mean an area of 20 x 20 pixels, or do you mean a linear dimension of 400 pixels, so Jupiter actually falls over an area of approx 400 x400 pixels (160,000 pixels).

Those sums, above, give you your answer.
But I can't help feeling that 400pxl linear gives you no chance to do really smart sharpening or any of the other clever enhancements that over sampling would allow. It must be a matter of optimum practice, based on lots of factors.

 

[russ_watters]

Those sums, above, give you your answer.
But I can't help feeling that 400pxl linear gives you no chance to do really smart sharpening or any of the other clever enhancements that over sampling would allow. It must be a matter of optimum practice, based on lots of factors.

For Jupiter, it wouldn't hurt to double that since it is so bright. Oversampling may help a little since the pixels are square.

Other problems do creep in though: Planets won't stand still in the frame so you need to actvely track it. Saturn is dim enough you'll start needing longer exposures, which make atmospheric blurring worse.

 

[russ_watters]

Looks like I misremembered the resolution: I just looked it up and my C11 has a max resolution of about 0.4 arcsec. I checked one of my photos and Jupiter is 300 pixels across, so I'm oversampled by a factor of 3.

Another issue to consider though: Image scale for focusing and viewing on a monitor.

There are a lot of resolutions to consider:
-Sky
-Telescope
-Camera
-Monitor
-Eye

 

[sophiecentaur]

Whaaat?
I can't quite read that word on the bottom. It's gone all blurrry.

 

[digitaldave]

About the 2 image sensors, webcam vs DSLR.

The telescope generates a full image format roughly the same size of the webcam, filling the entire surface of the chip with light. The DSLR sensor cannot be filled with the image the telescope creates because its sensor is too big.

Thus a mismatch, much like trying to mount a 110 CAMERA sized lens (0.51 inch × 0.67 inch negative/sensor format size) on a medium format camera (2 1/4 inch x 2 1/4 inch negative/sensor format size).

The light transmitted by the telescope couldn't fill the DSLR sensor with light, only filling a very small area of the sensor thus creating an extremely tiny image.

*There are many size formats on DSLR's made today.

http://en.wikipedia.org/wiki/Image_sensor_format.

 

[sophiecentaur]

I have a feeling that this effectively boils down to 'f number', used all the time in photography. For a bigger sensor area, you need a bigger aperture for the same field of view and the same 'exposure' if the sensor elements have the same sensitivity / noise performance. Obviously, the purpose designed astro cams will have been optimised for sensor area, compatibility with available apertures and focal lengths and there is a huge advantage in not having colour filters there when you don't actually want them. Also, they are incredibly neat little things that fit on the telescope very comportably.
I would love to have a good telescope - even if only to sit there and admire / stroke it. But it is in a queue, after a new marine diesel engine and a few other expensive bits of kit.

 

[Drakkith]

About the 2 image sensors, webcam vs DSLR.

The telescope generates a full image format roughly the same size of the webcam, filling the entire surface of the chip with light. The DSLR sensor cannot be filled with the image the telescope creates because its sensor is too big.

Thus a mismatch, much like trying to mount a 110 CAMERA sized lens (0.51 inch × 0.67 inch negative/sensor format size) on a medium format camera (2 1/4 inch x 2 1/4 inch negative/sensor format size).

The light transmitted by the telescope couldn't fill the DSLR sensor with light, only filling a very small area of the sensor thus creating an extremely tiny image.

If the two devices have the same pixel sizes, then the image of Jupiter will be the same. What does change is how many pixels just see black and don't contribute to the picture at all.

 

[russ_watters]

About the 2 image sensors, webcam vs DSLR.

The telescope generates a full image format roughly the same size of the webcam, filling the entire surface of the chip with light. The DSLR sensor cannot be filled with the image the telescope creates because its sensor is too big.

There are plenty of people who use DSLRs at prime focus for astrophotography with little or no vignetting. How a Barlow changes the light cone I'm not entirely sure, but it should widen the cone unless the internal structure of the barlow cuts part of it off.

 

[russ_watters]

I would love to have a good telescope - even if only to sit there and admire / stroke it. But it is in a queue, after a new marine diesel engine and a few other expensive bits of kit.

[shrug] Sounds like a problem of improperly conceived priorities to me.

Still, a local star party through an astronomy club or college would at least allow you to see what all the hubbub is about.

 

[Drakkith]

I have a feeling that this effectively boils down to 'f number', used all the time in photography. For a bigger sensor area, you need a bigger aperture for the same field of view and the same 'exposure' if the sensor elements have the same sensitivity / noise performance. Obviously, the purpose designed astro cams will have been optimised for sensor area, compatibility with available apertures and focal lengths and there is a huge advantage in not having colour filters there when you don't actually want them. Also, they are incredibly neat little things that fit on the telescope very comportably.

Actually the F ratio only really affects the exposure time. Big sensors are generally used equally as well on fast and slow scopes. However vignetting can become a major issue in some types of scopes when you use large sensors. Field of view is completely dependent on focal length, not aperture.