Webcam vs. DSLR?

[Ash2020]

Hi All.

I'm fiddling about with a SPC900 webcam that I did the LX mod on, years ago and trying to remember how the parallel port control works. I've got it imaging in daylight through my scope and my first impression was "what an awful picture"

Question is, what advantage does a 640 x 480 webcam have over a 20 megapixel DSLR? Could it be none? If so, I might file it away and just use my Canon for imaging.

Cheers

Andrew

[JemC]

i could be wrong but i think the spc900 would be ok for planetary imaging, if you was looking at doing dso imaging you would be better off with your DSLR

[Mick J]

Philips spc900 is still usb1 and its recommended to use low frame rates for video capture on planets (10fps or less or it gets compressed) for long exposure deep space it should be good for long exposures (you have the mod) and stacking of subs, there must be recommendations somewhere for this.

Depending on what dslr, you may be able to save short video for planets as above and take long exposure subs for stacking on deep space objects. The software and approach is different for planetary and deep space, your cameras may do both. Hope this is helpful, what canon are you thinking of.

[riklaunim]

SPC900 is an old webcam with an old sensor - not that efficient for planetary imaging. Nowadays dedicated fast planetary cameras are used. DSLR can be an entry into DS imaging, and much less into planetary imaging. Choose the camera to you imaging interests - either planetary camera, DSLR or DS camera (or one of the latest quasi-universal dedicated planetary camera capable of DS imaging).

[Ash2020]

Thanks for the replies. The question really was - isn't a 20 megapixel big sensor always going to be better than a 640 x 320 small sensor, whatever the application?

I have a Canon 550D and a full spectrum modded 500D. About to try some comparisons, but I believe the modded one may have some dust on the sensor.

Thanks

Andrew

[happy-kat]

Lucky you 550d great for both because it has video crop mode so gives better image size for planets when compared to other dslr.

[Davey-T]

You don't need a big sensor to image tiny planets, just end up with a spot in the middle.

A small number of DSLRs can do 640X480 1 to 1 video mode 60fps which works for planetary, there is a long thread on it somewhere if you do a search.

Dave

[RikM]

12 minutes ago, Ash2020 said:

Thanks for the replies. The question really was - isn't a 20 megapixel big sensor always going to be better than a 640 x 320 small sensor, whatever the application?

I have a Canon 550D and a full spectrum modded 500D. About to try some comparisons, but I believe the modded one may have some dust on the sensor.

Thanks

Andrew

A huge DSLR sensor is a waste of processing power on an object that only covers a few hundred pixels in the middle of the frame.

[Ash2020]

2 minutes ago, happy-kat said:

Lucky you 550d great for both because it has video crop mode so gives better image size for planets when compared to other dslr.

But its really annoying for the moon, it just clips a bit top & bottom!

6 minutes ago, Davey-T said:

You don't need a big sensor to image tiny planets, just end up with a spot in the middle.

A small number of DSLRs can do 640X480 1 to 1 video mode 60fps which works for planetary, there is a long thread on it somewhere if you do a search.

Dave

Sorry Dave, if I'm being dim, but if the spot you're trying to image is covered by 100 pixels, isn't it going to be a better result than if it is covered by 10 pixels?

Andrew

[Davey-T]

27 minutes ago, Ash2020 said:

But its really annoying for the moon, it just clips a bit top & bottom!

Sorry Dave, if I'm being dim, but if the spot you're trying to image is covered by 100 pixels, isn't it going to be a better result than if it is covered by 10 pixels?

Andrew

Not really, imaging planets is better done at a fast frame rate as they're generally fuzzy bouncing balls so you need to freeze a few thousand images and then sort out the best to combine.

Have a go with you're 550d in crop mode video and normal sensor to compare them.

Dave

[Ash2020]

5 minutes ago, Davey-T said:

Not really, imaging planets is better done at a fast frame rate as they're generally fuzzy bouncing balls so you need to freeze a few thousand images and then sort out the best to combine.

Have a go with you're 550d in crop mode video and normal sensor to compare them.

Dave

Thanks Dave. I will try it.

Andrew

 

[Davey-T]

There you go Andrew, if you've got an hour or two to spare 

Dave

https://stargazerslounge.com/topic/208610-planetary-imaging-with-dslr-video-mode/

 

[Ash2020]

24 minutes ago, Davey-T said:

There you go Andrew, if you've got an hour or two to spare 

Dave

https://stargazerslounge.com/topic/208610-planetary-imaging-with-dslr-video-mode/

 

Haha! That's all  I need! Thanks Dave.

Andrew

 

[ollypenrice]

1 hour ago, Ash2020 said:

Thanks for the replies. The question really was - isn't a 20 megapixel big sensor always going to be better than a 640 x 320 small sensor, whatever the application?

Andrew

No. The number of pixels is, of itself, entirely meaningless. The meaningful statistics are chip size and pixel size. If you are into fast frame imaging you need to add download speed (frames per second.)

In deep sky imaging (my thing) you are interested in pixel size because this decides your sampling rate, or pixel scale, in arcseconds per pixel. This should be matched with your seeing and guiding. If both will support a rate of one arcsecond per pixel or better then go for it. But they may not, in which case you'd do better with bigger pixels. You wouldn't lose any detail and you'll get more light per pixel. And then, alas, nobody makes very big CCD sensors with very small pixels so if you want a big CCD sensor you have to put up with pretty large pixels. Clearly chip size determines field of view for a given focl length.

There is a daytime camera shorthand which uses pixel count to mean resolution. This is simply wrong. Resolution in AP is measured in arcseconds per pixel. Field of view, at a given focal length, is governed by chip size. We shouldn't muddle them up.

Lots of DSLRs with small pixels have a video capture mode which is speeded up by not downloading the whole chip but only a crop from it. This gives you a faster frame rate which will be interesting for lunar/planetary. I don't know the camera models or details but only that priniciple. In fast frame imaging you can 'beat the seeing' by stacking only a proportion of the stills captured in video mode, so using only those with fluke-good seeing. I wish we could do that in deep sky imaging...

Olly

 

 

 

[Mick J]

"The software and approach is different for planetary and deep space, your cameras may do both."  looks like the 550d will be good for both