modded dslr or ccd

[paul j]

hi all could anyone tell me what's best for deep sky astrophotography a dslr or ccd ? I have a canon 1100d but I also use that for general use so I'm thinking of buying another dslr to mod but now I'm looking at ccd cams there obviously lighter too but more expensive.is there a ccd out there that's similar price to average dslr and that do same job or should I stick with a dslr?

[swag72]

A modded DSLR will give you a better sensitivity than an unmodded one, so certainly better in that regard. If you look in the DSO imaging section, some people are producing excellent DSLR images, with great detail and excellent star colour. Sensor size is an area where the DSLR comes up trumps over CCD's, generally. I say generally as the QHY8 is one APS sensor size OSC CCD that is roughly DSLR sensor sized with a fairly unscary pricetag. That comes in at about £850 I think. If you are thinking of a like for like comparison, based on money in your pocket, then you will not get it in a CCD. The QHY8 is the closest you will get.

Regulated temperature control was a big one for me. With my DSLR in Spain I was finding I was constantly fighting with the noise as the temperatures can be high. Now with the CCD I run it at a very easy 0 degrees through summer and winter and get next to no noise at all.

CCD's though, I think are brilliant for AP and so very versatile. A mono CCD and a full range of filters will set you back a fair bit of money, but the sensitivity you get over the DSLR is well worth it. Narrowband imaging (Ha, OIII and SII) is a joy with the CCD, whereas I always found the Ha filter for the DSLR a little tricky to focus and frame. With added sensitivity, you will collect more data with the CCD than the DSLR in the same space of time and using the same scope.

It's worth looking at CCDCalc or a similar fov calculator to see what field of view you get with different camera combinations on your scope. This was certainly a consideration for me.

From my reading and soaking up of info on here, the DSLR really needs a fast scope to get the best out of it as well. I don't know what scope you are planning to use it with.

If you go down the route of a CCD, then you have then got a further complication of OSC or mono, but that's for a different thread!!

[paul j]

ok thanks I think looking at the price tags it looks like a dslr for now.I wouldn't mind the qhy8 at some point though.I'm using a celestron c8 with a 6.3 reducer.I'm new to this hobbie I didn't realize it be so difficult with the noise problems by having take flat.dark.frames then having to stack etc.I'm learning though and enjoying it.I go pick up dslr and mod it.many thanks.

[Tinker1947]

You well want to consider Auto-guiding, this is used for longer exposures over 60 seconds or there about's depends on your Polar Alignment, and if you have a EQ mount, that's more expense depending on the set-up.........

[Tim]

CCD for me all the way! A Mono one will cost you more with filters and everything, but you get more use out of the skies, as it nearly always brings a full moon out at the same time as the sky is clear, but with a Ha filter you can carry on imaging

[umadog]

It's not so much dSLR vs CCD as CMOS vs CCD. These are different sensor types and pays to read up about them and see what's in the dSLR. I think they're mostly CMOS nowadays. CMOS has image processing functions on the chip. e.g. different gain for different regions (IIRC). CCD does not do this. I think CCD produces less noisy images at higher gains (higher ISO) which is good. Also, it's easier to process the images from CCD, I believe. Google that stuff to check and learn more.

Another thing to consider is pixel size. Over long exposures you will get better results with larger pixels (lower pixel count). The reason is that each pixel is connected to an amplifier and the amplifier adds noise. This is known as "read noise." Larger pixels capture more photons per unit time. As a result, the signal is bigger and so the signal to noise ratio with respect to the read noise is better (larger). dSLRs tend to have small pixels nowadays as marketing departments like high mega-pixel numbers. For astro imaging, though, you will get less noisy images if the pixel count is lower. Here's a discussion: http://astrogab.ning.com/profiles/blogs/cmos-vs-ccd

Finally, cooling the camera will make loads of difference. A CCD in a simple housing may be easier to cool or more come with cooling.

[paul j]

I do guide my scope using a qhy5 camera and my finder is a altair 10x60, so many people seem to have different opinions on dslr and ccd, now ive had chance to look at the prices the dslr comes out cheaper for me,if i could get a ccd camera for same price if probably go for that but then again i got the filters, i was thinking about a canon 450d modded which i can pick up for around £350 like in the previous post by swag the qhy8 is fairly pricey for me but to be honest id pay that if i could get less noise,is there any imaging equipment that virtually has no noise? maybe a daft question but im a newbie

[swag72]

The Sony chip CCD's will give you as noise free image as possible. They range from small (Atik 314L+) to the largest chip that they now do (Atik 460) - cooled, these chips will give you virtually no noise. I only cool to 0 degrees, but many will go to -10 or more. Almost noise free. The downside is the cost.

Other companies use the same chips, but I'm not familiar with the models. All roughly the same price though.

The QHY8 had cooling and people seem happy with the noise levels. Can't speak from experience though.

[umadog]

They all have dark noise, I'm afraid. It occurs in CCD and CMOS devices and it occurs in other sensors, such as photomultiplier tubes. The more you pay the less noise you'll get, mostly because the more expensive chips are cooled. Cooling is the main way of reducing dark noise. How much of a difference cooling makes will depend on the chip and the temperature you can achieve. Here's one example: http://astropetros.com/wp/?p=331 Here's another showing that dark noise is reduced by half for every 5 degree temperature difference: http://www.astrosurf.com/luxorion/howto-ccd3.htm With the right set up and technique you can definitely tame the noise to very acceptable levels.

There are some good books on this stuff (e.g. Making Every Photon Count).

[Ouroboros]

What stops the cooled CCD misting or even freezing up? Is the chip placed behind a vacuum window and cooled on the back face?