Should I get a CCD?

[Beardy Bob]

Sorry folks, this is a long one. Bear with me...

I currently use a Canon 350d (unmodded) mainly for DSOs. (Full setup: HEQ5 with QHY5/130 reflector autoguiding, unmodded 350d/C80ed imaging scope, side-by-side.) And it produces some great images of the brighter stuff, but obviously struggles with dimmer objects and deep reds etc.

What I like best about the images I've seen with CCD cameras (and therefore my primary reasons for wanting to upgrade) is the sharpness of the stars and nebulosity, and the range and intensity of colour.

What are the practicalities of achieving such results? How much is down to the CCD and how much to the telescope, etc? (A comparison of CCD versus DSLR through the same kit at the same site would be great!)

I like the large field of view that the relatively big chip in the 350d gives me. That leaves me with cameras beginning at the Atik 383L+ kind of price range, which is a massive leap from a £150 second hand canon 350d! I also like the simplicity of one-shot colour, but is RGB needed to really get the best out of one of these big CCD beasts (and if so, why)?

My site is nice and dark so I have little probs with light pollution - if that makes any difference to anything!

Thanks,

Bob

[riklaunim]

There is also color QHY8 QHY8 CCD CAMERA with APS-C CCD. Unmodded DSLR won't let much of H-alpha in so you won't get much of the red in nebulae. Modded Canon will be better, cooled more sensitive CCD in QHY8 will also be better and on the top - mono CCD with narrowband filters (for nebulas) or Ha-RGB imaging for DSO in general

[Deneb]

If you going down the ccd route, you might be better of going for a mono camera due to the uk weather climate with LRGB filters & a filter wheel. Can't comment about the QHY8 CCD cameras, but Atiks have a solid build on them.

BTW heres a site to compare fov's with different cameras.

http://www.12dstring.me.uk/fov.htm

Nadeem.

[Glider]

If I read your OP correctly your main worry is getting enough light to see the 'dimmer' DSO.

Getting a camera with higher sensitivity is one route with a certain price tag attached.

Since you already have a HEQ5 mount which can carry a decent weight why not get more light in the first place by increasing aperture.

How about a 200mm reflector? I think the price tag for this is less than the other route. You'd have to consider FOV, etc, etc.

Just a thought.

[riklaunim]

f/5 6" reflector for imaging will do the same as f/5 8" reflector (exposure times) - the scale will increase, but at the same focal ratio exposure times won't change - you will get the same light detail. A solution would be to use a focal reducer.

[ollypenrice]

Yes, it is important to understand that aperture has nothing to do with it. Focal ratio is all, when it comes to concentrating light on your chip. A 20 inch SCT at f10 (and pointed at the Pleaides) will get light from a couple of stars. A small f5 refractor will get light from all the cluster in its wide field.

CCD? I love it. There is an old saying, 'However much you sharpen a screwdriver it will still make a poor chisel.' CCD cameras are, in this analogy, chisels from birth...

Next week I am hoping to write a review comparing CCD with DSLR but this plan has had a setback; the DSLR half of the review, Frans Kroon, has sold out and bought an 8300 chipped CCD so maybe he won't be interested in using the DSLR any more!

What you get with a DSLR is a staggeringly budget price for a very large chip. What you get with a CCD is a smaller chip (unless you have over four grand to spend) in a package intended to do what you are trying to do. I would confidently say that CCD will give you better star shape and colour and far more of the faint stuff lurking in the background.

I vote for CCD but hats off to those who do wonders with DSLRs.

Also you do need some serious glass to cover a DSLR chip. If I wanted to do DSLR in the TEC 140 I would need the 600 dollar flattener. A bit of Photoshop thuggery sorts me out with the Atik 4000 CCD chip. Tell nobody!

Olly

[Glider]

There you go then.

You live and learn. Though now I'm a little confused about why people talk about 'aperture frenzy' if aperture has nothing to do with it.

[Beardy Bob]

I would confidently say that CCD will give you better star shape and colour and far more of the faint stuff lurking in the background.

That's what I suspected.

Also you do need some serious glass to cover a DSLR chip. If I wanted to do DSLR in the TEC 140 I would need the 600 dollar flattener.

Again, as I suspected!

A bit of Photoshop thuggery sorts me out with the Atik 4000 CCD chip.

As I hoped!!

From the general response I think that the only conclusion is that I really do need results from comparitive tests: DSLR (and perhaps a modded one) and a good quality CCD through a budget 'imaging' scope, and the same tests through a mid-/high-range scope. Then the same with one-shot-colour vs RGB. Only then could I judge the relative values of each (scope, CCD and one-shot-colour versus filters).

I'm happy to spend a grand or so on a decent CCD, but if to get marked image improvements I also need to invest long sessions grabbing separate R, G, B, etc or a further £1000+ on a scope then the it gets a bit much for the time I actually spend on the hobby (due to weather restraints, etc).

[ollypenrice]

There you go then.

You live and learn. Though now I'm a little confused about why people talk about 'aperture frenzy' if aperture has nothing to do with it.

Aperture fever is a visual observer's malady! (I have that as well...)

Because you can change the EP in visual use you can select between a variety of effective focal ratios.

However, in DS imaging there is no EP, you are working at prime focus, so the only focal length and focal ratio available are those of the telescope. In imaging, a 'light bucket' is not a large scope, it is a fast scope, one with an f ratio in the range 2 to 5, say. So if you take three incarnations of a 10 inch SCT the standard f10 is very slow and will take ages to get an image, the one with an f6.3 reducer is getting faster and the one with a Hyperstar conversion operating below f2 is a light guzzling demon that can do deep sky in one minute subs. But of course the field of view they cover is getting wider as the f ratio drops, which may or may not suit your target.

In imaging increasing your aperture will improve resolution and light grasp but if the increase maintains the original focal ratio then the light so grasped will come from a smaller source and so there will be less of it. Think of observing the moon. In a wide EP it can be painful. You need a filter. But whack it up to 300 times and now you are collecting light from a smaller area and it is comfortable. You haven't changed your aperture, you have increased your effective focal ratio and so dimmed the image. In astrophotography it desirable to do the reverse.

I hope my original post wasn't abrupt. It wasn't meant to be.

Cheers

Olly

[Glider]

No problem, i need to go and think about that now and get my head around it.

[ollypenrice]

Sorry, me again. I reviewed One Shot Colour vs Mono for Astronomy Now a while ago after some careful back to back test imaging sessions with Atik 4000s in a couple of refractors. One thing is dead certain, colour is slower than mono. The detector is slightly less sensitive because of the Bayer matrix and so for a given image quality mono is faster. Also you can save time in mono by binning colour 2x2 and taking full resolution only for the detail-holding luminance layer. It also has advantages in being able to do narrowband which makes moon time productive. However, I liked the OSC camera enough to buy it and it does well.

The Sony 285 chip in, among others, the Atik 314L is a dream to use with high sensitivity, low noise and no vices. The chip is not agonizingly cramped but can be covered by a user friendly small fast refractor. You can take literally world class images with it, viz those of Rob Hodgkinson, for instance, or Anthony (Greek Astronomy).

Olly

[MickD]

Bob,

I have some examples of the difference between DSLR & CCD.

DSLR was an unmodified Canon 350D

CCD was a QHY8 (colour)

Scope (SkyWatcher ED80 pro), location, guiding, mount all the same. The exposure time & number of subs was probably slightly different. The QHY8 images have been cropped as I was having problems with the edges of the sensor icing-up…. (fixed now).

As you can see the QHY8 is much more sensitive to red light & there is much less noise in the image due to the CCD being cooled (sometimes too much).

My vote is CCD always – it’s designed for the job.

Mick

[Psychobilly]

A modded 1000D makes a big difference compared to an unmodded 350D... even an unmodded 1000D is significantly better than the unmoded 350D...

It's no secret that I am biased towards DSLR's as I like to try and get as much as possible out of them...

Links to a couple of threads with my efforts with the Modified 1000D on a Megrez72 FFIII combo...

http://stargazerslounge.com/imaging-deep-sky/97178-b33-widefield-8h-30m-baader-modified-1000d.html

http://stargazerslounge.com/imaging-deep-sky/99302-re-processing-afetr-some-sleep-ic443-444-a.html

http://stargazerslounge.com/imaging-deep-sky/98884-monkey-head-nebula-ngc2174-sh-252-a.html

Peter...

[MickD]

Peter,

Your shots with the DSLR are constantly amazing (and better than my CCD images)

I agree with you comments about modded vs unmoded.

I should also have qualified my post with, “from someone who has only been imaging for 18 months” & “from someone who only ever has the time or commitment to capture 30mins of subs….”

Mick

[Psychobilly]

No worries...

[dph1nm]

Yes, it is important to understand that aperture has nothing to do with it. Focal ratio is all

Sorry, I can't let this go. Aperture IS king, provided you buy a CCD with the appropriate pixel size -i.e. one matched to your seeing. If you choose CCDs which give e.g. a 2 arcsecond pixel size then an 8 inch scope will always outperform a 4 inch. This idea that small focal ratio is faster comes about if you insist on sticking the same camera on different scopes. But why would you - if you are buying a new system then you should match the camera to the scope. its nuts trying to do DSOs by putting a CCD which gives e.g. 0.1" pixels on a scope in the UK!

The same considerations apply to tracking - if you choose your camera correctly then focal length is not an issue.

Now, it can be expensive to get CCDs with large pixels, and the range of sizes available is obviously limited, but this is a practical consideration, not physics. Physics says aperture wins ...

(rant over)

NigelM

[ncjunk]

My understanding is the pixel size and focal length give you the arcsecs per a pixel. The aperture has nothing to do with it.

An 80 mm f10 scope has the same arcsec per pixel (focal length 800 mm) as a 200 mm f4 but the 200 mm will be faster at taking photos.

Your mixing aperture and focal length up a bit in that previous post. (actually i am probably being a bit pedantic i think there is only one of the bits in the previous post that could be worded better)

[GuillermoBarrancos]

I think this is one fine (of many out there) example of why, even in imaging, aperture is king:

http://stargazerslounge.com/imaging-deep-sky/108869-eagle-nebula-m16-hubble-colors.html

And this site shows it as well:

Astrophotography by Bob and Janice Fera

But ofcourse location (dark sky), atmospheric conditions and the type of object you try to image plays a big role in the end result as well, about how much detail you can gather.

If you are in the middle of London or any other big city with tons of light polution. An extremely expensive 14" RC telescope is probably not gonna help you much. Not even with imaging.

[George]

Interesting thread

I'm still using DSLR's (1000D) at the moment for 2 key reasons.

1. Budget (no budget is tighter than mine )

2. My light pollution is quite bad and a CCD wouldn't be an improvement on that.

I can still squeeze more from the DSLR (cooling mod) so until I hit a brick wall with advances on the equipment I have I'm stuck with what Ive got.

[dph1nm]

My understanding is the pixel size and focal length give you the arcsecs per a pixel. The aperture has nothing to do with it.

An 80 mm f10 scope has the same arcsec per pixel (focal length 800 mm) as a 200 mm f4 but the 200 mm will be faster at taking photos. Your mixing aperture and focal length up a bit in that previous post.

Sorry, you are missing the point - maybe I wasn't clear. You should always match your CCD to the focal length of the scope, and then f-ratio is not relevant to how 'fast' you can image. If I have a 4" f5 scope with e.g. a 6um pixel CCD and a 4" f10 scope with a 12um CCD, I will get the same depth of image in the same time, and the tracking will be just as easy/hard on the f10 as the f5. And if I took an 8" f10 scope with a 24um CCD I could get the same image in half the time as the 4" f5.

I see so many post telling people not to start imaging with long focal length scopes as tracking will be too difficult and they will be very 'slow'. Neither of these statements is correct if you chose an appropriate CCD camera.

NigelM

[Beardy Bob]

Sorry to revive this thread so late in the day, but Mick's DSLR/CCD comparison shots really caught my eye.

What sort of processing has been done on the images? Is it just a straight stack or have you done some curves, etc?

[MickD]

Bob, Sorry for the late reply I missed your post (& I have been at SSP…). Both images were aligned & stacked in Nebulosity & then processed in Photoshop. The PS processing was done to the best of my ability at the time….using curves, levels, Noels Actions etc.

I found that the CCD images were easier to process as they were cleaner to start with and allowed me to stretch them further; however my possessing skill also improved, so if I went back and re-processed the DSLR images I may get a better result.

For me the difference between un-modified DSLR & CCD is that I can get a much better image with the CDD for the same or less effort (& being limited in how much imaging I can do due to work commitments this is good…)

Mick