Skipping DSLR and going straight to CCD ?

[Vox45]

Looking at your gear your weakest point for imaging is your scope, long focal length and slow optics makes it hard for a beginner.

A fast small refractor would give you pretty good results without guiding. A 6-8" newtonian would also work great, but you would need guiding for longer exposures.

Your mount is very good so no need to change that.

1000D is a good starting point, but a little higher noise than newer DSLR's like the 1100D, 550D, 600D that i recommend. 

Upgrade to a faster scope first, then autoguiding and after that you can start thinking about going for a CCD camera or upgrade to a better DSLR.

If you want advice on what scope to go for it would be great to know what you think you can afford.

Yes I see a lot of good imager here using 80mm refractors for DSO's, it was also my first choice, the 150mm reflector was not a choice but such a good bargain that I went for it as a stepping stone for later. The whole rig (mount, scope, solar filter, moto focus, case) was sold to me second hand for 500€... I could not say no to that

I'll be looking for a small refractor, I was thinking of a 80mm triplet apo...

[ollypenrice]

I have to admit that I am new to astrophotography, but coming from a photography background I am sure that I would not be satisfied to settle for a 1.3MP sensor (Atik 314L+). Looking at Olly's signature: Yes, if you can afford an Atik 11000 (or two of them )... but there you get into serious money. The camera would be twice as much as the rest of my gear combined. I am sure it will take me a long time to reach the potential of AP using a DSLR.

Only one of them's mine! 

Olly

[Xplode]

Yes I see a lot of good imager here using 80mm refractors for DSO's, it was also my first choice, the 150mm reflector was not a choice but such a good bargain that I went for it as a stepping stone for later. The whole rig (mount, scope, solar filter, moto focus, case) was sold to me second hand for 500€... I could not say no to that

I'll be looking for a small refractor, I was thinking of a 80mm triplet apo...

If you can afford it i can recommend the Skywatcher Esprit ED80 APO. It's fast and the optics and mechanics are very good.

The older Evostar ED80 DS-Pro is a scope i won't recommend for a DSLR, it's just too slow. It's also very big because of the tube being the same diameter as a 100mm scope and non retractable dew shield.

[sgazer]

I don't think you'd be wasting much money as you have a dslr already. Not all ccd are better, you have to get a good one and not everyone moves to ccd. Is it worth bypassing something you already have to blow 1000quid+ on something that may or may not work out?

The actual imaging device is a small part of the puzzle. Setting up the mount, aligning, tracking, guiding, image processing are all a big part of it too and will apply no matter what the camera.

Moving from dslr to ccd is expensive (for a good one), then there are always better ccds for a bit (a lot) more money!

[Chris]

I had a look at www.sensorgen.info and the Pentax K-30 is listed at 66% QE. Most other disadvantages of the larger chip could be negated when you crop down to the CCD image size. But you do have the option of having high resolution images of nebulas without resorting to mosaics. I cannot see how I could justify the expense.

Fair point and cropping my DLSR images is what I've done in the past to get closer to objects.

What I noticed with cropping in with DLSR's images is the image degrades quite quickly. I end up compromising between image quality and how close up I want to get. Even with the cheapest mono CCD's such as the Brightstar Mammut, or Atik 16/titan with there not so good chips, the image is still much cleaner and sharper close in. I think the cooling and the mono chip has a lot to do with this.

Having said this the most modern DLSR's I've used are the 1100D and 500D, more modern DLSR's do look better in terms of QE and read noise as your link suggests. The Canon 600 D looks good, not sure how easy the Pentax are to mod but there's lots out there on modding Canons

[frugal]

Fair point and cropping my DLSR images is what I've done in the past to get closer to objects.

What I noticed with cropping in with DLSR's images is the image degrades quite quickly. I end up compromising between image quality and how close up I want to get. Even with the cheapest mono CCD's such as the Brightstar Mammut, or Atik 16/titan with there not so good chips, the image is still much cleaner and sharper close in. I think the cooling and the mono chip has a lot to do with this.

Technically you are not "getting closer" to the image by cropping it. The scale of the image in arc seconds per pixel will be the same, you will just have less pixels in your image.

One of the reasons that DSLRs images appear to degrade when you zoom in on them more than mono CCDs is because for each pixel in a DSLR colour image, the software has to guess two of the colour components from what is going on around. If the pixel in question is a blue cell on the camera, the software has to work out what the red and green amounts should be based on what is going on around that blue cell.

[Chris]

Technically you are not "getting closer" to the image by cropping it. The scale of the image in arc seconds per pixel will be the same, you will just have less pixels in your image.

One of the reasons that DSLRs images appear to degrade when you zoom in on them more than mono CCDs is because for each pixel in a DSLR colour image, the software has to guess two of the colour components from what is going on around. If the pixel in question is a blue cell on the camera, the software has to work out what the red and green amounts should be based on what is going on around that blue cell.

Yes agreed of course cropping an image isn't going to change the resolution of the image, I'm not sure what expression is best to use in place of 'getting closer' ??

Yes agreed again With a Bayer matrix in the way there will be lower resolution and the camera interpolates the 'gaps', kind of joining the dots I guess. Olly P says this interpolation is quite clever though.

One other reason for degradation I feel is all the noise of a non cooled camera, it's as if you're zooming in on the noise as well as the target.

[frugal]

Yes agreed again With a Bayer matrix in the way there will be lower resolution and the camera interpolates the 'gaps', kind of joining the dots I guess. Olly P says this interpolation is quite clever

This PDF goes through the different algorithms well:

http://www.stark-labs.com/craig/resources/Articles-%26-Reviews/Debayering_API.pdf&ved=0CCYQFjAD&usg=AFQjCNHcoMyJSK-Z5z3VTcQzi821ePgoAg&sig2=bwoudi0crQcptc3fN3Pt1g

[Chris]

This PDF goes through the different algorithms well:

http://www.stark-labs.com/craig/resources/Articles-%26-Reviews/Debayering_API.pdf&ved=0CCYQFjAD&usg=AFQjCNHcoMyJSK-Z5z3VTcQzi821ePgoAg&sig2=bwoudi0crQcptc3fN3Pt1g

Anyone else getting an Error 404 message for this link?

[ollypenrice]

Fair point and cropping my DLSR images is what I've done in the past to get closer to objects.

 

No, you have never done this. All you have done is zoom in on the image you already had. There is a huge difference between 'getting closer in' and enlarging the existing picture.

To get closer in you need a longer focal length. Using a finer resolution (smaller pixels) at that focal length will give you more detail, seeing and guiding permitting, too.

Perhaps you really meant this but I have explained to quite a few guests that a smaller chip does not make the image in the frame larger. It's focal length or nothing!

Olly

[ollypenrice]

Anyone else getting an Error 404 message for this link?

Yes.

Olly

[Chris]

No, you have never done this. All you have done is zoom in on the image you already had. There is a huge difference between 'getting closer in' and enlarging the existing picture.

To get closer in you need a longer focal length. Using a finer resolution (smaller pixels) at that focal length will give you more detail, seeing and guiding permitting, too.

Perhaps you really meant this but I have explained to quite a few guests that a smaller chip does not make the image in the frame larger. It's focal length or nothing!

Olly

Maybe saying small chip cameras better frame galaxies would have been better?

It would be good if I could look at the shop at the end of my street through a straw and actually be there

[johnrt]

Maybe saying small chip cameras better frame galaxies would have been better?

It would be good if I could look at the shop at the end of my street through a straw and actually be there

Why do you say small chip cameras frame galaxies better? It depends on the focal length of the scope and size of the pixels in the chip.

[Chris]

No one stated a particular telescope so I didn't think I needed to be specific. Yes if I I used my C8 to image a galaxy then an APC sized sensor will frame the galaxy nicely (unless it's M31 of course). But if I used an APC sized sensor with my WO66 then there will be a lot of space around the galaxy. 

If I use a 1/3" chip CCD on my WO66 then a small galaxy will be more tightly framed.

If I use a 1/3" chip CCD on my C8, I'd probably be lucky to find the target, but it would frame small PN's and small apparent sized galaxies tightly if I did manage it (never tried).

Maybe it would have been better if I said a small chipped CCD will frame a small galaxy such as M109 more tightly than APC sized sensor using a focal length of 400mm.

[Xplode]

I think framing galaxies tight takes away the feeling that it's a part of something larger. In my images i have dozens of smaller galaxies and hundreds of very far away galaxies that look like faint yellow stars.

Here's one of my images as an example, cropped and uncropped.  Look at all those smaller galaxies you are missing with a smaller FOV. That galaxy at the top is my favourite galaxy i got as an extra to the main target.

[Chris]

ahh! you just wanted to show of your image Very nice by the way! I saw this image on your thread I think, didn't you also post M63 and one other? I've got to agree that M106 looks better with it's buddies  

The bottom image is what I would call reasonably tightly framed, probably similar or less than my little 314L's chip would give with my WO66. The top image is very very tight, not sure many folk would prefer that?

What I don't like galaxy wise is when I've used an APC sized sensor on a short frac, all you see of the main target galaxy is a little oval, and when you crop/zoom in the image degrades  

I also really like the edge on galaxy near M106

[Chris]

Yes it's a similar FOV and very usable "/pixel when using the 314L with either my WO66 or 130pds.

[ollypenrice]

The real question, perhaps, is how does a small chip, short FL CCD rig compare with a long focal length, large chip DSLR rig?

DSLRs are getting better at shorter FLs (for their small unbinnable pixels) and with fast F ratios. If the target needs lots of NB input to shine then it will certainly be the small CCD which will win. If it's a reflection nebula or galaxy then it becomes more questionable.

Olly

[Chris]

Now this is the question! 

My old 350D plus C8 reduced gave roughly the same FOV as my WO66 plus Atik 16 mono. Despite repeated mount issues with an eq6 the last 6 months, a quick test so far showed the fine detail on small apparent sized objects appeared very good with the WO66 and Atik 16 mono, and I've not been that impressed with my C8 with DLSR.

The C8 at f7 with 350D gave 1 "/pixel, and the WO66 with Atik 16 mono gave 4.5 "/pixel ! so I'm not sure why? 

More testing is needed obviously, the above was based on a quick shot of the bow tie neb with the C8 and a quick shot of M1 with the WO66. Really I need to shoot the same object with both setups to be sure but that will have to wait. I'm trying the Atik 314 OSC with 130pds next.

[ollypenrice]

Now this is the question! 

My old 350D plus C8 reduced gave roughly the same FOV as my WO66 plus Atik 16 mono. Despite repeated mount issues with an eq6 the last 6 months, a quick test so far showed the fine detail on small apparent sized objects appeared very good with the WO66 and Atik 16 mono, and I've not been that impressed with my C8 with DLSR.

The C8 at f7 with 350D gave 1 "/pixel, and the WO66 with Atik 16 mono gave 4.5 "/pixel ! so I'm not sure why? 

More testing is needed obviously, the above was based on a quick shot of the bow tie neb with the C8 and a quick shot of M1 with the WO66. Really I need to shoot the same object with both setups to be sure but that will have to wait. I'm trying the Atik 314 OSC with 130pds next.

If you are not able to hold the guiding to 1 arcsec per pixel for the imager then you have your explanation. You could work this out from your guide trace. However, that's not beyond the capacity of most mounts to deliver.

The other thing is signal. With lots of signal you can sharpen and contrast-enhance in processing. With poor signal you just enhance thoe noise!

Olly

[sharkmelley]

Then there's quantum efficiency and well depth. My Canon 350D had a QE of just 27% Most astronomical CCD's have much higher QE so are therefore more sensitive, especially mono CCD's.

Not sure how OSC CCD's are as I've only just got hold of one to try out.

I have both a modified Canon 350D and a cooled SXV-M25C - a OSC CCD.  This has enabled me to do a side by side comparison.  In terms of sensitivity, the SXV-M25C picks up 1.1x as many photons as the 350D in all spectral bands: Blue, Green, Red and even H-alpha.  So it's not much of a difference to be honest.  The read noise of the SXV-M25C is much higher than the Canon 350D (at ISO 800). So in terms of imaging quality, the SXV-M25C only gives a noticeable improvement over the 350D when cooling is required.

I've also tested the modified Canon 550D which has better response than the modified 350D and SXV-M25C in Blue and Green but is identical to the 350D in H-alpha.

However, in answer to the original poster, there is no reason why anyone should do DSLR imaging before buying a mono CCD.  And I speak as a hardened DSLR imager!

Mark

[Chris]

If you are not able to hold the guiding to 1 arcsec per pixel for the imager then you have your explanation. You could work this out from your guide trace. However, that's not beyond the capacity of most mounts to deliver.

The other thing is signal. With lots of signal you can sharpen and contrast-enhance in processing. With poor signal you just enhance thoe noise!

Olly

That all makes perfect sense now you mention it, thanks!  

[Chris]

I have both a modified Canon 350D and a cooled SXV-M25C - a OSC CCD.  This has enabled me to do a side by side comparison.  In terms of sensitivity, the SXV-M25C picks up 1.1x as many photons as the 350D in all spectral bands: Blue, Green, Red and even H-alpha.  So it's not much of a difference to be honest.  The read noise of the SXV-M25C is much higher than the Canon 350D (at ISO 800). So in terms of imaging quality, the SXV-M25C only gives a noticeable improvement over the 350D when cooling is required.

I've also tested the modified Canon 550D which has better response than the modified 350D and SXV-M25C in Blue and Green but is identical to the 350D in H-alpha.

However, in answer to the original poster, there is no reason why anyone should do DSLR imaging before buying a mono CCD.  And I speak as a hardened DSLR imager!

Mark

Now that's a bit surprising! I won't expect the world from my 314L OSC then, even though it cost 10x more than the 350D

[frugal]

Anyone else getting an Error 404 message for this link?

sorry, I tried to get rid of the google bumf at the end of the link, my own fault for trying to cut and paste a link to a PDF on a tablet. https://www.google.co.uk/url?sa=t&source=web&rct=j&ei=YEgNVbamE6y17gbP-IGACA&url=http://www.stark-labs.com/craig/resources/Articles-%26-Reviews/Debayering_API.pdf&ved=0CCkQFjAB&usg=AFQjCNHcoMyJSK-Z5z3VTcQzi821ePgoAg&sig2=__jlK84DyFxUB8REbFtkhg

If that still does not work, then if you google for "debayer vng" it is the second entry.

[Chris]

Works! Thanks:)

I recognise this article but have probably forgot most of it so I'll have a read through.