Need a suggestion for an astro-cam

[Quentin]

Hello.

I am newly registered here as I found in the past a lot useful information here and now I am kind of confused what to choose.

I am coming from conventional photography (only hobby), I own a full frame equipment with a Canon 5D Mark IV and some nice lenses I use on vacation trips here and there.

Last year, I wanted to start a bit with astronomy. I bought a Celestron NexStar 127 SLT, a Maksutov with 1500mm focal length and a 127mm opening. I did my first tries attaching my DSLR to this baby using a T2 to EF adapter. With this combination I also tried here and there catching a glimpse of Jupiter (which ended up in a thumbnail sized unsharp image, but you could recognize it including the right colors).

After having been quite astonished by a friend's Coronado PST, I wanted to join the world of solar telescopes, too. After a lot reading in several boards, including here, I got hold of a used Lunt LS35THa DX with the B600 etalon. And there "my problems started". First I wanted to do visuals, but the Ploessl 17mm the guy had put into the box just roughly showed something the size of a finger nail. Hard to spot anything there. I ordered a Hyperion 8-24 zoom eyepiece along with a Hyperion Barlow 2.25x and was satisfied with what I saw.

When I started to try to use my DSLR, I had to learn it is simply impossible to get focus on the sun with the Lunt because of the backfocus. There were two options. Ocular projection buying a M43 adapter (did that, see attachment for my very first Canon 5D Mark IV single frame pic on the 8-24mm@24mm - I didn't even crop the image, it was that big with the Barlow... but you get CRAZY with the turning focus and the heavy camera). Option two would be an astro cam, lighter weight than my DSLR and a uniform shape, so it doesn't turn by itself.

I've read discussions about CCD vs. CMOS here. I don't want (yet) to do deep-space stuff, I would love to stick to planetary imaging (moon+sun for now, but Jupiter and Saturn to follow). The sun would stay with my Lunt on 400mm focal length (or 900 with the Barlow), the rest would go with my Celestron NexStar 127 SLT @1500mm focal length (maybe with Barlow bringing it to 3375mm, thank god I also bought the JMI MotoFocus or I would die finding the focus on that weak mount). So CMOS would be favorable, color as well (with the known limitations especially when limiting to h-alpha) - especially from a price point.

I've found a guide how to calculate the required sensor size depending on your focal length and the desired object. And here I went nuts. Either I don't understand the formulas right or I miscalculate it all the time. The numbers don't make sense. I've looked at the huge offerings of ZWO with all the ASI series cameras. But hell, I don't know which one to pick. Those they call "planetary" cameras have a resolution that a 20 year old webcam laughs his ass off. My DSLR has 30.8mpix and I could get at least for moon+sun nearly full frame pictures. I don't know what a 0.8mpix astro cam would bring me more in terms of details (highlights on the sun or craters on the moon surface) - sure you can stack, but that still gives you a 0.8mpix image, right? And: from terrestal photography I normally think: smaller sensor = less sensitivity but farer reach (multiplicator on the focal length.... APS-C on Canon = 1.6x focal length). Looking at those formulas, in astro imaging seems vice versa?! They tell me for "big things" like sun/moon I should take a super small sensor with nearly no resolution. So I wonder how I should get a high-resolution image here... Especially if I need to crop for Saturn or Jupiter in the future?

Maybe somebody could enlight me a bit :).

Just to set the bar, I attached another pic from me, having made with my DSLR (not the Mark IV but the Mark III on a normal 400mm lens). I'd like to make this kind of pic with even a lot more details.

Thanks,
Nick

[wimvb]

Hi, and welcome to the forum.

I don't do solar imaging, but you could read up on the solar imaging sub forum, or check published images on astrobin.com.

As for general AP, the book "Making every Photon Count" by Steve Richards, available from FLO, should get you started.

General AP differs from daytime photography in mainly two ways:

1. noise because of the low light conditions. Both camera noise and "sky" and target noise.

2. Resolution in arcseconds per pixel. This determines the amount of detail you can hope to catch. Number of pixels and sensor size is not always important. With your large full frame sensor of the Canon Mk IV, you will have problem filling that. Most telescopes don't illuminate a full frame sensor, and those that do are expensive.

More on this in the recommended book.

[Merlin66]

I use the ZWO ASI 174MM camera for solar imaging/ spectroheliograph. The pixel size of 5.86 micron and 11.34 x 7.13mm chip size give very good results on Ha scopes with a focal length >1000mm (the chip is not big enough for full disk imaging at these focal lengths - mosaics required)

It does unfortunately suffer from Newton rings in some situations, but these can be removed using a T2 tilter.

For shorter focal lengths I'm about to trial an ASI 1600MM, 3.84 micron pixel and 17.7 x 13.4mm chip. (The previous ASI 183MM, 2.4 micron/ 13.2 x 8.8mm unfortunately was found not to be suitable for Ha solar  imaging due to technical issues)

The larger chip size means easier full disk imaging.

 

The detail and resolution comes from good seeing conditions, the ability to capture "lucky images" - at the moments of best seeing. Normally an AVI/SER video file of 2000+ frames with the best 10% or so selected. These are then stacked and processed with wavelets (or similar) to pull out all the detail.

I use AutoStarkket 3 for selection and stacking and Registax 5 (or 6) for processing.

Hope this helps.

 

[Quentin]

Thank you for the suggestions.

Just to repeat myself: the ASI174MM has a resolution of 2.3mpix. Does stacking those images give a higher resolution? I'd like to produce an image with a higher resolution than that... So far I never tried to stack images. I had a few tries with Autostakkert and registax, but for some reason they all don't like the images produced by my DSLR. Either they complain about too high resolution or they hang while processing.

Is for planetary/sun/moon photography a cooled camera recommended? Or is the cooling only interesting for DSO?

Best regards,
Nick

[wimvb]

8 minutes ago, Quentin said:

Does stacking those images give a higher resolution?

No, stacking is used to reduce noise in an image, and get rid of artefacts such as satellite trails.

9 minutes ago, Quentin said:

Either they complain about too high resolution or they hang while processing

Probably due to memory issues on your computer. A full frame dslr with 30 Mp (?) produces large files.

11 minutes ago, Quentin said:

Is for planetary/sun/moon photography a cooled camera recommended? Or is the cooling only interesting for DSO?

Generally only needed for DSO, where you collect a lot less light, and need to bring the noise from the camera down as much as possible. For planetary/lunar/solar imaging, you want frame rate and small(-ish) pixels.

Like I wrote before, have a look in the solar imaging section and on astrobin, to see what other people are using. It's the best way to get oriented.

[newbie alert]

A warm welcome to you...the sun is really alot of fun..visually and imaging..

I can highly recommended flo astromany tools app and they have a ccd one too..you can choose your target,camera and scope combination giving you the fov and with the ccd one whether you be over or undersampled...i put the links up below...can I recommend a mono camera thou..and add the false colour in the processing software..Theres also a really great u tube video showing capture and a processing demo which I also put a link up too..enjoy..

https://astronomy.tools/calculators/ccd_suitability

https://astronomy.tools/

 

[Stub Mandrel]

On 15/07/2018 at 12:53, Quentin said:

Those they call "planetary" cameras have a resolution that a 20 year old webcam laughs his ass off. My DSLR has 30.8mpix and I could get at least for moon+sun nearly full frame pictures. I don't know what a 0.8mpix astro cam would bring me more in terms of details (highlights on the sun or craters on the moon surface) - sure you can stack, but that still gives you a 0.8mpix image, right? 

The moon and sun are best imaged with large sensors - if you want full frame images. They are both bright and you aren't trying to max out the resolution.

For planets, or closeups of crates/sunspots etc. the challenge is very different. The resolving power of the optics sets a 'wall' of resolution.

This means it's not the number of pixels, it's pixel size that counts. Ideally, the pixel scale needs to be about 1/3 the resolution of the telescope, so the resulting image is oversampled, but not by too much.

Too small pixels and you need too-long exposures which reduce your chance of beating the seeing.

For my setup I use a effective focal length of 3,600mm and still Jupiter (largest of the planets in relative view terms) fits easily in a 400 pixel square image. I've got three DSLRs but my little 1280 x 960 planetary cams whip them intro a cocked hat for planets.

For planetary work, you also need quick capture to get lots of frames before planetary rotation causes excessive blur in the stacked image. For Jupiter I'm currently cropping to 480 pixels square (0.2Mp) so I can get 5,000 ~12ms exposures at 80 fps. That gives me 1GB of raw video every minute, which translates to 2 GB once put through a program to centre and crop the data ready for stacking.

This means  that a large sensor is redundant for planetary work, better to have a relatively small sensor and optimise the camera for rapid video, low amp glow and good  heatsinking from the sensor to the case (or built in cooling).

Where you can use a DSLR is if it allows you to record cropped video at high speed. My 18Mb bridge camera can hit 100fps  for 4x speed video - at 480 x 360 pixels, but it does this largely by reducing the resolution, not cropping.

By the way stacking CAN increase resolution. If the data is undersampled by virtue of great seeing, excellent focus etc. you can use a process called drizzle to increase the resolution of the data.

 

[Merlin66]

Nick,

It's not the Mp count that's important to astrophotography. As has been said, it's the pixel size v's the target..... With larger camera chips you can always reduce the ROI (Region of interest) to further increase the frame rates.

Check out CCDCalc for your proposed camera/ object and it will give you some guidance.

http://www.newastro.com/book_new/camera_app.html

 

[Demonperformer]

Hi, Nick, and welcome to SGL.

 

[Quentin]

Hi and thank you for the warm welcome. Hey, what welcome could be warmer than talking about the sun?

Thanks for all the nice explanations and links, I'll have now a lot to read and learn.

Let me digest all you said.

Thanks,
Nick

[Quentin]

Hey guys,

one more expert question: in the meantime I bought a ZWO ASI174MC (non-cooled) for the first steps, and had my fun with it trying to capture the moon and Saturn and Jupiter.

As I have a Lunt LS35THa DX, I tried to set it up to take some stacks of the sun. I fail to find a focus, it looks like the camera would need to go even "deeper" onto the focusing tube, but I can assure you, there is no mm to move it further down. If I put the Barlow 2.25x in-between, I can easily get focus and all is fine - but of course now the sun is bigger than the sensor area. And combining a Barlow with a reducer is even for my beginner's optimism too crazy

Does anyone have a suggestion (or should I ask this question in a separate thread over at the "Imaging - Solar" area?) on how to get a focus with the ZWO ASI174MC on a Lunt LS35THa DX?

Best regards,
Nick

[wimvb]

Are you using the Lunt with or without the diagonal? If with, try without.

[tooth_dr]

6 minutes ago, wimvb said:

Are you using the Lunt with or without the diagonal? If with, try without.

I’m nearly certain the blocking filter is in the diagonal so don’t be using it without  it.

@Quentin There are problems getting focus with the Lunt 35. Plenty of info online if you do a quick search 

[tooth_dr]

https://www.cloudynights.com/topic/393644-lunt35-problem-with-focuser-when-attaching-dslr/

[wimvb]

1 hour ago, tooth_dr said:

I’m nearly certain the blocking filter is in the diagonal so don’t be using it without  it.

Glad you caught that, I wouldn't want to be the reason someone injures himself (or ruins a camera).

[cjdawson]

Hi and welcome to SGL.

I'd like to throw a few things into this conversation as it may help.   I've personally used, a Canon 30D, Canon 70D, and am in the process of switching over to a ZWO ASI290-MM  (uncooled) and I'm building a cooling unit for it.   My intent is to use it for deep sky.  That said, I'm also planing on doing some planetary and lunar.    It's nice to have options.

 

For the 290MM, I've also got the ZWO Mini Filter wheel, and a set of LRBG filters.   This is where the main difference between the cameras will come into play.  The Canon Cameras have a Bayer matrix in play when you take a photo.  That matrix means that you are getting about 1/4 of the 50 Mega pixel image of the full frame camera for each colour (one of the colours has two pixels, green I think, so that's 1/2 of the overall colour data)  This is important, as whilst you are able to compare a 50 MegaPixel camera against a 2 mega pixel camera.  The reality is that it's more like a 2Mp v 10Mp.   Granted it's still a big difference, but it does close the gap a bit.

 

For planetary and lunar imaging, it is normal to take a movie and stack it to mitigate noise and seeing issues.  Typically, an image will be made up from about 2000 movie frames.   For planetary this isn't a big deal as you can capture at a high frame rate - my ZWO I think will run at about 70fps in full frame mode, and if the image is at a lower resolution can go up to 170fps.  The advantage of the higher frame rate is that on Jupiter, it only takes a few minutes of video to register the rotation in the planet.  At that point, the image will get motion blur.  So, lower resolution high speed capture and there you go.

In additon, whilst the camera may seem small in terms of mega pixels there's nothing stopping you from making a mosaic of images to cover a large surface like a full moon.    Done correctly, that little 2 mega pixel camera, will be able to get incredibly sharp images of the moon which when stacked and stitched together can make for an incredibly high resolution.   As the resolution of the camera is lower, this means that it is easier to find the best focus position that trying to get perfect focus over a while 50 mega pixel image of the sphere of the lunar surface.

 

Just a few thoughts for you.