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Planetary camera advice


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Hi everyone

I'm keen to make a move into astrophotography, although I know my setup is not designed for that pursuit.  I have a manual Orion Optics VX14 1/10 dobsonian with Nexus DSC pro.  I'm aware that a dob isn't the best for photography, however, I got it for visual and that is where my passion is.  But I thought it would be good to take some planetary photos at the end of a session.

I have absolutely no idea what makes a good camera for my setup for planetary (and possibly some basic DSO if possible - globular clusters?).  It's a f4.6  FL1600 aperture 350mm, although with the Parracor it's f5.3 FL1,840 (parracor needed?).  I want a dedicated astro camera - ZWO:

- I assume I need a large sensor as it is manual to try to keep the image in view?  What is deemed to be large for this?

- What resolution/sized pixels would be best to get a good clear view?

- What other stats are important for planetary viewing with a dob? I see things such as well depth, noise, black etc - no idea what I am looking for!

- Was looking at the ASI662MC (2.9 um 1,920x1,080 5.6mm x 3.1mm) or the ASI678MC (2um 3,840 x 2,160 7.7mm x 4.3mm)- they give good close up views, but is the sensor too small?  Then there is the ASI585MC (2.9 um 3,840 x 2,160 11mm x 6.3mm)- nice large sensor and resolution but a smaller view......what do I need?

Any manual dob users out there who can offer some advice would be great.

ps, not interested in getting a dedicated photography rig - I realise that would be much better and that it won't be easy with a dob, but I have seen some great results with manual dobs so would like to give it a try.

Many thanks!

Nic

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56 minutes ago, Astro_Nic said:

Was looking at the ASI662MC (2.9 um 1,920x1,080 5.6mm x 3.1mm) or the ASI678MC (2um 3,840 x 2,160 7.7mm x 4.3mm)- they give good close up views, but is the sensor too small?  Then there is the ASI585MC (2.9 um 3,840 x 2,160 11mm x 6.3mm)- nice large sensor and resolution but a smaller view......what do I need?

Have you considered the ASI224MC? Small sensor but great specs for planetary AP. Of the 3 you have listed the 662 would be better as it has faster frame rate which is good for planetary

Edited by AstroMuni
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Hard to advise. As you note, a Dob is not ideal for the purpose.  I am currently using an ASI462MC, which is an improvement on the ASI224MC in that the former has smaller pixels, tending to capture more planetary detail.  The ASI462 has a small rectangular sensor, and in use I crop the region-of-interest down to 320x240 pixels, which with my SCT means that Jupiter fills most of the cropped frame(!).  This minimises the amount of data and storage wasted capturing a lot of black sky.  I imagine this would be impossible without a good, powered mount, and you will at least need to use a much larger ROI.

With the focal length of your scope you will need to use either a small-pixel camera (e.g. 2.9um) or a Barlow lens to get adequate image scale.

Getting the planet image on the (full) chip, centering, switching to desired ROI and fine focusing will all be more difficult without a driven mount.

There is an imager who has posted some fine images in 'Planetary Imaging' using a Dob.

Your 14" will be (even) more affected by bad seeing than my 8".

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Thanks.  The 662 does look appealing, but a lot of people have suggested the 585 to help keep the target on the sensor more easily.  Having not done this before, I don't know which is more important.

 

Cheers

 

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2 hours ago, Astro_Nic said:

but a lot of people have suggested the 585 to help keep the target on the sensor more easily. 

That should work, but try to find out what amount of data 5000 full-size frames represents with this camera, and what the maximum frame rate would be., before you invest £400 in it.  (With an ASI 224 or ASI462, 5000 frames of 320x240 px = about 350MB, and frame rate is about 250 frames/sec with short exposures of a few ms on bright planets). 

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1 hour ago, Cosmic Geoff said:

That should work, but try to find out what amount of data 5000 full-size frames represents with this camera, and what the maximum frame rate would be., before you invest £400 in it.  (With an ASI 224 or ASI462, 5000 frames of 320x240 px = about 350MB, and frame rate is about 250 frames/sec with short exposures of a few ms on bright planets). 

I guess 5,000 frames at 16.6mb a frame would be 83gb....that an issue?

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The advise you got from @Cosmic Geoff is spot on. To add to that, I have an 8" Dob with manual tracking. I use the asi462mc (I upgraded from asi120mc-s). I shoot with a ROI of 640x480 planetary and ISS (see planetary session and wide field). It is a lot of work and takes patience as you need to keep recentring every few secs. I easily get 15-20K frames per recording at 300fps but at that ROI it is roughly 8-10GB. I am using an external ssd with 500gb on it and it gets filled quickly with several captures per session. If you go down the manual Dob and planetary route get a RACI it will save your back and frustration.

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Important to note is that you will always want to cut down your ROI for planetary, so having a huge sensor is a bit of a waste. I would say ~3000mm focal length is really the upper limit for manual tracking  at a sufficiently shrunken ROI (800x600 or lower).

Pixel size is not something you should consider just by looking at the size; it has to match your focal ratio. Given that you’ll be using a 2x barlow at most, and perhaps a 1.5/6x by screwing it onto the nosepiece, you need to find a camera that matches your resulting f/ratio by multiplying the pixel size by 5x. I.e., if you’re imaging at ~f/10 with the 2x barlow, you’ll want pixel size of 2um. The problem is most planetary cameras have pixels much larger than this because planetary favours slower scopes (larger image scale given the already bright target). 

Apologies that I haven’t suggested specific cameras, but focus on getting one matched as closely to your imaging f ratio as you can, along with a sufficiently high FPS and low noise. 

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Good advice above.  You need lots of focal length, the smallest chip area possible and thus fastest frame rate possible.  For example I run my SCT 9.25 with a 2.5x barlow so fl around 5 metres with a ZWOASI174MM.  This gives me a f/ of about 25 which is close to the sweet spot of 4x to 5x the pixel size for that camera.

You may also benefit from an ADC but that's too fiddly for me.

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I’d recommend whatever camera has the smallest pixels.

With a 14” dob your focal lengths are going to be long which on an undriven dob makes things very difficult.

Going with smallest pixels means you can image with shorter focal lengths which should make things a bit easier. 

I’d be going with the 678mc with it’s 2um pixels, you would only need about 1.6x - 1.8x barlow power with that camera. 

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wow this is complicated!  So putting a 678 into the FOV calculator on the FLO website with a 2x barlow shows a very large square and a small jupiter.  Using a 585 with a 4x barlow shows a smaller square and larger jupiter.....or is a 4x barlow too difficult for manual tracking?  Or am I looking at the wrong thing to decide?

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46 minutes ago, Astro_Nic said:

wow this is complicated!  So putting a 678 into the FOV calculator on the FLO website with a 2x barlow shows a very large square and a small jupiter.  Using a 585 with a 4x barlow shows a smaller square and larger jupiter.....or is a 4x barlow too difficult for manual tracking?  Or am I looking at the wrong thing to decide?

You won’t use the full sensor size of any camera for planetary imaging, you cut it down using the RoI function (region of interest). So don’t worry about how large the overall black square is. 
 

Manual tracking your scope with a 4x barlow would be something I’d really not want to try! 
 

And don’t worry about the size of the planet in the field of view calculators, when viewed at 100% on a display screen the planet will always be the same size whatever the camera, assuming you sampled appropriately with each camera. 

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I think the focal length/f-ratio (hence which barlow) to use is related to the pixel size and desirable RoI… So a camera with 2 micron pixels at F10 with a 2x barlow will be just as easy (or more likely just as hard) as a camera with 4micron pixels at F/20 with a 4x barlow…

There are a few things that could make it planetary imaging easier:

1. Simple Tracking…you may not need or want GoTo, but could you get an equatorial platform for your dob?

2. A bigger RoI…easier to keep the planet in the RoI but this is going to limit frame rate and gobble up your HDD.

3. Capture at ‘sub optimal’ image scale…You may find a camera with 2micron pixels at F5 gives a reasonable image ….but you should know that you’ll not be capturing all that your optics could show you…but if imaging is only an aside, it could be all that you need…

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Just to answer your question specifically about 4x and manual tracking. In my own experience with an 8” (not sure whether this would be easier or harder than a 14” to manoeuvre in practice), 3000mm fl really is the upper limit before you’re just losing far too many frames trying to let the planet drift. It’s not so much that finding the planet is impossible, rather that getting enough complete planet frames within 3 minutes in a smaller ROI to enable higher FPS. This is my own advice from my own experience, so YMMV and it could be worth trying a 3x with an asi462 and being at optimum sampling. 

I would have to slightly disagree with catburglar above, as even though your level of detail would be the same with the 4x and 4um pixels, it would be virtually impossible to get the planet on the sensor, let alone on a shrunken ROI to get sufficient frames.

Also, a word of warning that pixel size isn’t the only consideration. If you find a camera with small enough pixels, there’s a chance it may not have planetary level FPS or low read noise. With your set up, there’s always compromise, just as there is with my manual 8” dob and asi224. 

Best of luck

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Tracking may come later, but trying to get this work for now.

I am going to 'build' a laptop, so I'll definitely get one with a 1TB SSD but will probably add at least another one and maybe add an 8TB external, so I'm not too bothered about file sizes.

It looks like the choices are the 678 with 2um pixel sizes - so 2 x 5 = f10 (FL 3,200).  With my f4.6 I would then need a 2x barlow (x2 televue powermate, so that I could also use it for visual).

The other choice would be the 585 with 2.9 um pixel size - so 2.9 x 5 = f14.5 (FL 4,800).  With my f4.6 that would mean a 3x barlow (no 3x powermate so would have to be the barlow - cheaper at least).

Which is better?  Do they work for under/over sampling?  Is there a calculator somewhere?

Thanks!  

Edited by Astro_Nic
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678 undoubtedly. The lower read noise in the 585 won’t come close to the difference between optimum sampling and significantly undersampling. Even if you struggle with 3200mm, the closer you are to optimum sampling the better.

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15 hours ago, sorrimen said:

678 undoubtedly. The lower read noise in the 585 won’t come close to the difference between optimum sampling and significantly undersampling. Even if you struggle with 3200mm, the closer you are to optimum sampling the better.

Thanks for your advice.  Looks like a 678 and a 2x powermate :) 

 

What else do I need to get started?  Filters? ADC? any adapters to get it all fixed together?  Also need a laptop!  Costs mounting up....lol....plus buying a new car on Saturday!  Don't tell the 'boss' !

 

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UV-IR filter for the 678. It has a wider pass antireflection coating on its sensor and without a filter blocking ultraviolet and especially infrared you will get weird colours in the image in the end. This doesn't need to be a cutting edge perfect filter, just get some affordable 1.25'' one.

The 678 comes with a filter threaded nosepiece where you can thread the filter to, and you just plop that into the barlow and the barlow into the focuser and you're set. An ADC will help when the planets are low in the sky, but i would say you dont "need" one straight off the bat as Jupiter and Mars later on in the year will be reasonably high in the sky this year. Probably better to start without and get the whole process going without any extra trinkets to worry about since you have a lot of new things to get accustomed to anyway.

Re: laptop. File sizes get large really fast with lucky imaging at high framerates. 60s recordings with my 678MC in 8-bit mode and 640x480 resolution are almost 4 gigabytes a piece, so the laptop should have a fair bit of ram and an SSD that can write large files fast. If the disk cannot write fast enough your framerates will tank during capture and you'll lose some data. Pretty much anything with USB-3 capabilities and an SSD will do, but in case you are looking for used ones its probably best to skip the older or cheaper models that lack USB3 and an SSD.

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Thanks.  In terms of running the videos, do I keep the scope stable and let the planet drift across the view, rinse and repeat, or do I attempt to permanently keep the planet in the view? 

Thanks

Nic

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You need an ADC for good results, but you may find difficulty in getting it to work with a Newtonian.  You might also have trouble getting the camera to focus with a Newtonian not built for imaging, but a barlow might help here. 

80GB sounds a lot. If that's correct, how long do you think it will take your equipment to move this amount of data around, and to process it?

A gentle reminder that getting the right astro kit for the job, (e.g. a GoTo SCT) will enable you to:

1) let the hardware take care of tracking

2) let you hang any kit on the scope without worrying whether you will run out of focus travel

3) Allow you to get the planet on chip without too much trouble, potentially reducing chip size and camera cost.

4) Reduce data storage requirements and hence laptop cost.

5) Reduce size of video files to be processed

6) If you can't crop the videos after recording, recording with a small ROI will make it practical to archive your videos and re-process them months or years later.

7) Reduce time and labour required.

 

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7 minutes ago, Cosmic Geoff said:

You need an ADC for good results, but you may find difficulty in getting it to work with a Newtonian.  You might also have trouble getting the camera to focus with a Newtonian not built for imaging, but a barlow might help here. 

80GB sounds a lot. If that's correct, how long do you think it will take your equipment to move this amount of data around, and to process it?

A gentle reminder that getting the right astro kit for the job, (e.g. a GoTo SCT) will enable you to:

1) let the hardware take care of tracking

2) let you hang any kit on the scope without worrying whether you will run out of focus travel

3) Allow you to get the planet on chip without too much trouble, potentially reducing chip size and camera cost.

4) Reduce data storage requirements and hence laptop cost.

5) Reduce size of video files to be processed

6) If you can't crop the videos after recording, recording with a small ROI will make it practical to archive your videos and re-process them months or years later.

7) Reduce time and labour required.

 

Now you've got me worried I'll spend all of this and not be able to focus and it will all be a waste!  Is there a way to find out prior to I spend a small fortune?

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3 minutes ago, Astro_Nic said:

Now you've got me worried I'll spend all of this and not be able to focus and it will all be a waste!  Is there a way to find out prior to I spend a small fortune?

I'm not sure. You could buy a cheap, nasty astro camera on ebay and see if it comes into focus. If it doesn't, you will have only wasted £10 or so.

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1 hour ago, Astro_Nic said:

Thanks.  In terms of running the videos, do I keep the scope stable and let the planet drift across the view, rinse and repeat, or do I attempt to permanently keep the planet in the view? 

Thanks

Nic

I have only ever done untracked planetary/lunar stuff twice, with an AZ5 and a small refractor, but i would say let the planet drift for at least a few seconds untouched before nudging it. Nudging will slightly will shake everything and those frames will probably not go towards the final stack so are "lost" in a sense. If you mess up and lose the planet, but get it back on the chip a few seconds later dont worry about it, you can use PIPP: https://sites.google.com/site/astropipp/  To preprocess and keep only the frames that have the full planet on the chip. I use 640x480 ROI on my tracked setup, and with that Jupiter wouldn't spend more than a few seconds on the chip without tracking, so you might need to use a larger ROI to give yourself some time.

@Kon regularly posts stunning images taken with a manual dob over in the planetary imaging section of SGL. They might be able to give you more tips on the manual dob aspect specifically.

The focus issue mentioned above is not going to hamper you by the way. The 678 or any other planetary camera for that matter has a very shallow backfocus of 12.5mm so if you can focus an eyepiece you can almost certainly focus the camera. The barlow you will be using will also kick up the focal point a bit, so no worries. If you were planning to do imaging with a long flange distance camera like a DSLR some newtonians fall out of focus. But you dont so no problem.

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2 hours ago, Astro_Nic said:

Now you've got me worried I'll spend all of this and not be able to focus and it will all be a waste!  Is there a way to find out prior to I spend a small fortune?

Personally, I wouldn't bother with an ADC for now, the advantage on Jupiter and Mars now they are reasonably high up would be marginal, plus it adds complications putting one in the light path, and it's likely that you would have insufficient in travel with a Newtonian Reflector. The ZWO ADC for example adds about 40 mm to the light path, so you would need this extra amount of in travel available, although you can reduce it by adding a 2" In Travel adaptor and/or replacing the 1.25 in barrel on the ADC by a male/male T thread adaptor which will connect directly to a ZWO camera. 

On the other hand, you should be able to reach focus with a Barlow, as they typically add about 20-30 mm out travel distance, but I can't guarantee it, so maybe a good idea to check with a cheap camera first.

In addition, if you purchased the camera from FLO, and found then you couldn't reach focus, I think that they would allow you to return it for a refund. 

John 

Edited by johnturley
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