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Selecting a camera

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#1 capella07

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Posted 02 February 2019 - 10:49 AM

While researching for a camera to get started in EAA, the one constant that I've found is that there are a lot of differing opinions when someone asks what camera they should get when getting started in EAA. There are a lot of trade-offs from one camera to another, from price to pixel size to resolution to framerate and more! Two people could be starting out with the same goal (DSOs for outreach, for example) and each could be happy with different cameras.

 

So, with that in mind, I'm not asking what you think I should get, but how do I decide what to get. My main purpose would be near-real-time imaging of DOSs (mainly, but planets also) for outreach. I live in rural Minnesota, so have very dark skies and I'm not looking to win any awards for images - just casual viewing and outreach.

 

I've been approved a budget by the "treasurer", but she's fortunately interested in EAA too, so I have a decent price range to work with! wink.gif

 

I've put together a chart of the cameras that I'm considering/comparing and as I said, I understand there are trade-offs from one camera to the next. I'm just not sure how to decide on which of those I should decide on to meet my needs.

 

Here's the chart that I've put together (sorry it's so dang big - it's a screenshot of an Excel table and I didn't really want to fiddle with sizing it down!):

 

EAA%20Cameras%20Comparison%20Chart.png



#2 OleCuss

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Posted 02 February 2019 - 04:38 PM

Cool that you set all that up!

 

But to help you I'd really want/need to know a whole lot more.

 

1.  What is your budget?

2.  With what OTA do you plan to use this camera?  Also, do you plan to use a focal reducer?

3.  With what mount to you plan to use this OTA and camera?

4.  How will the image be viewed?  Little computer screen or a big 4K screen - or something else?  Will you be wanting to zoom/crop down to small parts of the image?

5.  I just want to confirm that you will be in a dark site when used.  Otherwise I'd want to know if you have any filters already?

6.  Do you prefer a wider FOV (like being able to frame the entirety of M31 in a single shot with the sensor) or will you be going for the narrow/tight views of the DSOs and planets?

 

Without more information I'd just go to one of the IMX294 cameras.  That works for most of us doing OAP.  But there are cases where that just isn't the best choice.



#3 capella07

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Posted 05 February 2019 - 12:20 PM

Cool that you set all that up!

 

But to help you I'd really want/need to know a whole lot more.

 

1.  What is your budget?

2.  With what OTA do you plan to use this camera?  Also, do you plan to use a focal reducer?

3.  With what mount to you plan to use this OTA and camera?

4.  How will the image be viewed?  Little computer screen or a big 4K screen - or something else?  Will you be wanting to zoom/crop down to small parts of the image?

5.  I just want to confirm that you will be in a dark site when used.  Otherwise I'd want to know if you have any filters already?

6.  Do you prefer a wider FOV (like being able to frame the entirety of M31 in a single shot with the sensor) or will you be going for the narrow/tight views of the DSOs and planets?

 

Without more information I'd just go to one of the IMX294 cameras.  That works for most of us doing OAP.  But there are cases where that just isn't the best choice.

Great questions and I can see that I didn't provide nearly enough info for people to help, so here goes:

 

1 - up to $1,000, but I'd like to keep it under $500 if possible

2 - Not sure what "OTA" is referring to, but yes, I will be using a focal reducer.

The scope I'll be using for this is a Celestron Nexstar GPS 8 with an f/ratio of 10 and focal length of 2032, so I'll be getting an f/6.3 reducer.

3 - I think the scope info above answers this.

4 - The image will be viewed on a laptop. Zooming - didn't think of that, but probably not.

5 - I live in rural Minnesota and have very dark skies, but as far as filters I do plan on getting an O3 filter for nebula viewing

6 - Wider FOV would be preferable to be able to show galaxies. Being able to show M31 is a good example.

 

Thanks!



#4 OleCuss

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Posted 05 February 2019 - 02:19 PM

The OTA is the Optical Tube Assembly which is pretty much the tube and everything which is not frequently or easily removed (like a focuser).

 

With your NexStar, even with the reducer you simply will not be able to image the entirety of M31 in one frame.  You may be able to create a mosaic (in conventional AP mode), but your focal length is simply too long to allow imaging it in a single frame.

 

Given an 8" OTA with a long focal length, a decent image circle and that you'll be doing OAP (Observational AP) rather than CAP (Conventional AP)?  I'd go with an IMX294 camera.  Since cooling doesn't seem to help much with OAP that drops your price a bit.  I'm assuming you will have USB3 available because if you are doing USB2 I'd probably insist on the extra memory and getting the memory probably means getting cooled.

 

The IMX294 camera means you get a fairly wide FOV.  The larger pixels mean you won't be over-sampling as much as if you used a sensor with smaller pixels.  The great dynamic range of the IMX294 means you'll have better images of dim targets without over-exposing the brighter stuff in your FOV.  The SNR1 of the IMX294 is very good indeed which means it is very good for short exposures.

 

I would tend to favor the ASI294 over those made/sold by others because of the price point and the slightly enlarged sensor along with good SharpCap compatibility.  One of the ToupTek cameras would also work well but the compatibility that I want with SharpCap is not quite as good.


Edited by OleCuss, 05 February 2019 - 02:20 PM.

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#5 saguaro

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Posted 05 February 2019 - 02:49 PM

With your Nexstar mount, you will need to keep in mind the clearance between the eyepiece end of the scope and the base of the mount with your camera and focal reducer attached. Your best bet is probably the 294 uncooled version which has a shorter length and provides the advantages that OleCuss describes.


Edited by saguaro, 05 February 2019 - 02:50 PM.

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#6 capella07

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Posted 06 February 2019 - 06:07 AM

Thanks, saguaro and OleCuss!

 

So the 295 should be on my radar. What would be a decent alternative to that in my chart?

 

Also, considering OleCuss's comment that my scopes' focal length probably wouldn't allow me to get all of M31 in the image at one time, is there any way to know what I can expect to see with a particular camera with my scope so I can get an idea of what to expect?


Edited by capella07, 06 February 2019 - 06:10 AM.


#7 OleCuss

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Posted 06 February 2019 - 09:33 AM

Do an Internet search for CCDCalcFull and run that with the specifications for your camera and OTA.

 

I think there are other astronomy FOV calculators which you may like even better and an internet search is likely to turn up several of them.

 

And the thing about not being able to fit all of M31 into the FOV is not a "probably".  That is definite.  The rule-of thumb is that for getting all of M31 into a single frame with an APS-C sized sensor you need to have a focal length of no more than 600mm.  There are some little variations and quibbles about that with which one can play but you cannot violate that by much..

 

But even when you get a 0.63x reducer and pair it with that OTA your focal length is 1280mm and your IMX294 sensor is smaller than is the APS-C sensor.  You simply cannot make that work for a single-frame image of the totality of M31.

 

Now if you got a 0.33x reducer you'd be bringing your focal length down close to where it would need to be with an APS-C sensor, but that reducer would produce such a small image circle that you'd still not have all of M31, you'd have a little bit of M31 and a whole lot of horrible vignetting.

 

Fortunately there are a lot of targets which are much smaller than is M31.  You can have a lot of enjoyment without capturing M31 in its entirety.



#8 descott12

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Posted 06 February 2019 - 10:16 AM

One other option is to get a Hyperstar instead of a traditional FR. That will convert your scope to F2 with a very wide FOV and M31 will fit nicely. I don't recall if your scope is Hyperstar-compatible. I think you can tell if the secondary mirror assembly says something like "Fastar" on it.  I think all Nexstars are compatible...

 

The Hyperstar has the added advantage of attaching to the front of the scope so there a no issues of running out of space on the back end and you can usually point your scope all the way to vertical.

 

I use the Evo 8 + Hypersar + the ASI 294 cooled and I think it is a great combination.  The hyperstar is pricely (about $1100) but it is worth it IMO and is something you will use for years.

 

EDIT: actually, M31 may not fit completely. My images probably don't capture it's full extent but it looks really nice to me.

 

EDIT again: the FOV of my setup is 3436 x 23.2 mm / 404 mm = 197 arc-min so M31 just fit.


Edited by descott12, 06 February 2019 - 09:40 PM.


#9 capella07

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Posted 07 February 2019 - 10:51 AM

Do an Internet search for CCDCalcFull and run that with the specifications for your camera and OTA.

 

I think there are other astronomy FOV calculators which you may like even better and an internet search is likely to turn up several of them.

 

And the thing about not being able to fit all of M31 into the FOV is not a "probably".  That is definite.  The rule-of thumb is that for getting all of M31 into a single frame with an APS-C sized sensor you need to have a focal length of no more than 600mm.  There are some little variations and quibbles about that with which one can play but you cannot violate that by much..

 

But even when you get a 0.63x reducer and pair it with that OTA your focal length is 1280mm and your IMX294 sensor is smaller than is the APS-C sensor.  You simply cannot make that work for a single-frame image of the totality of M31.

 

Now if you got a 0.33x reducer you'd be bringing your focal length down close to where it would need to be with an APS-C sensor, but that reducer would produce such a small image circle that you'd still not have all of M31, you'd have a little bit of M31 and a whole lot of horrible vignetting.

 

Fortunately there are a lot of targets which are much smaller than is M31.  You can have a lot of enjoyment without capturing M31 in its entirety.

I'll take a look around for a FOV calculator.

 

Thanks for the info about M31. I didn't have my heart set on getting all of M31, but that info gives me a good idea of what to expect and what I can do to address it.

 

One other option is to get a Hyperstar instead of a traditional FR. That will convert your scope to F2 with a very wide FOV and M31 will fit nicely. I don't recall if your scope is Hyperstar-compatible. I think you can tell if the secondary mirror assembly says something like "Fastar" on it.  I think all Nexstars are compatible...

 

The Hyperstar has the added advantage of attaching to the front of the scope so there a no issues of running out of space on the back end and you can usually point your scope all the way to vertical.

 

I use the Evo 8 + Hypersar + the ASI 294 cooled and I think it is a great combination.  The hyperstar is pricely (about $1100) but it is worth it IMO and is something you will use for years.

 

EDIT: actually, M31 may not fit completely. My images probably don't capture it's full extent but it looks really nice to me.

 

EDIT again: the FOV of my setup is 3436 x 23.2 mm / 404 mm = 197 arc-min so M31 just fit.

I looked it up and there is a Hyperstar compatible with my scope - pricey, though, so I'll put that on the wishlist...

 

------

 

If I were to go with something other than the 294 to keep the price down, what would you suggest?



#10 Jeff Lee

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Posted 07 February 2019 - 11:01 AM

If you go with a smaller chip (like the 224) you can find a used Meade FR3.3 and then your are in business. Because I had a Gx8 (m43 Panasonic) and SharpCap introduce the watch folder which gave me large sensor image, I addedthe 224 on the C8 @ f3.3 and it rocks. You are looking at around $300-350 for this setup and it is perfect for a C8. Better cameras (meaning larger sensor) of course would work well with the FR6.3 and the subjects your are interested in, well DSO's are small so you may even end up doing what my friend does with a goto 16" dob - lots of very short exposures -and as long as you are USB 3.0 and have a fast frame rate (say 60 FPS and 1 or 3 second exposures you should meet your criteria.

 

On my Alt-AZ/EQ mount I run my C8 @ fr6.3 or 3.3 and my ES102 @ f7 or f3.5 (inexpensive .5 reducer). A C8 and fast camera gives you F20/F11/f6.3/F3.3  - So you might thing about an uncooled 294 & 223 would give you an amazing set of focal lengths for planets and DSO's.

 

I've found EAA to be a lot of trial and error, some folks even stack 2 FR6.3 (I think you might get some vignetting but you can slightly enlarge the image on screen if that bothers you.

 

Good luck.


Edited by Jeff Lee, 07 February 2019 - 11:05 AM.


#11 saguaro

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Posted 07 February 2019 - 03:31 PM

+1 on using a Meade 3.3 focal reducer with your 8-inch SCT. For my 8-inch SCT on an Evolution Alt-Az mount, I use a Meade 3.3 focal reducer and a 385MC (larger sensor than the 224 but with similar sensitivity). I got my 3.3 FR by putting a "wanted" ad here on CN and also on Astromart.

 

Here are some recent screenshots of this combo using SharpCap Pro 3.2 live stacking:

https://www.cloudyni...92#entry9097239

https://www.cloudyni...92#entry9097244

https://www.cloudyni...92#entry9097245

 

I also highly recommend getting Starsense, which will do the alignment for you. With the smaller sensors in the 224 and even the 385MC, getting an accurate alignment is even more important. After letting Starsense do the alignment, my target is always in the camera's field of view.


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#12 descott12

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Posted 07 February 2019 - 03:59 PM

 

 

Here are some recent screenshots of this combo using SharpCap Pro 3.2 live stacking:

https://www.cloudyni...92#entry9097239

https://www.cloudyni...92#entry9097244

https://www.cloudyni...92#entry9097245

 

 

Those are amazing views of the horsehead! I wish I could get that where I live.  I may have to move...


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#13 eekeek77

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Posted 15 February 2019 - 05:58 PM

Lots of good advice. If I may add a few points...   

 

Uncooled IMX294 cameras are available for ¾ the price of the cooled versions. It's a very useful thing to have if you're doing looooong exposures. But you don't need to here.

 

You can do a lot with the 6.3 reducer. Lots of them available second hand. You'll need up to 100mm of extension tubes to go with this depending on the camera. You'll have to shift the OTA forward a lot before you can point near the zenith.

 

3.3 is an extreme reduction. It works but the image goes bad very quickly out from the centre of the image circle. So you partner it with a small sensor that only sees the centre of the image circle. But this makes it really hard to do your alignment... I'm not a fan. I'm much happier with the larger IMX294 sensor. Horses for courses!

 

Hyperstars are great! But they are expensive and heavy. The scope becomes top heavy. Again the nexstar might not be up to it.

 

I find   astronomy.tools/calculators/field_of_view/   much easier to use than ccdcalc. But that's because I like pictures and pretty colours!

 

Sharpcap is amazing! If you have a wide enough field of view, (pretty wide), it will do the plate solving and alignment that the Starsense does, using your imaging camera. I admit I've not got that working yet!


Edited by eekeek77, 15 February 2019 - 06:00 PM.

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