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Choosing a camera (sensor size)

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#1 chilldaddy

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Posted 17 February 2019 - 06:16 PM

Hello CN!  Though I've been reading for a while, this is my first post and I look forward to interacting with this great community.

 

With a C8 on an EVO mount, I am looking at a first camera for EAA.  I'd like to find the best option that will display a reasonably wide range of object sizes.  I have studied the Agena Buyer's Guide to ZWO Astronomy Cameras  https://agenaastro.c...pixelsizeandres  as well as spent a lot of time with the FOV calculator at astronomy.tools both of which have been very helpful.  It appears that no single camera will be ideal for planets and small DSOs all the way up to large DSOs, therefore I'm considering three approaches with a budget of around $750.

 

#1 Small sensor (ASI224 or 290) 

Planets/small DSOs - 2X Barlow

Med DSOs - .63 and .5 focal reducers

Large DSOs - not happening

 

#2 Medium sensor (ASI183)

Planets/small DSOs - 2X Barlow (zoom in w/Sharpcap?)

Med DSOs - .63 and .5 focal reducers

Large DSOs - better with reducers but still not quite enough

      

#3 Large sensor (ASI294)

Planets/small DSOs - 2X Barlow not enough (3X, 4X, zoom in w/Sharpcap?)

Med DSOs - reducers/Barlow

Large DSOs - pretty close

 

I have a 2X Barlow and plan to purchase a .63 SCT reducer and a .5 camera reducer.  The $250 ASI224 is appealing at roughly 1/3 the cost of the $700 ASI294 but if it means another camera purchase is necessary or a shorter focal length system is needed, then that becomes irrelevant.  The larger sensor ASI294 with a much wider FOV won't display the planets well, unless zooming in with software works better than I expect.

 

The solution may be two cameras or two OTAs.  A small refractor would be a very nice option in the future, but I'd prefer to not swap cameras or OTAs if I'm trying to keep the interest of friends and family.

 

Questions:

1. Am I looking at this properly or are there other factors I should be considering?

2. Will zooming in with Sharpcap be acceptable for small objects if using a large sensor camera?

3. Would a 3X or 4X Barlow work well or is that pushing it?

4. Would you recommend one of the three options or do you have a better one?

 

I'm excited to see and share more from my Bortle 7 backyard and appreciate any advice and suggestions you may have!

 

Thanks,

 

Greg


Edited by chilldaddy, 18 February 2019 - 12:17 AM.

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#2 Gary Z

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Posted 17 February 2019 - 08:33 PM

Welcome Greg,

 

I can tell you as an owner of both the 224 and the 294, the 224 will be great for planetary, and, as you surmised, not great for you for DSO observing.

 

Now, here's a tool to help gauge field of view specifying optics:
 
 
I have used the 294 with my AT72 and have been pleased with the outcome for DSOs.  I have also used the 294 on my C8 for lunar imaging and love the wider view it gives.  
 
Sharpcap has a live view which allows you to save the image as you see it in live view.  This makes for some interesting EAA imaging.  I have used the circle reticle to help keep the view centered when I'm imaging using the EVO mount which also helps.
 
Gary


#3 chilldaddy

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Posted 18 February 2019 - 07:48 PM

Thanks Gary,

 

It looks like starting with the 224 and adding a 294 later might be a good plan since funds for both are not available right now.  I suppose the real question then is whether something in between, like the 183, would be "good enough" and not limiting in the future.  In other words, are the planets still big enough to enjoy and is fitting most of the larger DSOs (M31, M42, M45) in the FOV still satisfying?  This is obviously subjective but since I don't have any of these cameras, I'm interested in other users' experience and opinions.

 

Thanks,

Greg


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#4 ACFrost

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Posted 18 February 2019 - 09:46 PM

A couple of other options that can be incorporated and make available larger DSO while still using a small sensor camera are the hyperstar (blowing the budget probably), or a small, inexpensive, fast finder scope such a the relatively budget friendly Orion Deluxe Mini 50mm guide scope.

 

I use the deluxe mini guide scope, piggybacked using an adapter, with a C6 on evolution mount and very much enjoy the convenience & versatility of this set up for EAA. The little finder scope with ASI 290 mono provides a great FOV for the larger DSO, and the evo 6 covers pretty much everything else using reducers.

 

Mono camera is a better choice for the little guide scope than the color 224 though, I pretty much reserve the color camera for use on the 6" SCT. Everything has it's limitations one way or another.



#5 mikenoname

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Posted 19 February 2019 - 01:52 AM

How does the 6" SCT and 224 do on galaxies and planetary nebulae (you know, the small stuff)? Is there enough focal length there to be able to resolve them well or is an 8 really needed?



#6 chilldaddy

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Posted 19 February 2019 - 02:33 AM

A couple of other options that can be incorporated and make available larger DSO while still using a small sensor camera are the hyperstar (blowing the budget probably), or a small, inexpensive, fast finder scope such a the relatively budget friendly Orion Deluxe Mini 50mm guide scope.

 

I use the deluxe mini guide scope, piggybacked using an adapter, with a C6 on evolution mount and very much enjoy the convenience & versatility of this set up for EAA. The little finder scope with ASI 290 mono provides a great FOV for the larger DSO, and the evo 6 covers pretty much everything else using reducers.

 

Mono camera is a better choice for the little guide scope than the color 224 though, I pretty much reserve the color camera for use on the 6" SCT. Everything has it's limitations one way or another.

A small 50 mm is a great idea for wide FOV at a low cost.

 

Would you elaborate on why mono is better than color for this?

 

Thanks,

Greg


Edited by chilldaddy, 19 February 2019 - 02:34 AM.


#7 nic35

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Posted 19 February 2019 - 11:19 PM

Greg:

 

I don't do planetary stuff, but I think it is worth pointing out that nothing says you have to run the the 294 at full frame and hope for zooming in sharpcap.  The 294 supports small frames - down to 320x240, and gets high frame rates at those smaller sizes - up to 180 or so frames per second.

 

At full frame, you'd get only 20 or so frames per second.

 

The key differences, as I see it are that the pixels on the 224 are somewhat smaller  3.75 vs 4.63 microns, and  the 224 is somewhat more sensitive.  See https://www.webastro...x294-et-imx183/ if you are into the details (and can reasonably translate scientific french).

 

I suspect that with the right combinations of resolution, barlows and exposures, the 294 will perform similar to the 224 for planetary work.

 

On the other hand, nothing can make the 224 perform like a 294 in terms of Field of view and resolution.

 

john 


Edited by nic35, 19 February 2019 - 11:19 PM.

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#8 ACFrost

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Posted 19 February 2019 - 11:41 PM

8" SCT is not absolutely needed  with 224/290 but in truth I prefer the views and image scale I have seen posted from others using 8" SCTs over the 6". If I was buying and could afford the 8" that is what I would go with. Not much downside going with the 8 over the 6, but already having the 6 I don't really feel the need to upgrade to more aperture for my purposes.

 

The inexpensive little guide scope is an achromat, so the inherent issues of an achromat (chromatic abberation, star bloat, etc) is there when using color camera. Not as much of a concern if using mono camera.

 

The 6" SCT+ 224/290 does fine on galaxies and planetary nebula, at least I am pleased with it. But 8" would be better. I spend most of my time looking at galaxies.

 

The 50mm guide scope at F/3.2 is great for big things (m31, m42, larger nebula, etc).

 

If I were going for mostly planetary nebulae or alot of really deep tiny stuff, or just wanted a bigger & more detailed image I would prefer something better suited than the 6" sct., but would expect other compromises (cost, convenience, etc)

 

Using reducers to get to roughly F/4 with the 6" SCT gives a nice size image on a 14" laptop screen for lots of medium-ish sized galaxies. The smaller the object appears, using less focal reduction makes sense, at the cost of increasing exposure/stack time needed.

 

Using the astronomy tools FOV calculator should give you some sense of the image scale available. With focal reducers I can use the 6" SCT at F/10, F/6.3, F/5, or F/4. I spend most of my time with the 6" SCT at F/4 ish with .63 + .5 reducers combined. It's a very versatile FOV and image scale but does have limitations.

 

Native focal length of F/10 SCT is nice for tiny stuff but I often just use zoom when I don't feel like fiddling with the reducer combination. Can be tricky finding objects in FOV at longer focal lengths, but starsense helps speed up acquisition. If i am really struggling, I find/center at shorter FL then decrease reduction after finding/centering/tracking.

 

If I can find some time I will try to dig out some saved sharpcap images at the various focal lengths with this set up to maybe give a sense of image scale but I wouldn't hold your breath, free time is at a premium for me these days.

 

All that said, I do want a 294 camera...smile.gif


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#9 chilldaddy

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Posted 20 February 2019 - 12:17 AM

Greg:

 

I don't do planetary stuff, but I think it is worth pointing out that nothing says you have to run the the 294 at full frame and hope for zooming in sharpcap.  The 294 supports small frames - down to 320x240, and gets high frame rates at those smaller sizes - up to 180 or so frames per second.

 

I suspect that with the right combinations of resolution, barlows and exposures, the 294 will perform similar to the 224 for planetary work.

 

On the other hand, nothing can make the 224 perform like a 294 in terms of Field of view and resolution.

 

john 

So John, are you saying that reducing the capture area to a lower resolution will produce similar quality to a smaller sensor camera?  It appears you'd then have to zoom to fill the screen again and I don't understand how that is different from zooming from the start.  Is it about frame rates where the advantage is seen?  I am just starting to play with Sharpcap so this is all new to me.

 

Thanks!

Greg



#10 Howie1

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Posted 20 February 2019 - 07:34 PM

chilldaddy, heaps of options as you can see from folk helping you out here! 

 

And I can offer even one more option which I've seen done. 

 

C8 + small 50mm x 162mm finder-guider with helical focuser + one or two small chip cameras (IE highly magnifying due to small chip) + 0.5x reducer

 

This will give you ............

 

Finderguider with helical focuser + 224 yields 1.7 deg FOV at fast f/3.2 for big stuff like M31, M45, NGC224 (rosette) etc

 

C8 + 0.5 reducer + 224 yields almost 1/3 deg (FOV 17') at reasonably fast f/5 for the medium and also for the small stuff. Planets with the 224 are easily done with 2x barlow or bit of software zoom

 

If you think M31 doesnt quite show its very outer arm extremities with the 224 in the finder guider with helical focuser .... then a slightly bigger sensor like the 385 (which is close to the 224 in terms of sensitivity) will give you ....

 

Finderguider with helical focuser + 385 yields 2-1/2 deg (2.57 deg) FOV at fast f/3.2 for big stuff like M31, M45, NGC2244 etc, etc

 

C8 + 0.5 reducer + 385 yields almost 1/2 deg (FOV 25') at reasonable fast f/5 for medium and small stuff. Again planets are nicely viewed with 2x barlow or a bit of software zoom.

 

If you do decide to investigate further .... be absolutely sure to look at the 50mm x 162mm finder guiders WITH helical focuser. It allows fine tuning of the focus with the camera inserted (EASILY) .... vs trying to focus by undoing thumbscrews and adjusting manually pulling the camera in and out in order to focus (HARD) if the finderguider doesnt have the helical focuser.



#11 chilldaddy

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Posted 21 February 2019 - 09:57 PM

Thanks everyone for some great ideas!  I think a short focal length refractor, whether a 50 mm guidescope or a higher quality AT60 perhaps will be a great combo with the C8 providing small and large FOVs between both instruments.  Those are both available at very low prices and I can work towards that as a next project.  This approach also allows for visual use whereas a second camera would require always using a computer screen.

 

As a result, I decided on the smaller sensor of the ASI385.  It's essentially the big brother of the ASI224 with the same sensitivity and speed but with a slightly wider FOV and a much higher resolution.  The cost was $370 compared to $250 for the 224.  The large frame ASI294 still looks like a great camera, but at $700 is a bit more than I want to spend just starting out considering I'm also buying two focal reducers.  I need to get my feet wet with EAA and see if this works as well as I'm hoping.

 

Thanks again for the input!

Greg


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#12 mclewis1

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Posted 22 February 2019 - 07:40 PM

Greg, 

 

The IMX 224 and 385 sensors will deliver exactly the same resolution when used in the same scope configurations since they have the same size pixels. The fields of view will indeed be different (different aspect ratios and more pixels in both horizontal and vertical dimensions with the 385 sensor), but the resolving capability of each sensor will be the same.


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#13 chilldaddy

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Posted 22 February 2019 - 09:03 PM

Mark,

 

Yes, I understand now.  I was thinking of the increased pixel count of the sensor when I said resolution.  Thanks for pointing that out.  I'm learning.

 

Greg



#14 chilldaddy

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Posted 12 March 2019 - 09:44 PM

After my first week with the ASI385 I have to say I am very pleased with the purchase.  My first couple attempts were surprisingly successful and my first extended session last week was a thrill.  The only thing that stopped me that night was the clouds.  This is why I got into EAA!  I saw things that have only been colorless smudges in the eyepiece.  Seeing detail in galaxies has been particularly fun.

 

For anyone wondering if EAA really works, it does.  Getting enough stars for alignment can sometimes be tricky depending on the target, but when you can watch them stack and reveal more and more detail and color, it's enough to keep you coming back for more.

 

These images are by no means great, but for me, they represent seeing more than I've ever seen before and give me hope for far better observing as I learn how to use the gear. Being able to learn from others on this forum has been extremely helpful, so Thank You to all you generous people out there who contribute and share your experience. This is going to be a lot of fun!

 

Greg

 

All images were obtained with an ASI385MC and C8 at F/5 on an Evo mount using Sharpcap.  They were saved as viewed and cropped.

 

M1 Crab Nebula cropped copy.png

M1 209x5sec

 

NGC 3242 Ghost of Jupiter  crop tight copy.png

NGC 3242 Ghost of Jupiter Nebula 99x3.5sec


Edited by chilldaddy, 12 March 2019 - 10:33 PM.

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#15 chilldaddy

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Posted 12 March 2019 - 09:46 PM

M51 Whirlpool Galaxy cropped copy.png

M51 157x4s

 

M65 cropped copy.png

M65 111X6S


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#16 chilldaddy

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Posted 12 March 2019 - 09:47 PM

M81 crop copy.png

M81 220x4.5s

 

M82 crop copy.png

M82 202x6s


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#17 Alien Observatory

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Posted 12 March 2019 - 10:38 PM

Greg, I think you made a wonderful choice with a SCT 8" and the ASI385 cam.  You can use the SCT Reducers and Barlow adapters to extend the range of your telescope (from F2 Hyperstar to F25 using a 2.5 Barlow)...and that will cover almost everything visible in the sky...Many start with a 6" scope then upgrade after some time...this is (in my own opinion) one of the best starter combinations available today...

 

Your images are very good, and if I could ask one small favor please take a screen shot of your SC stack and post it along with the cropped image....that is very helpful for those having an interest in EAA, but not sure what they can see with any combo (tele and cam)...

 

Pat Utah waytogo.gif


Edited by Alien Observatory, 12 March 2019 - 10:41 PM.


#18 Rickster

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Posted 12 March 2019 - 11:57 PM

Congratulations Greg.  It looks like you are off to a good start.


Edited by Rickster, 13 March 2019 - 11:46 AM.


#19 Ptarmigan

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Posted 13 March 2019 - 07:22 PM

ASI385 is a good choice. I have the Altair GPCAM3 385c, which uses the same sensor as ASI385. 

 

Great camera. cool.gif waytogo.gif



#20 chilldaddy

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Posted 14 March 2019 - 03:30 PM

Greg, I think you made a wonderful choice with a SCT 8" and the ASI385 cam.  You can use the SCT Reducers and Barlow adapters to extend the range of your telescope (from F2 Hyperstar to F25 using a 2.5 Barlow)...and that will cover almost everything visible in the sky...Many start with a 6" scope then upgrade after some time...this is (in my own opinion) one of the best starter combinations available today...

 

Your images are very good, and if I could ask one small favor please take a screen shot of your SC stack and post it along with the cropped image....that is very helpful for those having an interest in EAA, but not sure what they can see with any combo (tele and cam)...

 

Pat Utah waytogo.gif

Thanks Pat!  I agree that there is a lot of flexibility with reducers and barlows and appreciate your confirmation of my decision on this combination.

 

That's also a great suggestion to post a screen shot.  I have learned from others by looking at their settings or watching them use it live or on video.  I didn't even think of that my first time out as I was figuring out how to use the software! smile.gif

 

Greg


Edited by chilldaddy, 14 March 2019 - 03:31 PM.


#21 chilldaddy

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Posted 14 March 2019 - 03:32 PM

Thanks Risckster and Ptarmigan!  I appreciate the encouragement.

 

Greg




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