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Large aperture, 32 inch (810mm)...what camera?

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#1 ToxMan

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Posted 22 January 2014 - 09:11 AM

In southern Arizona, north of Tucson, at Mt Lemmon Sky Center, some of our group of amateur astronomers may have an opportunity in the near future to take a stab at capturing video of planets when there is an off night from capturing subs for DSOs by our professionals. In all likelihood, during time around full moon. (Or, it might not happen at all.)

In the past, a few folks have shared images taken on very large aperture telescopes...I seem to remember images from Pic du Midi, 1 meter telescope, for instance.

In preparation, we are looking at our cameras, trying to decide which one would pair up nicely (if at all) with such a large telescope. We have DMK31, DMK21AU618 and ASI120MM. We are not sure we can get a good sampling, as there could be a point where unless you have the appropriate pixel size, sensor size, resolution and such, it doesn't gain us a thing over our personal equipment...I'm thinking a barlow is not needed. But, I don't know. And, I can't find a "plug-in the specifications" formula...

Well, which one would you use? Or, would you need something entirely different? Thanks.

Paul

#2 Sunspot

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Posted 22 January 2014 - 09:26 AM

Paul,

I'm not sure what camera I'd use, but it's a problem I'd love to have. I'm thinking perhaps 2x2 binning would help in the final decision?

#3 DesertRat

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Posted 22 January 2014 - 11:20 AM

Paul, you would need a barlow to reach the resolution expected from a 0.8m scope. At the F/7 prime your focal length will be 5.7m, so Jupiter would fit easily on the ASI120 camera. A barlow might be useful.

Use the formula here:

S=(D*EFL)/(206.265*C)

where
EFL- focal length in millimeters
C - size of ccd pixels in microns
D - size of object in arc-seconds
S - size of object in pixels

So with Jupiter at 46 arc-sec, and using the ASI pixels of 3.75u at a focal length of 5700mm we get:

S=(46*5700)/(206.265*3.75) --> 339 pixels.

Not doing the 32 inch justice at that size - but you could turn the gain way down for sure. Even at prime you would get a nice image because of that.

Take a barlow for fun!

Glenn

#4 DesertRat

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Posted 22 January 2014 - 11:31 AM

Paul,

It occurs to me that a nice camera to take would be a DSLR. Small pixels, and no filters needed to capture color. And even without a barlow a chance to get some lucky images assuming you can snap off a bunch.

Glenn

#5 MvZ

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Posted 22 January 2014 - 12:01 PM

Between those three camera's, the DMK31 is not nearly as sensitive (and slower) than the ASI120MM. The DMK618 has probably too few pixels for Jupiter for when the conditions are perfect.

I would probably try to get somewhere around 10 meters focal length with the ASI120MM camera, so perhaps a 2x barlow preferably a bit less. When you use filter wheels or other extension tubes, a 2x barlow can effectively be (much) more like 3x, so take that into account.

Run the camera in ROI (probably something like 800x600 or so), and you can still get high FPS. Match the exposure time to the FPS time, it would be a pity to lose photons because the camera is not fast enough.

I would much rather undersample a little bit and have high FPS (and a MATCHING relatively short exposure times), than oversample with low FPS and matching long exposure times or non-matching short exposure times. There is no such thing as capturing too many photons, don't throw photons away: pick a fast enough camera.

If the seeing isn't working out - or the optics of the scope just around very good for high resolution planetary stuff - just stick with the default focal length, capture at 640x480 with the ASI120MM and use 100FPS or so.


#6 Jesper

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Posted 22 January 2014 - 12:14 PM

Point Grey has a new camera with Sony's new IMX174 global shutter CMOS.

Grasshopper3 2.3 MP Mono USB 3.0
Sony IMX174 1/1.2" Global Shutter CMOS
1920 x 1200 at 162 fps
Mono
Peak Qe 76%
Read Noise 7 e-
Pixel Size 5.86 µm
Prize 1295.00 USD

It sounds great except for the prize :scared:

#7 bunyon

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Posted 22 January 2014 - 03:10 PM

I'd do just what Emil says.

Sounds fun. I hope to see some images...

:)

#8 PiotrM

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Posted 22 January 2014 - 03:32 PM

Whats the f/ratio of the telescope?

#9 ToxMan

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Posted 22 January 2014 - 07:44 PM

Thanks, Folks. This is a great help.

Glenn, appreciate the formula...we are going to get together Sunday and crunch the numbers. We are considering using a DSLR in video mode, too. If nothing else, DSLR will document our efforts.

Great tips, Emil. We have several barlows...1.5x, 2x, 2.5x and 3x. I was thinking the 1.5x on ASI120MM. I figured the sensor on the DMK21 was too small and the DMK31 too slow.

Piotr, it is a Ritchey-Chretien...I'll get the f/ratio as soon as I can. I forgot that would be a helpful piece of information.

We will keep you posted.

Thanks again.

Paul

#10 John Boudreau

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Posted 23 January 2014 - 01:47 AM

Piotr, it is a Ritchey-Chretien...I'll get the f/ratio as soon as I can. I forgot that would be a helpful piece of information.


According to this, it's an f7 scope:
http://sierrastars.c...C32/MLSC32.aspx

Sounds like it could be an interesting night. Hope all goes well!

#11 PiotrM

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Posted 23 January 2014 - 02:06 AM

At f/7 Jupiter will be "small" :D http://www.12dstring...684&barlow=1...

But at ~/f20 it won't fit VGA frame of D*K21: http://www.12dstring...684&barlow=3...

At ~f/17.5 (smaller pixels) it would fit on ASI120 http://www.12dstring...684&barlow=o...

#12 ToxMan

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Posted 23 January 2014 - 07:33 AM

Thanks, John. I thought it was f/7...By the way, Jupiter looks fantastic through this scope with my 22mm type 4 Nagler from TeleVue. I'm taking my 12mm and 9mm eyepieces up this week.

Thanks, Piotr. I went to "12dstring" site. I had forgotten about it when Darryl turned me on to it. Got it bookmarked, now.

Paul

#13 Tellescópio

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Posted 23 January 2014 - 09:08 AM

Sorry, but instead of you think to use ASI120, why you don't use QHY5L-II? It is a very superior and sensible camera. Everybody in a whole world say it.

#14 MvZ

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Posted 23 January 2014 - 09:15 AM

> Everybody in a whole world say it.
In the Tellescópio-webshop-world that sells that particular camera on their front page??

It know the QHY5L-II is a good camera, but really not significantly different from the ASI120MM, and they already have that camera available. But you already said you were sorry, so I forgive you ;)

#15 Sunspot

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Posted 23 January 2014 - 09:32 AM

F/7....yeah, you'll need amplification to do it justice. I can't wait to see what you get. (Saturn maybe?)

#16 ToxMan

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Posted 23 January 2014 - 10:58 AM

I happen like the QHY5L. Don't think we will buy one just for this. But, if I happen to be able to get one for my own kit, we will try it.

I think we are in good shape, Paul. We have a wide range of barlows and the right adapters...extension tubes...you name it. Adam has captured some nice images of Saturn using the 24 inch that is up there, too. I don't know of any great shots of Jupiter obtained with the 32 inch. I know it has been tried with mixed results. We need to get a nice one!

Thanks,

Paul

#17 GeorgeInDallas

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Posted 22 February 2014 - 03:52 PM

Did you ever get an image with the 32 inch?

George

#18 StrangeDejavu

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Posted 22 February 2014 - 04:18 PM

Wow, I will be very excited to see how Saturn or Mars turns out in a 32" scope. Favoriting this thread for future viewing. :waytogo:

#19 Gendo

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Posted 22 February 2014 - 09:53 PM

You could be lazy like me, and just plug the camera specs, barlow specs, and scope specs into Stellarium. You will need to know the individual pixel well size in microns, chip size in millimeters, and pixel count width and height. Barlow is just simple 3X or whatever it is. Scope you need the mirror diameter and focal ratio. It will simulate how it should look. It does eyepieces too. Doesn't seem like Stellarium used to have this feature, but as of v12.4 it does. I could do math, or I could just let this fancy shmancy quad core computer do it for me, quick and easy. LOL

#20 ToxMan

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Posted 23 February 2014 - 01:46 AM

We got clouded out over the weekend we planned to try...But, we aren't giving up. The bulk of the imaging is done trying to get 25 to 30 hours of data of DSOs, which only leaves time around the full moon open for planetary.

I have Starry Nights; but I believe one of the other guys has Stellarium. So, that sounds like a good idea. We will try again for some time mid-March.

It is a team effort...Alan (Lost Plieads Observatory), Dale and me. Thanks for asking. I will keep you posted.

#21 Gendo

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Posted 23 February 2014 - 05:29 AM

I believe Stellarium is open source. If you see those 4 icons in the upper right corner, then you can add in as many scopes, eyepieces, amplifiers, and cameras as you like. Then mix and match them to your heart's content. Might have to enable the ocular icon first in the bottom toolbar that auto-hides itself before the four icons at the top show up. I forget if they were up in that corner to begin with.

I'm not sure how accurate it really is, but it seems to be close. Regular barlows tend to amplify either more or less the further the sensor is from the lens group, so it may not be a perfect simulation for those. My Klee with Chameleon through the C11 made a somewhat larger image than what Stellarium portrays, but then again, I never was sure if I put the lenses to that barlow back together correctly (made a dumb mistake while cleaning it years ago, which forced a surgery, lol). Telenegatives like Tele Vue's Powermates should only change very slightly with distance, if at all.

btw, the 8" f/4.2 newt is my crazy mirror making adventure, in case that had anyone thrown off. :grin:

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#22 ToxMan

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Posted 23 February 2014 - 08:30 AM

Thanks, Justin. We have all the parameters of the cameras, barlows and the telescope. We will be going over our plans when we meet to work on our image capture and processing techniques. I'm looking at the "Ides of March" and the next full Moon for the attempt. :fingerscrossed:

#23 thonybear

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Posted 23 February 2014 - 11:12 AM

Hi Paul,

Please use the 2x or 3x Barlow lens for only GRS zoom!
Overview of Jupiter can be normally archive by any telescope.
But for 1 m aperture a specific picture like GRS or GRS JR, only IO etc.

Cheers!

#24 ToxMan

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Posted 23 February 2014 - 03:34 PM

We'll do our best, Tony. I would like to get some "closeups" of certain features, too. If we have ample time, we will like try several combinations. Thanks.






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