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Help me photography Jupiter with a 115mm refractor

beginner refractor astrophotography
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#1 GoateeAP

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Posted 03 July 2020 - 04:07 PM

This is my first CN post. I have been doing DSLR AP for one year with the stock Canon 75-300mm lens. After much research I've purchased the AT115EDT has a balance between DSO and planetary AP.

 

I have:

  • Astro-Tech AT115EDT triplet APO
  • Astro-Tech 1.0 Flattener and 0.8 Reducer
  • Canon T3i stock crop sensor
  • Canon 6D stock full frame
  • SkyWatcher EQ6R Pro Mount
  • Generic T ring adapter for prime focus and eye piece projection
  • Assortment of Orion eyepieces

I want to take best possible shots of Jupiter and Saturn coming up, and I am willing to buy whatever else I need to make that happen (Tele Vue PowerMate, etc.).

 

Reading posts and watching videos my head is spinning. There are so many combinations and so much math.

  • Should I use prime focus or eye piece projection?
  • At 805mm focal length I'm going to need a Barlow or PowerMate to reach the planets. 2x, 2.5x, 4x?
  • Crop sensor or full frame?

I would appreciate all advice for the best possible results with this gear, and I would like to invest in a PowerMate pending recommendations. Thanks.

 

Mr. Ashley, Columbus, Ohio

 


Edited by GoateeAP, 03 July 2020 - 04:17 PM.

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#2 scopewizard

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Posted 03 July 2020 - 04:52 PM

Best thing to do is to to this site and use the field of view/imaging.

 

https://astronomy.tools

 

Select your scope data, possible barlow mentioned and possible needed camera.

DSLR with either full-frame or DX are not normally suitable due to large sensor.

 

I use the ZWO ASI385 and ASI178 on C8 with 2x barlow.


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#3 petert913

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Posted 03 July 2020 - 05:16 PM

Yes, at only 800mm focal length you will need a 4x-5x Barlow.  I shoot Jupiter with my C8 with a 2x Barlow and little ASI120 camera.  So my F/L is 4000mm and Jupiter is still a bit small.  Your DSLR has such a large sensor, it will appear even smaller.


Edited by petert913, 03 July 2020 - 05:20 PM.

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#4 FlankerOneTwo

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Posted 03 July 2020 - 05:34 PM

Probably some of the super knowledgeable folks will chime in at some point, but this is what's worked for me so far.

 

For planets, best imaging technique is going to be "lucky imaging", which involves taking video at high frame rates and short exposures in order to minimize the effects of atmospheric movement ("seeing"), and stacking the best few percent. I'm getting 185 fps from my ASI290 in a C11 with no barlow with a 400x400 pixel ROI and 4ms exposures. With my local seeing (best described as "meh") I might end up stacking 1-2% of 50,000+ frames before I start losing sharpness of fine details. If conditions are really good, I'll bump up to a 2x PowerMate. I don't know if you can specify an ROI for video on your cameras, nor what the maximum frame rate is. This is important for Jupiter in particular because the rapid rotation of the planet limits you to about 3-4 minutes of video before rotational movement become significant at usual imaging scales, and you have to use additional software like WinJuPos to "undo" the rotation. You might want to consider getting something like an ASI224MC or ASI290MC so that you can do this effectively.

With this technique, you want your pixel sampling to be fairly high, close to the theoretical limits for your aperture. Because the planets are fairly small, you can use small regions of interest (ROI) to increase the camera throughput. For Jupiter, (very) rough rule of thumb is to expect around 1 pixel per mm of aperture, so 115px across the disk for your scope. Or you can use Dawes Limit, or some have proposed 6-7 pixels across the theoretical Airy disk. If your seeing is really good, you could go higher, if it's not so good you might want to go lower. For example, with my setup and no barlow, I'm at 4.6 px/disk, a 2x puts me at 9.2 px/disk. I'll run through the numbers for your setup below.

 

Astronomy.tools is excellent for figuring out the numbers for your individual setup.

At 115mm aperture and 4.3 micron pixel pitch, your Dawes Limit (measure of theoretical resolving power, depends only on aperture) is 1.01 arcsec. At native focal length, your pixel scale with the T3i is 1.1 arcsec/px (depends on focal length and pixel size). You typically want pixel scale to be no larger than 1/2 of your Dawes Limit in order to adequately sample a feature of that size; this is known as the Nyquist criterion. So you would want at least a 2x barlow. That's just a minimum, higher such as 3-4x may certainly be usable depending on your seeing.

If we want to use the Airy disk criteria, the calculator at http://www.calctool....ptics/spot_size calculates a spot size of 9.4 microns (depends on f ratio only, but also wavelength of light - green is used as a middle of the road color), meaning that an infinitesimally small point of (green) light will produce a central spot no smaller than 9.4 microns on your sensor. So at native focal length and no barlow, you are at a little over 2 pixels per Airy disk (9.4 / 4.3). So a 3x barlow would get you to a reasonable sampling for average seeing.

 

If your seeing is excellent, you can use a barlow of higher power. If your seeing is not so good, you might want to go lower. A highly magnified image of a blurry planet is ... still blurry, just bigger.

 

Prime focus, always, for best image quality. You probably should use AutoStakkert for stacking, as it stacks small image segments based around alignment points, which yields a better result than stacking entire frames only. I like FireCapture for acquisition, although I don't if that will work with the Canon.

Hope this helps and makes some of the terminology a bit more understandable! Have fun!


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#5 GoateeAP

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Posted 03 July 2020 - 05:38 PM

Best thing to do is to to this site and use the field of view/imaging.

 

https://astronomy.tools

 

Select your scope data, possible barlow mentioned and possible needed camera.

DSLR with either full-frame or DX are not normally suitable due to large sensor.

 

 

Nice web site! Wow, that's helpful. Thanks!



#6 Tulloch

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Posted 03 July 2020 - 05:40 PM

This is my first CN post. I have been doing DSLR AP for one year with the stock Canon 75-300mm lens. After much research I've purchased the AT115EDT has a balance between DSO and planetary AP.

 

I have:

  • Astro-Tech AT115EDT triplet APO
  • Astro-Tech 1.0 Flattener and 0.8 Reducer
  • Canon T3i stock crop sensor
  • Canon 6D stock full frame
  • SkyWatcher EQ6R Pro Mount
  • Generic T ring adapter for prime focus and eye piece projection
  • Assortment of Orion eyepieces

I want to take best possible shots of Jupiter and Saturn coming up, and I am willing to buy whatever else I need to make that happen (Tele Vue PowerMate, etc.).

 

Reading posts and watching videos my head is spinning. There are so many combinations and so much math.

  • Should I use prime focus or eye piece projection?
  • At 805mm focal length I'm going to need a Barlow or PowerMate to reach the planets. 2x, 2.5x, 4x?
  • Crop sensor or full frame?

I would appreciate all advice for the best possible results with this gear, and I would like to invest in a PowerMate pending recommendations. Thanks.

 

Mr. Ashley, Columbus, Ohio

Hi there, for best results in planetary imaging you would generally need a large aperture - 8"+, as this will give better resolution of the planetary features. With a 4.5" aperture you will struggle to get fine features no matter what additional add-ons you use.

 

However, given that "I am willing to buy whatever else I need to make that happen" probably doesn't include a 14" SCT lol.gif, I would recommend a dedicated planetary camera (most people use the ASI224MC for colour imaging of the planets, including me) and a barlow lens to suit. The generally used rule of thumb for planetary imaging is to set your focal ratio to be approximately 5x the pixel size of the camera. The ASI224MC has 3.75 micron sized pixels, so you should aim for f/18.75 with this camera - so in your case, a 2.5x or 3x Barlow would match pretty well with your scope with this camera. Now the new ASI462MC has just been released and is currently being testing right now by a planetary expert, it has 2.9 micron pixels so best focal ratio is around f/15, so a 2x Barlow is well suited for this camera.

 

Use the dedicated capture software to take the videos (I use Firecapture), use Austostakkert 3 for stacking the frames, Registax for sharpening and your favourite photo editing tool (Photoshop or equivalent).

 

It is possible to use your Canon DSLR to take good planetary images using a program like BackyardEOS, but I would probably recommend going straight for the ASI224MC.

 

Also, watch these tutorial videos, they will teach you a lot. (at least, they did me).

http://planetaryimagingtutorials.com/

 

Andrew


Edited by Tulloch, 03 July 2020 - 05:44 PM.

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#7 GoateeAP

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Posted 03 July 2020 - 05:50 PM

So for prime focus how do I count my crop or full sensor camera compared to an EP size for calculation?



#8 WarmWeatherGuy

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Posted 03 July 2020 - 05:53 PM

 

 


I want to take best possible shots of Jupiter and Saturn coming up, and I am willing to buy whatever else I need to make that happen (Tele Vue PowerMate, etc.).

 


 

Mr. Ashley, Columbus, Ohio

ASI224MC

IR-Cut filter

3x Barlow

ADC


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#9 Tulloch

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Posted 03 July 2020 - 05:59 PM

So for prime focus how do I count my crop or full sensor camera compared to an EP size for calculation?

Assuming you are using your DSLR, use the 5x zoom feature in LiveView (so you only sample the central part of the sensor), and a 2x/2.5x/3x Barlow. So your effective "magnification" (for want of a better word) is 5x2 = 10x, 5x2.5 = 12.5x or 5x3 = 15x.



#10 Tulloch

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Posted 03 July 2020 - 06:00 PM

P.S. I find this tool better, it includes a camera option.

https://www.12dstrin....uk/fovcalc.php



#11 FlankerOneTwo

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Posted 03 July 2020 - 08:03 PM

So for prime focus how do I count my crop or full sensor camera compared to an EP size for calculation?

Assuming you're asking about astronomy.tools. Click "FOV Calculator" then "Imaging Mode"



#12 BQ Octantis

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Posted 03 July 2020 - 11:23 PM

G'day Mr. Ashley,

 

Since you posted in the DSLR forum, I assume you want to use your DSLR vice buying a planetary camera. I've done extensive planetary work with my stock T3i. I would recommend it over the full frame for all planets from Saturn inward—its pixels are much smaller, which will get you to peak resolution with less optical magnification than the full frame. Here are my pointers:

 

  • Magnify. Not enough, and you'll wind up with processing artifacts from scaling. Too much and you'll lose SNR. For my T3i, I get the best results with ≤f/57 for Jupiter and ≤f/25 for Saturn. I do eyepiece projection, but I own Abbes. Plössls work ok, but if you have anything else, get a high-quality Barlow.
  • Do LiveView capture. I use AstroDSLR 1.3 for Mac. BackyardEOS is the Windows standard. You need to capture and stack thousands of frames. Stack three minutes of frames for Jupiter and six minutes for Saturn.

 

Here's a site with the math to calculate magnification over prime for eyepiece projection (you'll need to measure the distance between your eyepiece and your camera sensor:

 

http://www.astronomy...ece-projection/

 

If you choose eyepiece projection, I recommend you get all T2-thread attachments instead of using the scope's eyepiece clamp. I am unfamiliar with the threading on the back of the A5115EDT, so I don't know if this is possible. But with just clamp, the moment arm of the eyepiece projection optical chain with a heavy DSLR at the end will guarantee a sag, which will tilt your sensor relative to the collimation axis and cause haloing around the planet. An all-T2 threaded chain will stay collimated, even in the gustiest of conditions and after a tripod bump.

 

Cheers,

 

BQ


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#13 GoateeAP

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Posted 25 July 2020 - 06:08 PM

I did it! This is Saturn. I still have to figure out WINJUPOS and process Jupiter. Results and specs are here:
https://www.astrobin.com/tmwoco/

An 80mm spacer did the trick. I could probably add in the 35mm spacer as well and use less focuser travel.

So this was a test to see if I could do planetary with a 115mm refractor, and I can. It is not the same quality as an SCT, but I can get there by stretching magnification with the following optical chain:
AT115EDT + 80mm Astro-Tech spacer + Televue PowerMate 4x + PowerMate T ring adapter + generic T ring + Canon T3i
Then the trick is using 10x digital zoom on the T3i in 1920x1080 30fps video mode. Hold the DISP button up front beside the ISO button, then press +/- zoom to get up to 10x.


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#14 BQ Octantis

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Posted 25 July 2020 - 09:13 PM

Well done, mate!

 

BQ



#15 RedLionNJ

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Posted 26 July 2020 - 10:03 AM

The "10x digital zoom" achieves nothing in the way of increased information (resolution).  You're still going to be limited to the resolution from a 115mm objective.

 

And from the latitude of Ohio (as somebody already suggested), an ADC is mandatory to remove the dispersion effect.



#16 Tulloch

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Posted 26 July 2020 - 04:25 PM

While you have achieved a reasonable result for Saturn, as stated by RedLion above, you are not achieving anything by recording at 10x zoom, in fact you are almost certainly making the image worse by using it as the camera is re-sampling the image to achieve the extra zoom. If you want to achieve higher quality results you need to capture the frames using the LiveView mode at 5x zoom using the technique shown below, capturing the stream continuously to a computer connected to the camera.

https://www.astropix...resolution.html

 

Using a program like BackyardEOS (my preferred application) is excellent for this purpose, and has also be setup to handle DSO imaging as well.

 

You will not need to use WinJupos to process Jupiter (yet).

 

This is a good start, but you should look into the 5x zoom LiveView method if you want better results.

 

Hope this helps, Andrew



#17 ewave

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Posted 26 July 2020 - 07:07 PM

Here is a good site that talks about 1:1 pixel resolution as well as planetary photography for certain Canon DSLRs

 

https://www.astropix...resolution.html

 

Too bad the T3i doesn't have the 1 to 1 crop feature, yet the T2i before it did.

 

Your picture of Saturn was pretty good, now try again during times of good seeing.

 

Look for the nearest Clear Sky Chart in your area for the seeing and transparency forecast.

 

Happy planet hunting!




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