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Question on possibilities - Astrophotography

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#1 LIVS

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Posted 06 July 2020 - 05:03 PM

Hello all,

 

I am just starting out in this area. First, I have a 10” collapsible Dobsonian SkyWatcher with tracking, Canon EOS Rebel and a Cannon adapter with a 3x Barlowe lens . Is there any adaptor that will, say, mimic the detail and magnification if a 4mm eyepiece and allow me to shoot at that magnification or does all image enhancement happen post in the editing software of your choosing? 



#2 APshooter

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Posted 06 July 2020 - 05:47 PM

Astrophotography requires special telescopes and mounts.  The short answer is no on the adapter question.  Magnification comes from coupling a camera to a specific telescope.  I would guess you'd need to be shooting through a 8" or larger SCT to get as much magnification as a 4mm eyepiece would give you visually.  The  task would be daunting to pull off well if you've not done imaging before.  Most folks shooting through long FL scopes are advanced imagers.



#3 Stelios

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Posted 06 July 2020 - 06:28 PM

"Magnification" in AP can be achieved by just zooming in. It's totally unlike visual. This is done with a 70mm scope. 

 

The equivalent concept in AP is "image scale"--how much of the sky fits on one pixel. This, in conjunction with the seeing and the optical resolution of your telescope, limits how far you can push the zooming before no more detail can be seen--the AP equivalent of "empty magnification."

 

You can do planetary photography with what you have, but you'd need an equatorial platform to do DSO photography, and a DOB is just about the worse possible mount for that. You need an equatorial mount and you will find life easier starting with a short focal length scope, though of course you don't have to--but longer focal length scopes require guiding *and* quality ($$$$) mounts.


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#4 bjulihn

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Posted 06 July 2020 - 06:39 PM

Hi LIVS;

 

My first question is what do you want to image? If you are wanted to image at the equivalent magnification of that scope with a 4mm eyepiece you are in the neighborhood of 300X. So problem number 1 is that tracking might keep the object reasonably centered but a Dob mount is an alt-az system. The scope does not rotate with the sky so you have to keep exposures very short to avoid blurring from field rotation. If you are trying to image planets, they are reasonably bright and you can stack multiple very short exposures and possibly get a result. DSO's generally require hours of data(multiple longer exposures stacked), with autoguiding, on an equatorial mount. It is a challenging just to learn at a 400-500mm focal length of an 80 mm refractor with a good mount. To attempt to learn AP on a scope above a 1000mm is only something attempted by masochists!!! 

 

Another problem is using a Barlow. It does change the focal length to increase magnification, but crucially it also increases the focal ratio by the square of the Barlow's power. I think a 3X barlow would increase your focal ratio 9 times! Someone smarter than me can tell you the math but that creates a massively "slow" focal ratio. By "slow" we mean that focal ratio is critical to how much exposure time is required. I think an f4 scope gathers light 4 times faster than an f6 scope of the same diameter. You could try that Barlow on a bright planet but pretty much everything will require all night vigils for a week to see anything else. I don't know, I never tried it. But I think it could be brutal.

 

You can play with an EOS Rebel and a Dob for planets. But if AP really intrigues you, think good equatorial mount with a small fast(f4-f6) scope. Or if money is a big challenge, think about getting a camera tracker to start with.

 

Brad



#5 Stelios

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Posted 06 July 2020 - 07:53 PM

Another problem is using a Barlow. It does change the focal length to increase magnification, but crucially it also increases the focal ratio by the square of the Barlow's power. I think a 3X barlow would increase your focal ratio 9 times! Someone smarter than me can tell you the math but that creates a massively "slow" focal ratio. By "slow" we mean that focal ratio is critical to how much exposure time is required. I think an f4 scope gathers light 4 times faster than an f6 scope of the same diameter. You could try that Barlow on a bright planet but pretty much everything will require all night vigils for a week to see anything else. I don't know, I never tried it. But I think it could be brutal.

 

You can play with an EOS Rebel and a Dob for planets. But if AP really intrigues you, think good equatorial mount with a small fast(f4-f6) scope. Or if money is a big challenge, think about getting a camera tracker to start with.

 

Brad

 

A clarification: The focal ratio increases with the linear Barlow power (so 3X Barlow increases focal ratio by 3, or "slows" focal ratio by 3). What increases by the square of the focal ratio is the exposure time required to get the equivalent signal. So you need to image 9 times as long with a 3X Barlow to get the same signal as without it.


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#6 TelescopeGreg

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Posted 07 July 2020 - 01:16 PM

What the other have said.

 

You've got a great platform for imaging the Moon or planets.  Deep Sky stuff is far too big, and far too dim, for your configuration. 



#7 Phil Sherman

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Posted 07 July 2020 - 01:45 PM

If you want more magnification than the Barlow gives you, you could try using an eyepiece projection adapter. You control the magnification by using different focal length eyepieces and the exact position of the eyepiece in the adapter. Do a search on Amazon for "T thread camera adapter" to see products. Prices range from $18 to over $50.



#8 Phil Sherman

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Posted 07 July 2020 - 01:46 PM

If you want more magnification than the Barlow gives you, you could try using an eyepiece projection adapter. You control the magnification by using different focal length eyepieces and the exact position of the eyepiece in the adapter. Do a search on Amazon for "T thread camera adapter" to see products. Prices range from $18 to over $50.



#9 LIVS

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Posted 20 July 2020 - 05:31 PM

So basically I’ve bought the wrong equipment is what I’m seeing. Hmm, ok. I will start researching what you guys are mentioning here. I appreciate the feedback without judgment!! Thanks all!!



#10 JAS62

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Posted 20 July 2020 - 07:06 PM

So basically I’ve bought the wrong equipment is what I’m seeing. Hmm, ok. I will start researching what you guys are mentioning here. I appreciate the feedback without judgment!! Thanks all!!

 

No.  Not quite.  You can image DSOs with your DOB.  It's just a bit more challenging and you going to need to set expectations about what your going to be able to achieve.  you should know you'll not get any where near some of the better examples you may have seen.  However, you'll need excellent skies,  a decent dedicated astro-camera (the Canon and barlow are a no-go), and develop an understanding of the light collecting capabilities for your DOB.  It's going to take time and a lot of trial and error.  However, there are several example of people who have done exactly this.

 

Check out this gentleman's Facebook feed.  (go back to mid-2019)  He started with a Skywatcher 14" collapsible goto and QHY163m and ZWO ASI294mc cameras.  He shoots up to 2 hours of 5 - 15 second subs and stacks them live with SharpCap.  SharpCap stacking handles the de-rotation.  Some of his early mono images are very good.  He's very helpful and forthcoming with how he images.  I am sure he won't mind sharing his information with you.  Your 10" is going to be a bit harder to get dimmer objects, however there are plenty of brighter candidates to choose from.

 

Clear skies!




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