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Is this enough to achieve focus with using a barlow?

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#1 patindaytona

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Posted 19 September 2019 - 11:03 AM

https://www.amazon.c...YXLG45C22&psc=1

 

I read alot of reviews that say they needed a barlow lens to achieve focusing distance with these.



#2 james7ca

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Posted 19 September 2019 - 11:27 AM

Depends upon your scope and the range of focus adjustment that it offers.



#3 the Elf

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Posted 19 September 2019 - 12:20 PM

The bomb proof way: put up your scope, rear end open (no camer, no eye piece, no nothin') and point at the moon. When you look in and move around and look into the open end you won't see the actual moon but you will see if you have it because it is very bright (no danger to your eyes, though). Now hold a piece of card board behind the scope and move it until you see a sharp image of the moon. Depending on the focal length it may be the size of a $ coin or a penny. Now grab your DSLR. There is a white line with a circle on the top. This is where the sensor is. You have to attach the camera so that the actual image is in the sensor plane. Get whatever amount of spacers or tubes you need to get there. The focuser should be about half way out, rather less than more. You probably don't need a long tube but a T-ring and a short 2'' tube you can sink in the focuser like an eye piece. Don't use a barlow.


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#4 patindaytona

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Posted 19 September 2019 - 01:00 PM

The bomb proof way: put up your scope, rear end open (no camer, no eye piece, no nothin') and point at the moon. When you look in and move around and look into the open end you won't see the actual moon but you will see if you have it because it is very bright (no danger to your eyes, though). Now hold a piece of card board behind the scope and move it until you see a sharp image of the moon. Depending on the focal length it may be the size of a $ coin or a penny. Now grab your DSLR. There is a white line with a circle on the top. This is where the sensor is. You have to attach the camera so that the actual image is in the sensor plane. Get whatever amount of spacers or tubes you need to get there. The focuser should be about half way out, rather less than more. You probably don't need a long tube but a T-ring and a short 2'' tube you can sink in the focuser like an eye piece. Don't use a barlow.

I will have to order it to find out one way or another.

It does come with various lengths of attachments.

Usually from what i've seen, the camera is too far away.  I don't understand how attaching a barlow would make it "closer"??

I guess the barlow's focal plane makes that.......closer in spite of the physical length of the barlow.

But, yea, ok, wont' use a barlow.

Just have to wait and see what it does. Thanks



#5 the Elf

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Posted 19 September 2019 - 01:39 PM

A barlow pushes the image further out. A reducer (the opposite of a barlow) drags the image even closer to the scope. A barlow increases magnification and thereby often exceeds the optical capabilities of beginner scopes. It reduces intensity and so introduces more noise. It increases magnification and thus need a better tracking. That is why a barlow is causing nothing but trouble. The only way to gain a benefit from a barlow is get a high quality one, use it on a large and very good scope and use it for planetary. Planets are very bright. For DSO you rather use a reducer that does the opposite of all: tracking is less demanding, the image is brighter and a lower magnification rather hides the scopes limits.

How do you want to connect to the scope? A 2'' slide in? A 1.25'' slide in? A threaded connection? If there is a thread at the focuser end this is the best way to connect. If your focuser is 2'' wide (most are) go for 2'' adapter. If you enter T-ring at amazon you find a wide selection. What scope model do you have?


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#6 patindaytona

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Posted 19 September 2019 - 02:22 PM

A barlow pushes the image further out. A reducer (the opposite of a barlow) drags the image even closer to the scope. A barlow increases magnification and thereby often exceeds the optical capabilities of beginner scopes. It reduces intensity and so introduces more noise. It increases magnification and thus need a better tracking. That is why a barlow is causing nothing but trouble. The only way to gain a benefit from a barlow is get a high quality one, use it on a large and very good scope and use it for planetary. Planets are very bright. For DSO you rather use a reducer that does the opposite of all: tracking is less demanding, the image is brighter and a lower magnification rather hides the scopes limits.

How do you want to connect to the scope? A 2'' slide in? A 1.25'' slide in? A threaded connection? If there is a thread at the focuser end this is the best way to connect. If your focuser is 2'' wide (most are) go for 2'' adapter. If you enter T-ring at amazon you find a wide selection. What scope model do you have?

I see T-rings alone, and T-rings with short adapters and with long adapters.

I don't know what to get. If i get a T-ring alone or even with a short adapter, I'm afraid when i try it, it will not be within focal range.

I have a XT10i telescope. 

So, barlows, weather you use them for the astrophotography, or otherwise, they are not a good investment, unless you buy a expensive one?



#7 kathyastro

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Posted 19 September 2019 - 04:44 PM

The Xt10 is a Newtonian.  Your focusing problem with a Newtonian is that the camera sensor is already too far away.  You need either the shortest adapter you can find ( a "zero-length" adapter) or a barlow or both.

 

Furthermore, that adapter is for eyepiece projection.  It is way, way, way, too long for use in your scope without an eyepiece: probably even a barlow won't allow it to focus.  With an eyepiece in the adapter, you have a whole different setup that is difficult to focus.  It is possible, though no guarantees, that you could make it focus, but you run the risk of having such an extreme magnification that you can't image anything.

 

The adapter you need is something like this: https://www.amazon.c...eed an adapter.

 

So, backing up entirely, what is it that you wish to photograph?  Use that information to pick a suitable scope, mount, and camera that will do the job.


Edited by kathyastro, 19 September 2019 - 04:46 PM.


#8 bobzeq25

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Posted 19 September 2019 - 04:56 PM

https://www.amazon.c...YXLG45C22&psc=1

 

I read alot of reviews that say they needed a barlow lens to achieve focusing distance with these.

This forum is almost entirely for DSO imagers.  They generally don't use Barlows, the dim DSOs cannot stand the loss in optical speed.  An F4 telescope with a 2X Barlow is now F8.

 

DSO imagers go the other way.  They'll put on a reverse Barlow, say a 0.75 reducer, to convert that scope to F3.  That's better.

 

Barlows are a planetary/lunar deal, and you'll get better advice on Barlows on the Solar System Imaging forum.

 

For DSOs, putting a Barlow on the scope, even if it's the only way to achieve focus, is shooting yourself in the foot.  It simply says you have a bad scope for DSOs.

 

You _really_ need to separate planetary and DSO imaging, they're two completely different activities.  With two completely different forums here.


Edited by bobzeq25, 19 September 2019 - 05:04 PM.


#9 the Elf

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Posted 20 September 2019 - 12:52 AM

Agree to Kathy. Not only is the image too close to the focuser, you need a coma corrector as well. There is one called Paracor that corrects and slightly magnifies the image but that thing is expensive. Your scope is a dob and for DSO photography you need a German equatorial mount (GEM) that rotates in parallel to the earth axis. So for photography forget the Dob. Rethink the project. Get the book "The deep ski imaging primer" by Charles Bracken and pick up the basic information first. It will soon become clear why the dob is a dead end. If you just want to play, get the zero lenght adapter and the thinnest T-Ring you can get or try to get a mirrorless camera. The sensor is more to the front than in a DSLR. But again: this is not recommended for photography, this is just snapshotting.




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