astrophotography astrophotography with a newtonian

[dwayne dias]

Hi guys,

i own an 8 inch newtonian telescope with a focal length of 1200mm and a focalratio of f/6. My big concern is the focal length though. can this newtonian be used for astrophotography or do i need to buy an astrograph so i can start with imaging. Or is there anything else i can do to reduce the focal length or of my current newtonian so i can start with imaging...???

[mikeyj1]

No reason to think it cannot be used for astrophotography, however you dont say the model or the mount its fitted to.  Some Newtonian's cannot get focus on a DSLR as the focuser doesnt have the range (mostly older models), check on that, maybe with the manufacturer.  then the mount needs to be sturdy enough to avoid vibration.  is it tracked, or manual?  you can only use short exposures if you have a manual mount.  Youtube can help, look up Forrest Tanaka, he did 3-4 videos which are an excellent introduction, and mentions the possibilities and issues.

[Jokehoba]

Perfectly feasible to image with that scope but as you are just starting, a shorter focal length may be easier on you. There's  a lot to learn as @mikeyj1 implies. 

[dwayne dias]

56 minutes ago, mikeyj1 said:

No reason to think it cannot be used for astrophotography, however you dont say the model or the mount its fitted to.  Some Newtonian's cannot get focus on a DSLR as the focuser doesnt have the range (mostly older models), check on that, maybe with the manufacturer.  then the mount needs to be sturdy enough to avoid vibration.  is it tracked, or manual?  you can only use short exposures if you have a manual mount.  Youtube can help, look up Forrest Tanaka, he did 3-4 videos which are an excellent introduction, and mentions the possibilities and issues.

My telescope model is a GSO 8 inch..and i have built my own mount which i have already tested with my scope mounted . The dec axis completes an exact  360° in 24 hours. And the mount is very sturdy.

[dwayne dias]

1 hour ago, mikeyj1 said:

No reason to think it cannot be used for astrophotography, however you dont say the model or the mount its fitted to.  Some Newtonian's cannot get focus on a DSLR as the focuser doesnt have the range (mostly older models), check on that, maybe with the manufacturer.  then the mount needs to be sturdy enough to avoid vibration.  is it tracked, or manual?  you can only use short exposures if you have a manual mount.  Youtube can help, look up Forrest Tanaka, he did 3-4 videos which are an excellent introduction, and mentions the possibilities and issues.

My telescope model is a GSO 8 inch..and i have built my own mount which i have already tested with my scope mounted . The dec axis completes an exact  360° in 24 hours. And the mount is very sturdy.

I have already tried imaging without the ea mount i built just so i could understand how to get my dslr into focus. The problem is that u really need to move away from to secondary mirror to achieve that which may cause a lot of shake in the images also if i need to go close, i might have to modify my telescope focuser so that my dslr moves closer to the secondary mirror. I can use a 2x barlow head lens to solve the issue. But im not sure if the images will b clear enough as there will b a lot of coma and vignetting....

[happy-kat]

When you say change the focal length, do you mean just so your dslr will reach focus?

The skywatcher p-ds newtonians are geared for imaging the primary mirror is that bit closer so a camera will focus which means for visual use with an eye piece an extension tube is used. (Very simplified view of the change there is bound to be other differences). Do you know what the diffeences are with the astrograph to your telescope.

If your barlrow enables your to reach focus now why not just try it and see what you get and whether you can post process the worst out.

If you look at the 200p that does reach focus reading posts something about removing eyepiece holder it reveals camera thread. Does your gso focus unit do something similar. Did you try searching on here to see what others might have done?

[dwayne dias]

11 hours ago, happy-kat said:

When you say change the focal length, do you mean just so your dslr will reach focus?

The skywatcher p-ds newtonians are geared for imaging the primary mirror is that bit closer so a camera will focus which means for visual use with an eye piece an extension tube is used. (Very simplified view of the change there is bound to be other differences). Do you know what the diffeences are with the astrograph to your telescope.

If your barlrow enables your to reach focus now why not just try it and see what you get and whether you can post process the worst out.

If you look at the 200p that does reach focus reading posts something about removing eyepiece holder it reveals camera thread. Does your gso focus unit do something similar. Did you try searching on here to see what others might have done?

Many have modified the ficuser. I have tried my best to achieve focus . For me the only thing that works is using an extension and mounting my dslr which is risky. A slight slip and the dslr might fall off. In order to gain focus close to the secondary mirror, i might have to move inside my gso focuser which is not possible unless i modify my scope focuser and replace it with a lower profile one. My second option is that i might have to push my primary mirror upwards which again might b risky. Gso offers a range of astrographs too. The diff between that and my telescope is that it has a shorter focal length and is used for prome focus astrophotography and there is no need for any extension tubes. My last option is to try out eyepiece projection n see the results.

[happy-kat]

I'm confused.

You say you could use a barlow lens. Generally that would be not enough in focus travel.

Then you say you need to use an extension tube. That would be not enough out focus travel.

?

I use a 2 inch extension tube with my refractor, it has fixing screws so camera is held steady.

 

[dwayne dias]

1 hour ago, happy-kat said:

I'm confused.

You say you could use a barlow lens. Generally that would be not enough in focus travel.

Then you say you need to use an extension tube. That would be not enough out focus travel.

?

I use a 2 inch extension tube with my refractor, it has fixing screws so camera is held steady.

 

What i meant to say is if i use a barlow head lens to correct the focus point. I dont use it as of now. I have just watched videos on youtube as to how to solve a focus problem while using a newtonian. But i use an extension tube and also have tried eyepiece projection for astrophotography. These methods required the dslr to be away from the secondary mirror to gain focus. And is i convenient while using an eq mount. I am more intereated in prime focus astrophotography which requires the camera sensor to b close to the sec mirror to gain focus. This is tough to achieve with my gso scope. I wanted to know if anyone knows how can this problem b solved.

[happy-kat]

A barlow is used for when you run out of inward focus travel, the barlow pushes the focal point closer.

An extension tube is used for when you run out of outward focus travel.

You don't use both to try to fix the same problem.

You need to know in what direction you are going as you almost did but don't reach focus.

[dwayne dias]

In my case i need to move the camera sensor inwards. And is not possible because of the focuser. For my telescope , inorder to do promw astrophotography il have to move inwards and need help as to how 

38 minutes ago, happy-kat said:

A barlow is used for when you run out of inward focus travel, the barlow pushes the focal point closer.

An extension tube is used for when you run out of outward focus travel.

You don't use both to try to fix the same problem.

You need to know in what direction you are going as you almost did but don't reach focus.

I need to go inwards in order for prime focus astrophotography. My telescope does not let me do that. I need help as to how to go about with it

[themos]

Hello,

If you have the stomach for it, you can hack an inch or so off the bottom of the tube and reattach the mirror cell. Perhaps you will lose some light as the secondary will be closer to the primary and may have been sized to the limit, but you are doing astrophotography so you can always get more light by increasing exposure length. I've done this with a cheap f/8 Newtonian. 

[happy-kat]

what about longer mirror bolts to raise the primary mirror that way

[dwayne dias]

46 minutes ago, themos said:

Hello,

If you have the stomach for it, you can hack an inch or so off the bottom of the tube and reattach the mirror cell. Perhaps you will lose some light as the secondary will be closer to the primary and may have been sized to the limit, but you are doing astrophotography so you can always get more light by increasing exposure length. I've done this with a cheap f/8 Newtonian. 

Thanx themos...just another thought. What if i instead modify my focuser so that the dslr sensor is pushed further and is closer to the secondary murror. Where it reacher its focus point.??

Will this work..?? My newtonian has a ratio of F/6 .

[themos]

First thing to do is to figure out how far from focus you are. You need two numbers: the focal length of your scope and the distance to the farthest object you CAN focus. 

[Louis D]

15 hours ago, dwayne dias said:

In my case i need to move the camera sensor inwards. And is not possible because of the focuser. For my telescope , inorder to do promw astrophotography il have to move inwards and need help as to how 

I need to go inwards in order for prime focus astrophotography. My telescope does not let me do that. I need help as to how to go about with it

Get a GSO coma corrector and mount it to a T-mount for your camera with a 15mm spacer ring in between.  I was able to reach prime focus on my Newt despite my infinity focus point normally being only 20mm above the fully inward focuser position.  There's only a 1.1x magnification associated with it.  It also helps to flatten the image as well which is important in imaging.

[skfboiler]

I can get prime focus with my DSLR with my Orion Astroview 6, a 6 inch f/5 two ways.  One, with my 2x Barlow.  I attach a t-ring with t-adapter to the camera and place then put it into the Barlow.  The second way is that I found out, the instructions didn't say, that my eyepiece holder can be removed exposing threads.  Now my camera with the t-ring, no t-adapter, can be attached to the focuser for prime focus.  Perhaps your focuser is similar where you can remove the eyepiece holder if it has one.  If not you may have to replace your focuser with a low profile one.  There are several vendors like GSO or moonlight that has one for your 8 inch OTA.