Astrophotography eyepiece question

[Seoras]

Hello, I’m a beginner and I’m trying to understand as much as I can about all the equipment needed for astrophotography. One of the many things that puzzle me is the use of an eyepiece when using a camera with my telescope. I know that it’s the eyepiece that magnifies what I’m looking at and the telescope gathers the light so, how does this work if I connect my dslr directly to the telescope? For context I have a Celestron Nexstar 8se and I’ve just bought a used Nikon 3100 which is in mint condition. It’ll be a while before I get around to taking photos but this question has been puzzling me. Please bear in mind I’m very new so not too technical!

[Cosmic Geoff]

In plain English, you would be using the telescope as a huge camera lens, in place of the Nikon camera lens.

I think you are about to discover that the SE mount is of little use for imaging, other than planetary.  And a DSLR is less than ideal for planetary imaging.

[barbulo]

Precisely, you have to connect the camera directly to the telescope (primary focus). You´ll need an adaptor from NIKON to T2 and another one from T2 to 2 inches. Then just focus and shoot!

[allworlds]

Assuming you have a camera lens, for deep sky I'd start with that. Either piggyback the camera on the scope, or remove the scope altogether and fit the camera to the mount with a bracket. You'll need to keep subs short because an alt-az mount experiences field rotation.

Cracking scope for planetary imaging but you'd ideally want a different camera for that.

https://www.sdfalchetti.com/blog-1/2021/1/16/astrophotography-with-the-nexstar-8se

[AstroMuni]

1 hour ago, Seoras said:

One of the many things that puzzle me is the use of an eyepiece when using a camera with my telescope.

When you are doing astrophotography with a DSLR or astro camera you dont need an eyepiece. But if you are using a phone camera then you would attach it to the back of the eyepiece. You might need to add lenses in between (eg. barlow to zoom in or a focal length reducer to zoom out). Hope this helps.

Edited October 17, 2022 by AstroMuni

[RT65CB-SWL]

33 minutes ago, barbulo said:

Precisely, you have to connect the camera directly to the telescope (primary focus). You´ll need an adaptor from NIKON to T2 and another one from T2 to 2 inches. Then just focus and shoot!

And afocal is using the eyepiece and connecting the camera to the telescope with an eyepiece projection unit [aka EPU]. Below is an image of mine,...

<--- the EPU is in the centre.

 

Below is an afocal image of Montes Appennius on the Moon, taken with an Olympus C-2040 digital compact camera and 20mm Plossl in the EPU attached to my ETX105...

[johnturley]

If you want to take photographs of planets with a digital SLR you will need to use eyepiece projection, otherwise the image scale even if using a barlow lens will be far too small.

You can use either an eyepiece projection tube, or an adaptor available from Baader which fits their Hyperion and Morpheus range of eyepieces.

Attached is a photo of Mars I took in September 2020 using a Canon 6D digital SLR attached to my 14in Newtonian, and using eyepiece projection with a 9.7 mm Plossl eyepiece. Not too bad maybe, but nothing like as good as can be achieved with a dedicated planetary camera. 

John 

 

[Seoras]

Looks like I got it wrong with my camera 🥴. Thanks very much for all your help, I’ll have a look through them and try to establish the least expensive option. As I said, I’m new to all this so no doubt there are many more mistakes to come……..

[Freddie]

3 hours ago, johnturley said:

If you want to take photographs of planets with a digital SLR you will need to use eyepiece projection, otherwise the image scale even if using a barlow lens will be far too small.

Why? I believe the Nikon pixels are 5 micron so with a 8SE a 2x Barlow would be about right for typical seeing.

[johnturley]

6 hours ago, Freddie said:

Why? I believe the Nikon pixels are 5 micron so with a 8SE a 2x Barlow would be about right for typical seeing.

Well try it, but I think you will find that the image size will be extremely small with the size of sensor you get with most digital SLR's, and I don't think that many (if any) allow you to crop the capture area so as to enlarge the image scale, I can't with my Canon 6D.

John 

Edited October 17, 2022 by johnturley

[The Lazy Astronomer]

43 minutes ago, johnturley said:

Well try it, but I think you will find that the image size will be extremely small with the size of sensor you get with most digital SLR's

John 

It will be, but making the planets appear larger on the sensor does not lead to more detail captured once you hit the limit imposed by atmosphere/optics.

As a general rule, I usually go for an f/ratio of 5x pixel size. With 5um pixels, this would be f/25, so a 2.5x barlow would fit the bill nicely. This gives a sampling rate of ~0.2"/px and would make Jupiter about 240px wide.

[Freddie]

1 hour ago, johnturley said:

Well try it, but I think you will find that the image size will be extremely small with the size of sensor you get with most digital SLR's, and I don't think that many (if any) allow you to crop the capture area.

John 

I think you are mixing up resolution with image size. Image resolution, as described by "Lazy" is what is important, it really doesn't matter how big that image is on the sensor. Sensor size does however bring other issues such as frame rate but that's not what is being discussed here.

[Seoras]

15 hours ago, The Lazy Astronomer said:

It will be, but making the planets appear larger on the sensor does not lead to more detail captured once you hit the limit imposed by atmosphere/optics.

As a general rule, I usually go for an f/ratio of 5x pixel size. With 5um pixels, this would be f/25, so a 2.5x barlow would fit the bill nicely. This gives a sampling rate of ~0.2"/px and would make Jupiter about 240px wide.

Hmm, I’m starting to feel dizzy 😵‍💫 , So many numbers…….. I certainly have a lot to learn 🥴

Edited October 18, 2022 by Seoras