<p>I'm not an astrophotographer but I'd like to make sure that you know that there are (at least) two ways to put a camera on a telescope from an optical perspective.</p>
<ol>
<li><p>The first is to keep the eyepiece on which produces a virtual image at infinity, and keep the camera lens on, focused at infinity.</p>
</li>
<li><p>The second is to remove both the eyepiece and the camera's lens, which leaves the camera's CCD sensor right on the primary focal plane of the telescope.</p>
</li>
</ol>
<p>The first method is the quickest, and it seems to be called <a href="https://en.wikipedia.org/wiki/Afocal_photography" rel="nofollow noreferrer">Afocal photography</a> (I didn't know that!). <em>If you are careful and the image is very bright</em>, say for example the moon, then you can just set the camera focus to infinity, hold it up to the eyepiece, moving around sideways until the inevitable <a href="https://en.wikipedia.org/wiki/Vignetting" rel="nofollow noreferrer">vignetting</a> is at least centered, and click! You can try to manage the vignetting by moving the camera closer or farther from the eyepiece. Ideally you want to place the <a href="https://en.wikipedia.org/wiki/Entrance_pupil" rel="nofollow noreferrer">entrance pupil</a> of your camera's lens on top of the <a href="https://en.wikipedia.org/wiki/Exit_pupil" rel="nofollow noreferrer">exit pupil</a> of your telescope's eyepiece.</p>
<p><strong>I predict</strong> you will quickly move to the second method which is called <em>Prime Focus Photography</em>. Find an eyepiece-to-camera body adapter and then you are a <em>bona fide</em> astrophotographer!</p>
<p>If you want to take advantage of your very nice f/1.8 lens then lose the telescope and just photograph the milky way or meteor showers. This works best if your camera can be programmed to take a sequence of regularly spaced images, because you can merge them later with a computer with offsets so that the motion of the stars doesn't produce trails.</p>
<p>For more on all of these, search questions tagged <a href="https://space.stackexchange.com/questions/tagged/photography">photography</a> here and <a href="https://photo.stackexchange.com/questions/tagged/astrophotography">astrophotography</a> in Photography SE.</p>
<hr />
<p>For completenes' sake only, I'll mention a third way, called <em>Eyepiece projection</em>. While a properly focused eyepiece produces a virtual image at infinity, if you move it out, away from the telescope, it will produce a real image out past the eyepiece. If you are looking at the Moon or something very bright you could put a piece of paper out a ways away from the eyepiece, say 6 to 20 cm, and with some practice produce an image on the paper. You can then imagine having your camera's sensor at that plane. This gives you more magnification compared to prime focus photography, but it may not be <em>useful magnification!</em></p>
<p>Further reading:</p>
<ul>
<li><a href="https://www.astronomyforbeginners.com/astrophotography/the-prime-focus-method/" rel="nofollow noreferrer">The Prime-Focus Method</a></li>
<li><a href="https://astronomysource.com/2011/10/13/eyepiece-projection/" rel="nofollow noreferrer">Eyepiece Projection</a></li>
<li><a href="https://www.skyatnightmagazine.com/advice/what-is-eyepiece-projection-how-do-it/" rel="nofollow noreferrer">What is eyepiece projection and how do I do it?</a></li>
<li>Sky &amp; Telescope's <a href="https://skyandtelescope.org/astronomy-resources/astrophotography-with-a-digital-camera/" rel="nofollow noreferrer">Astrophotography With a Digital Camera</a></li>
<li><a href="http://www.hrastro.com/astrophotography_tips/afocal_projection/" rel="nofollow noreferrer">Afocal method</a></li>
<li><a href="http://community.dur.ac.uk/nigel.metcalfe/astro/afocal.html" rel="nofollow noreferrer">Afocal Deep Sky Astrophotography</a> where you can clearly see what vignetting looks like!</li>
</ul>

CC BY-SA 4.0
2020-08-06T06:49:59.010Z
I'd like to add that with prime focus photography, you are simply using the telescope as your "camera lens." In the case of your telescope, this is effectively a 1325mm f/13 lens. You can use Barlow lenses as teleconverters to extend the focal length, but as with ordinary teleconverters this will cause the image to be dimmer (the f-number increases by the same factor as the focal length). Depending on the telescope, prime focus photography may not be possible (at least without serious adjustments to the telescope) if the image plane is too far inside the telescope to put on the camera sensor.
Puk
CC BY-SA 4.0
2020-08-06T09:29:05.103Z
@a_donda I'm not aware of a book on the matter unfortunately. It is worth mentioning that collapsible Newtonian reflectors can also be used for prime focus photography, without having to move the primary mirror. The image plane position can be conveniently adjusted by collapsing the telescope: the more it is collapsed, the further out the image plane moves.
Puk
CC BY-SA 4.0
2020-08-06T09:37:14.593Z
I use a small pocket size theatre scope to shoot the moon via smartphone. At first I got nice pics by keeping the phone on autofocus. Shouldn't be better to use the macro mode as for the camera lens is a couple of centimeters away the image formed on the scope eyepiece? When I have tried this second logical option I failed.... No much tests as it is very stressful and hard (no mounting or tripod of sort, yet with patience I got something nice).
Alchimista
CC BY-SA 4.0
2020-08-06T16:46:39.170Z
@Alchimista You shouldn't be using the macro mode, because ordinarily (when the focuser is adjusted for viewing), the image through the eyepiece will not actually be near the eyepiece. If you are viewing the image with a relaxed eye, the image you are looking at is actually at infinity or otherwise very far away (unless you are near/farsighted and not using corrective lenses). It's better to use autofocus if your phone is able to do this with whatever you are looking at, or ideally manual focus if that is an option and you can mount/adapt your phone.
Puk
CC BY-SA 4.0
2020-08-06T18:57:20.387Z
@Puk thank you. So the image is kind of virtual and it is not at eyepiece... Now I understand. Yes I know about mounting ecc... Often I like the push the limit of the things I have at hand. Unfortunately I can't post here the moons I got with just patience and stunts (I even click with my nose tip :))
Alchimista
CC BY-SA 4.0
2020-08-06T02:59:38.497Z
2020-08-06T03:27:29.313Z
2020-08-06T03:27:29.313Z
uhoh
<p>I am considering using a 50mm f1.8 maybe even try aN 85mm f1.8 on my Astro FI 102MM Telescope have you any thoughts or suggestions?</p>
<p>I have never taken images via a telescope so this is a whole new learning curve. Need to get my brain back in gear, stopped shooting over 5yrs ago due to the gear being too heavy and my back injury not coping so this will be a much easier way of holding the camera...I HOPE.</p>

CC BY-SA 4.0
2020-08-05T19:14:28.560Z
Hello! This question might be better on Photography SE. Also, do I understand correctly that you wnat to use both a telescope *and* a camera lens for astrophotography? Thanks!
jng224
CC BY-SA 4.0
2020-08-05T20:22:09.820Z
@Jonas It might get better answers over there, but it is certainly welcome here. No need to migrate unless the asker requests it.
called2voyage
CC BY-SA 4.0
2020-08-05T20:36:36.917Z
@called2voyage I did not know that questions about astrophotography are on-topic here. Thanks for the information!
jng224
CC BY-SA 4.0
2020-08-05T20:39:56.860Z
@Jonas Since private beta first launched it has been seen as falling under the first bullet on our topic guidelines: "Setting up, using and maintaining your astronomy related equipment" https://astronomy.stackexchange.com/help/on-topic
called2voyage
<telescope><photography>
50mm f1.8 for Astrophotography
John Lumb
# 50mm f1.8 for Astrophotography

(Asked by: username_0 on 2020-08-05)

I am considering using a 50mm f1.8 maybe even try aN 85mm f1.8 on my Astro FI 102MM Telescope have you any thoughts or suggestions?

I have never taken images via a telescope so this is a whole new learning curve. Need to get my brain back in gear, stopped shooting over 5yrs ago due to the gear being too heavy and my back injury not coping so this will be a much easier way of holding the camera...I HOPE.

**Tags:** telescope, photography
> **Comments:**
> **username_1**: Hello! This question might be better on Photography SE. Also, do I understand correctly that you wnat to use both a telescope *and* a camera lens for astrophotography? Thanks!  
> **username_2**: @Jonas It might get better answers over there, but it is certainly welcome here. No need to migrate unless the asker requests it.  
> **username_1**: @called2voyage I did not know that questions about astrophotography are on-topic here. Thanks for the information!  
> **username_2**: @Jonas Since private beta first launched it has been seen as falling under the first bullet on our topic guidelines: "Setting up, using and maintaining your astronomy related equipment" https://astronomy.stackexchange.com/help/on-topic  

---

## 1 answers

### Answer by username_3 on 2020-08-06. Score: 2

I'm not an astrophotographer but I'd like to make sure that you know that there are (at least) two ways to put a camera on a telescope from an optical perspective.

1. The first is to keep the eyepiece on which produces a virtual image at infinity, and keep the camera lens on, focused at infinity.
2. The second is to remove both the eyepiece and the camera's lens, which leaves the camera's CCD sensor right on the primary focal plane of the telescope.

The first method is the quickest, and it seems to be called [Afocal photography](https://en.wikipedia.org/wiki/Afocal_photography) (I didn't know that!). *If you are careful and the image is very bright*, say for example the moon, then you can just set the camera focus to infinity, hold it up to the eyepiece, moving around sideways until the inevitable [vignetting](https://en.wikipedia.org/wiki/Vignetting) is at least centered, and click! You can try to manage the vignetting by moving the camera closer or farther from the eyepiece. Ideally you want to place the [entrance pupil](https://en.wikipedia.org/wiki/Entrance_pupil) of your camera's lens on top of the [exit pupil](https://en.wikipedia.org/wiki/Exit_pupil) of your telescope's eyepiece.

**I predict** you will quickly move to the second method which is called *Prime Focus Photography*. Find an eyepiece-to-camera body adapter and then you are a *bona fide* astrophotographer!

If you want to take advantage of your very nice f/1.8 lens then lose the telescope and just photograph the milky way or meteor showers. This works best if your camera can be programmed to take a sequence of regularly spaced images, because you can merge them later with a computer with offsets so that the motion of the stars doesn't produce trails.

For more on all of these, search questions tagged [photography](https://space.stackexchange.com/questions/tagged/photography) here and [astrophotography](https://photo.stackexchange.com/questions/tagged/astrophotography) in Photography SE.

---

For completenes' sake only, I'll mention a third way, called *Eyepiece projection*. While a properly focused eyepiece produces a virtual image at infinity, if you move it out, away from the telescope, it will produce a real image out past the eyepiece. If you are looking at the Moon or something very bright you could put a piece of paper out a ways away from the eyepiece, say 6 to 20 cm, and with some practice produce an image on the paper. You can then imagine having your camera's sensor at that plane. This gives you more magnification compared to prime focus photography, but it may not be *useful magnification!*

Further reading:

* [The Prime-Focus Method](https://www.astronomyforbeginners.com/astrophotography/the-prime-focus-method/)
* [Eyepiece Projection](https://astronomysource.com/2011/10/13/eyepiece-projection/)
* [What is eyepiece projection and how do I do it?](https://www.skyatnightmagazine.com/advice/what-is-eyepiece-projection-how-do-it/)
* Sky & Telescope's [Astrophotography With a Digital Camera](https://skyandtelescope.org/astronomy-resources/astrophotography-with-a-digital-camera/)
* [Afocal method](http://www.hrastro.com/astrophotography_tips/afocal_projection/)
* [Afocal Deep Sky Astrophotography](http://community.dur.ac.uk/nigel.metcalfe/astro/afocal.html) where you can clearly see what vignetting looks like!

> **Comments:**
> **username_4**: I'd like to add that with prime focus photography, you are simply using the telescope as your "camera lens." In the case of your telescope, this is effectively a 1325mm f/13 lens. You can use Barlow lenses as teleconverters to extend the focal length, but as with ordinary teleconverters this will cause the image to be dimmer (the f-number increases by the same factor as the focal length). Depending on the telescope, prime focus photography may not be possible (at least without serious adjustments to the telescope) if the image plane is too far inside the telescope to put on the camera sensor.  
> **username_4**: @a_donda I'm not aware of a book on the matter unfortunately. It is worth mentioning that collapsible Newtonian reflectors can also be used for prime focus photography, without having to move the primary mirror. The image plane position can be conveniently adjusted by collapsing the telescope: the more it is collapsed, the further out the image plane moves.  
> **username_5**: I use a small pocket size theatre scope to shoot the moon via smartphone. At first I got nice pics by keeping the phone on autofocus. Shouldn't be better to use the macro mode as for the camera lens is a couple of centimeters away the image formed on the scope eyepiece? When I have tried this second logical option I failed.... No much tests as it is very stressful and hard (no mounting or tripod of sort, yet with patience I got something nice).  
> **username_4**: @Alchimista You shouldn't be using the macro mode, because ordinarily (when the focuser is adjusted for viewing), the image through the eyepiece will not actually be near the eyepiece. If you are viewing the image with a relaxed eye, the image you are looking at is actually at infinity or otherwise very far away (unless you are near/farsighted and not using corrective lenses). It's better to use autofocus if your phone is able to do this with whatever you are looking at, or ideally manual focus if that is an option and you can mount/adapt your phone.  
> **username_5**: @Puk thank you. So the image is kind of virtual and it is not at eyepiece... Now I understand. Yes I know about mounting ecc... Often I like the push the limit of the things I have at hand. Unfortunately I can't post here the moons I got with just patience and stunts (I even click with my nose tip :))  

---

