How is magnification attained with a camera connected to the scope?

[GUS]

Hi,

 

I've always wondered how magnification is achieved with a camera connected to a telescope, given that whenever I see pictures of a telescope and dslr or dedicated camera setup, there's never an eyepiece to magnify the image. How do you get a closeup image without a short focal length eyepiece?

 

Thanks,

Gus

[PeterCPC]

Magnification is not the correct word - it's image scale. The size of the image that you get with a camera attached will depend primarily on the size of the sensor in the camera. So a DSLR will give a larger FOV that say a CCD camera with a smaller sensor so an image with a CCD camera will appear to have a larger image of the target. The size of the target will also be affected by what is in the image train so, if you include a 2X barlow, the image size will be doubled.

Peter

[MarsG76]

The native "magnification" is also determined by the focal length of the telescope vs the size of the sensor... like mentioned above that magnification is a inaccurate, description. 

Using a barlow lens can increase the image scale, magnification, but there are also tele-extender tubes where you can insert a eyepiece and attach a dslr to the tele-extender to magnify even more, it works like a T adapter there the T mount can be screwed on to... this is known as the projection method.

Mind you tho, I have only ever used the tele-extender a handful of times, and I find that projection delivers softer images than using a barlow lens, also if magnified too much your tracking and PA has to be much more accurate.

I dare say that you will be more than happy with what your scope captures "magnification" wise using a prime, or native focal length, or via a focal reducer if your scope focal length is high, like for example 2000mm.

[Ouroboros]

Or think of the telescope as a lens attached to your DSLR camera. The longer the focal length of the lens, the larger will be the image captured on the sensor.  For example a typical zoom lens for a DSLR might have a maximum focal length of 300mm.  Such a lens might be used to capture closeup images of wildlife.  A typical telescope for amateur astronomy might have a focal length of 1000mm - just over three times the focal length of a 300mm lens - and it will form an image three times larger than the zoom lens on the same DSLR sensor. 

[ronin]

As Peter says you do not have a "magnification", the objective creates an image on the sensor that is determined by the angular size of the object and the focal length of the objective (lens or mirror).

In approximate terms the image created on the sensor is: Size = Tan(obj) * Focal Length

So with say the Pleiades at 1 degree and a 650mm scope you have:

Tan(1) = 0.0175 (Close), FL = 650mm, so image = 0.0175 * 650 = 11.34mm.

Longer focal length = bigger image, smaller = smaller image.

All the school geometry could have a use after all.

[MarsG76]

8 minutes ago, Ouroboros said:

Or think of the telescope as a lens attached to your DSLR camera. The longer the focal length of the lens, the larger will be the image captured on the sensor.  For example a typical zoom lens for a DSLR might have a maximum focal length of 300mm.  Such a lens might be used to capture closeup images of wildlife.  A typical telescope for amateur astronomy might have a focal length of 1000mm - just over three times the focal length of a 300mm lens - and it will form an image three times larger than the zoom lens on the same DSLR sensor. 

Yes, good analogy.

 

[michael.h.f.wilkinson]

33 minutes ago, MarsG76 said:

The native "magnification" is also determined by the focal length of the telescope vs the size of the sensor... like mentioned above that magnification is a inaccurate, description. 

Using a barlow lens can increase the image scale, magnification, but there are also tele-extender tubes where you can insert a eyepiece and attach a dslr to the tele-extender to magnify even more, it works like a T adapter there the T mount can be screwed on to... this is known as the projection method.

Mind you tho, I have only ever used the tele-extender a handful of times, and I find that projection delivers softer images than using a barlow lens, also if magnified too much your tracking and PA has to be much more accurate.

I dare say that you will be more than happy with what your scope captures "magnification" wise using a prime, or native focal length, or via a focal reducer if your scope focal length is high, like for example 2000mm.

Tele-extender isn't really the right word: eyepiece-projection adapter. The Meade TeleXtender is a tele-centric Barlow, like the TeleVue PowerMate, and gives even sharper images than regular Barlow. The word tele-extender is sometimes also used for tele-converter, which is like a Barlow for camera lenses.

[GUS]

Thanks everyone, that was thorough. Finally!!

[Ouroboros]

1 hour ago, GUS said:

Thanks everyone, that was thorough. Finally!!

I quite often get asked the question "what magnification is this" when people look at my astro images, expecting a straight forward answer like 40 times or whatever.  They often look a bit puzzled when I start saying "Well, it doesn't really work like that ... you see .....". But now you know why. Cheers.

[ollypenrice]

We must be careful not to imagine that a smaller sensor gives a 'closer' view of a target. It doesn't. The confusing term 'crop factor' has a lot to answer for and shouldn't be used in astronomy (or anywhere else!!!)

In any digital photographic image seen on screen at full size (AKA 100%) one camera pixel is given one screen pixel. This means that, for all but small sensors, not all of the image will fit on the PC screen at full size. You need to move it around to see all of it at full size.

Now the size of the image of a galaxy projected onto a chip is dependent entirely and only upon the focal length of the scope.

But  the size of that particular projected image on your PC screen is dependent not on the size of the chip but on the size of the pixels. Camera x has large pixels. Camera y has pixels half that size, so camera y puts 4x as many pixels under the projected image of the galaxy. (Twice as many sideways and twice as many up and down.) So camera y will make an image of the galaxy on the PC which is 4x by area bigger than size of the image produced by camera x.

So two things decide the size of the final image of our galaxy, the focal length of the telescope and the size of the pixels. The useful unit here is arcseconds of sky per pixel, often written as "P/P.

Olly

[MarsG76]

17 hours ago, michael.h.f.wilkinson said:

Tele-extender isn't really the right word: eyepiece-projection adapter. The Meade TeleXtender is a tele-centric Barlow, like the TeleVue PowerMate, and gives even sharper images than regular Barlow. The word tele-extender is sometimes also used for tele-converter, which is like a Barlow for camera lenses.

Yeah, perhaps.... I'm quite sure that celestron called the one I got a "tell extender" than I might be getting confused with all the other gear and not remembering it correctly since I haven't even touched it for years.

[MarsG76]

17 hours ago, michael.h.f.wilkinson said:

Tele-extender isn't really the right word: eyepiece-projection adapter. The Meade TeleXtender is a tele-centric Barlow, like the TeleVue PowerMate, and gives even sharper images than regular Barlow. The word tele-extender is sometimes also used for tele-converter, which is like a Barlow for camera lenses.

They did, I looked it up... http://www.celestron.com/browse-shop/astronomy/astroimaging-accessories/other-astroimaging-accessories/deluxe-tele-extender

 

either way, "a rose by any other name will still smell just as sweet".

[MarsG76]

15 hours ago, Ouroboros said:

I quite often get asked the question "what magnification is this" when people look at my astro images, expecting a straight forward answer like 40 times or whatever.  They often look a bit puzzled when I start saying "Well, it doesn't really work like that ... you see .....". But now you know why. Cheers.

If someone asks me about magnification, I just say "its imaged  at 2000mm" or why ever focal length I use. Sometimes I explain to them to think of it like their camera lenses, "when you photograph at 35mm or 100mm using your lens, you get that particular magnification, I imaged "this" at 500mm/1280mm/2000mm... usually they understand.

[MarsG76]

12 hours ago, ollypenrice said:

We must be careful not to imagine that a smaller sensor gives a 'closer' view of a target. It doesn't. The confusing term 'crop factor' has a lot to answer for and shouldn't be used in astronomy (or anywhere else!!!)

In any digital photographic image seen on screen at full size (AKA 100%) one camera pixel is given one screen pixel. This means that, for all but small sensors, not all of the image will fit on the PC screen at full size. You need to move it around to see all of it at full size.

Now the size of the image of a galaxy projected onto a chip is dependent entirely and only upon the focal length of the scope.

But  the size of that particular projected image on your PC screen is dependent not on the size of the chip but on the size of the pixels. Camera x has large pixels. Camera y has pixels half that size, so camera y puts 4x as many pixels under the projected image of the galaxy. (Twice as many sideways and twice as many up and down.) So camera y will make an image of the galaxy on the PC which is 4x by area bigger than size of the image produced by camera x.

So two things decide the size of the final image of our galaxy, the focal length of the telescope and the size of the pixels. The useful unit here is arcseconds of sky per pixel, often written as "P/P.

Olly

Also when printing its DPI.

 

[Big Phil]

Hi all, complete newbie here reading this thread with interest as Im in the same boat.

Recently bought a Bresser 127L refractor on a EQ5 mount. Ive also bought a motor to fit for tracking and a power pack to run it. It still hasn't been taken out of the box yet....

I use the eyepiece it came with plus a 9m eyepiece and a 2x barlow Celestron make I believe.

The 9m gives good close ups and the standard one, 20mm I think gives good wide angle. Use the 9mm and the barlow...crap  

Started to use my phone camera to take a few snaps and by changing the eyepieces and lining up the camera got some half decent shots!

Now the shop bloke said I need a Altair AstroCam V2 colour jobbie which replaces the eyepiece which then means no or little magnification! Hence me reading this post!

I contacted Altair who sent me 2 jpegs one with camera just slotted into holder and one with 5x barlow. One pic was miniscule and one was amazing!

It seems adding a camera that replaces the eyepiece can only work if you use a barlow? Otherwise its a tiny dot?

cheers

Phil

 

 

 

[GUS]

Big Phil, 

Could you attach those two pics?

Cheers

[GUS]

On 7/10/2017 at 08:06, Big Phil said:

Hi all, complete newbie here reading this thread with interest as Im in the same boat.

Recently bought a Bresser 127L refractor on a EQ5 mount. Ive also bought a motor to fit for tracking and a power pack to run it. It still hasn't been taken out of the box yet....

I use the eyepiece it came with plus a 9m eyepiece and a 2x barlow Celestron make I believe.

The 9m gives good close ups and the standard one, 20mm I think gives good wide angle. Use the 9mm and the barlow...crap  

Started to use my phone camera to take a few snaps and by changing the eyepieces and lining up the camera got some half decent shots!

Now the shop bloke said I need a Altair AstroCam V2 colour jobbie which replaces the eyepiece which then means no or little magnification! Hence me reading this post!

I contacted Altair who sent me 2 jpegs one with camera just slotted into holder and one with 5x barlow. One pic was miniscule and one was amazing!

It seems adding a camera that replaces the eyepiece can only work if you use a barlow? Otherwise its a tiny dot?

cheers

Phil

 

 

 

Big Phil, 

Could you attach those two pics, for comparison's sake and to get a better picture (haha) of what you mean?

Cheers

[ollypenrice]

On 10/07/2017 at 14:06, Big Phil said:

Hi all, complete newbie here reading this thread with interest as Im in the same boat.

Recently bought a Bresser 127L refractor on a EQ5 mount. Ive also bought a motor to fit for tracking and a power pack to run it. It still hasn't been taken out of the box yet....

I use the eyepiece it came with plus a 9m eyepiece and a 2x barlow Celestron make I believe.

The 9m gives good close ups and the standard one, 20mm I think gives good wide angle. Use the 9mm and the barlow...crap  

Started to use my phone camera to take a few snaps and by changing the eyepieces and lining up the camera got some half decent shots!

Now the shop bloke said I need a Altair AstroCam V2 colour jobbie which replaces the eyepiece which then means no or little magnification! Hence me reading this post!

I contacted Altair who sent me 2 jpegs one with camera just slotted into holder and one with 5x barlow. One pic was miniscule and one was amazing!

It seems adding a camera that replaces the eyepiece can only work if you use a barlow? Otherwise its a tiny dot?

cheers

Phil

 

 

 

What you are doing here is using the barlow to extend the effective focal length of the telescope. The longer the focal length the larger the image of an object projected onto the chip. If you have a 500mm native focal length and add a 5X Barlow you will be imaging at an effective focal length of 2500mm. That really is the best way to think about it because it has a universal currency. Everyone knows exactly what you mean.

Olly

 

 

[Luna-tic]

I didn't see anyone specifically speak about it, but EPP, or eyepiece projection photography is another way to achieve a "magnified" image over a prime projection. The extenders some have mentioned, that increase the distance to the camera's sensor, increasing the focal length, also come such that you can insert one of your telescope EP's into it, then attach your camera via the T-ring, and then insert the whole thing in the focuser of your telescope. In this manner, you can choose a wider range of image size.  Whether your DSLR is a crop sensor or full sensor will also determine the image size.

These are poor images, but illustrate the difference. Telescope is a Edge HD 8" SCT; first image is prime with a DSLR of the Moon. Second image is a 13mm EP and I believe I also had a 2.5x Barlow attached to the front of the camera and then into the rear cell of the telescope (or focuser if it were a refractor or Newt). Easy to see the difference in "magnification" between the two. I had a couple of issues focusing when I made these, since resolved.  DSO imaging doesn't really benefit from EPP, though, just planetary or Lunar.

 

[ddefoe]

2 hours ago, Luna-tic said:

I didn't see anyone specifically speak about it, but EPP, or eyepiece projection photography is another way to achieve a "magnified" image over a prime projection. The extenders some have mentioned, that increase the distance to the camera's sensor, increasing the focal length, also come such that you can insert one of your telescope EP's into it, then attach your camera via the T-ring, and then insert the whole thing in the focuser of your telescope. In this manner, you can choose a wider range of image size.  Whether your DSLR is a crop sensor or full sensor will also determine the image size.

These are poor images, but illustrate the difference. Telescope is a Edge HD 8" SCT; first image is prime with a DSLR of the Moon. Second image is a 13mm EP and I believe I also had a 2.5x Barlow attached to the front of the camera and then into the rear cell of the telescope (or focuser if it were a refractor or Newt). Easy to see the difference in "magnification" between the two. I had a couple of issues focusing when I made these, since resolved.  DSO imaging doesn't really benefit from EPP, though, just planetary or Lunar.

 

Thanks for this, really helpful.

Do you have any thoughts on my other post in imaging, would be good to have your input, i've asked a few questions.

[Luna-tic]

3 hours ago, ddefoe said:

Thanks for this, really helpful.

Do you have any thoughts on my other post in imaging, would be good to have your input, i've asked a few questions.

I've only used a DSLR so far, don't have a dedicated AP camera yet. I'm still learning myself about pixel size, large sensor, small sensor, etc., and how they affect the image, as well as stacking and processing.

Lots of things seem to trade off on each other when imaging. For instance, those two Moon pictures above had quite a bit of difference in ISO and shutter speed between them. 1st image was 1/60 sec, ISO 400. 2nd image was 1/80 sec, ISO 12800. The more "magnification" and lenses you put into the light path, the dimmer the image becomes. You then have to weigh a high ISO (more noise) against a slower shutter speed (object movement) in order to get an exposure bright enough to show contrast and detail, yet not be blurred from sidereal motion or poor tracking.

The Moon isn't all that hard, it's a big, bright object. Planets become more difficult, higher magnification not only dims the image, it decreases the detail and sharpness even though the image is larger. I can't say whether or not it would be better to get a really crystal sharp image that is tiny, but has good detail and color, and then crop it to make the image larger. It would depend in great part on how high the camera's resolution is.  And then there's DSO, when stuff is so dim that exposures get timed on a calendar, it seems. Then its much more than just the camera, the mount and its tracking accuracy become paramount, and stacking multiple images and processing. Still working on getting there, single image is all I've done so far, and even there, I've a long way to go. From what I understand, (to address one of your questions from the other thread), you can shoot either multiple single images or a video; the stacking software can separate the video images. You'd need to ask someone with much more expertise than I (currently I'm at  1 to the minus 10th power level) about the advantages of one over the other for processing.