Fundamental question

[piprees]

Hi, being a complete beginner to imaging, I have a very basic question. I read somewhere that the only stupid question is the one that's never asked so here goes. When a camera is attached to a telescope both the camera lens and the telescope eyepiece are removed, so where does any magnification come from, or is it only in the image enlargement. (Bet all beginners think about this but are too embarrassed to ask).

[leemanley]

Firstly, there's no such thing of a stupid question on here !, if it wasn't for all the learned folk on here I wouldn't have been able to achieve what I have

so far.

The telescope you attach your camera to acts as a lense, so, depending on things like scope appeture, focal length etc. this determines what magnification is achieved with your imaging set-up.

What scope/cam are you using ?

Lee

[Jannis]

There is no magnification in that way. The telescop basically is a huge "camera lens".

Let's say, you have a canon dslr with a kit lens 18-55mm. When you take off this lens, and put on let's say a skywatcher explorer 200p (1000mm), then you basically put on a 1000mm lens with manual focus and a very long "minimum focus distance".

To calculate the field of view with a given camera and a telescope, you can use this link:

http://www.12dstring.me.uk/fov.htm

[romi]

All what mentioned above is correct, and indeed connecting the lensless camera to the scope, instead of the eyepiece, will result in projecting the image of the entire FOV, captured by the apperture, onto the CCD at the focal plane.

However, remember that attaching a camera WITH the lens to a telescope WITH or without the ocular IS possible and can easily be experimented with suitable adaptors......

[piprees]

Thanks guys, I'll be hopefully using a canon 40D with a skywatcher 200 on an EQ5 mount. Any and all suggestions will be gratefully received.

[lensman57]

Hi, being a complete beginner to imaging, I have a very basic question. I read somewhere that the only stupid question is the one that's never asked so here goes. When a camera is attached to a telescope both the camera lens and the telescope eyepiece are removed, so where does any magnification come from, or is it only in the image enlargement. (Bet all beginners think about this but are too embarrassed to ask).

Hi,

There is no stupid question, but there are stupid people who do not ask questions. As to the answer to your question , a telescope is in effect a long "telephoto" lens. Lets say that you have a 100 mm aperture telescope at a native ratio of F5 or 100 X 5 = 500mm focal length, lets say that you have another 100 mm aperture telescope with a focal ratio of F7.5 or 100 X 7.5 = 750 mm focal length. If you point these two telescopes to the same object in the sky, lets say the Moon, the scope with the 750 mm focal length will show you an image 1.5 X larger than the 500 mm telescope, 750/ 500=1.5X if you use the same eyepiece or the same camera, however the telescope with the shorter focal length F5, the faster one, will have a brighter image, 1.5X brighter.

You can have the same magnification with the faster F5 scope as with the slower F7.5 , if you use an eyepiece that is 1.5X shorter in focal length, ie: a 15 mm eyepiece will give you 750/15= 50 times magnification and a 10 mm eyepiece will give you exactly the same magnification with the faster scope, 500 / 10= 50. When it comes to cameras it is more meaningful to think about things in terms of Field Of View, FOV, rather than magnification, as a telescope will form the same size image on a sensor be it a DSLR or a high resolution Cooled CCD imager, the size of the chip is what determines the apparent FOV, things are not so simple and straight forward but I think that will do for starters.

Regards,

A.G

[Jannis]

My (very strong) suggestion is to get the HEQ5 Pro and the explorer 200 PDS instead of the standard P.

The PDS makes focusing a bit easier, as well as the mirror is moved futher up in the telescope tube, making it easier to reach focus.

Basically, the 200P is exelent for viewing, the 200 PDS is exelent for viewing AND imaging.

The EQ5 isn't performing very well for astro-photo, and you're going to regret not going for the HEQ5 Pro instead (ask anyone else here who have had EQ5 and thought it would be OK for long exposure imaging).

HEQ5 Pro is the "minimum" for imaging through a telescope, because of the gear and motors operate at a much "higher resolution", moving the scope a lot more smooth across the sky.

If i had to choose, i'd actually get the HEQ5 Pro mount alone, and use only a camera with camera lens to begin with instead of the DSLR on an EQ5 through the 200p option - and upgrade with a scope later, if money for both at the same time is an issue.

PS, this was not a stupid question of you at all. In fact, me myself, and probably plenty of others here, was wondering the very exact same thing when we first started with this.

[VigdisVZ]

Hi

Last season I made a few pictures to demonstrate how a DSLR attatches to a Skywatcher Explorer telescope, you can chek it out here: http://stargazerslounge.com/topic/171765-direct-slr-camera-connection/#entry1753560

Lots of solid advice in this thread already. I would firstly look at the PDS instead of the P. Also would strongly recommend getting the sturdiest mount you can afford HEQ-5 preferably, and get a cheaper scope if you want to save. With imaging you can only go as far as the mount will let you, but a cheaper scope will still yield good results. The focal length to chose is also dependant on what you're planning to shoot. In this case you get a more zoomed view with the 200PDS while the 150PDS will give you a wider view good for larger objects (check my gallery for some 150PDS work, no coma corrector or guiding).

The 200PDS on the HEQ-5 mount will be slightly slightly wobbly (with a guide scope) but not bad at all (or something slightly smaller like the 150PDS or the 80ED) , you'll be able to get great results from that equipment. Before you take the plunge think once about the NEQ-6. It's definetly more capable if you want to put more stuff on like a guide scope.

With this being said, people are banging out some amazing stuff with even smaller mounts and scopes, but if you plan on investing, try to invest in somehting that you suspect you wont need to upgrade too soon.

Hope this helps a bit.

[lensman57]

My (very strong) suggestion is to get the HEQ5 Pro and the explorer 200 PDS instead of the standard P.

The PDS makes focusing a bit easier, as well as the mirror is moved futher up in the telescope tube, making it easier to reach focus.

Basically, the 200P is exelent for viewing, the 200 PDS is exelent for viewing AND imaging.

The EQ5 isn't performing very well for astro-photo, and you're going to regret not going for the HEQ5 Pro instead (ask anyone else here who have had EQ5 and thought it would be OK for long exposure imaging).

HEQ5 Pro is the "minimum" for imaging through a telescope, because of the gear and motors operate at a much "higher resolution", moving the scope a lot more smooth across the sky.

If i had to choose, i'd actually get the HEQ5 Pro mount alone, and use only a camera with camera lens to begin with instead of the DSLR on an EQ5 through the 200p option - and upgrade with a scope later, if money for both at the same time is an issue.

PS, this was not a stupid question of you at all. In fact, me myself, and probably plenty of others here, was wondering the very exact same thing when we first started with this.

Hi,

I beg to differ, the only limitation of the EQ5 pro is its weight capacity and the length of the optical tube that is to be mounted on the mount as this will increase the inertia and the load on the mount. Ofcourse I agree with you that if one could afford it an HEQ5 pro will be the preferable mount but so far as the OP is concerned if he or she has decided to go for a 200 PDS with a tube length of approaching one meter and a weight of nearly 10 Kg, by the time a guider, camera and other bits and pieces are mounted up, the preferable mount is an NEQ6 as even the excellent HEQ5 pro is right on the limit of its imaging capacity. I have been imaging quite well for a novice using an EQ5 PRO from my location, a back garden less than 3 miles from an international airport with limited vsibilty. I attach a sub of 1200s exposure from NGC 6888, straight out of Fits liberator, no stretching or adjustments.and converted to Jpeg, it was taken a couple weeks ago using the EQ5 PRO and an ED80 scope @f7 in broadband H- alpha. Looking at the stars I don't see anything wrong with the traclking or the shape of the stars, but I do take time over polar alignment.

Regards,

A.G

[ollypenrice]

Magnification is absolutely meaningless in astrophotography. Nobody magnifies an astronomical target. M31 is what, 150,000 lightyears across? You want to magnify it? How big i your screen???? What we are all doing is massively reducing the size of our targets so that we can see them in full. I'm serious.

No, think in terms of image scale, or what the professionals call plate scale. Take a few arcseconds of sky and see how many mm across that will be on your chip. This is governed only by the focal length of your optics. In reality a DSLR chip with optics of about 300mm will just about take the full M31. If you want M27 to fill your chip you'll need around 3 metres of FL.

The term 'magnification' comes from visual observing when what is being magnified is the image scale on your retina when observing naked eye. In a pair of 10x binoculars the image on your retina becomes 10x larger. In this case 10x means something. In photography it means nothing.

Olly

http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/22435624_WLMPTM#!i=2277139556&k=FGgG233

[Jannis]

Hi,

I beg to differ, the only limitation of the EQ5 pro is its weight capacity and the length of the optical tube that is to be mounted on the mount as this will increase the inertia and the load on the mount. Ofcourse I agree with you that if one could afford it an HEQ5 pro will be the preferable mount but so far as the OP is concerned if he or she has decided to go for a 200 PDS with a tube length of approaching one meter and a weight of nearly 10 Kg, by the time a guider, camera and other bits and pieces are mounted up, the preferable mount is an NEQ6 as even the excellent HEQ5 pro is right on the limit of its imaging capacity. I have been imaging quite well for a novice using an EQ5 PRO from my location, a back garden less than 3 miles from an international airport with limited vsibilty. I attach a sub of 1200s exposure from NGC 6888, straight out of Fits liberator, no stretching or adjustments.and converted to Jpeg, it was taken a couple weeks ago using the EQ5 PRO and an ED80 scope @f7 in broadband H- alpha. Looking at the stars I don't see anything wrong with the traclking or the shape of the stars, but I do take time over polar alignment.

Regards,

A.G

Thanks for correcting me then.

I've never had an EQ5 pro, so i can't say how it is. But the standard EQ5 is as far as i know quite different form the pro though - when it comes to motors and gears (as in, are the optional additional tracking motors as high resolution as the pro verson)?

From what i've heard and read, EQ5 pro is not nearly as stable as the HEQ5 pro (when it comes to weight capacity, as you mentioned), as well as the resolution of the EQ5 pro is 0.288 arc sec, while it's 0.144 on the HEQ5 pro.

I don't know how long focal lenght you need to have this make any difference, but i guess it's (oviously form your pic ) not a problem with your focal lenght. The SW Exp 200 is 1000mm though, while yours is 600mm, so there is a significant difference here - but like i said, unsure how much it matters.

Personally, i have the HEQ5 pro, with the 200PDS, finderscope, green laser, and a DSLR without battery (use AC adapter), and i regret not going for the NEQ6 as i find the HEQ5 a bit under-sized for this scope - and that's without a seperate guide-scope.

In the end, the mount is the one thing one usually keep if it's not "saved on" to begin with, so therefore, based on that and my personal experience with the HEQ5 and exp. 200, i don't recommend the EQ5 (as i feel the HEQ5 is at the minimum of what i'd accept in stability). But of course, i'm not saying it's not up for the job at all.

Please correct me if i'm wrong.

[lensman57]

Thanks for correcting me then.

I've never had an EQ5 pro, so i can't say how it is. But the standard EQ5 is as far as i know quite different form the pro though - when it comes to motors and gears (as in, are the optional additional tracking motors as high resolution as the pro verson)?

From what i've heard and read, EQ5 pro is not nearly as stable as the HEQ5 pro (when it comes to weight capacity, as you mentioned), as well as the resolution of the EQ5 pro is 0.288 arc sec, while it's 0.144 on the HEQ5 pro.

I don't know how long focal lenght you need to have this make any difference, but i guess it's (oviously form your pic ) not a problem with your focal lenght. The SW Exp 200 is 1000mm though, while yours is 600mm, so there is a significant difference here - but like i said, unsure how much it matters.

Personally, i have the HEQ5 pro, with the 200PDS, finderscope, green laser, and a DSLR without battery (use AC adapter), and i regret not going for the NEQ6 as i find the HEQ5 a bit under-sized for this scope - and that's without a seperate guide-scope.

In the end, the mount is the one thing one usually keep if it's not "saved on" to begin with, so therefore, based on that and my personal experience with the HEQ5 and exp. 200, i don't recommend the EQ5 (as i feel the HEQ5 is at the minimum of what i'd accept in stability). But of course, i'm not saying it's not up for the job at all.

Please correct me if i'm wrong.

Hi Jannis,

You are absolutely correct, if I were starting again I'd probably go for either an HEQ5 PRO or the new Celestron AVX . The HEQ5 has the better resolution motors (compared to EQ5) but slightly coarser gears and is more stable due to beefier build and weight, for me I find the EQ5 PRO adequate and more easily movable as anytime I wish to either image or observe I need to carry and set everything up in the garden so weight is an issue, I have used the EQ5 PRO successfuly for imaging using my 100 mm F9 APO ED, scope but I think that was the limit for imaging, I normally use either of my two 80 mm ED scopes at focal lengths of between 440 mm~ 510 mm and it seems to be fine up to about 5.5Kg of weight provided that balance is near perfect and there are no overhangs. I think that guiding a long heavy scope such as a 200 PDS presents its own set of challenges and I take my hat off to those who manage it well.

Regards,

A.G