Lodestar live with a C11

[m.tweedy]

I have tried with the above set up and Lodestar x2 mono but cannot achieve focus.

Do i need to focal reduce it and if so will a celestron 6.3 reducer do the trick?

Thank you.

I do have other scopes that have a shorter focal length but thought the light grasp of the C11 would enable me to see fainter objects.

[Merlin66]

Michael,

How are you mounting the camera on the C11?

I regularly use the Lodestar for guiding the spectroscope on the C11 at f10.

No issues, no drama.

[HiloDon]

Hi Michael,

SCT's have a large range of focus, so you should be able to focus the Lodestar X2 easily. However, at the native focal length of 2800mm, the field of view with the small sensor in the LS will be extremely narrow. I would suggest trying the 6.3 FR and possibly a 3.3 if you have one. You can get an inexpensive .5x reducer and use it with your 6.3. Here's a link to explain the best way to install these. Your resultant FL will be about 935mm which is still a fairly narrow FOV with the Lodestar.

http://www.mallincam.net/uploads/2/6/9/1/26913006/focal_reduction_for_dummies.pdf

Hope this helps.

Don

[m.tweedy]

Thank you. i will have another go at it. Maybe just too long a focal length to get the whole of M101 in. I was just picking up a few bloated stars that would not quite come to focus.

[nytecam]

Thank you. i will have another go at it. Maybe just too long a focal length to get the whole of M101 in. I was just picking up a few bloated stars that would not quite come to focus.

The "bloated stars" bit probably sums it up eg too long a fl aggrevated by seeing conditions. 

Whilst a good image scale is needed for the planets [and the good seeing to go with it] the advantage of the strong focal reduction on a big scope like yours is that seeing is rarely an issue and so most evenings are productive.  Most Messiers then fill the frame nicely except for the Giant Messiers like M31/M45 etc and these are best shot with a short focus refractor or camera lens.  Good luck ;-).   

[HiloDon]

Michael,

To get all of M101 with your scope and the LS, you will need a focal reduction of .33. I use an app called AstroAid on my iPad and iPhone. I think it's cheap.

Don

[m.tweedy]

The "bloated stars" bit probably sums it up eg too long a fl aggrevated by seeing conditions. 

Whilst a good image scale is needed for the planets [and the good seeing to go with it] the advantage of the strong focal reduction on a big scope like yours is that seeing is rarely an issue and so most evenings are productive.  Most Messiers then fill the frame nicely except for the Giant Messiers like M31/M45 etc and these are best shot with a short focus refractor or camera lens.  Good luck ;-).   

thank you. I have used it successfully with the GT81 but i wanted to try it with my C11. The ultimate aim is to use it with our society 14inch Meade Lx 200 on the EQ8 streamed to the main room so groups of 50+ people can see the object then go out to observe with other scopes.  People with mobility issues would also then be able to have a good experience. (that is my dream).

It would have been useful on one of our events when we had 900 people there.

As  said this is my dream and it is SLOWLY coming together.

[m.tweedy]

Michael,

To get all of M101 with your scope and the LS, you will need a focal reduction of .33. I use an app called AstroAid on my iPad and iPhone. I think it's cheap.

Don

I am an idiot. I already have that App but did not realise (until you pointed it out) that it would give an image scale with the Lodestar.

Thank you very much for that. the information is invaluable for choosing targets.

[Dom543]

The assumprion that a larger aperture the scope will give brighter image of faint objects is incorrect. The number determining the brightness of the image is the focal ratio. An f10 SCT will deliver a 16x fainter image of the same object than an f2.5 photo lens or finder scope, irrespective of the apertures involved.

Clear Skies!

--Dom

[aparker]

The assumprion that a larger aperture the scope will give brighter image of faint objects is incorrect. The number determining the brightness of the image is the focal ratio. An f10 SCT will deliver a 16x fainter image of the same object than an f2.5 photo lens or finder scope, irrespective of the apertures involved.

Clear Skies!

--Dom

I think that may be only partially correct.

The image scale (dimension of the image in arcminutes of sky covered) for any astrograph is a product of the sensor dimension (typically X by Y mm rectangle) and the focal length of the optical system used to illuminate it.  It is, as many have pointed out, independent of aperture.

To get an exposure of a given "brightness" (typically measured as degree of pixel saturation for the brightest pixels, but just eyeballed by many of us) it is typically understood that you can either increase exposure time or reduce focal ratio (f-stop).  The critical difference here is that one option (++ exposure) does not affect image scale, whereas the other (faster f-stop) DOES, for an astrograph (not the same story for a typical camera lens where the f-stop is set by an internal aperture stop).  

So for example for a given aperture (say my 200mm Celestron) and sensor (say my Lodestar X2M), if I put a focal reducer in the optical train to go from f/10 to f/5, I get an acceptably bright image sooner - BUT, that image covers a wider swath of sky, and as such provides less detail for small objects.  This makes intuitive sense when you think of the astrograph as a device for concentrating photons from a given area of sky on to the imaging sensor - all things equal, a bigger swath of sky delivers more total photons to the detector per second, hence a shorter exposure.

Conversely, and contrary to the "you just need a faster f-ratio" intuition, if you want a shorter exposure FOR A GIVEN IMAGE SCALE - e.g. if I want to stick to a 20 x 15 arcmin field so I can frame M51 nicely - then the only way to get a shorter exposure time is to increase the aperture.  Again, think of the astrograph as a photon-concentrating device.  Just as in visual observing, if you want a brighter view of a given chunk of sky, more aperture is the answer.  The reason the f-stop changes is this: to keep my image scale constant, if I keep the same sensor, then I have to keep the same focal length.  To keep the same focal length while I increase the aperture, I must purchase or build a faster system - i.e. one with a smaller f-ratio.  But the change in f-ratio is purely a side effect of needing to increase the aperture to gather more light, while holding the focal length constant - it's the bigger aperture that makes a brighter image in a set amount of time.

[m.tweedy]

I think that may be only partially correct.

The image scale (dimension of the image in arcminutes of sky covered) for any astrograph is a product of the sensor dimension (typically X by Y mm rectangle) and the focal length of the optical system used to illuminate it.  It is, as many have pointed out, independent of aperture.

To get an exposure of a given "brightness" (typically measured as degree of pixel saturation for the brightest pixels, but just eyeballed by many of us) it is typically understood that you can either increase exposure time or reduce focal ratio (f-stop).  The critical difference here is that one option (++ exposure) does not affect image scale, whereas the other (faster f-stop) DOES, for an astrograph (not the same story for a typical camera lens where the f-stop is set by an internal aperture stop).  

So for example for a given aperture (say my 200mm Celestron) and sensor (say my Lodestar X2M), if I put a focal reducer in the optical train to go from f/10 to f/5, I get an acceptably bright image sooner - BUT, that image covers a wider swath of sky, and as such provides less detail for small objects.  This makes intuitive sense when you think of the astrograph as a device for concentrating photons from a given area of sky on to the imaging sensor - all things equal, a bigger swath of sky delivers more total photons to the detector per second, hence a shorter exposure.

Conversely, and contrary to the "you just need a faster f-ratio" intuition, if you want a shorter exposure FOR A GIVEN IMAGE SCALE - e.g. if I want to stick to a 20 x 15 arcmin field so I can frame M51 nicely - then the only way to get a shorter exposure time is to increase the aperture.  Again, think of the astrograph as a photon-concentrating device.  Just as in visual observing, if you want a brighter view of a given chunk of sky, more aperture is the answer.  The reason the f-stop changes is this: to keep my image scale constant, if I keep the same sensor, then I have to keep the same focal length.  To keep the same focal length while I increase the aperture, I must purchase or build a faster system - i.e. one with a smaller f-ratio.  But the change in f-ratio is purely a side effect of needing to increase the aperture to gather more light, while holding the focal length constant - it's the bigger aperture that makes a brighter image in a set amount of time.

That was a comprehensive (and very understandable in my laymans opinion) reply and i think i understand the aperture/focal length discussion a whole lot better now.

I have been informed the society have a f3.3 reducer so it looks like i will be giving it a run in the near future.

[m.tweedy]

I also have kept a 1.25 ha nb filter that i may screw onto the Lodestar x2 when i look at some "gassy Stuff" to see if that enhances the view.

it is an Astronomik 12nm filter so not too narrow a bandpass.

[HiloDon]

I also have kept a 1.25 ha nb filter that i may screw onto the Lodestar x2 when i look at some "gassy Stuff" to see if that enhances the view.

it is an Astronomik 12nm filter so not too narrow a bandpass.

Hi Micheal,

I have really enjoyed using an NB Ha filter with the LS X2 on emission nebulae. It enhances the view and eliminates virtually all LP. Here's a link to captures taken during some of my viewing sessions with it. Mine is a 7nm, but the 12 should do a good job, too.

http://stargazerslounge.com/gallery/album/3415-narrowband-ha-and-lodestar/

Also good to see you have access to the .33 reducer. That set up should work well for you. Post some results for us.

Don

[m.tweedy]

Hi Micheal,

I have really enjoyed using an NB Ha filter with the LS X2 on emission nebulae. It enhances the view and eliminates virtually all LP. Here's a link to captures taken during some of my viewing sessions with it. Mine is a 7nm, but the 12 should do a good job, too.

http://stargazerslounge.com/gallery/album/3415-narrowband-ha-and-lodestar/

Also good to see you have access to the .33 reducer. That set up should work well for you. Post some results for us.

Don

they are impressive.

if i can get members of the public to see anything close to those then i guarantee they will be hooked.

this set up is going to be mainly used for public outreach either at the observatory with the 14 inch or "in the field" with my C11.

my own set up is very close to getting the Atik 460.