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Robert Anstruther

Aperture size and effect on video

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Hi all,

I've been happily and quietly using my PD colour camera for around 2 years and love it.  I know there are better cameras and tech out there but for once I have been absorbed in the hobby and not the gear!  You all helped me get my setup together and its wonderful, great to look outside to the freezing cold whilst nestled up with a cuppa in the early hours controlling my scope from indoors :)  Definetly found my corner of astronomy.  Thanks for helping me get there!

I have been trying to contact Phil Dyer for some questions but so far he has not responded and isn't picking up the phone - does anyone know if he is still in business?

My question is I have recently moved and my new house is a pig for gear storage and setup and as such my scope is upstairs.  Hauling that 12" goto Dob up and down isn't fun and I am worried I break something.  I am thinking of downgrading to something easier to handle, my questions is what effect from going from 12" to say 8" would have?  Would i notice a huge difference or minor? I don't mind loosing some but if the chnage is huge then I will need to rethink my strategy!

Hope someone can help!

Thanks

Rob

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Hi Rob

An 8" is perfectly fine for EAA. Mine is a fast 'astrograph' f/4, which helps. 800mm focal length seems like a good compromise -- there are some larger nebulae and open clusters (and dark nebulae too) that don't fit onto a small chip, and plenty of small galaxies/galaxy groups that are difficult to resolve, but in the middle of the range there are tonnes of interesting objects that work perfectly well with this focal length. You'll almost certainly find it easier to track for longer at 8" too. The only thing you'll lose going from 12 to 8" is resolution.

If you're planning to use the same camera, I recommend checking out the arcsecs per pixel of whatever focal length you choose.

One thing I've learned is that usability is the most important factor, and hauling a 12" would definitely restrict the number of sessions for me.

Cheers

Martin

 

 

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Agree - 6 to 8 inches and a sensitive camera is fine for EAA of almost any object you care to see.  You can do a lot even with a 3" refractor, if you want super-portable.

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In visual astronomy they say "Aperture wins". In camera assisted astronomy it's "Focal ratio wins".

Faster optics delivers brighter images and allows for shorter exposure times. If the camera is your primary means of observing, then try to get a fast (e.g. f/4) scope.

Clear Skies!     --Dom

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Great thanks for the advice, now to find a scope suitable!

I was looking a compact 8", something like a Nexstar 8 or similar but they are slow scopes.  Do you have any suggestions for something portable and compact but fast?

Thanks

Rob

 

Edited by Robert Anstruther

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Hi again

I'm looking at a 6" f10 (1500mm) SCT.  I have a 1.25" 0.5x focal reducer. However I have forgot what I need for astro video, do I need something different, like the meade  f6.3 reducer? Sorry I can't remember the formula for this. Hope someone can help!

 

Thanks

 

Rob

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Hi Rob

An 8" SCT work fine if you can get your hands on an F3.3 reducer - my primary EAA setup is a C8 with F3.3, although I also use a 4" MAK with the F3.3 at about F4 to good effect.

A combination of F6.3 and 0.5x 1.25" reducer can also be used on these SCT/MAKs  - your target should be F4 or there about's (lower better) - the F6.3 reducer is an x0.63 (only F6.3 if you use it with an F10 SCT).

You can use your existing 0.5 reducer with the 6" SCT (or any other scope for that matter) - SCT/MAKs have a wide focus range and can accommodate many different reducer configurations.

The benefits of the smaller SCT (6") is shorter focal length and corresponding wider FoV with your camera along with a reduced mount requirements.

My travel set up is  a Skywatcher AZ Gtot and the 102MAK with F3.3 reducer - I used to use this wiht my SDC435 camera before upgrading to a Lodestar:

gallery_24614_1502_1338790519_14366.jpg

The flip mirror was useful in getting objects centered  on the camera but I eventually stopped using it - at this time I was using a combination of an F6.3 SCT reducer and an x0.5 1.25" reducer - hence the extension tube on the flip mirror for the eyepiece (need to make the camera and eyepiece parafocal).

 

gallery_11951_1244_36484.jpg

 

I upgraded the tripod to increase stability - even tried the C8 on this - OK for EAA but goto accuracy was not really good enough at that focal length.

If  you go with the 6" Celestron SCT you can upgrade to Hyperstar later for increased speed - especially useful if you move to CCD based EAA such as Ultrastar.

HTH

Paul

 

Edited by DoctorD

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On 17/10/2016 at 11:45, DoctorD said:

Hi Rob

An 8" SCT work fine if you can get your hands on an F3.3 reducer - my primary EAA setup is a C8 with F3.3, although I also use a 4" MAK with the F3.3 at about F4 to good effect.

A combination of F6.3 and 0.5x 1.25" reducer can also be used on these SCT/MAKs  - your target should be F4 or there about's (lower better) - the F6.3 reducer is an x0.63 (only F6.3 if you use it with an F10 SCT).

You can use your existing 0.5 reducer with the 6" SCT (or any other scope for that matter) - SCT/MAKs have a wide focus range and can accommodate many different reducer configurations.

The benefits of the smaller SCT (6") is shorter focal length and corresponding wider FoV with your camera along with a reduced mount requirements.

My travel set up is  a Skywatcher AZ Gtot and the 102MAK with F3.3 reducer - I used to use this wiht my SDC435 camera before upgrading to a Lodestar:

gallery_24614_1502_1338790519_14366.jpg

The flip mirror was useful in getting objects centered  on the camera but I eventually stopped using it - at this time I was using a combination of an F6.3 SCT reducer and an x0.5 1.25" reducer - hence the extension tube on the flip mirror for the eyepiece (need to make the camera and eyepiece parafocal).

 

gallery_11951_1244_36484.jpg

 

I upgraded the tripod to increase stability - even tried the C8 on this - OK for EAA but goto accuracy was not really good enough at that focal length.

If  you go with the 6" Celestron SCT you can upgrade to Hyperstar later for increased speed - especially useful if you move to CCD based EAA such as Ultrastar.

HTH

Paul

 

Hi Paul

 

Thanks for the info, that nailed it on the head.  I sold my 12" Dob so now looking for a scope and mount to replace and primarily to do astro video, I was looking at the Skyprodigy series for the laziness and auto align function (meaning I don't have to go outside).  I have noted down your points on the reducer and optical train, the only pieces I need are the f3.3 or f6.3, I have time to decide which one while I wait for a scope to come up, thanks for the taking the time.  I'll update once I get a setup ready to go.

 

Rob

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The Celestron Evolution 6" and 8" SCTs are very popular for video astronomy/EAA and appear to work well with the starsense accessory for auto setup. I have been very tempted by one of these myself. They are not cheap but I believe the quality of the mount and tripod is a step up from the Sky Prodigy. Might need to mount the camera on a diagonal to get clearance from the mount, but it must be doable if they are so popular.

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On ‎29‎-‎12‎-‎2016 at 01:34, RobertI said:

The Celestron Evolution 6" and 8" SCTs are very popular for video astronomy/EAA and appear to work well with the starsense accessory for auto setup. I have been very tempted by one of these myself. They are not cheap but I believe the quality of the mount and tripod is a step up from the Sky Prodigy. Might need to mount the camera on a diagonal to get clearance from the mount, but it must be doable if they are so popular.

Tne Evo 8 is a great scope for EAA. Very quick/light setup.

The StarSense is a very helpful tool in case of obstructed horizon. Just do a "SS manual align" instead of a "Auto".

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