upgrade opinion- from ed800 to f4 newt??

[lookus]

i am looking at getting an orion or bintel(whichever lands first) 8" f4 newtonian astrograph. i will also employ a coma corrector.i already have an ed80 which i am using for imaging now with a zenithstar 66 for guiding.

will the astrograph be a "better" upgrade? i know the focal length is a bit longer, but i am more wanting to know if people here think tha quality of the images will be better than with the ed80. i have a eq6 pro mount and use a 450d camera.

your opinions would be appreciated. thanks.

[NorthernLight (Max)]

Hi Lookus,

I started the other way around but a 6" f/5 newton and I can tell that in terms of the wow effect the ed80 has it.
The newton suffers a bit from its short focal lenght. In images you can see when its miscollimated and you get vignetting and curved edges on my 450D.
For newton speaks the bigger apperture, no question. And with faint objects, you want focal lenght (as they are small) and apperture to hold the shot as short as possible.
Imagequality wise I´d say you will find more detail in your images as it gathers a lot more light in time but the colours are not quite the same as with the ed80. I suppose it depends on what you wanted it for.
I was actually thinking of ramping up my omniXLT and cut it off at 580mm and install a larger secondary to overcome the distortion issues but I am a little hesitant as I am soon moving to NZ and came to think that after all it might be cheaper and time saving just to buy.
Let me know how you go!
Cheers
Max

[Moon (James)]

F4 is quite fast, so I guess it will be a challenge to focus and collimate. Having said that, it will have a nice big FOV and should be easy to guide.
So if you are willing to make the effort to collimate it properly, then yes, it will give better results IMHO.
I'm thinking of getting one myself.
James

[tlgerdes (Trevor)]

I have a Bintel 8"F4. FOV 1.5x1deg on an APS sized chip.

Collimation is your biggest issue. You will need to buy Jim Fly's collimation tools, a laser is not going to cut it. F4 is very fast and collimation has to be spot on because of it.

Also worthwhile to get it flocked. I am in the city and went from 90s to 150s exposures, before light pollution got the better of me after flocking.

[chris lewis]

Hi ! just wondering - I was looking to get the GSO 8 in. F/4 also for some A.P. I see GSO sell a 8in. F/5 [as sold by Andrews]. I had a 8in. F/4 many years ago for visual only so I am aware of the importance of collimation.
I was wondering if the F/5 version would be just that easier to collimate and keep collimated but would it still be 'fast' enough for A.P. ? unsure what the secondary mirror size is - the F/4 is 63 mm. I believe the F/5 may be smaller at 50 mm so unsure if this is enough for full illumination - but unable confirm what size it this.

Thanks for any thoughts

Chris

[asimov (John)]

I also have an 8" F4 newt. I'd rather it than an F5 for AP. They are not that much harder to collimate than an F5. It's all about secondary mirror placement, & once you've done that, it'll hold for a very lengthy period of time. Primar mirror collimation is a seperate issue, but very easy.

[Moon (James)]

Here is an interesting comparision of a TEC 140 APO and GSO 200mm f/4 newt with MPCC by Michael Fulbright:
http://msfastro.net/articles/gso_tec...c_compare.html

James

[multiweb (Marc)]

Originally Posted by lookus

will the astrograph be a "better" upgrade? i know the focal length is a bit longer, but i am more wanting to know if people here think tha quality of the images will be better than with the ed80.

The ED80 may give you sharper pictures but has a wider field and a bigger image scale [1.78asp]. The 8" f/4 newt will capture a lot more light and has a smaller image scale so you'll get more details [1.34asp]. The field will also be narrower. It'll be a bit of a learning curve too as you'll have to budget for an MPCC and a collimation KIT. Also you'll have to consider tight guiding in the vicinity of +/- 1.5arcsec at prime focus so a very steady mount is a must. If you got away with +/- 2 and over with the ED80, oblong stars will show in the pics taken with the newt from now on.