Astrophotograpy : 80ED versus 100ED

[DJ N]

By all accounts, it seems quite a number of people are using the 80ED Pro Series for astrophotography. In terms of photography, would there be any pros or cons of considering the 100ED (f9 in lieu of f7.5, heavier, more $$, greater aperture????). Look forward to some comments, especially from any owners of either the 80ED/100ED out there!

Cheers.

[[1ponders] (Paul)]

Hi DJ

From my perspective, while the 100 will give you slightly higher resolution, the trade off is the slower f ratio. In case you aren't clear on what this means. eg: if an f/8 shot requires 1/125 of a second an f/11 shot will require 1/60 of a sec, twice as long. Transposing that to the ED then you are looking at somewhere around 1.5 time the exposure length to get the same results (I'm sure someone here will do that actual calc for me ). This mightn't be too bad on things like Omega Cent or M42 where short exposures are the norm, but what about 8-10 min shots. Thats upping your exposure time quite a bit.

I will happily admit I haven't imaged through the 100, but boy I'm happy with the 80. It's a fantastic little scope. Plus it matches up pretty well with the Meade f6.3 focal reducer to drop the f ratio to 4.7. I don't know how it will work with the 100. For best bang for the buck in a low cost semi apo imaging scope I don't think you could do better than the ED80.

Besides at around $1200 - $1500 for the 100 you could get an ED80, a Williams Optic 10:1 dual speed focuser upgrade and a FR/field flattener for the same price

[Geoff45 (Geoff)]

The focal ratio only comes into play with extended objects. For stars, which are point objects, aperture wins every time--you'll get fainter stars with the same exposure. Also the image size will be smaller in the 80ED (about 60% 0f the size in the 100ED), so yes you will need a longer exposure, but at the end of it you'll have a better image to work with. The other thing you can do is invest in a focal reducer to use with the 100ED, so you can get the benefit of both aperture and short focal ratio. IMO go for the 100ED.
Geoff

[mick pinner]

l have had both and at the moment still have the ED100, as you would expect image quality is the same in both although the ED100 as you would expect again has the advantage with fainter objects and increased magnification on closer objects and therefore better detail.
l use the ED100 with a Meade 6.3 focal reducer (see pic m42 ), as Paul has said both great scopes and both great value for money and you would be happy with either although the ED100 can be picked up for quite a bit less than Paul mentioned as l found out.