Celestron 9.25 standard w FF, vs Edgehd 800

[Legoman]

Hello there cool people,
Eventually looking to purchase an OTA both for imaging and observing, using up to a 36mm sensor (in theory on occasion I will have opportunity to use a larger medium format sensor, but as I understand it the edgehd's still only have a 42mm circle).
My question is the differences and qualities between a Celestron 9.25 with field flattener/focal reducer and an edgehd 800.
Points of interest;
Focal Length
Frame size
Flatness of frame, and sharpness
General differences of either setup
Thank you
-Leon

Ps, If there is already a similar thread anywhere on the fine interwebs, I shall happily accept a link and go off reading. (:

Ps again, as this is my first post, Me.. I am a student from Perth studying photography with a keen interest in general science, physics primarily, as well as thoroughly enjoying all that is above our heads. Up until now I've only ever imaged 'space' with a static tripod and various lenses up to 800mm with 2x teleconverter. I am hopefully in the process of purchasing a CGEM (tomorrow :) )... the eventual plan when my student income allows is to add an OTA.

[Camelopardalis]

:welcome: to Ice in Space Leon!

All Edge HD models have a flatter field than their equivalent non-Edge HD model due to the field flattener in the baffle tube.

According to Celestron's Edge HD white paper (your favourite search engine should find the PDF), the Edge HD 9.25" has the largest imaging circle, and the 11" and 14" are just sufficient for a full frame DSLR sensor.

The only problem is that currently there is no reducer (from Celestron) for the 9.25" model, unlike the rest of the range, so you'd be limited to f/10 or an alternative third-party solution.

The Edge HD 8" is only suitable for APS-C sizes sensor as the baffle tube is only 38mm in diameter. It is however the smallest and lightest of the range by far.

Using your 800mm setup on an equatorial mount is a good place to start, although maybe try without the teleconverter, and or any other lenses you have, as at this time of year the Milky Way rising is quite a sight :D

But anyways...what are your objects of interest? That will really give the best determination of which scopes would be most suitable for your interests, as telescopes are just like lenses, different focal lengths for different purposes.

[Legoman]

Hi, my question was not so much a 925 hd v 800 hd, but a 925 normal xlt with a field flattener (added), v the 800HD with it built in.

And I have already read the white paper, celestron still states the 800hd will give a 42mm circle, same as the others? as you say the baffle in the end is only 38mm, however this wont change the final image area. Many DSLR lenses have small final elements still with the ability to spread the light across a 36mm frame, the ff in the edge models is in the baffle at the end doing the same thing is it not?

<my interests, well everything really, presently I have only imaged; Carina Nebula, Orion Nebula, Jupiter, The moon and the general milky way including more condensed views of constellations. The telescope will be primarily for deep field, as I have lenses to fill every point up to 1600mm.

Thanks- Leon :)

[Camelopardalis]

I've not seen any specs for the f/6.3 reducer for the XLT scopes, but it's the least expensive option. The clear aperture is about the same as the baffle diameter on the C8. I'd be really surprised to learn it could illuminate a full frame chip, so you'd want to check what the vignetting situation is, as the light drop off will be more noticeable in long exposures than it is visually.

The C9.25 is slightly flatter than the other scopes in the range due to having slower mirrors, but it's not much.

The flattener in the Edge HD scopes is located somewhere in the baffle tube, it depends on the model and is shown schematically in the white paper. It doesn't change the focal ratio, but reduces coma and flattens the field somewhat. The reducers for the Edge HD scopes are just that...reducers.

Another option to consider is the Ritchey Chretien type scopes, as they are also long focal length scopes, and they're popular with a number of folk in here.