Field Flattener Query

[RayD]

I have had to return my Esprit 80 field flattener as there was an issue with the machining on the matching adaptor.  This coupled with my Esprit 100 from FLO unfortunately failing its Es Reid checks means I am currently without any proper wide field  imaging set up.  

I've been thumbing through some of my bits and bobs this morning and came across a Hotech SCA ff, which it says is for f5 - f8.  I used to use this on my ES 80 but that died so it's no longer needed.  Now given that the Esprit is f5, would you think I would be able to use this until my new SW ff is returned?  I don't really want to go through setting everything up to find out it doesn't, or was never likely to, work.  

I guess my question is what is the difference between the Hotech ff and the Esprit's matching ff (other than the aperture), and would you think it is the aperture that makes the difference so could lead to curvature, or would this only be on larger sensors than my Atik 460EX?

Sorry for all the questions but not being able to image at all is really becoming pretty frustrating.

Thanks.

[Leveye]

I'd pass on the Hotech. Even though I loved the self centering design I had very unsatisfying results using it with my SV80ED. The AstroTech AT2FF is the only one that has worked for me and the only one I use with my refractor now. Highly recommended.

Here is an example of the very edge using the AT2FF and this was even using a full frame sensor DSLR

 

[RayD]

Thanks for this, that's quite an impressive example.  

To be honest the Hotech seemed to work ok with the ES 80ED, albeit I didn't really have much time with it before I broke the OTA, but I'm not sure how it would work with the Esprit 80. 

The Esprit has a "matching" FF which I had to return, but does this mean I can effective use any one as long as it is designed to work at f5, such as the Hotech or the AT2FF?

[James Vincent]

Hi Ray

Have you tried the telescope without the field flattener ?

 

[James Vincent]

What happened to the ES OTA ?

 

[RayD]

Hi Jim.  I've only tried it briefly for visual without the ff, not imaging. 

Unfortunately I had a mishap with a piece of threaded bar which bounced around and took a chunk out of the lens cell.  All the rest is fine so I'm hoping one day to find one come up for sale with a dented tube or broken focuser as it was a great little OTA.

[James Vincent]

Give it a go, you may not require the flatterer it i s a triplet after all.

[Astrofriend]

Maybe I'm wrong, but I think the main difference between a doublett and a tripplet are the color correction. The curvature of the field isn't very much different, or?

 

/Lars

[James Vincent]

yes you are correct, its the 4 lens type like the  Petzval  corrects for field curvature . The third lens can be used to correct some off axis aberrations. The standard refactor or reflector the field curvature  is related to the focal length of the telescope, the shorter the focal length the greater the curvature . :}