TS-Optics focal reducer for Newtonians

[Zubenel]

Hi there , I am curious to see if there are folks out there that have used one of these successfully on a newton telescope for imaging purposes? Currently running a ZWOASI071 MC pro camera on "Zamar" 20" F5 and would like to fasten the system up a bit . I don't suffer from Coma ATM :)but if I understand correctly by reducing the FL by a factor of 0.27 that could introduce Coma... https://www.teleskop-express.de/shop/product_info.php/language/en/info/p9779_TS-Optics-NEWTON-Coma-Corrector-0-73x-Reducer---2--Connection.html :thumbsup:

[Camelopardalis]

Wes, that reducer is for a smaller imaging circle than the 071 sensor, and even then it’s looking a bit wooly out towards the edges.

Don’t see why it would introduce coma though ??

[Zubenel]

Dunk ,

Thanks for the reply :thumbsup: I suppose I'm looking for the Holy Grail when it comes to correcting Coma *AND** reducing effective focal length. I have read may posts on Cn and apparently if you make the system faster you get more COMA( physics ??) hence very fast systems have to have a sips system to make them work at all. So I'd be looking for something like this but with a bigger image circle. The search continues.........

[billdan]

According to the TS link, that 0.73 reducer (F5 reduced to F3.65) is also a coma corrector.

This coma corrector and reducer turns your Newtonian telescope into a high-speed astrograph. The focal length is reduced and the field is corrected.

Image circle is 30mm diag, however its fully corrected field is only 22mm (ASI-1600 or ASI-294 cameras).

[Zubenel]

Thanks Bill .

If you got those numbers from their graph for some reason I'm haven't got the resolution to do so.How would one calculate ? What would my ZWO ASI071MC Pro come in at since it's listed at 28.4mm? Would a bit of drop off be acceptable( probably not?). Or to rephrase what would be an acceptable limit for a fully corrected field?:thumbsup:

[billdan]

Hi Wes,

I got those numbers from their text. I did a google search on the Ackermann reducer and came across this CN thread.

It is not very encouraging as the slightest mis-collimation of the mirrors will make the reducer useless. This user says its not worth the money (approx $1000 Aus).

https://www.cloudynights.com/topic/503573-asa-2-inch-newton-coma-corrector-and-073x-reducer-for-astrophotography/

It would be nice if these suppliers allowed a 30 day trial and a refund if you didn't like it.

[Zubenel]

For the record...
So I emailed the supplier with this and got a reply back quickly. Looks as if I'm stuck in the middle !
Hi There , i am wanting to purchase a focal reducer and flattener for my 20" F5 SDM pimped Obsession for mainly AP however when matching your TS-Optics NEWTON Coma Corrector 0.73x Reducer - 2" Connection with my ZWO ASI071MCPro Camera the fully corrected field only goes to 22mm however the camera is 28.4mm giving a total uncorrected field of 6.4mm. Do you sell similar unit that will give a wider field to suit my camera? THX Wes


And their reply.They acknowledged the above issue and they do have a version that would give fully coverage but the catch is I would need a 3" focuser.
cheers

[Camelopardalis]

Wes, you could always just crop the image down to size :shrug:

Unless you're tracking accurately equatorially, you'll be seeing field rotation at the corners anyhow. That would be easily noticeable even at the reduced focal length with relatively short exposures, and especially so in the corners.

Would certainly be an interesting experiment :D