Placing of OAG

[ribuck]

Hi all,

I have a 4" refractor which came with a field Flattener / reducer. I also use a CCD & Filter wheel. ( CCD --> Filterwheel ----> Flattener )

I also have a Telescope Service 9mm slimline OAG that i would like to use, but i am not sure where i can fit this into the optical train. I cannot move the flattener as it needs to be about 55mm from the surface of the ccd chip, which is currently is.

Can the OAG be placed anywhere in the optical chain, i.e. after the flattener or does it need to be as close as possible to the ccd chip ?

Many Thanks,

Rich.

[Steve25]

Hi Rich,

I would place it like this :-

(CCD -->> Filterwheel ---> OAG --->>> Flattner)

Steve

[Steve25]

Rich,

Sorry not reading you post correctly. You need 55mm from CCD to Flattener. The problem you are going to have is the disstance the OAG ccd is going to need to be if you place it after the Flattener.

(CCD -> Filterwheel -> Flattener -> OAG)

Its going to be difficult to get the OAG ccd focused and its going to nee to be a fair way out (back focus).

So I woudl still go with my first suggestion.. But you will need to loose some mm somware to place the flattener at the correct distance.

Steve

Steve

Steve

[ribuck]

Thanks Steve, it's what i feared. Looks like i'm pretty snookered then, as i literally only used about 2mm spacer to achieve the perfect distance from the ccd surface. Looks like i'll have to use a dual saddle configuration and use a second ota for a guide scope.

Rich.

[ollypenrice]

Yup, looks like it. Personally I find it easier and cheaper to piggyback the guidescope, though.

Olly

[ribuck]

Well just before I put my Castro gear into storage I did drill holes in my guide scope mount bar which allowed me to mount in on top of the 102mm refractor, just never had a chance to test it. Role on June when new house is ready and astro gear can come out and play again.

[daz]

The 55mm flatteners are usually for DSLRs - I bought a TSFLAT2 which gives 109mm for my ED80/Atik 383, but can be adjusted with spacers. I have

Atik383 -> SX Filter Wheel -> SX OAG -> 2" Nosepiece -> Flattener

[ribuck]

Hi Daz, i know a lot of flatteners out there are around the 55mm, such as baader MPCC, Televeue Parracorr etc....and they are definitely used for imaging, and i dont think they are aimed at just DSLR's. I looked at the one you are using and it does look interesting. How long are your extension pieces to achieve focus with the guide cam ?

Regards,

Richard.

[daz]

There are, currently, no spacers in the train for camera or guide camera- BUT, I have an issue with the flattener not inserting all the way into my drawer tube (if ain't one thing, it's another!!!)

So I need to find a short nosepiece and will then put an extension between the OAG and nosepiece.

My distance from flattener to CCD is bang on 109mm, but I know I am not square because of the above.

I know there are lots of 55mm's but there are very few thin filter wheels and OAGs that will allow you to reach that distance, I think - at least not without spending heaps! I could be wrong - not looked in ages since I got the TSF2!